MAP-Me : Managing Anchorless Mobility in Content Centric Networking
draft-irtf-icnrg-mapme-04

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icnrg                                                       J. Auge, Ed.
Internet-Draft                                             G. Carofiglio
Intended status: Informational                            L. Muscariello
Expires: May 3, 2020                                         M. Papalini
                                                      Cisco Systems Inc.
                                                        October 31, 2019

  MAP-Me : Managing Anchorless Mobility in Content Centric Networking
                       draft-irtf-icnrg-mapme-04

Abstract

   Consumer mobility is supported in ICN by design, in virtue of its
   connectionless pull-based communication model; producer mobility
   though is not natively supported.  This document describes MAP-Me, an
   anchor-less solution to manage micro-mobility of content producers in
   the CCN (Content Centric Networking) and NDN (Named Data Networking)
   architectures, with support for latency-sensitive applications.  MAP-
   Me consists in the combination of two data plane protocols, triggered
   by producer movements, and leveraging ICN named-based data plane.
   The main protocol consists in a lightweight FIB update process,
   complemented by a mechanism of local notification and scoped
   discovery suitable for low latency applications and fast mobility.

Status of This Memo

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Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  MAP-Me overview . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Anchor-less mobility management . . . . . . . . . . . . .   4
     2.2.  Design principles . . . . . . . . . . . . . . . . . . . .   4
     2.3.  MAP-Me protocols  . . . . . . . . . . . . . . . . . . . .   5
   3.  Update protocol . . . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Rationale . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  Update propagation  . . . . . . . . . . . . . . . . . . .   6
     3.3.  Concurrent updates  . . . . . . . . . . . . . . . . . . .  10
   4.  Notification protocol and scoped discovery  . . . . . . . . .  12
     4.1.  Interest Notification . . . . . . . . . . . . . . . . . .  12
     4.2.  Scoped discovery  . . . . . . . . . . . . . . . . . . . .  13
     4.3.  Full approach . . . . . . . . . . . . . . . . . . . . . .  13
   5.  Implementation  . . . . . . . . . . . . . . . . . . . . . . .  13
     5.1.  MAP-Me messages . . . . . . . . . . . . . . . . . . . . .  13
     5.2.  Data structures and temporary state . . . . . . . . . . .  14
     5.3.  Algorithm description . . . . . . . . . . . . . . . . . .  15
       5.3.1.  Producer attachment and face creation . . . . . . . .  15
       5.3.2.  IU/IN transmission at producer  . . . . . . . . . . .  15
       5.3.3.  IU/IN transmission at network routers . . . . . . . .  15
       5.3.4.  Reliable transmission . . . . . . . . . . . . . . . .  16
       5.3.5.  Consumer request forwarding in case of producer
               discovery . . . . . . . . . . . . . . . . . . . . . .  17
       5.3.6.  Producer departure and face destruction . . . . . . .  18
   6.  Security considerations . . . . . . . . . . . . . . . . . . .  18
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  18
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  18
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20

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1.  Introduction

   With the phenomenal spread of portable user devices, mobility has
   become a basic requirement for almost any communication network as
   well as a compelling feature to integrate in the next generation
   networks (5G).  The need for a mobility-management paradigm to apply
   within IP networks has striven a lot of efforts in research and
   standardization bodies (IETF, 3GPP among others), all resulting in a
   complex access-dependent set of mechanisms implemented via a
   dedicated control infrastructure.  The complexity and lack of
   flexibility of such approaches (e.g.  Mobile IP) calls for a
   radically new solution dismantling traditional assumptions like
   tunneling and anchoring of all mobile communications into the network
   core.  This is particularly important with the increase in rates and
   mobile nodes (IoT), a vast amount of which never moves.

   The Information Centric Network (ICN) paradigm brings native support
   for mobility, security, and storage within the network architecture,
   hence emerging as a promising 5G technology candidate.  Specifically
   on mobility management, ICN has the potential to relieve limitations
   of the existing approaches by leveraging its primary feature, the
   redefinition of packet forwarding based on "names" rather than
   "network addresses".  Removing the dependence on location identifiers
   is a first step in the direction of removing the need for any
   anchoring of communications into fixed network nodes, which may
   considerably simplify and improve mobility management.  Within the
   ICN paradigm, several architectures have been proposed, as reported
   in [SURVEY12] and [SURVEY14].

   As a direct result of CCN/NDN design principles, consumer mobility is
   natively supported: a change in physical location for the consumer
   does not translate into a change in the data plane like for IP.  The
   retransmission of requests for data not yet received by the consumer
   takes place without involving any signaling to the network.  Producer
   mobility and realtime group communications present more challenges,
   depending on the frequency of movements, latency requirements, and
   content lifetime.  The topology does not reflect the naming
   structure, and the mobility management process has to preserve key
   functionalities such as multipath, caching, etc.  In all cases,
   beyond providing connectivity guarantees, additional transport-level
   mechanisms might be required to protect the flow performance (see
   [WLDR] for instance).

   MAP-Me aims at tackling such problems by exploiting key CCN/NDN
   characteristics.  Previous attempts have been made in CCN/NDN (and
   ICN in general) literature to go beyond the traditional IP
   approaches, by using the existing CCN/NDN request/data packet
   structures to trace producer movements and to dynamically build a

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   reverse-forwarding path (see [SURVEY16b] for a survey).  They still
   rely on a stable home address to inform about producer movements or
   on buffering of incoming requests at the producer's previous point of
   attachment (PoA), which prevents support for latency-sensitive
   streaming applications.  The approach presented in this document
   makes a particular focus on this class of applications (e.g. live
   streaming or videoconferencing) as they have the most stringent
   performance requirements: negligible per-packet loss-rate and delays.
   In addition, they typically originate from a single producer and
   don't allow for the use of caching.

   MAP-Me defines a name-based mechanism operating in the forwarding
   plane and completely removing any anchoring, while aiming at latency
   minimization.  Its performance and guarantees of correctness,
   stability and bounded stretch are analyzed in [MAPME].

2.  MAP-Me overview

2.1.  Anchor-less mobility management

   Many efforts have been made to define mobility-management models for
   IP networks in the last two decades, resulting in a variety of
   complex, often not implemented, proposals.  A survey of these
   approaches is proposed in [RFC6301].  Likewise, within ICN, different
   approaches to mobility management have been presented [SURVEY13].
   Specifically for the CCN/NDN solutions, several surveys of mobility-
   management approaches can be found [SURVEY16a] [SURVEY16b].

   We follow here the classification presented in [MAPME] which
   highlights their reliance on indirection/rendez-vous points.  In
   particular, a new class of anchor-less approaches is introduced, in
   which the present proposal fits.  Such solutions are less common and
   have been introduced in ICN to remove the need for anchor points in
   the data plane, but also in the control plane in the form of
   resolution or mapping services.  These solutions completely remove
   the use of locators and extend the ICN forwarding mechanisms with
   mobility support.

2.2.  Design principles

   o  *Micro-Mobility* : MAP-Me addresses micro (e.g. intra Autonomous
      Systems) producer mobility.  Addressing macro-mobility is a non-
      goal of the proposal.  We are focusing here on complementary
      mechanisms able to provide a fast and lightweight handover,
      preserving the performance of flows in progress.

      *  *Control Plane Agnostic* : MAP-Me _is control-plane agnostic as
         it does not rely on routing updates or path computation_, which

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         would be too slow and too costly, but rather works at a faster
         timescale propagating forwarding updates on a single path.  It
         also leverages real-time notifications left as breadcrumbs by
         the producer to enable live tracking of its content prefixes
         and avoid buffering at intermediate nodes.  MAP-Me shares the
         use of data plane mechanisms for ensuring connectivity with
         [DATAPLANE] which was originally proposed for link failures.
         This enables the support of high-speed mobility and real-time
         group applications.  In addition, MAP-Me mobility updates are
         issued at prefix granularity, rather than content or chunk/
         packet granularity, to minimize signaling overhead and
         temporary state kept by in-network nodes, and scale to large
         and dynamic mobile networks.

   o  *Access-agnostic* : MAP-Me handles mobility at Layer 3 and is
      designed to be access-agnostic, to cope with highly heterogeneous
      wireless access and multi-homed/mobile users.

   o  *Decentralized and localized* : MAP-Me is designed to be fully
      _decentralized_, to enhance robustness w.r.t. centralized mobility
      management proposals subject to single point-of-passage problem.
      MAP-Me updates are _localized_ and affect a minimum number of
      routers at the edge of the network to restore connectivity.  This
      effectively realizes traffic off-load close to the end-users.

   o  *Transparent* : MAP-Me does not involve any name nor modifications
      to basic request/reply operations to be compatible with standard
      CCN/NDN design and to avoid issues caused by name modifications
      like triangular routing, caching degradation, or security
      vulnerabilities.  It does not require consumers or producers to be
      aware of the mobility of the remote endpoint, nor to perform any
      handover prediction.

   o  *Robust* : to network conditions (e.g. routing failure, wireless
      or congestion losses, and delays), by implementing hop-by-hop
      retransmissions of mobility updates.

2.3.  MAP-Me protocols

   As a data plane protocol, MAP-Me handles producer mobility events by
   means of dynamic FIB updates with the objective of minimizing
   unreachability of the producer.  It relies on the existence of a
   routing protocol responsible for creating/updating the FIB of all
   routers, possibly with multipath routes, and for managing network
   failures (eg.  [NLSR]).

   MAP-Me is composed of:

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   o  an Update protocol, detailed in Section 3, which is the central
      component of the proposal;

   o  a Notification/Discovery protocol, presented in Section 4, which
      is coupled with the Update protocol to enhance reactivity for
      realtime/latency-sensitive application, and reduce overhead during
      fast mobility events.

3.  Update protocol

3.1.  Rationale

   The rationale behind MAP-Me is that the producer announces its
   movements to the network for all served prefixes, by sending a
   special Interest packet - named Interest Update (IU) - to "itself"
   after it reattaches to the network.  Such a message looks like a
   regular Interest packet named with the prefix advertised by the
   producer.  As such, it is forwarded according to the information
   stored in the FIBs of traversed routers towards all previous
   locations of the producer known by router FIBs.  A special flag
   carried in the header of the IU enables all routers on the path to
   identify the Interest as a mobility update and to process it
   accordingly to update their FIBs (a detailed description of the IU
   processing is provided in Section 5.3).

   The key aspect of the proposal is that it removes the need for a
   stable home address by directly leveraging name-based forwarding
   information created by CCN/NDN routing protocols, and eventually
   further updated due to mobility.  FIB updates are triggered by the
   reception of mobility updates in a fully decentralized way and allow
   an on-the-fly modification to point to the latest known location of
   the producer.

3.2.  Update propagation

   The role of the update process is to quickly restore global
   reachability of mobile prefixes with low signaling overhead, while
   introducing a bounded maximum path stretch (the ratio between the
   selected and the shortest path in terms of hops).

   Let us illustrate its behavior through an example where a single
   producer serving prefix /p moves from position P0 to P1 and so on.
   Figure 1 (a) shows the initial tree formed by the forwarding paths to
   the name prefix /p, and on which any IU initiated by the producer
   will propagate.

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                            +---+                        +---+
                            | 0 | P0                      | 0 | P0
                            +---+                         +---+
                             ^ ^                           ^ ^
                            /   \                         /   \
                        +---+    +---+                +---+    +---+
                        | 0 |    | 0 |                | 0 |    | 0 |
                        +---+    +---+                +---+    +---+
                         ^ ^                           ^ ^
                        /   \                         /   \
                    +---+    +---+                +---+    +---+
                    | 0 |    | 0 |                | 0 |    | 0 |
                    +---+    +---+             A  +---+    +---+
                     ^ ^                  IU1 /    ^ ^
                    /   \                    /    /   \
                +---+    +---+          .... .+---+.   +---+
                | 0 |    | 0 |         .   P1 | 1 | .  | 0 |
                +---+    +---+        .       +---+ .  +---+
                 ^ ^                  .        ^ ^    .
                /   \                 .       /   \     .
            +---+    +---+            .   +---+    +---+  .
            | 0 |    | 0 |            .   | 0 |    | 0 |  .
            +---+    +---+            .   +---+    +---+ .
                                       ..................

                     (a)                       (b)

                     Figure 1: IU propagation example

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                                                   .................
                            +---+               ...       +---+     ..
                            | 0 | P0           .          | 1 | P0    .
                            +---+             .        A  +---+       .
                             ^ ^             .  IU(1) /    / ^        .
                            /   \            .       /    V   \       .
                        +---+    +---+      .         +---+    +---+  .
                        | 0 |    | 0 |     .          | 1 |    | 0 |  .
                        +---+    +---+    .        A  +---+    +---+  .
                         ^ ^              . IU(1) /    / ^           .
                        /   \            .       /    V   \         .
            ........+---+.   +---+      .         +---+    +---+   .
           .        | 1 | .  | 0 |     .          | 1 |    | 0 |   .
          .  FIB    +---+ .  +---+    .        A  +---+    +---+   .
         . updated   / ^   .          . IU(1) /    / ^            .
         .          V   \   ....      .      /    V   \          .
         .      +---+    +---+  .     .       +---+    +---+   .
         .  P1  | 1 |    | 0 |  .     .    P1 | 1 |    | 0 |   .
         .      +---+    +---+  .     .       +---+    +---+   .
         .       ^ ^            .     .        ^ ^            .
         .      /   \          .       .      /   \         .
         .  +---+    +---+    .        .  +---+    +---+  .
         .  | 0 |    | 0 |   .         .  | 0 |    | 0 |  .
         .  +---+    +---+  .          .  +---+    +---+  .
          ..................            ..................

                     (a)                       (b)

                     Figure 2: IU propagation example

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                            +---+
                            | 1 | P1
                            +---+
                           ^  A  ^
                         /    |    \
                    +---+   +---+   +---+
                    | 0 |   | 0 |   | 1 |
                    +---+   +---+   +---+
                                     ^ ^
                                    /   \
                                +---+    +---+
                                | 0 |    | 1 |
                                +---+    +---+
                                          ^ ^
                                         /   \
                                     +---+    +---+
                                 P0  | 1 |    | 0 |
                                     +---+    +---+
                                      ^
                                     /
                                 +---+
                                 | 0 |
                                 +---+

                     Figure 3: IU propagation example

   Network FIBs are assumed to be populated with routes towards P0 by a
   name-based routing protocol.  After the relocation of the producer
   from P0 to P1, once the layer-2 attachment is completed, the producer
   issues an IU carrying the prefix /p and this is forwarded by the
   network toward P0 (in general, toward one of its previous locations
   according to the FIB state of traversed routers).

   Figure 1 (b) illustrates the propagation of the IU.  As the IU
   progresses, FIBs at intermediate hops are updated with the ingress
   face of the IU (Figure 2 (a) and (b)).  IU propagation stops when the
   IU reaches P0 and there is no next hop to forward it to.  The result
   is that the original tree rooted in P0 becomes re-rooted in P1
   (Figure 3).  Looking at the different connected regions (represented
   with dotted lines), we see that IU propagation and consequent FIB
   updates have the effect of extending the newly connected subtree : at
   every step, an additional router and its predecessors are included in
   the connected subtree.

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3.3.  Concurrent updates

   Frequent mobility of the producer may lead to the propagation of
   concurrent updates.  To prevent inconsistencies in FIBs, MAP-Me
   maintains a sequence number at the producer end that is incremented
   at each handover and associated to all sent IU packets.  Network
   routers also keep track of such sequence number in their FIBs to
   validate the relative freshness of received updates.  The
   modification of FIB entries is only triggered when the received IU
   carries a higher sequence number than the locally stored one, while
   the reception of a less recent update triggers the transmission of a
   more up-to-date IU backwards in order to fix the not-yet-updated
   path.

   An example reconciliation of concurrent updates is illustrated in
   Figure 4 (a), when the producer has moved successively to P1 and then
   to P2 before the first update could complete.

                            +---+                         +---+
                            | 0 | P0                      | 2 | P0
                            +---+                      A  +---+
                             ^ ^                IU(2) /    / ^
                            /   \                    /    V   \
                        +---+    +---+                +---+    +---+
                        | 0 |    | 0 |           <!>  | 2 |    | 0 |
                        +---+ A  +---+             A  +---+ A  +---+
                         ^ ^   \            IU(1) /    ^ \   \
                        /   \   \  IU(2)         /    /   V   \ IU(2)
                    +---+    +---+                +---+    +---+
                    | 0 |    | 2 | P2             | 1 |    | 2 |
                 A  +---+    +---+             A  +---+    +---+
          IU(1) /    ^ ^                  IU1 /    / ^
               /    /   \                    /    V   \
                +---+    +---+                +---+    +---+
             P1 | 1 |    | 0 |             P1 | 1 |    | 0 |
                +---+    +---+                +---+    +---+
                 ^ ^                           ^ ^
                /   \                         /   \
            +---+    +---+                +---+    +---+
            | 0 |    | 0 |                | 0 |    | 0 |
            +---+    +---+                +---+    +---+

                     (a)                       (b)

                                 Figure 4

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                            +---+                      +---+
                            | 2 | P0                   | 2 | P2
                            +---+                      +---+
                             / ^                         ^
                            V   \                        |
                        +---+    +---+                 +---+
                    <!> | 2 |    | 2 |                 | 2 |
             IU(2)  /   +---+    +---+                 +---+
                   /     ^ \                           ^   ^
                  V     /   V                         /     \
                    +---+    +---+                +---+     +---+
                    | 2 |    | 2 | P2         P0  | 2 |     | 2 |
          IU(2)  /  +---+    +---+                +---+     +---+
                /    / ^                           ^         ^ ^
               V    V   \                         /    P1   /   \
                +---+    +---+                 +---+    +---+   +---+
             P1 | 1 |    | 0 |                 | 0 |    | 2 |   | 0 |
                +---+    +---+                 +---+    +---+   +---+
                 ^ ^                                     ^ ^
                /   \                                   /   \
            +---+    +---+                          +---+    +---+
            | 0 |    | 0 |                          | 0 |    | 0 |
            +---+    +---+                          +---+    +---+

                     (a)                                 (b)

                                 Figure 5

   Both updates propagate concurrently until the one with sequence
   number 1 (IU(1)) crosses a router that has been updated with fresher
   information.  In the example shown in Figure 4 (b), the junction
   router has already received an IU with higher sequence number
   (IU(2)).  In this case, the router stops the propagation of IU(1) and
   sends back along its path a new IU with an updated sequence number
   (Figure 5 (a)).  The update proceeds until the whole network has
   ultimately converged towards P2 (Figure 5 (b)).

   MAP-Me protocol reacts at a faster timescale than routing - allowing
   more frequent and numerous mobility events - and over a localized
   portion of the network edge between current and previous producer
   locations.  This allows to minimize disconnectivity time and reduce
   link load, which are the main factors affecting user flow
   performance, as shown in [MAPME] evaluations.

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4.  Notification protocol and scoped discovery

   IU propagation in the data plane is designed to accelerate forwarding
   state re-convergence w.r.t. routing or resolution-based approaches
   operating at control plane, and w.r.t. anchor-based approaches
   requiring traffic tunneling through an anchor node.  Still, network
   latency makes IU completion not instantaneous and before an update
   completes, it may happen that a portion of the traffic is forwarded
   to the previous PoA and dropped because of the absence of a valid
   output face leading to the producer.

   Previous work in the Anchor-Less category has suggested the buffering
   of Interests at previous producer location to prevent those losses.
   However, such a solution is not suitable for applications with
   stringent latency requirements (e.g. real-time) and may be
   incompatible with IU completion times.  Moreover, the negative
   effects on latency performance might be further exacerbated by IU
   losses and consequent retransmissions in case of wireless medium.  To
   alleviate such issues, we introduce two enhancements to the
   previously described behavior, namely (i) an "Interest Notification"
   mechanism for frequent, yet lightweight, signaling of producer
   movements to the network and (ii) a scoped "Producer Discovery"
   mechanism for consumer requests to proactively search for the
   producer's recently visited locations.

4.1.  Interest Notification

   An Interest Notification (IN) is a breadcrumb left by producers at
   every encountered PoA.  It looks like a normal Interest packet
   carrying a special identification flag and a sequence number, like
   IUs.  Both IU and IN share the same sequence number (producers
   indistinctly increase it for every sent message) and follow the same
   FIB lookup and update processes.  However, unlike IU packets, the
   trace left by INs at the first hop router does not propagate further.
   It is rather used by the discovery process to route consumer requests
   to the producer even before an update process is completed.

   It is worth observing that updates and notifications serve the same
   purpose of informing the network of a producer movement.  The IU
   process restores connectivity and as such has higher latency/
   signaling cost than the IN process, due to message propagation.  The
   IN process provides information to track producer movements before
   update completion when coupled with a scoped discovery.  The
   combination of both IU and IN allows to control the trade-off between
   protocol reactivity and stability of forwarding re-convergence.

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4.2.  Scoped discovery

   The extension of MAP-Me with notifications relies on a local
   discovery phase: when a consumer Interest reaches a PoA with no valid
   output face in the corresponding entry, the Interest is tagged with a
   "discovery" flag and labeled with the latest sequence number stored
   in FIB (to avoid loops).  From that point on, it is broadcasted with
   hop limit equal to one to all neighbors and discarded unless it finds
   a breadcrumb left by the producer with a higher sequence number.  The
   notifications can either allow to forward consumer Interests directly
   to the producer or give rise to a repeated broadcast in case of no
   valid output face.  The latter is the case of a breadcrumb left by
   the producer with no associated forwarding information because the
   producer has already left that PoA as well.  A detailed description
   of the process is reported in Section 5.3.

   The notification/discovery mechanism proves important to preserve the
   performance of flows in progress, especially when latency-sensitive.

4.3.  Full approach

   The full MAP-Me approach consists in the combination of Updates and
   Notifications through a heuristic allowing the producer or its PoA to
   select which type of packet to send.  One such heuristic consist in
   sending a IN immediately after an attachment and a IU at most every
   Tu seconds, which allows to reduce signaling overhead during periods
   of high-mobility.  The Tu parameter allows to tune the timescale at
   which Updates occur, and leads to a trade-off between signaling and
   discovery overhead [MAPME].  The definition of more advanced
   heuristics is out of scope for the present draft.

5.  Implementation

   In this section we describe the changes to a regular CCN/NDN
   architecture required to implement MAP-ME and detail the above-
   described algorithms.  This requires to specify a special Interest
   message, additional temporary information associated to the FIB entry
   and additional operations to update such entry.

5.1.  MAP-Me messages

   MAP-Me signaling messages are carried within user plane as special
   Interest messages corresponding to "update" and "notification", and
   their corresponding acknowledgements.

   Two new optional fields are introduced in a CCN/NDN Interest header:

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   o  an "Interest Type" (T) used to specify one of the four types of
      messages: Interest Update (IU), Interest Notification (IN), and as
      well as their associated acknowledgment (Ack) messages (IU_Ack and
      IN_Ack).  Those flags are recognized by the forwarding pipeline to
      trigger special treatment;

   o  a "sequence number" to handle concurrent updates and prevent
      forwarding loops during signaling, and to control discovery
      Interests' propagation;

5.2.  Data structures and temporary state

   FIB entries are augmented with information required for mobility
   management, that we denote as Transient FIB buffer, or simply TFIB,
   and sketch in Figure 6:

   o  a "sequence number" which is incremented upon reception of IU/IN
      messages.  It can be assumed this counter is set to 0 by the
      routing protocol.

   o  a list of so-called "previous next hop(s)" (further denoted as
      PrevHops), similar to the list of NextHops in the original FIB,
      which temporarily stores information about faces that were
      previously next hops, and should still be memorized to allow for
      retransmissions and thus ensure the consistency of MAP-Me
      operations.  They typically correspond to nodes for which an IU
      has been sent, but no acknowledgement (ACK) has yet been received
      (upon which they are cleared).  In case of notifications, no ACK
      is expected, and those entries serve as a memory of the former
      tree structure that will be restored upon producer departure.  We
      flag those entries with a boolean marker indicating if they
      correspond to an IU (and thus should be monitored for
      retransmissions) or an IN (in which case they just serve as memory
      for further use).

         IU (IN) input face(s)            IU (IN) output face

   +-----------+-------------------+.......+..........................+
   |  /prefix  |  { next hop(s) }  |  seq  | { previous next hop(s) } |
   +-----------+-------------------+.......+..........................+
    \_____________ _______________/ \_______________ _______________/
                  V                                 V
             original FIB                      TFIB section

                   Figure 6: MAP-Me FIB/TFIB description

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5.3.  Algorithm description

5.3.1.  Producer attachment and face creation

   MAP-Me operations are triggered by a change of adjacencies in the
   network, reflected in the forwarder by the creation or removal of a
   face.  This can be for instance the layer 2 detachment and attachment
   following a mobility/handover event, but also any other mechanism
   such as point-to-point IP link or UDP tunnel for instance, as allowed
   by the forwarder implementation.

   One realization of this architecture is to delegate face management
   to a third party agent, keeping the ICN forwarder state synchronized
   with the underlying topology, and having MAP-Me only react to changes
   in the face table.

5.3.2.  IU/IN transmission at producer

   The creation of a new face on the producer triggers the increase of
   MAP-Me sequence number and the transmission for every locally served
   prefix, of an IU or IN carrying the updated sequence number.

5.3.3.  IU/IN transmission at network routers

   At the reception of IU/IN packets, each router performs a name-based
   Longest Prefix Match lookup in FIB to compare sequence number from
   IU/IN and from FIB.  According to that comparison:

   o  if the IU/IN packet carries a higher sequence number, the existing
      next hops associated to the lower sequence number in FIB are used
      to forward further the IU (INs are not propagated) and temporarily
      copied into TFIB to avoid loss of such information before
      completion of the IU/IN acknowledgement process.  The ingress face
      of the IU/IN is then added to FIB to route consumer requests to
      the latest known location of the producer.

   o  If the IU/IN packet carries the same sequence number as in the
      FIB, the originating face of the IU/IN is added to the existing
      ones in FIB without additional packet processing or propagation.
      This may occur in presence of multiple forwarding paths.

   o  If the IU/IN packet carries a lower sequence number than the one
      in the FIB, FIB entry is not updated as it already stores 'fresher
      information'.  To advertise the latest update through the path
      followed by the IU/IN packet, this one is re-sent through the
      originating face after having updated its sequence number with the
      value stored in FIB.

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   The operations in the forwarding pipeline for IU/IN processing are
   reported in Figure 7, where we make use of the following primitives:
   - Send(Interest, Face) is used to send the specified Interest on the
   specified Face.  - ProcessTFIB() sends an IU for all flagged entries
   in the TFIB, using the latest sequence number stored in the FIB
   entry, and schedule the entry to be checked for retransmissions.

  | Algorithm 1:ForwardSpecialInterest(SpecialInterest SI,IngressFace F)
  |
  |  CheckValidity()
  |  // Acknowledge reception
  |  s <- e.seq
  |  e.seq <- SI.seq
  |  Send(IU_Ack(e.seq), F)
     flag <- (SI.type == IU)
  |  // Retrieve the FIB entry associated to the prefix
  |  e <- FIB.LongestPrefixMatch(SI.name)
  |  if SI.seq >= e.seq then
  |  .   //Process special interest
  |  .   e.TFIB = e.TFIB \ { F }
  |  .   if SI.seq > s then
  |  .   .   e.TFIB = e.TFIB U { (f, flag) | f in (e.NextHops \ F) }
     .   .   ProcessTFIB()
  |  .   .   e.NextHops = {}
  |  .   e.NextHops = e.NextHops U { F }
  |  else
  |  .   // Send updated IU backwards
  |  .   SI.seq = e.seq
  |  .   e.TFIB = e.TFIB U { (F, flag) }
  |  .   ProcessTFIB()

                                 Figure 7

5.3.4.  Reliable transmission

   MAP-Me ensure the reliable delivery of signaling messages thanks to a
   retransmission timer which reissue Interest Updates (eventually
   carrying updated sequence number as found in the FIB), if no
   corresponding ACK has been received in a predefined interval, and
   whose sequence number has to match the one stored in the FIB.

   A slotted implementation of such scheme is possible by using a single
   timer, and keeping a list of FIB entries that require to be checked
   for pending retransmissions in the next slot.  Upon timer expiration,
   if all required ACKs have been received, the TFIB will be empty and
   the entry does not have to be tracked anymore.  Otherwise, necessary
   retransmissions are performed and the entry will be checked again in

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   the next slot.  When no entry has to be monitored, the process can
   sleep until the next mobility event.

5.3.5.  Consumer request forwarding in case of producer discovery

   The forwarding of regular Interests is mostly unaffected in MAP-Me,
   except in the case of discovery Interests that we detail in Figure 8.
   The function SendToNeighbors(I) is responsible for broadcasting the
   Interest I to all neighboring PoAs.

  | Algorithm 2:  InterestForward(Interest I, Origin face F)
  |
  |  // Regular PIT and CS lookup
  |  e <- FIB.LongestPrefixMatch(I.name)
  |  if e = 0 then
  |  .   return
  |  if I.seq = 0 then
  |  .   // Regular interest
  |  .   if hasValidFace(e.NextHops) or DiscoveryDisabled then
  |  .   .   ForwardingStrategy.process(I, e)
  |  .   else
  |  .   .   // Enter discovery mode
  |  .   .   I.seq <- e.seq
  |  .   .   SendToNeighbors(I)
  |  else
  |  .   // Discovery interest: forward if producer is connnected
  |  .   if hasProducerFace(e.NextHops) then
  |  .   .   ForwardingStrategy.process(I, e)
  |  .   // Otherwise iterate iif higher seq and breadcrumb
  |  .   else if e.seq >= I.seq and EXISTS f |(f -> NULL) in e.TFIB then
  |  .   .   I.seq <- e.seq
  |  .   .   SendToNeighbors(I)

                                 Figure 8

   When an Interest arrives to a PoA which has no valid next hop for it
   (because the producer left and the face got destroyed), it enters a
   discovery phase where the Interest is flagged as a Discovery Interest
   and with the local sequence number, then broadcasted to neighboring
   PoAs.

   Upon reception of a Discovery Interest, the PoA forwards it directly
   to the producer if still attached, otherwise it repeats the one-hop
   brodcast discovery to neighboring PoAs if it stores a recent
   notification of the producer presence, i.e. an entry in TFIB having
   higher sequence number than the one in the Discovery Interest.
   Otherwise, the Discovery Interest is discarded.

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   It is worth observing that the discovery process is initiated only in
   the case of no valid next hop, and not every time a notification is
   found in a router.  This is important to guarantee that the
   notification/discovery process does not affect IU propagation and
   completion.

5.3.6.  Producer departure and face destruction

   Upon producer departures from a PoA, the corresponding face is
   destroyed.  If this leads to the removal of the last next hop, then
   faces in TFIB corresponding to IN are restored as next hops in the
   FIB so as to preserve the original forwarding tree and thus global
   connectivity.

6.  Security considerations

   All mobility management protocols share the same critical need for
   securing their control messages which have a direct impact on the
   forwarding of users' traffic.  [SEC] reviews standard approaches from
   the literature and proposes a fast, lightweight and decentralized
   approach based on hash chains that can be applied to MAP-Me and fits
   its design principles.

7.  Acknowledgements

   The authors would like to thank Giulio Grassi (UPMC/UCLA), Giovanni
   Pau (UPMC/UCLA) and Xuan Zeng (UPMC/SystemX) for their contribution
   to the work that has led to this document.

8.  IANA Considerations

   This memo includes no request to IANA.

9.  References

9.1.  Normative References

   [RFC6301]  Zhu, Z., Wakikawa, R., and L. Zhang, "A Survey of Mobility
              Support in the Internet", RFC 6301, DOI 10.17487/RFC6301,
              July 2011, <https://www.rfc-editor.org/info/rfc6301>.

9.2.  Informative References

   [DATAPLANE]
              J, ., A, ., A, ., B, ., M, ., and . S, "Ensuring
              connectivity via data plane mechanisms.", 2013.

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   [KITE]     Zhang, Y., Zhang, H., and L. Zhang, "Kite", Proceedings of
              the 1st international conference on Information-centric
              networking - INC '14, DOI 10.1145/2660129.2660159, 2014.

   [MAPME]    Auge, J., Carofiglio, G., Grassi, G., Muscariello, L.,
              Pau, G., and X. Zeng, "MAP-Me: Managing Anchor-Less
              Producer Mobility in Content-Centric Networks", IEEE
              Transactions on Network and Service Management Vol. 15,
              pp. 596-610, DOI 10.1109/tnsm.2018.2796720, June 2018.

   [NLSR]     Hoque, A., Amin, S., Alyyan, A., Zhang, B., Zhang, L., and
              L. Wang, "NISR", Proceedings of the 3rd ACM SIGCOMM
              workshop on Information-centric networking - ICN '13,
              DOI 10.1145/2491224.2491231, 2013.

   [SEC]      Compagno, A., Zeng, X., Muscariello, L., Carofiglio, G.,
              and J. Auge, "Secure producer mobility in information-
              centric network", Proceedings of the 4th ACM Conference on
              Information-Centric Networking - ICN '17,
              DOI 10.1145/3125719.3125725, 2017.

   [SURVEY12]
              Ahlgren, B., Dannewitz, C., Imbrenda, C., Kutscher, D.,
              and B. Ohlman, "A survey of information-centric
              networking", IEEE Communications Magazine Vol. 50, pp.
              26-36, DOI 10.1109/mcom.2012.6231276, July 2012.

   [SURVEY13]
              Tyson, G., Sastry, N., Rimac, I., Cuevas, R., and A.
              Mauthe, "A survey of mobility in information-centric
              networks", Proceedings of the 1st ACM workshop on Emerging
              Name-Oriented Mobile Networking Design - Architecture,
              Algorithms, and Applications - NoM '12,
              DOI 10.1145/2248361.2248363, 2012.

   [SURVEY14]
              Xylomenos, G., Ververidis, C., Siris, V., Fotiou, N.,
              Tsilopoulos, C., Vasilakos, X., Katsaros, K., and G.
              Polyzos, "A Survey of Information-Centric Networking
              Research", IEEE Communications Surveys & Tutorials Vol.
              16, pp. 1024-1049, DOI 10.1109/surv.2013.070813.00063,
              2014.

   [SURVEY16a]
              Feng, B., Zhou, H., and Q. Xu, "Mobility support in Named
              Data Networking: a survey", EURASIP Journal on Wireless
              Communications and Networking Vol. 2016,
              DOI 10.1186/s13638-016-0715-0, September 2016.

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   [SURVEY16b]
              Zhang, Y., Afanasyev, A., Burke, J., and L. Zhang, "A
              survey of mobility support in Named Data Networking", 2016
              IEEE Conference on Computer Communications Workshops
              (INFOCOM WKSHPS), DOI 10.1109/infcomw.2016.7562050, April
              2016.

   [WLDR]     Carofiglio, G., Muscariello, L., Papalini, M., Rozhnova,
              N., and X. Zeng, "Leveraging ICN In-network Control for
              Loss Detection and Recovery in Wireless Mobile networks",
              Proceedings of the 2016 conference on 3rd ACM Conference
              on Information-Centric Networking - ACM-ICN '16,
              DOI 10.1145/2984356.2984361, 2016.

Authors' Addresses

   Jordan Auge (editor)
   Cisco Systems Inc.
   11, rue Camille Desmoulins
   Issy-les-Moulineaux  92130
   France

   Email: augjorda@cisco.com

   Giovanna Carofiglio
   Cisco Systems Inc.
   11, rue Camille Desmoulins
   Issy-les-Moulineaux  92130
   France

   Email: gcarofig@cisco.com

   Luca Muscariello
   Cisco Systems Inc.
   11, rue Camille Desmoulins
   Issy-les-Moulineaux  92130
   France

   Email: lumuscar@cisco.com

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   Michele Papalini
   Cisco Systems Inc.
   11, rue Camille Desmoulins
   Issy-les-Moulineaux  92130
   France

   Email: micpapal@cisco.com

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