BSS & NSS

ISDN (Integrated Services Digital Network)

A set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the public switched telephone network. The key feature of ISDN is that it integrates speech and data on the same lines,

AuC

Authentication Center validates subscriber identity with its IMSI. Stores MSs Ki (Authentication Key). Maintains A3 and A8 algorithms. Responsible for generating Kc (Session Key), RAND, and SRES (Triplets). A3 & A8 algorithms only stored in AuC & MS.

BSC

Base Station Controller a small network controller responsible for a group of BTSs within a certain LAC. Size could range from 10s-100s. Responsible for: Radio resource allocation to a MS, frequency administration, BTS handoffs, passing info to and from MS to NSS (Network Switching Subsystem)

BSS

Base Station Subsystem is the front line echelon of the network. Provides the link between the MS and the rest of the network. Consists of the BTS (Base Transceiver Station - The Tower) and the BSC (Base Station Controller)

BTS

Base Transceiver Station is a fixed site that includes: Antenna equipment, radio transmitters, and receivers that define the cell and connect to MS over AI (Air Interface). Handles: Encryption and deciphering, channel encoding or decoding, and frequency hopping

EIR

Equipment Identity Register is a database that validates IMEI. International EIR maintained in Dublin, Ireland. Contains identity and status of all telecommunications devices in the network. Must contain white list at minimum. (WHITE = Valid ME) (BLACK = Barred ME) (GRAY = Known Problem: faulty software, suspected fraud, etc. not fatal enough to bar)

GMSC

Gateway Mobile Switching Center acts as an "entrance" from exterior portions of the PSTN onto other provider's network, except those that have high-cap MSCs. Any MSC can serve as a GMSC depending on the call. Determines where a MS is currently located and interfaces directly with the PSTN. All mobile to mobile and PSTN to mobile calls are routed through one.

HLR

MS database that contains each customer's IMSI and IMEI to uniquely identify each customer. USUALLY one HLR per PLMN. Can have multiple "physical" locations. Permanently stores permanent MS data such as: services provided, roaming agreements, IMSI, MSISDN. And temporary MS data: LAI and MSRN (Mobile Station Roaming Number).

MSC

Mobile Switching Center is an ISDN (Integrated Services Digital Network) switch that controls NSS elements. Entire GSM network is divided into MSC regions. Each region is composed of at least one LAC.

NSS

Network Switching Subsystem is the component of a GSM system that carries out call switching and mobility management functions for mobile phones roaming on the network of base stations.

Mobility Management

One of the major functions of a GSM or a UMTS network that allows mobile phones to work. The aim of mobility management is to track where the subscribers are, allowing calls, SMS and other mobile phone services to be delivered to them.

VLR

Visitor Location Register usually co-located with the MSC. Each LAC has one. Responsible for assigning and storing each MS its TMSI. Temporarily stores permanent MS data such as: Services provided, roaming agreements, IMSI and MSISDN.