4.23 Support of Load Balancing

23.2283GPPIP Multimedia Subsystem (IMS)Release 18Stage 2TS

4.23.1 General

An IMS network may implement functionality for IMS serving network nodes (S‑CSCF, Transit Function) to handle load balancing, i.e. the technique to distribute workload evenly across two or more network nodes implementing the same functions, in order to get optimal resource utilization.

For S‑CSCFs, load balancing may be applied for received initial registration requests (see clause 4.23.2).

For Transit Functions, load balancing may be applied for received service requests, i.e. initial SIP requests requesting a service (see clause 4.23.3).

4.23.2 Registration-based load balancing of S-CSCFs

Load balancing of S‑CSCFs for received initial registration requests may be based on load balancing functionality performed by an I‑CSCF or it may be based on mechanisms outside IMS functional entities (such as DNS). An example of the DNS-based load balancing approach is the use of functionality that collects load information of S‑CSCFs, applies a load balancing algorithm and provides the outcome to a (Dynamic) DNS, which subsequently is used implicitly by I‑CSCFs.

An I‑CSCF that performs load balancing of S‑CSCFs for initial registration requests shall assign a received registration request to one of the available and suitable S‑CSCFs using a load balancing algorithm. Such load balancing algorithm may take load information of the S‑CSCFs into consideration if available. Load information may be obtained via management interfaces, via proprietary interfaces, or via other mechanisms.

4.23.3 Registration independent load balancing of Transit Functions

Load balancing of Transit Functions for received service requests may be based on load balancing functionality performed by an IMS functional entity that is the immediate source of the service request to the Transit Function (e.g. an IBCF or an I‑CSCF), or it may be based on mechanisms outside IMS functional entities (such as DNS). An example of the DNS-based load balancing approach is the use of functionality that collects load information of Transit Functions, applies a load balancing algorithm and provides the outcome to a (Dynamic) DNS, which subsequently is used implicitly by IMS functional entities that require the IP-address of a Transit Function for routing a service request.

An IMS functional entity that performs load balancing of Transit Functions for service requests shall assign a received service request to one of the available and suitable Transit Functions using a load balancing algorithm. Such load balancing algorithm may take load information of the Transit Functions into consideration if available. Load information may be obtained via management interfaces, via proprietary interfaces, or via other mechanisms.