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Asynchronous Transfer Mode (ATM) Protocol Architecture: Virtual Paths and Connections, Study notes of Data Communication Systems and Computer Networks

University of Texas - San AntonioData Communication Systems and Computer Networks

An overview of asynchronous transfer mode (atm) protocol architecture, focusing on virtual paths and connections. The similarities between atm and packet switching, the structure of atm cells, and the establishment and management of virtual channel connections (vcc) and virtual path connections (vpc). It also discusses the advantages of using virtual paths and the role of control signaling in atm.

Typology: Study notes

Pre 2010

Uploaded on 08/16/2009

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William Stallings
Data and Computer
Communications
7th Edition
Chapter 11
Asynchronous Transfer Mode
Protocol Architecture
•Similarities between ATM and packet switching
—Transfer of data in discrete chunks
—Multiple logical connections over single physical
interface
•In ATM flow on each logical connection is in
fixed sized packets called cells
•Minimal error and flow control
—Reduced overhead
•Data rates (physical layer) 25.6Mbps to
622.08Mbps
Protocol Architecture (diag) Reference Model Planes
•User plane
—Provides for user information transfer
•Control plane
—Call and connection control
•Management plane
—Plane management
•whole system functions
—Layer management
•Resources and parameters in protocol entities
ATM Logical Connections
•Virtual channel connections (VCC)
•Analogous to virtual circuit in X.25
•Basic unit of switching
•Between two end users
•Full duplex
•Fixed size cells
•Data, user-network exchange (control) and network-
network exchange (network management and routing)
•Virtual path connection (VPC)
—Bundle of VCC with same end points
ATM Connection Relationships
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Download Asynchronous Transfer Mode (ATM) Protocol Architecture: Virtual Paths and Connections and more Study notes Data Communication Systems and Computer Networks in PDF only on Docsity!

William Stallings

Data and Computer

Communications

7 th^ Edition

Chapter 11 Asynchronous Transfer Mode

Protocol Architecture

  • Similarities between ATM and packet switching —Transfer of data in discrete chunks —Multiple logical connections over single physical interface
  • In ATM flow on each logical connection is in fixed sized packets called cells
  • Minimal error and flow control —Reduced overhead
  • Data rates (physical layer) 25.6Mbps to 622.08Mbps

Protocol Architecture (diag) Reference Model Planes

  • User plane —Provides for user information transfer
  • Control plane —Call and connection control
  • Management plane —Plane management - whole system functions —Layer management - Resources and parameters in protocol entities

ATM Logical Connections

  • Virtual channel connections (VCC)
  • Analogous to virtual circuit in X.
  • Basic unit of switching
  • Between two end users
  • Full duplex
  • Fixed size cells
  • Data, user-network exchange (control) and network- network exchange (network management and routing)
  • Virtual path connection (VPC) — Bundle of VCC with same end points

ATM Connection Relationships

Advantages of Virtual Paths

  • Simplified network architecture
  • Increased network performance and reliability
  • Reduced processing
  • Short connection setup time
  • Enhanced network services

Call

Establishment

Using VPs

Virtual Channel Connection

Uses

  • Between end users —End to end user data —Control signals —VPC provides overall capacity - VCC organization done by users
  • Between end user and network —Control signaling
  • Between network entities —Network traffic management —Routing

VP/VC Characteristics

  • Quality of service
  • Switched and semi-permanent channel connections
  • Call sequence integrity
  • Traffic parameter negotiation and usage monitoring
  • VPC only —Virtual channel identifier restriction within VPC

Control Signaling - VCC

  • Done on separate connection
  • Semi-permanent VCC
  • Meta-signaling channel — Used as permanent control signal channel
  • User to network signaling virtual channel — For control signaling — Used to set up VCCs to carry user data
  • User to user signaling virtual channel — Within pre-established VPC — Used by two end users without network intervention to establish and release user to user VCC

Control Signaling - VPC

  • Semi-permanent
  • Customer controlled
  • Network controlled

Use of HALT

  • To limit effective data rate on ATM
  • Should be cyclic
  • To reduce data rate by half, HALT issued to be in effect 50% of time
  • Done on regular pattern over lifetime of connection

Two Queue Model

  • Two counters —GO_CNTR_A, GO_VALUE_A,GO_CNTR_B, GO_VALUE_B

Header Error Control

  • 8 bit error control field
  • Calculated on remaining 32 bits of header
  • Allows some error correction

HEC Operation at Receiver

Effect of

Error in

Cell Header

Impact of Random Bit Errors on

HEC Performance

Transmission of ATM Cells

  • 622.08Mbps
  • 155.52Mbps
  • 51.84Mbps
  • 25.6Mbps
  • Cell Based physical layer
  • SDH based physical layer

Cell Based Physical Layer

  • No framing imposed
  • Continuous stream of 53 octet cells
  • Cell delineation based on header error control field

Cell Delineation State Diagram

Impact of Random Bit Errors on

Cell Delineation Performance

Acquisition Time v Bit Error

Rate SDH Based Physical Layer

  • Imposes structure on ATM stream
  • e.g. for 155.52Mbps
  • Use STM-1 (STS-3) frame
  • Can carry ATM and STM payloads
  • Specific connections can be circuit switched using SDH channel
  • SDH multiplexing techniques can combine several ATM streams

UBR

  • May be additional capacity over and above that used by CBR and VBR traffic —Not all resources dedicated —Bursty nature of VBR
  • For application that can tolerate some cell loss or variable delays —e.g. TCP based traffic
  • Cells forwarded on FIFO basis
  • Best efforts service

ABR

  • Application specifies peak cell rate (PCR) and minimum cell rate (MCR)
  • Resources allocated to give at least MCR
  • Spare capacity shared among all ARB sources
  • e.g. LAN interconnection

Guaranteed Frame Rate (GFR)

  • Designed to support IP backbone subnetworks
  • Better service than UBR for frame based traffic — Including IP and Ethernet
  • Optimize handling of frame based traffic passing from LAN through router to ATM backbone — Used by enterprise, carrier and ISP networks — Consolidation and extension of IP over WAN
  • ABR difficult to implement between routers over ATM network
  • GFR better alternative for traffic originating on Ethernet — Network aware of frame/packet boundaries — When congested, all cells from frame discarded — Guaranteed minimum capacity — Additional frames carried of not congested

ATM Adaptation Layer

  • Support for information transfer protocol not based on ATM
  • PCM (voice) —Assemble bits into cells —Re-assemble into constant flow
  • IP —Map IP packets onto ATM cells —Fragment IP packets —Use LAPF over ATM to retain all IP infrastructure

ATM Bit Rate Services Adaptation Layer Services

  • Handle transmission errors
  • Segmentation and re-assembly
  • Handle lost and misinserted cells
  • Flow control and timing

Supported Application types

  • Circuit emulation
  • VBR voice and video
  • General data service
  • IP over ATM
  • Multiprotocol encapsulation over ATM (MPOA) —IPX, AppleTalk, DECNET)
  • LAN emulation

AAL Protocols

  • Convergence sublayer (CS) —Support for specific applications —AAL user attaches at SAP
  • Segmentation and re-assembly sublayer (SAR) —Packages and unpacks info received from CS into cells
  • Four types —Type 1 —Type 2 —Type 3/ —Type 5

AAL Protocols

Segmentation and Reassembly

PDU

AAL Type 1

  • CBR source
  • SAR packs and unpacks bits
  • Block accompanied by sequence number

AAL Type 2

• VBR

  • Analog applications