Alex_R
2013-01-08, 12:24 AM
1.MS à BTS (Channel Request message) on the RACH:
•Based on a Channel Request message, a maximum of 32 MSs are distinguished.
•The UA response messages on the Um interface are used to distinguish more MSs.
•The message is composed of 8 bits which provide:
•Establish Cause : Varies from 3 to 6 bits.
•Random Reference: Varies from 2 to 5 bits which carry the identifier.
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2.BTS à BSC (Channel Required message) Contains:
•Request Reference IE: Contains the random access reference value and the absolute frame number of the received access burst.
•Access Delay parameters: Contains the delay of the access burst.
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3.BSC à BTS (Channel Activation message) to activate the resources. The Channel Activation message carries the activation type, channel description, level, and time advance (TA).
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4.BTS à BSC (Channel Activation Acknowledge message) contains the absolute frame number so that the BSC can determine the Starting Time parameter. Before sending this message the BTS must Turn on the power amplifier on the specified channel to receive information in the uplink direction.
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5.BSC à MS (Immediate Assignment Command message)
•On the Um interface, the message is sent on the AGCH and start timer T3101.
•carries the Immediate Assignment Extend message so that the channel efficiency is enhanced.
The Immediate Assignment Extend message contains the assignment information about two MSs.
6.MS à BTS (SABM frame) on the main DCCH.
•The SABM is a frame in the LAPDm protocol at the data link layer.
•It is the first frame to establish a multiframe acknowledged mode.
•Two types of message flows co-exist on the Um interface: signaling and short messages, they are identified by the Service Access Point Identifier (SAPI).
•The service access point is the point at which the data link layer provides services to layer 3.
•SAPI0 supports the transfer of signaling, and SAPI3 supports the transfer of short messages.
•In the GSM network, an SABM frame carries the layer 3 service request message, which contains the identity of the MS and indicates which service the MS is requesting.
•The layer 3 service request messages are categorized into CM service requests, location update requests, IMSI detach, and paging responses. All these messages contain the IMSI of the MS, detailed access cause, and MS classmarks.
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7.BTS à MS (UA frame) on the main DCCH.
•The UA frame is an unnumbered acknowledge frame of the LAPDm protocol at the data link layer.
•It confirms the SABM frame. When the Channel Request messages sent by two MSs have the same contents, the two MSs may be assigned the same dedicated channel.
•Upon receiving the SABM frame, the BTS sends the MS a UA frame that contains the same information as the received SABM frame.
•If the IMSI contained in the SABM frame is different from that in the UA frame, the MS leaves this channel and starts another access attempt. If the IMSI contained in the SABM frame is the same as that in the UA frame, the MS stays on the assigned channel.
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8.BTS à BSC (Establish Indication message).
•Indicates the establishment of a radio connection in multi-frame mode and stop timer T3101.
•Contains parameters Link Identifier and L3 Information.
•The Link Identifier parameter identifies the signaling channel type and the message priority of SAPI and SAPI 0. L3 Information is a complete layer 3 message.
9.BSC à MSC (SCCP Connection Request message)
•Upon receiving the Establish Indication message from the BTS
•Carries the target CGI based on the MCC, MNC, LAC, and CI parameters.
•conveyed on an A interface PCM timeslot chosen by the BSC (called COC) à TDM TX Only.
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10.MSC à BSC (SCCP Connection Confirm message)
•conveyed on a COC chosen by the MSC which can be located on a different PCM than the one of the COC used by the BSC to send signaling messages to the MSC à TDM TX Only.
•Based on a Channel Request message, a maximum of 32 MSs are distinguished.
•The UA response messages on the Um interface are used to distinguish more MSs.
•The message is composed of 8 bits which provide:
•Establish Cause : Varies from 3 to 6 bits.
•Random Reference: Varies from 2 to 5 bits which carry the identifier.
●
●
2.BTS à BSC (Channel Required message) Contains:
•Request Reference IE: Contains the random access reference value and the absolute frame number of the received access burst.
•Access Delay parameters: Contains the delay of the access burst.
●
3.BSC à BTS (Channel Activation message) to activate the resources. The Channel Activation message carries the activation type, channel description, level, and time advance (TA).
●
4.BTS à BSC (Channel Activation Acknowledge message) contains the absolute frame number so that the BSC can determine the Starting Time parameter. Before sending this message the BTS must Turn on the power amplifier on the specified channel to receive information in the uplink direction.
●
5.BSC à MS (Immediate Assignment Command message)
•On the Um interface, the message is sent on the AGCH and start timer T3101.
•carries the Immediate Assignment Extend message so that the channel efficiency is enhanced.
The Immediate Assignment Extend message contains the assignment information about two MSs.
6.MS à BTS (SABM frame) on the main DCCH.
•The SABM is a frame in the LAPDm protocol at the data link layer.
•It is the first frame to establish a multiframe acknowledged mode.
•Two types of message flows co-exist on the Um interface: signaling and short messages, they are identified by the Service Access Point Identifier (SAPI).
•The service access point is the point at which the data link layer provides services to layer 3.
•SAPI0 supports the transfer of signaling, and SAPI3 supports the transfer of short messages.
•In the GSM network, an SABM frame carries the layer 3 service request message, which contains the identity of the MS and indicates which service the MS is requesting.
•The layer 3 service request messages are categorized into CM service requests, location update requests, IMSI detach, and paging responses. All these messages contain the IMSI of the MS, detailed access cause, and MS classmarks.
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7.BTS à MS (UA frame) on the main DCCH.
•The UA frame is an unnumbered acknowledge frame of the LAPDm protocol at the data link layer.
•It confirms the SABM frame. When the Channel Request messages sent by two MSs have the same contents, the two MSs may be assigned the same dedicated channel.
•Upon receiving the SABM frame, the BTS sends the MS a UA frame that contains the same information as the received SABM frame.
•If the IMSI contained in the SABM frame is different from that in the UA frame, the MS leaves this channel and starts another access attempt. If the IMSI contained in the SABM frame is the same as that in the UA frame, the MS stays on the assigned channel.
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8.BTS à BSC (Establish Indication message).
•Indicates the establishment of a radio connection in multi-frame mode and stop timer T3101.
•Contains parameters Link Identifier and L3 Information.
•The Link Identifier parameter identifies the signaling channel type and the message priority of SAPI and SAPI 0. L3 Information is a complete layer 3 message.
9.BSC à MSC (SCCP Connection Request message)
•Upon receiving the Establish Indication message from the BTS
•Carries the target CGI based on the MCC, MNC, LAC, and CI parameters.
•conveyed on an A interface PCM timeslot chosen by the BSC (called COC) à TDM TX Only.
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10.MSC à BSC (SCCP Connection Confirm message)
•conveyed on a COC chosen by the MSC which can be located on a different PCM than the one of the COC used by the BSC to send signaling messages to the MSC à TDM TX Only.