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).
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
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
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
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); or using SIGTRAN.
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 Core 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