ATM Asynchronous Transfer Mode Networks ATM 1 Voice

ATM Asynchronous Transfer Mode Networks: ATM 1

Voice AAL A/D s 1 , s 2 … cells Digital voice samples Video Compression … A/D AAL picture frames Data AAL Bursty variable-length packets Copyright © 2000 The Mc. Graw Hill Companies cells compressed frames Leon-Garcia & Widjaja: Communication Networks: ATM cells Figure 9. 3 2

Asynchronous Transfer Mode (ATM) Voice Data packets MUX Wasted bandwidth Images TDM 4 3 2 1 4 ATM Leon-Garcia & Widjaja: Communication Networks: ATM 2 1 ` 4 Copyright © 2000 The Mc. Graw Hill Companies 3 3 1 3 2 Figure 7. 37 3

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 fixedsized packets. Basic ATM Cell Format 5 Bytes Header Copyright © 2000 The Mc. Graw Hill Companies 48 Bytes Payload Leon-Garcia & Widjaja: Communication Networks: ATM Figure 9. 1 4

Assumptions for ATM Conceptual Model 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 (a channel) must be established before any cells are sent. Networks: ATM 5

Assumptions for ATM Conceptual Model (cont. ) • two levels of ATM connections are defined: virtual path connections virtual channel connections These are indicated by the two fields in the cell header: virtual path identifier VPI virtual channel identifier VCI Networks: ATM 6

Private ATM network Private UNI X X Private NNI X NI U c Public ATM network A bli u P X X NNI Public UNI X B-ICI Public ATM network B X Public UNI X Leon-Garcia & Widjaja: Communication Networks: ATM X Copyright © 2000 The Mc. Graw Hill Companies Figure 9. 5 7

ATM Virtual Connections Virtual Paths Physical Link Virtual Channels Copyright © 2000 The Mc. Graw Hill Companies Leon-Garcia & Widjaja: Communication Networks: ATM Figure 7. 40 8

Assumptions for ATM Conceptual Model (cont. ) 3. Vast majority of ATM networks will run on optical fiber networks with extremely low error rates. 4. ATM supports low cost attachments • This decision lead to a significant decision – to prohibit cell reordering in ATM networks. ATM switch design is more difficult. Networks: ATM 9

UNI Cell Format ATM cell header GFC (4 bits) VPI (4 bits) VCI (8 bits) VCI (4 bits) PT (3 bits) CLP (1 bit) HEC (8 bits) Payload (48 bytes) Copyright © 2000 The Mc. Graw Hill Companies Leon-Garcia & Widjaja: Communication Networks: ATM Figure 9. 7 10

Networks: ATM 11

ATM Cell Switching 1 voice 67 1 video 67 2 data 39 3 video 25 5 video 61 N 1 75 32 61 3 2 39 67 67 … 6 data 32 voice 32 25 32 … … Switch Copyright © 2000 The Mc. Graw Hill Companies N video 75 N Leon-Garcia & Widjaja: Communication Networks: ATM Figure 7. 38 12

VP 3 a b c d e ATM Sw 1 a VP 5 ATM Sw 2 ATM DCC ATM Sw 3 b c VP 2 VP 1 ATM Sw 4 Sw = switch d e Digital Cross Connect Only switches virtual paths Copyright © 2000 The Mc. Graw Hill Companies Leon-Garcia & Widjaja: Communication Networks: ATM Figure 7. 39 13

Networks: ATM 14

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. Issue: How many adaptation layers should there be? Networks: ATM 15

Management plane Higher layers Plane management User plane Layer management Control plane ATM adaptation layer ATM layer Physical layer Copyright © 2000 The Mc. Graw Hill Companies Leon-Garcia & Widjaja: Communication Networks: ATM Figure 9. 2 16

User information AAL ATM ATM PHY PHY … End system Copyright © 2000 The Mc. Graw Hill Companies Network Leon-Garcia & Widjaja: Communication Networks: ATM End system Figure 9. 4 17

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. B. C. D. Constant bit-rate applications CBR Variable bit-rate applications VBR Connection-oriented data applications Connectionless data application Networks: ATM 18

ATM Architecture • The AAL is further divided into: – The Convergence Sublayer (CS) – to manage flow of data to and from SAR sublayer. – The Segmentation and Reassembly Sublayer (SAR) – responsible for breaking data into cells at the sender and reassembling cells into larger data units at the receiver. Networks: ATM 19

Networks: ATM 20

ATM layer Transmission convergence sublayer Physical medium dependent sublayer Physical medium Copyright © 2000 The Mc. Graw Hill Companies Leon-Garcia & Widjaja: Communication Networks: ATM Figure 9. 6 21

ATM Architecture {original} • The AAL interface was initially defined as classes A-D with SAP (service access points) for AAL 1 -4. • AAL 3 and AAL 4 were so similar that they were merged into AAL 3/4. • The data communications community concluded that AAL 3/4 was not suitable for data communications applications and they pushed for standardization of AAL 5 (also referred to as SEAL – the Simple and Efficient Adaptation Layer). • AAL 2 was not deployed. Networks: ATM 22

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ATM Service Categories {revised} Class Description Example --------------------------------------CBR Constant Bit Rate T 1 circuit RT-VBR Real Time Variable Bit Rate Real-time videoconferencing NRT-VBR Non-real-time Variable Bit Rate Multimedia email ABR Available Bit Rate Browsing the Web UBR Unspecified Bit Rate Background file transfer Networks: ATM 24

Qo. S, PVC, and SVC • Quality of Service requirements are handled at connection time and is 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. Networks: ATM 25

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AAL 1 Payload (b) CS PDU with pointer in structured data transfer 47 Bytes AAL 1 Pointer 1 Byte 46 Bytes optional (a) SAR PDU header CSI 1 bit SNP Seq. Count 3 bits Copyright © 2000 The Mc. Graw Hill Companies 4 bits Leon-Garcia & Widjaja: Communication Networks: ATM Figure 9. 11 27

AAL 1 Higher layer b 1 b 2 … b 3 User data stream CS PDUs Convergence sublayer 47 47 47 SAR PDUs SAR sublayer 1 ATM layer Copyright © 2000 The Mc. Graw Hill Companies 1 47 47 H H 5 H H H 48 5 1 47 ATM Cells H 48 5 48 Leon-Garcia & Widjaja: Communication Networks: ATM Figure 9. 10 28

AAL 3/4 CS and SAR PDUs (a) CPCS-PDU format Trailer Header CPI Btag BASize 1 1 2 (bytes) CPCS - PDU Payload 1 - 65, 535 (bytes) Pad AL Etag Length 0 -3 1 1 2 (bytes) (b) SAR PDU format Trailer (2 bytes) Header (2 bytes) ST SN MID 2 4 10 (bits) Copyright © 2000 The Mc. Graw Hill Companies SAR - PDU Payload 44 (bytes) Leon-Garcia & Widjaja: Communication Networks: ATM LI CRC 6 10 (bits) Figure 9. 16 29

AAL 3/4 Higher layer Information User message Service specific convergence sublayer Common part convergence sublayer SAR sublayer Assume null H Information PAD 4 4 2 44 Pad message to multiple of 4 bytes. Add header and trailer. T 2 ATM layer 2 44 2 … 2 44 2 Each SAR-PDU consists of 2 -byte header, 2 -byte trailer, and 44 -byte payload. … Figure 9. 15 Copyright © 2000 The Mc. Graw Hill Companies Leon-Garcia & Widjaja: Communication Networks: ATM 30

AAL 5 Convergent Sublayer Format Information 0 - 65, 535 (bytes) Pad UU CPI 0 -47 1 1 (bytes) Length CRC 2 4 SAR Format ATM Header 48 bytes of Data 1 -bit end-of-datagram field (PTI) Copyright © 2000 The Mc. Graw Hill Companies Leon-Garcia & Widjaja: Communication Networks: ATM Figure 9. 19 31

AAL 5 Information Higher layer Service specific convergence sublayer Assume null Common part convergence sublayer SAR sublayer Information T … 48 (0) ATM layer 48 (0) 48 (1) … PTI = 0 Copyright © 2000 The Mc. Graw Hill Companies PAD PTI = 1 PTI = 0 Networks: ATM Leon-Garcia & Widjaja: Communication Networks 32 Figure 9. 18