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Computer Networks: ATM1 ATM Asynchronous Transfer Mode.

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Presentation on theme: "Computer Networks: ATM1 ATM Asynchronous Transfer Mode."— Presentation transcript:

1 Computer Networks: ATM1 ATM Asynchronous Transfer Mode

2 Computer Networks: ATM2 Issues Driving LAN Changes Traffic Integration –Voice, video and data traffic –Multimedia became the ‘buzz word’ One-way batchWeb traffic Two-way batchvoice messages One-way interactiveMbone broadcasts Two-way interactivevideo conferencing Quality of Service guarantees (e.g. limited jitter, non-blocking streams) LAN Interoperability Mobile and Wireless nodes

3 Computer Networks: ATM3 Stallings “High-Speed Networks”

4 Computer Networks: ATM4 Stallings “High-Speed Networks”

5 Computer Networks: ATM5 A/D Voice s 1, s 2 … Digital voice samples A/D Video … Compression compressed frames picture frames Data Bursty variable-length packets cells Figure 9.3 Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies AAL ATM Adaptation Layers

6 Computer Networks: ATM6 MUX ` Wasted bandwidth ATM TDM Voice Data packets Images Figure 7.37Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Asynchronous Transfer Mode (ATM)

7 Computer Networks: ATM7 ATM ATM standard (defined by CCITT) is widely accepted by common carriers as mode of operation for communication – particularly BISDN. ATM is a form of cell switching using small fixed- sized packets. [ to facilitate hardware switches ] Header Payload 5 Bytes 48 Bytes Figure 9.1 Basic ATM Cell Format Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies

8 Computer Networks: ATM8 ATM Conceptual Model Four Assumptions 1.ATM network will be organized as a hierarchy. User’s equipment connects to networks via a UNI (User- Network Interface). Connections between provided networks are made through NNI (Network-Network Interface). 2.ATM will be connection-oriented. A connection (an ATM channel) must be established before any cells are sent. [ The connection setup phase is called signaling.]

9 Computer Networks: ATM9 X X X X X X X X X Private UNI Public UNI NNI Private NNI Private ATM network Public UNI B-ICI Public UNI Public ATM network A Public ATM network B Figure 9.5 Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies

10 Computer Networks: ATM10 ATM Connections two levels of ATM connections: virtual path connections virtual channel connections indicated by two fields in the cell header: virtual path identifier VPI virtual channel identifierVCI

11 Computer Networks: ATM11 Physical Link Virtual Paths Virtual Channels Figure 7.40 ATM Virtual Connections Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies

12 Computer Networks: ATM12 ATM Conceptual Model Assumptions (cont.) 3.Vast majority of ATM networks will run on optical fiber networks with extremely low error rates. 4.ATM must supports low cost attachments This decision lead to a significant decision – to prohibit cell reordering in ATM networks.  ATM switch design is more difficult.

13 Computer Networks: ATM13 Figure 3.16 ATM Cell Format at the UNI P&D slide

14 Computer Networks: ATM14 GFC (4 bits) VPI (4 bits) VCI (4 bits) VCI (8 bits) VCI (4 bits) PT (3 bits) CLP (1 bit) HEC (8 bits) ATM cell header Payload (48 bytes) Figure 9.7 UNI Cell Format Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies

15 Computer Networks: ATM N 1 Switch N 1 … 5 6 video 25 video voice data N video75 voice67 data 39 video 67 Figure 7.38 … … ATM Cell Switching Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies

16 Computer Networks: ATM16 c ATM Sw 1 ATM Sw 4 ATM Sw 2 ATM Sw 3 ATM DCC a b d e VP3 VP5 VP2 VP1 a b c d e Sw = switch Figure 7.39 Digital Cross Connect Only switches virtual paths Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies

17 Computer Networks: ATM17 ATM Protocol Architecture ATM Adaptation Layer (AAL) – the protocol for packaging data into cells is collectively referred to as AAL. Must efficiently package higher level data such as voice samples, video frames and datagram packets into a series of cells. Design Issue: How many adaptation layers should there be?

18 Computer Networks: ATM18 Plane management Management plane Control planeUser plane Physical layer ATM layer ATM adaptation layer Higher layers Layer management Figure 9.2 Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies

19 Computer Networks: ATM19 AAL ATM User information AAL ATM PHY ATM PHY ATM PHY … End system Network Figure 9.4Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies

20 Computer Networks: ATM20 Original ATM Architecture CCITT envisioned four classes of applications (A-D) requiring four distinct adaptation layers (1-4) which would be optimized for an application class: A.Constant bit-rate applications CBR B.Variable bit-rate applications VBR C.Connection-oriented data applications D.Connectionless data application

21 Computer Networks: ATM21 ATM Architecture An AAL is further divided into: Convergence Sublayer (CS) manages the flow of data to and from SAR sublayer. Segmentation and Reassembly Sublayer (SAR) breaks data into cells at the sender and reassembles cells into larger data units at the receiver.

22 Computer Networks: ATM22 Figure 3.17 Segmentation and Reassembly in ATM ■ ■ ■ AAL ATM AAL ATM P&D slide

23 Computer Networks: ATM23 Original ATM Architecture

24 Computer Networks: ATM24 Transmission convergence sublayer Physical medium dependent sublayer Physical medium ATM layer Physical layer Figure 9.6Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies

25 Computer Networks: ATM25 The AAL interface was initially defined as classes A-D with SAP (service access points) for AAL1-4. AAL3 and AAL4 were so similar that they were merged into AAL3/4. SEALSE ALThe data communications community concluded that AAL3/4 was not suitable for data communications applications. They pushed for standardization of AAL5 (also referred to as SEAL – the Simple and Efficient Adaptation Layer). AAL2 was not initially deployed. Original ATM Architecture

26 Computer Networks: ATM26 Revised ATM Architecture

27 Computer Networks: ATM27 Revised ATM Service Categories ClassDescriptionExample CBRConstant Bit RateT1 circuit RT-VBRReal Time Variable Bit Rate Real-time videoconferencing NRT-VBRNon-real-time Variable Bit Rate Multimedia ABRAvailable Bit RateBrowsing the Web UBRUnspecified Bit RateBackground file transfer

28 Computer Networks: ATM28 QoS, PVC, and SVC Quality of Service (QoS) requirements are handled at connection time and viewed as part of signaling. ATM provides permanent virtual connections and switched virtual connections. –Permanent Virtual Connections (PVC) permanent connections set up manually by network manager. –Switched Virtual Connections (SVC) set up and released on demand by the end user via signaling procedures.

29 Computer Networks: ATM29 (b) CS PDU with pointer in structured data transfer AAL 1 Pointer 1 Byte 46 Bytes 47 Bytes Figure 9.11 AAL 1 Payload Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies optional (a) SAR PDU header CSI SNP Seq. Count 1 bit 3 bits 4 bits

30 Computer Networks: ATM30 … Higher layer User data stream Convergence sublayer SAR sublayer ATM layer CS PDUs SAR PDUs ATM Cells H H H 5 48 H H H b 1 b 2 b 3 Figure 9.10 AAL 1 Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies

31 Computer Networks: ATM31 Figure 3.18 AAL 3/4 CPIBtagBASizePad0EtagLen 816 0─ < 64 KB8 User data P&D slide (a) CPCS-PDU format CPI Btag BASize CPCS - PDU Payload , (bytes)(bytes)(bytes) AL Etag Length Pad Header Trailer Convergent Sublayer PDUs

32 Computer Networks: ATM32 Figure 3.19 AAL 3/4 P&D slide (b) SAR PDU format ST SN MID SAR - PDU Payload (bits)(bytes) (bits) LI CRC Header (2 bytes) Trailer (2 bytes) Segmentation and Assembly PDU

33 Computer Networks: ATM33 Figure 3.20 Encapsulation and Segmentation for AAL3/4 P&D slide

34 Computer Networks: ATM34 Higher layer Common part convergence sublayer SAR sublayer ATM layer Service specific convergence sublayer Information Assume null T PAD User message Pad message to multiple of 4 bytes. Add header and trailer. Each SAR-PDU consists of 2-byte header, 2-byte trailer, and 44-byte payload. H … … Information Figure 9.15 AAL 3/4 Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies

35 Computer Networks: ATM35 Information , (bytes)(bytes) UU CPI Length CRC Pad Figure 9.19 AAL 5 Convergent Sublayer Format Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies CRC-32 < 64 KB0─47 bytes16 ReservedPadLen 32 Data Figure 3.21 ATM Adaptation Layer 5 P&D slide

36 Computer Networks: ATM36 Figure 9.19 AAL 5 SAR Format 48 bytes of Data ATM Header 1-bit end-of-datagram field (PTI) Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies

37 Computer Networks: ATM37 Higher layer Common part convergence sublayer SAR sublayer ATM layer PTI = 0 Service specific convergence sublayer Assume null 48 (1) Information T PAD … … Information 48 (0) PTI = 0 PTI = 1 Figure 9.18 AAL 5 Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies

38 Computer Networks: ATM38 Figure 3.22 Encapsulation and Segmentation for AAL5 P&D slide

39 Computer Networks: ATM39 P&D slide Figure 3.28 ATM Switch

40 Computer Networks: ATM40 P&D slide Figure x 4 Crossbar Switch

41 Computer Networks: ATM41 Figure 3.31 Self-Routing Headers P&D slide

42 Computer Networks: ATM42 Figure 3.32 Banyan Switching P&D slide


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