Cisco ASR 5000 Series User Manual

Serving Gateway Overview
▀ Features and Functionality - Base Software
▄ Cisco ASR 5000 Series Product Overview
OL-22938-02
Network Operation Management Functions
This section describes the following features:
Support Interfaces (Reference Points)
Multiple PDN Support
Congestion Control
IP Access Control Lists
Support Interfaces (Reference Points)
S1-U (E-UTRAN EPC)
In an E-UTRAN network S1-U is the per-bearer user plane tunneling reference interface between the S-GW and
eNodeB. The S-GW provides the local mobility anchor point for inter-eNodeB hand-overs. It provides inter-eNodeB
path switching during hand-overs when the X2 handover interface between base stations cannot be used. The S1-U
interface uses GPRS tunneling protocol for user plane (GTP-Uv1). GTP encapsulates all end user IP packets and it relies
on UDP/IP transport.
In order to support S1-U hand-overs the source eNodeB initiates the hand-over by sending the hand-over required
message over the S1-MME interface to the MME. The MME then determines if the S-GW needs to be relocated. The
eNodeB decides which EPS bearers are subject to forwarding to the target base station. In the S1-U hand-over, the hand-
off occurs indirectly from the source eNodeB to the target via the source and target S-GWs.
S11 (E-UTRAN EPC)
S11 is the reference interface that provides the control plane protocol (GTP-Cv2) between the MME and S-GW. As with
all GTP-based interfaces S11 relies on UDP/IP transport. A GTP tunnel is identified in each node with a Tunnel
Endpoint ID (TEID), IP address and UDP port number. The TEID values are exchanged between the tunnel endpoints
using GTP-C. There is one GTP-C tunnel between the MME and S-GW for each mobile terminal. The GTP protocol
provides the following functions:
Bearer management function: This functionality is responsible for bearer management; setting up, modifying
and releasing EPS bearers, which are triggered by the MME. The release of EPS bearers may be triggered by
the P-GW or HSS as well. The messages include Create Session request, Create Bearer request, Create bearer
response etc. Additionally GTP tunnel management messages may be sent for any of the following reasons:
Initial UE attachment
UE requests connection to an additional PDN
Tracking Area Update with S-GW change
S1/X2 handover with S-GW change
GERAN or UTRAN to E-UTRAN Inter-RAT handover with SGW change.
Path management function: This functionality is responsible for managing the path between the tunnel
endpoints. It includes messages like ECHO request, ECHO response and version not supported indication.
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.

Cisco ASR 5000 Series Specifications

General

Brand	Cisco
Model	ASR 5000 Series
Category	Network Router
Language	English