Cisco Cisco Packet Data Gateway (PDG)
Evolved Packet Data Gateway Overview
▀ Features and Functionality
▄ ePDG Administration Guide, StarOS Release 17
24
Step Description
13
On successful authentication the ePDG selects the P-GW based on Node Selection options.The ePDG sends Create Session
Request (IMSI, [MSISDN], Serving Network, RAT Type (WLAN), Indication Flags, Sender F-TEID for C-plane, APN,
Selection Mode, PAA, APN-AMBR, Bearer Contexts, [Recovery], [Charging characteristics], [Additional Protocol
Configuration Options (APCO)]), Private IE (P-CSCF, AP MAC address). Indication Flags shall have Dual Address Bearer
Flag set if PDN Type is IPv4v6.Handover flag shall be set to Initial or Handover based on the presence of IP addresses in
the IPv4/IPv6_Address configuration requests.Selection Mode shall be set to “MS or network provided APN, subscribed
verified”. The MSISDN, Charging characteristics, APN-AMBR and bearer QoS shall be provided on S2b interface by
ePDG when these are received from AAA on SWm interface.The control plane TEID shall be per PDN connection and the
user plane TEID shall be per bearer created.
Request (IMSI, [MSISDN], Serving Network, RAT Type (WLAN), Indication Flags, Sender F-TEID for C-plane, APN,
Selection Mode, PAA, APN-AMBR, Bearer Contexts, [Recovery], [Charging characteristics], [Additional Protocol
Configuration Options (APCO)]), Private IE (P-CSCF, AP MAC address). Indication Flags shall have Dual Address Bearer
Flag set if PDN Type is IPv4v6.Handover flag shall be set to Initial or Handover based on the presence of IP addresses in
the IPv4/IPv6_Address configuration requests.Selection Mode shall be set to “MS or network provided APN, subscribed
verified”. The MSISDN, Charging characteristics, APN-AMBR and bearer QoS shall be provided on S2b interface by
ePDG when these are received from AAA on SWm interface.The control plane TEID shall be per PDN connection and the
user plane TEID shall be per bearer created.
14.
The P-GW allocates the requested IP address session and responds back to the ePDG with a Create Session Response
(Cause, P-GW S2b Address C-plane, PAA, APN-AMBR, [Recovery], Bearer Contexts Created, [Additional Protocol
Configuration Options (APCO)], Private IE (P-CSCF)) message.
(Cause, P-GW S2b Address C-plane, PAA, APN-AMBR, [Recovery], Bearer Contexts Created, [Additional Protocol
Configuration Options (APCO)], Private IE (P-CSCF)) message.
15.
The ePDG calculates the AUTH parameter which authenticates the second IKE_SA_INIT message
16.
The ePDG sends the assigned Remote IP address in the configuration payload (CFG_REPLY).The AUTH parameter is sent
to the UE together with the configuration payload, security associations and the rest of the IKEv2 parameters and the
IKEv2 negotiation terminates.
to the UE together with the configuration payload, security associations and the rest of the IKEv2 parameters and the
IKEv2 negotiation terminates.
17.
Router Advertisement will be sent for IPv6 address assignments, based on configuration.
P-GW Selection
The P-GW selection function enables the ePDG to allocate a P-GW to provide PDN connectivity to the WLAN UEs in
the untrusted non-3GPP IP access network. The P-GW selection function can employ either static or dynamic selection.
the untrusted non-3GPP IP access network. The P-GW selection function can employ either static or dynamic selection.
Static Selection
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 ePDG performs
static selection of the P-GW.
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 ePDG 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.
in the flow.