Asynchronous Transfer Mode (ATM)meseec.ce.rit.edu/eecc694-spring2000/694-4-13-2000.pdf · EECC694 - Shaaban #15 lec # 10 Spring2000 4-13-2000 ATM Switch Functions • The main function

EECC694 - ShaabanEECC694 - Shaaban#1 lec # 10 Spring2000 4-13-2000

Asynchronous Transfer Mode (ATM)Asynchronous Transfer Mode (ATM)• ATM is a specific asynchronous packet-oriented information, multiplexing and

switching transfer model standard, originally devised for digital voice and videotransmission, which is– Based on 53-byte fixed-length cells.– Each cell consists of a 48 byte information field and a 5 byte header, which is

mainly used to determine the virtual channel and to perform the appropriaterouting.

– Cell sequence integrity is preserved per virtual channel. Thus all cells belongingto a virtual channel must be delivered in their original order.

– Original primary rate: 155.52 Mbps. Additional rate: 622.08 Mbps

• ATM is connection-oriented.– Header values including virtual path/circuit numbers are assigned to each

section of a connection for the complete duration of the connection.

• The information field of ATM cells is carried transparently through thenetwork. No processing like error control is performed on it inside the network.

• All services (voice, video, data, ) can be transported via ATM, includingconnectionless services.

– To accommodate various services an appropriate adaptation layer is provided tofit information of all services into ATM cells and to provide service specificfunctions (e.g. clock recovery, cell loss recovery, ...).


Synchronous Vs. AsynchronousData Transmission

Synchronous Transmission in a T1 LineSynchronous Transmission in a T1 Line

Asynchronous Transmission in an ATM LineAsynchronous Transmission in an ATM Line


Virtual CircuitsVirtual Circuits• When a virtual circuit is established:

– The route is chosen from beginning to end (circuit setup needed).– Routers or switches along the circuit create table entries used to

route data transmitted on the virtual circuit.– Permanent virtual circuits - Switched virtual circuits


ATM Cells & SwitchesATM Cells & SwitchesATM Cell FormatATM Cell Format

An ATM switchAn ATM switch

InputInput side side OutputOutput

side side

Fixed cell size = 53 bytesFixed cell size = 53 bytesCell Duration: ~ 2.7 µsecfor 155.52 Mbps ATMs ~ 700 nsec for 622.08 Mbps ATMs


ATM Layer HeadersATM Layer Headers

ATM layer header at User-Network Interface UNIATM layer header at User-Network Interface UNI

ATM layer header at Network-Network Interface NNIATM layer header at Network-Network Interface NNI

8 bits 16 bits

12 bits

4 bits

16 bits

3 bits

3 bits

HEC:

1

1

8 bits

8 bits


Values of PTI ATM Header FieldValues of PTI ATM Header Field


Layers ofLayers ofThe ATMThe ATM

ModelModel


Functions of ATM Layers/SublayersFunctions of ATM Layers/Sublayers


The Network Layer In ATM NetworksThe Network Layer In ATM Networks• The ATM layer handles the functions of the network

layer:– Moving cells from source to destination in order.– Routing algorithms within ATM switches, global

addressing.

• Connection-oriented without acknowledgments.

• The basic element is the unidirectional virtual circuit orchannel with fixed-size cells.

• Two possible interfaces:– UNI (User-Network Interface): Boundary between an

ATM network and host.

– NNI (Network-Network Interface): Between two ATMswitches (or routers).


ATM Network Connection Setup/ReleaseATM Network Connection Setup/Release

Connection SetupConnection Setup

Connection ReleaseConnection Release


ATM Layer Messages Used ToATM Layer Messages Used To Establish/Release Connections Establish/Release Connections


ATM Virtual Path Re-routing ExampleATM Virtual Path Re-routing Example

Rerouting a virtual path re-routes all of its virtual circuitsRerouting a virtual path re-routes all of its virtual circuits


ATM Routing ExampleATM Routing Example

Possible routes through the Omaha ATM switch


ATM Routing Example: Table EntriesATM Routing Example: Table Entries

Table entries corresponding to routes through the Omaha ATM switch


ATM Switch FunctionsATM Switch Functions• The main function of an ATM switch is to relay user data cells from input ports to

the appropriate output ports. The switch processes only user data cell headers andthe payload is carried transparently.

– As soon as the cell comes in through the input port, Virtual Path/Channel Identifiers(VPI/VCI) information is extracted from the cell and used to route the cells to theappropriate output port.

– This function can be divided into three functional blocks: the input module at the inputport, the cell switch fabric (or switch matrix) that performs the actual routing, and theoutput modules at the output ports.

• Establishment and control of the VP/VC connections.– Unlike user data cells, information in signaling or control cells payload is not transparent to

the network.– The switch identifies signaling cells, and even generates some itself.– Connection Admission Control (CAC) carries out the major signaling functions required.– Signaling/control information may not pass through the cell switch fabric, and instead is

exchanged through a separate signaling network.

• Network management functions, concerned with monitoring the controlling thenetwork to ensure its correct and efficient operation.

– Fault management functions,– Performance management functions,– Configuration management functions.

• Connection admission control, usage/network parameter control and congestioncontrol, usually handled by input modules.


A Generic ATM Switching ArchitectureA Generic ATM Switching Architecture

IM IM = Input Module= Input Module OM OM = Output Module= Output Module CAC CAC = Connection Admission Control= Connection Admission Control SM SM = Switch Management= Switch Management

OMOM

OMOM

OMOM

:.

IM IM

IM IM

IM IM

:.

CellCellSwitchSwitchFabricFabric

CACCAC SMSM

ATM/SONETLines

ATM/SONETLines

Input Side Output Side

}} Switch InterfaceSwitch Interface


ATM Switch InterfaceATM Switch InterfaceInput Modules

– The input module first terminates the incoming signal (incase of a SONET signal) and extracts the ATM cell stream:

• Signal conversion and recovery.• Processing SONET overhead, and cell delineation and rate

decoupling.

– For each ATM cell the following functions should beperformed:

• Error checking the header using the Header Error Control (HEC)field.

• Validation and translation of VPI/VCI values.• Determination of the destination output port.• Passing signaling cells to CAC and OAM cells to Switch

Management• Addition of an internal tag containing internal routing and

performance monitoring information for use only within theswitch.


ATM Over SONET ExampleATM Over SONET Example• The 53 bytes ATM cells are mapped into STS-3c or OC-3 frame payload as

shown:

• An STS-3c frame has a payload capacity of 3 * (90 - 3 - 1) columns * 9 rows or 2340 bytes.• Because of the STS-3c payload capacity is not an integer multiple of the ATM cell, a cell

is allowed to cross the frame boundary.

ATM cellsScrambled ATM Cell Payload

ATM cells

90 Columns (bytes)

3 bytes line overhead + 1 byte path overhead per row

9rows

STS-3c STS-3c or OC-3 or OC-3 Frame Frame

Cell continuedin next frame


Output Modules

Prepare ATM cell streams for physical transmission by:

– Removing and processing the internal tag.

– Possible translation of VPI/VCI values.

– HEC field generation.

– Possible mixing of cells from CAC and SwitchManagement with outgoing cell streams.

– Cell rate decoupling.

– Mapping cells to SONET payloads and generation ofSONET overhead.

– Conversion of the digital bit stream to an optical signal.

ATM Switch InterfaceATM Switch Interface


Connection Admission Control (CAC)Connection Admission Control (CAC)Establishes, modifies and terminates virtual path/channel

connections. Responsible for:– Signaling ATM Adaptation Layer (AAL) functions to

interpret or generate signaling cells.

– Interface with a signaling network.

– Negotiation of traffic contracts with users requesting newVPCs/VCCs.

– Renegotiation with users to change establishedVPCs/VCCs.

– Allocation of switch resources for VPCs/VCCs, includingroute selection.

– Admission/rejection decisions for requested VPCs/VCCsgeneration of usage/network parameter control(UPC/NPC) parameters.


The Cell Switch FabricThe Cell Switch Fabric• The cell switch fabric is primarily responsible for

transferring cells between the other functional blocks(includes data cells and possibly signaling and managementcells as well). Other possible functions include:

– Cell buffering and queuing.– Traffic concentration and multiplexing– Redundancy for fault tolerance– Multicasting or broadcasting– Cell scheduling based on delay priorities– Congestion monitoring.

• Fabric Connection Types:– Fully Interconnected fabrics.– Fabrics using Multistage interconnection networks

(MINs).


Fully Interconnected ATM Switch FabricFully Interconnected ATM Switch Fabric

– Independent paths exist between all N2 possible pairs ofinputs and outputs.

– Broadcast all incoming cells on separate buses to all outputs.– Address filters pass the appropriate cells to the output

queues.

Input Side

Output Side


Fully Interconnected ATM Switch Fabric: Fully Interconnected ATM Switch Fabric:

The Knockout SwitchThe Knockout Switch

Output SideOutput Side


An ATM Switch Fabric Using An ATM Switch Fabric Using MINsMINs::

BatcherBatcher-Banyan-Banyan

Switching fabric of a Batcher-Banyan ATM switchSwitching fabric of a Batcher-Banyan ATM switch

Input Side Output Side


Batcher-Banyan ATM SwitchBatcher-Banyan ATM SwitchCell Routing ExampleCell Routing Example

Four cells being routed through an 8-input Batcher-Banyan switchFour cells being routed through an 8-input Batcher-Banyan switch


ATM Switch Queuing ModesATM Switch Queuing Modes

An ATM switch with input side queuing

An ATM switch with output side queuing


Running TCP/IP Over An ATM SubnetRunning TCP/IP Over An ATM Subnet


ATM LANsATM LANs

ATM LAN Emulation

LANEmulationServer

Documents

Asynchronous Transfer Mode (ATM)meseec.ce.rit.edu/eecc694-spring2000/694-4-13-2000.pdf · EECC694 - Shaaban #15 lec # 10 Spring2000 4-13-2000 ATM Switch Functions • The main function