Asynchronous Transfer Mode (ATM) Member’s Name:Chen Sing Tiong(KL003676) (L) Cheng Chin Tat (KL003832) Low Mei Ee(KL003796) Ng Shook Kien(KL003795) Pang Yin Yee(KL003719) Tan Lay Koon(KL003809) Tan Lay Koon(KL003809) Tan Wee Khoon(KL003844) Yong Yen Jen(KL003797) Yong Yen Jen(KL003797)

What is ATM? A transfer mode in which information is organised into cells International Telecommunication Union-Telecommunications Standards Section (ITU-T) standard for cell relay wherein information for multiple service types, such as voice, video, or data, is conveyed in small, fixed-size cells. Based on the efforts of the ITU-T Broadband Integrated Services Digital Network (B-ISDN) standard. It was originally conceived as a high-speed transfer technology over public networks. –Operates at Layer 2 of the OSI-RM Switching technology in WAN backbone network Minimal functionality in the network Provide faster packet switching

–ATM Layer, common to all services and provides packet transfer capabilities: fixed size cells logical connections –ATM Adaptation Layer (AAL), that is service dependent: supports information transfer protocols not based on ATM, by mapping the information into ATM cells

Objectives 1.Explain the cell establishment connection in ATM. 2.Explain the protocol architecture of ATM in relation with OSI model. 3.ATM cell structure and it effect on the performance of ATM network.

ATM Cell Establishment When an ATM device wants to establish a connection with another ATM device, it sends a signaling-request packet to its directly connected ATM switch. This request contains the ATM address of the desired ATM endpoint, as well as any Quality of Services parameters required for the connection.

The ATM Connection Establishment Process ATM signaling uses the one-pass method of connection setup. An ATM connection setup proceeds in the following manner: - Source end system sends a setup message - Send call proceeding message - Destination end system receives setup message - Send a connect message - Send acknowledge message

The ATM Connection Establishment Process (Con’t) First, source end system sends a setup message - a setup message is forwarded to the first ATM switch (ingress switch) in the network. Send call proceeding message - This switch sends a call proceeding message and invokes an ATM routing protocol. The signaling request is propagated across the network

The ATM Connection Establishment Process (Con’t) Destination end system receives setup message - The exit switch (egress switch) that is attached to the destination end system receives the setup message. Send a connect message - The egress switch forwards the setup message to the end system across its UNI, and the ATM end system sends a connect message if the connection is accepted.

The ATM Connection Establishment Process (Con’t) Send acknowledge message - The connect message traverses back through the network along the same path to the source end system, which sends a connect acknowledge message back to the destination to acknowledge the connection. Data transfer can then begin.

ATM Devices Establish Connections Through the One-Pass Method ATM Call Establishment

ATM Protocol Architecture The ATM architecture is divided into 3 layers: –ATM Adaptation Layer (AAL) Convergence Sub-layer (CS) Segmentation and Reassembly Sub-layer (SAR) –ATM Layer –Physical Layer (PHY) Physical Layer Medium Dependent Sub-layer (PM) Transmission Convergence Sub-layer (TC)

ATM vs. OSI Application Presentation Session Transport Network Data Link Physical OSI Reference Model B-ISDN Protocol Reference Model (**) Common for all services Source: ITU-T; I.371

Functions of B-ISDN Functions of the B-ISDN in relation to the Protocol Reference Model. Source: ITU-T; I.371

B-ISDN and ATM B-ISDN is based on ATM (ITU-T et al: ) ATM is used to implement B-ISDN B-ISDN uses optical fibre A service requiring transmission channels capable of supporting rates greater than the primary rate (ITU- T)

Layered Architecture ATM PHY AAL ATM Network UNIUNI ATM AAL PHY Physical Layer (PHY) User Network Interface (UNI) Different AAL Protocols for Different Traffic Types (e.g., data, voice, video)

Cell Switching End Station Switch Voice Data Video AALAALAALAAL PHYPHY PHYPHY ATMATM PHYPHY ATMATM PHYPHY ATMATM AALAALAALAAL Voice Data Video Cells AAL: Inserts/extracts information into 48 byte payload ATM Layer: Adds/removes 5 byte header to payload PHY: Converts to appropriate electrical or optical format

Physical Layer (PHY) Speed Matching and Framing CablePlants Wide Range of Speeds LAN, MAN, WAN Compatibility Use Existing Media Twisted Pair CoaxFiber TransmissionFrame

PHY Sub-layers PM: –Transmission medium, bit timing –Probably use existing standards and technology TC: –Specific to the PM –Cell delineation (identify beginning of cell) –Cell rate decoupling (inserting empty cells during idle periods) Transmission Convergence Sub- layer (TC) Physical Layer Medium Dependent Sub- layer (PM)

ATM Layer Provide call transfer for all services Functions: –Generic Flow Control –Cell header generation/extraction –Cell VPI/VCI translation –Cell MUX/DEMUX

ATM Layer In Minor Detail } 48-BytePayloads From AAL 5-Byte Header Header Contains Virtual Path and Channel Identifiers 53-Byte Cell To Physical Layer Adds/Removes Header To 48 Byte Payload Header Contains Connection Identifier (VCI/VPI) Multiplexes 53 Byte Cells Into Virtual Connections Sequential Delivery Within A Virtual Connection

Source: ATM Forum ATM Adaptation Layer (AAL) Provide service dependent functions to higher layer Examples Class A: 64 Kbps digital voice Class B: Variable bit rate encoded video? Class C: Frame Relay over ATM Class D: CCITT I.364 (SMDS) over ATM

AAL continue … This division leads to four types of services: –Class A: Constant Bit Rate (CBR) service, connection-oriented, with timing relation –Class B: Variable Bit Rate (VBR) service, connection-oriented, with timing relation –Class C: VBR, connection-oriented, no timing relation –Class D: VBR, connection-less, no timing relation

ATM Adaptation Layer 48 Bytes AALTypes 1 Circuit Emulation -Constant Bit Rate (CBR) Low Bit Rate Voice (Real Time) -Variable Bit Rate (VBR) -Variable Bit Rate (VBR) Time Invariant Data (bursty data) “Simple” Data 2 3/4 5 Provides Mapping Of Applications To ATM Service Of The Same Type Segments/Reassembles Into 48 Payloads Hands 48 Bytes Payloads To ATM Layer (4 Bytes to adapt)

AAL Sub-layers Segmentation and Reassembly (SAR) –segment data in native format into fixed length ATM cells and vice versa Convergence Sub-layer (CS) –error checking, removal of corrupted cells –service specific

ATM In Use DataCell VideoCell VoiceCell

In Detail ATM Cell Creation Transmission AdaptationLayer ATMLayerPhysicalLayer Conversion to ATM Data Types, 48-Byte Length Forward Cell Through Network Add 5-Byte Header Convert To Correct Electrical Or Optical Format VoiceCell DataCell VideoCell Services

ATM Cell Structure (cont.) Two types of header –User-Network Interface (UNI) –Network-Network Interface (NNI) UNI headeroctetNNI header Generic Flow ControlVirtual Path Identifier1 VCI 2 Virtual Path Identifier VCI Virtual Channel Identifier3 VCI Payload TypeCLP4VCI Payload TypeCLP Header Error Control5

ATM Cell Structure fixed size of 53 bytes. –5 byte header Virtual Channel Information (VCI) Virtual Path Information (VPI) Payload Type Information (PT) Cell Loss Priority (CLP) –48 bytes information ATM cell 48 bytes information 5 byte header

ATM Cell Structure (cont.) Header Fields: –Generic Flow Control (GFC)- 4 bits. Used only for flow control protocols on shared medium user access networks. (UNI format only) –Virtual Path Identifier- 8 (UNI) or 12 bits (NNI). Field constitute a routing field for the network. Allowing for more virtual paths to be supported within the network. –Virtual Channel Identifier- 16 (UNI) or 20 bits (NNI). Field is used for routing to and from the end user.

ATM Cell Structure (cont.) –Payload Type - 3 bits. Used mainly for Operations and Maintenance purposes. (5 th edition, pg 335) –Cell Loss Priority-1 bit. Used for congestion control purposes. –Header Error Control (HEC)- 8 bits. Used for header error protection. Allows to correct single bit errors in the header. Also used in the cell delineation process (used to determine on which bit position the cell starts, i.e. cell synchronisation)

ATM Cells Fixed size( 5 octet header and 48 octet information field) Small cells reduce queuing delay for high priority cells Small cells can be switched more efficiently Easier to implement switching of small cells in hardware

Conclusion Asynchronous Transfer Mode is the cell relay protocol designed by the ATM forum and adopted by the ITU-T The ATM data packet is called cell and composed of 53 bytes The cell network is based on permanent virtual circuit routing The ATM standard define three layers  AAL  ATM  Physical layer

Conclusion (cont.) ATM can handle or minimize the severity of:  Out of sequence packets  Delay time between packets of a message  Bit errors ATM cell have 2 types  UNI  NNI

Questions and Answers (1) What is the definition of ATM? Answer: A transfer mode in which information is organised into cells; for cell relay wherein information for multiple service types, such as voice, video, or data, is conveyed in small, fixed- size cells. (2) What is the method used by ATM signaling for setup connection? Answer: one-pass method

Questions and Answers (cont.) (3) What are the 3 lower layer of the OSI stack which the ATM specific function ca be found? Answer: ATM adaptation Layer (AAL), ATM layer, and Physical layer (4) In AAL, which types of services that required timing between source and definition? Answer: Class A, and Class B.

Questions and Answers (cont.) (5) What is the header field consist in UNI ATM cell format? Answer: GFC, VPI, VCI, PT, CLP and HEC. (6) What is the 2 types header in ATM cell structure? Answer: UNI and NNI