Global Title Translation

As I mentioned in the earlier post, Addressing and Information Routing in SS7 Global Title Translation is used when the message has to deliver to a different network and the point code details of the destination node is not available. The Global Title Translation method reduces the burden of keeping the point code and sub system number of the actual destination. In a larger network, there will be many intermediate GTT to route the information to the next possible node and the final GTT will provide the point code and subs system number of the final destination. 

Addressing and Information Routing in SS7

In SS7, the SCCP layer routes the messages between different network elements using Destination Point Code (DPC) plus the Sub System Number (SSN) or Global Title (GT) plus SSN (Optional) combination. Normally, the application layer expects the SCCP to route the message and also specifies to the lower layer whether to route the message on the DPC or the GT.

SCCP uses the first combination when the application layer is aware of the destination point code and the SSN located at that point code. The second combination is used when the destination entity can be identified by the combination of elements within the GT. Normally the second combination is used when the message has to deliver to a different network and the point code of the end node is not available. In such scenarios, the network determines the destination point code and the SSN by performing a GT Translation.

As per ITU-T SCCP recommendation Q.713, SCCP should support the following elements when GT is used for addressing:

·         Address Indicator

·         GT Indicator

·         Translation Type

·         Numbering Plan

·         Encoding Scheme

·         GT Address Information

CAMEL Network Architecture

HLR: Home Location Register
VLR: Visited Location Register
MSC: Mobile Switching Center
GMSC: Gateway Mobile Switching Center
SSF: Service Switching Function
SRF: Specialized Resource Function

Information Flows used by CAMEL

CAP Information flows between network entities in circuit switched call control.

SSF to SCF

·         Activity Test

·         Apply Charging Report

·         Call Information Report

·         Disconnect

·         Release

·         Event Report BCSM

·         Initial Call Attempt Ack

·         Initial DP

·         Move Leg Ack

·         Split Leg Ack

SCF to SSF

·         Activity Test

·         Apply Charging

·         Call Gap

·         Call Information Request

·         Cancel

·         Collect Information

·         Connect

·         Connect To Resource

·         Continue

·         Continue with Argument

·         Disconnect Forward Connection

·         Disconnect Forward Connection with Argument

·         Disconnect Leg

·         Establish Temporary Connection

·         Furnish Charging Information

·         Initiate Call Attempt

·         Move Leg

·         Play Tone

·         Release Call

·         Request Report BCSM Event

·         Reset Timer

·         Send Charging Information

·         Split Leg

SCF to SRF

·         Activity Test

·         Cancel

·         Play Announcement

·         Prompt And Collect User Information

SRF to SCF

·         Activity Test

·         Assist Request Instructions

·         Prompt And Collect User Information Ack

Specialized Resource Report