atm & bisdn

8/4/2019 ATM & BISDN

1/56

3/26/98EE/CS 5516 ATM - 1

$V\QFKURQRXV7UDQVIHU0RGH

By Scott Midkiff

ECpE/CS 5516, VPI

Spring 1997

(modified by Marc Abrams for Spring 1998)


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3/26/98EE/CS 5516 ATM - 2

Welcome to ATM!s Loooooooooooooooots of acronyms!

s A lot of whats in ATM came from the phone and switchingworlds, not the LAN world, so the terminology may beunfamiliar.

s OSI model doesnt really apply!


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3/26/98EE/CS 5516 ATM - 3

Asynchronous Mode Transfers ATM (asynchronous transfer mode) is

q Something of a revolution in both local and wide area

networksx Innovations for LANs: scalable, switching-only,

quality-of-service guarantees

x Innovations for WANs: scalable,

cell (packet)-switched, bandwidth-on-demandq Both a type of switching and a set of standards

q Becoming widely used, but is not without real or

proposed competitionx 100-Mbps and 1-Gbps Ethernet

x 100-Mbps FDDI

x DS3, SMDS, Frame relay services


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3/26/98EE/CS 5516 ATM - 5

WAN Transmission: Fiber Optics and SONETs Fiber optic transmission

q AT&T completed first transcontinental fiber system in

1986q Nearly all high-density trunks are now fiber

s SONET (Synchronous Optical NETwork) hierarchy

Name Rate (Mbps) Equivalent

OC-1 51.84 28 DS1 or 1 DS3

OC-3 155.52 3 OC-1

OC-12 622.08 12 OC-1 or 4 OC-3OC-48 2.488 48 OC-1

OC-192 9.953


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3/26/98EE/CS 5516 ATM - 6

WAN Transmission: ISDN (1)s Integrated Services Digital Network (ISDN) provides two

standard types of service

q Basic rate (basic service)q Primary rate (primary service)

s Basic Rate Interface(BRI): 2B+D

q Delivers ISDN services over standard atwisted-pair telephone line to subscribers

q Two 64 Kbps B channels -- Voice, circuit-switchedconnection, access to a packet switched network

q One 16 Kbps D channel -- User packet data at 16 Kb/sand call control signals


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3/26/98EE/CS 5516 ATM - 7

WAN Transmission: ISDN (2)s Primary Rate Interface(PRI)

q Delivers ISDN services to digital PBXs, LANs, hosts, ...

q Divides 1.544 Mbps T1 into:x 23 B channels, each at 64 Kbps

x One D channel for messaging, also at 64 Kbps


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3/26/98EE/CS 5516 ATM - 8

B-ISDN Concept (1)s B-ISDN: Broadband Integrated Services Digital Network

q Designed to provide similar services as ISDN

q B-ISDN is substantially more capable than ISDN

s B-ISDN versus ISDN(or N-ISDN for narrowband ISDN)

q

N-ISDN uses existing telephone network (copperpairs); B-ISDN uses optical fiber

q N-ISDN is primarily circuit switched; B-ISDN uses onlypacket switching (specifically ATM switching)

q N-ISDN uses predefined channel rates; B-ISDN usesvirtual channels without prespecified rates (bandwidthon demand)


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3/26/98EE/CS 5516 ATM - 9

B-ISDN Overview (2)s Integrated network for data, voice, video

q Single system needed for the local loop

q Single system for WANs and LANs

q Economies of scale for collection of services

q However, must support varied traffic types

q Many political, economic, social issues

s Changes from traditional data and voice networksq Low processing complexity critical for high data rates

q Voice/video require fixed bit rate/delay, but

data networks have varying delays/data ratesq Data rates may vary (1 bps to 100s of Mbps); but

voice networks support constant data rates


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3/26/98EE/CS 5516 ATM - 10

B-ISDN Componentss B-ISDNservices to users

s Asynchronous Transfer Mode(ATM) for switching

s Synchronous Digital Hierarchy(SDH) or SynchronousOptical Network(SONET) for transmission

B-ISDN

ATMSONET


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3/26/98EE/CS 5516 ATM - 11

SONETs A synchronousprotocol (unlike ATM or packet switching)

s A physicalprotocol (so its can be used under ATM)

s Used for optical fibers Frame of 810 bytes

s Doesnt use headers as were used to.

s Does use pointers to demultiplex traffic sent over onefiber path.

s Circuit switched: Allows a stream of ATM packets to besent long distances purely at physical layer without ATM

switches in the path


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3/26/98EE/CS 5516 ATM - 12

ATM Overviews ATM now exceeds BISDN in relevance

q ATM first deployed in the LAN environment

q ATM WANs dominated by data and video applications

s ATMversus Synchronous Transfer Mode (STM)

x STM is circuit-switched; ATM is packet-switched

x STM would require all channels to use somestandard multiple of 64 Kbps; ATM is more flexible High complexity if many standard rates Inefficiencies if few standard rates

x ATM benefits from high-speed packet switching --very large scale integration (VLSI) circuitsCell processingSwitching


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3/26/98EE/CS 5516 ATM - 13

ATM versus STM

A B C D A B C D A B C D A B C

A

B

C

D

STM -- Synchronous Transfer Mode

A B B C D A B B A C B B B A B

A

B

CD

ATM -- Asynchronous Transfer Mode


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3/26/98EE/CS 5516 ATM - 14

ATM Functionalitys ATM is difficult to map onto the OSI Reference Model

q Performs layer 3 functions, such as switching

q Used as a data link layer in some applications

s An Adaptation Layerabove ATMq at sender, divides messages or bit streams from above into ATM

cells(packets)q at receiver, reconstructs messages or streams

q thus performs some layer 4 functions

Data Link

ATM Adaptation Layer (AAL)

Asynchronous Transfer Mode (ATM)

Control Data Voice Video


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3/26/98EE/CS 5516 ATM - 15

B-ISDN Protocol Reference Model

Physical layer

ATM layerATM adaptation layer

higher layer higher layer

Control plane User plane

Management plane

Planemgmt.

Layermgmt.


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3/26/98EE/CS 5516 ATM - 16

Reference Model: Another View

SONET, ...

ATMAAL

Q.2931 Voice, video, ...

Control plane User plane

Management plane: SNMP

Planemgmt.

Layermgmt.

Q.2931: for call setup/release

Management plane: uses management protocol like SNMP


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3/26/98EE/CS 5516 ATM - 17

ATM Basics (1)s ATM is a connection-oriented (virtual circuit) network

q Permanent virtual circuit (PVC) -- connections and paths throughthe network are established when network is established

q Switched virtual circuit (SVC) -- connections and paths through thenetwork are established on an as-needed basis

s Connection-oriented eliminates need forq Source and destination addresses in header

q Sequence number for resequencing

s Error & flow control are only done on an end-to-end basisif needed either byq application or

q special signalling


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3/26/98EE/CS 5516 ATM - 18

ATMs Virtual Circuits

s Two multiplexing hierarchies:

q Virtual Path Identifier (VPI):x

Correspond to something that a switch switchesx A bundle of Virtual Channels

q Virtual Channel Identifier (VCI):x Correspond to sessions in an application

s Virtual Circuitis VPI + VCI

VPI 1

VPI 2

ATMChannel

VCI 1

VCI 2

VCI 1

VCI 2

VCI2,VPI1


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3/26/98EE/CS 5516 ATM - 19

Virtual Channels and Virtual Paths (1)s Virtual channel identifier (VCI) -- 16-bit field in header

q

Identify a virtual channel on a link between two ATM switchesq Up to 216 = 64K different channels can be carried over one link

s Virtual path identifier (VPI) -- 8- or 12-bit field in header

q Identify a path over which the VCI does not changeq Used for semi-permanent connections

q Up to 28 = 256 or 212 = 4K paths can be carried over one link

q There can be 64K VCIs over one VPI


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3/26/98EE/CS 5516 ATM - 20

Virtual Channels and Virtual Paths (2)

VP

switch

VC

switch

VC

switch

path

Simple case:Same VCI is used at source, destination

Multiple paths (hence VPIs are used)

Complex case: Multiple VCIs are used (e.g., cross MCI/Sprint boundary)


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3/26/98EE/CS 5516 ATM - 21

Virtual Channels and Virtual Paths (3)

VPI=1VCI=9

A

VPI=1

VCI=8B

VPI=2VCI=7

C

VPI=3VCI=9

AVPI=3VCI=8

B

VPI=2VCI=7

C

VPI=3VCI=6

D

VPI=3VCI=8

D

VPI=2VCI=5

C

VPI=3VCI=4

B

VPI=3VCI=9

A

VPswitch

VCswitc

h

VCswitch


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3/26/98EE/CS 5516 ATM - 22

ATM Basics (2)

s ATMs basic unit of transfer is a fixed-length cell

s

Fixed cell size simplifies switches (processing in hardwarerather than software)

s Small size minimizes packetization delay for voicetransmission

s Larger cell size would be more efficient for data -- due toper packet processing and header overhead

DataHeader

5 bytes 48 bytes


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3/26/98EE/CS 5516 ATM - 23

ATM Header Format (1)

s There are two header formats:

q User network interface (UNI): user to subnet

q Network node interface (NNI): internal subnet

UNI Header Format

GFC VPI

VPI VCIVCI

VCI PTI CLP

HECNNI Header Format

VPI

VPI VCIVCI

VCI

HEC

8 5 4 1 8 5 4 1

1

23

4

5

1

23

4

5

PTI CLP


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3/26/98EE/CS 5516 ATM - 24


s The address field (channel identifier) consists of twosubfields:q Virtual channel identifier (VCI): 16 bits

q Virtual path identifier (VPI): 8 bits in UNI format, 12 bits in NNIformat

s VCI and VPI together identify the virtual connectionq 24 bits in UNI format

q 28 bits in NNI format

s A special reserved address indicates unassigned oridle cells which carry no data but are needed to fill up acell slot in transmission


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3/26/98EE/CS 5516 ATM - 25


s 4-bit Generic Flow Control (GFC):q Can be used by the user to multiplex data from multiple

applications or devices onto the access link to the network

s 3-bit PTI: Payload type indicator:q user data versus network control information

s 1-bit CLP: Cell loss priority bit

s 8-bit Header error control (HEC):q CRC check over the header (does not include data)

q Not only detects, but corrects single bit errors

q One bit error in VCI is deadly!


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3/26/98EE/CS 5516 ATM - 26

Reference Model -- Layers and Sublayers

Convergence CS AAL

Segmentation and reassembly SAR

Generic flow control ATM

Cell VPI/VCI translation

Cell multiplex and demultiplex

Cell rate decoupling TC PHY

HEC header sequence generate/verify

Cell delineation

Transmission frame adaptation

Transmission frame generate/recoveryBit timing PM

Physical medium

CS:convergence

sublayerSAR:segmentationand reassembly

TC:transmissionconvergence

PM:

physicalmedium

HEC: headererror checking


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3/26/98EE/CS 5516 ATM - 27

Quality of Service (QoS) and Cell Loss

s Quality of service

q Cell loss

q Cell delay

q Cell delay variation

s ATM standard provides for a cell loss priority (CLP) bit inthe header; allows a user to identify two levels of prioritiesfor each cell

q CLP = 0 for high priority cells (e.g., voice)q A switch can discard CLP=1 cell (e.g., data)q Network can monitor high priority and low priority traffic and

compare to negotiated bandwidth


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3/26/98EE/CS 5516 ATM - 28

Network Termination and Generic Flow Control

s Customer premises equipment, or Broadband TerminalEquipment-1 (B-TE1), connects to ATM network atBroadband Network Termination-1 (B-NT1) or BroadbandNetwork Termination-2 (B-NT2)

s Multiple devices may share access to the SB interface

s Each device should be ensured fair access to the

interfaces Generic flow control is intended to support contention for

the local interface

B-TE1 B-NT2 B-NT1UBTBSB

transmission


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3/26/98EE/CS 5516 ATM - 29

ATM Adaptation Layer -- AAL (1)

s The ATM Adaptation Layer (AAL) is responsible forbreaking incoming source data into 48-byte pieces andreconstructing the data at the receiver

q Used at entry and exit from network

q If ATM is viewed as a network layer, then AAL is atransport layer

ATM Adaptation Layer (AAL)

Asynchronous Transfer Mode (ATM)

Control Data Voice Video


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3/26/98EE/CS 5516 ATM - 30

ATM Adaptation Layer -- AAL (2)

s Operation depends on the type of source traffic:

q Class 1 Constant bit rate (CBR) traffic,

e.g. 64 Kbps voice and fixed-rate video

q Class 2 Variable bit rate (VBR) traffic to be deliveredwith fixed delay, e.g. compressed and

packetized voice, video

q Class 3/4 Non-real-time data in messaging orstreaming modes (may be connection-oriented)

q Class 5 Similar to class 3/4, but without multiplexingor error detection (always connection-oriented)

s Other classes being defined, e.g. for MPEG-2 video


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3/26/98EE/CS 5516 ATM - 31

ATM Adaptation Layer

Adaptation Layer Sublayers (1)

ATM

Segmentation & Reassembly (SAR) Sublayer

Convergence Sublayer

Service Specific

Common Part

Physical


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3/26/98EE/CS 5516 ATM - 32

Adaptation Layer Sublayers (2)

s Convergence Sublayer (CS)

q Upper-layer frames are basic data units

q

Concerned with flow control and error recovery forClass 3 (connection-oriented traffic)

s Segmentation and Reassembly (SAR) Sublayer

q Segments of upper-layer frames are basic data units

q Concerned with segmenting frames at source and

reconstructing frames at destination


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3/26/98EE/CS 5516 ATM - 33

Class 1 AAL

s Class 1 traffic is constant bit rate traffic and has noframing structure on input

s SAR sublayer must segment incoming data stream

s Occasional errors can be tolerated, but these need to bedetected to maintain framing

s One-byte header (no trailer):

q 1-bit convergence sublayer indicatorq 3-bit segment number

q 4-bit CRC


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3/26/98EE/CS 5516 ATM - 34

Class 2 AAL

s Class 2 traffic is similar to Class 1 traffic except that thereis a frame structure on input

s Occasional errors can be tolerated, like Class 1

s Some Class 3/4 type functions needed to maintain inputframe structure


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3/26/98EE/CS 5516 ATM - 35

Class 3/4 AAL (1)

s Non-real-time data

s Connection is coordinated by peer communication

between the CS and SAR sublayers using header andtrailers

H T

User frame

CS sublayer

H TSAR sublayer H H T ... H TT

HATM layer H HH TH H T H TT


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3/26/98EE/CS 5516 ATM - 36

Class 3/4 AAL (2)

s Segmentation and reassembly SAR sublayer

q Two-byte header

x

Segment Type(2 bits): Indicates if this is firstsegment of a CS frame, middle segment, lastsegment, or an entire CS frame

x Sequence Number(4 bits): Used to check fordropped or misdirected cells (cells delivered in order)

x Reserved/Multiplexing Identifier(10 bits): May beused for multiplexing multiple user sessions on asingle connection


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3/26/98EE/CS 5516 ATM - 37

Class 3/4 AAL (3)

s Segmentation and reassembly SAR sublayer (continued)

q Two-byte trailer

x

Length Indicator(6 bits): For last segment andsingle segment SAR PDUs with less than 44 bytes ofdata

x CRC(10 bits)


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3/26/98EE/CS 5516 ATM - 38

Class 3/4 AAL (4)

s Common part convergence sublayer -- CPCS

q Header

x

Common part indicator (CPI) (1 byte): indicates unitfor length and size fields (possible future uses formultiplexing identifier allocation andoperations/maintenance)

x Beginning tag (Btag) (1 byte): Sequence numberplaced in header and trailer

x Buffer allocation size indication (BAsize) (2 bytes):buffer requirements for this CPCS-PDU


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3/26/98EE/CS 5516 ATM - 39

Class 3/4 AAL (5)

s Common part convergence sublayer -- CPCS (continued)

q In PDU

x

Padding (PAD) (0 to 3 bytes): padding in headerq Trailer

x Alignment (AL) (1 byte): puts trailer on 32-bitboundary

x End tag (Etag) (1 byte): matches Btag valuex Length(Length) (2 bytes): length of CPCS-PDU


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3/26/98EE/CS 5516 ATM - 40

Class 5 AAL (1)

s Class 5 AAL is similar to class 3/4 AAL

q Lower overhead

q

No error detection in the SAR (just at CPCS)q No multiplexing

q No buffer allocation information (BA field in class 3/4)

q Supports connection-oriented only -- class 3/4 AAL

supports both connection-oriented and connectionless

s Promoted by the ATM Forum to better match the needs of

q LAN equipment manufacturersq High data rate, connection-oriented data service users


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3/26/98EE/CS 5516 ATM - 41

Class 5 AAL (2)

s The only SAR information for each SAR-PDU is

q BOM/COM (beginning/continuation ofmessage) -- AUU=0

q EOM/SSM (end of message/single segmentmessage) -- AUU=1

s AAU (ATM-user-to-ATM-user) indication is in one bit ofthe ATM header, specifically payload type (PT) field


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3/26/98EE/CS 5516 ATM - 42

Class 5 AAL (3)

T

User frame

CS sublayer

SAR sublayer ...

HATM layer H H

T

T


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3/26/98EE/CS 5516 ATM - 43

Class 5 AAL (4)

Payload(40-48)

Payload(0-40) Pad(0-40) Reserved(2) Length(2) CRC(4)EOM/SSM

Pad*(0-7)

BOM/COM

SAR payload (48 bytes)

CPCS-PDU PayloadPad

Trailer

BOM COM COM EOM

H

CPCS

SAR

ATM


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3/26/98EE/CS 5516 ATM - 44

Class 5 AAL (5)

s AAU indicator is in ATM header PT field

q AAU = 0: BOM/COM

q AAU = 1: EOM/SSM

s Length is number of bytes in CPCS PDU payload

s Reserved (2 bytes) may be:

q CPCS User-to-User indication (1 byte)

q Comon Part Indicator (1 byte)

s BOM/COM padded only on next to last SAR-PDU (i.e.,next is EOM) and following SAR-PDU (the EOM) has no

payload


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3/26/98EE/CS 5516 ATM - 45

ATM Congestion Control

s Even with high data rates supported by a B-ISDN network,it is inevitable that congestion will occur

s Three elements of congestion control:

1) Rate, burstiness, and quality of service are negotiatedby user and network per connection

2) Network can monitor (at CS of AAL) rate and

burstiness of user traffic3) Priority bit in ATM header (CLP) indicates cells that

can be dropped


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3/26/98EE/CS 5516 ATM - 46

Negotiated Rate, Burstiness, QoS

s The user and network can agree upon a data rate,burstiness of data, and quality of service (QoS) to beprovided by the network

s Effects of constant bit rate traffic is fairly easy todetermine, however, the effects of variable bit rate trafficis a complex and open issue

s Required quality of service varies for broadband servicesq Delivery latency

q Variance of interframe delay

q Probability of frame loss

q ...


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3/26/98EE/CS 5516 ATM - 47

Monitoring and Regulating Incoming Traffic

s Network must monitor incoming traffic to ensure that itmeets agreed upon limits

s Could accept excess traffic, if bandwidth is available, butmark it so that it can be discarded in the event ofcongestion

q E.g., using the cell loss priority (CLP) bit in the ATM

headers Other schemes possible


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3/26/98EE/CS 5516 ATM - 48

Cell Loss Priority Bit

s Priority bit in ATM header indicates cells that may bediscarded

s Can be used by the network to mark traffic beyond anegotiated limit

s Can be used by a user to mark data that can be lost, e.g.video frames


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3/26/98EE/CS 5516 ATM - 49

ATM Switches

s A single 155 Mbps connection can produce155 Mb/s [(8 b/B)(53 B/cell)] 366,000 cells/secor 2.7 s/cell

s Switches need to range from a few input ports tothousands of input ports

s VLSI and parallel implementation critical to achieve

throughput


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3/26/98EE/CS 5516 ATM - 50

General Structure of an ATM Switch (1)

switchfabric

1

2

N

controlprocessor

1

2

N

inputports

outputports

InputControllers

OutputControllers

IC

IC

IC

OC

OC

OC


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3/26/98EE/CS 5516 ATM - 51

General Structure of an ATM Switch (2)

s The control processor is used only for high-level functionssuch as connection establishment and release, bandwidthallocation, maintenance, and management

s All switching done by input controllers (ICs), switch fabric,and output controllers (OCs)

s Cell headers are aligned and IC, OC, and switch fabric

operations are synchronouss Input controllers translate a cells VCI, VPI, or VPI/VCI to

an output port -- contention may occur

s Design issues: switch fabric topology, cell bufferlocations, contention mechanisms


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3/26/98EE/CS 5516 ATM - 52

Example Switching Fabric Topology

s Banyan network provides a single path from each input toeach output

s An nnswitch is constructed from ddcrossbar switches

s Requires logdn columns of n/d switches, orlogdn/logdp columns of n/p chips for chips with pinputs

Switchingcell modes

n=8, d=2


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3/26/98EE/CS 5516 ATM - 53

ATM in Local Area Networks

s ATM switches are available now for LAN applications

bridge/router

Ethernet

router

FDDI

DS3 orSONET

computer

computer

computer

OC-3 (155 Mbps)

ATMswitch

ATM

switch ATMswitch


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3/26/98EE/CS 5516 ATM - 54

ATM WAN Applications

s LAN-to-LAN internetworking

s Video services

q Switched access television

q Video-on-demand

s High resolution still image transfer

q Medical imaging

s Multimedia services

q Multimedia conferencing/class

q Multimedia databases

q Multimedia mail


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3/26/98EE/CS 5516 ATM - 55

Video-on-Demand Network

TelephoneCircuitSwitch

Real-Time

Compression

Real-TimeCompressionB

roadca

st

Video ATM

Concentrator

Games

Server

VideoServer

ATMSwitch

ADSLAccess

ADSLUnitTwisted

Pair

OC-3

TV

(

ADSL = asymmetrical digital subscriber line

SONETBackbone

OC-12


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3/26/98EE/CS 5516 ATM - 56

VISTAnet Network Configuration

ATMswitch

broadbandremote

mux/demux

mux/demux

broadbandremote

circuitswitch

OC-48 (2.488 Gbps)

medicalworkstation

Pixel-Planes 5

MasParMP-1

CRAYY-MP

OC-12(622 Mbps)

OC-12(622 Mbps)

D. S. Stevenson and J. G. Rosenman, VISTAnet gigabit testbed,IEEE J. Selected Areas in Communications, vol. 10, no. 9, pp. 1413-1420, Dec. 1992.

atm & bisdn

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