High Speed Networks 9

7/29/2019 High Speed Networks 9

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High Speed Networks

Lecture 9Uday Prakash Pethakamsetty

Uday3prakash @gmail.com


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ATM Addressing

Addressing required for unique identification of

the individuals

Process of assigning unique numerical identifiers

to network entities for purpose of locating or

identifying these entities

Popular addressing formats:

E.164 addressto route telephony calls

Internet Addressing255.255.255.255

NSAP addressing--- Based on Service Access Point

2/28/2013 2HSN Dept. of ECE JNTUH CEH


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ATM Addressing

Internet Addressing For identification & message routing

ATM addressing only for establishment of virtual circuits(VPC/VCC pair)

Among Various addressing schemes, ATM end systemaddress (AESA) is based on NSAP format

NSAPNetwork service access point (NSAP)addressing, defined by ISO, based on concept of serviceaccess point (SAP).

The 20 bit AESA or ATM-NSAP address is designedfor use with private ATM networks , while publicnetworks typically continue to use E.164 addresses.



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Classification of ATM Addressing

1) Scope based addressing Based on scope or geographical extent in which a given address is applicable

a) Globally Unique addressing

b) Locally Unique addressing

2) Utility based addressing Based on utility (purpose) that an address serves

a) Locators

b) Identifiers

3) Layer based addressing Based on OSI layers

a) Link layer addressing

b) Network addressing

4) Functionality based addressing Based on the number of entities being addressed

a) Unicast addressing

b) Multicast addressing

c) Broadcast addressing

d) Any-cast addressing



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NSAP addressing

In ATM, the generic NSAP format is of 20 octets.

NSAP is divided into two parts:

Initial Domain Part (IDP)identifies a particular network addressing domain

that is part of global network addressing domain.

AFI-specifies authority controlling the IDI & format of IDI.

IDIIdentifies authority controlling assignment of DSP

Domain Specific Part (DSP)



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NSAP addressing

2/28/2013 HSN Dept. of ECE JNTUH CEH 6


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ATM end system address

(AESA) format

AESA is of four format variants.



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ATM end system address

(AESA) format The last format is Local AESA format which doesnt contain the

IDI.

Local AESA format is used within a private network. Suchaddressing are used when interconnection with other networks is notrequired.

DCC3 bit digital fieldspecifies country to which the address isregistered

ICD4 digit fieldIdentifies an authority responsible for allocation& assignment of values in DSP.

E.164--- 15 digitspecifies ISDN number

ESI- 6 octetsIdentifies end-system

For a particular IDP+HO-DSP, the ESI field is unique.

Selector fieldI octet fieldnot used for routing purpose, used toidentify a protocol within an end-system.



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ATM group addressing

To identify a source, instead of end-system

Used for anycast service

Have different AFI than that used for individual

addresses. Ex: LAN emulation configuration Server (LECS) service

ATM group is formed by one or more ATM end-systems

An ATM end system can enter/leave a group anytimeusing ILMI registration & deregistration procedures.

Group address---called party number



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Acquiring ATM address

Requires permission from appropriate organization

Different AESA format are controlled by differentbodies

ICDcontrolled by British standards institute, onbehalf of 150.

DCC3 digit fieldcontrols by ISO

E.164 controlled by ITU-T Identify interfaces to

ATM service provider networks. Local AESAUsed for private networksNo control or

monitoring.



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ATM Name System

Drawbacks of any numeric addressing scheme isdifficulty in handling both from users point of view(remembering address) and network administratorspoint of view (allocating /updating address)

Similar to DNS; ATM had ATM Name Space (ANS).

ANS maintains mapping between names to ATMaddress & vice Versa.

ANS also facilitates discovering the location of servicesin a switched virtual circuit (SVC) environment.

ANS is based on IETF DNS [RFC 1034]



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ATM architecture


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Virtual paths and virtual circuits


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Virtual circuits

Normally unicast, but one-way Multicasting supported

Unidirectional, but a pair can be created with same ID

Effectively full-duplex

Customers can lease a VP, then allocate VCs within it(Permanent VP)

Types of VCs:

Standard VC (PVC)static route

Soft VCRoute can be changed in event of failure Signaled VC (SVC)Demand connection initiated by user


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VC connection messages


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VC set-up process


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Pre-allotted VCI-VPI numbers


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ATM cell format


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ATM interfaces


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Broadcast inter-carrier interface

Public Network-to-Network

Interface

Based on Broadband ISDN User-Part

(B-ISUP) messages


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NNI interface

Switch to switch interfaceprotocol

Two versions: Public and private

(similar, more flexibility inprivate version)

NNI includes:

Routing protocol (Link-state/OSPF) Signaling protocol for link setup/tear-down


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NNI header fields


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UNI Interface


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UNI header fields


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PTI field codes


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ATM adaptation layer

An impedance matcher between ATM and

higher-level protocols with variable-length cells.


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Service class & ATM adaptation layer

Service classcharacteristics of traffic offered

by an application to the network

Traffics Characteristic Parameters

Bit Rate (CBR or VBR)

Timing Relationship. Ex: voice, ftp

Nature of connection

Connection orientedlow transit delay

Connection less---no end-to-end connection

establishment delay


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Evolution of AALs


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Cell Format


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ATM classes of Services


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ATM QoS


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QoS Parameters

Parameter Meaning

PCR Peak Cell Rate Maximum Rate Required

SCR Sustained Cell Rate Average Rate Required

MCR Minimum Cell Rate Minimum acceptance rate (Used in ABR

service)

CDVT Cell delay variation tolerance Max. acceptable jitter

CLR Cell Loss Ratio Fraction of cells lost or late

CTD Cell Transfer Delay Delivery time (mean and max.)

CDV Cell Delay Variation Measured jitter

CER Cell Error Rate Fraction with one or more errors

SECBR Severely Errored Cell Block Ratio Fraction of M cell blocks with N or more

errored cells

CMR Cell Mis-insertion Rate Fraction delivered to wrong destination

BT Burst Tolerance Max. Burst that can be sent at peak rate


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ATM Adaptation Layer

ATM Adaptation Layer (AAL)

AAL 1

AAL 2

AAL 3 / 4

AAL 5


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AAL 1

Designed to support Class A

traffic (Voice)

Voice has good error tolerance

No bit error control (CRC) needed

Sequence numbers needed to ID

missing cells.


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AAL 1 Convergence Sub-layer

Detect lost cells

Detects mis-delivered (mis-inserted)

cells

Smoothes incoming traffic to minimizejitter

Breaks bit stream into 47 / 46-byte

segments for SAR sub layer

Does not add headers or trailers


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AAL 1 SAR PDU (non-pointer type)

Adds sequence no. With protection

(checksum)

Adds parity bit (even) over header


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AAL 1 SAR PDU (Pointer Type)

Pointer field gives offset to

start of next message (0-92

bytes).


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AAL 2

Designed to support Variable Bit

Rate (BANDWIDTH ON DEMAND)

Provides for partial payloads to

support low-rate data with low

latency

Error protection over full PDU

Simple flag to indicate position

in message.


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AAL 2 SAR PDU


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AAL 3/4

Originally TWO separate AALs:

AAL 3: connection-oriented packet

switched virtual circuits (X.25)

AAL 4: Connectionless switchedvirtual circuits (IP)

Eventually combined into a single

type for all data services Data support overtaken by AAL 5.


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AAL 3/ 4 CS PDU


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AAL 3/ 4 SAR PDU


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AAL 5

Pushed by computer industry as a lower-overhead data

format.

IDEA: Instead of using some of the 48-byte cell payload for

SAR info, steal a bit from the cell to denote end of message.


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AAL 5 CS PDU


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AAL 5 SAR

Simply breaks CS PDU into 48-byte

chunks and passes them to ATM

layer.

No overhead bytes added.


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Traffic Shaping


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IP over ATM connection setup process

One of the applications of ATM


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Multi-protocol Over ATM (MPOA)

Application of ATM

LANE supports a single legacy LAN format over

ATM.

MPOA extends this to multiple LAN types.


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ATM Service Categories

CBR : Constant Bit Rate

rt-VBR : Real-time Variable Bit Rate

nrt-VBR : Non Real-time Variable Bit Rate

UBR : Unspecified Bit Rate

ABR : Available Bit Rate


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ABR

VBR

CBR

Trunk Bandwidth

Feedback from Network

Elastic ABR

traffic

VBR

CBR

ABR

UBR

ATM Service Categories


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Constant Bit Rate (CBR)

Emulates a copper wire or optical fiber (circuit

emulation)

No error checking or processing

Provides reserved bandwidth with minimum cell lossor variation in delay (Jitter)

Suitable for

Voice grade PCM, Real-time audio and video systems,

constant bit rate videos


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Real-time Variable Bit Rate(rt-VBR)

Variable bit rate

Stringent real-time requirements - tight bound ondelay

Acceptable loss rate and jitter are specified

Suitable for

Compressed real-time video (MPEG) and Audio

services


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Non Real-time VBR(nrt-VBR)

VBR with less stringent bound in loss rate, delay

and delay variation Suitable for Multimedia Email and Frame Relay

The loss rate allows for statistical multiplexing


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Unspecified Bit Rate (UBR)

Provides best effort delivery

No guarantee on cell loss or delay variation

Open loop system : no feedback about congestion

UBR is designed to allow use of excess bandwidth


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Unspecified Bit Rate (UBR)

In case of congestion, UBR cells will be dropped

Well suited for TCP/IP packets, non real-time

bursty data traffic


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Available Bit Rate (ABR)

Suitable for Data Traffic

Uses excess network bandwidth

Data traffic is extremely bursty and it can not be

carried using CBR or VBR without disturbing otherconnections

Bandwidth requirements may vary dynamically in

time and resource allocation is not an efficient

solution


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ABR

Based on closed loop feedback mechanism

Reports network congestion

Allows end stations to reduce their transmission rate

to avoid cell loss Ideal for transmitting LAN and other bursty

unpredictable date traffic over ATM networks


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Traffic Descriptors

Peak Cell rate (PCR)

Maximum allowable cell rate on a circuit

Minimum Cell rate (MCR)

the minimum cell rate guaranteed by the serviceprovider


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Traffic Descriptors

Sustainable Cell Rate (SCR)

the expected or required cell rate averaged over a

long time interval

Cell Delay Variation Tolerance (CDVT) variation in cell transmission time

Burst Tolerance (BT)

the limit to which a transmission can run at its Peak

Cell Rate (PCR)


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Quality of Service

Loss Guarantees

Cell Loss Ratio (CLR) : Lost Cell / Total Cells

Delay Guarantees

Cell Transfer Delay (CTD) Cell Delay Variation (CDV)

Rate Guarantees

On PCR, SCR, MCR, and ACR (Actual Cell Rate)


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QoS for Service Classes

CBR

PCR, CTD and CDV, CLR

rt-VBR

SCR, CTD and CDV, CLR

nrt-VBR

SCR, no delay guarantee, CLR


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QoS for Service Classes

ABR

MCR and ACR (Allowed Cell Rate - Dynamically

Controlled)

No delay guarantee, CLR (Network Specific) UBR

No rate guarantees

No delay guarantees

No loss guarantees


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ATM + and -

+ QoS

Multimedia Support

Hardware switching High Speed

Connection-oriented (-?)-

IP support

LAN arena dominated by huge installedEthernet base

Ethernet growing toward MAN, WAN

Connection-oriented (+?)

Living up to the hype of the early 90s


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Summary

User describe Traffic Descriptors for a connection

User can negotiate QoS parameters from the service

provider

Classes of Service : CBR, rt-VBR, nrt-VBR, ABR, andUBR

Date post:	04-Apr-2018
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High Speed Networks 9

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