Routing Binding Indication

Description

The Routing Binding Indication is a concept introduced in 3GPP Release 19 as part of the Service Based Architecture (SBA) enhancements for the 5G Core network. It is information included in a request or notification that can be used by the Service Communication Proxy (SCP) for discovery and associated selection of a suitable target Network Function (NF). The Routing Binding Indication has a similar syntax to a Binding Indication, but it serves a different purpose: while a Binding Indication is used to bind a service instance to a specific NF or NF set, the Routing Binding Indication provides the receiver (i.e., the SCP) with information enabling it to route an HTTP request to an HTTP server that can serve the request. Crucially, the Routing Binding Indication is not stored by the receiver; it is used transiently for routing decisions.

In the 5G SBA, NFs communicate via HTTP/2-based APIs. When an NF needs to send a request to another NF, it may not know the exact target NF instance or may need to delegate the discovery and selection to the SCP. The Routing Binding Indication allows the originating NF to include routing information in the request, which the SCP can use to discover and select an appropriate target NF. This is particularly useful in scenarios where the originating NF has some knowledge about the target (e.g., a preferred NF set or a specific NF instance) but does not perform the full discovery itself. The SCP can then use this information to route the request efficiently.

The Routing Binding Indication is defined in 3GPP TS 23.501, clauses 3.1, 6.3.1.0, and 7.1.2. It is typically included in the HTTP request headers or in the payload of the service request. The syntax is similar to the Binding Indication, which is used in the context of NF binding to indicate the NF set, NF instance, or service instance that should be used for a particular service. However, the Routing Binding Indication is not stored by the SCP; it is used only for the duration of the request routing. This ensures that the SCP does not maintain state about routing preferences, which could become stale.

The introduction of the Routing Binding Indication in Release 19 addresses the need for more flexible and efficient routing in the 5G Core, especially with the proliferation of network slicing and edge computing. It allows the SCP to make routing decisions based on information provided by the originating NF, reducing the need for the SCP to perform full discovery for every request. This can improve latency and reduce signaling load. It also enables scenarios where the originating NF has specific routing requirements that cannot be expressed through standard discovery parameters.

Overall, the Routing Binding Indication is a key enhancement to the 5G SBA, providing a standardized way for NFs to influence routing decisions without requiring the SCP to store state. It complements existing mechanisms like Binding Indication and NF discovery, and is expected to be widely used in Release 19 and beyond.

Purpose & Motivation

The Routing Binding Indication was introduced to solve the problem of efficient and flexible routing in the 5G Service Based Architecture. In earlier releases, when an NF needed to send a request to another NF, it either had to perform full discovery itself or rely on the SCP to perform discovery based on limited information. This could lead to suboptimal routing, increased latency, and unnecessary signaling. The Routing Binding Indication allows the originating NF to provide specific routing information to the SCP, enabling the SCP to select a suitable target NF without performing a full discovery. This is particularly important in scenarios where the originating NF has knowledge about the target NF set or instance, or where specific routing policies need to be applied.

Another motivation was the need to support network slicing and edge computing, where requests may need to be routed to specific NF instances based on slice or location. The Routing Binding Indication provides a standardized way to convey such routing information. It also addresses the limitation of the Binding Indication, which is used for binding but not for routing. By separating the two concepts, the 3GPP specifications allow for more precise control over routing without affecting binding state.

Furthermore, the Routing Binding Indication is not stored by the receiver, which means it does not create state in the SCP. This is important for scalability and to avoid stale routing information. It allows the SCP to remain stateless with respect to routing preferences, which simplifies implementation and improves resilience.