1 Andreas Ißleiber [email protected] Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen

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Andreas IßleiberAndreas Iß[email protected]@gwdg.de

Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen

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Results and facts from the ADSL field test in Göttingen Results and facts from the ADSL field test in Göttingen

Characteristics of the xDSL Technologies Overview of the different xDSL Technologies Criteria for suitable ADSL-Devices Measurements of bandwidth, measuring methods Modulation methods DMT vs. CAP Structure of the Ericsson ADSL-System Integration in our existing Network, called GöNET (University Network) Connection of Institutes and Students´ hostel (dormitory) to ADSL Perspectives, Results, Interoperabiliy, future plans

Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen, eMail: [email protected]

Index:


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Fast data-communication on old copper wiresFast data-communication on old copper wires

The DSL-Technologie was introduced for the first time at the end of the 80's by Bell core in the USA

So far only the frequency range between 3-4Khz in the telephone network was used for data transmission

Because of signal-to-noise ratio (S/N) in the telephone network, usable bandwidth confined to approx. 30-35 Kbit/s, (see V.34 Modems)

By reduction the (S/N-ratio), the bandwidth in one direction can be improved (see 56 Kbit/s modem technology, downstream).

The idea at that time was to use the higher frequency range for the digital data communication

Copper line, usually installed nowadays in telecommunication networks, can deliver higher bandwidths than 30-35 kbps

Telephone-switching-centers reduce substantially the bandwidth a direct connection between both ends is necessary for an ADSL operation (leased

lines, no bandwidth-limiting switching centers) Better modulation techniques combined with higher frequency range can clearly

improve the data rates


xDSL-Technologies:


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xDSL is a general term for the different DSL techniques

The xDSL technologies differ in...

Transfer frequency System impedances Signal levels Modulation methodsAttainable data rate reachable distance

xDSL-Devices are called simply „modem“


xDSL Technologies:


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HDSL...

first generation of xDSL technology Needs 2 or 3 copper pairs, ADSL needs only one! pairUsed symmetrical transferrates in send- and receive-directionData rate: 1,544 Mbit/s or 2,048 Mbit/s

SDSL

the modulation procedure is the same as HDSLuses only one copper-pairsmaller reachable distance compared with HDSL (distance between user and provider)


HDSL and SDSL:


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(A)synchronus (D)igital (S)ubscriber (L)ineADSL, is an improvement of the HDSL technique Very promising technique, good relationship between bandwidth and reachable distance Defined in ANSI Standard (ANSI: T1.413)Uses only one copper-pairCharacterized by the typical asynchronous data transmission rates matches to the typical internet-user behavior, because..

high datarate from provider to user up to 8 Mbit/s (Downstream) a lower datarate of 0,8Mbit/s from user to the provider (Upstream)

Adaptive modulation procedure, which automatically (dynamically) adapts to different line qualities


ADSL-Technique:


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(V)ery-High-Data-Rate (D)igital (S)ubscriber (L)ineAn ADSL-similar TechnologieUses the asynchronous transfer mode (see ADSL)Uses only one copper-pairdepends on the line length, VDSL allows data rates up to 52MBit/sin downstream direction (low distance: up to a few hundret meters)VDSL devices are not available todayVDSL uses frequency ranges up to 30MHz, but possible distance is shorter, compared with ADSL line qualities and patches extremely limit available bandwidthUsable for high-speed inhouse connections


VDSL-Technique:


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xDSL-Data at a glance:xDSL-Data at a glance:


xDSL-Type HDSL SDSL ADSL VDSL Bitrate (Upstream) 1,544 Mbit/s

2,048 Mbit/s 1,544 Mbit/s 2,048 Mbit/s

16-768 Kbit/s 1,5-2,3 Mbit/s

Bitrate (Downstream)

1,544 Mbit/s 2,048 Mbit/s

1,544 Mbit/s 2,048 Mbit/s

1,5-8 Mbit/s 13-52 Bit/s

No of pairs 1 (1,544 Mbit/s) 2 (2,048 Mbit/s)

1 1 1

Max. distance 3-5 km 2-3 km 2-5,5 km 0,3-1,5 km Usable bandwidth 240kHz 240kHz bis 1,1 MHz bis 30MHz

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Criteria for the selection of suitable ADSL devices Criteria for the selection of suitable ADSL devices

High attainable bandwidth Stable ADSL-Modulationmethods

DMT, Discrete MultiToneCAP, Carrierless Amplitude/Phase Modulation

Large bridgeable distance High availability compared with analog modem connections High stability Ability to connect entire networks over ADSL to the university backbone Simple integration into our existing network infrastructure A central ADSL-Management (SNMP) Costs


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Testing the transferrates, measurement methodsTesting the transferrates, measurement methods

ADSL ADSL

SnifferEthernet-

packet generator

DA-30Receiver/packet counter

100 m pair

0,6mm²

isolated Ethernet

Ethernetpacketsfrom 151 ...1514Byte

Ethernet packets with different packet length were transmitted over the ADSL-Line. Thus collisions (CSMA/CD) can be avoided (isolated Ethernet)

The recipient (DA30) counted the incomming ethernet packets per second The measurement was made in UP- and DOWN-Streamdirection The result shows the max. transfer rate in [bits/s]

The ethernet packet size was changed in an range from 64 to 1514 Byte The Interframe gap is set to 20µs (constant)


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DMT is much more stable compared to CAP, because it better adjusts to the transfer characteristic of the copper wireswires. For this reason DMT improves the bandwidths.

DMT and CAP works with „Rate Adaption“ , which can automatically adapts to the different line qualities

DMT uses smaller gradations than CAP (32 KBit/s by DMT) (300 KBit/s by CAP) and can better react to changing line qualities

Modulations Methods DMT and CAPModulations Methods DMT and CAP

Depend on the line-quality (noise) and frequency range; number of bits, which are transmitted by using DMT with one channel, may vary

– POTS-Splitter (analog telephone)– Upstreamband– Downstreamband

DMT partitions the frequency ranges in 4 KHz-steps 32 x 4 khz (for upstream) and 256 x 4 khz (for downstream)

20Khz

PO TS UP-Stre am DOWN-Stre am

40Khz 100Khz 1100khz

20Khz

PO TS

40Khz 100Khz 1100khz

CAPCAP

DMTDMT

f

f


The ADSL frequency band of approx. 30... 1100 kHz is separated into three different areas :

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Bandbreite[Paketgröße]

309730973083307330503030

2670

2157

1547

920

9671021 1042 1051 1057 1063 1061 1067 1069 1069

0

500

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Framesize [byte]

Ban

dw

idth

[kb

ps]

Bandwidth Up kbit/s

Bandwidth Down kbit/s

Transferrates of the 3COM TCH (Total Control Hub)Transferrates of the 3COM TCH (Total Control Hub)Because of the used

modulation method (CAP) , the TCH in our test lab environment has a max. data rate of only 3 MBit/s (downstream).

The ethernet packet size has an influence on the max. data rate (low processor performance)

The relation between Ethernet-overhead and transfered data is worse with smaller packages, however it has no substantial influence on the attainable bandwidth

With small package size, the ADSL-System sends/receives more packages/s, which „stresses“ clearly the processor of the ADSL system

3COM TCH und Viper DSL


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Transferrates of the Ericsson ANxDSLTransferrates of the Ericsson ANxDSL

Bandbreite[Paketgröße]

8214

761

74447109

78598207

8720

666868427209

4354

2633

764764 764 766 767 816 766 770 767 766

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 200 400 600 800 1000 1200 1400 1600

Framesize [byte]

Ban

dw

idth

[kb

ps]

The relation between UP/DOWN-Stream is adjusted automatically

The Upstream rate can be increased by manual adjustment of the UP/DOWN relation. In this case, downstream rate will be reduced

Already with small ethernet packets, transfer rates of 7MBit/s are achieved

The upstream rate is constant and independent of the ethernet-packet-size

With DMT as modulation method, a higher data transmission rate is attainable

as experience proves

downstream

upstream

ANxDSL


In some cases, the bandwidth can be improved by tuning the UP/Downstreamvalue manually. If it runs stable, we can fix this values afterwards

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Structure and implementation of Structure and implementation of the Ericsson-ADSL-Systemsthe Ericsson-ADSL-Systems

ANxMS HPOV

ADSL-NT

Ethernet/Fastethernet

ATM-Switch

ANxDSL, 30 Kanäle

CP

Ethernet

Ethernet

Telefon (analog)

Zweidraht Telefonleitung

Management

STM1 / 155MBit

Internet

ATM

SUN Sparc 5

über POTS-Splitter

Ethernet

Behind the ADSL-NT (Network Terminal), an entire network ! (not only one PC) can be connected

A SUN Sparcstation acts as Control Processor (CP) and manages the ADSL-connections

Another SUN Sparcstation contains the management system, operates under HP-Openview

The connection to the backbone network is made by the ANxDSL system via STM1 over an ATM-SWITCH (which can make RFC1483 conforming connections) to the Ethernet

The NT operates as bridge, protocolls other than TCP/IP will be transfered (e.g. IPX/SPX)

For each ADSL connection, a " PVC „-call must be created

In this case, the use of an ethernet switch ist necessary to separate the local ethernet traffic from the adsl network

1. RFC 1483: Multiprotocol Encapsulation over ATM Adaption Layer 5

On the user side an ADSL-NT (called Network Terminal) will be used. The NT has one ATM-Port, one Ethernet port (RJ45), as well as a simple telephone port, separated by a POTS-Splitter

NT

8 Mbit/s 0,8 Mbit/s

A central Rack (ANxDSL) contains up to 30 ADSL-Lines (two lines per slot-card)


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Inplementation in the University-Network GöNETInplementation in the University-Network GöNET

So far 33 buildings were successfully connected to the GöNET over ADSL. Most of it had no link before, or only insufficient connections with dial modems.

The max. bandwidth is good enough for an Internet access today

The institutes feel the Internet access over ADSL-lines as stable and very fast compared with older connection technologies like modems

Each ADSL connection can be done within 10 minutes (..10 Minuten to make the ATM cross-connection in the management system)

The University of Goettingen has its own extended telephone network, which is an ideal prerequisite for the use of a central ADSL system like Ericsson´s ANxDSL

For a connection over ADSL, a leased line without any „switches station“ is necessary

Some institutes were could not connect (for financial reasons), with other media (e.g. LWL, radio lan, laser)


Some institutes/student´s hostels are connected over Telekom lines

The data rates with Telekom lines are, because of different line lengths, smaller compared with the GÖNET internal lines, but good enough for basic internet access

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Connection of Institutes and Students´ hostel (dormitory) to ADSL

Bandwidth reducing factors: Bandbreite [Leitungslänge]

7840

4352

7968

7968

7968

7456

7264

6720

7968

7712

6688

5824

6560 65

92

4736

4320

5536

3872

2304

0

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6200

Leitungslänge [m]

Ba

nd

bre

ite

[kb

it/s

]

DownUp

– diameter– Tapering – Use of line with different

square– Patches– Isolation defects

A linear dependency between line length and bandwidth is not given, because the line qualities are very different

In Göttingen, lines with cross sections of 0.4 and 0.6 mm² are used

Wire, with more than one patches and different diameters


In two cases, we had connection problems, because both lines were bundled in one large cable. The reason for this instable connection was crosstalk between both lines.

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- Interoperability : ADSL-Devices from different manufacturers are not compatible. ADSL from 3COM and Ericsson or Ascend normally don´t work together, 3COM offers a compatible NT unit.

+/- ADSL cannot replace a high(est) speed connection (like ATM, Fastethernet, Gigabit), but ADSL can be an intermediate solution, until faster connections are available

Further extension, Results, PerspectivesFurther extension, Results, Perspectives

+ ADSL is cheaper than other connections like radio lan, laser bridges and mostly sufficient in such environments

+ Because of the positive experiences and the demand of the institutes, the ADSL system in Goettingen was extended in 1999 by further 30 (if necessary 60) channels. If necessary, we will get the next ADSL-rack containing further 30 channels.

+ Today, we have 58 channels, 33 of it are in use. The last 25 channels will be connected in the next few weeks.

+ The bit rates, which the ADSL management displays, can be achieved in normal use. With FTP, the transfer rates over ADSL are usually 5%..10% below the values given by the management (gross values)

- ADSL is not the best solution for institutes, which need very fast connections to the Universitynetwork, because of the different up/downstremrates. Some customers (e.g. in Göttingen -> Geophysics) need to transfer large data to the GWDG-parallel computer IBM SP2.


- Because of crosstalk(NEXT) and other disturbances, ADSL cannot connect a greater number of institutes simultaneous on the same cable bundle

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More information ...More information ...

http://www.gwdg.de/adsl/vortraege

This and other lectures about ADSL...

For further information...

http://www.gwdg.de/adsl

Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen, eMail: aisslei@gwdgde

eMail: [email protected]


Documents

1 Andreas Ißleiber [email protected] Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen