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