| Internet-Draft | CATS-MUP | June 2024 |
| Tran & Kim | Expires 30 December 2024 | [Page] |
The document [I-D.draft-mhkk-dmm-srv6mup-architecture] describes the Mobile User Plane (MUP) architecture for Distributed Mobility Management. The proposed architecture converts the user mobility session information from the control plane entity to an IPv6 dataplane routing information. When there are multiple candidate instances located at different location to serve an user request, the MUP Provider Edge (PE) might prioritize the closest service location. However, the closest routing path might not be the optimal route.¶
This document discusses how the mentioned MUP architecture can be leveraged to set up dataplane routing paths to the optimal service instance location with the assistance of computing-aware traffic steering capabilities. For each session request, based on the up-to-date collected computing and network information, the MUP controller can convert the session information to the optimal route.¶
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The document [I-D.draft-mhkk-dmm-srv6mup-architecture] describes the Mobile User Plane architecture for Distributed Mobility Management. This architecture is composed of a MUP controller and multiple MUP PEs. When applying the MUP architecture in 5G network, the MUP PEs accomodate the N3 RAN network as Interwork Segment or the N6 DN network as Direct Segment. The MUP PEs advertises the Interwork and Discovery Segment dataplane network reachability (e.g. Segment Routing IPv6 segment identifier (SRv6 SID)) to the MUP network via the interwork and direct segment Discovery routes. Meanwhile, the MUP controller transformed the received user mobility session information to the corresponding interwork and direct segment information. Then, it advertises the transformed information to MUP PEs via Session Transformed routes. The MUP PEs use the matching Discovery routes to resolve the Session Transformed routes and forward the packet through the MUP SRv6 network.¶
This document discusses the optimal route configuration problem when applying the mentioned MUP architecture in a network scenario where an user request can be served by multiple computing instances of the same service located at different locations. The closest geographical service location to users might not be the optimal service instance's location as pointed out in the problem statement document of IETF Computing-Aware Traffic Steering (CATS) working group [I-D.draft-ietf-cats-usecases-requirements]. In this scenario, an optimal service instance location can be decided at the mobile control plane or data plane.¶
In the control plane case, it is possible to use an Application Function (AF) to determine the optimal service instance and influence the 5G control plane to select the DN corresponding to the chosen instance. The MUP-C only needs to transform the optimal DN information in the session information into the corresponding route. Meanwhile, in the data plane approach, the MUP-C should decide the optimal service instance location by itself and transform the unoptimal session information into the optimal route based on its decision. The data plane approach can avoid additional signalling procedure at the control plane of the other approach. It also supports IP Routing paradigm benefit of SRv6 mobile user plane as mentioned in the edge computing use case of the document [I-D.draft-ietf-dmm-srv6mob-arch].¶
Therefore, a solution to integrate CATS capabilities into the mentioned MUP architecture is presented in this document. By considering service computing and network information of all candidate service instances, the MUP controller can convert the session information into the optimal dataplane route.¶
This document is proposed to discuss a possible extension consideration of the original MUP architecture document[I-D.draft-mhkk-dmm-srv6mup-architecture]. Regarding the Distributed Mobility Management requirements described in [RFC7333], the MUP architecture can partly address the "Non-optimal routes" problem and the "Multicast considerations" requirement by integrating CATS capabilties. As described in [RFC4786], anycast is the practice of making a particular service address available in multiple locations. Anycast support could be in the scope of multicast support for distributed mobility management.¶
CATS-MUP-C: Computing-aware traffic steering MUP-C which integrates CATS path selection and MUP-C features.¶
Besides, this document uses the following terminologies which has been defined in [I-D.draft-ldbc-cats-framework]¶
CATS: Computing-Aware Traffic Steering takes into account the dynamic nature of computing resource metrics and network state metrics to steer service traffic to a service instance.¶
Service: An offering that is made available by a provider by orchestrating a set of resources (networking, compute, storage, etc.). The same service can be provided in many locations; each of them constitutes a service instance.¶
Service instance: An instance of running resources according to a given service logic.¶
Service contact instance: A client-facing service function instance that is responsible for receiving requests in the context of a given service. A single service can be represented and accessed via several contact instances that run in different regions of a network.¶
CATS Path Selector (C-PS): A functional entity that computes and selects paths towards service locations and instances and which accommodates the requirements of service requests. Such a path computation engine takes into account the service and network status information.¶
CATS Service Metric Agent (C-SMA): A functional entity that is responsible for collecting service capabilities and status, and for reporting them to a C-PS.¶
CATS Network Metric Agent (C-NMA): functional entity that is responsible for collecting network capabilities and status, and for reporting them to a C-PS.¶
+----------------+
| Mobility |
| Management |
| System |
+----------------+
|
UE Location, Session Info, Service Anycast Address
|
+--------v-------+ *Direct
| CATS-MUP-C | Segment
+----------| +------+ |---------+ community
| | | C-PS | | | S1 Service1
| +----------------+ | +----------+ Contact
UE- | | | C-SMA |/Instance
\+---+ +------+ +-----+ +------+ |----------|\
UE--|RAN|---| PE | |C-NMA| | PE |---| Service | Service2
+---+ +------+ +-----+ +------+ | Site 1 | Contact
UE-/ | | +----------+ Instance
| |
| MUP | Service1
UE- | Network | Contact
\+---+ +------+ +------+ +----------+ Instance
UE--|RAN|---| PE | | PE |---| Service |/
+---+ +------+ +------+ | Site 2 |\Service2
UE-/ | | |----------| Contact
+-------------------------------------+ | C-SMA | Instance
+----------+
*Direct
Segment
community
S2
Figure 1 describes the MUP architecture when integrating with CATS capabilties. This architecture separates the CATS-based service instance's location selection from the upper control plane and integrates to the MUP-C. The optimal route configuration procedure based on this architecture is described as follows:¶
Initially, when a service site joins the MUP network, the connecting MUP-PE advertises the Direct Segment Discovery Route with the direct segment community value of the service site and the corresponding SRv6 SID. Different service sites have different direct segment community values.¶
When an UE request a service, during the session establishment process, the mobility management system provides necessary information to the MUP-C. Besides session information, UE location and the requested service anycast address of the session are also provided.¶
The controller MUP-C in previous mentioned document is enhanced with CATS capabilities and renamed to CATS-MUP-C. Application servers computing and underlay network information are collected by C-SMA and C-NMA respectively. The sub-component C-PS inside the CATS-MUP-C is responsible for select optimal service instance's location/service site to serve the requested anycast service. The decision is based on the current collected CATS metrics from C-NMA and C-SMA, and UE location.¶
Based on this decision, the CATS-MUP-C attaches the corresponding direct segment community value of the chosen service site to the Session Transformed route along with the session tunnel endpoint identifier. The CATS-MUP-C then advertises this Session Transformed route to the MUP PE connecting to the N3 RAN.¶
After receiving the Session Transformed route, the MUP PE resolve it with the Direct Segment Discovery Route that has the matching direct segment community value. Because this value is the value of the optimal service site selected by the CATS-MUP-C, the UE packets are forwarded to the optimal service instance.¶
Note that the CATS measurement data collection, data delivery mechansim, and CATS optimal path selection algorithm are in the scope of CATS, not in this document.¶