Chapter 9 ATM Networks Why ATM? BISDN Reference Model ATM Layer ATM Adaptation Layer ATM Signaling...

Chapter 9ATM Networks

Why ATM? BISDN Reference Model

ATM LayerATM Adaptation Layer

ATM SignalingPNNI Routing

Classical IP over ATM


Why ATM?

The Integrated Services Vision Initially telephone network all-analog

Transmission & Switching Gradual transition to all-digital core

1960’s: transmission in backbone became digital 1970’s: switching became digital Subscriber loop from customer to network remained analog

Integrated Services Vision: Network should be digital end-to-end Network should support all services: telephone, data, video

Three attempts at achieving Integrated Services Network ISDN in 1980s ATM/BISDN in 1990’s Internet in 2000’s

Basic rate interface (BRI): 2B+D

BRI

PRI

BRI

PRI

Circuit-switched network

Private channel-switched network

Signalingnetwork

Packet-switched networks

Integrated Services Digital Network (ISDN)

Primary rate interface (PRI): 23B+D

ISDN: Integrated access to end-to-end digital communication services through a standard set of user-to-network interfaces

Network consisted of separate networks for voice, data, signaling

B=64 kbpsD=16 kbps

Broadband ISDN

BISDN: A single universal network that is flexible enough to provide all user services in a uniform manner ISDN not enough: Needed 10s to 100s Mbps for LAN

interconnect and for digital TV

Synchronous Transfer Mode (connections at nx64 kbps) was initial candidate for BISDN, but

Asynchronous Transfer Mode (ATM) chosen Multiplexing & switching framework connection-oriented virtual circuits fixed-length packets, “cells”, with short headers

Benefits of ATM Network infrastructure and management simplified

by using a single transfer mode for the network Expected to cover LAN, MAN, and WAN

Extensive bandwidth management capabilities SONET-like grooming capabilities, but at arbitrary

bandwidth granularities

ATM is not limited by speed or distance limitations 50-600 Mbps the sweet spot for ATM

QoS attributes of ATM allow it to carry voice, data, and video thus making it suitable for an integrated services network.

ATM Anticipated Scope All information transferred by network that handles 53-byte cells Scalable in terms of speed Switched approach operates in LAN, MAN, or WAN

ATM fibre backboneWide Area Network (WAN)

ATM fibre backboneWide Area Network (WAN)

supercomputersupercomputer

wirelessinterface

wirelessinterface

multimediaterminal

local areanetwork(LAN)

local areanetwork(LAN)

User informationNetwork header

5 bytes 48 bytes

videoserver

data base

ATMAdaptation

Layer

ATMAdaptation

Layer

ATM Network

Video PacketVoiceVideo PacketVoice

ATM Networking

AAL converts Info into Cells

A/D AAL

Voice

s1 , s2 …

Digital voice samples

cells

AALDataBursty variable-length

packets

cells

A/D AAL

Video

… Compression

compressed frames

picture frames

cells

Connection setup establishes virtual circuit by setting pointers in tables in path across network

All cells for a connection follow the same path Abbreviated header identifies connection Cells queue for transmission at ATM switches & multiplexers Fixed and Variable bit rates possible, negotiated during call set-up Delay and loss performance negotiated prior to connection setup

Cell-Switching – Virtual Circuit

Switches

Cells

Destination

Source

Cells

Cells

Cells

Switch carries out table translation and routing

ATM switches can be implemented using shared memory,shared backplanes, or self-routing multi-stage fabrics

ATM Switching

2

3

N

1

Switch

N

1

5

6

video

video

voice

data

25

32

3261

75

67

39

67

N

1

32

video 75

voice

data

video

……

…

32

25 32

61

39

67

67

1

2

N

1

2

N

Packet traffic multiplexed onto input lines

Demultiplexed at input port

Forwarded to output port

Multiplexing in ATM Switches

Call Admission Control based on Traffic Descriptors & QoS Reqts Cell streams policed at User Network Interface Cell Enqueueing Policy, Cell Transmission Scheduling, Flow

Control Generalized Processor Sharing, Weighted Fair Queueing, etc. Multiplexing Gain Cell Multiplexing implies Delay, Jitter, Loss

VCswith

different TDs&

differentQoS reqts

ATM Support for Multiple QoS Levels


BISDN Reference Model

BISDN Reference Model

User Plane: transfer of user information; flow control; error recovery

Control Plane: setting up, management, and release of connections

Layer Management Plane: management of layer entities & OAM

Plane Management: management of all the planes

Physical Layer

ATM Layer

ATM Adaptation Layer

Higher Layers

User PlaneControl Plane

Management Planes

Layer M

anag

emen

tP

lane M

anag

emen

t

Planes Explained

Three types of logical networks are involved in delivering communication services User Network: transfers user information Control (Signaling) Network: carries signaling

messages to establish, maintain, terminate connections

Management Network: carries management information: monitoring information, alarms and usage statistics

A separate protocol stack, “plane”, is defined for each of these three networks

ATM Adaptation Layer (AAL)

ATM Network Layer

Physical Layer

Higher Layers


ATM Network Layer

Physical Layer

Higher Layers

ATM Network Layer

Physical Layer

USER NETWORK USER

ATM Layered Architecture

ATM Layered ArchitectureATM Adaptation Layer

standard interface to higher layers adaptation functions end-to-end between end systems segmentation into cells and reassembly

ATM Layer Transfer of Cells Cell-Header Generation/Extraction VPI/VCI Translation Cell multiplexing/demultiplexing Flow and congestion control

Physical Layer Cell stream / bit stream conversion Digital transmission


ATM Network Layer

Physical Layer

Higher Layers

ATM Interfaces

X

X

X

X

X

X

X

X

X

Private UNI

Public UNI

NNI

Private NNI

Private ATM

network

Public UNI B-ICI

Public UNIPublic ATM network A

Public ATM network B

UNI: User-Network InterfaceNNI: Network-Network InterfaceB-ICI: Broadband Inter-carrier i/f

The ATM Physical Layer

TC Sublayer: Cell Delineation Header Error Checking Cell Rate Decoupling

(Insertion of Idle Cells) Specific to PMD

PMD Sublayer: Line code Connectors Re-use of existing physical

layer standards

Transmission

convergence sublayer

Physical medium dependent sublayer

Private UNI Physical Layers

UTP = Unshielded twisted pair STP = Shielded twisted pair MMF = Multimode fiber SMF = Single-mode pair

Frame format Bit rate Media

Cell stream 25.6 Mbps UTP-3

STS-1 51.84 Mbps UTP-3

FDDI 100 Mbps MMF

STS-3c, STM-1 155.52 Mbps UTP-3, UTP-5, STP, SMF, MMF coaxial pair

Cell stream 155.52 Mbps MMF, STP

STS-12, STM-4 622.08 Mbps SMF, MMF

Public UNI Physical Layers

Frame format Bit rate Media

DS-1 1.655 Mbps Twisted pair

DS-3 44.736 Mbps Coaxial

STS-3c, STM-1 155.52 Mbps SMF

E-1 2.048 Mbps Twisted pair

Coaxial

E3 34.368 Mbps Coaxial

J2 6.312 Mbps Coaxial


ATM Layer

The ATM Layer

Concerned with sequenced transfer of cells across network connections

ATM Connections Point-to-Point: unidirectional or bidirectional Point-to-Multipoint: unidirectional Permanent Virtual Connections (PVC): long-term

connections to provision bandwidth between endpoints in an ATM network

Switched Virtual Connections (SVC): shorter-term connections established in response to customer requests

Virtual Channel Connections: virtual circuit Virtual Path Connections: bundle of virtual connections ATM Header contains virtual connection information:

8-bit Virtual Path Identifier 16-bit Virtual Channel Identifier

ATM Virtual Connections

Virtual paths

Virtual channels

Why 53 Bytes?

The effect of delay on packet voice influenced selection of cell size

The packetization delay grows with the cell size @64kbps: packetization delay = cell size * 125 sec

If delay is too long, echo cancellation equipment needs to be introduced

Europe has short transmission lines and no echo cancellers so it proposed 32 byte payload

U.S. has long transmission lines and echo cancellers in place, so it proposed 64 byte payload

Compromise: 48 byte payload

The ATM Cell

GFC-undefinedUNI cells has GFC fieldNNI cells allocate these 4 bits to VPI; 4096 VPs

GFC (4 bits) VPI (4 bits)

VPI (4 bits) VCI (4 bits)

VCI (8 bits)

VCI (4 bits) PT (3 bits)CLP

(1 bit)

HEC (8 bits)AT

M c

ell h

eade

r

Payload (48 bytes)

Virtual Path Identifier 8-bits: 256 VC bundles

Virtual Channel Identifier 16 bits: 65,536 VCs/VP

Payload Type Indicator Bit 3: data vs. OAM cell Bit 2: Congestion indication in

data cells Bit 1: Carried transparently end-

to-end; Used in AAL5

Cell Loss Priority if 1, cell can be discarded by

network

Header Error Check

The HEC only covers the 5 bytes of the header to protect against cell misdelivery

Since VPI/VCI changes at every switch, HEC must be recomputed

HEC used for cell delineation Two modes: Header Error Detection / Correction Generating Polynomial: g(x)=x8+ x2+ x+ 1 The pattern 01010101 is XORed to r(x); keeps idle cells

from having HEC=0 and preventing cell delineation The pattern 01010101 is XORed to r(x) in received

header prior to error checking

ATM Permanent Virtual Connections

Operator “manually” sets up VPI/VCI tables at switches and terminals

Long set-up time, long-lived connections

ATMSwitch

ATMSwitch

Operator atNetwork Control Center

ATM Switched Virtual Connections

Terminals and switches use pre-defined VPI/VCI to setup connections dynamically, on-demand

Signalling protocol used to communicate with call-processing system

ATMSwitch

ATMSwitch

Traffic Contract

During connection setup the user and the network negotiate two sets of parameters for a connection

Traffic descriptor: the user specifies the traffic that it will expect the network to transfer on its behalf

QoS requirements: the user specifies the type of network performance that is required by its cells

Traffic Contract The user is expected to conform to traffic descriptor The network is expected to deliver on its QoS

commitments

Quality of Service Parameters

Six QoS parameters are defined Three are intrinsic to network performance and are

not negotiated during connection setup: Cell error ratio: fraction of delivered cells that

contain bit errors Cell mis-insertion ratio: average number of

cells/second that are misdelivered Severely errored cell block ratio: M or more out of N

cells are lost, in error, or misdelivered

Negotiable QoS Parameters

D0 Peak-to-Peak CDVDmax

prob

abili

ty d

ensi

ty o

f ce

ll de

lay

Cell Loss Ratio (CLR): fraction of cells that are lost Determined by buffer priority

Cell Transfer Delay (CTD): negotiate “maximum delay” Dmax: 1- of cells have delay less than Dmax Determined by cell scheduling

Cell Delay Variation (CDV): Peak-to-Peak variation: Dmax-D0

Traffic Descriptors Peak Cell Rate: rate in cells/second that a source

is never allowed to exceed Sustainable Cell Rate: average cell rate produced

by the source over a long time interval Maximum Burst Size: maximum number of

consecutive cells that may be transmitted by a source at the peak cell rate (PCR)

Minimum Cell Rate: minimum average cell rate, in cells per second, that the source is always allowed to send

Cell Delay Variation Tolerance: cell delay variation that must be tolerated for in a given connection.

CBRVBR

real-timeVBR

non-real-timeABR UBR

Cell LossRate

Cell TransferDelay

Cell DelayVariation

TrafficDescriptors

Flow Control

specified

specified

specified

unspecified

unspecified

unspecified

PCR/CDVTPCR/CDVT

SCR/BTPCR/CDVT

& othersPCR/CDVT

no yes no

CBR = Constant Bit RateVBR = Variable Bit RateABR = Available Bit RateUBR = Unspecified Bit Rate

PCR = Peak Cell RateCDVT = Cell Delay Variation Tolerance SCR = Sustainable Cell Rate BT = Burst Tolerance

Cell transfer services provided by ATM Network

ATM Service Categories

Multiplexing & QoS Guarantees

ATM provides per-connection QoS guarantees Many cell flows are multiplexed onto a common stream, so

how are guarantees delivered? CBR: scheduler must ensure transmission opportunities are

regularly available for each connection Real-time VBR: expect some multiplexing gain from

combining VBR flows; however need to meet delay and loss requirements

Non-real-time VBR: can attempt higher multiplexing gains, subject only to loss requirement

UBR: no guarantees, but excellent performance at light traffic ABR: some degree of guarantee: low CLR if source

responds to network feedback; MCR can be negotiated

Traffic Contract & Call Admission Control

Traffic contract: includes the ATM service category, the traffic descriptors, and the QoS requirements

Connection admission control (CAC) determines whether request for a connection should be accepted or rejected Each switch in path must determine whether it can accommodate

new flow and still meet commitments to existing flows; if yes, resources allocated

CAC is not standardized, each operator is free to select own procedures Different degrees of overbooking possible to attain different

multiplexing gains Different types of tariffs for service offerings

Policing, Traffic Shaping, and Congestion Control

QoS guarantees are valid only if the user traffic conforms to the connection contract

Usage parameter control (UPC) is the process of enforcing the traffic agreement at the UNI Generic Cell Rate Algorithm can be used for UPC; related to the leaky-

bucket algorithm Non-conforming cells can be tagged (CLP=1) or dropped

Traffic shaping can be used by source to ensure that its traffic complies to the connection contract Token bucket can be used for shaping

Congestion control CLP=1 cells are dropped first when congestion occurs ABR connections must respond to congestion feedback information that

is received from the network These topics were discussed in Chapter 7


ATM Adaptation Layer

ATM Adaptation Layer AAL: end-to-end protocol to adapt the cell transfer service provided by ATM network to the

requirements of specific application classes Includes conversion to cells and back, and additional adaptation functions, e.g. timing recovery,

reliable transfer ITU defined the following service classes

Class

End-to-End Timing

Bit Rate

ConnectionMode

A B C D

required not required

constant variable

connection-oriented connectionless

Class A = circuit emulationClass B = variable bit-rate videoClass C & D = packet transmission

AAL Protocol Structure

AAL has two sublayers: Segmentation &

Reassembly Segments PDUs into cell

payloads; Reassembles PDUs from received cell payloads

Convergence Common Part: packet framing

and error detection functions required by all AAL users

Specific Part: functions that depend on specific requirements of AAL user classes

ATM

Higher Layers

Segmentation and

Reassembly Sublayer

AAL Layer

Convergence Sublayer

Common Part

Service Specific Convergence

Sublayer

AAL1

Higher layer User data stream

Convergence sublayer

SAR sublayer

ATM layer

CS PDUs

SAR PDUs

ATM Cells

…

47 47 47

1 47 1 47 1 47

H H H

5 48

H

5 48

H

5 48

H

b1 b2 b3

Provides constant bit rate transfer

AAL1

Convergence Sublayer: Adaptation to cell-delay variation, constant bit rate delivery AAL-

SDUs Detection of lost or out-of-sequence cells Source clock recovery Forward error correction on user data Forward error correction on Sequence Number (SN)

1-bit CS to indicate pointer (used for partially-filled cells) 3-bit sequence count

Time-stamp option uses 4 consecutive CS bits for residual TS SAR: Add 1-byte header to 47-byte payload

SN SNP

4 bits 4 bitsPointeroptional

46 or 47 octets

Payload

8 bits

AAL1 services

Structured & Unstructured Transfer Unstructured: take bits from T1 and group into

8-bit bytes; since T1 frame has 193 bits, bytes are never aligned to frame

Structured: take 24 T1 bytes and map into CS PDUs; use CS PDU pointer to indicate beginning of T1 frame

Forward error control options:1. Insert parity cell every 15 cells, correct lost cell2. Interleaving of 124 cells, correct up to 4 cell

losses

SAR PDU header

CS PDU with pointer in structured data transfer

AAL 1 Pointer

1 Byte

CSI SNPSeq. Count

1 bit 3 bit 4 bits

SN SNP

4 bits 4 bitsPointeroptional

46 or 47 octets

Payload

8 bits

AAL1 PDUs

46 Bytes

AAL2

New AAL2 intended for bandwidth-efficient transfer of low-bit rate, short-packet traffic with low-delay requirement

Adds third level of multiplexing to the VP/VC hierarchy of ATM, so low-bit-rate users can share an ATM connection.

AAL 2 ATM cells

Low bit rate Short voice packets

Mobile switching

office

AAL2Higher layer

This example assumes 24 byte packets

Common part convergence

sublayer

SAR sublayer

ATM layer

1 47

5 48

H

P3

Service specific convergence

sublayer

P2P1

Assume null

1 47

3 243 243 24

PAD

5 48

H

Add 3-byte header to each user packet

Segment into SAR PDUs

H H H

CPS packet header

LI (6 bits)PPT

(2 bits)

CID (8 bits)

UUI (3 bits) HEC (5 bits)

Payload

AAL2 Common Part CS PDU

Max length CPCS PDU 64 bytes

Channel ID Identifies user

Length Indicator Payload length – 1

Packet payload type 3: OAM cell ≠3: application cell

User-to-user indication End-to-end info for

application cells End-to-end for AAL mgmt

when OAM cell Error detection

g(x)=x5+x2+1

Start field (STF)

CPS-PDU payload

OSF (6 bits)SN (1 bit)

Cell Header

PAD

P (1 bit)

Packing ATM SDU in AAL2 CPCS PDU’s concatenated, segmented into 48 byte chunks,

and packed into ATM SDU’s ATM SDU format: Offset Field (6 bits)

From end of the field to start of first CPCS PDU or to start of PAD

Max CPCS PDU may span 2 SDUs

Sequence Number 0 or 1

Parity bit PAD

0-47 bytes

AAL3/4 Why 3 / 4 ?

AAL3: For connection-oriented transfer of data AAL4: For connectionless transfer of data

All connectionless packets use the same VPI/VCI at the UNI Multiplexing ID (MID) introduced to distinguish connectionless packets

AAL3 and AAL4 combined into AAL that can be used for connection-oriented or connectionless transfer

AAL3/4 allows multiple users to be multiplexed and interleaved in the same ATM VC Message mode: single user message segmented into ATM

payloads Stream mode: one or more messages segmented into ATM

payloads and delivered without indication of boundaries Assured mode: error-free delivery of messages Non-Assured mode: messages may be delivered in error, or not at

all

Higher layer


sublayer

SAR sublayer

ATM layer


sublayer

Information

Assume null

TPAD

User message

Pad message to multiple of 4 bytes. Add header and trailer.

Each SAR-PDU consists of 2-byte header, 2-byte trailer, and 44-byte payload.

H

4 4

2 44 2 2 44 2 2 44 2

…

…

Information

AAL 3/4

CPI Btag BASize CPCS - PDU Payload

1 1 2 1 - 65,535 0-3 1 1 2 (bytes) (bytes) (bytes)

AL Etag LengthPad

Header Trailer

AAL3/4 Common Part CS PDU

Common Part Indicator How subsequent fields are to

be interpreted Beginning Tag & Ending Tag

Used to match header & trailer at destination

Buffer Allocation size: Buffer size required at destination

Length: of payload PAD: aligns trailer to 32-bit boundary Alignment: byte of 0s to make trailer 32

bits long

User Data

ST SN MID SAR - PDU Payload

2 4 10 44 6 10 (bits)

(bytes) (bits)

LI CRC

Header (2 bytes)

Trailer (2 bytes)

AAL3/4 SAR PDU

Segment Type 10 Beginning of Message 00 Continuation 01 End of Message 11 Single segment Message

Sequence Number Of SAR PDU within CPCS PDU

MID allows SAR sublayer multiplexing Up to 210 AAL users on 1 ATM VC

Length Indicator: size of payload Except for last cell, all cells have LI=44 Last cell has LI = 4 to 44

Each cell payload has 10-bit CRC

Multiplexing in AAL3/4Higher layer Assume two packets

from different users

Common part convergence and SAR sublayers

ATM layer


sublayer

P2P1

Each packet is segmented separately. SAR PDUs identified by MID.

Cells from two packets are interleaved.

Interleaved cells

MID = bMID = a

CPCS SAR

CPCS SAR

Interleaver

SPDUA2

SPDUA1

SPDUB2

SPDUB1

AAL3/4 Overhead

8 bytes added to each message at CPCS sublayer

Each ATM payload has 4 out of 48 bytes additional overhead

9 bytes out of 53 ATM cell bytes overhead Too much overhead! Let to development of AAL5

Higher layer


sublayer

SAR sublayer

ATM layerPTI = 0


sublayer

48 (1)

Information

TPAD

…

…

Information

48 (0)

48 (0)

PTI = 0 PTI = 1

AAL5

Simpler than AAL3/4

48 bytes payload Single packet at

a time per VCI PTI in ATM

header indicates last cell for a given packet

Information

0 - 65,535 0-47 1 1 2 4 (bytes) (bytes)

UU CPI Length CRCPad

AAL5 Common Part CS PDU

User-to-User: 1 byte CPI aligns trailer to 8 bytes Length: 2 bytes to indicate length of CPCS PDU

payload 40-byte CRC

Signaling AAL

AAL standard for BISDN control plane Provides reliable transport for signaling messages

exchanged among endsystems and switches to set up ATM VCs.

SAAL: common part & a service-specific part Service specific part:

service-specific connection-oriented protocol (SSCOP) Service-Specific Coordination Function (SSCF).

SSCF supports the signaling applications (UNI and NNI).

SAAL ProcessSignaling application

SSCF

CSCP and SAR of AAL 5

ATM layer

SSCS

SSCF maps SSCOP service to service required by SSCF user

Message

SSCOP identifies gaps in SDU sequence and requests retransmissions (Selective Repeat ARQ)

AAL 5 provides non-assured service

…

As per AAL 5

SSCOP

Message

Message T

Information

0 - 65,535 0-3 2 2 4 24 (bytes) (bytes)(bits)(bits) (bits) (bits)

PL RSVD PDU SN Type

Pad

SSCOP PDU

Padding: 0-3 bytes Pad Length Indicator Reserved (unassigned) PDU type

Sequenced data message; poll and control messages 24-bit sequence number for large delay-bandwidth product Depends on error detection provided by AAL5

Applications, AALs, and ATM Service Categories

Applications impose requirements Voice, video, connectionless data

AALs provide segmentation & reassembly, and possibly additional adaptation functions AAL1, AAL2, AAL3/4, AAL5, SAAL

ATM service category provides cell transfer with certain QoS attributes CBR, rt-VBR, nrt-VBR, UBR, ABR

Overall system requirements determine what combination of AAL and ATM service category is used

Application Requirements

Feature

transfer granularity

stream message

bit rate constant variable

reliability non-assured assured

accuracy error tolerant error intolerant

delay sensitivity delay/jitter sensitive delay/jitter insensitive

multiplexing single user multiple users

payload efficiency

bandwidth inexpensive

bandwidth expensive

Summary of AAL CapabilitiesSublayer Feature AAL1 AAL2 AAL3/4 AAL5 SAAL

SSCS Forward Error Control optional optional optional optional no

ARQ no no optional optional SSCOP

Timing Recovery optional optional no optional no

CPCS Multiplexing no 8-bit CID 10-bit MID no no

Framing Structure yes no no no no

Message Delimiting no yes yes PTI PTI

Advance Buffer Alloc no no yes no no

User-to-User Indication no 3 bits no 1 byte no

Overhead 0 3 bytes 8 bytes 8 bytes 4 bytes

Padding 0 0 4 bytes 0-44 byte 0-47 byte

Checksum no no no 32 bit 32 bit

Sequence Numbers no no no no 24-bit

SAR Payload/Overhead 46-47 byte 47 bytes 44 bytes 48 bytes 48 bytes

Overhead 1-2 bytes 1 byte 4 bytes 0 bytes 0

Checksum no no 10 bits no no

Timing Information optional no no no no

Sequence Numbers 3-bit 1 bit 4 bit no no

Examples: Voice and Video

Voice AAL1 for individual PCM

voice calls AAL1 with structured

transfer for nx64 kbps AAL2 for low-bit-rate

cellular voice AAL5 for inexpensive

voice

CBR MPEG2 Video Timing recovery at AAL

or at MPEG systems layer?

Error detection & correction at which layer?

Timing recovery at MPEG2 systems level and AAL5 over CBR ATM was selected

Example: ATM & ADSL

IP over PPPoE frames segmented by AAL5 into ATM cells at ADSL modem

ATM cells flow through DSLAM and ATM network to Internet Service Provider

ISP

AD

SL

AT

M

DSL Access Mux

User PremiseCentral Office

TelephoneSwitch Telephone

Network

ATMNetwork

IPPPPoEAAL5ATMADSL

splitter

splitterSubscriber

loop


ATM Signaling

ATM Signaling

Signaling: means for dynamically setting up and releasing virtual connections in ATM

Signaling involves message exchange across: User-Network-Interface Network-Network Interface Broadband Inter-Carrier Interface

Signaling requires: Network addressing framework Protocols

ATM Addressing

Telephony E-164 Addresses For public networks Up to 15-digit E-164 (telephone) numbers In North America, 1-NPA-NXX-ABCD,

ATM End-System Addresses (AESAs) For private networks ISO Network Service Access Point (NSAP) format 20 bytes long Data Country Code (DCC) International Code Designator (ICD) E.164 (contained within the AESA format)

(c) E.164 ATM format

1 3 13 19 20

AFI DCC HO-DSP ESI SEL

IDI

(a) Data Country Code ATM format

Domain Specific Part IDP

1 3 13 19 20

AFI ICD HO-DSP ESI SEL

IDI

(b) International Code Designator ATM format

IDP DSP

1 9 13 19 20

AFI E.164 HO-DSP ESI SEL

Initial Domain Identifier

Initial Domain Part DSP

AESA Address Format

ATM Signaling

Telephone Signaling ISDN signaling (Q.931) used in call setup messages at the

user-network-interface Within the network, ISUP protocol of Signaling System #7

used to establish a connection from a source switch to a destination switch

For ATM, need UNI, NNI, & B-ICI signalling UNI: Q.2931 & ATMF UNI 4.0 NNI: ATMF PNNI based on UNI 4.0 B-ICI based on B-ISUP

UNI 4.0

ATM connections involve many more parameters than narrowband ISDN

Signaling messages carry Information Elements, that describe the user requests

Signaling messages transferred across the UNI using the services of the SAAL layer in the control plane

The signaling cells that are produced by AAL5 use the default virtual channel identified by VPI=0 and VCI=5.

Capability TerminalEquipment

SwitchingSystem

1 Point-to-Point calls M M

2 Point-to-multipoint calls O M

3 Signaling of individual QoS parameters O M

4 Leaf initiated join M M

5 ATM Anycast O O

6 ABR signaling for point-to-point calls O Note 1

7 Generic Identifier transport O O

8 Virtual UNIs O O

9 Switched virtual path (VP) service O O

10 Proxy signaling O O

11 Frame discard O O (Note 2)

12 Traffic parameter negotiation O O

13 Supplementary services - -

13.1 Direct dialing in (DDI) O O

13.2 Multiple subscriber number (MSN) O O

13.3 Calling line identification presentation (CLIP) O O

13.4 Calling line identification restriction (CLIR) O O

13.5 Connected identification presentation (COLP) O O

13.6 Connected line identification restriction (COLR) O O

13.7 Subaddressing (SUB) O Note 3

13.8 User-user siglnaling (UUS) O O

Notes

1 This capability is optional for public networks/switching systems and is mandatory for privatenetworks/switching systems

2 Transport of the Frame Discard indication is Mandatory.

3This capability is mandatory for networks/switching systems (public and private) that supportonly native E.164 address formats.

Capabilities of UNI 4.0

Signaling Messages

Meaning (when sent by host)

Meaning (when sent by network)

SETUP Requests that a call be established

Indicates an incoming call

CALL PROCEEDING

Acknowledges the incoming call

Indicates the call request will be attempted

CONNECT Indicates acceptance of the call

Indicates the call was accepted

CONNECT ACK Acknowledges acceptance of the call

Acknowledges making the call

RELEASE Requests that the call be terminated

Terminates the call

RELEASE ACK Acknowledges releasing the call

Acknowledges releasing the call

Source Destination

SETUP

SETUP

CONNECT

CONNECT

CONNECT ACK

CONNECT ACK

CALL PROCEEDING

CALL PROCEEDING

Network

UNI UNI

RELEASE

RELEASERELEASE COMPLETE

RELEASE COMPLETE

UNI Signaling Example

PNNI Signaling

ATM Forum developed PNNI for use between private ATM switches (Private Network Node

Interface) between group of private ATM switches (Private

Network-to-Network Interface)

PNNI

Network A Network B

PNNI

PNNI Protocols

A routing protocol that provides for the selection of routes that can meet QoS requirements

A signaling protocol for the exchange of messages between switches and between private networks. Based on UNI 4.0 with extensions for:

source routing crankback (a feature of the routing protocol) alternate routing of connection requests in the case of

connection setup failure. Also includes modifications in the Information

Elements to carry routing information.

Source Switch

Transit Switch

Destination Switch

Source A Destination B

SETUPSETUP

SETUPSETUP

CONNECTCONNECT

CONNECT

CONNECT

CONNECT ACKCONNECT ACK

CONNECT ACKCONNECT ACK

CALL PROCEEDINGCALL PROCEEDING

CALL PROCEEDINGCALL PROCEEDING

RELEASE

RELEASE

RELEASE

RELEASE

RELEASE COMPLETE

RELEASE COMPLETE

RELEASE COMPLETE

RELEASE COMPLETE

PNNI Signaling Example


PNNI Routing

PNNI Routing Protocol

A routing protocol for the selection of routes that can meet QoS requirements

For intra-domain and inter-domain routing Link-state approach: each node has network

topology Introduces hierarchy in the ATM network that

provides a switch: Detailed routing information in its immediate vicinity Summary information about distant destinations

PNNI Terminology

Peer Group: collection of nodes that maintain an identical view of the group

Logical Group Node: abstract representation of a peer group at a higher level in the routing hierarchy

Peer Group Leader: node in peer group that executes functions of LGN for the PG Summarizes topology info within the PG Injects summary info into higher order groups and

into the PG

A B

PG(A)

PG(B)

A.1A.2

PG(A.1) PG(A.2)

A.1.1

A.1.2

A.1.3A.2.1

A.2.2

A.2.3 A.2.4

B.1

B.2

B.3

B.4

Peer Group Leader

Logical Link

Physical Link

Logical Group Node

PNNI Routing Hierarchy PGL passes topology summary upward in hierarchy and

downwards to its PG Multiple levels of hierarchy allowed

PNNI Source Routing PNNI source node specifies entire path across its PG using designated

transit list (DTL) Rest of path specified using higher levels in the hierarchy Example: station in A.1.1 requests path to B.3 Path: (A.1.1, A.1.2, A.2, B)

A B

PG(A)

PG(B)

A.1A.2

PG(A.1) PG(A.2)

A.1.1

A.1.2

A.1.3A.2.1

A.2.2

A.2.3 A.2.4

B.1

B.2

B.3

B.4

Peer Group Leader

Logical Link

Logical Group Node

DTL Stacks & Pointers DTLs organized in a stack according to level A pointer indicates current level

From node B.1DTL: [B.1, B.3] pointer-2DTL: [A, B] pointer-1

A B

PG(A)

PG(B)

A.1A.2

PG(A.1) PG(A.2)

A.1.1

A.1.2

A.1.3A.2.1

A.2.2

A.2.3 A.2.4

B.1

B.2

B.3

B.4

From node A.1.1DTL:[A.1.1, A.1.2] pointer-2DTL: [A.1, A.2] pointer-1DTL: [A, B] pointer-1

From node A.1.2DTL: [A.1, A.2] pointer-2DTL: [A, B] pointer-1

From node A.2.1DTL: [A.2.1, A.2.3, A.2.4] pointer-2DTL: [A.1, A.2] pointer-2DTL: [A, B] pointer-1 From node A.2.4

DTL: [A, B] pointer-1

From B.3null

PNNI Features

Call setup involves connection admission control at each node PNNI uses Generic Connection Admission Control

(GCAC) to select path Call request can be blocked from lack of resources

PNNI provides for crankback & alternate routing Upon blocking, call setup is “cranked back” to creator

of DTL, which considers alternate routes from that point onwards


Classical IP over ATM (RFC 2255) IP treats ATM as subnetwork

Logical IP subnetwork (LIS) is part of ATM network that belongs to same IP subnetwork All members of a LIS use same IP address prefix (network

# & subnetwork #) Members in same LIS communicate using ATM VC Each LIS in an ATM network operates independently of

other LIS’s in the same ATM network LIS’s communicate via routers

LIS1LIS2

LIS3 LIS4 LIS5LIS6

ATM network

RouterRouter Router

Router

Router

Logical IP Subnetworks (LIS’s)

Address Resolution Suppose host S want to send packet to host D in

same LIS Host S sends message to ATM ARP server in the LIS,

requesting ATM address corresponding to IP address of host D

(All hosts in LIS know ATM address of ATM ARP server) ATM ARP replies with ATM address, and Host S sets up

ATM connection to Host D If host D is in another LIS, host S sets up ATM

connection to the router in its LIS Router determines next hop router & sets up VC to it Packets between hosts in different LIS’s always use

intermediate routers, even if hosts are in the same ATM network

Chapter 9 ATM Networks Why ATM? BISDN Reference Model ATM Layer ATM Adaptation Layer ATM Signaling...

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Transcript of Chapter 9 ATM Networks Why ATM? BISDN Reference Model ATM Layer ATM Adaptation Layer ATM Signaling...