Network Working Group L. Dunbar
Internet Draft Futurewei
Intended status: Standard K. Majumdar
Expires: September 8, 2021 CommScope
H. Wang
Huawei
March 8, 2021
BGP NLRI App Meta Data for 5G Edge Computing Service
draft-dunbar-idr-5g-edge-compute-app-meta-data-02
Abstract
This draft describes a new BGP Network Layer Reachability
Information (BGP NLRI) Path Attribute, AppMetaData, for egress
router to advertise the running status and environment of the
directly attached 5G Edge Computing servers. The AppMetaData
can be used by the ingress routers in the 5G Local Data
Network to make intelligent path selection for flows from UEs.
The goal is to improve latency and performance for 5G Edge
Computing services.
The extension enables a feature, called soft anchoring, which
makes one Edge Computing Server at one specific location to be
more preferred than others for the same application to receive
packets from a specific source (UE).
Status of this Memo
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provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction.............................................. 3
1.1. 5G Edge Computing Background......................... 3
1.2. 5G Edge Computing Network Properties................. 4
1.3. Problem#1: ANYCAST in 5G EC Environment.............. 6
1.4. Problem #2: Unbalanced Anycast Distribution due to UE
Mobility.................................................. 7
1.5. Problem 3: Application Server Relocation............. 7
2. Conventions used in this document......................... 8
3. Usage of App-Meta-Data for 5G Edge Computing.............. 9
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3.1. Assumptions.......................................... 9
3.2. IP Layer Metrics to Gauge Application Behavior....... 9
3.3. To Equalize among Multiple ANYCAST Locations........ 11
3.4. BGP Protocol Extension to advertise Load & Capacity. 11
3.5. Ingress Node BGP Path Selection Behavior............ 12
3.5.1. AppMetaData Influenced BGP Path Selection...... 12
3.5.2. Forwarding Behavior............................ 12
3.5.3. Forwarding Behavior after a UE moving to a new 5G
Site.................................................. 13
4. The NLRI Path Attribute for App-Meta-Data................ 14
4.1. Load Measurement sub-TLV format..................... 16
4.2. Capacity Index sub-TLV format....................... 17
4.3. The Site Preference Index sub-TLV format............ 17
5. AppMetaData Propagation Scope............................ 18
6. Soft Anchoring of an ANYCAST Flow........................ 18
7. Manageability Considerations............................. 20
8. Security Considerations.................................. 20
9. IANA Considerations...................................... 20
10. References.............................................. 20
10.1. Normative References............................... 20
10.2. Informative References............................. 21
11. Acknowledgments......................................... 22
1. Introduction
This document describes a new BGP Network Layer Reachability
Information (BGP NLRI) Path Attribute, AppMetaData, for egress
routers to advertise the running status and environment of the
directly attached Edge Computing servers. The AppMetaData can
be used by the ingress routers in the 5G Local Data Network to
make intelligent path selection for flows from UEs. The goal
is to improve latency and performance for 5G Edge Computing
services.
1.1. 5G Edge Computing Background
As described in [5G-EC-Metrics], one Application can have
multiple Application Servers hosted in different Edge
Computing data centers that are close in proximity. Those Edge
Computing (mini) data centers are usually very close to or co-
located with the 5G base stations, to minimize latency and
optimize the user experience.
When a UE (User Equipment) initiates application packets using
the destination address from a DNS reply or its cache, the
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packets from the UE are carried in a PDU session through 5G
Core [5GC] to the 5G UPF-PSA (User Plan Function - PDU Session
Anchor). The UPF-PSA decapsulates the 5G GTP outer header and
forwards the packets from the UEs to the Ingress router of the
Edge Computing (EC) Local Data Network (LDN). The LDN for 5G
EC, which is the IP Networks from the 5GC perspective, is
responsible for forwarding the packets to the intended
destinations.
When the UE moves out of coverage of its current gNB (next-
generation Node B) (gNB1), handover procedures are initiated
and the 5G SMF (Session Management Function) also selects a
new UPF-PSA. The standard handover procedures described in
3GPP TS 23.501 and TS 23.502 are followed. When the handover
process is complete, the UE has a new IP address and the IP
point of attachment is to the new UPF-PSA. 5GC may maintain a
path from the old UPF to new the UPF for a short time for the
SSC [Session and Service Continuity] mode 3 to make the
handover process more seamless.
1.2. 5G Edge Computing Network Properties
In this document, 5G Edge Computing Network refers to multiple
Local IP Data Networks (LDN) in one region that interconnect
the Edge Computing mini-data centers. Those IP LDN networks
are the N6 interfaces from 3GPP 5G perspective.
The ingress routers to the 5G Edge Computing Network are the
routers directly connected to 5G UPFs. The egress routers to
the 5G Edge Computing Network are the routers that have a
direct link to the Edge Computing servers. The servers and the
egress routers are co-located. Some of those mini Edge
Computing Data centers may have Virtual switches or Top of
Rack switches between the egress routers and the servers. But
transmission delay between the egress routers and the Edge
Computing servers is too small to be considered in this
document.
When one mini data center has multiple Edge Computing Servers
attached to one App Layer Load Balancer, only the App Layer
Load Balancer is visible to the 5G Edge Computing Network. How
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the App Layer Load balancer manages the individual servers is
out of the scope of the network layer.
The Edge Computer Services are specially managed services that
need to utilize the network topology and balance among
multiple mini Edge Computing Data Centers with the same
ANYCAST address. UEs can access many services that are not
part of the registered 5G Edge Computing Services.
+--+
|UE|---\+---------+ +------------------+
+--+ | 5G | +--------+ | S1: aa08::4450 |
+--+ | Site +--+-+---+ +----+ |
|UE|----| A |PSA1| Ra| | R1 | S2: aa08::4460 |
+--+ | +----+---+ +----+ |
+---+ | | | | | S3: aa08::4470 |
|UE1|---/+---------+ | | +------------------+
+---+ |IP Network | L-DN1
|(3GPP N6) |
| | | +------------------+
| UE1 | | | S1: aa08::4450 |
| moves to | +----+ |
| Site B | | R3 | S2: aa08::4460 |
v | +----+ |
| | | S3: aa08::4470 |
| | +------------------+
| | L-DN3
+--+ | |
|UE|---\+---------+ | | +------------------+
+--+ | 5G | | | | S1: aa08::4450 |
+--+ | Site +--+--+---+ +----+ |
|UE|----| B |PSA2| Rb | | R2 | S2: aa08::4460 |
+--+ | +--+-+----+ +----+ |
+--+ | | +-----------+ | S3: aa08::4470 |
|UE|---/+---------+ +------------------+
+--+ L-DN2
Figure 1: App Servers in different edge DCs
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1.3. Problem#1: ANYCAST in 5G EC Environment
Increasingly, Anycast is used extensively by various
application providers and CDNs because ANYCAST makes it
possible to dynamically load balance across server locations
based on network conditions.
Using Anycast address leverages the proximity information
present in the network (routing) layer and eliminates the
single point of failure and bottleneck at the DNS resolvers
and application layer load balancers. Another benefit of using
the ANYCAST address is removing the dependency on UEs. Some
UEs (or clients) might use their cached IP addresses instead
of querying DNS for an extended period.
But, having multiple locations of the same ANYCAST address in
the 5G Edge Computing environment can be problematic because
all those edge computing Data Centers can be close in
proximity. There might be a very small difference in the
routing cost to reach the Application Servers in different
Edge DCs. This list elaborates the issues in detail:
a) Path Selection: When a new flow comes to an ingress node
(Ra), how to select the optimal egress router to reach an
ANYCAST server.
The mechanism described in this draft is for solving this
Path Selection problem.
b) How Ingress node keeps the packets from one flow to the
same ANYCAST server.
a.k.a. Flow Affinity, or Flow-based load balancing, which
is supported by many commercial routers.
The ingress node, (Ra/Rb) uses Flow ID (in IPv6 header)
or UDP/TCP port number combined with the source address
to enforce packets in one flow being placed in one tunnel
to one Egress router. No new features are needed.
c) When a UE moves to a new Cell Tower, a method is needed
to stick the flow to the same ANYCAST server, which is
required by 5G Edge Computing: 3GPP TR 23.748.
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This problem is Out of scope for this draft. [5g-edge-
compute-sticky-service] describes several approaches to
solve this problem.
BGP is an integral part of the way IP Anycast usually
functions. Within BGP routing there are multiple routes for
the same IP address which are pointing to different locations.
This draft describes the BGP UPDATE extension to allow the App
Servers Running status and environment to be included in the
BGP UPDATE messages, so that ingress routers can optimize its
path selection algorithm to select an optimal ANYCAST location
based on the combination of network delay, the App Server load
index, the location capacity index and the location
preference.
1.4. Problem #2: Unbalanced Anycast Distribution due to UE
Mobility
UEs frequent moving from one 5G site to another can make it
difficult to plan where the App ANYCAST servers should be
hosted. When one App server is heavily utilized, other App
servers of the same address close-by can be very
underutilized. Since the condition can be short-lived, it is
difficult for the application controller to anticipate the
move and adjust.
1.5. Problem 3: Application Server Relocation
When an Application Server is added to, moved, or deleted from
a 5G Edge Computing Data Center, the routing protocol needs to
propagate the changes to 5G PSA or the PSA adjacent routers.
After the change, the cost associated with the site [5G-EC-
Metrics] might change as well.
Note: for ease of description, the Edge Application Server and
Application Server are used interchangeably throughout this
document.
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2. Conventions used in this document
A-ER: Egress Router to an Application Server, [A-ER] is
used to describe the last router that the
Application Server is attached. For a 5G EC
environment, the A-ER can be the gateway router to
a (mini) Edge Computing Data Center.
Application Server: An application server is a physical or
virtual server that hosts the software system for
the application.
Application Server Location: Represent a cluster of servers at
one location serving the same Application. One
application may have a Layer 7 Load balancer,
whose address(es) are reachable from an external
IP network, in front of a set of application
servers. From an IP network perspective, this
whole group of servers is considered as the
Application server at the location.
Edge Application Server: used interchangeably with Application
Server throughout this document.
EC: Edge Computing
Edge Hosting Environment: An environment providing the support
required for Edge Application Server's execution.
NOTE: The above terminologies are the same as
those used in 3GPP TR 23.758
Edge DC: Edge Data Center, which provides the Edge
Computing Hosting Environment. An Edge DC might
host 5G core functions in addition to the
frequently used application servers.
gNB next generation Node B
L-DN: Local Data Network
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PSA: PDU Session Anchor (UPF)
SSC: Session and Service Continuity
UE: User Equipment
UPF: User Plane Function
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
interpreted as described in BCP 14 [RFC2119] [RFC8174] when,
and only when, they appear in all capitals, as shown here.
3. Usage of App-Meta-Data for 5G Edge Computing
3.1. Assumptions
From IP Layer, the Application servers are identified by their
IP (ANYCAST) addresses. Here are some assumptions about the 5G
Edge Computing services:
- Only the registered Edge Computing services need special
consideration in path selection.
- The 5G Edge Computing controller or management system can
configure the ACLs to filter out those applications on
the routers adjacent to the 5G PSA and the routers to
which the Application servers are directly attached.
- The ingress routers' local BGP path compute algorithm
includes a special Plugin that can compute the path to
the optimal Next Hop (egress router) based on the BGP
AppMetaData TLV received for the registered Edge
Computing services.
The proposed solution is for the egress routers, i.e. A-ER,
that have direct links to the Application Servers to collect
various measurements about the Servers' running status [5G-EC-
Metrics] and advertise the metrics to other routers in 5G EC
LDN (Local Data Network).
3.2. IP Layer Metrics to Gauge Application Behavior
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[5G-EC-Metrics] describes the IP Layer Metrics that can gauge
the application servers running status and environment:
- IP-Layer Metric for App Server Load Measurement:
The Load Measurement to an App Server is a weighted
combination of the number of packets/bytes to the App Server
and the number of packets/bytes from the App Server which
are collected by the A-ER to which the App Server is
directly attached.
The A-ER is configured with an ACL that can filter out the
packets for the Application Server.
- Capacity Index
Capacity Index is used to differentiate the running
environment of the application server. Some data centers can
have hundreds, or thousands, of servers behind an
Application Server's App Layer Load Balancer that is
reachable from an external world. Other data centers can
have a very small number of servers for the application
server. "Capacity Index", which is a numeric number, is used
to represent the capacity of the application server in a
specific location.
- Site preference index:
[IPv6-StickyService] describes a scenario that some sites
are more preferred for handling an application server than
others for flows from a specific UE.
In this document, the term "Application Server Egress Router"
[A-ER] is used to describe the last router that an Application
Server is attached. For the 5G EC environment, the A-ER can be
the gateway router to the EC DC where multiple Application
servers are hosted.
From IP Layer, an Application Server is identified by its IP
(ANYCAST) Address. Those IP addresses are called the
Application Server IDs throughout this document.
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3.3. To Equalize among Multiple ANYCAST Locations
The main benefit of using ANYCAST is to leverage the network
layer information to equalize the traffic among multiple
Application Server locations of the same Application, which is
identified by its ANYCAST addresses.
For the 5G Edge Computing environment, the ingress routers to
the LDN need to be notified of the Load Index and Capacity
Index of the App Servers at different EC data centers to make
the intelligent decision on where to forward the traffic for
the application from UEs.
[5G-EC-Metrics] describes the algorithms that can be used by
the routers directly attached to the 5G PSA to compare the
cost to reach the App Servers between the Site-i or Site-j:
Load-i * CP-j Pref-j * Delay-i
Cost-i=min(w *(----------------) + (1-w) *(------------------))
Load-j * CP-i Pref-i * Delay-j
Load-i: Load Index at Site-i, it is the weighted
combination of the total packets or/and bytes sent to and
received from the Application Server at Site-i during a
fixed time period.
CP-i: capacity index at Site-i, a higher value means higher
capacity.
Delay-i: Network latency measurement (RTT) to the A-ER that
has the Application Server attached at the site-i.
Pref-i: Preference index for the Site-i, a higher value
means higher preference.
w: Weight for load and site information, which is a value
between 0 and 1. If smaller than 0.5, Network latency and
the site Preference have more influence; otherwise, Server
load and its capacity have more influence.
3.4. BGP Protocol Extension to advertise Load & Capacity
The goal of the protocol extension:
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- Propagate the Load Measurement Index for the attached App
Servers to other routers in the LDN.
- Propagate the Capacity Index &
- Propagate Site Preference Index.
The BGP extension is to add the Load Index Sub-TLV, Capacity
Sub-TLV, and the Site Preference Sub-TLV in the NLRI
associated with the routes.
3.5. Ingress Node BGP Path Selection Behavior
3.5.1. AppMetaData Influenced BGP Path Selection
In this scenario, an ingress router will receive one ANYCAST
address's multiple routes from different egress routers that
have the direct links to the ANYCAST servers. The ingress
router's BGP engine will do path selection, select the best
route, and download to FIB. And BGP engine will also download
the other paths to FIB that with the AppMetaData taken into
the consideration.
Assume that both Ra and Rb in Figure 1 have BGP Multipath
enabled. As a result, Dst Address: S1:aa08::4450 is resolved
via multiple NextHop: R1, R2, R3.
Suppose the local BGP special Plugin for AppMetaData finds R1
is the best for the flow towards S1:aa08::4450. Then this
special Plugin can insert a higher weight for the path R1 so
that BGP Best Path is locally influenced by the weight
parameter based on the local decision.
3.5.2. Forwarding Behavior
When the ingress router receives a packet and lookup the FIB,
get the destination prefix's whole path and AppMetaData. The
Forwarding Plane will do computing for the packet and choose
the suitable path as the result of the computing. Then the
Forwarding Plane encapsulates the packet destined towards the
optimal Nexthop node.
For subsequent packets belonging to the same flow, the ingress
router needs to forward them to the same egress router unless
the selected egress router is no longer reachable. Keeping
packets from one flow to the same egress router, a.k.a. Flow
Affinity, is supported by many commercial routers.
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How Flow Affinity is implemented is out of the scope for this
document. Here is one example to illustrate how Flow Affinity
can be achieved. This illustration is not to be standardized.
For the registered Edge Computing services, the ingress node
keeps a table of
- Service ID (i.e. ANYCAST address)
- Flow-ID
- Sticky Egress ID
- A timer
The Flow-ID in this table is to identify a flow, initialized
to NULL. How Flow-ID is constructed is out of the scope for
this document. Here is one example of constructing the Flow-
ID:
- For IPv6, the Flow-ID can be the Flow-ID extracted from
the IPv6 packet header with or without the source
address.
- For IPv4, the Flow-ID can be the combination of the
Source Address with or without the TCP/UDP Port number.
The Sticky Egress ID is to record the egress node address
that the packets of the same flow that have been forwarded
to. [5G-Sticky-Service] describes several methods to derive
the Sticky Egress ID.
The Timer is always refreshed when a packet with the
matching ANYCAST address is received by the node.
If there is no Stick Egress ID present in the table for the
ANYCAST address, the forwarding plane computes the optimal
path to a NextHop with the AppMetaData taken into
consideration. The forwarding plane encapsulate the packet
with the tunnel to the chosen NextHop. The chosen NextHop
and the Flow ID are recorded in the table entry of the
ANYCAST ID.
When the selected optimal egress router is no longer
reachable, refer to Section 6 Soft Anchoring on how another
path is selected.
3.5.3. Forwarding Behavior after a UE moving to a new 5G Site
When a UE moves to a new 5G Site, the new ingress router might
use the pre-computed Egress Router which is passed from the
neighboring router. [5G-Edge-Sticky] describes the method for
the ingress router connected to the UPF in the new site to
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take into consideration the information passed from other
ingress routers in selecting the optimal egress router. The
detailed algorithm is out of the scope of this document.
4. The NLRI Path Attribute for App-Meta-Data
The App-Meta-Data attribute is an optional transitive BGP Path
attribute to carry application-specific data, such as running
status, capacity, and site preference. Will need IANA to
assign a value as the type code of the attribute. The
attribute is composed of a set of Type-Length-Value (TLV)
encodings. Each TLV contains information corresponding to
metrics to a specific Application Server. An App-Meta-Data
TLV is structured as shown in Figure 1:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AppMetaData Type (2 Octets) | Length (2 Octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Value |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: App Meta Data TLV Value Field
AppMetaData Type (2 octets): identifies a type of Application
related metadata. The field contains values from the IANA
Registry "BGP AppMetaData Types". To be added.
o Length (2 octets): the total number of octets of the
Value field.
o Value (variable): comprised of multiple sub-TLVs.
Each sub-TLV consists of three fields: a 1-octet type, a 1-
octet or 2-octet length field (depending on the type), and
zero or more octets of value. A sub-TLV is structured as
shown in Figure 2:
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+--------------------------------+
| Sub-TLV Type (1 Octet) |
+--------------------------------+
| Sub-TLV Length (1 or 2 Octets) |
+--------------------------------+
| Sub-TLV Value (Variable) |
+--------------------------------+
Figure 3: App Metadata Sub-TLV Value Field
o Sub-TLV Type (1 octet): each sub-TLV type defines a
certain property about the AppMetaData TLV that contains
this sub-TLV. The field contains values from the IANA
Registry "BGP AppMetaData Attribute Sub-TLVs".
o Sub-TLV Length (1 or 2 octets): the total number of
octets of the sub-TLV value field. The Sub-TLV Length field
contains 1 octet if the Sub-TLV Type field contains a value
in the range from 0-127. The Sub-TLV Length field contains
two octets if the Sub-TLV Type field contains a value in the
range from 128-255.
o Sub-TLV Value (variable): encodings of the value field
depend on the sub-TLV type as enumerated above. The
following sub-sections define the encoding in detail.
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4.1. Load Measurement sub-TLV format
Two types of Load Measurement Sub-TLVs are specified. One is
to carry the aggregated cost Index based on a weighted
combination of the collected measurements; another one is to
carry the raw measurements of packets/bytes to/from the App
Server address. The raw measurement is useful when the egress
routers cannot be configured with a consistent algorithm to
compute the aggregated load index and the raw measurements are
needed by a central analytic system.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD2) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Measurement Period |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Aggregated Load Index to reach the App Server |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Aggregated Load Index Sub-TLV
Raw Load Measurement sub-TLV has the following format:
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD3) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Measurement Period |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| total number of packets to the AppServer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| total number of packets from the AppServer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| total number of bytes to the AppServer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| total number of bytes from the AppServer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Raw Load Measurement Sub-TLV
Type =TBD2: Aggregated Load Measurement Index derived from
the Weighted combination of bytes/packets sent to/received
from the App server:
Index=w1*ToPackets+w2*FromPackes+w3*ToBytes+w4*FromBytes
Where wi is a value between 0 and 1; w1+ w2+ w3+ w4 = 1;
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Type= TBD3: Raw measurements of packets/bytes to/from the
App Server address;
Measure Period: BGP Update period or user-specified period.
4.2. Capacity Index sub-TLV format
The Capacity Index sub-TLV has the following format:
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD4) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Capacity Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Note: "Capacity Index" can be more stable for each site. If
those values are configured to nodes, they might not need to
be included in every BGP UPDATE.
4.3. The Site Preference Index sub-TLV format
The site Preference Index is used to achieve Soft Anchoring
[Section 5] an application flow from a UE to a specific
location when the UE moves from one 5G site to another.
The Preference Index sub-TLV has the following format:
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD5) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Note: "Site Preference Index" can be more stable for each
site. If those values are configured to nodes, they might not
need to be included in every BGP UPDATE.
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5. AppMetaData Propagation Scope
AppMetaData is only to be distributed to the relevant ingress
nodes of the 5G Edge Computing local data networks. Only the
ingress routers that are configured with the 5G Edge Computing
services ACLs need to receive the AppMetaData for specific
services.
For each registered Edge Computing service, a corresponding
filter group can be formed on RR to represent the interested
ingress routers that are interested in receiving the
corresponding AppMetaData information.
6. Soft Anchoring of an ANYCAST Flow
"Sticky Service" in the 3GPP Edge Computing specification
(3GPP TR 23.748) requires a UE to a specific ANYCAST location
when the UE moves from one 5G Site to another.
"Soft Anchoring" is referring to forwarding the Application
flow from a UE to a preferred location of the ANYCAST servers
when the preferred location is in good condition. But if
there is any failure reaching the preferred location, the
Application flow from the UE will be forwarded to another
location of the ANYCAST servers.
This section describes a solution that can softly anchor an
application flow from a UE to a preferred location.
Lets' assume one application "App.net" is instantiated on
four servers that are attached to four different routers R1,
R2, R3, and R4 respectively. It is desired for packets to the
"App.net" from UE-1 to stick with one server, say the App
Server attached to R1, even when the UE moves from one 5G
site to another. When there is a failure reaching R1 or the
Application Server attached to R1, the packets of the flow
"App.net" from UE-1 need to be forwarded to the Application
Server attached to R2, R3, or R4.
We call this kind of sticky service "Soft Anchoring", meaning
that anchoring to the site of R1 is preferred, but other
sites can be chosen when the preferred site encounters a
failure.
Here are the details of this solution:
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- Assign a group of ANYCAST addresses to one application.
For example, "App.net" is assigned with 4 ANYCAST
addresses, L1, L2, L3, and L4. L1/L2/L3/L4 represents
the location preferred ANYCAST addresses.
- For the App.net Server attached to a router, the router
has four Stub links to the same Server, L1, L2, L3, and
L4 respectively. The cost to L1, L2, L3, and L4 is
assigned differently for different routers. For example,
o When attached to R1, the L1 has the lowest cost,
say 10, when attached to R2, R3, and R4, the L1 can
have a higher cost, say 30.
o ANYCAST L2 has the lowest cost when attached to R2,
higher cost when attached to R1, R3, R4
respectively.
o ANYCAST L3 has the lowest cost when attached to R3,
higher cost when attached to R1, R2, R4
respectively, and
o ANYCAST L4 has the lowest cost when attached to R4,
higher cost when attached to R1, R2, R3
respectively
- When a UE queries for the "App.net" for the first time,
the DNS reply has the location preferred ANYCAST
address, say L1, based on where the query is initiated.
- When the UE moves from one 5G site-A to Site-B, UE
continues sending packets of the "App.net" to ANYCAST
address L1. The routers will continue sending packets to
R1 because the total cost for the App.net instance for
ANYCAST L1 is lowest at R1. If any failure occurs making
R1 not reachable, the packets of the "App.net" from UE-1
will be sent to R2, R3, or R4 (depending on the total
cost to reach each of them).
If the Application Server supports the HTTP redirect, more
optimal forwarding can be achieved.
- When a UE queries for the "App.net" for the first time,
the global DNS reply has the ANYCAST address G1, which
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has the same cost regardless of where the Application
servers are attached.
- When the UE initiates the communication to G1, the
packets from the UE will be sent to the Application
Server that has the lowest cost, say the Server attached
to R1. The Application server is instructed with HTTPs
Redirect to reply with a location-specific URL, say
App.net-Loc1. The client on the UE will query the DNS
for App.net-Loc1 and get the response of ANYCAST L1. The
subsequent packets from the UE-1 for App.net are sent to
L1.
7. Manageability Considerations
To be added.
8. Security Considerations
To be added.
9. IANA Considerations
To be added.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4364] E. rosen, Y. Rekhter, "BGP/MPLS IP Virtual Private
networks (VPNs)", Feb 2006.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in
RFC 2119 Key Words", BCP 14, RFC 8174, DOI
10.17487/RFC8174, May 2017, <https://www.rfc-
editor.org/info/rfc8174>.
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[RFC8200] s. Deering R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", July 2017
10.2. Informative References
[3GPP-EdgeComputing] 3GPP TR 23.748, "3rd Generation
Partnership Project; Technical Specification Group
Services and System Aspects; Study on enhancement of
support for Edge Computing in 5G Core network
(5GC)", Release 17 work in progress, Aug 2020.
[5G-EC-Metrics] L. Dunbar, H. Song, J. Kaippallimalil, "IP
Layer Metrics for 5G Edge Computing Service", draft-
dunbar-ippm-5g-edge-compute-ip-layer-metrics-00,
work-in-progress, Oct 2020.
[5G-Edge-Sticky] L. Dunbar, J. Kaippallimalil, "IPv6 Solution
for 5G Edge Computing Sticky Service", draft-dunbar-
6man-5g-ec-sticky-service-00, work-in-progress, Oct
2020.
[RFC5521] P. Mohapatra, E. Rosen, "The BGP Encapsulation
Subsequent Address Family Identifier (SAFI) and the
BGP Tunnel Encapsulation Attribute", April 2009.
[BGP-SDWAN-Port] L. Dunbar, H. Wang, W. Hao, "BGP Extension
for SDWAN Overlay Networks", draft-dunbar-idr-bgp-
sdwan-overlay-ext-03, work-in-progress, Nov 2018.
[SDWAN-EDGE-Discovery] L. Dunbar, S. Hares, R. Raszuk, K.
Majumdar, "BGP UPDATE for SDWAN Edge Discovery",
draft-dunbar-idr-sdwan-edge-discovery-00, work-in-
progress, July 2020.
[Tunnel-Encap] E. Rosen, et al "The BGP Tunnel Encapsulation
Attribute", draft-ietf-idr-tunnel-encaps-10, Aug
2018.
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11. Acknowledgments
Acknowledgements to Donald Eastlake for their review and
contributions.
This document was prepared using 2-Word-v2.0.template.dot.
Authors' Addresses
Linda Dunbar
Futurewei
Email: ldunbar@futurewei.com
Kausik Majumdar
CommScope
350 W Java Drive, Sunnyvale, CA 94089
Email: kausik.majumdar@commscope.com
Haibo Wang
Huawei
Email: rainsword.wang@huawei.com
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