ITU / CoE DSL Technologies and Services Workshop Cairo, 4-6 March Introduction to DSL Abdelfattah Abuqayyas Coordinator Arab Centre of Excellence ITU BDT DSL Technologies and Services Workshop Cairo, 4-6 March 2003

ITU / CoE DSL Technologies and Services Workshop Cairo, 4-6 March The Issues  The rapid growth of the Internet combined with the increase in computer hardware and software availability to people has placed an increasing demand on the telecommunications providers to supply faster data rates to the home.  ‘Last mile’ connection between exchange buildings and the user of the network services is usually on a pair of copper wires (twisted pair)  DSL technology uses special modulation and encoding methods to achieve broadband speeds over these ordinary telephone copper wires

ITU / CoE DSL Technologies and Services Workshop Cairo, 4-6 March xDSL Definition  xDSL can be defined as the “… dedicated, point-to-point, public network access technologies that allow multiple forms of data, voice, and video to be carried over twisted-pair copper wire on the local loop (‘last mile’) between a network service provider’s central office and the customer site.”  xDSL because of the many variations,  Most xDSL technologies today can be used in addition to a normal telephone or ISDN service.  The main goal of xDSL was and is to provide affordable broadband services for homes and offices.

ITU / CoE DSL Technologies and Services Workshop Cairo, 4-6 March xDSL Overview

ITU / CoE DSL Technologies and Services Workshop Cairo, 4-6 March Asynchronous Digital Subscriber Line ADSL  The most popular variation of DSL is ADSL.  ADSL was developed in 1989 by Bellcore Labs  This technology was intended to permit the local exchange carriers to compete with the cable television companies.  But today the subscriber also wants a broadband Internet access and ADSL meets this requirement, too.

ITU / CoE DSL Technologies and Services Workshop Cairo, 4-6 March ADSL-Distance and Speed  ADSL requires a maximum cable distance of 5.5 Km and provides different download speeds and upload speeds.  Typical rates are T1 or E1 downstream and 176 Kbit/s upstream.  The range and the bit rate depend on each other. Without repeaters downstream bit rates of 2Mbit/s can be transmitted over 4km, 4Mbit/s over 3km and 6Mbit/s over 2km

ITU / CoE DSL Technologies and Services Workshop Cairo, 4-6 March Problems  Although ADSL is being rapidly deployed, there are numerous problems.  frequent outages especially at the limits of the distance, and difficulty determining the availability of ADSL  load coils on the telephone line.  multiple splices between the customer and the CO.  To avoid such problems:  many local telephone companies are systematically eliminating the coils and improving the quality of the splices to permit ADSL.

ITU / CoE DSL Technologies and Services Workshop Cairo, 4-6 March ADSL Principles  ADSL operates by using higher frequencies than those traditionally used in telephone operations (300 Hz to about 4 KHz).  The copper wire is capable of handling higher frequency signals but the signal strength degrades rapidly, hence the distance and splice limitations.  ADSL and ISDN or POTS over the same telephone line

ITU / CoE DSL Technologies and Services Workshop Cairo, 4-6 March ADSL Principles  Each end of an ADSL circuit has a special ADSL modem connected to it.  At the customer site a special splitter is employed to separate the high frequency ADSL signals from the telephone signals.  The ADSL modem uses frequency division multiplexing to break the bandwidth into multiple channels.  These channels are combined into a small upstream band, usually at the lower frequencies, and a large downstream band, usually at the higher frequencies.

ITU / CoE DSL Technologies and Services Workshop Cairo, 4-6 March ADSL Connection

ITU / CoE DSL Technologies and Services Workshop Cairo, 4-6 March Rate Adaptive Digital Subscriber Line (RADSL)  RADSL is very similar to ADSL. The major difference is in its ability to dynamically adjust the transmission speed to compensate for line noise, long distances, and poor splices  This technology allows people just beyond the ADSL distance limitations to get reasonable Internet speeds and reliability. It can provide services at distances up to 7km with speeds of 640 Kbit/s downstream and 128 Kbit/s upstream.  RADSL requires a splitter at the customer site to filter the higher frequency data signals from the voice channel.

ITU / CoE DSL Technologies and Services Workshop Cairo, 4-6 March ADSL-Lite IDSL  ADSL-Lite  ADSL-Lite, also called DSL-Lite and G-Lite, is often called splitter less DSL, it is designed to work without a customer site splitter.  The ADSL-Lite methodology yields lower download and upload speeds.  Typical speeds are 1.5 Mbs download and 512 Kbit/s upload  ISDN Digital Subscriber Line (IDSL)  (IDSL) is DSL over ISDN lines, it does not permit voice traffic, the entire line is dedicated to data.  In many areas ADSL is not available but ISDN is and sometimes IDSL can be purchased after the ISDN line is installed.

ITU / CoE DSL Technologies and Services Workshop Cairo, 4-6 March High Bit-Rate Digital Subscriber Line (HDSL)  HDSL is a variation of DSL technology that requires multiple pairs of wires, but provides fast, symmetric data speeds.  The goal: to replace old T1 or E1 repeatered lines by repeater less systems  The average range is 3 km. 2 twisted pairs for Mbit/s in both directions (USA) twisted pairs for Mbit/s in both directions (Europe)  Some of the popular uses of HDSL include connecting PBX systems, Internet servers, and campus based networks.

ITU / CoE DSL Technologies and Services Workshop Cairo, 4-6 March SDSL, HDSL-2  SDSL - Symmetric single-pair high bit-rate DSL is a form of Digital Subscriber Line similar to HDSL but providing scalable bit rates between 64 kbit/s and 2048 kbit/s over a single twisted-pair copper line.  HDSL-2 is a symmetric technology intended to replace T1 lines and older generation HDSL technology.  HDSL-2 transports data at rates of up to 1.5 Mbit/s over a single pair of copper wires at distances of up to 3650 m.  HDSL-2 supports voice, data, video ATM, private-line T1 service, and frame relay  G.SHDSL, a multiple-rate version promoted by the ITU. It can accommodate line rates from 384 kbit/s to 2.3 Mbit/s off a single line card.

ITU / CoE DSL Technologies and Services Workshop Cairo, 4-6 March Very High Bit-Rate Digital Subscriber Line (VDSL)  VDSL is designed to deliver very high-speed data over short distances utilizing existing copper technologies for the final cable segment.  The cost and effort is significant when using Fiber To The Home (FTTH). As an interim solution, Fiber To The Neighborhood (FTTN) or Fiber To The Basement (FTTB) is implemented. Then high-speed data is transmitted over copper for the remaining distance, often called the home run.  It is intended to deliver broadband services and can be used as a bridge to transport both ATM and SDH carriers in the access network.

ITU / CoE DSL Technologies and Services Workshop Cairo, 4-6 March VDSL  The downstream data rates can reach up to 52 Mbit/s and the upstream data rates up to 26 Mbit/s.  Both data channels will be separated in frequency from bands used for POTS and ISDN, ReachDownstream data rateUpstream data rate 300 m52 Mbit/s6.4 Mbit/s 300 m (S)26 Mbit/s m26 Mbit/s3.2 Mbit/s m (s)13 Mbit/s m13 Mbit/s1.6 Mbit/s

ITU / CoE DSL Technologies and Services Workshop Cairo, 4-6 March xDSL Comparison DSL TypeDistanceUpstream Transmission Rate Downstream Transmission Rate IDSL, ISDN Digital Subscriber Line m128 Kbps HDSL, High Data rate digit. Subsc. Line Up to 4000 m768 Kbps - 1,544 Mbps with 2 twisted-pair lines - 2,048 Mbps with 3 twisted pair lines 768 Kbps - 1,544 Mbps with 2 twisted-pair lines - 2,048 Mbps with 3 twisted pair lines SDSL, Single line Digit. Subsc. Line Up to 3000 m1,544 Mbps with 1 line - 2,048 Mbps with 1 line ADSL, Asymmetric Digit. Subsc. Line Downstream is affected by distance: from 3000 up to 6000 m for decreasing speed From 16 to 640 KbpsFrom 1,5 to 9 Mbps RADS, Rate-Adaptive Digit. Subsc. line mFrom 128 Kbps to 1 Mbps From 600 Kbps to 7 Mbps VDSL, Very high data rate Digit. Subsc. Line From 300 up to 1500 m for decreasing speed From 1,5 to 2,3 MbpsFrom 13 to 52 Mbps

ITU / CoE DSL Technologies and Services Workshop Cairo, 4-6 March Bitrate and reach of xDSL Systems

ITU / CoE DSL Technologies and Services Workshop Cairo, 4-6 March Comparison DSLDial UpISDNT1, E1 Speed DSL offers guaranteed speeds (symmetrical up to 1 Mbit/s or 35 times faster than 28.8 Kbit/s analog modem). and asymmetrical up to 7 Mbit/s). Dial-Up access offers speeds up to a maximum of only 56 Kbit/s ISDN offers guaranteed speeds only up to 128 Kbit/s T 1, E1 is on a dedicated, closed circuit and there- fore provides guaranteed speeds up to 1.54Mbit/s (T1) and M (E1) Flexibility DSL provides Internet access to multiple PCs/ end users on one single connection, thereby not charging extra for all additional PC/end-user DSL is a fully scalable service possessing a wide range of potential speeds Dial-Up access is capable of providing internet access to only one PC/end-user, thereby charging extra for each additional PC/end-user access. Dial-Up access is not a scalable service due to its bandwidth limitations ISDN is not a scalable service; its maximum bandwidth is 128 Kbit/s making it unable to accommodate growing bandwidth demand. T 1, E1 is a fully scalable service; T 1, E1 often times has more growth potential than DSL because it is not distant-sensitive.

ITU / CoE DSL Technologies and Services Workshop Cairo, 4-6 March Comparison DSLDial UpISDNT1, E1 Reliability DSL, by being dedicated, avoids disruptive and time consuming process of dialing in for Internet access.It has a low risk of ownership due to minimal hardware requirements. DSL is distant sensitive. Dial-Up access is faced with the sometimes tedious process of dialing in for Internet access. ISDN has a high risk of ownership due to extensive hardware requirement. T 1, E1 is on a dedicated, closed circuit and therefore receives guaranteed speeds T 1, E1 is not distant sensitive Price DSL is priced on a flat monthly rate with no additional usage/toll charges.It can be cost- effectively divided among multiple end-users for simultaneous access on a single connection. Dial-Up access can have costly per- monthly usage/toll charges in addition to Internet access.access must be provided with individual lines. ISDN can have costly per monthly usage/toll charges in addition to Internet access. T 1, E1 often has costly startup (line and hardware install) and per- monthly fees from line usage charges in addition to bandwidth.

ITU / CoE DSL Technologies and Services Workshop Cairo, 4-6 March Thank You DSL Services and Technologies Workshop Cairo, 4-6 March 2003