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xDSL Technologies

Access Networks

lectures 2008/09

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Introduction

Some notes and new terms:

- PSTN and Internet

- digital / analog

- frequency bands, bandwidths

- busy time of circuit

- bandwidth, delay, latency

- utilizing of twisted pairs (of metallic networks)

- several forms of DSLs xDSL

- ‘bonded channels’

- statistical multiplexing

- and others – see next pages

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Fig.1 Shared transport of both voice and data

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Fig.2 „Digital – only“ DSL transmission

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Fig.3 History of DSL technology

year

da

ta s

pe

ed

[M

bp

s]

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Fig.4 Review of xDSL technologies

xDSL

HDSLgroup

ADSL group

VDSL PDSL FDSL

standardsHDSLHDSL2

variations:MVLSDSLMDSLIDSL

standardsADSLRADSLG.liteADSL2ADSL2+RE-ADSL2

variations1-MPEG modem

CDSLEZ-DSLeXtremeDSLMAXFasADSL

standards:

VDSL

variations:VDSL2VDSLPlusTotalVDSL

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Tab.1 Review of xDSL technologies and their specifications [3]

NameITU-T standard

Down stream [Mbps]

Up stream [Mbps]

Link code Reach [km] Application

DSL (IDSL)

- 0,128 0,128 2B1Q 6Videoconf., Internet access

HDSL G.991.1 2 2CAP

2B1Q

2-3... 1 pair

4 .......2 pairs

5,5.....3 pairsE1 transmission, LAN interconnection, Frame RelaySDSL - Up to 2,3 Up to 2,3 2B1Q 2 to 5

SHDSL G.991.2 Up to 2,3 Up to 2,3 16 PAM 3 to 6

ADSL Lite G.992.1 Up to 1,5 Up to 0,5 DMT 4 to 7 Internet access

ADSL

R-ADSLG.992.2 1,5 to 8 Up to 1 DMT 3 to 6

Internet access,

Video on Demand

VDSL G.993.113 to 52

or 26

1,5 to 6,4

or 26

QAM

DMT0,3 to 1,5

Multimed.access to Internet, HDTV

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Fig.5 DSL in local loop (splitter = LF filter – it devides off voice channel and reroutes it into PSTN)

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- standard ITU – T I.430, european ETSI ETR 80

Fig. 6 IDSL system

Digital Only

144 kbps Down

144 kbps Up

IDSL (ISDN DSL)

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Specifications of IDSL:

•…

•…

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HDSL group

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HDSL

Fig.7 HDSL time frame for 2-pairs system

data blocks

synchro -group

1st pair

2nd pair

H - HDSL service bits, S - stuffing symbols, Zn – identification bits of both pair and data block

13Fig.8 HDSL transmission principle

2 x3 x

DLL = Dig.Local Line

pairs service channel

Tab. Comparision of 2- and 3-pair HDSL (for unique pair HDSL is vp = 2320 kbps)

User side

HDSL link portion

terminal unit exchange unit

I – application interfaceM – mapping circuitsC – common circuits of link terminationREG – regeneratorH – HDSL transmitter and receiver

14Fig. General reference configuration for xDSL systems [6]

15Fig. HDSL reference model vs. xDSL general reference model [6]

Note: - HDSL can consist of 1, 2 or 3 pc. of H, REG and DLL, in the dependence from data transmission intensity

- REG is not obligatory

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SHDSL

Fig .9 Functional model of SHDSL transmission chain

STU – SHDSL Termination Unit – Remote/Central

PMD- Physical Media Dependent

PMS-TC - Physical Media-Specific TC layer

TPS-TC – Transmission Protocol-Specific ...

SRU – repeater = SHDSL Regenerator Unit

γR , γC –reference points of transport protocol

α, β – ref. point of application

user interfaces

application depence subbloc

application indepence subbloc

application depence subbloc

application indepence subbloc

not obligatory

optional optional

application interface

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Fig.10 Layer reference model

user data interface

transmission medium

link termination

transport layer (e.g. SDH) transport layer (e.g. SDH)

not

spec

ifica

ted

not

spec

ifica

ted

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Fig. SHDSL reference model in the relation to general xDSL ref. model [6]

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Fig.11 SHDSL frame structure

12 user subblocks

Synchr. word

head user data block head head headuser data

blockuser data block

user data block

stuffing bits

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HDSL2

MSDSL

-2nd HDSL generation – not standardized

- foregoer of SHDSL

...self study …

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Other xDSL systems are described in next presentations.

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References

[1] V.Kapoun: Přístupové a transportní síte (Access and Transport networks, czech language). VUT v Brně, 1999.[2] Vaculík: Prístupové siete (Access Networks, slovak l.). ŽU v Žiline, 2000.[3] J. Vodrážka: Přenosové systémy v přístupové síti (Transport Systems in Access Natworks, czech l.). ČVUT, 2003.

[4] T. Anttalainen: Introduction to Telecom. Network Engineering, Norwood (USA - MA), 2003.

[5] L. Harte: Introduction to Digital Subscriber Line (DSL): Technologies, Operation and Systems. ALTHOS, 2005.

[6] Recommendation ITU_T G.995.1