Cisco Cisco ASR 5000
Serving GPRS Support Node (SGSN) Overview
▀ Features and Functionality
▄ SGSN Administration Guide, StarOS Release 18
The LTE terminals 'register' in the circuit switched domain when powered and attaching to LTE. This is handled
through an interaction between the MME and the MSC-Server in the circuit-switched network domain over the SGs
interface.
through an interaction between the MME and the MSC-Server in the circuit-switched network domain over the SGs
interface.
Consider the following scenarios:
Voice calls initiated by the mobile user: If the user makes a voice call, the terminal switches from a LTE system
to a system with circuit-switched voice support. Depending on where the UE latches on after completion of the
voice call:
voice call:
The packet-based services that are active on the end-user device at this time are handed over and
continue to run in a system with circuit-switched voice support but with lower data speeds.
OR
The packet-based services that are active on the end-user device at this time are suspended until the
voice call is terminated and the terminal switches back to LTE again and the packet services are
resumed.
resumed.
Voice calls received by the mobile user: If there is an incoming voice call to an end-user that is currently
attached to the LTE system, the MSC-Server requests a paging in the LTE system for the specific user. This is
done through the SGs interface between the MSC Server and the MME. The terminal receives the page, and
temporarily switches from the LTE system to the system with circuit-switched voice support, where the voice
call is received. Once the voice call is terminated, the terminal switches back to the LTE system.
done through the SGs interface between the MSC Server and the MME. The terminal receives the page, and
temporarily switches from the LTE system to the system with circuit-switched voice support, where the voice
call is received. Once the voice call is terminated, the terminal switches back to the LTE system.
For a detailed feature description of this feature refer to the chapter “ISR with Circuit Switched Fallback” in this
document.
document.
ISD / DSD Message Handling and HSS Initiated Bearer Modification
The Home Subscriber Server (HSS) / Home Location Register (HLR) maintains the subscriber database. Insert
Subscriber Data (ISD) and Delete Subscriber Data (DSD) messages are generated by the HSS/HLR. These messages are
used to communicate the subscribers current subscription data to the S4-SGSN. The subscription data for a subscriber
can include one of the following:
Subscriber Data (ISD) and Delete Subscriber Data (DSD) messages are generated by the HSS/HLR. These messages are
used to communicate the subscribers current subscription data to the S4-SGSN. The subscription data for a subscriber
can include one of the following:
GPRS subscription data.
EPS subscription data.
Both GPRS and EPS subscription data.
The PDP is either modified or deleted based on the subscription data received by the S4-SGSN.
The S4-SGSN deletes the PDP context if any form of barring is detected or if the APN-name or PDP-type of the PDP
address is changed. The S4-SGSN modifies the PDP if QoS is changed or APN-AMBR is changed (in case of EPS
subscription).
address is changed. The S4-SGSN modifies the PDP if QoS is changed or APN-AMBR is changed (in case of EPS
subscription).
If a PDP modification is required based on the subscription data received but the associated UE is disconnected or in an
inactive state, such PDP contexts are deleted by the S4-SGSN.
inactive state, such PDP contexts are deleted by the S4-SGSN.
If the UE is connected or in a ready state, the S4-SGSN sends an updated bearer command (with subscribed QoS) to the
S-SGW or P-GW and the P-GW initiates a PDP modify procedure.
S-SGW or P-GW and the P-GW initiates a PDP modify procedure.
HSS initiated bearer modification
The Modify bearer command is a notification sent to the S-GW/P-GW which notifies a change in the subscribed QoS.
The message is sent to S-GW/P-GW if the UE is in ready or connected state. Modify Bearer command is not sent when
the PDP is in preserved state and when ISR is active, in such cases the S4-SGSN initiated modify request using Modify
The message is sent to S-GW/P-GW if the UE is in ready or connected state. Modify Bearer command is not sent when
the PDP is in preserved state and when ISR is active, in such cases the S4-SGSN initiated modify request using Modify