| Description | This table identifies the paths established on a GSN. The
path may be established between a GGSN and SGSN or GGSN
and charging gateway or GGSN and MAP converting GSN.
The path between GGSN and charging gateway is established
when the charging gateway is configured on the GGSN.
The path between GGSN and MAP converting GSN is established
when the MAP converting GSN is configured on the GGSN.
The path between a GGSN and SGSN is established in the
following series of steps:
1. When Mobile System (MS) wants service, it sends packets
to a SGSN with specific APN.
2. SGSN uses the DNS to resolve this APN to the IP address
of the GGSN which is the designated as the gateway to
this APN.
3. SGSN establishes a path to the GGSN using GTP protocol.
4. 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. A SGSN can have multiple GGSN as peers,
while a GGSN can have multiple SGSN peers, depending
on routing path. Moreover, a GSN can have more than one
path to a peer, each of which will have a unique port. |