Requirements

NEs Involved

Table 2 NEs involved in this feature

UE	eNodeB	MME	Gn/Gp SGSN	S4 SGSN	S-GW	P-GW	PCRF	M2000
√	√	√	-	-	√	√	√	-

http://localhost:7904/pages/31185560/15/31185560/15/resources/public_sys-resources/icon-note.gif NOTE:

In Table 2, "√" indicates that the NE is required, and "-" indicates that the NE is not required.

Table 3 NE functions

NE	Function
UE	Short for SRVCC-capable user equipment, used to initiate a calling procedure or respond in a called procedure. Used to indicate SRVCC-capable user equipment.
MME	Short for mobility management entity, used to receive Handover Request messages sent by the eNodeB, split voice bearers from non-voice bearers, and initiate the PS-CS handover procedure for the voice bearer to the mobile switching center (MSC). Performs the function of splitting PS bearers, that is, splits voice bearers from non-voice bearers.
eNodeB	Short for E-UTRAN NodeB, used to identify subscribers and forward messages for radio access.
MSC	Supports handover requests sent by the MME. Supports handovers from IMS to CS. Anchors voice sessions on the IMS network.
S-GW	Short for serving gateway, used to provide service bearer tunnels and fast forwarding.
P-GW	Short for PDN gateway, used to provide service bearer tunnels and fast forwarding.
PCRF	Short for policy and charging rules function, used to deliver policies for subscribers.

Supporting Versions

Table 4 USN9810 and UGW9811 versions that support this feature

Product	Supporting Version
USN9810	V900R011C00 and later
UGW9811	V900R001C05 and later

License Requirement

This is an optional feature of the USN9810; the license control item is SRVCC.

This is an optional feature of the UGW9811; a license is required.

Impact on the System

None

Application Limitations

• Only packet switched (PS)-to-circuit switched (CS) handovers are supported.

• Only LTE-to-GSM/UMTS handovers are supported.

• Only voice service handovers are supported.

• Only handovers in non-emergency sessions are supported.

Interaction with Other Features

Table 5 Interaction with other features

Feature	Interaction
GWFD-110601 IMS Access	The SRVCC feature is available only when the IMS access feature is enabled on the UGW9811.

Application Scenario

The SRVCC feature is mainly applied to hybrid networks. When a subscriber roams to a GSM/UMTS network from an LTE network, this feature is used to ensure voice call continuity in a handover from LTE to GSM/UMTS.

Implementation Principles

This section contains the following contents:

• Related Concepts
• System Implementation
• Differences Between an Attach Procedure in the SRVCC Solution and a Normal Attach Procedure
• Service Flow
• Parameter Description
• Feature Measurement Counter