Andreas Ißleiber aisslei@gwdg.de

1. Andreas Ißleiberaisslei@gwdg.de Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen

2. 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 Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen, eMail: aislei@gwdg.de Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen

3. 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 Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen, eMail: aislei@gwdg.de Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen

4. 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“ Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen, eMail: aislei@gwdg.de Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen

5. 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) Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen, eMail: aislei@gwdg.de Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen

6. 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 Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen, eMail: aislei@gwdg.de Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen

7. 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/sin 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 Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen, eMail: aislei@gwdg.de Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen

8. xDSL-Data at a glance: Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen

9. Criteria for the selection of suitable ADSL devices • High attainable bandwidth • Stable ADSL-ModulationmethodsDMT, 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 Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen

10. Testing the transferrates, measurement methods Sniffer DA-30 Ethernet- Receiver/packet counter packet generator Ethernetpackets from 151 ...1514Byte 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] Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen

11. Modulations Methods DMT and CAP • The ADSL frequency band of approx. 30... 1100 kHz is separated into three different areas : CAP • POTS-Splitter (analog telephone) • Upstreamband • Downstreamband f • DMT and CAP works with „Rate Adaption“ , which can automatically adapts to the different line qualities DMT • DMT uses smaller gradations than CAP (32 KBit/s by DMT) (300 KBit/s by CAP) and can better react to changing line qualities 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. Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen

12. 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). 3COM TCH und Viper DSL • 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 Ethernet-overhead and transfered data is worse with smaller packages, however it has no substantial influence on the attainable bandwidth Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen

13. Transferrates of the Ericsson ANxDSL • Already with small ethernet packets, transfer rates of 7MBit/s are achieved ANxDSL • The upstream rate is constant and independent of the ethernet-packet-size • The relation between UP/DOWN-Stream is adjusted automatically downstream • The Upstream rate can be increased by manual adjustment of the UP/DOWN relation. In this case, downstream rate will be reduced upstream • With DMT as modulation method, a higher data transmission rate is attainable as experience proves • In some cases, the bandwidth can be improved by tuning the UP/Downstreamvalue manually. If it runs stable, we can fix this values afterwards Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen

14. Structure and implementation of the Ericsson-ADSL-Systems Ethernet NT • A SUN Sparcstation acts as Control Processor (CP) and manages the ADSL-connections über POTS-Splitter 8 Mbit/s 0,8 Mbit/s • Another SUN Sparcstation contains the management system, operates under HP-Openview • A central Rack (ANxDSL) contains up to 30 ADSL-Lines (two lines per slot-card) • 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 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 Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen

15. 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 Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen

16. Connection of Institutes and Students´ hostel (dormitory) to ADSL • Bandwidth reducing factors: • diameter • Tapering • Use of line with different square • Patches • Isolation defects • In Göttingen, lines with cross sections of 0.4 and 0.6 mm² are used • A linear dependency between line length and bandwidth is not given, because the line qualities are very different • 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. Wire, with more than one patches and different diameters Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen

17. 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. Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen

18. More information ... For further information... http://www.gwdg.de/adsl This and other lectures about ADSL... http://www.gwdg.de/adsl/vortraege eMail: aisslei@gwdg.de Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen, eMail: aisslei@gwdgde Andreas Ißleiber, Gesellschaft für wissenschaftliche Datenverarbeitung Göttingen