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GSM Terminology

This page on GSM terminology covers very useful gsm terms such as BS_AG_BLKS_RES,BS_PA_MFRMS,CCCH_CONF, BS_CC_CHANS,BS_CCCH_SDCCH_COMB,outing area,location area, Cell Global Identity,PLMN and more.

BS_AG_BLKS_RES

BS_AG_BLKS_RES is transmitted over BCCH SI-3 message. It is a 3 bit field and hence range from 0 to 7. This field indicates how many of the CCCH blocks of a 51 frame MF on a TS0 are reserved for AGCHs(access grant channels). The number of PCH channels are reduced accordingly from total CCCH blocks of 8(noncombined mode). In combined mode, CCCH blocks per TS is 4 rather than 8.

In noncombined mode, BS_AG_BLKS_RES=3 means the first 3 CCCH blocks are used for AGCH and remaining 5 are used for PCH on time slot TS0.

BS_PA_MFRMS

BS_PA_MFRMS is transmitted over BCCH SI-3 message.It is a 3 bit field and hence range from 0 to 7. It indicates to all the mobiles in a cell that after how many MFs the content of the PCH has to be analyzed or sniffed for the information related to them.
BS_PA_MFRMS = 3 means after every 3 multiframes MS need to look for information in multiframe structure transmitted by BTS.

BS_CC_CHANS

It indicates how many TSs(time slots) on the BCCH frequency are reserved for CCCHs(common control channels). Value of 0 indicates none are reserved for CCCH. BS_CC_CHANS are not transmitted by BTS but is derived from CCCH_CONF.

BS_CCCH_SDCCH_COMB

It indicates whether the SDCCHs and CCCHs share a given time slot or not. BS_CCCH_SDCCH_COMB are not transmitted by BTS but is derived from CCCH_CONF.

CCCH_CONF

CCCH_CONF Transmitted over BCCH SI-3 message. It informs the mobile about the actual CCCH configuration in a cell.

Relation Between CCCH_CONF, BS_CC_CHANS and BS_CCCH_SDCCH_COMB

CCCH_CONF BS_CC_CHANS BS_CCCH_SDCCH_COMB
0 1 NO
1 1 YES
2 2 NO
4 3 NO
6 4 NO

PLMN

It is considered as highest level of hierarchy in GSM/GPRS network. It is identified globally by PLMN identifier. It is the network providing mobile cellular services. PLMN identifier is composed of MCC(Mobile Country code) and MNC(Mobile Network Code).

MCC length is 3 digits and MNC length is 2 or 3 digits.

GSM Routing Area vs Location Area

Location Area(LA)

Area in which MS move freely without updating its current location at the VLR. In case MS moves out of LA, it will inform VLR of its current location using LAU(Location Area Update) procedure.

An Location Area(LA) includes one or more cells. This grouping helps in efficient location management. Each LA is identified by an LAI(Location Area Identity).

LAI = MCC(3 digits) + MNC(2/3 digits) + LAC(2 octets)

Routing Area(RA)

RA of GPRS is analogous to LA of GSM. It is the area in which an MS move freely without updating its current location with SGSN. If MS moves out of Routing area it will inform SGSN of its current location using RAU(Routing Area Update) procedure.

Like an Location Area(LA), an Routing Area(RA) too may include one or more cells. This grouping helps in efficient location management. Each RA is identified uniquely by RAI(Routing Area Identity).

RAI=LAI +RAC(1 octet), RAC is Routing Area Code

LA may contain one or more RA.

Cell Global Identity(CGI)

The cell is considered as the lowest level of hierarchy in GSM/GPRS network, identified by Cell Identity(CI). CI is unique within LA. To identify a cell across PLMN, Cell Global Identity(CGI) is defined.

CGI = MCC + MNC + LAC + CI(2 octets)

Useful GSM Links

GSM mobile originated call flow   GSM Mobile Terminated Call flow 
GSM protocol stack   GSM physical layer   GPRS protocol stack   GPRS tutorial  

Other useful Terminologies

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GSM TERMINOLOGY
LTE TERMINOLOGY
SATELLITE TERMINOLOGY
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RF and Wireless Terminologies


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