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1
Access Networks
Lecture 3 - 2008/09 – w.t.
Part 3. : Classification of Access Networks
Lectures
2
AN:
- users networks
- hybrid n. (xDSL)
- optical…
- radio communications network
- TV cable distribution system (network)
- power lines communications network
3
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)
4
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
5
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
6
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)
7
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
9
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
10
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!
11
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
12
Service lines of ISDN - BRA
- PRA
13
ISDN – line – for rarely connecting to the Internet
[2] Fig. llustration of ISDN lines
14
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
15
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
17
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.
18
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.