Chapter 5 Asynchronous Transfer Mode ATM 1 Introduction

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Chapter 5 Asynchronous Transfer Mode (ATM) 1

Chapter 5 Asynchronous Transfer Mode (ATM) 1

Introduction ATM Protocol Architecture l Logical connections l ATM cell structure l Service levels/categories

Introduction ATM Protocol Architecture l Logical connections l ATM cell structure l Service levels/categories l ATM Adaptation Layer (AAL) l Chapter 5 ATM 2

Introduction l ATM evolved from B-ISDN development efforts – Frame Relay: high-speed WAN (1.

Introduction l ATM evolved from B-ISDN development efforts – Frame Relay: high-speed WAN (1. 5+ Mbps) – ATM: very high speed WAN (155 Mbps and 622 Mbps) l ATM, like Frame Relay, was built on the assumption that the underlying physical media was reliable and flexible – minimal error and flow control capabilities – even more streamlined, therefore faster, than Frame Relay l Specifications developed by ITU-T and ATM Forum Chapter 5 ATM 3

ATM Protocol Architecture l Fixed-size packets called cells l 2 primary protocol layers relate

ATM Protocol Architecture l Fixed-size packets called cells l 2 primary protocol layers relate to ATM functions: – “cell switching” like packet switching – Common layer providing packet transfers, logical connections (ATM) – Service dependent ATM adaptation layer (AAL) l AAL maps other protocols to ATM – like IP (AAL 5) Chapter 5 ATM 4

Protocol Model has 3 planes User – provides for user information transfer and associated

Protocol Model has 3 planes User – provides for user information transfer and associated controls (flow control, congestion control) l Control – performs call control and connection control functions (signaling) l Management – provides plane management and layer management and coordination functions l Chapter 5 ATM 5

ATM Protocol Reference Model Map data to the ATM cell structure Framing, cell structure

ATM Protocol Reference Model Map data to the ATM cell structure Framing, cell structure & Logical Connections Various data rates (155. 52 Mbps, 622. 08 Mbps) over various physical media types (Fiber Optic, SONET, UTP, etc. ) Chapter 5 ATM 6

User Plane Layers User information AAL ATM ATM PHY PHY … End system Chapter

User Plane Layers User information AAL ATM ATM PHY PHY … End system Chapter 5 ATM Network End system 7

User Plane Layers User information Chapter 5 ATM User information 8

User Plane Layers User information Chapter 5 ATM User information 8

Logical Connections l VCC (Virtual Channel Connection): a logical connection analogous to a virtual

Logical Connections l VCC (Virtual Channel Connection): a logical connection analogous to a virtual circuit in X. 25, or Frame Relay data link connection – full-duplex flow between end users – user-network control signaling – network-network management/routing l VPC (Virtual Path Connection): a bundle of VCCs with the same end points (not necessarily same endusers) – and switched along the same path Chapter 5 ATM 9

ATM Connection Relationships Virtual Channel: basic logical communications channel Virtual Path: groups of “common”

ATM Connection Relationships Virtual Channel: basic logical communications channel Virtual Path: groups of “common” virtual channels Physical Transmission Path: physical communications link Chapter 5 ATM 10

Advantages of Virtual Paths l l Simplified network architecture – allows separation of functionality

Advantages of Virtual Paths l l Simplified network architecture – allows separation of functionality into individual logical connections and related groups of logical connections Increased network performance and reliability – network consists of fewer aggregated entities l Reduced processing and short connection setup time – complex setup tasks are in virtual paths, simplifies setup of new virtual channels over existing virtual path l Enhanced network services – supports userspecified closed groups/networks of VC bundles Chapter 5 ATM 12

Virtual Path/Virtual Channel Terminology Virtual Channel (VC) A generic term used to describe unidirectional

Virtual Path/Virtual Channel Terminology Virtual Channel (VC) A generic term used to describe unidirectional transport of cells associated by a common unique identifier Virtual Channel Identifier (VCI) A unique numerical tag for a particular VC link Virtual Channel Link A means of unidirectional transport of cells between the point where a VCI is assigned and where it is translated or terminated Virtual Channel Connection (VCC) A concatenation of VC links that extends between two connected ATM end-points Chapter 5 ATM 13

Virtual Path/Virtual Channel Terminology Virtual Path Identifier Virtual Path Link Virtual Path Connection Chapter

Virtual Path/Virtual Channel Terminology Virtual Path Identifier Virtual Path Link Virtual Path Connection Chapter 5 ATM (VP) A generic term which describes unidirectional transfer of cells that are associated with a common unique identifier (VPI) Identifies a particular VP A group of VC links identified by a common identifier between the point where the identifier (VPI) is assigned and where it is translated or terminated (VPC) A concatenation of VP links that extends between ATM end-points where the VCIs are assigned and where they are translated or terminated 14

ATM VPC/VCC VP 3 a b c d e ATM Sw 1 a VP

ATM VPC/VCC VP 3 a b c d e ATM Sw 1 a VP 5 ATM Sw 2 ATM DCC ATM Sw 3 VP 6 b c VP 2 VP 1 Sw = switch ATM Sw 4 d e DCC = Cross-connect switch Chapter 5 ATM 15

ATM Connection Relationships Chapter 5 ATM 16

ATM Connection Relationships Chapter 5 ATM 16

VPC/VCC Characteristics Quality of Service (Qo. S) l Switched and semi-permanent virtual channel connections

VPC/VCC Characteristics Quality of Service (Qo. S) l Switched and semi-permanent virtual channel connections l Cell sequence integrity l Traffic parameter negotiation and usage monitoring l – average rate, peak rate, burstiness, peak duration, etc. l (VPC only) virtual channel identifier restriction within a VPC Chapter 5 ATM 17

Control Signaling A mechanism to establish and release VPCs and VCCs (per ITU-T Rec.

Control Signaling A mechanism to establish and release VPCs and VCCs (per ITU-T Rec. I. 150) l 4 methods for VCCs: l – Semi-permanent VCC: no control signaling required – Meta-signaling channel: permanent, low data rate channel for setting up signaling channels – User-to-network signaling virtual channel: set up between user and network – User-to-user signaling virtual channel: set up between users within a VPC, allowing users to set up and tear down VCCs, without network intervention Chapter 5 ATM 20

ATM Cells l Fixed size – 5 -octet header – 48 -octet information field

ATM Cells l Fixed size – 5 -octet header – 48 -octet information field Small cells may reduce queuing delay for high-priority cells (essential for low delay) l Fixed size facilitates more efficient switching in hardware (essential for very high data rates) l Chapter 5 ATM 22

ATM Cell Format (p. 98) Chapter 5 ATM 23

ATM Cell Format (p. 98) Chapter 5 ATM 23

Header Format Generic flow control (more ->) l Virtual path identifier (VPI) l Virtual

Header Format Generic flow control (more ->) l Virtual path identifier (VPI) l Virtual channel identifier (VCI) l Payload type (3 bits: identifies cell as user data or network management cell, presence of congestion, SDU type) l Cell loss priority (0: high; 1: low) l Header error control (more ->) l Chapter 5 ATM 24

Generic Flow Control l Used to control traffic flow at usernetwork interface (UNI) to

Generic Flow Control l Used to control traffic flow at usernetwork interface (UNI) to alleviate short-term overload conditions – Note: not employed in network core l When GFC is enabled at the UNI, two procedures are used: – Uncontrolled transmission: not subject to flow control – Controlled transmission: flow control constraints (using GFC mechanism) are in force Chapter 5 ATM 25

Header Error Control l 8 -bit field - calculated based on the other 32

Header Error Control l 8 -bit field - calculated based on the other 32 bits in the header – CRC based on x 8 + x 2 + x + 1 -> generator is 100000111 error detection l in some cases, error correction of single-bit errors in header l 2 modes: l – Error detection – Error correction Chapter 5 ATM 27

HEC Operation at Receiver Based on recognition of fact that bit errors occur in

HEC Operation at Receiver Based on recognition of fact that bit errors occur in bursts. Chapter 5 ATM 28

ATM Service Categories l Real-time service – Constant bit rate (CBR) – Real-time variable

ATM Service Categories l Real-time service – Constant bit rate (CBR) – Real-time variable bit rate (rt-VBR) l Non-real-time service – Non-real-time variable bit rate (nrt-VBR) – Available bit rate (ABR) – Unspecified bit rate (UBR) – Guaranteed frame rate (GFR) Chapter 5 ATM 31

ATM Bit Rate Service Levels Chapter 5 ATM 32

ATM Bit Rate Service Levels Chapter 5 ATM 32

ATM Adaptation Layer (AAL) l Support higher-level protocols and/or native applications – e. g.

ATM Adaptation Layer (AAL) l Support higher-level protocols and/or native applications – e. g. , PCM voice, LAPF, IP l AAL Services – Handle transmission errors – Segmentation/reassembly (SAR) – Handle lost and misinserted cell conditions – Flow control and timing control Chapter 5 ATM 33

ATM Adaptation Layer (AAL) Chapter 5 ATM 34

ATM Adaptation Layer (AAL) Chapter 5 ATM 34

Applications of AAL and ATM Circuit emulation (e. g. , T-1 synchronous TDM circuits)

Applications of AAL and ATM Circuit emulation (e. g. , T-1 synchronous TDM circuits) l VBR voice and video l General data services l IP over ATM l Multiprotocol encapsulation over ATM (MPOA) l LAN emulation (LANE) l Chapter 5 ATM 35

AAL Protocol and Services Basis for classification: • requirement for a timing relationship between

AAL Protocol and Services Basis for classification: • requirement for a timing relationship between source and destination • requirement for a constant bit rate data flow • connection or connectionless transfer Chapter 5 ATM 36

AAL Protocols l AAL layer has 2 sublayers: – Convergence Sublayer (CS) Supports specific

AAL Protocols l AAL layer has 2 sublayers: – Convergence Sublayer (CS) Supports specific applications/protocols using AAL l Users attach via the Service Access Point (like a port number) l Common part (CPCS) and application service -specific part (SSCS) l – Segmentation and Reassembly Sublayer (SAR) l Chapter 5 ATM Packages data from CS into ATM cells and unpacks at other end 37

AAL Protocols and PDUs Chapter 5 ATM 38

AAL Protocols and PDUs Chapter 5 ATM 38

AAL Protocol Descriptions Chapter 5 ATM 39

AAL Protocol Descriptions Chapter 5 ATM 39

Segmentation and Reassembly PDUs Chapter 5 ATM 40

Segmentation and Reassembly PDUs Chapter 5 ATM 40

AAL Type 1 Constant-bit-rate source l SAR simply packs bits into cells and unpacks

AAL Type 1 Constant-bit-rate source l SAR simply packs bits into cells and unpacks them at destination l One-octet header contains 3 -bit SC field to provide an 8 -cell frame structure l No CS PDU structure is defined since CS sublayer primarily for clocking and synchronization l Chapter 5 ATM 41

AAL Type 1 Chapter 5 ATM 42

AAL Type 1 Chapter 5 ATM 42

AAL Type 2 l Intended for use with applications with variable bit-rate service on

AAL Type 2 l Intended for use with applications with variable bit-rate service on multiple channels (multiplexing), or low bit rate, short-frame traffic AAL Type 3/4 l l l Intended for variable bit rate applications that generate bursty data and demand low loss Originally, connectionless (AAL 4) or connection (AAL 3) oriented, now combined into single format (AAL 3/4) Provides comprehensive sequencing and error control mechanisms Chapter 5 ATM 43

AAL 3/4 Chapter 5 ATM 45

AAL 3/4 Chapter 5 ATM 45

AAL Type 5 l Streamlined transport for connection oriented protocols – Reduce protocol processing

AAL Type 5 l Streamlined transport for connection oriented protocols – Reduce protocol processing overhead – Reduce transmission overhead – Ensure adaptability to existing transport protocols – primary function is segmentation and reassembly of higher-level PDUs Chapter 5 ATM 46

AAL 5 Chapter 5 ATM 48

AAL 5 Chapter 5 ATM 48