GSM Network architecture [Under GSM]
Below diagram shows the GSM elements and their interfaces.
» GSM Network architecture - 23.002 «
Mobile Station (MS) consists of Mobile Equipment (ME)
plus Subscriber Identity Module (SIM). ME is identified by
"burnt in" IMEI (International Mobile Equipment Identity) and SIM
is identified by IMSI (International Mobile Subscriber Identity).
ME is hardware and software which does signaling and transmission
through wireless access. SIM has subscriber and network specific
information, important being IMSI, Authentication/Encryption keys,
Preferred Network (typically this is Network operator who provided
the SIM). Note that ME is capable of making a call even without
SIM, but that would fail due to authentication and security
procedures. Emergency calls should succeed without SIM (as mandated
by 3GPP specification). SIM is small card (1x0.5 inch) that need
to be inserted into ME. Terminal Adaptation Functions (TAF)
located in ME allow ME to be connected to external device for
example connecting MS to computer for internet browsing. TAF's
main function would be (transmission data) rate adaptation
(between MS and that of external device). Note that rate
adaptation is required on Network side too when one network
interwork with another network; this is known InterWorking
Function (IWF).
Base Transceiver Station (BTS) takes care air access. Um is the air interface between MS and BTS. BTS is a radio antenna covering a area known as "Cell".
Base Station Controller (BSC) controls number of BTSs through A-bis interface and manages Base Station System (BSS). BSS consist of BSC and connected BTSs. BSS is also known Access Network (AN).
We will continue with GSM network elements in next article.
References: 23.002 360 (GSM Network architecture), GSM Networks book by Heine, GSM book by Mouly and Pautet
© Copyright Samir Amberkar 2010
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