2G/GSM

Channel Request

Channel Request has various functionalities and the one right after power-on is is equivalent to RACH process of UMTS and LTE. Simply put, this message is to tell the network "I want to camp on you, please allocate me a radio resource that I initiate the connection process".

The one for the initial registration is as follows. (In good channel condition and in open space, the first Channel Request would reach the NW and get the immdediate Assignement with only one Channel Request. Following is a kind of worst case where the initial channel request fail to decoded by NW or UE fails to decode initial immediate assignements)

Note : T3126 starts when the last retransmission of 'Channel Request' and it stops when UE gets 'Immediate Assignement'. If UE does not get 'Immediate Assignement' until T3126 expires, UE starts cell reselection.

The exact functionality of a channel request is determined by the first 8 bits of its message and the description of the first byte is specified by the following table in 44.018.

< 44.018 - Table 9.1.8.1: CHANNEL REQUEST message content >

NOTE 1: Examples of these procedures are: IMSI detach, Short Message Service (SMS), Supplementary Service management, Location Services, sending of application-specific data.

NOTE 2: If such messages are received by a network, an SDCCH shall be allocated.

NOTE 2a: If such messages are received by a network, an SDCCH may be allocated.

NOTE 2b: This value shall not be used by the mobile station on RACH. If such message is received by the network, it may be ignored. The value is used by the network to answer to a 11 bits EGPRS Packet Channel request.

NOTE 2c: If the MS is Location Updating as part of a CS Fallback Mobile Originating call setup then the MS shall instead use the appropriate Originating call Establishment cause value. If the MS is Location Updating as part of a CS Fallback for other Mobile Originating services (e.g. USSD or Location Services) then the MS may either use the Establishment cause for the other service or the Establishment cause for Location Updating. If the MS is Location Updating as part of a Mobile Terminating CS Fallback procedure then the MS shall instead use the appropriate Answer to paging Establishment cause value as specified below Table 9.1.8.2.

Example 1 : 1D C2 E3

00011101 11000010 11100011

Example 2 : 79 C9 C3  

01111001 11001001 11000011   

Example 3 : 78 D1 D6  

01111000 11010001 11010110