Cisco Cisco Packet Data Gateway (PDG)
SaMOG Gateway Overview
▀ SaMOG Services
▄ SaMOG Administration Guide, StarOS Release 19
24
Step
Description
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
records. The Weight field specifies a relative weight for entries with the same priority. Larger weights are given a
proportionately higher probability of being selected. The SaMOG Gateway uses the value of (65535 minus NAPTR
preference) as the statistical weight for NAPTR resource records in the same way as the SRV weight is used for SRV
records, as defined in RFC 2782.
multiple entries with same priority, calls are distributed to these P-GWs according to the Weight field in the resource
records. The Weight field specifies a relative weight for entries with the same priority. Larger weights are given a
proportionately higher probability of being selected. The SaMOG Gateway uses the value of (65535 minus NAPTR
preference) as the statistical weight for NAPTR resource records in the same way as the SRV weight is used for SRV
records, as defined in RFC 2782.
When both topology-based and weight-based selection are enabled on the SaMOG Gateway, topology-based selection is
performed first, followed by weight-based selection. A candidate list of P-GWs is constructed based on these, and the
SaMOG Gateway selects a P-GW from this list for call establishment. If the selected P-GW does not respond, the
MRME service selects the alternate P-GW(s) from the candidate list.
performed first, followed by weight-based selection. A candidate list of P-GWs is constructed based on these, and the
SaMOG Gateway selects a P-GW from this list for call establishment. If the selected P-GW does not respond, the
MRME service selects the alternate P-GW(s) from the candidate list.
GGSN Selection—MRME
The SaMOG Gateway uses the Gn’ reference point between the SaMOG and GGSN. The SaMOG (acting like an
SGSN) initiates the creation of PDP context a GTP tunnel with the GGSN for each UE. The SGTP is compliant to
Release 7 for GTPv1 specification 29.060. The GGSN selection is based on the DNS query.
SGSN) initiates the creation of PDP context a GTP tunnel with the GGSN for each UE. The SGTP is compliant to
Release 7 for GTPv1 specification 29.060. The GGSN selection is based on the DNS query.
The GGSN node is selected as per the 3GPP standard for resolving the IP address using DNS query. The DNS query
contains the dns-apn string in the form of <apn-name>.mncXXX.mccYYY.gprs, and the apn-name is obtained from
AAA-Server during Access-Accept message. The MCC and MNC values are derived in the following priority:
contains the dns-apn string in the form of <apn-name>.mncXXX.mccYYY.gprs, and the apn-name is obtained from
AAA-Server during Access-Accept message. The MCC and MNC values are derived in the following priority:
From the NAI sent by UE in Access-Request message in the form of
IMSI@wlan.mncXXX.mccYYY.3gppnetwork.org.
Local configuration
When SaMOG interacts with pre-release 7 network elements (RADIUS based interfaces) it uses A/AAA queries. When
SaMOG interacts with post-release 7 network elements (Diameter based interfaces) it uses the NAPTR queries.
SaMOG interacts with post-release 7 network elements (Diameter based interfaces) it uses the NAPTR queries.
RADIUS Accounting Proxy—MRME