isdn slides day3

8/12/2019 ISDN Slides Day3

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Communication Systems - 3rd

LectureISDN

Chair in Communication Systems

Department of Applied Sciences

University of Freiburg

2010


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11/0/10 2

Communication SystemsPlan for this lecture

!oday "e "ill tal# about

$SD% layers from &hysical to %et"or# layer

'eference points and device groups

(ard"are specification

)*+21 protocol of the data lin# layer

)*+,1 protocol of the net"or# layer

$SD% call setup

-.ercises on net"or# analysis and pac#et inspection


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Communication SystemsLast lecture

'ecapitulate from last lecture

$SD% is a circuit s"itched net"or#

Circuit path bet"een t"o parties reserved for theduration of the call

'eleased upon disconnect

'emember the S$/$S stac#

$SD% implements several layers

&hysical layer implemented eg in '$ and &'$ Data lin# layer in )*+21

%et"or# layer in )*+,1


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Communication SystemsISDN and the OSI protocol stack (mostly D channel)


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Communication Systemsunction !roups " #eference Points

'eference points defining elements and servicedefinitions

LTfunction and the -! function communicatevia the interface

Devices connecting to the S/T3or S4 interfaceinclude $SD% capable telephones and FA5machines6 video teleconferencinge7uipment6 bridge/routers6 and terminaladapters

Uinterface is a t"o8"ire 3single pair4 interfacefrom the phone s"itch6 the same physicalinterface provided for &!S lines


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;!9 ;ine !ermination

(andles termination of 2 "ire pair at the e.change6operating 21) or ,! line coding

!A9 !erminal Adaptor

-7uipment that supports $SD% call set up andprovides an interface for connecting to non $SD%e7uipment


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!-19 !erminal -7uipment 1

!-1 is a device that is $SD%8ready*


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11/0/10 10

Communication SystemsISDN $uildin% &lock

earer channels 3 channels4 and Data channels 3Dchannels4

channels transmit customer bitstreams of any typeli#e video6 voice6 and data

D channel for call8control6 signaling

Channels multiple.ed into a single phyiscal bitstream using time8division multiple.ing 3!D


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Communication SystemsISDN Physical Layer

asic 'ate $nterface

'$ provides a total data rate of 1=0#bit/s

Standard end user connection

2 channels 3>bearer? 8 for data6 digiti@edvoice6 ***4 of =#bit/s each

1 D channel 3data channel for out8of8bandsignaling4 of 1=#bit/s

Synchroni@ation/Stuffing of 1=#bit/s


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Communication Systems'cho cancellation

-cho cancellation is used on '$ circuits becausethere is only a single pair for both transmitting andreceiving information

&'$ circuits do not have this problem because they

run off of either coa.ial cable or t"o coppert"isted pairs6 one pair for transmit and one forreceive

-cho cancellation is designed to remove the signalecho from a circuit so that your e7uipment #no"s

"hat information is being sent to it


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!he echo canceller on the right sends a signale7uivalent to a ,v charge6 and the echo cancelleron the left sends a signal e7uivalent to a B1vcharge*

!o figure out "hat is being sent to it6 the echocanceller on the right ta#es the total voltage ofthe circuit 3B1v B ,v 2v4*

ith the total line voltage #no"n6 the echo cancellerthen applies the voltage of "hat it transmitted6 but

in the opposite polarity9 ,v becomes B,v*

!he final e7uation9 2v B B,v B1v* $t is no" #no"nthat a signal of B1v "as meant for its receiver*


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11/0/10 1

Communication SystemsISDN $asic #ate Interface

&hysical layer specifications of the U#0

perates over t"o8"ire cable up to #m3depending on cable diameter and 7uality4

S"itching center/central office provides a +0

current to po"er the %!A and one device3emergency function to be independent onlocal po"er supply for at least one telephone4

ther physical layer specifications for alternate Uinterfaces


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11/0/10 1=


'$ net"or# termination is defined by the U#0interface

A special encoding 3,!4 is used9 bit digital to ,baud ternary

,! is a Ebloc# codeE that uses 'eturn8to8ero

states

Allo"s reduction of symbol rate to 120 #aud 3Gth4and thus distances up to : #m

'eduction of lo" fre7uencies in the signal spectrum

etter detection of code errors

!hree states9 negative pulse6 no pulse6 positive pulse


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11/0/10 1H


%e.t state 3S1 8 S4 to be transmitted is indicated incolumn labled Io


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11/0/10 1:


Alternate encoding 3e*g* used in the US49 21) 2bit digital to 1 baud 7uaternary representation

21) transmission can be simply described as anamplitude modulation scheme for DC pulses

$nput voltage level can be one of distinct levels

rdering of data bloc#s depends on the encodingused

its )uarternary oltage

00 8, 82*001 81 80*:,

10 B, 2*0

11 B, 0*:,


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11/0/10 1+

Communication SystemsISDN rame ormat

-ach frame 20 bits long For data rate of 1=0 #b/s each frame 1* ms

Frame overhead 8 1= #b/s

D channel 8 1= #b/s

2 channels at = #b/s 8 12: #b/s


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11/0/10 20

Communication SystemsISDN rame ormat

Sync field consists of + )uaternaries 32 bits each4 inthe pattern B, B, 8, 8, 8, B, 8, B, 8,*

1 B 2 B D is 1: bits of data consisting of : bitsfrom the first channel6 : bits from the second

channel6 and 2 bits of D channel data


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11/0/10 21

Communication Systemsk &it streams from s*itchin% center to N+$,

-ach frame consists of 120 ternary steps 2JB1JD ta#es 10: steps in ternary bloc#s 3!4

"ith 2H steps each

Sync channel occupies 11 steps and a

>maintenance? channel 3


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11/0/10 22

Communication Systemsk &it streams from N+$, to s*itchin% center

Connection is full8duple. over the t"o "ires -cho compensation and terminating set is needed

%!A splits the data streams to separate up anddo"n onto the S

0bus

C i i S


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11/0/10 2,


$nstead of the traditional "all soc#et 3analogtelephony4 a %!A 3net"or# terminal baseadapter4 is needed at end users site

%!A provides the S0bus to "hich end user devices

are connected Unidirectional on pair of "ires for each direction

Allo"s up to 12 "all soc#ets6 : $SD% devices 3oranalogous devices via a/b converter4

&rovides device po"er up to 6

C i i S


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11/0/10 2

Communication SystemsISDN S

&rovides the same and D channels as U#0


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11/0/10 2

Communication SystemsS ,-I code


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11/0/10 2=

Communication SystemsISDN Data Link Layer

'elevant for the control channel %o distinct layering for channels

&C< or data directly put into frames as sho"n onprevious slides

;A&D ;in# Access &rocedure on D channel

Derived from (igh8;evel Data ;in# Control &rotocol3(D;C4

roadcasts only for net"or# termination device

D2 frame margin octet of binary pattern9 01111110

C i ti S t


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11/0/10 2H

Communication SystemsData link layer for the D channel

Keeping of frame se7uence -rror discovery


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11/0/10 2:

Communication SystemsLayer . for the D channel

Flag Character is part of the (eader information6

he.adecimal H-

Address is t"o bytes 3octets4 long6 and consists of

up to five fields Service Access &oint $dentifier 3SA&$4

Command/'esponse 3C/'4 bit

Address -.tension 3-A04 bit indicates "hether final

octet of the address or not !erminal -ndpoint $dentifier 3!-$4

Address -.tension 3-A14 bit6 same as -A0

Communication Systems


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11/0/10 2+

Communication SystemsLayer . for the D channel

Control one or t"o octets 3bytes4 in length6 indicatesone of three frame formats

$nformation

Supervisory

Unnumbered

$nformation carries ;ayer , Call Control 3)*+,14 data

$t may carry Unnumbered Informationdata 3!-$assignment4 or 5$D 3Connection


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11/0/10 ,0


Service Access &oint $dentifier 3SA&$4 =8bit fieldidentifying the point "here ;ayer 2 provides aservice to ;ayer ,

SAPI Description

0 Call control procedures1 &ac#et


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11/0/10 ,1


&rotocol handles the !-$ 3!erminal -ndpoint$dentifier4 allocation

All devices on S0using the same bus and have to

be addressable

!-$ assignment started by the connected devicesafter successful initiali@ation of physical layersynchroni@ation

%on automatic assignment uses $D0 =,6automatic = 12=

!here is a special group !-$ 12H

&rotocol elements

$nformationlo"ermost bit is set to 0



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11/0/10 ,2


&rotocol elements Receive Ready 8 3014

Set Asyncronous Balance Mode E.tended 83=F/HF4

Unnumbered Information 8 30,4 Disconnect 8 3,/,4

Unnumbered Ac#no"ledgement 3=,/H,4

Flo" control uses se7uence numbers for sending

and receiving

00:E1:04:00:...

ctets M for sending and M for receiving in theinformation frame



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11/0/10 ,,

Communication SystemsData link layer for the D channel error detection

D channel protocol uses rather sophisticated errordetection protocol

Ienerates frame chec#sums

Ienerator polynom

g(x) = (x +1)(x15+x14+x13+x12+x4+x2+x +1)

g(x) = x16+x12+x5+1

1= bit frame chec#sum

$nverted residue of binary division

p1(x) = xk (x15+x14+...+x2+x +1)

p2(x) = x16d(x)



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11/0/10 ,

Communication SystemsData link layer for the D channel error detection

Chec#ing for added or lost binary @eros !hus cyclic (amming codes implemented

-rror detection for one6 t"o and three bit error



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11/0/10 ,

Communication SystemsLink 'sta&lishment

;ayer 2 establishment process1* !- 3!erminal -ndpoint4 and the %et"or# initially

e.change 'eceive 'eady 3''4 frames6 listeningfor someone to initiate a connection

2* !- sends an Unnumbered $nformation 3U$4 frame"ith a SA&$ of =, 3management procedure6 7uerynet"or#4 and !-$ of 12H 3broadcast4

,* %et"or# assigns an available !-$ 3in the range =812=4



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11/0/10 ,=

Communication SystemsLink 'sta&lishment

;ayer 2 establishment process 3cont*4*!- sends a Set Asynchronous alanced


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11/0/10 ,H

Communication SystemsISDN Net*ork Layer

$SD% %et"or# ;ayer specified by the $!U )8seriesdocuments )*+,0 L +,+

;ayer , used for the establishment6 maintenance6 andtermination of logical net"or# connections bet"een t"odevices



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11/0/10 ,:

Communication SystemsNet*ork layer for the D channel

DSS1 protocol handles the call setup of the callingand called site

Call destruction after finishing the session

'estarting and par#ing if re7uired

-rror handling



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11/0/10 ,+

yDSS/ layer 0 protocol

&rotocol Discriminator &art of the ;ayer , header information

Single byte 3octet4 that is usually set to a value of00001000 3he.adecimal E0:E4 8 meaning )*+,1 callmaintenance

'eference alue consists of either t"o or three bytes3octets4

'$ systems have a H8bit Call 'eference value 312Hreferences4

%o particular end8to8end significance

-ither end can assign an arbitrary value

Used to associate messages "ith a particularlychannelconnection



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11/0/10 0

yDSS/ layer 0 protocol


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11/0/10 1

yDSS/ layer 0 protocol messa%e types


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11/0/10 2

yDSS/ layer 0 protocol information elements

-ach type of message has


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11/0/10 ,

yDSS/ layer 0 protocol information elements

%et"or# Specific Facilities 3Useful for %orthAmerican &'$ calls 8 identifies net"or# type6Carrier $D6 Carrier Service!ypeNA!S/SD%/ASDS6etc*O4

Calling &arty %umber 3caller $D4

Calling &arty %umber sub8address

Called &arty %umber 3destination number6 type ofnumberNun#no"nO6 numbering plan4

Called &arty %umber sub8address

hen $nformation -lements consist of multipleoctets6 the follo"ing octet describes ho" manybytes 3octets4 are in the $nformation -lement



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11/0/10

Layer 0 Call Setup

Follo"ing steps setup an $SD% call1*Caller sends a S-!U& to the S"itch*

2* $f the S-!U& is K6 the s"itch sends a CA;;&'Ceeding to the Caller6 and then a S-!U& tothe 'eceiver*

,*'eceiver gets the S-!U&* $f K6 then rings thephone and sends an A;-'!$%I message to theS"itch

*S"itch for"ards the A;-'!$%I message to the

Caller



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11/0/10

Layer 0 Call Setup

Follo"ing steps setup an $SD% call 3cont*4*hen the receiver ans"ers the call6 is sends a

C%%-C! message to the S"itch

=*S"itch for"ards the C%%-C! message to theCaller

H*Caller sends a C%%-C! ACKno"ledge messageto the S"itch

:*S"itch for"ards the C%%-C! ACK message tothe 'eceiver

+*All DoneP connection no" up



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Practical '1ercise ISDN

y no" completely prepared for $SD% &hysical to%et"or# analysis

;oo# into the pac#ets

'elate actions to pac#ets on the $SD% bus

$dentify different layers ;imited hard"are again

!hus the class is split again Qust changing the t"oe.ercises 32 R ,4 from last Friday

&lease re8seat appropriately

Communication SystemsP i l ' i ISDN


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Practical '1ercise ISDN

ou see the typical users premises installations3basic rate interface '$4 "ith UK0

and S0

connectors in operation

S0

bus can connect up to eight devices

e careful "ith bus setup 3"iring4

-very device >sees? the complete traffic

As# your neighbors for advice 3they might havedealt "ith the tas# already last time4

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