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asdasLayer 3 Message in GSM

GSM Layer III Messages

Signaling Protocol In GSM

In telecommunication system, signaling is required to coordinate the distributed entitiesof the network.

The signaling protocol in GSM is structured into three general layers as shown in thefollowing figure.

Layer 1 (Physical layer)It uses the data channel structures over the air interface

Layer 2 (Data link layer)It provides error-free transmission between adjacent entities, based on the ISDNs LAPDprotocol for the Um and Abis interfaces, and on SS7s Message Transfer Protocol (MTP) forthe other Layer interfaces

Layer 3 (Networking or messaging layer)

Responsible for the communication of network resources, mobility, code format and call-related management messages between various network entities

Layer III is the GSM signaling protocol, which is divided into 3 sub-layers:Radio Resource Management to control the setup, maintenance, and termination ofradio and fixed channels, including handovers;Mobility Management to manage the location updating and registration procedures, aswell as security and authentication; andConnection Management to handles general call control and manages SupplementaryServices and the Short Message Service.

System Information Type 1

When MS need to know which frequency band to use and which frequencies within theband it should use during frequency hoppingThe ARFCN for all frequencies used in the cell.

RACH control parameters
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Information is also provided instructing the MS how to perform access to the system. Thisinformation is provided in the RACH control parameters information element

Cell Bar access (CBA, CELL_BAR_ACCESS)Cell barred for access is denoted by using one bit only (yes/no).Call reestablish permitted (RE)MAXRET (Max retransmissions)Tx-IntergerAccess control class ( ACC) is described using a bit map with 16 bits. All MSs are spreadout on ACC 0-9. Priority group MSs use ACC 11-15. A bit set to 1 indicates that the class isbarred for access.Emergency calls EC=0 means that all MSs are allowed to make emergency calls, whileEC=1 means that only MSs belonging to priority classes 11-15 are allowed to makeemergency calls.

System Information Type 2The neighbor cells description information element denotes the frequencies of the BCCHcarriers to be monitored by the MSs in the cell.BA-INDThis is a BCCH allocation sequence number indication. BAIND can have the value 0 or 1.When the operator changes the frequency list, the BA-IND changes from 1 to 0 or viceversa.BA ARFCNThese are absolute RF channels on which the MSs should signal strength perform

measurements.
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System Information Type 3

SI3 msg are showing the information of CGI, Cell selection and basic idle modeparameter.Location Area Identification (LAI)MCC Mobile Country Code (3 digits)MNC Mobile Network Code (2-3 digits)LACLocation Area Code (2 octets: 0-65535 different LACs)Cell Selection ParametersMaximum power level of control channel (MS_TXPWR_MAX_CCH)Minimum receiving level of MS permitted to access (RXLEV_ACCESS_MIN)Additional reselection parameter indicator (ACS)Half-rate supported(NECI)Power control indication (PWRC): The power control indicator equal to 1 means setDiscontinuous transmission (DTX)Radio link timeout (RLT)ATT Attach/Detach allowed

AGBLK (BS_AG_BLKS_RES) This is the number of CCCH blocks reserved for the AGCHCCCH_CONFThis is the number of Basic Physical Channels used for the CCCHCCCH-CONF : (0) 1 basic physical channel used for CCCH, not combined with SDCCHsMFRMS (BS_PA_MFRMS) This is the number of 51 multiframe periods for transmission ofPaging Request messages in the same paging group (2-9).T3212 This is the time-out value for MS periodic location updating. T3212 has values from0 to 255. (Time for periodic LU = 6min * T3212 value)

System Information Type 4In system information type 4, MSs are informed if the cell broadcast function is used inthis cell and on what frequency the CBCH is found.

The LAI, the cell selection parameters, the RACH control parameters and rest octets arealso included in the type 4 message.CBCH Channel Description (Optional)In this information element, the channel used for SMS cell broadcast is described. CHANNEL TYPEThis is the channel combination and sub-channel used for CBCH. For example, SDCCH/4 +SACCH/C4 or CBCH, sub channel 2TN : This represents the time slot numberTSC : This is the training sequence code. BCC part of BSIC is recommended.
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H : This is the hopping parameter, where H=0 means single RF channel and H=1 means RFhopping channel.type 3 rest octets. These are PI, CBQ, CELL_RESELECT_OFFSET, TEMPORARY_OFFSET, andPENALTY_TIME

System Information Type 5It describes the neighbor cell BCCH frequencies(BA2 list). It is mandatory and istransmitted on SACCH. MS can read the frequency described in SYS INFO 5 in dedicatedmode, report the relevant information of neighbor cells in measurement report, and useit as the basis for handover.

Neighbor Cells DescriptionThe neighbor cells description information element denotes the frequencies of the BCCHcarriers to be monitored by the MSs in the cell.

System Information Type 6When in active mode, the MS needs to know if the LAI changes. In case the LAI changesthe MS must perform location updating when the call is released.If the MS changes between cells (within the location area) where RDLINKOUT or DTX

conditions differ the new cell options must be reported to the MS. NCC permitted information element is also included
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1. EDGE modulations

Scheme Modulation Maximum rate [kb/s]

MCS-9

8PSK

59.2MCS-8 54.4MCS-7 44.8MCS-6 29.6 / 27.2MCS-5 22.4MCS-4

GMSK

17.6MCS-3 14.8 / 13.6MCS-2 11.2MCS-1 8.8

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