Description: GSN peer table. The SGSN-GGSN peer relationship is established as following: o A table in DNS listing the APN and corresponding ip address of GGSN. o When Mobile System (MS) wants service, it sends packets to a SGSN with specific APN. o SGSN asks DNS for ip address of a GGSN that service this APN. o DHCP returns a GGSN. o SGSN requires a path to the GGSN using GTP protocol. o The SGSN and GGSN peer maintains path by sending echo request message to each other. If one side fails in echo reply for certain times, the other side will send a trap to NMS.

Note: o Multiple-Multiple peer relationship, i.e. a SGSN have multiple GGSN as peers, while a GGSN have multiple SGSN peers, depending on routing path. o Path is kept in database.