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Andreas Ißleiber
[email protected]
1
Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen
Results and facts from the ADSL field test in Göttingen
Index:
 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
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Andreas Ißleiber, Gesellschaft
Andreas
für wissenschaftliche
Ißleiber, Gesellschaft
Datenverarbeitung
für wissenschaftliche
Göttingen, Datenverarbeitung
eMail: [email protected]
Göttingen
Fast data-communication on old copper wires
xDSL-Technologies:
 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
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Andreas Ißleiber, Gesellschaft
Andreas
für wissenschaftliche
Ißleiber, Gesellschaft
Datenverarbeitung
für wissenschaftliche
Göttingen, Datenverarbeitung
eMail: [email protected]
Göttingen
Fast data-communication on old copper wires
xDSL Technologies:
xDSL is a general term for the different DSL techniques
The xDSL technologies differ in...
Transfer frequency
System impedances
Signal levels
Modulation methods
Attainable data rate
reachable distance
xDSL-Devices are called simply „modem“
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Andreas Ißleiber, Gesellschaft
Andreas
für wissenschaftliche
Ißleiber, Gesellschaft
Datenverarbeitung
für wissenschaftliche
Göttingen, Datenverarbeitung
eMail: [email protected]
Göttingen
Fast data-communication on old copper wires
HDSL and SDSL:
HDSL...
first generation of xDSL technology
Needs 2 or 3 copper pairs, ADSL needs only one! pair
Used symmetrical transferrates in send- and receive-direction
Data rate: 1,544 Mbit/s or 2,048 Mbit/s
SDSL
the modulation procedure is the same as HDSL
uses only one copper-pair
smaller reachable distance compared with HDSL (distance between user and
provider)
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Andreas Ißleiber, Gesellschaft
Andreas
für wissenschaftliche
Ißleiber, Gesellschaft
Datenverarbeitung
für wissenschaftliche
Göttingen, Datenverarbeitung
eMail: [email protected]
Göttingen
Fast data-communication on old copper wires
ADSL-Technique:
 (A)synchronus (D)igital (S)ubscriber (L)ine
ADSL, 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-pair
Characterized 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
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Andreas Ißleiber, Gesellschaft
Andreas
für wissenschaftliche
Ißleiber, Gesellschaft
Datenverarbeitung
für wissenschaftliche
Göttingen, Datenverarbeitung
eMail: [email protected]
Göttingen
Fast data-communication on old copper wires
VDSL-Technique:
 (V)ery-High-Data-Rate (D)igital (S)ubscriber (L)ine
An ADSL-similar Technologie
Uses the asynchronous transfer mode (see ADSL)
Uses only one copper-pair
depends on the line length, VDSL allows data rates up to 52MBit/s
in downstream direction (low distance: up to a few hundret meters)
VDSL devices are not available today
VDSL uses frequency ranges up to 30MHz, but possible distance is shorter,
compared with ADSL
line qualities and patches extremely limit available bandwidth
Usable for high-speed inhouse connections
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Andreas Ißleiber, Gesellschaft
Andreas
für wissenschaftliche
Ißleiber, Gesellschaft
Datenverarbeitung
für wissenschaftliche
Göttingen, Datenverarbeitung
eMail: [email protected]
Göttingen
xDSL-Data at a glance:
xDSL-Type
Bitrate (Upstream)
Bitrate
(Downstream)
No of pairs
Max. distance
Usable bandwidth
HDSL
1,544 Mbit/s
2,048 Mbit/s
1,544 Mbit/s
2,048 Mbit/s
1 (1,544 Mbit/s)
2 (2,048 Mbit/s)
3-5 km
240kHz
SDSL
1,544 Mbit/s
2,048 Mbit/s
1,544 Mbit/s
2,048 Mbit/s
1
ADSL
16-768 Kbit/s
VDSL
1,5-2,3 Mbit/s
1,5-8 Mbit/s
13-52 Bit/s
1
1
2-3 km
240kHz
2-5,5 km
bis 1,1 MHz
0,3-1,5 km
bis 30MHz
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Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen
Criteria for the selection of suitable ADSL devices
 High attainable bandwidth
 Stable ADSL-Modulationmethods
DMT, Discrete MultiTone
CAP, 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
 Simple integration into our existing network infrastructure
 A central ADSL-Management (SNMP)
 Costs
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Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen
Testing the transferrates, measurement methods
Sniffer
DA-30
Ethernetpacket generator
Receiver/packet counter
Ethernetpackets
from 151 ...1514
Byte
isolated
Ethernet
ADSL
ADSL
100 m pair
0,6mm²
 Ethernet packets with different packet length were transmitted over the ADSL-Line. Thus
collisions (CSMA/CD) can be avoided (isolated Ethernet)
 The ethernet packet size was changed in an range from 64 to 1514 Byte
 The Interframe gap is set to 20µs (constant)
 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]
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Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen
Modulations Methods DMT and CAP
 The ADSL frequency band of approx. 30... 1100 kHz is separated into three different
areas :
– POTS-Splitter (analog telephone)
– Upstreamband
– Downstreamband
CAP
POTS
20Khz 40Khz
 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
DOWN-Stream
UP-Stream
100Khz
1100khz
f
DMT
POTS
20Khz 40Khz
100Khz
1100khz
f
 DMT partitions the frequency ranges in
4 KHz-steps 32 x 4 khz (for upstream) and 256 x 4 khz (for downstream)
 Depend on the line-quality (noise) and frequency range; number of bits, which are
transmitted by using DMT with one channel, may vary
 DMT is much more stable compared to CAP, because it better adjusts to the transfer
characteristic of the copper wires. For this reason DMT improves the bandwidths.
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Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen
Transferrates of the 3COM TCH (Total Control Hub)
Bandbreite[Paketgröße]
Bandwidth Up kbit/s
3COM TCH und Viper DSL
Bandwidth Down kbit/s
3500
3030
3050
3073
3083
3097
3097
1057
1063
1061
1067
1069
1069
3000
2670
2500
Bandwidth [kbps]
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)
With small package size, the
ADSL-System
sends/receives more
packages/s, which „stresses“
clearly the processor of the
ADSL system
The relation between Ethernetoverhead and transfered data
is worse with smaller
packages, however it has no
substantial influence on the
attainable bandwidth
2157
2000
1547
1500
1021
1042
1051
967
1000
920
500
0
0
200
400
600
800
1000
1200
1400
1600
Framesize [byte]
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Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen
Transferrates of the Ericsson ANxDSL
Already with small ethernet
packets, transfer rates of
7MBit/s are achieved
Bandbreite[Paketgröße]
ANxDSL
10000
The upstream rate is
constant and independent of
the ethernet-packet-size
The Upstream rate can be
increased by manual
adjustment of the
UP/DOWN relation. In this
case, downstream rate will
be reduced
8207
8000
7859
7209
6842
7000
Bandwidth [kbps]
The relation between
UP/DOWN-Stream is
adjusted automatically
8720
9000
7109
6668
7444
8214
downstream
6000
4354
5000
4000
3000
upstream
2633
2000
764
764
764
1000
766
767
816
770
766
767
766
761
0
0
200
400
600
800
1000
1200
1400
1600
Framesize [byte]
 With DMT as modulation
method, a higher data
In some cases, the bandwidth can be improved by
transmission rate is attainable tuning the UP/Downstreamvalue manually. If it runs
as experience proves
stable, we can fix this values afterwards
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Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen
Structure and implementation of
the Ericsson-ADSL-Systems
Ethernet
T elefon (analog)
NT
 A SUN Sparcstation acts as Control Processor (CP)
and manages the ADSL-connections
über POTS-Splitter
ADSL-NT
8 Mbit/s
 Another SUN Sparcstation contains the management
system, operates under HP-Openview
0,8 Mbit/s
Zweidraht T elefonleitung
CP
 A central Rack (ANxDSL) contains up to 30 ADSL-Lines (two
lines per slot-card)
ANxDSL, 30 Kanäle
 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
Ethernet
SUN Sparc 5
 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
 Behind the ADSL-NT (Network Terminal), an entire network ! (not only
one PC) can be connected
 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
ST M1 / 155MBit
Management
AT M
ANxMS
HPOV
Ethernet
AT M-Switch
Ethernet/Fastethernet
Internet
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Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen
Inplementation in the University-Network GöNET
 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
 Some institutes were could not connect (for financial reasons), with other media (e.g. LWL,
radio lan, laser)
 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.
 For a connection over ADSL, a leased line without any „switches station“ is necessary
 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)
 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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Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen
Connection of Institutes and Students´ hostel (dormitory) to ADSL
 Bandwidth reducing factors:
– diameter
– Tapering
– Use of line with different
square
– Patches
– Isolation defects
77
12
79
68
55
36
38
72
43
20
43
52
47
36
6000
5000
65
60
65
92
58
24
7000
66
88
67
20
74
56
72
64
79
68
79
68
79
68
78
40
8000
4000
3000
23
04
 A linear dependency between
line length and bandwidth is not
given, because the line qualities
are very different
9000
Bandbreite [kbit/s]
 In Göttingen, lines with
cross sections of 0.4 and
0.6 mm² are used
Down
Up
Bandbreite [Leitungslänge]
2000
1000
6200
5100
3650
3600
3500
3500
3200
2900
2900
2750
2700
2600
2000
2000
2000
1900
1700
800
0
500
 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.
Leitungslänge [m]
Wire, with more than one patches and
different diameters
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Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen
Further extension, Results, Perspectives
-
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 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.
+/- ADSL cannot replace a high(est) speed connection (like ATM, Fastethernet, Gigabit),
but ADSL can be an intermediate solution, until faster connections are available
-
Because of crosstalk(NEXT) and other disturbances, ADSL cannot connect a greater
number of institutes simultaneous on the same cable bundle
+ ADSL is cheaper than other connections like radio lan, laser bridges and mostly
sufficient in such environments
+ 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)
+ 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.
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Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen
More information ...
For further information...
http://www.gwdg.de/adsl
This and other lectures about ADSL...
http://www.gwdg.de/adsl/vortraege
eMail: [email protected]
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Andreas Ißleiber, Gesellschaft
Andreas
für wissenschaftliche
Ißleiber, Gesellschaft
Datenverarbeitung
für wissenschaftliche
Göttingen, Datenverarbeitung
eMail: aisslei@gwdgde
Göttingen