Cisco Cisco Packet Data Gateway (PDG)
Evolved Packet Data Gateway Overview
▀ Features and Functionality
▄ ePDG Administration Guide, StarOS Release 18
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DNS Request Support
During IPSec tunnel establishment, the WLAN UEs can request an IP address for the DNS in the CP payload
(CFG_REQUEST). The ePDG retrieves the request from the CFG_REQUEST attribute of the first IKE_AUTH
message exchange and includes it in the PBU (Proxy-MIP Binding Update) message sent to the P-GW.
(CFG_REQUEST). The ePDG retrieves the request from the CFG_REQUEST attribute of the first IKE_AUTH
message exchange and includes it in the PBU (Proxy-MIP Binding Update) message sent to the P-GW.
The ePDG sends the PBU message by framing the MIPv6 APCO VSE (Additional Protocol Configuration Options
Vendor Specific Extension) with an IPv6 and/or IPv4 DNS request to the P-GW. Once the response is received from the
P-GW with the list of IPv6 and/or IPv4 DNS addresses in the returned MIPv6 APCO VSE, the ePDG includes the final
address(es) in the CP payload (CFG_REPLY) of the final IKE_AUTH Response message sent to the UE.
Vendor Specific Extension) with an IPv6 and/or IPv4 DNS request to the P-GW. Once the response is received from the
P-GW with the list of IPv6 and/or IPv4 DNS addresses in the returned MIPv6 APCO VSE, the ePDG includes the final
address(es) in the CP payload (CFG_REPLY) of the final IKE_AUTH Response message sent to the UE.
In case the Protocol used on S2b is GTPv2 then APCO is used in Create Session Request message for requesting the
IPv4 or IPv6 DNS server address request and then P-GW communicates the DNS server addresses in the APCO IE in
the Create Session Response Message, the ePDG includes the final address(es) in the CP payload (CFG_REPLY) of the
final IKE_AUTH Response message sent to the UE.
IPv4 or IPv6 DNS server address request and then P-GW communicates the DNS server addresses in the APCO IE in
the Create Session Response Message, the ePDG includes the final address(es) in the CP payload (CFG_REPLY) of the
final IKE_AUTH Response message sent to the UE.
Note that the ePDG includes a maximum of two IPv4 DNS addresses and/or a maximum of two IPv6 DNS addresses in
the CP payload (CFG_REPLY).
the CP payload (CFG_REPLY).
P-CSCF Request Support
To connect to the IMS core network, the WLAN UEs perform P-CSCF discovery as part of session establishment. This
feature supports P-CSCF attributes in CFG_REQUEST and CFG_REPLY messages as part of the CP payload in the
IKE_AUTH Request and Response messages the ePDG sends and receives from the UEs. The P-CSCF attribute can be
sent on SWu as private or with standard value.
feature supports P-CSCF attributes in CFG_REQUEST and CFG_REPLY messages as part of the CP payload in the
IKE_AUTH Request and Response messages the ePDG sends and receives from the UEs. The P-CSCF attribute can be
sent on SWu as private or with standard value.
The WLAN UEs request a P-CSCF address in IKE_AUTH messages to establish IMS PDN connections. The ePDG
receives the P-CSCF attribute in the CP payload (CFG_REQUEST) of the first IKE_AUTH message exchange and
includes a P-CSCF Request message in the PBU (Proxy-MIP Binding Update) message to the P-GW. The ePDG sends
the PBU message by framing the MIPv6 PCO VSE (Protocol Configuration Options Vendor Specific Extension) within
the P-CSCF Request message to the P-GW. Once the ePDG receives the response from the PGW with the list of P-
CSCF addresses, the ePDG shall include the P-CSCF addresses in the CP payload (CFG_REPLY) of the final
IKE_AUTH Response message sent to the UE.
receives the P-CSCF attribute in the CP payload (CFG_REQUEST) of the first IKE_AUTH message exchange and
includes a P-CSCF Request message in the PBU (Proxy-MIP Binding Update) message to the P-GW. The ePDG sends
the PBU message by framing the MIPv6 PCO VSE (Protocol Configuration Options Vendor Specific Extension) within
the P-CSCF Request message to the P-GW. Once the ePDG receives the response from the PGW with the list of P-
CSCF addresses, the ePDG shall include the P-CSCF addresses in the CP payload (CFG_REPLY) of the final
IKE_AUTH Response message sent to the UE.
In case protocol used on S2b is GTPV2 ePDG has flexibility to use either APCO IE or Private Extension IE based on
ePDG configuration. Once the ePDG receives the response from the P-GW with the list of P-CSCF addresses in the
APCO / Private Extension IE, the ePDG includes the P-CSCF addresses in the CP payload (CFG_REPLY) of the final
IKE_AUTH Response message sent to the UE.
ePDG configuration. Once the ePDG receives the response from the P-GW with the list of P-CSCF addresses in the
APCO / Private Extension IE, the ePDG includes the P-CSCF addresses in the CP payload (CFG_REPLY) of the final
IKE_AUTH Response message sent to the UE.
On SWu interface the ePDG is able to handle the private attribute value for the P-CSCF address and this private
attribute value is configurable on ePDG. By default 16384 is used for P-CSCF IPv4 address and 16390 is used for the
IPv6 P-CSCF address. The values 16384-32767 are for private use among mutually consenting parties.
attribute value is configurable on ePDG. By default 16384 is used for P-CSCF IPv4 address and 16390 is used for the
IPv6 P-CSCF address. The values 16384-32767 are for private use among mutually consenting parties.
The P-CSCF v4 and v6 are recently assigned values by IANA so ePDG shall be supporting those values as well in
addition to the private configured value. ePDG should respond to UE with same attribute value as received in the
request. Private values are maintained for the devices which are already in market as they may not comply to standard
values.
addition to the private configured value. ePDG should respond to UE with same attribute value as received in the
request. Private values are maintained for the devices which are already in market as they may not comply to standard
values.
UE should include P-CSCF_V4_ADDR attribute only once in IKE_AUTH request and no specific P-CSCF address is
included because it is a request. ePDG is enhanced to support both IPv4 and IPv6 P-CSCF address handling together.
ePDG also supports maximum of 3 IPv4 and 3 IPv6 P-CSCF addresses. The exceeding P-CSCF address will be ignored.
In case of invalid P-CSCF address are received the P-CSCF address is ignored and have no impact on the call
establishment.
included because it is a request. ePDG is enhanced to support both IPv4 and IPv6 P-CSCF address handling together.
ePDG also supports maximum of 3 IPv4 and 3 IPv6 P-CSCF addresses. The exceeding P-CSCF address will be ignored.
In case of invalid P-CSCF address are received the P-CSCF address is ignored and have no impact on the call
establishment.
On S2b interface the P-CSCF is enhanced to support both APCO IE and private Extension IE. ePDG continues to use
existing "vendor-specific-attribute" configuration present under epdg-service to decide whether to use APCO IE or
existing "vendor-specific-attribute" configuration present under epdg-service to decide whether to use APCO IE or