Network Working Group L. Dunbar
Internet Draft Futurewei
Intended status: Standard K. Majumdar
Expires: January 6, 2024 Microsoft
H. Wang
Huawei
G. Mishra
Verizon
Z. Du
China Mobile
July 6, 2023
BGP Extension for 5G Edge Service Metadata
draft-ietf-idr-5g-edge-service-metadata-04
Abstract
This draft describes a new Metadata Path Attribute and some
sub-TLVs for egress routers to advertise the Edge Service
Metadata of the directly attached edge services (ES). The Edge
Service Metadata can be used by the ingress routers in the 5G
Local Data Network to make path selections not only based on
the routing cost but also the running environment of the edge
services. The goal is to improve latency and performance for
5G edge services.
The extension enables an edge service at one specific location
to be more preferred than the others with the same IP address
(ANYCAST) to receive data flow from a specific source, like
specific User Equipment (UE).
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
This Internet-Draft is submitted in full conformance with the
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modified, and derivative works of it may not be created,
except to publish it as an RFC and to translate it into
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Internet-Drafts are working documents of the Internet
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Table of Contents
1. Introduction.............................................. 3
2. Conventions used in this document......................... 4
3. BGP Protocol Extension for Edge Service Metadata.......... 5
3.1. Ingress Node BGP Path Selection Behavior............. 6
3.1.1. Edge Service Metadata Influenced BGP Path
Selection.............................................. 6
3.1.2. Ingress Router Forwarding Behavior.............. 6
3.1.3. Forwarding Behavior when UEs moving to new 5G
Sites.................................................. 6
4. Edge Service Metadata Encoding............................ 7
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4.1. Metadata Path Attribute.............................. 7
4.2. The Site Preference Index sub-TLV format............. 8
4.3. Capacity Availability Index Metadata................. 8
4.3.1. Site Index Associated to Routes................ 10
4.3.2. BGP UPDATE with standalone Site Availability
Index................................................. 10
4.4. Service Delay Prediction Index...................... 10
4.4.1. Service Delay Prediction Sub-TLV............... 11
4.4.2. Service Delay Prediction Based on Load
Measurement........................................... 12
4.4.3. Raw Load Measurement Sub-TLV................... 14
5. Service Metadata Influenced Decision Process............. 14
5.1. Integrating Network Delay with the Service Metrics.. 14
5.2. Integrating with BGP decision process............... 15
6. Service Metadata Propagation Scope....................... 17
7. Minimum Interval for Metrics Change Advertisement........ 17
8. Manageability Considerations............................. 17
9. Security Considerations.................................. 18
10. IANA Considerations..................................... 18
11. References.............................................. 18
11.1. Normative References............................... 18
11.2. Informative References............................. 19
12. Appendix A.............................................. 20
12.1. Example of Flow Affinity........................... 20
13. Acknowledgments......................................... 21
1. Introduction
[5g-edge-Compute] describes the 5G Edge Computing background
and how BGP can be used to advertise the running status and
environment of the directly attached 5G edge services. Besides
the Radio Access, 5G is characterized by having edge services
closer to the Cell Towers reachable by Local Data Networks
(LDN) [3GPP TS 23.501]. From IP network perspective, the 5G
LDN is a limited domain with edge services a few hops away
from the ingress nodes. Only selective services by UEs are
considered as 5G Edge Services.
This document describes a new Metadata Path Attribute and some
sub-TLVs for egress routers to advertise the Edge Service
Metadata of the directly attached edge services. The Edge
Service Metadata in this document includes the site
availability index, the site preference, and the service delay
prediction index, which are further explained in Section 4.
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Note: the proposed Edge Service Metadata are not intended for
the best-effort services reachable via the public internet.
The Edge Service Metadata can be used by the ingress routers
to make path selections for selective low latency services
based on not only the network distance but also the running
environment of the edge cloud sites. The goal is to improve
latency and performance for 5G ultra-low latency services.
The extension is targeted for a single domain with RR
controlling the propagation of the BGP UPDATE. The Edge
Service Metadata is only attached to the services (routes)
hosted in the 5G edge cloud sites, which are only a small
subset of services initiated from UEs. E.g., not for UEs
accessing many internet sites.
2. Conventions used in this document
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.
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 Hosting
Environment for the edge services. An Edge DC
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might host 5G core functions in addition to the
frequently used application servers.
gNB next generation Node B
RTT: Round-trip Time
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. BGP Protocol Extension for Edge Service Metadata
The goal of the BGP extension is for egress routers to
propagate the metrics about their running environment to
ingress routers, which are called the Edge Service Metadata
throughout the document. Here are some examples of the
metrics propagated by the egress routers:
- The site Capacity Availability Index,
- The Site Preference Index,
- The Service Delay Predication Index for the attached edge
services.
This section specifies how those Metadata impact the ingress
nodes' path selections.
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3.1. Ingress Node BGP Path Selection Behavior
3.1.1. Edge Service Metadata Influenced BGP Path Selection
When an ingress router receives BGP updates for the same IP
address from multiple egress routers, all those egress routers
are considered as the next hops for the IP address. For the
selected edge services, the ingress router's BGP engine would
call an Edge Service Management function that can select paths
based on the Edge Service Metadata received. [5G-EC-Metrics]
has an example algorithm to compute the weighted path cost
based on the Edge Service Metadata carried by the sub-TLVs
specified in this document.
Section 5 has the detailed description of the Edge Service
Metadata influenced optimal path selection.
3.1.2. Ingress Router Forwarding Behavior
When the ingress router receives a packet and lookup the route
in the FIB, it gets the destination prefix's whole path. It
encapsulates the packet destined towards the optimal egress
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. Most
registered EC services have relatively short flows.
How Flow Affinity is implemented is out of the scope for this
document. Appendix A has one example illustrating achieving
flow affinity.
3.1.3. Forwarding Behavior when UEs moving to new 5G Sites
When a UE moves to a new 5G gNB which is anchored to the same
UPF, the packets from the UE traverse to the same ingress
router. Path selection and forwarding behavior are same as
before.
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If the UE maintains the same IP address when anchored to a new
UPF, the directly connected ingress router might use the
information passed from a neighboring router to derive the
optimal Next Hop for this route. [5G-Edge-Sticky] describes
some methods for the ingress router connected to the UPF in
the new site to consider the information passed from other
ingress routers in selecting the optimal paths. The detailed
algorithm is out of the scope of this document.
4. Edge Service Metadata Encoding
4.1. Metadata Path Attribute
The Metadata Path Attribute is an optional transitive BGP Path
attribute to carry the Edge Service Metadata described in this
document. Will need IANA to assign a value as the Type code
of the Path Attribute. The Metadata Path Attribute,
illustrated below, consists of a set of sub-TLVs, with each
sub-TLV containing the information corresponding to a specific
metrics of the Edge Service Metadata.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Attr. Flags |Svc-Metadata-T | Length (2 Octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Value (multiple Metadata sub-TLVs) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Edge Service Metadata Path Attribute
Attr. Flags are defined as:
o The high-order bit (bit 0): set to 1.
o The second high-order bit (bit 1): set to 0 to indicate
that the service-metadata is not transitive. Only
intended for the receiving router.
o The third high-order bit (bit 2): same as specified by
RFC4721.
o The fourth high-order bit (bit 3): set to 1 to indicate
there are two octets for the Length field.
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Svr-Metadata-T: Service-Metadata Path Attribute Type: identify
the Metadata Path Attribute, to be assigned by IANA.
Length (2 octets): the total number of octets of the value
field.
Value (variable): comprised of multiple sub-TLVs.
The Edge Service Metadata sub-TLVs specified by this document
include the Capacity Availability Index Value, the Site
Preference Index Value, the Service Delay Predication Index,
and the Load Measurement.
All values in the Sub-TLVs are unsigned 32 bits integers.
4.2. The Site Preference Index sub-TLV format
The Site Preference Index is one of the factors integrated
into the total cost for path selection. One Edge Cloud site
can have fewer computing servers, less power, or lower
internal network bandwidth than another. E.g., one micro edge
computing center located at a remote cell site has less
preference index value than an edge site in a metro area that
hosts management systems, analytics functions, and security
functions.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Site-Preference Sub-Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference Index value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Preference Index Sub-TLV
Preference Index value: 1-100, with 1 being the least
preferred, and 100 being the most preferred.
4.3. Capacity Availability Index Metadata
Capacity Availability Index indicates if an Edge Site has full
capacity, reduced capacity, or completely out of service.
Therefore, the value is 0-100, with 100% indicating the site
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is fully functional, 0% indicating the site is completely
dark, and 50% indicating the site is 50% degraded.
Cloud Site/Pod failures and degradation include, but not
limited to, a site capacity degradation or entire site going
down caused by a variety of reasons, such as fiber cut
connecting to the site or among pods within one site, cooling
failures, insufficient backup power, cyber threats attacks,
too many changes outside of the maintenance window, etc.
Fiber-cut is not uncommon within a Cloud site or between
sites.
When those failure events happen, the Edge (egress) router
visible to the ingress routers can be running fine. Therefore,
the ingress routers with paths to the egress routers can't use
BFD to detect the failures.
When there is a failure occurring at an edge site (or pod),
many instances can be impacted. In addition, the routes (i.e.,
the IP addresses) in an Edge Cloud Site might not be
aggregated nicely. Instead of many BGP UPDATE messages for
each instance to the impacted ingress routers, the egress
router can send one single BGP UPDATE indicating the capacity
availability of the site. The ingress routers can switch all
or a portion of the instances that are associated with the
site depending on how much the site is degraded.
The Capacity Availability Index sub-TLV:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CapAvailIdx-SubType | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Site-ID (2 octets) | Site Availability Percentage |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Capacity Availability Index Sub-TLV
- CapAvailIdx subtype: (TBD by IANA)
- Site ID: identifier for a site, which can be one pod, one row
of server racks, or entire DC site. One site can host many
service instances. There could be more than one sites (or
Pods) connected to the egress router (a.k.a. Edge DC GW)
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- Site Availability Percentage: represent the percentage of the
site availability, e.g., 100%, 50%, or 0%. When a site goes
dark, the Index is set to 0. 50 means 50% capacity
functioning.
4.3.1. Site Index Associated to Routes
An egress router needs to append the Site Capacity
Availability Index metadata with a BGP route update so that
the ingress routers can associate the Site reference
Identifier to the route in the Routing table.
However, it is unnecessary to include the Site Capacity
Availability Index for every BGP Update message if there is no
change to the site-reference identifier or the Capacity
Availability value for the service instances.
4.3.2. BGP UPDATE with standalone Site Availability Index
When there are failures or degradation to a site, the
corresponding egress router can send one BGP UPDATE with the
Capacity Availability Site Index without attaching any routes.
When an ingress router receives a BGP Update message from
Router-X with the Capacity Availability Sub-TLV without routes
attached, the new Capacity Availability value is applied to
all routes that have the Router-X as their next hops and are
associated with the Site-ID in the Sub-TLV.
4.4. Service Delay Prediction Index
It is desirable for an ingress router to select a site with
the shortest processing time for a ultra-low latency service.
But it is not easy to predict which site has "the fastest
processing time" or "the shortest processing delay" for an
incoming service request because:
- The given service instance shares the same physical
infrastructure with many other applications & service
instances. Service requests by other applications, UEs, or
applications running behavior can impact the processing time
for the given service instance.
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- The given service instance can be served by a cluster of
servers behind a Load Balancer. To the network, the service
is identified by one service ID.
- The service complexity is different. One service may call
many microservices, need to access multiple backend
databases, and need to go through sophisticated security
scrubbing functions, etc. Another service can be processed
by a few simple steps. Without the application internal
logic, it is not easy to estimate the processing time for
future service requests.
Even though utilization measurements, like those below, are
collected by most data centers, they cannot indicate which
site has the shortest processing time. A service request might
be processed faster on Site-A even if Site-A is overutilized.
o Server utilization for the server where the instance is
instantiated
o The network utilization for the links to the server where the
instance is instantiated
o The number of databases that the service instance will access
o The memory utilization of the databases
The remaining available resource at a site is a more
reasonable indication of process delay for future service
requests.
o The remaining available Server resources.
o The remaining available network utilization for the links to
the server where the instance is instantiated.
o The number of databases that the service instance will access.
o The remaining storage available for the databases.
The Service Delay Prediction Index is a value that predicts
processing delays at the site for future service requests. The
higher the value, the longer of the delay.
4.4.1. Service Delay Prediction Sub-TLV
While out of scope, we assume there is an algorithm that can
derive the Service Delay Prediction Index that can be assigned
to the egress router. When the Service Delay Prediction value
is updated, which can be triggered by the available resources
change, etc., the egress router can attach the updated Service
Delay Predication value in a sub-TLV under the Metadata Path
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Attribute of the BGP Route UPDATE message to the ingress
routers.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| subType=ServiceDelayPred | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Delay Predication Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Service Delay Prediction Index Sub-TLV
4.4.2. Service Delay Prediction Based on Load Measurement
When data centers detailed running status are not exposed to
the network operator, historic traffic patterns through the
egress nodes can be utilized to predict the load to a specific
service. For example, when traffic volume to one service at
one data center suddenly increases a huge percentage compared
with the past 24 hours average, it is likely caused by a
larger than normal demand for the service. When this happens,
another data center with lower-than-average traffic volume for
the same service might have a shorter processing time for the
same service.
Here are some measurements that can be utilized to derive the
Service Delay Predication for a service ID:
- Total number of packets to the attached service instance
(ToPackets);
- Total number of packets from the attached service
instance (FromPackets);
- Total number of Bytes to the attached service instance
(ToBytes);
- Total number of bytes from the attached service instance
(FromBytes);
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- The actual load measurement to the service instance
attached to a CATS-ER can be based on one of the metrics
above or including all four metrics with different
weights applied to each, such as:
- LoadIndex =
w1*ToPackets+w2*FromPackes+w3*ToBytes+w4*FromBytes
- Where 0<= wi <=1 and w1+ w2+ w3+ w4 = 1.
- The weights of each metric contributing to the index of
the service instance attached to a CATS-ER can be
configured or learned by self-adjusting based on user
feedbacks.
The Service Delay Prediction Index can be derived from
LoadIndex/24Hour-Average. A higher value means a longer delay
prediction. The egress router can use the ServiceDelayPred
Sub-TLV to indicate to the ingress routers of the delay
prediction derived from the traffic pattern.
Note: the proposed IP layer load measurement is only an
estimate based on the amount of traffic through the egress
router, which might not truly reflect the load of the servers
attached to the egress routers. They are listed here only for
some special deployments where those metrics are helpful to
the ingress routers in selecting the optimal paths.
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4.4.3. Raw Load Measurement Sub-TLV
When ingress routers have embedded analytics tool relying on
the raw measurements, it is useful for the egress router to
send the raw measurement.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| subType= Raw-Measurements | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Measurement Period |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| total number of packets to the Edge Service |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| total number of packets from the Edge Service |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| total number of bytes to the Edge Service |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| total number of bytes from the Edge Service |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Raw Load Measurement Sub-TLV
Raw-Measurement Sub-Type (TBD2): Raw measurements of
packets/bytes to/from the Edge Service address.
The receiver nodes can derive the Service Delay Prediction
for the Service based on the raw measurements sent from the
egress node.
Measure Period: BGP Update period in Seconds or user-
specified period.
5. Service Metadata Influenced Decision Process
5.1. Integrating Network Delay with the Service Metrics
As the service metrics and network delays are in different
units, here is an exemplary algorithm for an ingress router to
compare the cost to reach the service instances at Site-i or
Site-j.
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SerD-i * CP-j Pref-j * NetD-i
Cost-i=min(w *(----------------) + (1-w) *(------------------))
ServD-j * CP-i Pref-i * NetD-j
CP-i: Capacity Availability Index at Site-i. A higher value
means higher capacity available.
NetD-i: Network latency measurement (RTT) to the Egress
Router at the site-i.
Pref-i: Preference Index for Site-i, a higher value means
higher preference.
ServD-i: Service Delay Predication Index at Site-i for the
service (i.e., the ANYCAST address for the service).
w: Weight is a value between 0 and 1. If smaller than 0.5,
Network latency and the site Preference have more
influence; otherwise, Service Delay and capacity
availability have more influence.
5.2. Integrating with BGP decision process
When an ingress router receives BGP updates for the same IP
address from multiple egress routers, all those egress routers
are considered as the next hops for the IP address. For the
selected services configured to be influenced by the Edge
Service Metadata, the ingress router's BGP Decision process
would trigger the Edge Service Management function to compute
the weight to be applied to the route's next hop in the
forwarding plane. The decision process is influenced by the
Edge Service Metadata associated with the client routes, such
as Capacity Availability Index, Site Preference, and Service
Delay Prediction Index, in addition to the traditional BGP
multipath computation algorithm, such as the Weight, Local
preference, Origin, MED, etc., shown below:
BGP ANYCAST Update
+--------+ with Metadata +---------------+
| BGP |----------------->| EdgeServiceMgn|
|Decision|< - - - - - - - - | |
+---^-|--+ +-------|-------+
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| | BGP ANYCAST | Update Anycast
| | Route | Route Nexthops
| | Multi-path NH install | with weight
+---|-V--+ |
| RIB | |
+----+---+ |
| |
+---V------------------------------V-------+
| Forwarding Plane |
| |
+------------------------------------------+
Figure 6: Metadata Influenced Decision
When any of those metadata value goes to 0, the effect is the
same as the routes becoming ineligible via the egress router
who originates the metadata UPDATE. But when any of those
metadata just degrade, there is possibility, even though
smaller, for the egress router to continue as the optimal next
hop.
Suppose a destination address for aa08::4450 can be reached by
three next hops (R1, R2, R3). Further, suppose the local BGP's
Decision Process based on the traditional network layer
policies & metrics identifies the R1 as the optimal next hop
for this destination (aa08::4450). The Edge Service Metadata
might result in R2 as the optimal next hop for the prefix and
influence the Forwarding Plane.
The Edge Service Metadata influencing next hop selection is
different from the metric (or weight) to the next hop. The
metric to a next hop can impact many (sometimes, tens of
thousands) routes that have the node as their next hop. while
as the Edge Service Metadata only impact the optimal next hop
selection for a subset of client routes that are identified as
the edge services.
When the BGP custom decision [idr-custom-decision] is used,
the Edge Service Management function would have algorithm to
combine the Edge Service Metadata attributes with the custom
decision to derive the optimal next hop for the Edge service
routes.
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Note: For a BGP UPDATE message that only includes the Edge
Service Path Attribute without any NLRI, the Site Capacity
Availability Index value is applied to all the NLRIs with the
Site-ID indicated in the Edge Service Metadata Path Attribute.
6. Service Metadata Propagation Scope
Service Metadata are only distributed to the relevant ingress
nodes interested in the Service, which can be configured or
automatically formed.
For each registered low-latency Service, BGP RT Constrained
Distribution [RFC4684] can be used to form the Group
interested in the Service. The "Service ID," an IP address
prefix, is the Route Target. When an ingress router receives
the first packet of a flow destined to a Service ID, the
ingress router sends a BGP UPDATE that advertises the Route
Target membership NLRI per RFC4684. The ingress router must
assign a Timer for the Service ID, as the UE that uses the
Service ID might move away. Upon receiving a packet destined
for the Service ID, the ingress router must refresh the Timer.
The ingress router must send a BGP Withdraw UPDATE for the
Service ID upon expiration of the Timer.
7. Minimum Interval for Metrics Change Advertisement
As the metrics change can impact the path selection, the
Minimum Interval for Metrics Change Advertisement is
configured to control the update frequency to avoid route
oscillations. Default is 30s.
Significant load changes at EC data centers can be triggered
by short-term gatherings of UEs, like conventions, lasting a
few hours or days, which are too short to justify adjusting EC
server capacities among DCs. Therefore, the load metrics
change rate can be in the magnitude of hours or days.
8. Manageability Considerations
The Edge Service Metadata described in this document are only
intended for propagating between Ingress and egress routers of
one single BGP domain, i.e., the 5G Local Data Networks, which
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is a limited domain with edge services a few hops away from
the ingress nodes. Only the selective services by UEs are
considered as 5G Edge Services. The 5G LDN is usually managed
by one operator, even though the routers can be by different
vendors.
9. Security Considerations
The proposed Edge Service Metadata are advertised within the
trusted domain of 5G LDN's ingress and egress routers. There
are no extra security threats compared with iBGP.
10. IANA Considerations
Need IANA to assign the Metadata Path Attribute Type.
Metadata Path Attribute Type = TBD1.
Need IANA to assign three new Sub-TLV types under the
Metadata Path Attribute:
Type = TBD2: Site preference value sub-TLV
Type = TBD3: Site Capacity Availability Index sub-TLV
Type = TBD4: Service Delay Prediction Index.
Type = TBD5: Raw measurements of packets/bytes to/from the
Edge Service address.
11. References
11.1. 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.
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[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>.
[RFC7911] D. Walton, et al, "Advertisement of Multiple Paths
in BGP", RFC7911, July 2016.
11.2. Informative References
[3GPP TS 23.501] 3rd Generation Partnership Project;
Technical Specification Group Services and System
Aspects; System architecture for the 5G System (5GS)
[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-Compute] L. Dunbar, K. Majumdar, H. Wang, and G.
Mishra, "BGP Usage for 5G Edge Computing service
Metadata", draft-dunbar-idr-5g-edge-compute-bgp-
usage-00, work-in-progress, July 2022.
[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.
[IDR-CUSTOM-DECISION] A. Retana, R. White, "BGP Custom
Decision Process", draft-ietf-idr-custom-decision-
08, Feb 2017.
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[SDWAN-EDGE-Discovery] L. Dunbar, S. Hares, R. Raszuk, K.
Majumdar, "BGP UPDATE for SDWAN Edge Discovery",
draft-ietf-idr-sdwan-edge-discovery-03, July 2022.
12. Appendix A
12.1. Example of Flow Affinity
Here is one example to illustrate how Flow Affinity can be
achieved. This illustration is an informational example.
For the registered EC services, the ingress node keeps a table
of
- Service ID (i.e., IP address)
- Flow-ID
- Sticky Egress ID (egress router loopback address)
- 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 the egress node address for the same
flow. [5G-Edge-Sticky] describes several methods to derive the
Sticky Egress ID.
The Timer is always refreshed when a packet with the matching
EC Service ID (IP address) is received by the node.
If there is no Stick Egress ID present in the table for the EC
Service ID, the forwarding plane can select a NextHop
influenced by the Cost Compute Engine. The forwarding plane
encapsulates the packet with a path to the chosen NextHop. The
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chosen NextHop and the Flow ID are recorded in the EC Service
table entry.
When the selected optimal NextHop (egress router) is no longer
reachable, ingress router needs to select another path.
13. Acknowledgments
Acknowledgements to Adrian Farrel, Alvaro Retana, Robert
Raszuk, Sue Hares, Shunwan Zhuang, Donald Eastlake, Dhruv
Dhody, Cheng Li, and Vincent Shi for their suggestions and
contributions.
This document was prepared using 2-Word-v2.0.template.dot.
Authors' Addresses
Linda Dunbar
Futurewei
Email: ldunbar@futurewei.com
Kausik Majumdar
Microsoft
Email: kmajumdar@microsoft.com
Haibo Wang
Huawei
Email: rainsword.wang@huawei.com
Gyan Mishra
Verizon
Email: gyan.s.mishra@verizon.com
Zongpeng Du
China Mobile
Email: duzongpeng@foxmail.com
Contributors' Addresses
Cheng Li
Huawei
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Email: c.l@huawei.com
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