| Internet-Draft | Computing Aware Traffic Steering using I | February 2024 |
| Bernardos & Mourad | Expires 1 September 2024 | [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 for a terminal connected to a network infrastructure, to request a service with specific connectivity and computing requirements, so traffic is 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. The network does not have mechanisms yet to enable service-specific connectivity and computing-aware traffic steering, which benefit from optimal service instance location selection and traffic steering.¶
Based on the former, this document proposes solutions to enable the network to select the best site to instantiate a terminal service, taking into account service-specific requirements at both connectivity and computing levels. In particular, this document addresses the following questions: (i) what information does the network need to be able to select the best location for a service to be instantiated?; and, (ii) how to steer traffic between the terminal and the selected service site, in a way that is transparent to the network forwarding infrastructure, and even to the terminal?¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].¶
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 be able to select the best site to instantiate a service to be consumed by a terminal, so traffic can be steered simultaneously meeting connectivity and computing requirements. A CATS agent is defined to run on both the ingress (the router to which the terminal is attached to) and egress (a router close to or at the site where the service instance is running) routers, and also at the sites capable of instantiating services. Optionally, the CATS agent functionality can also run on the terminal to aid the network deciding or actively influence its site selection. The CATS agent might have the following functionality:¶
In the following we describe an extended terminal service request procedure enabling the network infrastructure to select a service instance meeting the connectivity and computing requirements of the service, and the setup of the required traffic steering for the service traffic. 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| +----+ +-----+ +--+----+---+-+ +----+----+---+-+ +--+----+---+-+ +----+ | | | | | | | | | | | | 1.Service request(service ID, CATS reqs.)| | | | | | |·····>| | | | | | | | | | | | | | | | | | | | | | | OPTION 1:| | | | | | | | | | | | |2a.CATS query(service ID, terminal ID, ICR ID, CATS reqs.) | |······>|<··>| | | | | | | | | | |························>|<··>| | | | | | | |········································>|<··>| | | 2b.CATS response(service ID, terminal ID, ECR ID, CATS cond., IP prefix) | |<······| | | | | | | | | | | |<························| | | | | | | | |<········································| | | | | | | | | | | | | | | | OPTION 2:| | | | | | | | | | | | 3a.CATS query(service ID, terminal ID, ICR ID, CATS reqs.) | |·······························································>| | | | | | | | | | | | | | 3b.CATS response(service ID, terminal ID, CATS cond., selected ECR) |<·······························································| | | | | | | | | | | | | | 4.Service anchor/ECR@site#n-1 is selected as best | | | | | | | | | | | | | | |5.CATS request(service ID, terminal ID, ICR ID, CATS reqs.) | |·······························>| | | | | | | | | | | | | | | | | | | |6.CATS ACK(service ID, terminal ID, ECR ID, CATS cond., IP prefix) |<·······························| | | | | | | | | | | | | | | | | | | | | 7. A tunnel is established | | | | | | | | | | | | | | | | | |8.Assigned IP prefix/address, service specific policy| | | |<·····| | | | | | | | | | | | | | | | | | | | | | | | 9. Service specific traffic| | | | | | | |<---->|<----------------------->|<------>| | | | | | | | | | | | | | | | |
A terminal wants to execute a service/app which is requires some functionality to be run on the network infrastructure (e.g., an AR/VR/XR service). This service has specific requirements in terms of both connectivity and computing. We refer to them as CATS requirements.¶
The terminal sends a Service request to the ICR, including a service ID and, optionally, if the terminal is CATS aware, a list of CATS requirements. Note that this request might be addressed to an ICR or just intercepted by an ICR. If present, the list of CATS requirements might include information such as (not limited to any particular combination of parameters):¶
There are two main options considered:¶
OPTION 1:¶
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:¶
Each ECR, possibly after checking with the CATS agent of the site(s) it provides connectivity, responds, including the following information:¶
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. Based on the received responses, the ICR selects an ECR. (step 4).¶
OPTION 2:¶
The ICR sends a query to a CATS controller in the domain, including the following parameters:¶
The CATS controller, which has the overall view of all the sites and ECRs of the domain, responds back including the following information:¶
The selected ECR, if it accepts the request, 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.¶
The CATS query message and request can be implemented as an extended Proxy Binding Update (PBU) message (defined in RFC 5213 [RFC5213]):¶
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence # |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|H|L|K|M|R|P|C|X| Reserved | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Mobility options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
¶
A CATS query can be sent by an ICR to an ECR, and also by an ICR to a CATS controller. A CATS request can be sent by an ICR to an ECR.¶
Message fields:¶
The following new options can be used in this message:¶
A CATS response / CATS ACK can be implemented as an extended Proxy Binding Acknowledgement (PBA) message (defined in RFC 5213):¶
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status |K|R|P|C|X|Rsrv.|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence # | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Mobility options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
¶
A CATS response can be sent by an ECR to an ICR, and also by a CATS controller to an ICR. A CATS ACK can be sent by an ECR to an ICR, and also by a CATS controller to an ICR.¶
Message fields:¶
The following new options can be used in this message:¶
The CR_ID 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 = TBA | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CR ID Length | CR ID Format |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ CR ID +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
¶
CR ID Format: 8-bit unsigned integer. Identifies the format of the CR ID. Possibles values:¶
The Service_ID 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 = TBA | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service ID Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Service ID +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
¶
The CATS requirements/conditions 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 = TBA | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ NetMinBandwidth +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NetMaxLatency |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NetMaxLatencyVariation |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NetMaxLoss |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CompMaxLatency |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Affinity |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
¶
The Service prefix 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 | Prefix Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Current Service Prefix + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+¶
TBD.¶
The work of Carlos J. Bernardos in this document has been partially supported by the Horizon Europe PREDICT-6G (Grant 101095890), DESIRE-6G (Grant 101096466) and UNICO I+D 6G-DATADRIVEN-04 project.¶