Multiple Pdn Support; Congestion Control - Cisco ASR 5000 Series Administration Manual

Serving Gateway Overview
Mobility management functions: This functionality consists of messages that are exchanged between GTP end
points to manage UE mobility. Messages such as Forward Relocation request/response are sent between end
points. These messages are not sent on the S11 interface.
S5/S8 GTP (E-UTRAN EPC)
In accordance with 3GPP TS 23.401 the Cisco S-GW platform supports GTPv2-C and GTPv1-U call control and user
plane tunnelling. A GTP tunnel is identified in each node with a Tunnel Endpoint ID (TEID), an IP address and a UDP
port number. The S-GW and P-GW nodes provision separate GTP tunnels for each attached subscriber and for the
individual PDN connections initiated by the UE. The StarOS distributed software architecture enables each function to
run as independent stand-alone services on separate chassis or as simultaneous combination services running on the
same platform.
The S5 reference interface provides user plane tunnelling and tunnel management between an S-GW and P-GW located
within the same administrative domain. It is used for S-GW relocation due to UE mobility and if the S-GW needs to
connect to a non-collocated P-GW for the required PDN connectivity.
The S8 reference interface is an inter-PLMN reference point providing user and control plane between the S-GW in the
VPLMN and the P-GW in the HPLMN. It is based on the Gp reference point as defined between SGSN and GGSN. S8a
is the inter PLMN variant of S5.

Multiple PDN Support

Enables an APN-based user experience that enables separate connections to be allocated for different services including
IMS, Internet, walled garden services, or offdeck content services.
The MAG function on the S-GW can maintain multiple PDN or APN connections for the same user session. The MAG
runs a single node level Proxy Mobile IPv6 tunnel for all user sessions toward the LMA function of the P-GW. When a
user wants to establish multiple PDN connections, the MAG brings up the multiple PDN connections over the same
PMIPv6 session to one or more P-GW LMAs. The P-GW in turn allocates separate IP addresses (Home Network
Prefixes) for each PDN connection and each one can run one or multiple EPC default & dedicated bearers. To request
the various PDN connections, the MAG includes a common MN-ID and separate Home Network Prefixes, APNs and a
Handover Indication Value equal to one in the PMIPv6 Binding Updates.

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.
Congestion control 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 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
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Features and Functionality - Base Software ▀
Cisco ASR 5000 Series Serving Gateway Administration Guide ▄