GSM InterfacesGSM Interfaces

(Um) Air interface - MS to BTS A bis interface - BTS to BSC A Interface - BSC to MSC B Interface - MSC to VLR C interface - MSC to HLR

GSM InterfacesGSM Interfaces

D Interface - VLR to HLR E Interface - MSC to MSC F Interface - MSC to EIR G Interface - VLR to VLR H Interface - HLR to AUC

MSC

BSC

VLRHLR

AUC

EIR

GMSC

MS

A Interface

A bis Interface

Air Interface

B Interface C Interface

F Interface

D Interface H Interface

To otherNetworks

GSM InterfacesGSM Interfaces

The interfaces between MSC and MS is called A, Abis and Um interfaces.

On these interfaces only three layers are defined.They are not corresponding to the OSI (Open System Interconnection) model.

A InterfaceA Interface

A interface between the BSC and the MSC The A interface provides two distinct types of

information, signalling and traffic, between the MSC and the BSC.

The speech is transcoded in the TRC and the SS7 (Signalling system) signalling is transparently connected through the TRC or on a separate link to the BSC.

Abis InterfaceAbis Interface

The A-bis interface responsible for transmitting traffic and signalling information between the BSC and the BTS.

The transmission protocol used for sending signalling information on the A-bis interface is Link Access Protocol on the D Channel (LAPD)

(Um) Air Interface (Um) Air Interface

This is the interface between the mobile station and the Base station.

The Air interface uses the Time Division Multiple Access (TDMA) technique to transmit and receive traffic and signalling information between the BTS and MS.

The TDMA technique is used to divide each carrier into eight time slots.These time slots are then assigned to specific users,allowing up to eight conversations to be handled Simultaneously by the same carrier.

7 5 6 3 4 1 2 0

1 2 43 5 7 6

Down Link

Up Link 0

Time Slot

• This interface is the radio interface between the mobile station and the network and uses layer Three messages. • On Layer three messages we have the division of message types into CM (communication Management), MM (Mobility Management), and RR (Radio Resource Management).

Connection Management Connection Management (CM)(CM)

There are three entities within CM: Call Control(CC) – Which handles the procedures

concerning call control. e.g. setup,Change of bearer service.

Supplementary Service (SS) – Which handles such as call bearing, call waiting , call forwarding etc.

Short Message Service (SMS) – Enables the MS to handle short message transfer to and from the network.

Mobility Management (MM)Mobility Management (MM)

Mobility management handles functions for authentication, location updating, identification and others concerning the mobility of the mobile station.

Radio Resource Management Radio Resource Management (RR)(RR)

It contains the functions concerning the radio link. Here we find the capability to establish,maintain and release the radio connection between the network and the mobile station, which includes the handover procedure.

B InterfaceB Interface

The B interface between the MSC and the VLR uses the MAP/TCAP protocol.

Most MSCs are associated with a VLR, making the B interface "internal".

Whenever the MSC needs access to data regarding a MS located in its area, it interrogates the VLR using the MAP/B protocol over the B interface.

C InterfaceC Interface

The C interface is between the HLR and a MSC. Each call originating outside of GSM (i.e., a MS

terminating call from the PSTN) has to go through a Gateway to obtain the routing information required to complete the call, and the MAP/TCAP protocol over the C interface is used for this purpose.

Also, the MSC may optionally forward billing information to the HLR after call clearing.

D InterfaceD Interface

The D interface is between the VLR and HLR. It uses the MAP/TCAP protocol to exchange the data

related to the location of the MS and to the management of the subscriber.

E InterfaceE Interface

The E interface interconnects two MSCs. The E interface exchanges data related to handover

between the anchor and relay MSCs using the -MAP/TCAP+ISUP/TUP protocol.

F InterfaceF Interface

The F interface connects the MSC to the EIR. It uses the MAP/TCAP protocol to verify the status of

the IMEI that the MSC has retrieved from the MS.

G InterfaceG Interface

The G interface interconnects two VLRs of different MSCs.

It uses the MAP/G protocol to transfer subscriber information, during e.g. a location update procedure.