High Availability Solution for IPsec in IP Multimedia Subsystem

The IP Multimedia Subsystem (IMS) refers to the standard for a telecommunication system that controls multimedia services accessing different networks. To be served by IMS, a User Equipment (UE) must establish a connection with the outbound proxy which is the first point of signaling handling of IMS. This proxy is Proxy-Call Session Control Function (P-CSCF) and the connection between it and UE is known as the Gm interface. For the Gm interface security, protection using Internet Protocol Security (IPsec) is specified. However, the anti-replay protection of IPsec is not compatible with the High Availability mechanism because not all information of IPsec is replicated from the active P-CSCF node to its standby node. In this paper, a solution is introduced to implement the anti-replay protection of IPsec with the High Availability mechanism of IMS. The proposed model guarantees that after the switchover process when one P-CSCF is out of order, messages sent from the new P-CSCF are not discarded by the anti-replay protection at UEs.