| Internet-Draft | CATS Service mobility IP addr anchoring | September 2024 |
| Bernardos & Mourad | Expires 7 March 2025 | [Page] |
The IETF CATS WG addresses the problem of how the network infrastructure can steer traffic between clients of a service and sites offering the service, considering both network metrics (such as bandwidth and latency), and compute metrics (such as processing, storage capabilities, and capacity).¶
This document defines new extensions and procedures for a terminal connected to a network infrastructure, to benefit from transparent service migration adapting to specific connectivity and computing requirements, so traffic is always steered to an instance meeting both requirements. Both CATS-aware and -unaware terminals are considered. Exemplary signaling control messages and operation extending the well-known Proxy Mobile IPv6 protocol are also defined.¶
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Let's consider a possible use case scenario, just for the sake of illustrating the scenario. A terminal is running an AR/VR/XR application (note that this is just an example, other services would also benefit from compute and connectivity traffic steering). Part of this service is executed in the network infrastructure, posing some requirements on the connectivity (e.g., delay between the terminal and the node where the service is executed on the network infrastructure) and computing resources (e.g., capabilities to render the XR video within a certain latency budget). Within the network domain where the terminal is connected to there are multiple sites capable of hosting the service, each with potentially different connectivity and computing characteristics. Figure 1 shows an exemplary scenario. Considering the connectivity and computing latencies (just as an example of metrics), the best service site is #n-1 in the example used in the Figure.¶
________________
( ---------- )
( | | )
( ---------- | )
________________ ( | | | ) ________________
( ---------- ) ( ---------- | | ) ( ---------- )
( | | ) ( |service | |- ) ( | | )
( ---------- | ) ( |contact | | ) ( ---------- | )
( | | | ) ( |instance|-- ) ( | | | )
( ---------- | | ) ( ---------- ) ( ---------- | | )
( |service | |- ) ( Serv. site #N-1 ) ( |service | |- )
( |contact | | ) -------+---------- ( |contact | | )
( |instance|-- ) Computing \ ( |instance|-- )
( ---------- ) delay:4ms \ ( ---------- )
( Serv. site #1 ) --------+-- ( Serv. site #N )
-------+-------- ----| ECR#N-1 |---- ---------+-----
\ Computing -- ----------- -- Computing /
\ delay:10ms Networking delay:5ms /
---+----- delay:7ms ------+--
( | ECR#1 | // | ECR#N | )
( --------- // --------- )
( Networking // Networking )
( delay:5ms // delay:15ms )
( // )
( // )
( // )
( // )
( // )
( --------- --------- )
-------| ICR#1 |---------------------| ICR#2 |--------
--------- ---------
(·)
(·)
------
| UE |
------
The main problem that this document tries to address is the following. Networking systems do not have mechanisms yet to service mobility mechanisms optimized for connectivity and computing-aware traffic steering, which consider both connectivity and computing status to dynamically select where a service runs for a given terminal.¶
Based on the former, this document proposes solutions to enable the network to react and adapt to connectivity and computing conditions, triggering optimal service migration based on service-specific IP anchor mobility. In particular, this document addresses the following questions: (i) what mechanisms does the network need to implement to facilitate the migration of a service so its requirements in terms of computing and networking are maintained?; and, (ii) how to steer traffic to a new service instance location after moving the service, in a transparent manner to the terminal, by using IP anchor mobility?¶
The following terms used in this document are defined by the IETF:¶
We describe next an example of operation and signaling for the network to perform service mobility. Three different embodiments are described next, for variations (OPTIONS) of the procedures: terminal initiated, ECR-initiated and CATS-controller initiated. In addition to the functionality defined in [I-D.bernardos-cats-ip-address-anchoring], this documents defines a new functionality:¶
Next, we assume service mobility is triggered by a CATS-aware terminal. By having a CATS agent running on the terminal, it can perform different monitoring actions to predict or detect the need to migrate a service from one site to another. This CATS agent might, for example, interact with other CATS agents deployed on ICRs, ECRs and service sites.¶
In the following we describe a service anchor mobility procedure for CATS, initiated by a CATS-aware terminal. Following the terminal initiation, the network infrastructure is capable to select a target service instance meeting the connectivity and computing requirements of the service, with signaling procedures defined to perform a transparent anchor migration to a new site, facilitating the service migration in a transparent way for the terminal. Extensions and new behavior are highlighted. Note that variations are possible over this exemplary signaling diagram.¶
+----+ +-----+ +-------------+ +---------------+ +-------------+ +----+ | | | | | site #1 | | site #N-1 | | site #N | |CATS| |term| |ICR#1| |ECR#1 ag. SCI| |ECR#N-1 ag. SCI| |ECR#N ag. SCI| |ctrl| +----+ +-----+ +--+----+---+-+ +----+----+---+-+ +--+----+---+-+ +----+ | | | | | | | | | | | | | | O. Service instance running at site #n-1. | | | | | Tunnel established between ICR#1 and ECR#N-1 | | | | | | | | | | | | | | | 1. An external or internal trigger is received regarding | | a change in the compute or networking conditions | | | | | | | | | | | | | |1a. CATS agent at terminal reports a perceived change on service| |·····>| | | | | | | | | | | | | | | | | | | | | | | | |2a.CATS query(service ID, terminal ID, ICR ID, CATS reqs.) | |······>|<··>| | | | | | | | | | |········································>|<··>| | | | 3a.CATS response(service ID, terminal ID, ECR ID, CATS cond.) | |<······| | | | | | | | | | | |<········································| | | | | | | | | | | | | | | | | 4a. Service anchor/ECR@site#n is selected as best | | | | | | | | | | | | | | 5a.CATS request(service ID, terminal ID, ICR ID, CATS reqs., IP pref.) |···············································>| | | | | | | | | | | | | | | | |6.CATS ACK(service ID, terminal ID, ECR ID, CATS cond., IP prefix) |<···············································| | | | | | | | | | | | | | | | | 7.New tunnel for IP pref. established beetween ICR#1 and ECR#N | | | | | | | | | | | | | | | 8.Service migration from site#N-1 to site#N | | | | | | | | | | | | | | | | 9. Service specific traffic| | | | | | | |<---->|<--------------------------------------->|<------>| | | | | | | | | | | | | |
Figure 2 shows the message sequence chart of the IP anchor mobility for CATS, initiated by a CATS-aware terminal (OPTION A), which is explained next:¶
The ICR sends a query to all (but currently used) ECRs of the domain, or a subset selected based on the location of the ICR. This query may include the following parameters:¶
Each ECR, possibly after checking with the CATS agent of the site(s) it provides connectivity, responds, including the following information:¶
The ICR sends a query to all ECRs of the domain, or a subset selected based on the location of the ICR. This query may include the following parameters:¶
A CATS agent at a site might be collocated with the ECR. Examples of a CATS agent at a site are network controllers or orchestrators at the site. Note that the way a CATS agent at an ECR may interact with the CATS agent of the site is out of the scope of this document. Examples include using monitoring and telemetry interfaces with an orchestrator managing the site.¶
The ICR requests the proposed/selected ECR to establish a traffic steering session with it, sending a CATS request. This request includes the same information that was included in the CATS query (to facilitate stateless operation of the ECRs while being queried), plus the following additional parameters:¶
The selected ECR responds back with an acknowledgement, including the following information:¶
The control plane extensions introduced in the previous section can be implemented over different protocols. This section specifies extensions to Proxy Mobile IPv6. Only new options additional to what is defined in [I-D.bernardos-cats-ip-address-anchoring] are included.¶
The new ECR option has the following format:¶
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Reserved | Addr. Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + New ECR IP address + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+¶
Message fields:¶
TBD.¶
The work of Carlos J. Bernardos in this document has been partially supported by the Horizon Europe PREDICT-6G (Grant 101095890), DESIRE6G (Grant 101096466) and UNICO I+D 6G-DATADRIVEN project.¶