Cisco Cisco Packet Data Gateway (PDG)
Evolved Packet Data Gateway Overview
Features and Functionality ▀
ePDG Administration Guide, StarOS Release 18 ▄
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private extension IE. The feature scope shall be limited to GTPv2 and shall not cover PMIPv6 as most of the customers
are showing interest in GTPv2 based deployment.
are showing interest in GTPv2 based deployment.
Multiple PDN Support
The multiple PDN feature enables the WLAN UEs to simultaneously establish multiple PDN connections towards the
P-GW. Each PDN connection has a separate IKE tunnel established between the UE and the ePDG.
P-GW. Each PDN connection has a separate IKE tunnel established between the UE and the ePDG.
Note that the ePDG supports multiple PDN connections to different APNs only and multiple PDN connections from the
same UE to the same APN are not allowed. The ePDG establishes each subsequent connection from the same UE to the
same APN via a new session and deletes the previous session before the new session gets established. These new PDN
connections use different IPSec/PMIPv6/GTPv2 tunnels.
same UE to the same APN are not allowed. The ePDG establishes each subsequent connection from the same UE to the
same APN via a new session and deletes the previous session before the new session gets established. These new PDN
connections use different IPSec/PMIPv6/GTPv2 tunnels.
To request a new session, the UE sends the APN information (in the IDr payload) along with the user identity (in the IDi
payload) in this first IKE_AUTH Request message, and begins negotiation of Child SAs. The ePDG sends the new APN
information in the Service Selection Mobility Option towards the P-GW, which treats each MN-ID+APN combination
as a separate binding and allocates a new IP address/prefix for each new binding.
payload) in this first IKE_AUTH Request message, and begins negotiation of Child SAs. The ePDG sends the new APN
information in the Service Selection Mobility Option towards the P-GW, which treats each MN-ID+APN combination
as a separate binding and allocates a new IP address/prefix for each new binding.
In case of S2b protocol being used as GTPv2 IMSI + APN is used for identifying the unique session.
Default APN Support
The ePDG supports a default APN when APN information is not available from the WLAN UEs over the SWu
interface.
interface.
When the APN information is received from the WLAN UEs, the information is sent towards the AAA server via DER
(Diameter EAP Request) messages. When the APN information is absent, the AAA server provides the default APN to
the ePDG in a DEA (Diameter EAP Answer) message.
(Diameter EAP Request) messages. When the APN information is absent, the AAA server provides the default APN to
the ePDG in a DEA (Diameter EAP Answer) message.
Congestion Control
The congestion control feature allows you to set policies and thresholds and specify how the system reacts when faced
with a heavy load condition.
with a heavy load condition.
The congestion control feature monitors the system for conditions that could potentially degrade performance when the
system is under heavy load. Typically, these conditions are temporary (for example, high CPU or memory utilization)
and are quickly resolved. However, continuous or large numbers of these conditions within a specific time interval may
have an impact on the system’s ability to service subscriber sessions. Congestion control helps identify such conditions
and invokes policies for addressing the situation.
system is under heavy load. Typically, these conditions are temporary (for example, high CPU or memory utilization)
and are quickly resolved. However, continuous or large numbers of these conditions within a specific time interval may
have an impact on the system’s ability to service subscriber sessions. Congestion control helps identify such conditions
and invokes policies for addressing the situation.
Congestion control operation is based on configuring the following:
Congestion Condition Thresholds: Thresholds dictate the conditions for which congestion control is enabled
and establishes limits for defining the state of the system (congested or clear). These thresholds function in a
way similar to operation thresholds that are configured for the system as described in the Thresholding
Configuration Guide. The primary difference is that when congestion thresholds are reached, a service
congestion policy and an SNMP trap, starCongestion, are generated. A threshold tolerance dictates the
percentage under the configured threshold that must be reached in order for the condition to be cleared. An
SNMP trap, starCongestionClear, is then triggered.
way similar to operation thresholds that are configured for the system as described in the Thresholding
Configuration Guide. The primary difference is that when congestion thresholds are reached, a service
congestion policy and an SNMP trap, starCongestion, are generated. A threshold tolerance dictates the
percentage under the configured threshold that must be reached in order for the condition to be cleared. An
SNMP trap, starCongestionClear, is then triggered.
Port Utilization Thresholds: If you set a port utilization threshold, when the average utilization of all ports in
the system reaches the specified threshold, congestion control is enabled.