Cisco Cisco Packet Data Gateway (PDG)
SaMOG Gateway Overview
SaMOG Services ▀
SaMOG Administration Guide, StarOS Release 18 ▄
23
Step
Description
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.
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.
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”.
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.
returns the IP address of the P-GW.
Dynamic Selection
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.
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.
step in the flow.
Figure 3. 335831.jpg
Table 2. P-GW Dynamic Selection
Step
Description
1.
The MRME service receives an APN name from the 3GPP AAA server.
2.
The MRME service constructs the APN FQDN from the received APN name and uses this as the query string to send to the
DNS.
DNS.
3.
The APN FQDN query returns NAPTR Resource Records (RRs) with an “s” flag.
4.
Result(s) from this operation are fed to a filter where only RRs with service-parameter "x-3gpp-pgw:x-s2a-gtp" are
considered by the MRME service.
considered by the MRME service.
5.
Each of the resulting NAPTR RRs for that record set will be resolved further by performing DNS SRV queries using the
replacement string pointed to by the NAPTR RRs.
replacement string pointed to by the NAPTR RRs.