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Access Networks

Lecture 3 - 2008/09 – w.t.

Part 3. : Classification of Access Networks

Lectures

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AN:

- users networks

- hybrid n. (xDSL)

- optical…

- radio communications network

- TV cable distribution system (network)

- power lines communications network

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Exchange

MDF

ED

user distrib.frame

network distr.frame

track distr.frame

Main distribution frame = MDF)

connecting cable

user c. (station line)

network cable

track cable

Obr.3.1 Example of flexible users network [1]

3.1 Users networks (PSTN)

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3.2 Hybrid networks

-partially Cu and partially optical cables = optical feeder + transmission system for Cu-wires pair

Obr. 3.2 Hybrid network architecture

OLT

OLT

ONU

ONU

NT

NT

ODN ADSL

VDSL

Customer

Local exchange (the services node)

SNI UNI

Cu-pairs

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Fig.3.3

- several different xDSL systems – the new systems in original Cu net with different distances (reach, range)

Cable distribution box

End Cable distribution box

Distribution cableMain cableLE

Main Network

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xDSL:

IDSL = ISDN DSL (ISDN-BRA dig. user connection)

HDSL – High bit rate DSL

SDSL – Symmetric DSL (Single line DSL)

VDSL - Very high bit-rate DSL

ADSL – Asymmetric DSL

then: - ADSL 2

- ADSL 2+

- RE-ADSL 2

- RADSL

(DSL = Digital Subscriber Line)

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Fig. 3.4 Telephone access + ADSL system

ADSL

Teleph. network

High speed channel

Control channel

V -interface T - interfaces

Network side Connecting line User side

LP LP

LP – low pass filter

HP – high pass filter

8Fig. 3.5 ADSL system in Cu-connecting lines principle

Telephone netw. /ISDN

User station

Splitter Splitter

e.g. ATM network

PA – Access point

T- interfaces

S- interface

Network interface

Connecting line: basic trunk, e.g. with 10 pairs of Cu wires

connecting line

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ADSL specifications:

- modems on each end of twisted pair....3 information channels, including basic teleph.service (POTS= Plain Old Telephone Service), filters

- modems are consistent with basic frames T1, E1 (see Switching technology)

- downstream speed – depends on : Cu-line length, wire diameters, bridged taps, crosstalks

- Attenuation of line increases with both its length and frequency, decreases with increasing wire diameter (or cross-section)

Data speed [Mbps] Diameter of wires [mm] Distance [km]

1,5 or 2 0,5 5,5

1,5 or 2 0,4 4,6

6,1 0,5 3,7

6,1 0,4 2,7

Tab.3.1 Requested phys. parameters of ADSL lines

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VDSL

Fig. 3.6 VDSL system in hybrid network - architecture

- statistical multiplex: . . .

(see also fig.3.2 and 3.3)

Telephone netw. /ISDN Cable branching

Splitter Splitter

T- interfaces

S- interface

e.g. ATM net

Network interfaces

Cu-connecting line

optical connecting line

User station

300m-500m!

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Name Meaning Data speed Type of connection

Reach Applications

DSL Digital subscriber Line

160kb/s Symmetrical

~5 km ISDN group, voice and data

HDSL High Data Rate Digital Subscriber Line

2Mb/s Symmetrical

4-5km no POTS, E1 LAN/WAN, Service access feeder plant.

SDSL Single Line Digital Subscriber Line

2Mb/s Symmetrical

3-4km Same as HDSL + POTS

ADSL Asymmetric Digital Subscriber Line

1.5 to 8Mb/s Down 128kb-768kb Up

Asymmetrical

3-6km Interest access, video on demand, simplex video, remote LAN access, interactive multimedia.

VDSL Very High Data Rate Digital Subscriber Line

13-52Mbp/s Down 1.5-2.3Mbp/s Up

Asymmetrical

0.3-1.5km Same as ADSL+ HDTV

Tab. 3.2 Comparison of xDSL technologies

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Service lines of ISDN - BRA

- PRA

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ISDN – line – for rarely connecting to the Internet

[2] Fig. llustration of ISDN lines

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Interfaces V5.x for user systems connecting

Fig. 3.7 Architecture of the network with interfaces V5.x

Users ANLocal Exchange

Transit network

V5.x

- interfaces between AN and exchange

- are defined by ETSI and ITU (G.964/965)

- they do not depend on outputs of differents AN types including radiowave AN

- possibility of interconnecting networks of different operators

- differences between V5.1 a V5.2: ... - see next tab.and figure

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Fig. 3.8 Example of architecture of AN with both interfaces V5.x

V 5.1 V 5.2

1 x PCM 30/32 each with 2048 kbps 16 x PCM 30/32 with 2048kbps

It does not have concentration (only 1 line between exchange and AN)

It can concentrate traffic and dynamically allocate time slots for users connecting thousands users

Static allocating of channels Dynamic allocating of channels – protocol BCC

It does not allow connecting ISDN-PRA, only –BRA (15xPOTS+15xISDN,or 30xPOTS)

ISDN-BRA aj -PRA

Signalling without back-up …saving data in the case of failed channel

Access device of AN

Access device of AN

Exchange

channels

channels

Network of ren circuits

16Obr. 3.9 V5.2 interface communications protocol

they support also analogue user lines

- interfaces protocols - see fig.3.9 and 3.10

switching system

control of access network control of access network

Physical layer of access network Physical layer of access network

Analogue user terminals

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Fig.3.10 An example of process of creating and aborting connecting, which was initiated from dig. user line.(by protocol BCC-part od protocol V5.2

from end point of AN – request for dispose communications channel...

-request for disconnect

- data transmission (by onother protocol)

KBPS-TE

Communicatio

ns

process

Access netw. Switching syst.

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Referencie:[1] V.Kapoun: Přístupové a transportní síte. VUT v Brně, 1999.[2] Vaculík: Prístupové siete. ŽU v Žiline, 2000.[3] J. Vodrážka: Přenosové systémy v přístupové síti. ČVUT, 2003.[4] Wikipedia, http://en.wikipedia.org/wiki/Image:Tdma-frame-structure.png#file[5] G.Fairhurst: MAC. http://www.erg.abdn.ac.uk/users/gorry/course/lan-pages/mac.html[6] K.Blunár, Z. Diviš: Telekomunikačné siete, časť IV..- skriptum ŽU v Žiline, 2000.