Mobile Application Part

SS7 protocol suite

OSI layer	SS7 protocols
Application	INAP, MAP, IS-41... TCAP, CAP, ISUP, ...
Network	MTP Level 3 + SCCP
Data link	MTP Level 2
Physical	MTP Level 1

The Mobile Application Part (MAP) is an SS7 protocol which provides an application layer for the various nodes in GSM and UMTS mobile core networks and GPRS core networks to communicate with each other in order to provide services to mobile phone users. The Mobile Application Part is the application-layer protocol used to access the Home Location Register, Visitor Location Register, Mobile Switching Center, Equipment Identity Register, Authentication Centre, Short message service center and Serving GPRS Support Node (SGSN).

Facilities provided

The primary facilities provided by MAP are:

• Mobility Services: location management (roaming), authentication, managing service subscription information, fault recovery,
• Operation and Maintenance: subscriber tracing, retrieving a subscriber's IMSI
• Call Handling: routing, managing calls whilst roaming, checking that a subscriber is available to receive calls
• Supplementary Services
• Short Message Service
• Packet Data Protocol (PDP) services for GPRS: providing routing information for GPRS connections
• Location Service Management Services: obtaining the location of subscribers

Published specification

The Mobile Application Part specifications were originally defined by the GSM Association, but are now controlled by ETSI/3GPP. MAP is defined by two different standards, depending upon the mobile network type:

• MAP for GSM (prior to Release 4) is specified by 3GPP TS 09.02
• MAP for UMTS ("3G") and GSM (Release 99 and later) is specified by 3GPP TS 29.002

Implementation

MAP is a Transaction Capabilities Application Part (TCAP) user, and as such can be transported using 'traditional' SS7 protocols or over IP using Transport Independent Signalling Connection Control Part (TI-SCCP);^[1] or using SIGTRAN.

MAP Signaling

In mobile cellular telephony networks like GSM and UMTS the SS7 application MAP is used. Voice connections are Circuit Switched (CS) and data connections are Packet Switched (PS) applications.

Some of the GSM/UMTS Circuit Switched interfaces in the Mobile Switching Center (MSC) transported over SS7 include the following:

B -> VLR (uses MAP/B). Most MSCs are associated with a Visitor Location Register (VLR), making the B interface "internal".

C -> HLR (uses MAP/C) Messages between MSC to HLR handled by C Interface

D -> HLR (uses MAP/D) for attaching to the CS network and location update

E -> MSC (uses MAP/E) for inter-MSC handover

F -> EIR (uses MAP/F) for equipment identity check

H -> SMS-G (uses MAP/H) for Short Message Service (SMS) over CS

There are also several GSM/UMTS PS interfaces in the Serving GPRS Support Node (SGSN) transported over SS7:

Gr -> HLR for attaching to the PS network and location update

Gd -> SMS-C for SMS over PS

Gs -> MSC for combined CS+PS signaling over PS

Ge -> Charging for Customised Applications for Mobile networks Enhanced Logic (CAMEL) prepaid charging

Gf -> EIR for equipment identity check

References

1. ^ ITU-T Recommendation Q.2220, Transport Independent Signalling Connection Control Part (TI-SCCP).