Lect1..ppt - 01/06/05 CDA 6505 Network Architecture and Client/Server Computing Lecture 5 Asynchronous Transfer Mode (ATM) by Zornitza Genova Prodanoff

ZGP002 Outline ATM Protocol Architecture Logical connections ATM Cells Service categories ATM Adaptation Layer (AAL)

ZGP003 ATM Protocol Architecture Fixed-size packets called cells Streamlined: minimal error and flow control 2 protocol layers relate to ATM functions: –Common layer providing packet transfers –Service dependent ATM adaptation layer (AAL) AAL maps other protocols to ATM

ZGP004 Protocol Model has 3 planes User Control management

ZGP005

ZGP006 Logical Connections VCC (Virtual Channel Connection): a logical connection analogous to virtual circuit in X.25 VPC (Virtual Path Connection): a bundle of VCCs with same endpoints

ZGP007

ZGP008 Advantages of Virtual Paths Simplified network architecture Increased network performance and reliability Reduced processing and short connection setup time Enhanced network services

ZGP009

ZGP0010 VCC Uses Between end users Between an end user and a network entity Between 2 network entities

ZGP0011

ZGP0012 VPC/VCC Characteristics Quality of Service (QoS) Switched and semi-permanent virtual channel connections Cell sequence integrity Traffic parameter negotiation and usage monitoring (VPC only) virtual channel identifier restriction within a VPC

ZGP0013 Control Signaling A mechanism to establish and release VPCs and VCCs 4 methods for VCCs: –Semi-permanent VCCs –Meta-signaling channel –User-to-network signaling virtual channel –User-to-user signaling virtual channel

ZGP0014 Control Signaling 3 methods for VPCs –Semi-permanent –Customer controlled –Network controlled

ZGP0015 ATM Cells Fixed size 5-octet header 48-octet information field Small cells reduce delay for high-priority cells Fixed size facilitate switching in hardware

ZGP0016 Header Format Generic flow control Virtual path identifier (VPI) Virtual channel identifier (VCI) Payload type Cell loss priority Header error control

ZGP0017

ZGP0018 Generic Flow Control Control traffic flow at user-network interface (UNI) to alleviate short-term overload conditions When GFC enabled at UNI, 2 procedures used: –Uncontrolled transmission –Controlled transmission

ZGP0019

ZGP0020 Header Error Control 8-bit field calculated based on remaining 32 bits of header error detection in some cases, error correction of single-bit errors in header 2 modes: –error detection –Error correction

ZGP0021

ZGP0022

ZGP0023

ZGP0024 Service Categories Real-time service –Constant bit rate (CBR) –Real-time variable bit rate (rt-VBR) Non-real-time service –Non-real-time variable bit rate (nrt-VBR) –Available bit rate (ABR) –Unspecified bit rate (UBR) –Guaranteed frame rate (GFR)

ZGP0025

ZGP0026 ATM Adaptation Layer (ATM) Support non-ATM protocols –e.g., PCM voice, LAPF AAL Services –Handle transmission errors –Segmentation/reassembly (SAR) –Handle lost and misinserted cell conditions –Flow control and timing control

ZGP0027 Applications of AAL and ATM Circuit emulation (e.g., T-1 synchronous TDM circuits) VBR voice and video General data services IP over ATM Multiprotocol encapsulation over ATM (MPOA) LAN emulation (LANE)

ZGP0028 Applications of AAL and ATM

ZGP0029 AAL Protocols AAL layer has 2 sublayers: –Convergence Sublayer (CS) Supports specific applications using AAL –Segmentation and Reassembly Layer (SAR) Packages data from CS into cells and unpacks at other end

ZGP0030

ZGP0032 AAL Type 1 Constant-bit-rate source SAR simply packs bits into cells and unpacks them at destination One-octet header contains 3-bit SC field to provide an 8-cell frame structure No CS PDU since CS sublayer primarily for clocking and synchronization

ZGP0033 AAL Type 3/4 May be connectionless or connection oriented May be message mode or streaming mode

ZGP0034

ZGP0035

ZGP0036

ZGP0037 AAL Type 5 Streamlined transport for connection oriented protocols –Reduce protocol processing overhead –Reduce transmission overhead –Ensure adaptability to existing transport protocols

ZGP0038