GSM Convention Architecture.


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In charge of the correspondence of system assets, portability, code organization and call-related administration messages between different system substances ...
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GSM Protocol Architecture Shariful Hasan Shaikot Graduate Student Computer Science Department Oklahoma State University

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Outline What is GSM? Classification GSM Protocol Architecture Overview of Interfaces GSM Protocol Stack Overview of Layer-I Overview of Layer-II Overview of Layer-III

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What is GSM? GSM , the Global System for Mobile Communications, is a computerized cell correspondences framework GSM gives – Digital Transmission ISDN similarity Worldwide meandering in other GSM systems Provides a model for 3G Cellular frameworks (UMTS)

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Nomenclature MS (Mobile Station) = ME (Mobile Equipment ) +SIM (Subscriber Identity Module) BSS (Base Station Subsystem) = BTS (Base Transceiver Station) + BSC (Base Station Controller) NSS (Network Switching Subsystem) MSC (Mobile Switching Center): communication exchanging capacity and confirmation of client

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GSM Protocol Stack In any media transmission framework, flagging is required to arrange the fundamentally appropriated utilitarian elements of the system. The exchange of flagging data in GSM takes after the layered OSI model Layer 1: Physical Layer Radio Transmission Layer 2 : Data Link Layer (DLL) gives mistake free transmission between nearby substances, in light of the ISDN\'s LAPD convention for the U m and A bis interfaces, and on SS7\'s Message Transfer Protocol (MTP) for the other Layer interfaces Layer 3: Networking or Messaging Layer Responsible for the correspondence of system assets, portability, code organization and call-related administration messages between different system elements

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GSM Protocol Architecture Layer 3 Layer 2 Layer 1 TDMA/FDMA

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Overview of Interfaces U m Radio interface amongst MS and BTS each physical channel bolsters various coherent channels A bis amongst BTS and BSC essential capacities: movement channel transmission, earthly channel administration, and radio channel administration An amongst BSC and MSC essential capacities: message exchange between various BSCs to the MSC

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The information join (layer 2) over the radio connection depends on an adjusted LAPD (Link Access Protocol for the D channel) alluded to as LAPDm (m like versatile). On the A-bis interface, the layer 2 convention depends on the LAPD from ISDN. The Message Transfer Protocol (MTP) level 2 of the SS7 convention is utilized at the An interface.

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User Data and Control at Air Interface Two sorts of ISDN "channels" or correspondence ways: B-channel The Bearer ("B") channel: a 64 kbps channel utilized for voice, video, information, or interactive media calls. D-channel The Delta ("D") channel: a 16 kbps or 64 kbps channel utilized essentially for interchanges (or "signaling") between exchanging hardware in the ISDN system and the ISDN gear

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User Data and Control at Air Interface In GSM: • Bm channel for activity/client information • Dm direct to signal As in ISDN the Dm divert in GSM can be utilized for client information if limit is accessible. GSM\'s Short Message Service (SMS) utilizes this.

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Layer I: Physical Layer Radio transmission shapes this Layer

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Layer I: Physical Layer Modulation Techniques – Gaussian Minimum Shift Keying (GMSK) Channel Coding Block Code Convolutional Code Interleaving To circulate burst mistake Power control procedure – to minimize the co-channel impedance Time synchronization approaches

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GSM Protocol Architecture for Speech – Air IF

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GSM Physical Layer (MS Side) Speech in GSM is digitally coded at a rate of 13 kbps 184 bits ( 20 ms) 260 bits each 20 ms Convolutional Encoder 456 bits each 20 ms 8 57 bits piece GMSK

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GSM Speech Transmission

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GSM Normal Burst Formatting

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GSM Frame Hierarchy

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Physical Vs. Coherent Channel

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Logical Channels in GSM Two noteworthy classes of sensible channels Traffic Channels (TCHs) Control Channels (CCHs)

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Traffic Channels in GSM Two sorts of TCHs Full-rate movement channel (TCH/F) Half-rate activity channel (TCH/H)

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Control Channels in GSM Three classes of control channels Broadcast Channels (BCH) Common Control Channels (CCCH) Dedicated Control Channels (DCCH)

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Layer II: Data Link Layer (DLL) sans error transmission between nearby substances

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GSM – Layer II Connection-based Network Traffic Signaling and Control Signaling and control information are passed on through Layer II and Layer III messages in GSM Purpose of Layer II is to check the stream of bundles for Layer III DLL checks the location and arrangement # for Layer III Also oversees Acks for transmission of the parcels Allows two SAPs for flagging and SMS activity is helped through a fake flagging bundle that conveys client data over flagging channels DLL permits SMS information to be multiplexed into flagging streams

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GSM – Layer II Signaling bundle conveyed to the physical layer is 184 bits which acclimates with the length of the DLL bundles in the LAPD convention utilized as a part of ISDN system The LAPD convention is utilized for An and A-bis interface The DLL for the U m interface is LAPDm

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LAPDm The Link Access Procedure on the Dm channel (LAPDm) is the convention for use by the information join layer on the radio interface. Capacities – association of Layer 3 data into casings – shared transmission of flagging information in characterized outline designs – acknowledgment of edge arrangements – foundation, upkeep, and end of one or more (parallel) information joins on flagging channels

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Frame group (LAPD)

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Frame position (LAPDm) Address field: is utilized to convey the administration access point identifier (SAPI), convention amendment sort, nature of the message SAPI: When utilizing order/control outlines, the SAPI recognizes the client for which a summon casing is proposed, and the client transmitting a reaction outline Control field: is utilized to convey Sequence number and to determine the sorts of the casing (charge or reaction) Length pointer: Identifies the length of the data field that is utilized to recognize the data conveying documented from fill-in bits Information Field: Carries the Layer III payload Fill-in bits: every one of the "1" bits to extend the length to the coveted 184 bits

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Types of Frame of LAPDm Three sorts of edges for Supervisory capacities Unnumbered data exchange and control capacities Numbered data exchange

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Address field configuration of LAPDm Link Protocol Discriminator: is utilized to indicate a specific suggestion of the utilization of LAPDm C/R: Specifies a charge or reaction outline Extended Address : is utilized to extend the location field to more than one octet (the EA bit in the last octet of the location ought to be set to 1, generally 0) Spare: saved for future use

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LAPD Vs. LAPDm utilizes no cyclic repetition check bits for blunder recognition WHY? Mistake adjustment and location instrument are given by a mix of square and convolutional coding utilized (in conjunction with bit interleaving) in the physical layer

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Layer II Messages Set nonconcurrent adjusted mode Disconnect Unnumbered affirmation Receiver prepared Receiver not prepared Reject These messages are sent in distributed Layer II interchanges, DLL ack. These messages don\'t have Layer III data bits Fill-in bits cover the "data bits" field

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Layer II Messages (contd… ) The Paging Channel (PCH) is 176 bits. The DLL parcel for this flagging channel just have an EIGHT piece length of the field 184 bits encoded into 456 bits The 456 bits transmitted more than 8 physical NBs The Stand-alone Dedicated Control Channel (SDCCH) is 160 bits. The DLL bundle for this flagging channel has 3 8-bits utilized for location, control and length of the data field The Slow Associated Control Channel (SACCH) is 144 bits. The DLL parcel for this flagging direct has 16 fill-in bits and 3 8-bits utilized for location, control and length of the data field

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Layer III: Networking or Messaging Layer The layer 3 conventions are utilized for the correspondence of system assets, versatility, code arrangement and call-related administration messages between different system elements

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Layer III various components expected to build up, keep up and end a portable correspondence session Layer III executes the conventions expected to bolster these components A flagging convention, the enrollment procedure, is made out of a grouping of correspondence occasions or messages Layer III characterizes the points of interest of usage of messages on the consistent diverts exemplified in DLL outlines

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Layer III Message Format Transaction Identifier (TI): to distinguish a convention that comprises of a succession of message, permits numerous conventions to work in parallel Protocol Discriminator (PD): Identifies the classification of the operation (administration, supplementary administrations, call control) Message Type (MT): Identifies the sort of messages for a given PD Information Elements (IE): A discretionary field for the time that a guideline conveys some data that is determined by an IE identifier (IEI) .

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MM Message Type

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Layer III Message Radio Resource Management (RR), Mobility Management (MM) and Connection Management (CM).

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Radio Resource Management (RR)

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Mobility Management (MM) Assumes a solid RR association Responsible for area administration and Security

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Mobility Management (MM) Location administration includes the methodology and motioning for area overhauling , so that the portable\'s present area is put away at the HLR, permitting approaching calls to be appropriately steered. Security includes the verification of the portable, to anticipate unapproved access to the system, and additionally the

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