Cisco Cisco Packet Data Gateway (PDG)
SaMOG Gateway Overview
▀ SaMOG Features and Functionality - Base Software
▄ SaMOG Administration Guide, StarOS Release 18
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The SaMOG Gateway does not support overlapping WLC-IP-Address for IPoVLAN and IPoGRE for
Radius/DHCP packets.
Secondary P-GW or GGSN Fallback
The SaMOG Gateway supports session establishment between the GTP interface and an alternate P-GW or GGSN when
connection establishment fails towards the primary P-GW or GGSN (response timeout or localized issues). Where
SaMOG selects the P-GW or GGSN using DNS queries, the secondary P-GW or GGSN IP address is determined using
the A/AAAA (Pre-release 8) or SNAPTR (Post-release 7) DNS procedure with the DNS server.
connection establishment fails towards the primary P-GW or GGSN (response timeout or localized issues). Where
SaMOG selects the P-GW or GGSN using DNS queries, the secondary P-GW or GGSN IP address is determined using
the A/AAAA (Pre-release 8) or SNAPTR (Post-release 7) DNS procedure with the DNS server.
A/AAAA DNS Query-based Selection
The SaMOG Gateway performs the pre-release 8 DNS procedure when the local policy has A/AAAA configured as the
DNS query type. As the DNS server returns a list of GGSN IP addresses that serve the APN, the SaMOG Gateway
selects the GGSN IP address from the list and tries to establish a GTPv1 session. The SaMOG Gateway will keep trying
to establish a connection with the GGSN IP addresses from the list provided by the DNS server until a session is
established. When the list is exhausted, or the session setup timer expires, the session setup attempt is aborted and the
session is cleared.
DNS query type. As the DNS server returns a list of GGSN IP addresses that serve the APN, the SaMOG Gateway
selects the GGSN IP address from the list and tries to establish a GTPv1 session. The SaMOG Gateway will keep trying
to establish a connection with the GGSN IP addresses from the list provided by the DNS server until a session is
established. When the list is exhausted, or the session setup timer expires, the session setup attempt is aborted and the
session is cleared.
SNAPTR DNS Query-based Selection
The SaMOG Gateway performs the post-release 7 DNS procedure when the local policy has SNAPTR configured as the
DNS query type. The SNAPTR query is performed on an APN FQDN or P-GW FQDN with a service string mapped to
the S2a-Gn, P-GW-Gn, and GGSN-Gn in the same order of preference. This results in a list of IP addresses of the P-
GW or GGSN whose interfaces corresponds to the service string that currently serves the specified APN.
DNS query type. The SNAPTR query is performed on an APN FQDN or P-GW FQDN with a service string mapped to
the S2a-Gn, P-GW-Gn, and GGSN-Gn in the same order of preference. This results in a list of IP addresses of the P-
GW or GGSN whose interfaces corresponds to the service string that currently serves the specified APN.
The SaMOG Gateway performs a topology or weight-based match (as configured) from the list and tries to establish a
GTPv2 or GTPv1 connection with the matched P-GW or GGSN. On failure, SaMOG performs a topology or weight-
based match with the rest of the IP addresses from the list until the list is exhausted. The SaMOG Gateway then builds a
list from the next service parameter in preference. When the list is exhausted, or the session setup timer expires, the
session setup attempt is aborted and the session is cleared.
GTPv2 or GTPv1 connection with the matched P-GW or GGSN. On failure, SaMOG performs a topology or weight-
based match with the rest of the IP addresses from the list until the list is exhausted. The SaMOG Gateway then builds a
list from the next service parameter in preference. When the list is exhausted, or the session setup timer expires, the
session setup attempt is aborted and the session is cleared.
Trigger for Secondary P-GW or GGSN Fallback
The SaMOG Gateway triggers fallback to the secondary P-GW or GGSN selection when the following GTP cause
values are received in the Create Session Response (CSR) and Create PDP Context Response (CPCR) messages:
values are received in the Create Session Response (CSR) and Create PDP Context Response (CPCR) messages:
CSR/CPC Request Rejection Cause
GTPv2 Cause Code GTPv1 Cause Code
Service not supported
68
200
No resources available
73
199
All dynamic addresses are occupied 84
211
Service denied
89
—
No memory available
91
212
APN congestion
113
229
The call setup attempt is terminated for all other cause values.
In addition to the above rejection causes, the P-GW or GGSN selection fallback is triggered when the primary P-GW or
GGSN fails to respond to the CSR/CPCR Request message.
GGSN fails to respond to the CSR/CPCR Request message.