Bài Giảng GSM Protocols

GSM Protocols GSM Architecture Interfaces Purpose of layering   Divides the complexity of internetworking into discrete steps. Protocol: Set of rules that end points in a telecommunication connection use when they communicate. OSI Model OSI Reference Model     Layer were independent each other. Physical layer: Modulation, What kind of channel, Decide the interface. Data link layer: Convert packets into frames,Error detection and correction. Network Layer: Every network node has to analyse.    Ms bts bsc msc (RR) Routing, freagmentation Transport Layer: Segmentation end to end ordering packets   Session Layer: Global synchronization Purpose.  To differentiate mobile terminating call, mobile,orginating call,location update. Presentation layer:   Compression and decompression Application Layer:  Provide the interface GSM Protocol Stack Physical layer LAPDm     Three different formats of identical length (23 bytes) are defined; their respective uses depend on the type of information to be transferred. A-Format B-Format Bibs-Format ISDN Channels LAPDm     maximum frame length of an LAPDm frame (= 23 byte or 184 bit) Information frame: 1st byte, bit 0 = 0 Supervisory frames: 1st byte, bit 0 = 1, bit 1 = 0 Unnumbered frames: 1st byte, bit 0 = 1, bit 1 =1 A-Format   Fill frame when no payload is available on an active connection Sent on any DCCH in both directions. Control Field Send Sequence Number and Receive Sequence Number Polling Bit (P-Bit), Final Bit (F-bit), and P/FBit    Polling Bit frame types that can be used only as commands Final Bit frame types that can be used only as Responses P/F-Bit frame types that can be used both command and Response B-Format  To transport the actual signaling data  Every DCCH and every ACCH use this format.  The maximum length of the Layer 3 information to be carried is restricted, depending on the channel type (FACCH, SACCH). B-format SAPI  The number of unacknowledged frames for the service access point identifier (SAPI) = 0 is two, and the number of unacknowledged frames for SAPI = 62 and for SAPI = 63 is one. C/R Bbis-format      For transmission of BCCH, PCH, and AGCH. There is no header in the Bbis-format that would allow for addressing or frame identification. Addressing is not necessary, since BCCH, PCH, and AGCH are CCCHs, in which addressing is not required. In contrast to the DCCH, the CCCH transports only point-to-multipoint messages. The Bbis format is required for the downlink only. LAPD Terminal Endpoint Identifier   distinguish among the various TRXs. One TEI is assigned to each TRX. That provides the ability to distinguish between TRXs during analysis of a trace file. Layer3(RR,MM,CM) MM CM CM  .. .GSM Architecture Interfaces Purpose of layering   Divides the complexity of internetworking into... Presentation layer:   Compression and decompression Application Layer:  Provide the interface GSM Protocol Stack Physical layer LAPDm     Three different formats of identical length (23