1. ASYNCHRONOUS TRANSFER MODE

2. WHAT IS ATM? ATM is a cell-switching and multiplexing technology that combines the benefits of circuit switching (guaranteed capacity and constant transmission delay) with those of packet switching (flexibility and efficiency for intermittent traffic)

3. Major Advantages Bandwidth Efficiency Scalability Transparency Network Flexibility

4. THE ATM PROTOCOL STACK

5. A 3 stage process o Segmentation of user data into cells o Transfer of cells through the network o Reconstruction of the original information at the receiving end

6. The ATM Adaptation layer (AAL) Divides higher level data streams into segments These segments are more compatible with the requirements of the ATM Layer The AAL process depends on the type of traffic being transmitted

7. Types of traffic 5 Classes of Traffic Class A: Constant Bit Rate (CBR) Class B: Variable Bit Rate ( VBR ) Connection-oriented Required timing relationship between source and destination [constant bit-rate video] Connection-oriented Required timing relationship between source and destination [packet-video, voice]

8. Types of traffic Class C: Variable Bit Rate (VBR) Class D: Variable Bit Rate ( VBR ) Connection-oriented No timing relationship required between source and destination [Bursty data traffic] Connectionless No timing relationship required between source and destination [Bursty datagram traffic]

9. Types of traffic Class X: User defined

10. The AAL Process Divided into two sub layers: o The convergence sub layer (CS) o The segmentation and reassembly sub layer (SAR)

11. The convergence Sub Layer (CS) Divides the application data stream into rational, fixed length protocol data units (PDUs) Length of PDU depends on the nature of the traffic being passed (such as 64 Kbytes for Class D traffic) Appends header and trailer to the CS payload

12. The SAR Sub Layer Divides CS-PDUs into small segments ranging from 44 to 48 bytes in length depending on the type of traffic being transmitted To form SAR-PDU header and trailer information is added to the basic payload segment

13. AAL Process

14. The ATM Layer The heart of the ATM communication process Packages data, received from the AAL into cells The ATM layer operates between adjacent network nodes

15. Physical Layer Defines the various transmission medium used for the transmission of the ATM cell Divided into two parts: o The Physical Medium Dependent (PMD) Sub layer o The Transmission Convergence(TC) Sub layer

16. The PMD Sub Layer Associated with a given media type and transmission speed Deals with the actual transfer of information bits between adjacent nodes of the network Concerned with specific characteristics of a particular transmission technology

17. The TC Sub Layer Independent of the underlying physical media Provides necessary framing and convergence operations required to fit the ATM cells into the physical transport media Calculates and inserts the header error control information into the HEC field of the ATM cell header; and, before passing a recovered cell to the ATM layer at the receiving end, checks the received HEC field and discards the cell if an error is indicated

18. The ATM Protocol Data Unit : The Cell The basic unit of ATM information transfer 53-byte in length A 5-byte header and a 48-byte payload field

19. The ATM Cell Structure

20. The ATM Cell Fields GFC(Generic Flow control) The last four bits of byte- 1 form the generic flow control Used to control the flow of traffic across the User- Network Interface (UNI) VPI/VCI This three-byte field makes the ATM address First byte contains virtual path identifier (VPI) Next two bytes contain the virtual channel identifier (VCI)

21. The ATM Cell Fields PT(Payload Type) Differentiates between user data and control messages Indicates if a cell has experienced congestion CLP(Cell Loss Priority) The first bit of byte-4 Cells with a CLP set to “1” are subject to discard prior to cells for which the CLP is “0” during periods of network congestion

22. The ATM Cell Fields HEC(Header Error Control) The final byte of the ATM cell header Detects errors in the cell header but not the Payload provides protection against miss-routing of ATM cells due to addressing errors PAYLOAD Field The remaining 48 bytes of the ATM Cell are reserved for the data inserted by the AAL

23. ATM TOPOLOGY Defines how the various network components and user terminal devices are interconnected Interfaces are divided into two groups o User-to-network interface (UNI) o Network-to-network or node interface (NNI)

24. The UNI Three variations in UNI o Public UNI o Private UNI o Residential UNI

25. The NNI Three versions of the NNI o Public NNI o Private NNI(PNNI) o Broadband Inter-Carrier Interface (B-ICI)

27. THE ATM COMMUNICATIONS PROCESS Based on a simple and fast transport relay mechanism Call connection, termination, addressing, sequencing, and payload error control are handled at the trans- mitting and receiving ends

28. Association between User and Network Functions

29. ATM Networking Connection-oriented service Establishes connections between adjacent Layer 2 ATM entities Uses virtual channels and virtual paths to establish end-to-end virtual circuit connections

30. ATM Transmission Path Virtual Channel (VC) Virtual Path (VP) Virtual Circuit Connection (VCC)

31. ATM Transmission Path

32. ATM Switching ATM switches operate very differently from analog or digital switches ATM switches use self-routing procedures A self-routing switch relies on information contained in the VPI/VCI fields of the cell The switch adds a temporary routing header or “tag” to the cell

33. Routing in a Switch

34. ATM Signaling ATM end-users require the capability to establish connections across the network Two Types of End-to-End Connections o Permanent Virtual Circuit (PVC) o Switched Virtual Circuit(SVC) The signaling mechanism used for ATM is based on ISDN Signaling System Number 7 (SS7)

35. The Q.2931 signaling protocol with Signaling ATM Adaptation Layer (SAAL) is adapted for ATM Signaling

36. Signaling ATM Adaptation Layer (SAAL) The SAAL provides reliable transport of signaling messages between two ATM systems Composed of two sub layers o Common part o Service-specific part

37. Service-Specific Part Subdivided into Service-Specific Coordination Function (SSCF) Service-Specific Connection Oriented Protocol (SSCOP)

38. Virtual Circuit Connection (VCC) Types 4 Classes Point-to-point (pt-pt) Point-to-multipoint (pt-mpt) Multipoint-to-point (mpt-pt) Multipoint-to-multipoint (mpt-mpt)

39. ATM-connected devices use an ATM end-system address (AES)

40. Initial Domain Part (IDP) This part contains Address Format Identifier (AFI) Initial Domain Identifier (IDI) The IDI o Data Country Code (DCC) o International Code Designator (ICD)

41. Domain Specific Part (DSP) Contains High-Order Part (HO-DSP) Lower-Order Part (LO-DSP)

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43. High-Order Part (HO-DSP) Contains Domain Format Identifier (DFI) Address Authority (AA) Routing Domain (RD) Area

44. Lower-Order Part (LO-DSP) Contains End-System Identifier (ESI) Selector (SEL)

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