Network Working Group L. Dunbar
Internet Draft H. Chen
Intended status: Standard Futurewei
Expires: September 7, 2021 Aijun Wang
China Telecom
March 8, 2021
OSPF extension for 5G Edge Computing Service
draft-dunbar-lsr-5g-edge-compute-ospf-ext-03
Abstract
This draft describes an OSPF extension for routers to
advertise the running status and environment of the
directly attached 5G Edge Computing servers. The
AppMetaData can be used by the routers in the 5G Local Data
Network to make intelligent decision to optimize the
forwarding of flows from UEs. The goal is to improve
latency and performance for 5G Edge Computing services.
Status of this Memo
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Table of Contents
1. Introduction........................................... 3
1.1. 5G Edge Computing Background...................... 3
1.2. Problem#1: ANYCAST in 5G EC Environment........... 4
1.3. Problem #2: Unbalanced Anycast Distribution due to
UE Mobility............................................ 5
1.4. Problem 3: Application Server Relocation.......... 5
2. Conventions used in this document...................... 5
3. Solution Overview...................................... 7
3.1. Flow Affinity to an ANYCAST server................ 7
3.2. IP Layer Metrics to Gauge App Server Running Status
....................................................... 9
3.3. To Equalize traffic among Multiple ANYCAST
Locations............................................. 10
3.4. Reason for using IGP Based Solution.............. 11
4. Aggregated Cost Computed by Egress routers............ 11
4.1. OSPFv3 LSA to carry the Aggregated Cost.......... 11
4.2. OSPFv2 LSA to carry the Aggregated Cost.......... 12
5. IP Layer App-Metrics Advertisements................... 12
5.1. OSPFv3 Extension to carry the App-Metrics........ 13
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5.2. OSPFv2 Extension to advertise the IP Layer App-
Metrics............................................... 13
5.3. IP Layer App-Metrics Sub-TLVs.................... 15
6. Soft Anchoring of an ANYCAST Flow..................... 17
7. Manageability Considerations.......................... 19
8. Security Considerations............................... 19
9. IANA Considerations................................... 19
10. References........................................... 19
10.1. Normative References............................ 19
10.2. Informative References.......................... 20
11. Acknowledgments...................................... 21
1. Introduction
This document describes an OSPF extension to distribute the
5G Edge Computing App running status and environment, so
that other routers in the 5G Local Data Network (LDN) can
make intelligent decision to optimize forwarding of 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 can be close in proximity.
Those Edge Computing (mini) data centers are usually very
close to, or co-located with, 5G base stations, with the
goal to minimize latency and to optimize the user
experience.
When a UE (User Equipment) initiates application packets
using the destination address from a DNS reply or its own
cache, the 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) which 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), the handover procedure is
initiated which includes the 5G SMF (Session Management
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Function) selecting a new UPF-PSA [3GPP TS 23.501 and TS
23.502]. 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 period of time for SSC [Session and
Service Continuity] mode 3 to make the handover process
more seamless.
+--+
|UE|---\+---------+ +------------------+
+--+ | 5G | +---------+ | S1: aa08::4450 |
+--+ | Site +--++---+ +----+ |
|UE|----| A |PSA| 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 |PSA| Rb | | R2 | S2: aa08::4460 |
+--+ | +--++----+ +----+ |
+--+ | | +-----------+ | S3: aa08::4470 |
|UE|---/+---------+ +------------------+
+--+ L-DN2
Figure 1: App Servers in different edge DCs
1.2. 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. With multiple
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servers having the same ANYCAST address, it eliminates the
single point of failure and bottleneck at the DNS resolvers
and application layer load balancers. Another benefit of
using ANYCAST address is removing the dependency on how UEs
get the IP addresses for their Applications. Some UEs (or
clients) might use stale cached IP addresses for extended
period.
But, having multiple locations of the same ANYCAST address
in 5G Edge Computing environment can be problematic because
all those edge computing Data Centers can be close in
proximity. There might be very little difference in the
routing cost to reach the Application Servers in different
Edge DCs, which can cause packets from one flow to be
forwarded to different locations, resulting in service
glitches.
1.3. 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 Servers should be
hosted. When one App server is heavily utilized, other App
servers of the same address close-by can be very under-
utilized. Since the condition can be short lived, it is
difficult for the application controller to anticipate the
move and adjust.
1.4. Problem 3: Application Server Relocation
When an Application Server is added to, moved, or deleted
from a 5G Edge Computing Data Center, not only the
reachability changes but also the utilization and capacity
for the Data Center might change.
Note: for the ease of description, the Edge Computing
server, Application server, App server are used
interchangeably throughout this document.
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
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Application Server is attached. For 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 host 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
external IP network, in front of a set of
application servers. From IP network
perspective, this whole group of servers are
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 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. It might be co-
located with 5G Base Station and not only host
5G core functions, but also host frequently
used Edge server instances.
gNB next generation Node B
LDN: Local Data Network
PSA: PDU Session Anchor (UPF)
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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. Solution Overview
From IP Layer, the Application Servers are identified by
their IP (ANYCAST) addresses. The 5G Edge Computing
controller or management system is aware of the ANYCAST
addresses that need the optimized forwarding. The 5G Edge
Computing controller or management system can configure the
ACLs on selected routers in LDN to filter out packets for
those applications.
The proposed solution is for the egress router (A-ER), to
which the Application Servers are directly attached to
collect various measurements about the Servers' running
status [5G-EC-Metrics] and advertise the metrics to other
routers in 5G EC LDN.
3.1. Flow Affinity to an ANYCAST server
When there are multiple Edge Computing Servers with the
same ANYCAST address located in different mini Edge
Computing Data Centers, each location is identified by its
A-ER unicast address(es). To the routers in an LDN,
achieving Flow Affinity is to send the packets of the same
flow to the same A-ER's unicast address. A-ER, e.g. R1 in
Figure 1, should deliver the packets destined towards the
ANYCAST address to its directly attached server even
through the same address is also reachable from other
routers, unless the directly attached server is no longer
reachable due to Server or Link failure.
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Many commercial routers today support some forms of flow
affinity to ensure packets belonging to one flow be
forwarded along the same path. For servers with the same
ANYCAST address attached to 3 different egress routers,
routers supporting the flow affinity feature should forward
the packets of one flow to the same egress router even if
the cost towards the egress router changes.
Editor's note: for IPv6 traffic, Flow Affinity can be
supported by the routers of the Local Data Network (LDN)
forwarding the packets with the same Flow Label in the
packets' IPv6 Header along the same path towards the same
egress router.
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3.2. IP Layer Metrics to Gauge App Server Running Status
Most application don't expose their internal logics to
network. Their communications are generally encrypted. Most
of them do not even respond to PING or ICMP messages
initiated by routers or network gears.
[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/bites to the App
Server and the number of packets/bytes from the App
Server which are collected by the A-ER that has the
direct connection to the App Server.
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 attached application server. Some
data centers can have hundreds, or thousands, of
servers behind an application server's App Layer Load
Balancer. Other data centers can have very small
number of servers for the application. "Capacity
Index", which is a numeric number, is used to
represent the capacity of the application server
attached to an A-ER.
- Site preference index:
[IPv6-StickyService] describes a scenario that some
sites are more preferred for handling an application
than others for flows from a specific UE.
For ease of description, those metrics, more may be added
later, are called IP Layer App-Metrics throughout the
document.
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3.3. To Equalize traffic among Multiple ANYCAST Locations
The main benefit of using ANYCAST is to leverage the
network layer information to balance the traffic among
multiple Application Server locations.
For 5G Edge Computing environment, the routers in the LDN
need to be notified of various measurement of the App
Servers attached to each A-ER 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 in LDN to compare the cost to reach the App
Servers between the Site-i or Site-j:
Load-i * CP-j Pref-j * Network-Delay-i
Cost-i=min(w *(----------------) + (1-w) *(-------------------------))
Load-j * CP-i Pref-i * Network-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 the site I, higher value means
higher capacity.
Network Delay-i: Network latency measurement (RTT) to
the A-ER that has the Application Server attached at the
site-i.
Noted: Ingress nodes can easily measure RTT to all the
egress nodes by existing IPPM metrics. But it is not so
easy for ingress nodes to measure RTT to all the App
Servers. Therefore, "Network-Delay-i", a.k.a. Network
latency measurement (RTT), is between the Ingress nodes
and egress nodes. The link cost between the egress nodes
to their attached servers are embedded in the "capacity
index".
Pref-i: Preference index for the site-i, 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;
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otherwise, Server load and its capacity have more
influence.
3.4. Reason for using IGP Based Solution
Here are some benefits in using IGP to propagate the IP
Layer App-Metrics:
- Intermediate routers can derive the aggregated cost to
reach the Application Servers attached to different
egress nodes, especially:
- The path to the optimal egress node can be more
accurate or shorter
- Convergence is shorter when there is any failure
along the way towards the optimal ANYCAST server.
- When there is any failure at the intended ANYCAST
server, all the transient packets can be optimally
forwarded to another App Server attached to a
different egress router.
- Doesn't need ingress node to establish tunnels with
egress nodes.
There are limitations of using IGP too, such as:
- The IGP approach might not suit well to 5G EC LDN
operated by multiple ISPs networks.
For LDN operated by multiple IPSs, BGP should be used.
AppMetaData NLRI Path Attribute [5G-AppMetaData]
describes the BGP UPDATE message to propagate IP Layer
App-Metrics crossing multiple ISPs.
4. Aggregated Cost Computed by Egress Routers
If all egress routers that have direct connection to the
App Servers can be configured with a consistent algorithm
to compute an aggregated cost that take into consideration
the Load Measurement, Capacity value and Preference value,
this aggregated cost can be considered as the Metric of the
link to the App Server.
In this scenario, there is no protocol extension needed.
4.1. OSPFv3 LSA to carry the Aggregated Cost
If the App Servers use IPv6 ANYCAST address, the aggregated
cost computed by the egress routers can be encoded in the
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Metric field [the interface cost] of Intra-Area-Prefix-LSA
specified by the Section 3.7 of the [ RFC5340].
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 6 (Intra-Area Prefix) | TLV Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 | Aggregated Cost to the App Server |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PrefixLength | PrefixOptions | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Prefix |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Aggregated Cost to App Server
4.2. OSPFv2 LSA to carry the Aggregated Cost
For App Servers in IPv4 address, the Aggregated Cost can be
encoded in the "Metric" field of the Stub Link LSA [Link
type =3] specified by the Section 12.4 of the [RFC2328].
5. IP Layer App-Metrics Advertisements
This section describes the OSPF extension that can carry
the detailed IP Layer Metrics when it is not possible for
all the egress routers to have a consistent algorithm to
compute the aggregated cost or some routers need all the
detailed IP Layer metrics for the App Servers for other
purposes.
Since only a subset of routers within an IGP domain need to
know those detailed metrics, it makes sense to use the
OSPFv2 Extended Prefix Opaque LSA for IPv4 and OSPFv3
Extended LSA with Intra-Area-Prefix TLV to carry the
detailed sub-TLVs. For routers that don't care about those
metrics, they can ignore them very easily.
It worth noting that not all hosts (prefix) attached to an
A-ER are ANYCAST servers that need network optimization.
An A-ER only needs to advertise the App-Metrics for the
ANYCAST addresses that match with the configured ACLs.
Draft [draft-wang-lsr-passive-interface-attribute]
introduces the Stub-Link TLV for OSPFv2/v3 and ISIS
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protocol respectively. Considering the interfaces on an
edge router that connects to the App servers are normally
configured as passive interfaces, these IP-layer App-
metrics can also be advertised as the attributes of the
passive/stub link. The associated prefixes can then be
advertised in the "Stub-Link Prefix Sub-TLV" that defined
in [draft-wang-lsr-passive-interface-attribute]. All the
associated prefixes share the same characteristic of the
link. Other link related sub-TLVs defined in [RFC8920] can
also be attached and applied to the calculation of path to
the associated prefixes.
5.1. OSPFv3 Extension to carry the App-Metrics
For App Servers using IPv6, the OSPFv3 Extended LSA with
the Intra-Area-Prefix Address TLV specified by the Section
3.7 of RFC8362 can be used to carry the App-Metrics for the
attached App Servers.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|7 (IPv6 Local-Local Address) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 AppServer (ANYCAST) address |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Load measurement sub-TLV |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Capability sub-TLV |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference sub-TLV |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: IPv6 App Server App-Metrics Encoding
5.2. OSPFv2 Extension to advertise the IP Layer App-Metrics
For App Servers using IPv4 addresses, the OSPFv2 Extended
Prefix Opaque LSA with the extended Prefix TLV can be used
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to carry the App Metrics sub-TLVs, as specified by the
Section 2.1 [RFC7684].
Here is the proposed encoding:
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Type | Prefix Length | AF | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Prefix (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Load Measurement Sub-TLV |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| capacity Index Sub-TLV |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Site Preference Sub-TLV |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: App-Metrix Sub-TLVs in OSPFv2 Extended Prefix TLV
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5.3. IP Layer App-Metrics Sub-TLVs
Two types of Load Measurement Sub-TLVs are specified:
a) The Aggregated Load Index based on weighted combination
of the collected measurements;
b) 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 or the
raw measurements are needed by a central analytic
system.
The Aggregated Load 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 (TBD2) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Measurement Period |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Aggregated Load Index to reach the App Server |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Aggregated Load Index Sub-TLV
Type=TBD2 (to be assigned by IANA) indicates that the
sub-TLV carries the 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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The 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 6: Raw Load Measurement Sub-TLV
Type= TBD3 (to be assigned by IANA) indicates that the
sub-TLV carries the Raw measurements of packets/bytes
to/from the App Server ANYCAST address.
Measurement Period: A user specified period in seconds,
default is 3600 seconds.
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 (TBD3) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Capacity Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Capacity Index Sub-TLV
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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 (TBD4) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: Preference Index Sub-TLV
Note: "Capacity Index" and "Site preference" can be more
stable for each site. If those values are configured to
nodes, they might not need to be included in every OSPF
LSA.
6. Soft Anchoring of an ANYCAST Flow
This section describes a solution that can anchor an
application flow from a UE to a specific ANYCAST Server
location even when the UE moves from one 5G Site to
another. This is called "Sticky Service" in the 3GPP Edge
Computing specification.
Lets' assume one application "App.net" is instantiated on
four servers that are attached to four different A-ERs:
R1, R2, R3, and R4 respectively. The "App.net" needs to be
Sticky means that the packets to the "App.net" from UE-1
needs to stick with one server, say the "App.net" Server
attached to R1, even when the UE moves from one 5G site to
another. When there is failure at 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 failure.
Here are the steps to achieving "Soft Anchoring":
- Assign a group of ANYCAST addresses to one
application. For example, "App.net" is assigned with
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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 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 replies 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 replies the ANYCAST address G1,
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which has the same cost regardless 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 respond back 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
The following Sub-TLV types need to be added by IANA
to OSPFv4 Extended-LSA Sub-TLVs and OSPFv2 Extended
Link Opaque LSA TLVs Registry.
- Aggregated Load Index Sub-TLV type
- Raw Load Measurement Sub-TLV type
- Capacity Index Sub-TLV type
- Preference Index Sub-TLV type
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.
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[RFC2328] J. Moy, "OSPF Version 2", RFC 2328, April 1998.
[RFC7684] P. Psenak, et al, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, Nov. 2015.
[RFC8200] S. Deering R. Hinden, "Internet Protocol, Version
6 (IPv6) Specification", July 2017.
[RFC8326] A. Lindem, et al, "OSPFv3 Link State
advertisement (LSA0 Extensibility", RFC 8362,
April 2018.
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-AppMetaData] L. Dunbar, K. Majumdar, H. Wang, "BGP NLRI
App Meta Data for 5G Edge Computing Service",
draft-dunbar-idr-5g-edge-compute-app-meta-data-
01, work-in-progress, Nov 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-01, work-in-progress, Nov 2020.
[5G-StickyService] 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.
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[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.
11. Acknowledgments
Acknowledgements to Acee Lindem, Jeff Tantsura, and Donald
Eastlake for their review and suggestions.
This document was prepared using 2-Word-v2.0.template.dot.
Authors' Addresses
Linda Dunbar
Futurewei
Email: ldunbar@futurewei.com
Huaimo Chen
Futurewei
Email: huaimo.chen@futurewei.com
Aijun Wang
China Telecom
Email: wangaj3@chinatelecom.cn
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