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Routing on Service Addresses

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This is an older version of an Internet-Draft whose latest revision state is "Replaced".
Authors Dirk Trossen , Luis M. Contreras , Jens Finkhäuser , Paulo Mendes , Daniel Huang
Last updated 2023-02-02
Replaced by draft-mendes-rtgwg-rosa-use-cases, draft-trossen-rtgwg-rosa-arch, draft-contreras-rtgwg-rosa-gaar
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Network Working Group                                         D. Trossen
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                           LM. Contreras
Expires: 6 August 2023                                        Telefonica
                                                          J. Finkhaeuser
                                                           Interpeer gUG
                                                               P. Mendes
                                                                D. Huang
                                                         ZTE Corporation
                                                         2 February 2023

                      Routing on Service Addresses


   This document proposes a novel communication approach which reasons
   about WHAT is being communicated (and invoked) instead of WHO is
   communicating.  Such approach is meant to transition away from
   locator-based addressing (and thus routing and forwarding) to an
   addressing scheme where the address semantics relate to services
   being invoked (e.g., for computational processes, and their generated
   information requests and responses).

   The document introduces Routing on Service Addresses (ROSA), as a
   realization of what is referred to as 'service-based routing' (SBR),
   to replace the usual DNS+IP sequence, i.e., the off-path discovery of
   a service name to an IP locator mapping, through an on-path discovery
   with in-band data transfer to a suitable service instance location
   for a selected set of services, not all Internet-based services.

   SBR is designed to be constrained by service-specific parameters that
   go beyond load and latency, as in today's best effort or traffic
   engineering based routing, leading to an approach to steer traffic in
   a service-specific constraint-based manner.

   Particularly, this document outlines sample ROSA use case scenarios,
   requirements for its design, and the ROSA system design itself.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Backdrop  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Design Goals  . . . . . . . . . . . . . . . . . . . . . .   5
     1.3.  Summary of Contribution . . . . . . . . . . . . . . . . .   5
     1.4.  Overview of Draft . . . . . . . . . . . . . . . . . . . .   7
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   7
   3.  Deployment and Use Case Scenarios . . . . . . . . . . . . . .   9
     3.1.  CDN Interconnect and Distribution . . . . . . . . . . . .   9
     3.2.  Distributed user planes for mobile and fixed access . . .  10
     3.3.  Multi-homed and multi-domain services . . . . . . . . . .  11
     3.4.  Micro-service Based Mobile Applications . . . . . . . . .  12
     3.5.  Constrained Video Delivery  . . . . . . . . . . . . . . .  13
     3.6.  AR/VR through Replicated Storage  . . . . . . . . . . . .  14
     3.7.  Cloud-to-Thing Serverless Computing . . . . . . . . . . .  14
     3.8.  Metaverse . . . . . . . . . . . . . . . . . . . . . . . .  15
     3.9.  Popularity-based Services . . . . . . . . . . . . . . . .  16
   4.  Analysis of Use Cases . . . . . . . . . . . . . . . . . . . .  16
     4.1.  Observations from Use Cases . . . . . . . . . . . . . . .  16
     4.2.  Suitability of Existing Internet Technologies . . . . . .  18
   5.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .  19

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   6.  Expected Benefits . . . . . . . . . . . . . . . . . . . . . .  24
   7.  ROSA Design . . . . . . . . . . . . . . . . . . . . . . . . .  25
     7.1.  System Overview . . . . . . . . . . . . . . . . . . . . .  25
     7.2.  Message Types . . . . . . . . . . . . . . . . . . . . . .  28
     7.3.  Changes to Clients to Support ROSA  . . . . . . . . . . .  30
     7.4.  SAR Forwarding Engine . . . . . . . . . . . . . . . . . .  31
     7.5.  Traffic Steering  . . . . . . . . . . . . . . . . . . . .  35
       7.5.1.  Ingress Request Scheduling  . . . . . . . . . . . . .  36
       7.5.2.  Routing Across Multiple SARs  . . . . . . . . . . . .  37
     7.6.  Interconnection . . . . . . . . . . . . . . . . . . . . .  39
   8.  Extensions to Base ROSA Capabilities  . . . . . . . . . . . .  40
     8.1.  Supporting Different Namespace Encodings  . . . . . . . .  40
     8.2.  Supporting Multi-Homing of Service Instances  . . . . . .  41
     8.3.  Supporting 0-RTT TLS  . . . . . . . . . . . . . . . . . .  41
     8.4.  Supporting Transaction Mobility . . . . . . . . . . . . .  42
     8.5.  Supporting Service Function Chaining  . . . . . . . . . .  42
     8.6.  Supporting Privacy-Compliant Communication  . . . . . . .  42
   9.  Prototype-based Insights  . . . . . . . . . . . . . . . . . .  43
   10. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . .  43
   11. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . .  43
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  44
   13. Privacy Considerations  . . . . . . . . . . . . . . . . . . .  45
   14. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  45
   15. Change Log  . . . . . . . . . . . . . . . . . . . . . . . . .  45
   16. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  46
   17. Informative References  . . . . . . . . . . . . . . . . . . .  46
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  52

1.  Introduction

   The centralization of Internet services has been well observed, not
   just in IETF discussions [Huston2021]
   [I-D.nottingham-avoiding-internet-centralization], but also in other
   efforts that aim to quantify the centralization, using methods such
   as the Herfindahl-Hirschman Index [HHI] or the Gini coefficient
   [Gini].  Dashboards of the Internet Society [ISOC2022] confirm the
   dominant role of CDNs in service delivery beyond just streaming
   services, both in centralization as well as resulting market
   inequality, which has been compounded through the global CV19
   pandemic [CV19].

   The impact on routing can be seen in, e.g., [TIES2021], which goes as
   far as centralizing service requests into a single IP address behind
   which data centre (DC) internal mechanisms take over.

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   Thus, ROSA is being motivated by the requirements stemming from use
   cases where the distribution of compute, storage, and networking
   resources associated with a service brings not just benefits but also
   its distributed, runtime utilization may yield in better performance,
   such as improved service completion latency, utilization, and others.

   At the same time, it is important to recognize that we do not aim for
   replacing existing service routing capabilities, most notably the DNS
   as the main form of resolving a service name into routing locator; we
   see those capabilities working perfectly well for many Internet
   services.  Instead, we argue in the following that some more
   challenging service scenarios, such as multi-access edge computing
   and cloud-to-thing, as well as more dynamic networking scenarios such
   as LEO constellations, may require service routing capabilities
   embedded in the networking stack, without relying on application
   layer translations or resolution services.

1.1.  Backdrop

   Providing the backdrop to this draft, [EI2021] addresses the
   challenge of overcoming the architectural stagnation of the Internet
   while supporting an increasing divergence of services, by means of an
   extensible Internet architecture able to support in-network services
   that go beyond best-effort packet delivery.  Within this extended
   Internet, novel network services are executed in Service Nodes (SNs)
   interconnected by networks running IP.  Deployment of SNs depends
   upon the use-case, but in general may be placed within Last Mile
   Providers (LMPs) or within Cloud Providers (CPs).  The proposed ROSA
   framework follows a similar architectural view.

   Evolving the IPv6 network layer has been part of its design from the
   very start.  Key enabler here are Extension headers (EHs), which are
   part of the IPv6 specifications [RFC8200], with some observed
   problems, e.g., firewall traversal, in real-world deployments
   [SHIM2014].  Recent solutions, such as Segment routing (SR)
   [RFC8402], specifically SRv6 [RFC8986] build on this capability by
   establishing a shim layer overlay (of SR-enabled routers), utilizing
   an extension header to carry needed information for realizing the
   source routing capabilities.  ROSA follows a similar approach, by
   using EHs to build a shim overlay above the IP layer.

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1.2.  Design Goals

   The key problem in service routing is that of determining the routing
   locator for a network endpoint that realizes a specific service.  For
   this, explicit resolution steps are usually implemented at the
   application level, through mechanisms such as DNS, GSLB, and Alto.
   The result of the explicit resolution is then used to establish a
   suitable communication at the application level, including transport
   sessions, to invoke a particular service, possibly followed by
   subsequent data transfer to the endpoint chosen in the resolution
   step (called 'affinity' in the following).

   This additional resolution does cost time in the form of the
   resolution latency, including the latency to access the resolver, but
   also requires for the resolver to have available the relevant (and
   up-to-date) mappings for any incoming resolution request.
   Furthermore, updating the mappings is a difficult problem, either
   requiring to push such updates to the resolver or pull suitable
   updates from elsewhere.  As outlined in [OnOff2022], both aspects
   lead to problems when wanting (or needing) to support shorter
   interactions with service instances, while interactions may be served
   by different service instances.

   Moreover, services that rely on application specific resolvers (e.g.
   DNS servers) may fail when facing intermittent connectivity to those
   resolvers, as can happen in moving networks (e.g. vehicle networks).

   This puts three goals in the foreground that are important for use
   cases for ROSA, namely (i) need for 'dynamicity' and (ii)
   'efficiency' as well as (iii) the 'service specificity' of the
   steering decision, i.e., the selection of the suitable service
   instance to send traffic to.  The first is about the support for fast
   changing relations with service endpoints, while the second aims to
   reduce any potential latency in doing so.  The third caters to the
   situation that the selection of one of the possibly many choices for
   a service endpoint is often defined through service-specific
   policies, including runtime decisions that may change from one
   transaction to another.

1.3.  Summary of Contribution

   The main contribution of Routing on Service Addresses (ROSA) is to
   replace the usual DNS+IP sequence, i.e., the off-path discovery of
   service name to IP locator mapping, through an on-path discovery with
   in-band data transfer to a suitable service instance location for a
   selected set of services, not all Internet-based services.

   The basic functionality of ROSA can be described as follows:

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   1  A client sends an initial IP packet, 'directed' to service address
      S, to a special shim (ROSA) overlay.

   2  The shim overlay routes the packet based on the service address to
      one of the possibly many service instances for S over an existing
      IP network.  For this, mappings between S and the known service
      instance locators are used by the ROSA overlay, replacing the role
      of DNS records, while the selection of the 'suitable' service
      instance locator may use service-specific policies (and

   3  The chosen service instance delivers its network locator SI in the
      response to the initial packet back to the client.

   4  The client will now continue to use SI in native IPv6 packets to
      direct any subsequent packets to the chosen service instance.
      This is to support possible ephemeral state created at service
      instance as a consequence of previous exchanges.

   Steps 1 through 4 are repeated for every new service transaction,
   allowing those transactions now to be served at any of the available
   service instances albeit keeping one transaction at one chosen
   service instance!  Steps 1 through 4 may also be repeated in case of
   mobility.  For stateless services, only steps 1, 2, and 3 are

   In order to react to system, e.g., network but more importantly
   service changes, ROSA achieves dynamicity, as mentioned in the
   previous section, by including a routing-based approach able to map
   service addresses to routing locators, where mappings of service
   addresses to routing locators are pushed to the (shim overlay)
   elements, enabling to perform the translation from a service
   addressed packet to an IP-addressed packet on the data path.  When
   using, e.g., eBPF-based techniques in SW-based routers, such approach
   can achieve 100s of thousands of resolution steps per ingress node,
   as discussed in Section 9.

   When it comes to efficiency, our design is positioned at L3.5, using
   an extension header based approach.  With this, the initial packet,
   realizing an in-band resolution step, can include upper layer, i.e.,
   transport and/or application-level, in-band data within the normal
   payload of the IP packet, further reducing the latency for completing
   a transaction, even opening the possibility for single packet
   transactions being completed in a single round trip.

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   Additionally, similar to application-level solutions, the positioning
   as a (L3.5) shim overlay faciliates the exposure of service-specific
   selection policies from the service to a ROSA provider through
   explicit commercial relations, separate from those defining the
   routing policies in the underlay network.

   Unlike name-based routing solutions at the underlay, routing
   scalability is achieved by limiting the resolution to those services
   explicitly announced to the service routing (i.e., ROSA) overlay.
   Thus, ROSA does not aim to replace ALL service routing through the
   above proposed steps, but focus on those services explicitly
   announcing their desire for a ROSA-based resolution to an appropriate
   ROSA provider.  The assumed explicit (often commercial) relationship
   between the service provider and the ROSA provider is what allows for
   controlling the scalability requirements of the elements realizing
   the ROSA overlay.

1.4.  Overview of Draft

   In the remainder of this document, we first introduce in Section 2 a
   terminology that provides the common language used throughout the
   remainder of the document.  We then introduce use cases in Section 3
   that drive the need for a routing on service address solution.  Our
   analysis in Section 4 then leads us to outline in Section 5 the
   requirements for ROSA and the expected benefits of ROSA in Section 6.

   The main part of the document focusses on introducing the ROSA design
   in Section 7, elaborating on the main idea presented above in more
   detail, followed by possible extensions to the design in Section 8.

2.  Terminology

   The following terminology is used throughout the remainder of this

   Service:  A monolithic functionality that is provided according to
      the specification for said service.  A composite service can be
      built by orchestrating a combination of monolithic services.

   Service Instance:  A running environment (e.g., a node, a virtual
      instance) that provides the expected service.  One service can
      involve several instances running within the same ROSA network at
      different network locations, thus providing service equivalence
      between those instances.

   Service Address:  An identifier for a specific service.

   Service Instance Address:  A locator for a specific service instance.

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   Service Request:  A request for a specific service, addressed to a
      specific service address, which is directed to at least one of
      possibly many service instances.

   Affinity Request:  A request to a specific service, following an
      initial service request, requiring steering to the same service
      instance chosen for the initial service request.

   Service Transaction:  A sequence of higher-layer requests for a
      specific service, consisting of at least one service request,
      addressed to the service address, and zero or more affinity

   Service Affinity:  Preservation of a relationship between a client
      and one service instance, with the initial service request
      creating said affinity and following affinity requests utilizing
      said affinity.

   ROSA Provider:  Realizing the ROSA-based traffic steering
      capabilities over at least one infrastructure provider by
      deploying and operating the ROSA components within its defining
      ROSA domain.

   ROSA Domain:  Domain of reachability for services supported by a
      single ROSA provider.

   ROSA Endpoint:  A node accessing or providing one or more services
      through one or more ROSA providers.

   ROSA Client:  A ROSA endpoint accessing one or more services through
      one or more ROSA providers, thus issuing services requests
      directed to one of possible many service instances that have
      previously announced the service address provided by the ROSA
      client in the service request.

   Service Address Router (SAR):  A node supporting the operations for
      steering service requests to one of possibly many service
      instances, following the procedures outlined in Section 7.5.

   Service Address Gateway (SAG):  A node supporting the operations for
      steering service requests to service addresses not announced to
      SARs of the same ROSA domain to suitable endpoints in the Internet
      or within other ROSA domains.

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3.  Deployment and Use Case Scenarios

   In the following, we outline examples for use cases that exhibit the
   degrees of distribution in which relationship management (through
   explicit mapping and/or gatewaying) may become complex and a possible
   hindrance for service performance.  The following sections only serve
   as illustrating examples with other work, such as the BBF Metro
   Compute Networking (MCN) [MCN], among others, having developed
   similar but also additional use cases.

3.1.  CDN Interconnect and Distribution

   Video streaming has been revealed nowadays as the main contributing
   service to the traffic observed in operators' networks.  Multiple
   stakeholders, including operators and third party content providers,
   have been deploying Content Distribution Networks (CDNs), formed by a
   number of cache nodes spread across the network with the purpose of
   serving certain regions or coverage areas with the proper quality
   levels.  In such a deployment, protection schemas are defined in
   order to ensure the delivery continuity even in the case of outages
   or starvation in cache nodes.

   In addition to that, novel schemes of CDN interconnection [RFC6770]
   [SVA] are being defined allowing a given CDN to leverage the
   installed base of another CDN to complement its overall footprint.

   As result, several caches are deployed in different Points of
   Presence in the network.  Then for a given content requested by an
   end user, several of those caches could be candidate nodes for
   delivery.  Currently, the choice of the cache node to serve the
   customer relies solely on the content provider logic, considering
   only a limited set of conditions to apply.

   For instance, the usage of cache-control [RFC7234] allows data
   origins to indicate caching rules downstream.  Since the original
   intent was quite limited, to operate between the data source and the
   data consumer (browser), Targeted Cache Control (TCC) [RFC9213]
   defines a convention for HTTP response header fields that allow cache
   directives to be targeted at specific caches or classes of caches.

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   The performance can be improved by the consideration of further
   conditions in the decision on what cache node to be selected.  Thus,
   the decision can depend of course on the requested content and the
   operational conditions of the cache itself, but also on the network
   status or any other valuable, often service-specific, semantic for
   reaching those nodes, such data validity, end to end delays, or even
   video analytics.  The latter is relevant since as the number of video
   files grows, so does the need to easily and accurately search and
   retrieve specific content found within them.

   Furthermore, those decision points may be dynamic and could even
   change during the lifetime of the overall service, thus requiring to
   revisit decisions and therefore assignments to the most appropriate
   CDN node.  An example encompasses the usage of satellites to enhance
   the content distribution efficiency in cooperation with the
   terrestrial network.  Combining satellites with CDNs may leverage LEO
   (low earth orbit) satellite mobility characteristics to cache and
   deliver content among different static caches in the terrestrial CDN,
   but may also include mobile satellites serving as couriers.

3.2.  Distributed user planes for mobile and fixed access

   5G networks natively facilitate the decoupling of control and user
   plane.  The 5G User Plane Function (UPF) connects the actual data
   coming over the Radio Area Network (RAN) to the Internet.  Being able
   to quickly and accurately route packets to the correct destination on
   the internet is key to improving efficiency and user satisfaction.
   For this, the UPF terminates the tunnel set carrying end user traffic
   permitting to route the end user traffic in the network towards its
   destination, e.g., providing reachability to edge computing

   Currently, UPF is planned to appear in two places, namely in the Core
   Network and at the Edge inside a Multi-Access Edge Controller (MEC).
   However, in a future 6G network, it is envisioned that several UPFs
   can be deployed in a distributed manner, not only for covering
   different access areas, but UPFs can also be distributed with the
   attempt of providing access to different services, linked with the
   idea of network slicing as means for tailored service
   differentiation.  For instance, some UPFs could be deployed very
   close to the access for services requiring either low latency or very
   high bandwidth, while others could be deployed in a more centralized
   manner for requiring less service flows.  Furthermore, multiple
   instances can be deployed for scaling purposes depending on the
   demand in a specific moment.

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   Similarly, to what happens in mobile access, fixed access solutions
   are proposing schemas of separation of control and user plane for BNG
   elements [I-D.wadhwa-rtgwg-bng-cups] [BBF].  From the deployment
   point of view, different instances can be deployed based on the
   coverage, the temporary demand, etc, as before.

   As a complement to both mobile and fixed access scenarios, edge
   computing capabilities are expected to complement the deployments for
   hosting service and applications of different purposes, for both
   services internal to the operator or hosting of services from third

   In this situation, either for both selection of the specific user
   plane termination instance, or from that point on, selection of the
   service endpoint after the user plane function, it makes sense the
   introduction of mechanisms enabling selection choices based on
   service-specific semantics.

3.3.  Multi-homed and multi-domain services

   Corporate services usually define requirements in terms of
   availability and resiliency.  This is why multi-homing is common in
   order to diversify the access to services external to the premises of
   the corporation, or for providing interconnectivity of corporate
   sites (and access to internal services such as databases, etc).

   A similar scenario in which external services need to be reached from
   within a specific location, is the Connecter Aircraft.  Exploiting
   solutions that allow for the exploitation of multi-connected
   aircrafts (e.g., several satellite connections, plus air-to-ground
   connectivity) are important to improve passenger experience, while
   helping make the crew more productive with networking solutions that
   enable seamless, high-speed broadband.  Managing a multi-connected
   Aircraft would benefit from mechanisms that would enable the
   selection of the best connection points based on service-specific
   semantics, besides the traffic related parameters considered by
   solutions such as SD-WAN, which aims to automate traffic steering in
   an application-driven manner, based on the equivalent of a VPN
   service between well defined points.

   The diversity of providers implies to consider service situations in
   a multi-domain environment, because of the interaction with multiple
   administrative domains.

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   From the service perspective, it seems necessary to ensure a common
   understanding of the service expectations and objectives
   independently of the domain traversed or the domain providing such a
   service.  Common semantics can facilitate the assurance of the
   service delivery and a quick adaptation to changing conditions in the
   internal of a domain, or even across different domains.

3.4.  Micro-service Based Mobile Applications

   Mobile applications, installed on mobile devices such as smartphones
   and deployed through 'marketplace' platforms, usually install a
   monolithic implementation of the device-specific functionality, where
   this functionality may explicitly utilize remote service
   capabilities, e.g., provided through cloud-based services.

   Application functionality may also be realized as micro-services
   themselves.  When such micro-services are jointly deployed (i.e.,
   installed) at the mobile device, its overall functionality resembles
   that of existing applications.

   Micro-services architectures are usually best suited to larger, more
   complex applications built for scalability and agile iteration.  In
   this scenario, a monolithic architecture can be a problem for
   applications as the codebase becomes unwieldy and difficult to

   However, micro-services may also be invoked on network devices other
   than the mobile device itself, utilizing service routing capabilities
   to forward the micro-service request (and its response) to the remote
   entity, effectively implementing an 'off-loading' capability.
   Efforts such as the BBF MCN work capture this aspect as 'edge-to-edge
   collaboration', where in our case here the edge does include the end
   user devices themselves.

   A distributed system like microservices inevitably introduces
   additional complexity as multiple moving parts need to be
   synchronized in a way that allows them to work as a unified software
   system.  If services are split across servers you will have to
   provision that multi-faceted infrastructure.  This is where a
   service-centric network solution able to coordinate the chain of such
   micro-services could plan an important role.

   The work in [I-D.sarathchandra-coin-appcentres] proposes such
   approach, positioning compute capabilities as forming a distributed
   (app-centric) data centre.  The simple example in
   [I-D.sarathchandra-coin-appcentres] outlines the distribution of
   video reception, processing, and displaying capabilities as
   individual micro-services.  With this, remote (edge computing)

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   capabilities may be used for complex processing beyond those of the
   mobile device.  This includes, for instance, to utilize hardware,
   such as displays, other than the device's built-in one.

   Interaction may be one driver for dynamicity in those scenarios.  For
   instance, the aforementioned display indirection may take place at
   high frequency, triggered by sensory input (e.g., gaze control) to
   decide which instance is best to direct the video stream to.  This
   may be beneficial for new, e.g., gaming experiences that utilize
   immersive device capabilities.  Other examples may include the
   offloading of processing capabilities (in case of 'better', i.e.,
   more capable, processing being available elsewhere).

   As briefly discussed in [I-D.sarathchandra-coin-appcentres], such
   micro-service design may well be integrated into today's application
   development frameworks, where a device-internal service registry
   would allow for utilizing device-local service instances first before
   directing the service invocation to the network to route the service

   In conclusiom, this concept of application-centric microservices,
   deployed within other edge devices, including end user devices
   themselves, extends the concept of 'edge computing', also captured in
   use cases of the BBF MCN initiative [MCN], by foreseeing more focus
   on the device applications, aiming at higher dynamicity in relations
   being realized.

3.5.  Constrained Video Delivery

   Chunk-based video delivery is often constrained to, e.g., latency or
   playout requirements, while the content itself may be distributed as
   well as replicated across several network locations.  Thus, it is
   required to steer client requests for specific content under specific
   constraints to one of the possibly many network locations at which
   the respective content may reside.

   The work in [I-D.jennings-moq-quicr-arch] proposes a publish-
   subscribe metaphor that connects clients to suitable relays for
   delivering the desired content under the specific constraint.  Within
   our context of service routing, the relays realize the service
   instances for a video delivery service, where the selection of the
   'right' instance is being constrained by the requirements for the
   video's delivery to the client.

   Instead, we suggest to complement QUICr by largely realizing the
   explicit publish/subscribe architecture in
   [I-D.jennings-moq-quicr-arch] through the traffic steering
   capabilities within a routing on service addresses infrastructure,

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   specifically replace the explicit lookup for a suitable relay in
   [I-D.jennings-moq-quicr-arch] through a service routing operation
   with the aim to not just reduce any lookup latencies involved in the
   relay selection but also to enable a high dynamicity in the selection

3.6.  AR/VR through Replicated Storage

   One aspect of dynamicity in selecting content storages in the
   previous use case has been investigated in [OnOff2022] through the
   example of an AR/VR service that underlies a tight delay budget but
   would like to benefit from any replication of content chunks across
   more than one network location.

   Here, a system of N clients is suggested to be retrieving content
   chunks from k service instances, where each chunk request is directed
   to any of the possible k instances; given the stateless nature of
   this service, any of the k instances is able to serve the chunk
   without knowledge of any previous one.

   As shown in [OnOff2022], a retrieval that utilizes any of the k
   replicas significantly reduces the variance of the retrieval latency
   experienced by any of the N clients.  Such reduced variance
   positively impacts the user experience through less buffering applied
   at the client side but also better adhering to the overall latency
   budget (often in the range of 100ms in AR/VR scenarios with pre-
   emptive chunk retrieval).  Although pre-emptive retrieval is also
   possible in systems with explicit lookup operations, the involved
   latencies for such resolution may make it difficult to adhere to the
   latency budget for an E2E operation (see [I-D.liu-can-ps-usecases]
   for example latency budgets).

3.7.  Cloud-to-Thing Serverless Computing

   The computing continuum is a crucial enabler of 5G and 6G networks as
   it supports the requirements of new services, such as latency and
   bandwidth critical ones, using the available infrastructure.  With
   the advent of new networks deployed beyond the edge, such as
   vehicular and satellite networks, researchers have begun
   investigating solutions to support the cloud-to-thing continuum, in
   which services distribute logic across the network, and storage is
   decentralized between cloud, the edge (most liked MEC) and the adhoc
   network of moving devices, such as aircraft and satellites.

   In this scenario, a serverless-based service architecture may be
   beneficial for the deployment and management of interdependent
   distributed computing functions, whose behavior can be redefined in
   real-time.  Serverless architecture is closely related to micro-

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   services.  The latter is a way to design an application and the
   former a way to run all or part of an application.  That is the key
   to their compatibility.  It is possible to code a micro-service and
   run it as a serverless function.

   The consideration of serverless architectures is important for the
   Cloud-to-Thing continuum, since resources beyond the edge, in the
   adhoc part of the continuum, may be constraint and intermittently
   available.  Hence it makes sense to leverage a serverless
   architecture that consists of a set of functions rather than
   services.  The difference is that a service is permanently available
   whereas a function has a lifecycle as it is triggered, called,
   executed, runs and is then removed as soon as it is no longer needed.
   Serverless functions only run when they are needed, potentially
   saving significant resources.

   In this scenario, the combination of a service oriented data plan
   with a model capable of delegating and adapting serverless functions
   in a cloud-to-thing continuum is important.  The former need to be
   aware of the presence of different functions in order to be able to
   execute services based on the correct selection and invocation of
   different functions, within their lifetime.  Most importantly, this
   awareness of the functions is likely to be highly dynamic in the
   nature of its distribution across network-connected nodes.

3.8.  Metaverse

   Large-scale interactive and networked real-time rendered tree
   dimension XR spaces, such as the Metaverse, follow the assumption
   that applications will be hosted on platforms, similarly to current
   web and social media applications.  However, the Metaverse is
   supposed to be more than the participation in isolated three
   dimension XR spaces.  The Metaverse is supposed to allow the
   internetworking among a large number of XR spaces, although some
   problems have been observed such as lock-in effects, centralization,
   and cost overheads.

   In spite of the general understanding about potential internetworking
   limitations, current technical discussions are ignoring the
   networking challenges altogether.  From a networking perspective, it
   is expected that the Metaverse will challenge traditional client-
   server inspired web models, centralized security trust anchors and
   server-style distributed computing, due to the need to take into
   account interoperability among a large number of XR spaces, low
   latency and the envisioned Metaverse pervasiveness.

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   In this context, an open and decentralized Metaverse, able to allow
   the internetworking of a large number of XR spaces, may be supported
   by intertwining distributed computing and networking.  Hence it is
   expected that Metaverse applications may gain from a network able to
   support the execution of services while taking advantage of storage,
   networking, and computing resources located as close as possible from
   users, with a dynamic assignment of client requests to those

3.9.  Popularity-based Services

   The BBF MCN use case report [MCN] outlines 'popularity' as a criteria
   to move from current explicit indirection-based approaches (such as
   DNS, GSLB, or Alto) to active service routing approaches.

   Here, popularity, e.g., measured in service usage over a period of
   time, is being used as a trigger to announce a popular service to an
   active service routing platform, while less popular service continue
   to be served via existing (e.g., DNS-based) methods.  Equally,
   services may be unannounced, thus retracted, from the service routing
   overlay to better control the overall cost for the provisioning of
   the service routing overlay.

   With this, one could foresee the provisioning of a service routing
   overlay, such as ROSA, as an optimization for a CDN platform
   provider, either through commercially interfacing to a separate ROSA
   provider or providing the ROSA domain itself.

4.  Analysis of Use Cases

   We now discuss observations and suitability of existing technologies
   for realizing the use cases in the previous section, leading to the
   requirements outlined in Section 5.  We then list the expected
   benefits for utilizing the ROSA design, presented in more detail in
   Section 7.

4.1.  Observations from Use Cases

   Several observations can be drawn from the use case examples in the
   previous section in what concerns their technical needs:

   1  The namespace for services and applications is separate from that
      of routable identifiers used to reach the implementing endpoints,
      i.e., the service instances.  Resolution and gateway services are
      often required to map between those namespace, adding management
      and thus complexity overhead, an observation also made in

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   2  Service instances for a specific service may exist in more than
      one network location, e.g., for replication purposes to serve
      localized demand, while reducing latency, as well as to increase
      service resilience.

   3  While the deployment of service instances may follow a longer term
      planning cycle, e.g., based on demand/supply patterns of content
      usage, it may also have an ephemeral nature, e.g., scaling in and
      out dynamically to cope with temporary load situations as well as
      with the temporary nature of serverless functions.

   4  Knowing which are the best locations to deploy a service instance
      is crucial and may depend on service-specific demands, realizing a
      specific service level agreement (with an underlying decision
      policy) that is tailored to the service and agreed upon between
      the service platform provider and the communication service

   5  Decisions for selecting the 'right' or 'best' service instance may
      be highly dynamic under the given service-specific decision policy
      and thus may change frequently with demand patterns driven by the
      use case.  For instance, in our examples of Section 3.4 or
      Section 3.8, human interaction may drive the requirement for
      selecting a suitable service instance down to few tens of
      milliseconds only, thus creating a need for high frequency updates
      on the to-be-chosen service instance.  As a consequence, traffic
      following a specific network path from a client to one service
      instance, may need to follow another network path or even utilize
      an entirely different service instance as a result of re-applying
      the decision policy.

   6  Minimizing the latency from the initiating client request to the
      actual service response arriving back at the client is crucial in
      many of our scenarios.  Any improvement on utilizing the best
      service instance as quickly as possible, thus taking into account
      any 'better' alternative to the currently used one, is crucial for
      reducing latency.

   7  A specific service may require the execution of more than one
      service instance, in an intertwining way, which in turn requires
      the coordination of the right service instances, each of which can
      have more than one replica in the network.

   We can conclude from our observations above that (i) distribution (of
   service instances), (ii) dynamicity in the availability of and
   chosing the the 'best' service instance, and (iii) efficiency in
   utilizing the best possible service instance are crucial for our use

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4.2.  Suitability of Existing Internet Technologies

   There exist a number of L4 through L7 based solutions that could be
   leveraged to fulfil the technical needs of the aforementioned use
   cases, with [I-D.liu-can-gap-reqs] providing an initial overview into
   the gaps that those solutions experience in the light of the
   observations above.

   A key takeaway from this analysis is that the explicit indirection
   for service discovery, realized for instance through DNS, GSLB, or
   other solutions, poses a challenge to the dynamicity also observed in
   our use cases here due to the additional latency incurred but also
   due to the relatively static mapping of service name onto network
   locator that is maintained in most of those solutions.  The work in
   [OnOff2022] investigates the impact of such off-path vs possible on-
   path decision making onto service performance and user experience.

   The identifier/locator split provided by LISP
   [I-D.ietf-lisp-introduction] provides a similar separation of (an
   endpoint) identifier from its routable locator.  In a way, a service
   address could be seen as an anycast EID in LISP.  However, the
   reliance in LISP on a federated mapping service also positions LISP
   as an off-path solution with explicit resolution latency being
   incurred; this is due to the desired scale of LISP in which a
   routing-based solution (in contrast to the pull-based mapping
   service) is not tractable in terms of scalability, while for most
   services, a pull-based mapping service suffices.  ROSA is based on
   the recognition that an explicit pull model (and its associated
   latency) may not be suitable for certain use cases (see Section 3),
   while still allowing for the traditional, e.g., DNS-based resolution
   methods being used for the wide range of services for which
   dynamicity and efficiency impact are not an issue.

   Furthermore, the inherent anycast nature of service routing, when
   applied to replicated service instances, requires the use of anycast
   IP addresses, in turn often relying on centralized anycast routing
   architectures for delivering the service to the 'best' instance under
   the given anycast address.  Lastly, communication over LISP does not
   see a difference between initial (service) requests and following
   (affinity) requests but instead realizes all communication through
   the EID abstraction.

   Service instances or network service functions can be used by network
   operators to provide a better quality of service and manage their
   networks more efficiently.  In this context, there is a growing
   interest in Service Function Chaining (SFC) [RFC7665], an ordered set
   of service functions that are applied to end-to-end traffic.  It is
   expected for mobile network operators or Internet service providers

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   to deploy SFCs in a geographically centralized manner, such as a data
   center where service function chains can be easily managed and
   configured.  However, in a Cloud-to-thing scenario, the configuration
   and management of the service function chain is significantly more
   complex, because careful orchestration strategies are required to
   discover proper service instances and connect them across multiple
   networks operated with different resource management and network

   The deployment of SFC in a cloud-to-thing scenario is even more
   complex if service instances are developed following a serverless
   architecture, in which case orchestration strategies to discover
   proper service instances need to consider the network function
   semantics, namely its intermittent availability in the network.

   In the next section, we outline requirements for a solution that
   would realize those use cases and address some of the gaps outlined
   in [I-D.liu-can-gap-reqs], with Section 7 presenting our initial
   design on how to address those requirements through a shim layer atop

5.  Requirements

   The following requirements for a routing on service addresses (ROSA)
   solution (referred to as 'solution' for short) have been identified
   from our use cases in the previous section

   One commonality of all use cases is the communication with a
   'service', realized at one or more network locations as equivalent
   'service instances'.  Associating the service to an 'owner' is key to
   avoid services being announced by fake entities, thus misdirecting
   the client's traffic, while obfuscating the purpose of communication
   (e.g., leaked through the specific name of a service) but also any
   possible policy to select one over another service instance may want
   to be kept private; this is likely the case across all of our use
   cases.  Hence, any solution

   REQ1:  MUST provide means to associate service instances with a
          single service address.

          (a)  MUST provide secure association of service address to
               service owner.

          (b)  SHOULD provide means to obfuscate the purpose of
               communication to intermediary network elements.

          (c)  MAY provide means to obfuscate the constraint parameters
               used for selecting specific service instances.

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   Across all our use cases, the knowledge of where service instances
   (realizing specific services) reside within the network, i.e.,
   possibly at different network locations, is crucial for the
   communication to happen, at least for the ROSA domain with which the
   service has an association with.  Such knowledge may be created by a
   service management platform, e.g., as part of the overall service
   deployment, and thus may not be initiated by the deployed service
   instance itself, such as in the example of Section 3.4.  Furthermore,
   service deployment may be delegated to service or CDN platforms,
   e.g., in the CDN, AR/VR and video distribution examples of
   Section 3.1, Section 3.6 or Section 3.5, respectively, albeit with
   linkages needed to the service routing capabilities of ROSA.
   Crucially, however, is that a solution ought to use proactive pushing
   of suitable reachability information to service instances into the
   ROSA system, i.e., pursuing a routing-based approach, allowing for
   faster availability of information to make suitable decisions on
   which service instance to choose among those available.  Hence, any

   REQ2:  MUST provide means to announce route(s) to specific instances
          realizing a specific service address, thus enabling service
          equivalence for this set of service instances.

          (a)  MUST provide scalable means to route announcements.

          (b)  MUST announce routes within a ROSA domain.

          (c)  SHOULD provide means to delegate route announcement.

          (d)  SHOULD provide means to announce routes at other than the
               network attachment point realizing the announced service

          (e)  MUST allow for removing service instances that are
               intermittently availab,e, i.e., revoking their service
               announcement after a defined timeframe.

   A client application may not just invoke services within a single
   ROSA domain.  While associating with different ROSA domain may be
   possible, clients may simply invoke services through their existing
   ROSA domain, e.g., for utilizing helper services in examples like
   Section 3.4, expecting the service transaction to be realized
   regardless.  The same goes for invoking services that may reside in
   the public Internet, without requiring an explicit awareness of the
   client to which ROSA domain (or the public Internet) to direct the
   invocation.  Thus, any solution

   REQ3:  MUST provide means to interconnect ROSA islands.

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          (a)  MUST allow for announcing services across ROSA domains.

          (b)  MUST allow for announcing services outside ROSA domains.

   Use cases like Section 3.4 but also video delivery ones such as
   Section 3.5 and Section 3.6 or the selection of an appropriate UPF
   (user plane functions) within a cellular sub-system in Section 3.2,
   may want to constrain the selection of 'suitable' service instances
   through service-specific constraints, such as the computing load (on
   the deployed service instances or their host platforms), service-
   level latency, but also, e.g., HW or SW, capabilities.  This may also
   be the case for multi-homed deployments (see Section 3.3), where
   constraints on the multi-connectivity of the service instance may
   constrain the suitability for specific clients.  Thus any solution

   REQ4:  Solution MUST provide constraint-based routing capability.

          (a)  MUST provide means to announce routing constraints
               associated with specific service instances and their
               realizing networking, computing and storaged resources.

          (b)  SHOULD allow for providing constraints in the service
               (address) announcement.

   The work in [OnOff2022] has shown the potential gains in making
   runtime decisions for every incoming service transaction, where
   transaction lenths may be as small as single (application-level)
   requests.  For use cases such as Section 3.5 or Section 3.6, this may
   lead to significant smoothening of the request completition latency,
   i.e., reducing the latency variance, thus enabling a better, smoother
   experience at the client.  However, the specific mechanism may vary
   and, more importantly, may be highly service-specific, with solutions
   such as [CArDS2022] providing a simple weighted round robin, while
   other methods may rely on regular (service) metric reporting.  Thus
   any solution

   REQ5:  MUST provide an instance selection at ROSA domain ingress
          nodes only.

          (a)  MUST allow for signalling selection mechanism and
               necessary input parameters for selection to the ROSA
               domain ingress nodes.

   Explicit resolution steps, such as those in DNS, GSLB, or Alto,
   suffer from the need for an explicit control plane exchange.  This
   causes additional latency before the data transfer to the chosen
   service instance may start.  In-band data, i.e., the inclusion of
   application-level data in the control messages, is not supported due

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   to the layering of such solutions at the application level itself.
   It is desirable, however, to already allow for the exchange of
   application data, including that needed for establishing secure
   connections, in the process that determines the most suitable service
   instance to further reduce any latency for completing a given
   application-level service transaction.  Thus any solution

   REQ6:  MUST provide an in-band data transfer capability in the
          process of determining the suitable service instance for any
          following data transfer within the same service transaction.

   While video delivery use cases like Section 3.5 or Section 3.6 may
   exhibit short lived transactions of just one (service-level) request,
   due to the replicated nature of the video content in each service
   instance, service transactions may last many requests after the
   initial one has been sent.  Ephemeral state may be created during
   this transaction, which would require that a change of the (initial)
   service instance during a transaction would share such ephemeral
   state with any new service instance being used.  While service
   platforms, like K8S, provide such ability through 'shared data layer'
   capabilities, those are often limited to single site deployments.
   Any support across sites would incur additional costs or even
   possibly latencies for such state sharing, thus often leading to
   completing an ongoing service transaction with the service instance
   that has been originally been used (note that a service instance in
   ROSA may use internal methods for serving incoming requests across
   which state sharing would be applied - from a ROSA perspective,
   however, only one service instance is being used).  We call the
   capability to retain an initial selection of a service instance for
   the length of a service transaction 'affinity'.  Thus, any solution

   REQ7:  MUST adhere to the affinity towards the service instance
          chosen in the initial service request of the service
          transaction, thus directing all subsequent service transaction
          requests to the same instance.

   All of our use cases are likely being deployed over existing network
   infrastructure, which makes a consideration to use its existing
   solutions in any realization of ROSA very important.  Specifically,
   any solution

   REQ8:  Solution SHOULD use IPv6 for the routing and forwarding of
          service and affinity requests.

          (a)  Solution MAY use IPv4 for the routing and forwarding of
               service and affinity requests.

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   Most of our use cases, specifically Section 3.4 but also our video
   delivery examples, may be realized in inherently mobile settings with
   clients moving about for their experience.  While mobile IP solutions
   exist, the service initialization in ROSA needs to be equally
   supported in order to allow for invoking ROSA services on the move.
   Thus, any solution

   REQ9:  SHOULD support in-request mobility for a ROSA client.

   Mobility of clients, but also varying loads in scenarios of no client
   mobility, may also lead to situations where moving on ongoing service
   transaction to another service instance may be beneficial, termed
   'transaction mobility'.  In other words, service instances may be
   replaced mid-transaction, in order to ensure the service level
   agreement.  This may happen if, for instance, the local node where
   the service instance was initially installed is running out of
   resources, or its accessibility is reduced (which be periodically).
   Thus, any solution

   REQ10: SHOULD support transaction mobility, i.e., changing service
          instances during an ongoing service transaction.

   With most service transactions likely being encrypted for privacy and
   security reasons, supporting the appropriate transport layer methods
   is crucial in all our scenarios in Section 3, which is achieved by
   ROSA being positioned as a L3.5 solution, as presented in Section 7.
   While work in [OnOff2022] has shown that small service transactions
   in scenarios like Section 3.5 or Section 3.6 may be beneficial for
   significantly reducing the service-level latency, the challenge lies
   in initiating suitable transport layer security associations with
   frequently changing service instances.  Pre-shared certificates may
   address this to allow for 0-RTT handshakes being realized but come
   with well-known forward secrecy problems.  Thus, any solution

   REQ11: SHOULD support TLS 0-RTT handshakes without the need for pre-
          shared certificates.

   We envision the ROSA layer in ROSA endpoints to be transparently
   integrated in the operation of transport protocols, and thus
   applications, by provuding suitable interfaces to accessing the ROSA
   services of a specific ROSA domain.  Thus, any solution

   REQ12: SHOULD be transparent to applications in order to ensure a
          smooth deployment.

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6.  Expected Benefits

   We expect the following benefits to be realized through the ROSA
   design, discussed in the next section.  We here refer to
   investigations in several research works by reference for more detail
   on the findings:

   *  Dynamicity: Decisions to select one out of possibly many service
      instance can be highly dynamic, done per service transactions,
      including for single packet ones.  This is enabled by the move
      from an explicit off-path resolution step to an in-band, on-path
      mapping of a service address to its realizing service instance.
      Such dynamicity aims at improving transaction completion latency
      and variance, balancing load across service instances, as well as
      possibly deal with temporary network conditions.  The work in
      [OnOff2022] evaluates the impact of performing traffic steering
      decisions at the level of ROSA rather than at application level.

   *  Service-specifity: The constraints for selecting a suitable
      service instance should not be limited to network metrics like
      delay or bandwidth.  Instead, services should be able to define
      service-specific constraints, allowing for either multi-optimality
      routing or realising request-level and possibly compute-aware
      request scheduling for selecting one of possibly several service
      endpoints.  The mechanism in [CArDS2022] outlines an example for
      such steering decisions, taking into account service-specific
      compute information.  However, to avoid embedding full path
      information into the service routing itself, the consideration of
      service-specific constraints should be limited to the selection of
      service instances, while the forwarding of transaction data (in
      the form of subsequent affinity requests) solely follows the
      routing policies defined by the underlay network.

   *  Reduce dependency on DNS: Current service routing utilises a DNS-
      based approach, thereby requiring explicit off-path operations
      before being able to utilise a specific service.  We aim at
      reducing this dependency on the DNS.  The work in [OnOff2022]
      outlines the possible impact of reducing the use of the DNS, while
      also evaluating the capabilities enabled in flexible (small
      affinity) traffic steering under the constraint of a given latency

   *  Efficiently support higher degree of service distribution: Typical
      application or also L4-level solutions, such as GSLB, QUIC-based
      indirection, and others, lead effectively to egress hopping when
      performed in a multi-site deployment scenario in that the client
      request will be routed first to an egress as defined either
      through the DNS resolution or the indirection through a central

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      server, from which the request is now resolved or redirected to
      the most appropriate DC site.  In deployments with a high degree
      of distribution across many (e.g., smaller edge computing) sites,
      this leads to inefficiencies through path stretch and additional
      signalling that will increase the request completion time.
      Instead, direct or on-path solutions such as ROSA are expected to
      lead to a more direct traffic towards the site where the service
      will eventually be executed, while also allowing for application
      data to be already carried as part of the service instance
      selection process, thus keeping the request completion time close
      to its optimum in respect to the best site being used for
      execution of the request.

   *  Bring application namespace closer to communication relations:
      Reid et al [Namespaces2022] outline insights into the aspects and
      pain points experienced when deploying existing intra-DC service
      platforms in multi-site settings, i.e., networked over the
      Internet.  The main takeaway in is the lacking protocol support
      for routing requests of microservices that would allow for mapping
      application onto network address spaces without the need for
      explicitly managed mapping and gateway services.  While this
      results in management overhead and thus costs, efficiency of such
      additional mapping and gateway services is also seen as a
      hinderance in scenarios with highly dynamic relationships between
      distributed microservices, an observation aligned with the
      findings in [OnOff2022].  The use cases presented in Section 3,
      among others, exhibit the degrees of distribution in which
      relationship management (through explicit mapping and/or
      gatewaying) may become complex and a possible hinderance for
      service deployment and suitable performance.

7.  ROSA Design

   This section outlines the design of a shim layer relying upon IPv6 to
   provide routing on service addresses (ROSA).  It first outlines the
   system overview, before outlining the interfaces to the IP layer
   (Section 7.2 and applications in ROSA endpoints (Section 7.3),
   followed with the various operational methods of ROSA in terms of
   forwarding operations (Section 7.4), traffic steering methods
   (Section 7.5), and interconnection (Section 7.6).

7.1.  System Overview

   Figure 1 illustrates a ROSA domain, interconnected to other ROSA-
   supporting domains via the public Internet through the Service
   Address Gateway (SAG), where a ROSA domain may span one or more IPv6
   underlay domain.  Section 7.6 provides more detail on how to achieve
   interconnection between ROSA domains.

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   ROSA is positioned as a shim overlay atop IPv6, using Extension
   headers that carry the suitable information for routing and
   forwarding the ROSA service requests, unlike [I-D.eip-arch] which
   proposes to include extension processing directly into the transport

                          +-----------+  +-----------+   +-------+
                          +----+------+  +-------+---+   +----+--+
                               |                 |            |
          +-----------+   +----+-+           +----+-----------+--+
 Net|           |       DC Net      |
          +-----------+   +---+--+           +-------------+-----+
                             |                             |
                           +-+--+                        +-+--+
                     +-----+SAR4|                        |SAR5|
                     |     +-+--+                        +-+--+
   +------+        +-+--+                 +----+           |
   +Client+--------+SAR1+-------------+   +SAR6+           |
   +------+        +----+             |   +-+--+           |
                                      |     |              |
   +------+        +----+            ++-----+----+         |
   +Client+--------+SAR2+------------+IPv6 Net(s)+---------+
   +------+        +----+            +---+--+----+            (----)
                                         |  |                (      )
   +------------------+        +----+    |  |    +----+     (  Other )  +----+SAG1+----(  Domains )
   +------------------+        +----+            +----+     (        )

   SAR: Service Address Router
   SAG: Service Address Gateway

                       Figure 1: ROSA System Overview

   ROSA endpoints start with discovering their ingress Service Address
   Router (SAR), e.g., through DHCP extensions or through utilizing the
   Session Management Function (SMF) in 5G networks [TS23501].  An
   endpoint may discover several ingress SARs for different categories
   of services, each SAR being part of, e.g., a category-specific ROSA
   overlay, which in turn may be governed by different routing policies
   and differ in deployment (size and capacity).  The category discovery
   mechanism may be subject to specific deployments of ROSA and thus is
   likely outside the scope of this document at this point.

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   Services are realized by service instances, possibly at different
   network locations.  Those instances expose their availability to
   serve requests through announcing the service address of their
   service to their ingress SAR, which in turn distributes suitable ROSA
   routing state across the SARs in its domain.  The lacking tie of
   service addresses to the network topology, and thus the lacking
   possibility to aggregate relationships of service addresses to
   routing locators, poses a scalability challenge (specifically to
   address Req 2.a in Section 7.4) However, the routing tables in ROSA
   are bounded by the number of services explicitly announcing their
   service to ingress SARs, while utilizing explicit interconnection
   (see Section 7.6) to other ROSA domains or the Internet for any
   service requested in the domain that has not previously been

   To invoke a service, a ROSA client sends an initial request,
   addressed to a service, to its ingress SAR, which in turn steers the
   request (possibly via other SARs) to one of possibly many service
   instances.  See Section 7.4 for the required SAR-local forwarding
   operations and end-to-end message exchange and Section 7.3 for the
   needed changes to ROSA clients.  Conversely, non-ROSA services may
   continue to be invoked using existing means for service routing, such
   as DNS, GSLB, Alto and others.

   We refer to initial requests as 'service requests'.  If an overall
   service transaction creates ephemeral state, the client may send
   additional requests to the service instance chosen in the (preceding)
   service request; we refer to those as 'affinity requests'.  With
   this, routing service requests (over the ROSA network) can be
   positioned as on-path service discovery (winth in-band data),
   contrasted against explicit, often off-path solutions such as the

   In order to support transactions across different service instances,
   e.g., within a single DC, a sessionID may be used, as suggested in
   [SOI2020].  Unlike [SOI2020], discovery does not include mapping
   abstract service classes onto specific service addresses, avoiding
   semantic knowledge to exist in the ROSA shim layer for doing so.

   With the above, we can outline the following design principles that
   guide the development for the solutions described next:

   *  Service addresses have unique meaning only in the overlay network.

   *  Service instance IP addresses have meaning only in the underlay
      networks, over which the ROSA domain operates.

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   *  SARs map service addresses to the IP addresses for the next hop to
      send the service request to, finally directed to the service
      instance IP address.

   *  Within the underlay network, service instance IP addresses have
      both locator and identifier semantics.

   *  A service address within a ROSA domain carries both identifier and
      locator semantics to other nodes within that domain but also other
      ROSA domains (through the interconnection methods shown in
      Section 7.6).

   *  Affinity requests directly utilize the underlay networks, based on
      the relationships build during the service request handling phase.

   We can recognize similarities of these principles with those outlined
   for the Locator Identifier Separation Protocol (LISP) in
   [I-D.ietf-lisp-introduction] albeit extended with using direct IP
   communication for longer service transactions.

7.2.  Message Types

   Apart from affinity requests, which utilize standard IPv6 packet
   exchange between the client and the service instance selected through
   the initial service request, ROSA introduces three new message types,
   shown in Figure 2.

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     |  Next Header  |  Hdr Ext Len  |                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
     |    Instance=IP                                                |
     |    Service=ID                                                 |
     |    Constraint=txt                                             |
       Service Announcement

     |  Next Header  |  Hdr Ext Len  |                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
     |    Client=IP                                                  |
     |    Ingress=IP                                                 |
     |    Service=ID                                                 |
     |    Port=port                                                  |
       Service Request

     |  Next Header  |  Hdr Ext Len  |                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
     |    Client=IP                                                  |
     |    Ingress=IP                                                 |
     |    Service=ID                                                 |
     |    Port=port                                                  |
     |    Instance=IP                                                |
       Service Response

                        Figure 2: ROSA message types

   Given the overlay nature of ROSA, clients, SARs, and service
   instances are destinations in the IPv6 underlay of the network
   domains that the overlay spans across.  This is unlike approaches
   such as [I-D.huang-service-aware-network-framework], which place the
   service address into the destination address of the respective IPv6
   header field, although []
   also foresees the encapsulation into the IPv6 EH, as suggested here.

   Istead, we propose to use the destination option EH [RFC8200], where
   Figure 2 shows the options carried, proposed here as using a TLV
   format for the extension header with Concise Binary Object
   Representation (CBOR) [RFC8949] being studied as an alternative.  The
   EH entries shown are populated at the client and service instance,
   while read at traversing SARs.

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   A service address is encoded through a hierarchical naming scheme,
   e.g., using [RFC8609].  Here, service addresses consist of
   components, mapping existing naming hierarchies in the Internet onto
   those over which to forward packets, illustrated in the forwarding
   information base (FIB) of Figure 3 as illustrative URLs.  With
   components treated as binary objects, the hierarchical structure
   allows for prefix-based grouping of addresses, reducing routing table
   size, while the explicit structure allows for efficient hash-based
   lookup during forwarding operations, unlike IP addresses which
   require either log(n) radix tree search software or expensive TCAM
   hardware solutions.

   Note that other encoding approaches could be used, such as hashing
   the service name at the ROSA endpoint or assigning a service address
   through a mapping system, such as the DNS, but this would require
   either additional methods, e.g., for hash conflict management or
   name-address mapping management, which lead to more complexity.

   With the service announcement message, a service instance signals
   towards its ingress SAR its ability to serve requests for a specific
   service address.  Section 7.5 outlines the use of this message in
   routing or scheduling-based traffic steering methods.

   The service request message is originally sent by a client to its
   ingress SAR, which in turn uses the service address provided in the
   extension header to forward the request, while the selected service
   instance provides its own IP locator as an extension header entry in
   the service response.  In addition to the service address, suitable
   port information is being provided (through upper layer protocols),
   allowing to associate future affinity requests with their initial
   service requests.

   The next section describes the SAR-local forwarding operations and
   the end-to-end message exchange that uses the extension header
   information for traversing the ROSA network, while Section 7.6
   outlines the handling of service addresses that have not been
   previously announced within the client-local ROSA domain.

7.3.  Changes to Clients to Support ROSA

   Within endpoints, the ROSA functionality is realized as a shim layer
   atop IPv6 and below transport protocols.  For this, endpoints need
   the following adjustments to support ROSA:

   *  Adapting network layer interface: Introducing service addresses
      requires changes to the current network interface for discovering
      the ingress SAR and issuing service requests as well as
      maintaining affinity to a particular service instance, i.e.

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      mapping a service instance IP address to the initial service
      address.  As one possible choice, a new address type (e.g.,
      ADDR_SA) could be introduced at the socket interface, provided
      during socket creation and assigning the service address to the
      returned handle, while utilizing socket options to assign
      constraints to receiving sockets, utilized in the announcement of
      the service address.  Alternatively, supporting service addresses
      could be integrated with efforts such as [POSTSOCK2017] to
      redefine the transport interface towards applications.  Any OS-
      level client changes, as required by introducing new sockets,
      could be avoided by relying on, e.g., UDP-based, encapsulation of
      client traffic to the ingress SAR albeit with the drawback of
      needing to maintain client-state at the ingress SAR.

   *  Transport protocol integration: We see our design aligned with
      existing transport protocols, like TCP or QUIC, albeit with
      changes required to utilize the aforementioned new address type.
      For the application (protocol), the opening and closing of a
      transport connection would then signal the affinity to a specific
      instance, where the semantic of the 'connection' changes from an
      IP locator to a service address associated to that specific
      service instance.  With this, a new service transaction is
      started, akin to a fresh DNS resolution with IP-level exchange.

   *  Changes to application protocols: The most notable change for
      application protocols, like HTTP, would be in bypassing the DNS
      for resolving service names, using instead the aforementioned
      different (service) socket type.  These adaptions are, however,
      entirely internal to the protocol implementation.  Given the ROSA
      deployment alongside existing IP protocols, those changes to
      clients can happen gradually or driven through (e.g., edge SW)

7.4.  SAR Forwarding Engine

   The SAR operations are typical for an EH-based IPv6 forwarding node:
   an incoming service request or response is delivered to the SAR
   forwarding engine, parsing the EH for relevant information for the
   forwarding decision, followed by a lookup on previously announced
   service addresses, and ending with the forwarding action.

   Figure 3 shows a schematic overview of the forwarding engine with the
   forwarding information base (FIB) and the next hop information base
   (NHIB) as main data structures.  The NHIB is managed through a
   routing protocol, see Section 7.5, with entries leading to announced

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   incoming service request/response
   -------------------------------------||             Next Hop
                                        \/        Information Base
   Forwarding Information Base     +----------+   +-+--------+----+
   +------------------+--------+   |EH parsing|   |#|Next Hop|Cost|
   |Service address   |Next Hop|   +----||----+   |#|   IP   |Cost|
   +------------------+--------+        \/        +-+--------+----+
   |      | 4, 5, 0|   +----------+   |0|  SAR5  | 2  |
   +------------------+--------+   |   SAR    |   +-+--------+----+
   |          | 1      |-->|Forwarding|   |1|  SAR6  | 1  |
   +------------------+--------+   | Decision |   +-+--------+----+
   || 2      |   +----||----+   |2|  SAR2  | 4  |
   +------------------+--------+        \/        +-+--------+----+
   | *                | 3      |   +----------+   |3|  SAR1  | 2  |
   +------------------+--------+   |   SA/DA  |   +-+--------+----+
                                   |Adjustment|<--|4|  SI1   | -  |
                                   +----||----+   +-+--------+----+
                                        \/        |5|  SI2   | -  |
                                   +----------+   +-+--------+----+
                                   |IP packet |
                                   |forwarding|  Outgoing service
                                   |  engine  |  request/response

                   Figure 3: SAR forwarding engine model

   The FIB is dynamically populated by service announcements via the
   intyer-SAR routing protocol, with the FIB including only one (ROSA
   next hop) entry into the NHIB when using routing-based methods (rows
   0 to 3 in Figure 3), described in Section 7.5.2.  Scheduling-based
   solutions (see Section 7.5.1), however, may yield several dynamically
   created entries into the NHIB (items 0, 4 and 5 in Figure 3, where
   SI1 and SI2 represent the IPv6 address announced by the respective
   service instances) as well as additional information needed for the
   scheduling decision; those dynamic NHIB entries directly identify
   service instances locations (or their egress as in item 0) and only
   exist at ingress SARs towards ROSA clients.

   As stated in Section 1.2, we expect the number of forwarding entries
   to be limited by the explicit relations service providers may have
   with their ROSA provider.  In other words, we do not expect the FIB
   to include ALL possible service names but those explicitly announcing
   their service (and being authorized by the ROSA provider doing so).
   In our use cases of Section 3, those services may be very limited in
   numbers, particularly if we foresee dedicated ROSA providers to aim
   at realizing those use cases.

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   For a service request, a hash-based service address lookup (using the
   Service EH entry) is performed, leading to next hop (NH) information
   for the IPv6 destination address to forward to (the final destination
   address at the last hop SAR will be the instance serving the service

   Forwarding the response utilizes the Client and Ingress EH fields,
   where the latter is used by the service instance's ingress SAR to
   forward the response to the client ingress SAR, while the former is
   used to eventually deliver the response to the client by the client's
   ingress SAR, ensuring proper firewall traversal of the response back
   to the client.  We have shown in prototype realizations of ROSA that
   the operations in Figure 3 can be performed using eBPF [eBPF]
   extensions to Linux SW routers, while [SarNet2021] showed the
   possibility a realizing a similar design using P4-based platforms.

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   Client            Ingress              Service           Service
                       SAR                Instance          Instance
   (CIP)             (SAR IP)             (SI1 IP)          (SI2 IP)
   (ClientIP,SAR IP)
   (CIP, SAR IP, ServiceID)
                         \ Determine ROSA
                         / and, ultimately, IP Next Hop

                         (SAR IP, SI1 IP)
                         (CIP, SAR IP, ServiceID)
                                               \ Generate
                                               / Response
                         (SI1 IP, SAR IP)
                         (CIP, SAR IP, ServiceID, SI1 IP)

   (SAR IP, CIP)
   (CIP, SAR IP, ServiceID, SI1 IP)

   (CIP, SI1 IP)
                                               \ Generate
                                               / Response

                      Figure 4: ROSA message exchanges

   Figure 4 shows the resulting end-to-end message exchange, using the
   aforementioned SAR-local forwarding decisions.  We here show the IP
   source and destination addresses in the first brackets and the
   extension header information in the second bracket.

   We can recognize two key aspects.  First, the SA/DA re-writing
   happens at the SARs, using the EH-provided information on service
   address, initial ingress SAR and client IP locators, as described
   above.  Second, the selection of the service instance is signalled

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   back to the client through the additional Instance EH field, which is
   used for sending subsequent (affinity) requests via the IPv6 network.
   As noted in the figure, when using transport layer security, the
   service request and response will relate to the security handshake,
   thereby being rather small in size, while the likely larger HTTP
   transaction is sent in affinity requests.  As discussed in
   Section 12, 0-RTT handshakes may result in transactions being
   performed in service request/response exchanges only.

7.5.  Traffic Steering

   Traffic steering in ROSA is applied to service requests for selecting
   the service instance that may serve the request, while affinity
   requests use existing IPv6 routing and any policies constraining
   traffic steering in this part of the overall system.  At receiving
   service endpoints, service provisioning platforms may use additional
   methods to schedule incoming service requests to suitable resources
   with the ingress point to the service provisioning platform being the
   service endpoint for ROSA.

   In the following, we outline two approaches for traffic steering.
   The first uses ingress-based scheduling decisions to steer traffic to
   one of the possible service instances for a given service address.
   The second follows a routing-based model, determining a single
   destination for a given service address using a routing protocol,
   similar to what is suggested in

   We envision that some services may be steered through scheduling
   methods, while others use routing approaches.  The indication which
   one to apply may be derived from the number of next hop entries for a
   service address.  In Figure 3, uses a scheduling method
   (with instances connected to SAR5 being exposed as a single instance
   to ROSA, using DC-internal methods for scheduling incoming requests),
   while the other services are routed via SARs.

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   We furthermore envision an interface to exist between the ROSA
   provider and the underlying network provider, exchanging routing
   policy relation information.  The richness of this interface depends
   on the specific business relation between both providers, i.e., the
   ROSA and the network provider.  In integrated settings, where ROSA
   and network provider may belong to the same commercial entity, this
   interface may provide rich routing policy relation information, such
   as network latency and bandwidth information, which in turn may be
   used in the ROSA traffic steering decisions.  In other, more
   disintegrated deployments, the information may entirely be limited to
   SLA-level information with no specific runtime information exchanged
   between both providers.  The exact nature of this interface remains
   for further study.

   Important here is that traffic steering is limited to a single ROSA
   domain, i.e., traffic steering is not provided across instances of
   the same service in different ROSA domains; traffic will always be
   steered to (ROSA) domain-local instances only.

7.5.1.  Ingress Request Scheduling

   Traffic steering through explicit request scheduling follows an
   approach similar to application- or transport-level solutions, such
   as GSLB [GSLB], DNS over HTTPS [RFC8484], HTTP indirection [RFC7231]
   or QUIC-LB [I-D.ietf-quic-load-balancers]: Traffic is routed to an
   indirection point which directs the traffic towards one of several
   possible destinations.

   In ROSA, this indirection point is the client's ingress SAR.
   However, unlike application or transport methods, scheduling is
   realized in-band when forwarding service requests in the ingress SAR,
   i.e., the original request is forwarded directly (not returned with
   indirection information upon which the client will act), while
   adhering to the affinity of a transaction by routing subsequent
   requests in a transaction using the instance's IP address.
   Scheduling commences to a possibly different instance with the start
   of a new transaction.

   For this, the ingress SAR's NHIB needs to hold information to ALL
   announced service instances for a service address.  Furthermore, any
   required information, e.g., capabilities or metric information, that
   is used for the scheduling decision is signalled via the service
   announcement, with (frequent) updates to existing announcements
   possible.  Announcements for services following a scheduling- rather
   than a routing-based steering approach carry suitably encoded
   information in the Constraint field of the announcement's EH, leading
   to announcements forwarded to client-facing ingress SARs without NHIB
   entries stored in intermediary SARs.

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   In addition, a scheduling decision needs to be realized in the SAR
   forwarding decision step of Figure 3.  This may require additional
   information to be maintained, such as instance-specific state,
   further increasing the additional NHIB data to be maintained.
   Examples for scheduling decisions are:

   *  Random selection of one of the service instances for a given
      service address, not requiring any additional state information
      per service address.  Announcing the service instance is required

   *  Round robin, i.e., cycling through service instance choices with
      every incoming service request, requiring to keep an internal
      counter for the current position in the NHIB for the service
      address.  Announcing the service instance is only required once.

   *  Capability-based round robin: Cycle through service instances in
      weighted round robin fashion with the weight (as additional
      information in each NHIB entry) representing a capability, e.g.,
      number of (normalized) compute resources committed to a service
      instance.  Announcing the service instance requires an update when
      capabilities change (e.g., during re-orchestration).  Weights
      could be expressed as numerals, limiting the needed semantic
      exposure of service provider knowledge and thereby supporting the
      possible separation of service and communication network provider.
      The solution in [CArDS2022] realises a compute-aware selection
      through such decision.

   *  Metric-based selection: Select service instance with lowest or
      highest reported metric, such as load, requiring to keep
      additional metric information per service instance entry in the
      NHIB.  Frequent signalling of the metric is required to keep this
      information updated.

   Although each method yields specific performance benefits, e.g.,
   reduced latency or smooth load distribution, [OnOff2022] outlines
   simulation-based insights into benefits for realising the compute-
   aware solution of [CArDS2022] in ROSA.

7.5.2.  Routing Across Multiple SARs

   In order to send a service request to the `best' service instance
   (among all announced ones) using a routing-based approach, we build
   NHIB routing entries by disseminating a service instance's
   announcement for a given service address S, arriving at its ingress
   SAR.  This distribution may be realized via a routing protocol or a
   central routing controller or a hybrid solution.

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   If no particular constraint is given in the announcement's EH
   Constraint field, shortest path will be realized as a default policy
   for selecting the `best' instance, routing any client's request to S
   the nearest service instance available.

   Alternatively, selecting a service instance may use service-specific
   policies (encoded in the Constraint field of the EH, with the
   specific encoding details being left for future work).  Here,
   multiple constraints may be used, with [Multi2020] providing a
   framework to determine optimal paths for such cases, while also
   conventional traffic engineering methods may be used.

   Through utilizing the work in [Multi2020], a number of multi-criteria
   examples can be modelled through a dominant path model, relying on a
   partial order only, as long as isotonicity is observed.  Typical
   examples here are widest-shortest path or shortest-widest routing
   (see [Multi2020]), which allow for performance metrics such as
   capacity, load, rate of requests, and others.  However, metrics such
   as failure rate or request completion time cannot directly be
   captured and need formulation as a max metric.  Furthermore, metrics
   may not be isotonic, with Section 3.4 of [Multi2020] supporting those
   cases through computing a set of dominant attributes according to the
   largest reduction.  [Multi2020] furthermore shows that non-restarting
   or restarting vectoring protocols may be used to compute dominant
   paths and to distribute the routing state throughout the network.

   However, the framework in [Multi2020] is limited to unicast vectoring
   protocols, while the routing problem in ROSA requires selecting the
   'best' path to the 'best' instance, i.e., as an anycast routing
   problem.  To capture this, [Multi2020] could be extended through
   introducing a (anycast) virtual node, placed at the end of a logical
   path that extends from each service instance to the virtual node.
   Selecting the best path (over the announced attributes of each
   service instance) to the virtual node will now select the best
   service instance (over which to reach the virtual node in the
   logically extended topology).

   Alternatively, ROSA routing may rely on methods for anycast routing,
   but formulated for service instead of anycast addresses.  For
   instance, AnyOpt [AnyOpt2021] uses a measurement-based approach to
   predict the best (in terms of latency) anycast (i.e. service)
   instance for a particular client.  Alternatively, approaches using
   regular expressions may be extended towards spanning a set of
   destinations rather than a single one.  Realizations in a routing
   controller would likely improve on convergence time compared to a
   distributed vector protocol; an aspect for further work to explore.

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7.6.  Interconnection

   There are two cases for interconnection: access to (i) non-ROSA
   services in the public Internet and (ii) ROSA services not domain-
   locally announced but existing in other domains.

   For both cases, we utilize a reserved wildcard service address '*'
   that points to a default route for any service address that is not
   being advertised in the local domain.  This default route is the
   service address gateway (see Figure 1), ultimately receiving the
   service request to the locally unknown service.

   Upon arriving at the SAG, it searches its local routing table for any
   information.  If none is found, it consults the DNS to retrieve an IP
   address where the service is hosted; those mappings could be cached
   for improving future requests or being pre-populated for popular

   For case (i), the resolution returns a server's IP address to which
   the SAG sends the service request with its own IP address as source
   address.  The service response is routed back via the SAG, which in
   turn uses the Ingress EH information to return the response to the
   client via its ingress SAR.

   For case (ii), the IP address would be that of the SAG of the ROSA
   domain in which the service is hosted.  For this, a domain-local
   service instance would have exposed its service, e.g.,
   video Figure 1, by registering its domain-local SAG IP address with
   the mapping service.  To suitably forward the request, the SAG adds
   its own IP address as the value to an additional SAG label into the
   extension header.  At the destination SAG, the service address
   information, extracted from the extension header, is used to forward
   the service request based on ROSA mechanisms.  For the service
   response, the destination SAG uses the SAG entry in the EH to return
   the response to the originating ROSA domain's SAG, which in turn uses
   the Ingress information of the EH to return the response via the
   ingress to the client.

   Given the EH deployment issues pointed out in [SHIM2014], a UDP-based
   encapsulation may overcome the observed issues, not relying on the EH
   being properly observed during the traversal over the public
   Internet.  Furthermore, while Figure 1 shows the SAG as an
   independent component, we foresee deployments in existing PoPs.  This
   would allow combining provisioning through frontloaded PoP-based
   services and ROSA services.  Any service not explicitly announced in
   the ROSA system would lead to being routed to the PoP-based SAG,
   which may use any locally deployed services before forwarding the
   request to the public Internet.

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8.  Extensions to Base ROSA Capabilities

   ROSA, as defined in Section 7, can be extended to address various
   capabilities useful for specific or across a number of use cases.
   The following provides a list of those possible extended
   capabilities.  At this stage, we would expect those capabilities to
   be defined in more detail in separate drafts, complementing the ROSA
   'base' specification, as defined in this current draft.

8.1.  Supporting Different Namespace Encodings

   Although most of our examples assume the use of URL-based service
   addresses, encoded using [RFC8609], supporting other, e.g., corporate
   service, namespaces may be desired.  [RFC8609] generally supports
   this and could thus be used.

   As briefly alluded to in Section 7.2, other encodings to that
   following [RFC8609] may be used, focussing on different ways to
   represent a service address differently, including linking it to the
   service name used at the application level.

   One such encoding may be that of a unique service address per service
   name, with the linkage between both provided through the DNS.  Here,
   the client sends an initial DNS query with the URL of the purported
   service or application.  Instead of requesting a resolution to a
   locator, however, is the request for mapping between the URL and the
   service address of ROSA, where the service address has been assigned
   as part of the domain name registration (which may be done after
   initial registration of the domain name for backward compatibility).
   Service addresses here may be simply encoded as numerals, where
   uniqueness is achieved through linking to the domain name
   registration and thus DNS mapping.  Encoding in the respective EH
   header field (see Section 7.2) would be shorter and thus more
   efficient, still achieving the desired uniqueness in the SAR
   forwarding process to avoid ambiguity in forwarding decisions.  The
   drawback is the need for the additional DNS mapping step (albeit only
   required once per application, where the service address could be
   stored persistently for later use), while also the additional DNS
   mapping will need standardization (likely in the form of a new DNS

   Another possible encoding, without the aforementioned explicit DNS
   mapping step, could be to explicitly hash the service name into a
   service address at the ROSA endpoint, operating on those hash values
   for service announcement and requests.  Due to the large service
   namespace, hash conflicts may, however, occur, which needs resolving
   at the SAR (which may operate on a service address for a service
   request for a different, but same hashed, service address of an

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   announcement service).  Further study is needed into the probability
   for such hash conflicts and possible mitigation methods for such

   If the use of different encoding methods beyond [RFC8609] was to be
   considered, appropriate modifications to the EH fields need to be
   done to signal the used encoding method for the service address.

8.2.  Supporting Multi-Homing of Service Instances

   Multi-homed service instances may benefit from path-aware routing
   decisions after mapping service addresses to service instance
   addresses.  To that end, service instances would need to advertise
   multiple instance IPs as part of their service announcement.

   The optimal path may differ while a client communicates with a
   service instance; this is in particular likely for mobile clients.
   This provides some complication for affinity requests; in such a
   case, the service instance IP is no longer sufficient to identify a
   service instance, merely to locate a particular path.

   Multi-homing issues in connection with aircrafts also extend to
   Unmanned Aerial Systems (UAS).  Rather than focusing on passenger
   experience, multi-homing over commercial off-the-shelf (COTS)
   communications modules such as 5G or IEEE 802.11 provides command,
   control and communications (C3) capabilities to Unmanned Aerial
   Vehicles (UAV; drones).  Despite the difference in focus, the
   technical challenges in maintaining connection quality are largely

   Multi-homing thus either requires an undesirable further resolution
   step from a service instance identifier to a (optimal path) locator.
   Alternatively, ROSA message types may be extended to include a
   distinct service instance identifier and service instance locator
   identifiers, i.e., IP addresses, which provides sufficient
   information for SARs to map to specific and changing locators, while
   retaining the affinity to the service instance by identifier.

8.3.  Supporting 0-RTT TLS

   TBD Dirk

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8.4.  Supporting Transaction Mobility

   When it comes to the transaction mobility in which the serving
   service instance needs to be shifted to another selected alternative
   instance, the ROSA service address could provide a good starting as
   an location-independent ID.  Other than TCP for which the client and
   server have to maintain strict machine state, UDP-based protocol
   could be extended with the service address to be treated as the
   connection ID rather than the traditional 4-tuple including the host
   destination address when the server does not have to maintain session
   state.  The chief gain here is the service connection could remain
   intact when the serving service instance has been switched over at
   ROSA level (routing plane).

   As part of the ability to switch over from one service instance, ROSA
   may explicitly support that mobility in that the choice of the (new)
   service instance is explicitly made within the service-specific
   traffic steering method.  For this, ROSA may introduce a separate
   message alongside the service request message (see see Section 7.2),
   which not only allows for the ingress SAR to perform the same routing
   policy as if it was sent through a new service request message, but
   may also include application-specific context data to facilitate the
   needed application state transfer from the original service instance
   to the new one.  Here, the in-band capability of a ROSA request is
   being used to carry this context data as part of the new ROSA

8.5.  Supporting Service Function Chaining

   Service Function Chaining (SFC) [RFC7665] allows for chaining the
   execution of services at L2 or L3 level, targeting scenarios such as
   carrier-grade NAT and others.  The work in [RFC8677] extends the
   chaining onto the name level, using service names to identify the
   individual services of the chain, even allowing combinations of name
   and L2/L3-based chains.

   Although [RFC8677] is tied into a realization of the SFF (service
   function forwarder) using a path-based forwarding approach, the
   concept of name-based SFCs can equally be realized utilizing ROSA.

8.6.  Supporting Privacy-Compliant Communication

   The exposure of service-related information in the ROSA EHs may be
   seen as a privacy issue, particularly when utilizing the service name
   as the basis for the service address formulation.  Although
   Section 12 outlines the possible use of service categories (instead
   of finer-grained service names) as input into the service address
   formulation, it is also desirable to protect the privacy of fine-

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   grained service address information, should the specific ROSA
   deployment make use of them.

   Beyond using encryption methods to protect the ROSA EH information,
   such privacy methods could also include the obfuscation of client and
   transit information as well, thus moving into the space of routing
   privacy, as outlined for instance in

9.  Prototype-based Insights

   To come before IETF116 with description of planned demo to
   demonstrate some of the benefits outlined in Section 6.

10.  Open Issues

   There are a number of open issues with the following list providing a
   non-exhaustive list of examples:

   1  A ROSA control plane is required for handling aspects of ingress
      SAR discovery and signalling of service instance announcements to
      the ROSA network, either to ingress SARs only (for services
      utilizing traffic scheduling mode) or across all domain-internal
      SARs.  Here, the signalling for achieving interconnections, based
      on the methods outlined in Section 7.6, is also required to be

   2  Possible segmentation of ROSA service request and responses need

   3  Prototypical but also possibly simulation-based insights into
      benefits are desirable to motivate the adoption of ROSA.

11.  Conclusions

   This draft outlined a methods for service-specific traffic steering
   through an IPv6 EH-based shim overlay, allowing for routing on
   service addresses as either ingress-based instance selection or
   through multi-SAR routing methods.

   As next steps, we plan on extending various aspects of the ROSA
   operations, specifically to address the open issues listed in the
   previous section, e.g., control plane aspects such as SAR discovery
   and routing protocol, support for service request segmentation, and
   others.  We expect that aspects for a ROSA control plane, e.g., to
   signal suitable traffic steering parameters to the ingress SARs or to
   establish multi-SAR routing state, are captured in separate works.

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   We furthermore have plans on bringing an eBPF-based prototypical
   realization of the forwarding behaviour in Section 7.4 to future IETF
   events, e.g., for a hackathon participation to showcase ROSA-based
   applications in a test setup.

12.  Security Considerations

   Aligned with security considerations in existing service provisioning
   systems, we address aspects related to authenticity, i.e., preventing
   fake service announcements, confidentiality, both in securing
   relationship as well as payload information, and operational

   *  Announcement security: A key exchange between service and network
      provider may be used to secure the service announcement for
      ensuring an authorized announcement of services.  Self-certifying
      identifiers could be used for this purpose

   *  Relationship security: Using service addresses at the routing
      layer poses not just a privacy but possibly also a net neutrality
      problem, allowing for non-ROSA elements to discriminate against
      specific service addresses.  Similar to
      [I-D.per-app-networking-considerations], service addresses could
      reflect service categories, not services themselves.  Service
      endpoints to those category-level services can use information in
      the secured payload (e.g., the URL in an HTTP-based service
      invocation) to direct the traffic accordingly.  The downside of
      such model is a possible convergence towards a PoP-like model of
      service provisioning, since exposing an entire service category
      naturally requires provisioning many possible services under that
      category, likely favouring large-scale providers over smaller
      ones; an imbalance that ROSA intends to change, not favour.  Work
      on identity privacy in ILNP [ILNP2021] has shown that ephemeral
      identifiers may increase the private nature of the communication
      relation; a direction that needs further exploration in the
      context of our work.  Also, the service address in the extension
      header could be encrypted, based on a key exchange during the SAR
      discovery.  However, the impact of such mechanism would need
      further study.

   *  Transport-level security: Given the often sensitive nature of
      service requests, payload security is key.  We adopt techniques
      used in TLSV1.3 [RFC8446], providing a 1-RTT handshake for
      communication between formerly untrusted parties.  While the
      initial 'Client Hello' is sent as a service request, the
      subsequent communication uses the topological address of the
      responding server in an affinity request.  Using pre-shared keys
      may allow for communication between trusted client and service

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      instances, e.g., where the client is provided by the service
      authority and preconfigured with a pre-shared key.  This results
      in a 0-RTT handshake with the 'Client Hello' including the initial
      service data, encrypted with the pre-shared key.  This comes with
      known forward-secrecy issues and should be avoided in networks
      with untrusted intermediary nodes.  Alternatively, the service's
      public key could encrypt the initial security handshake, akin to
      the solutions proposed for Encrypted Client Hello (ECH), using the
      DNS for obtaining the public key.

   *  Bandwidth DoS: We assume network provider level mechanisms to
      restrict traffic injected both by the service provider and client,
      including for the number of service advertisements in order to
      control the routing traffic.

   *  Denying routing service: A SAR could maliciously deny forwarding
      of client requests, which is no different from denying IP packet
      forwarding.  In both cases, we assume an existing commercial
      relationship that avoids such situation.

13.  Privacy Considerations

   The exposure of service-related information in the ROSA EHs may be
   seen as a privacy issue, particularly when utilizing the service name
   as the basis for the service address formulation.  As discussed in
   Section 8.6, extensions to the base ROSA capabilities may address
   this issue to ensure the privacy of the clients' communication
   relations in ROSA deployments, where needed.

14.  IANA Considerations

   This draft does not request any IANA action.

15.  Change Log

   1   Restructured introduction to improve readability and
       argumentation for this draft

   2   Addressing IETF115 comments in various parts of the draft, e.g.,
       introduction, analysis (relation to other technologies), traffic
       steering (relation to anycast) etc

   3   Added six new use cases (mobile applications - Section 3.4, chunk
       retrieval - Section 3.5, AR/VR - Section 3.6, Cloud-to-Thing -
       Section 3.7, Metaverse - Section 3.8, and popularity-based
       services - Section 3.9)

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   4   Added separate analysis section, as derived from use cases
       (Section 4)

   5   Revised and linked requirements to use cases through additional
       text (Section 5)

   6   Discussed possible benefits from applying ROSA in identified use
       cases (Section 6)

   7   Revised ROSA messages figure (Figure 2)

   8   Added section on possible extended capabilities to 'base' ROSA
       (Section 8), including multi-homing support, namespace support.

   9   Added and maintaining open issues (Section 10)

   10  Added missing sections, like conclusions (Section 11) and privacy
       considerations (Section 13)

   11  Added Jens Finkhaeuser, Daniel Huang, and Paulo Mendes as co-

16.  Acknowledgements

   Many thanks go to Mohamed Boucadair, Tommy Pauly, Joel Halpern, and
   Russ White for their comments to the text to clarify several aspects
   of the motiviation for and technical details of ROSA.

17.  Informative References

              Zhang, Z., April, T., Chandrasekaran, B., Choffnes, D.,
              Maggs, B. M., Shen, H., Sitaraman, R. K., Yang, X., Zhang,
              X., and T. Sen, "AnyOpt: predicting and optimizing IP
              Anycast performance", Paper ACM SIGCOMM, 2021.

   [BBF]      ""Control and User Plane Separation for a disaggregated
              BNG"", Technical Report-459 Broadband Forum (BBF), 2020.

              Khandaker, K., Trossen, D., Khalili, R., Despotovic, Z.,
              Hecker, A., and G. Carle, "CArDS:Dealing a New Hand in
              Reducing Service Request Completion Times", Paper IFIP
              Networking, 2022.

   [CV19]     Feldmann, A., Gasser, O., Lichtblau, F., Pujol, E., Poese,
              I., Dietzel, C., Wagner, D., Wichtlhuber, M., Tapiador,
              J., Vallina-Rodriguez, N., Hohlfeld, O., and G.

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              Smaragdakis, "A Year in Lockdown: How the Waves of
              COVID-19 Impact Internet Traffic", Paper Communications of
              ACM 64, 7 (2021), 101-108, 2021.

   [eBPF]     "What is eBPF?", Technical Report eBPF Foundation, 2022,

   [EI2021]   Cidon, I., Culler, D., Estrin, D., Katz-Bassett, E.,
              Krishnamurthy, A., McCauley, M., McKeown, N., Panda, A.,
              Ratnasamy, S., Rexford, J., Schapira, M., Shenker, S.,
              Stoica, I., Tennenhouse, D., Vahdat, A., Zegura, E.,
              Balakrishnan, H., and S. Banerjee, "Revitalizing the
              public internet by making it extensible", Paper ACM
              Computer Communication Review, Vol. 51. 18-24. Issue 2,

   [Gini]     "Gini Coefficient", Technical Report Wikipedia, 2022,

   [GSLB]     "What is GSLB?", Technical Report Efficient IP, 2022,

   [HHI]      "Herfindahl-Hirschman index", Technical Report Wikipedia,
              2022, <

              Huston, G., "Internet Centrality and its Impact on
              Routing", Technical Report IETF side meeting on 'service
              routing and addressing', 2021,

              Salsano, S., ElBakoury, H., and D. Lopez, "Extensible In-
              band Processing (EIP) Architecture and Framework", Work in
              Progress, Internet-Draft, draft-eip-arch-01, 16 December

              Huang, D., Tan, B., and D. Yang, "Service Aware Network
              Framework", Work in Progress, Internet-Draft, draft-huang-
              service-aware-network-framework-01, 22 November 2022,

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              Cabellos-Aparicio, A. and D. Saucez, "An Architectural
              Introduction to the Locator/ID Separation Protocol
              (LISP)", Work in Progress, Internet-Draft, draft-ietf-
              lisp-introduction-15, 20 September 2021,

              Duke, M., Banks, N., and C. Huitema, "QUIC-LB: Generating
              Routable QUIC Connection IDs", Work in Progress, Internet-
              Draft, draft-ietf-quic-load-balancers-15, 24 October 2022,

              Finkel, M., Lassey, B., Iannone, L., and B. Chen, "IP
              Address Privacy Considerations", Work in Progress,
              Internet-Draft, draft-ip-address-privacy-considerations-
              03, 10 January 2022, <

              Jennings, C. and S. Nandakumar, "QuicR - Media Delivery
              Protocol over QUIC", Work in Progress, Internet-Draft,
              draft-jennings-moq-quicr-arch-01, 11 July 2022,

              Liu, P., Jiang, T., Eardley, P., Trossen, D., Li, C., and
              D. Huang, "Computing-Aware Networking (CAN) Gap Analysis
              and Requirements", Work in Progress, Internet-Draft,
              draft-liu-can-gap-reqs-00, 23 October 2022,

              Liu, P., Eardley, P., Trossen, D., Boucadair, M.,
              Contreras, L. M., Li, C., and Y. Li, "Computing-Aware
              Networking (CAN) Problem Statement and Use Cases", Work in
              Progress, Internet-Draft, draft-liu-can-ps-usecases-00, 23
              October 2022, <

              Ma, L., Zhao, D., Zhou, F., and D. Yang, "Encapsulation of
              SAN Header", Work in Progress, Internet-Draft, draft-ma-

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              intarea-encapsulation-of-san-header-00, 23 October 2022,

              Nottingham, M., "Internet Consolidation: What can
              Standards Efforts Do?", Work in Progress, Internet-Draft,
              draft-nottingham-avoiding-internet-centralization-07, 17
              January 2023, <

              Colitti, L. and T. Pauly, "Per-Application Networking
              Considerations", Work in Progress, Internet-Draft, draft-
              per-app-networking-considerations-00, 15 November 2020,

              Trossen, D., Sarathchandra, C., and M. Boniface, "In-
              Network Computing for App-Centric Micro-Services", Work in
              Progress, Internet-Draft, draft-sarathchandra-coin-
              appcentres-04, 26 January 2021,

              Wadhwa, S., Shinde, R., Newton, J., Hoffman, R., Muley,
              P., and S. Pani, "Architecture for Control and User Plane
              Separation on BNG", Work in Progress, Internet-Draft,
              draft-wadhwa-rtgwg-bng-cups-03, 11 March 2019,

   [ILNP2021] Yanagida, R., Bhatti, S., and G. Haywood, "End-to-end
              privacy for identity and location with IP", Paper 2nd
              Workshop on New Internetworking Protocols, Architecture
              and Algorithms, 29th IEEE International Conference on
              Network Protocols, 2021.

   [ISOC2022] "Internet Centralization", Technical Report ISOC
              Dashboard, 2022,

   [MCN]      ""Metro Compute Networking: Use Cases and High Level
              Requirements"", Technical Report-466 Broadband Forum
              (BBF), 2021.

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              Ferreira, M. A. and J. L. Sobrinho, "Routing on Multi
              Optimality Criteria", Paper ACM SIGCOMM, 2020.

              Reid, A., Eardley, P., and D. Kutscher, "Namespaces,
              Security, and Network Addresses", Paper ACM SIGCOMM
              workshop on Future of Internet Routing and Addressing
              (FIRA), 2022.

              Khandaker, K., Trossen, D., Yang, J., Despotovic, Z., and
              G. Carle, "On-path vs Off-path Traffic Steering, That Is
              The Question", Paper ACM SIGCOMM workshop on Future of
              Internet Routing and Addressing (FIRA), 2022.

              Kuehlewind, M., Trammell, B., and C. Perkins, "Post
              sockets: Towards an evolvable network transport
              interface", Paper IFIP Networking Conference (IFIP
              Networking) and Workshops, 2017.

   [RFC6770]  Bertrand, G., Ed., Stephan, E., Burbridge, T., Eardley,
              P., Ma, K., and G. Watson, "Use Cases for Content Delivery
              Network Interconnection", RFC 6770, DOI 10.17487/RFC6770,
              November 2012, <>.

   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              DOI 10.17487/RFC7231, June 2014,

   [RFC7234]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
              RFC 7234, DOI 10.17487/RFC7234, June 2014,

   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665,
              DOI 10.17487/RFC7665, October 2015,

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,

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   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,

   [RFC8484]  Hoffman, P. and P. McManus, "DNS Queries over HTTPS
              (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,

   [RFC8609]  Mosko, M., Solis, I., and C. Wood, "Content-Centric
              Networking (CCNx) Messages in TLV Format", RFC 8609,
              DOI 10.17487/RFC8609, July 2019,

   [RFC8677]  Trossen, D., Purkayastha, D., and A. Rahman, "Name-Based
              Service Function Forwarder (nSFF) Component within a
              Service Function Chaining (SFC) Framework", RFC 8677,
              DOI 10.17487/RFC8677, November 2019,

   [RFC8949]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", STD 94, RFC 8949,
              DOI 10.17487/RFC8949, December 2020,

   [RFC8986]  Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
              D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
              (SRv6) Network Programming", RFC 8986,
              DOI 10.17487/RFC8986, February 2021,

   [RFC9213]  Ludin, S., Nottingham, M., and Y. Wu, "Targeted HTTP Cache
              Control", RFC 9213, DOI 10.17487/RFC9213, June 2022,

              Glebke, R., Trossen, D., Kunze, I., Lou, Z., Rueth, J.,
              Stoffers, M., and K. Wehrle, "Service-based Forwarding via
              Programmable Dataplanes", Paper 1st Intl Workshop on
              Semantic Addressing and Routing for Future Networks, 2021.

   [SHIM2014] Naderi, H. and B. Carpenter, "Putting SHIM6 into
              practice", Paper 2014 Australasian Telecommunication
              Networks and Applications Conference (ATNAC), 2014.

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   [SOI2020]  Jiang, S., Li, G., and B. Carpenter, "A New Approach to a
              Service Oriented Internet Protocol", Paper IEEE INFOCOM
              2020 - IEEE Conference on Computer Communications
              Workshops (INFOCOM WKSHPS), 2020.

   [SVA]      ""Optimizing Video Delivery With The Open Caching
              Network"", Technical Report Streaming Video Alliance,

   [TIES2021] Giotsas, V., Kerola, S., Majkowski, M., Odinstov, P.,
              Sitnicki, J., Chung, T., Levin, D., Mislove, A., Wood, C.
              A., Sullivan, N., Fayed, M., and L. Bauer, "The Ties that
              un-Bind: Decoupling IP from web services and sockets for
              robust addressing agility at CDN-scale", Paper ACM
              SIGCOMM, 2021.

   [TS23501]  "System architecture for the 5G System (5GS); Stage 2
              (Release 16)", Technical Report 3GPP TS 23.501 V16.11.0
              (2021-12), 2021,

Authors' Addresses

   Dirk Trossen
   Huawei Technologies
   80992 Munich

   Luis M. Contreras
   Ronda de la Comunicacion, s/n
   Sur-3 building, 1st floor
   28050 Madrid

   Jens Finkhaeuser
   Interpeer gUG
   86926 Greifenberg

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   Paulo Mendes
   82024 Taufkirchen

   Daniel Huang
   ZTE Corporation

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