Cisco Cisco Packet Data Gateway (PDG)

 

▄  SaMOG Administration Guide, StarOS Release 16  

The PDN-GW-Allocation-Type AVP indicates whether the P-GW address is statically allocated or dynamically selected 
by other nodes, and is considered only if MIP6-Agent-Info is present. When the PDN-GW-Allocation-Type AVP is 
absent or is STATIC, and an initial attach occurs, or is DYNAMIC and a handoff attach occurs, the MRME service 
performs static selection of the P-GW. 

The figure below shows the message exchange for static selection. The table that follows the figure describes each step 
in the flow. 

 

 

 

1. 

The SaMOG Gateway’s MRME service receives the P-GW FQDN or P-GW IP address from the AAA server as part of the 
MIP-Home-Agent-Host AVP in the Diameter EAP Answer message. 

2. 

If it receives a P-GW FQDN, and if the FQDN starts with “topon”, the MRME service removes the first two labels of the 
received FQDN to obtain the Canonical Node Name (ID) of the P-GW. The MRME service uses this P-GW ID to send an 
S-NAPTR query to the DNS. 

3. 

The MRME service receives the results of the query and selects the replacement string (P-GW FQDN) matching the 
Service Parameters of “x-3gpp-pgw:x-s2a-gtp”. 

4. 

The MRME service then performs a DNS A/AAAA query with selected replacement string (P-GW FQDN). The DNS 
returns the IP address of the P-GW. 

 

For a given APN, when the HSS returns Dynamic Allocation Allowed for the P-GW ID and the selection is not for a 
3GPP-to-non-3GPP handover, the MRME service ignores the P-GW ID and instead performs dynamic selection. 

The figure below shows the message exchange for dynamic selection. The table that follows the figure describes each 
step in the flow.