Cisco Cisco Packet Data Gateway (PDG)
SaMOG Gateway Overview
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SaMOG Administration Guide, StarOS Release 16 ▄
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Figure 2. 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.
6.
The MRME service receives a list of P-GW FQDNs from the DNS. After all the SRV queries are completed, the MRME
service builds a candidate list of P-GW host names.
service builds a candidate list of P-GW host names.
7.
The resulting P-GW entries are compared against the configured MRME service FQDN and the longest suffix-matching
entry is chosen. If there are more than one pair of MRME service/P-GW combinations with the same degree of label match,
attributes from the RR may be used to break the tie. The attributes include priority, weight, and order. Load-balancing of P-
GWs occur based on weight, as per the procedure defined in RFC 2782.
entry is chosen. If there are more than one pair of MRME service/P-GW combinations with the same degree of label match,
attributes from the RR may be used to break the tie. The attributes include priority, weight, and order. Load-balancing of P-
GWs occur based on weight, as per the procedure defined in RFC 2782.
8.
The selected P-GW FQDN is further resolved using a DNS A/AAAA query to resolve to the IPv4/IPv6 address of the S2a
interface on the P-GW.
interface on the P-GW.
9.
The DNS returns the IP address of the P-GW.
Topology/Weight-based Selection
Topology/weight-based selection uses DNS requests to enable P-GW load balancing based on topology and/or weight.
For topology-based selection, once the DNS procedure outputs a list of P-GW hostnames for the APN FQDN, the
SaMOG Gateway performs a longest-suffix match and selects the P-GW that is topologically closest to the SaMOG
Gateway and subscriber. If there are multiple matches with the same suffix length, the Weight and Priority fields in the
NAPTR resource records are used to sort the list. The record with the lowest number in the Priority field is chosen first,
and the Weight field is used for those records with the same priority.
SaMOG Gateway performs a longest-suffix match and selects the P-GW that is topologically closest to the SaMOG
Gateway and subscriber. If there are multiple matches with the same suffix length, the Weight and Priority fields in the
NAPTR resource records are used to sort the list. The record with the lowest number in the Priority field is chosen first,
and the Weight field is used for those records with the same priority.
For weight-based selection, once the DNS procedure outputs a list of P-GW hostnames for the APN FQDN, if there are
multiple entries with same priority, calls are distributed to these P-GWs according to the Weight field in the resource
multiple entries with same priority, calls are distributed to these P-GWs according to the Weight field in the resource