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  1. 1. ASYMMETRIC DIGITAL SUBSCRIBER LINE A Project Report Presented To Mr. Fahrul Hakim Ayob Communications Technology and Networking Department Faculty of Computer Science and Information Technology University Putra Malaysia In Partial Fulfillment Of the Requirements for Advanced Computer Network (SAK5306) Course Subject For the Degree of Master By Che Rohani Bt. Ishak (GS12895) Saifuddin Bin Samsuddin (GS09785) Siti Ruzaimah Bt. Ghazali (GS12557) Tengku Mohd Dzaraif Bin Raja Abdul Kadir (GS10805) August 2003 1
  2. 2. TABLE OF CONTENT Page 1.0 Introduction 3 2.0 History of ADSL 5 3.0 ADSL Technology 6 3.1 System Architecture 7 3.1.1 System Reference Model 11 3.2 Modulation Technique 12 3.3 Different Types of ADSL 13 3.3.1 Full-Rate ADSL 13 3.3.2 G-Lite ADSL 13 3.4 Bandwidth 14 3.5 Connectors and Wiring Diagram 16 3.5.1 Connector Types 16 3.5.2 Wiring Diagram 18 4.0 Benefit 23 5.0 Problem 24 - Copper Loop Quality 24 6.0 Conclusion 25 Glossary 26 References 29 2
  3. 3. 1. INTRODUCTION Internet has become the most important tool in everyone life and it had changed the way of lives for communication and interaction between family and friends. New real-time applications such as video conferencing, peer to peer or multimedia communications require high bandwidth to allow smooth transmission of voice and video. The slant toward such multimedia traffic has far outstripped the capacity of the current consumer-level solutions for Internet access such as high-speed modems and ISDN (Integrated Services Digital Network). There are several high-speeds or broadband solutions have been introduced to extend the high-speed network solutions up to customer premise/home. These solutions included cable modems, satellite communications, UHF communications (Ultra High Frequency) and also DSL solutions (Digital Subscriber Line). Cable modems feature a very high bandwidth, up to 30Mbps; however, a key restriction is that this bandwidth is shared by as many as 500 to 2000 users connected to the same cable line. During times of congestion, users may see significant degradation in performance. For satellite or UHF communications (cable TV communications) the network is geared toward delivery only, one-way communication and it will require support from other connection for the uplink connection. These solutions are quite costing and required a new infrastructure. This paper will focus on ADSL (Asymmetric Digital Subscriber Line), a new broadband communication technology that creates high-speed access to the Internet and remote networks using the ordinary phone lines present in your home. This exciting technology not only helps to overcome the bandwidth limitation to customer but also save the cost since it is just using the existing infrastructure i.e. two wire telephone lines. It is seen to manipulate broadband markets where it will provide connection to almost every home user. 3
  4. 4. To date there are many forms of DSL. A few of the forms that are currently in use or development around the world are listed here: Service Downstream Upstream ADSL Asymmetric DSL 2M to 384k 256k to 128k HDSL High-bit-rate DSL 1.5M 1.5M SDSL Single-line DSL 1.5M 1.5M VDSL Very-High DSL 13M to 52M 1.5M to 2.3M IDSL ISDN DSL 144k 144k RADSL Rate Adaptive DSL 512k 278k UDSL Universal DSL 1M to 384k 384k to 128k Table 1 4
  5. 5. 2. HISTORY OF ADSL The evolution of the ADSL technology has been started since the year 1985 and it is predicted that ADSL will continue to increase and manipulate the world broadband market (refer to Figure 1).  1985 - Bell Labs discovers a new way to make traditional copper wires support new digital services - especially video-on-demand  1990 - Phone companies start deploying High-Speed DSL (HDSL) to offer T1 service on copper lines without the expense of installing repeaters - first between small exchanges. Phone companies begin to promote HDSL for smaller and smaller companies and ADSL for home Internet access.  1995 - Innovative companies begin to see ADSL as a way to meet the need for faster Internet access  1998 - DMT was adopted by almost all vendors following ANSI T1.413 - issue 2  1999 - ITU-T produced UADSL G.992.2 (G.lite) and G.922.1 (G.full) 5
  6. 6. Figure 2: Broadband Communications Evolution 3. ADSL TECHNOLOGY ADSL is asymmetrical, which means it provides higher transmission rates in the downstream transmission than the upstream transmission. Although this asymmetry sound unusual for a data transmission scheme, it is actually well suited to typical client network traffic, where they send smaller data and expect to receive voluminous data from the Internet (based on the web applications). ADSL refers to a modulation scheme used to deliver network traffic to a customer's residence using the same copper twisted-pair wiring used for voice and ISDN service. It coexists with both services, while offering 6 to 8Mbps speeds downstream and up to 640kbps upstream. ADSL divides available bandwidth of a single copper-loop is into three parts. See Figure 2. The first band normally between 0 and 25KHz, is used for normal telephone communications in the 0 to 4 kHz range; whilst the rest is used to as a guard band to separate voice from data channel. The second band, between 25 to 200KHz is used for upstream communication. The third band will use 200KHz to 1MHz band for the downstream communication. 6
  7. 7. Figure 2: Frequency Spectrum of ADSL 3.1 SYSTEM ARCHITECTURE The ADSL Forum develops technical guidelines for architectures, interfaces, and protocols for telecommunications networks incorporating ADSL transceivers. The overall network diagram below describes the network elements incorporated in multimedia communications, shows the scope of the Forum's work, and suggests a group of transport configurations ADSL will encounter as networks migrate from Synchronous Transfer Mode (STM) to Asynchronous Transfer Mode (ATM). At the consumer end, a remote ADSL Transceiver Unit (ATU-R) is placed at the customer’s site and configured as needed to support voice, data and video. If the location 7
  8. 8. is a high-rise building with multiple offices and apartments, or a campus with various data needs, the ATU-R can be equipped with additional functionality such as bridging, routing or multiplexing. At the exchange end, a Digital Subscriber Line Access Multiplexer (DSLAM) and ADSL Transceiver Unit (ATU-C) is installed. A single DSLAM can handle and route traffic from multiple ATU-R installations, keeping the cost low because it is shared among all service users. The existing telecommunications network then carries the data to the destination, such as a branch office, again going through a DSLAM and ATU-R at the receiving end. This is depicted in Figure 4. A key characteristic of ADSL modems compared to traditional modems is that the modems must be physically connected by the copper loop, rather than at either end of a switched telephone connection; thus, one modem must usually reside at the telephone company's switching station, and the other in the user's residence. 8
  9. 9. Figure 3: Home Connectivity Using ADSL For Video-On-Demand applications, MPEG-compressed video streams typically require 1.5Mbps of bandwidth for VHS quality. Thus, as many as four video streams can be delivered simultaneously over an ADSL link, or one broadcast-quality 6Mbps MPEG-2 stream. The video can then be decoded using a set-top box. (Veeneman, 838) Once in the home, ADSL traffic can potentially be carried over the existing phone wires. One proposal suggests a multi-carrier modulation system using the bandwidth available over 1.5MHz (Chow, 456). This system would allow multiple computers and set-top boxes to share the single ADSL transceiver, as well as continue to allow use of POTS. 9
  10. 10. Network traffic can be transmitted using a variety of methods--ATM has been fingered as a possible protocol, especially with respect to the transmission of real-time traffic such as video and voice. For this reason, ADSL supports transmission rates compatible with ATM. 10
  11. 11. 3.1.1 SYSTEM REFERENCE MODEL ADSL System reference model describes the basic blocks of an ADSL-system. The decomposed and routed data from the access module, is connected to an ATU-C (ADSL Transceiver Unit - Central Office) in which the data will be converted into analog signals. The analog signals are then carried with POTS signals to remote end. ATU-C also receives and decodes data coming from customers premises send by ATU-R (remote). The splitter either combines or separates the signals depending on the direction of the transmission. It protects MTS from voice-band interference generated by both ATU's and on the other hand it protects ATU's from MTS-related signals. 11
  12. 12. 3.2 MODULATION TECHNIQUES Most of the ADSL implementation originally using carrierless Amplitude/phase (CAP) but later Discrete Multitone (DMT) is used due to its higher throughput and greater resistance to adverse line conditions. It effectively compensates for widely varying line noise conditions and quality levels CAP is a modulation technique that is similar to QAM but the carrier signal is eliminated. The technique is more complex than QAM and has not been standardized. DMT combines QAM and FDM and this technique were standardized by ANSI. 12
  13. 13. 3.3 DIFFERENT TYPES OF ADSL 3.3.1 Full-rate ADSL i. Full-rate ADSL boasts data rates ranging from 1.5 to 8 Megabits per second “downstream” from the Internet to your computer ii. “Upstream” data rates from your computer to the Internet are as high as 1 Mbps iii. Potential data rates decrease with increased distance from the phone company’s CO (central office) iv. Costs for the service are more expensive than the new, lower data rate “G.Lite” ADSL 3.3.2 G-Lite ADSL i. G.Lite ADSL is a scaled-down version that delivers up to 1.5 Mbps downstream and 384 Kbps up ii. Service providers will offer slower rates for lower prices iii. Less expensive than full-rate ADSL iv. Easier to install Full-rate ADSL requires a splitter, to be installed on your phone line where it enters your home in order to separate the voice service from the data service. Whereas G.Lite ADSL will not usually require a splitter, although some homes with problematic wiring or certain types of telephones will require one. 13
  14. 14. 3.4 BANDWIDTH There are ten classes for ADSL transmission speeds. Classes 1-4 were developed with multiple channels of digital video as the primary application, and feature only low- speed upstream channels used for control and signaling. Classes 5-10 reflect the data- aware ADSL speeds. Class Downstream Upstream 1 6.144Mbps 64kbps 2 4.608Mbps 64kbps 3 3.072Mbps 64kbps 4 1.536Mbps 64kbps 5 6.2Mbps 576kbps 6 3.1Mbps 384kbps 7 1.544Mbps 160kbps 8 768kbps 64kbps 9 384kbps 32kbps 10 160kbps 16kbps Table 2 (Veeneman, 838-840) 14
  15. 15. The differing lengths of copper loops results in the following changes in useful bandwidth: Downstream Distance Notes speed 18,000 feet 1.544Mbps 24 gauge wire 16,000 feet 2.048Mbps 12,000 feet 6.312Mbps Average line 9,000 feet 8.448Mbps length for U.S. customers. Table 3 These estimates reflect optimal conditions. The actual bandwidth varies significantly depending on the particular hardware implementation used and the line conditions encountered. 3.5 CONNECTORS AND WIRING DIAGRAM 15
  16. 16. 3.5.1 CONNECTOR TYPES RJ-11 Broadband/Telephone Plug The US style RJ-11 plug is a 4-pin version of the RJ-45 pictured below. It is the smallest in size and is used in the UK for DSL/Broadband Internet connections (RJ-11 to RJ-11). British (Telecom) Plug The familiar British telephone plug used in over 30 countries around the world. Any analogue device that operates over a telephone line will be connected using this plug. You'll often find an RJ-11 plug on one end, and a BT plug on the other (RJ-11 to BT). USB Type A (Computer) Universal Serial Bus (USB) is the most popular way of connecting peripherals to your computer. To connect most devices, you'll require a type A to B cable (often supplied with the product). USB Type B (Peripherals) The other end of the USB wire features a square shape plug designed to connect to peripherals such as your USB DSL modem or router. RJ-45 Ethernet Network (Crimped Plug) The RJ-45 connector, featuring 8 pins, is the big brother of the RJ-11. It's used for data communications, specifically Local Area Networks (LANs). Cables can be 16
  17. 17. either straight (for normal use between a hub and a computer) or crossed (for use between two hubs or switches). Each computer requires a Network Interface Card (NIC) to connect to the network. RJ-45 Ethernet Network (Moulded Plug) The moulded RJ-45 plug shown to the left performs exactly the same purpose as the crimped version above. Professionally constructed cables are usually moulded by a machine instead of crimped using a special device called a "crimping tool". 3.5.2 WIRING DIAGRAM Basic diagrammatic scenarios are based upon: • Internet connection via a USB Modem 17
  18. 18. • Internet connection via an Ethernet router/modem • Connecting additional telephone sockets Beware of a certain amount of software configuration must also be carried out before computers and network peripherals are able to operate or communicate with each other. This includes software driver installation for USB modems and the correct assignment of IP addresses and related parameters for Ethernet networks. Figure : Key to Cable Types USB Modem The easiest and most popular way to get a single computer online with is via a USB modem. The process involves connecting the USB modem to the DSL side of your micro-filter, and your computer to the USB modem using a standard type A to B USB cable. Software installation procedure will vary depending upon the equipment purchased. 18
  19. 19. Many users choose to share their USB Broadband connection using software such as Microsoft Internet Connection Sharing (ICS). In this scenario, the computer will act as a gateway for other computers to access the Internet via a Local Area Network (LAN). The same concept can be extended to wireless network cards instead of the more restrictive fixed approach above. This configuration is often referred to as "ad-hoc networking mode" with the sharing computer operating in "infrastructure mode". Most users will find that sharing their USB connection over a wired network is adequate. 19
  20. 20. Ethernet Router & Local Area Network The following diagrams show sample configurations for Internet access via an Ethernet router/modem. Many routers feature a 2, 4 or 8 port inbuilt Ethernet hub or switch (a device used to connect computers together). In this scenario, computers can be connected directly to the router. Each computer is wired using a standard Ethernet cable with one end connected to a spare port on the inbuilt hub/switch and the other end connected to the computers network card. If your Ethernet router only has 1 network port, or you want to connect more devices to the network than there are available ports, a Ethernet switch can be used in combination with a crossover cable to extend the size of your network. 20
  21. 21. Micro-Filters and Additional Telephone Sockets Micro-filters must be used to separate the two different frequency bands used over your telephone line (voice and data) and prevent your analogue devices from interfering with the Broadband frequency ranges used by your modem/router. Simple method: Walk around your house and count how phones are plugged into a phone socket (on the same line) and order the same number of micro-filters. Simply unplug each phone, plug them into the splitter and reconnect to the phone line. 21
  22. 22. Cheaper method: Buy a single micro-filter and plug this into your master socket and run all the phone extensions off the phone side of the micro-filter. Finally, run an extension from the ADSL side of the splitter to where you want to use your ADSL modem. 22
  23. 23. 4. BENEFITS ADSL technology is far more advantageous than other access technologies currently available. The benefits of ADSL include: Connectivity Simultaneous Internet and telephone/fax capabilities over a single telephone line. A user is always connected and there is no need to dial up. Speed ADSL can endure the data rate necessary to handle all kinds of applications, such as very high fast data transfer and broadcast video: 1.544 to 9 Mbps downstream, 16Kbps to 1.544 Mbps upstream. Cost Effectiveness Because of the usage of existing copper pairs, the ADSL is a very cost-effective solution for residential users and small businesses. Reliability ADSL operates over the copper-based telephone network that is one of the most robust and proven infrastructures. 23
  24. 24. 5. PROBLEM Copper Loop Quality Several factors may affect the throughput of a twisted-pair copper loop: Loop length The length of the copper loop between the central station and the residence is the most prominent factor in available throughput. Signals are attenuated by an amount proportional to the loop length. In addition, the attenuation is a function of the frequency, such that higher frequencies are attenuated more than lower frequencies. (Aas) Bridged Taps Lengths of non-terminated twisted-pair cable connected in parallel to the primary pair. Ham and AM radio These radio transmissions fall within the spectrum used by ADSL and can be a severe disruption to the signal. Crosstalk Interference from adjacent wires in the feeder trunks running to the neighborhood. Increasing the transmission power cannot compensate for this distortion, since the noise from the higher-powered adjacent lines would also grow in proportion. Wire Gauge The effective range and throughput can be shortened by higher-gauge (smaller) wire. Some copper loops user different gauge wires at different points--this can cause reflections in the signal, effectively attenuating some frequencies. (Minoli, 341) 24
  25. 25. 6. CONCLUSION ADSL is poised to become the next revolutionary leap in remote data access technologies. It promises very high performance without a corresponding high cost, and does not require a large investment in infrastructure upgrades. ADSL increase the capacity of copper cable to support high-speed broadband data such as video conferencing, multi-media, high-speed Internet access and interactive services. Besides giving high bandwidth it is able to access almost every place in the world that provides phone connectivity. 25
  26. 26. GLOSSARY ADSL Asymmetric Digital Subscriber Line STM Synchronous Transfer Mode ATM Asynchronous Transfer Mode TE Terminal Equipment OS Operations System See System Reference Model for reference PDN Premises Distribution Network point definitions SM Service Module ATU-C ADSL Transmission Unit at the network end. The ATU-C may be integrated within an Access Node ATU-R ADSL transmission Unit at the customer premises end. The ATU-R may be integrated within an SM Access Node Concentration point for Broadband and Narrowband data. The Access Node may be located at a Central Office or a remote site. Also, a remote Access Node may subtend from a central access node B Auxiliary data input (such as a satellite feed) to Service Module (such as a Set Top Box) Broadcast Broadband data input in simplex mode (typically broadcast video) Broadband Switching system for data rates above 1.5/2.0 Mbps Network Loop Twisted-pair copper telephone line. Loops may differ in distance, diameter, age, and transmission characteristics depending on network. Narrowband Switching system for data rates at or below 1.5/2.0 Mbps Network POTS Plain Old Telephone Service POTS-C Interface between PSTN and POTS splitter at network end POTS-R Interface between phones and POTS splitter at premises end PDN Premises Distribution Network: System for connecting ATU-R to Service Modules. May be point-to-point or multipoint; may be passive wiring or an active network. Multipoint may be a bus or star PSTN Public Switched Telephone Network SM Service Module: Performs terminal adaptation functions. Examples are set top boxes, PC interfaces, or LAN router Splitter Filters which separate high frequency (ADSL) and low frequency (POTS) signals at network end and premises end. The splitter may be integrated into the ATU, physically separated from the ATU, or divided between high pass and low pass, with the low pass function physically separated from the ATU. The provision of POTS splitters and POTS- related functions is optional 26
  27. 27. T-SM Interface between ATU-R and Premises Distribution Network. May be same as T when network is point-to-point passive wiring. An ATU-R may have more than one type of T-SM interface implemented (e.g., a T1/E1 connection and an Ethernet connection). The T-SM interface may be integrated within a Service Module T Interface between Premises Distribution Network and Service Modules. May be same as T-SM when network is point-to-point passive wiring. Note that T interface may disappear at the physical level when ATU-R is integrated within a Service Module U-C Interface between Loop and POTS Splitter on the network side. Defining both ends of the Loop interface separately arises because of the asymmetry of the signals on the line U-C2 Interface between POTS splitter and ATU-C. Note that at present ANSI T1.413 does not define such an interface and separating the POTS splitter from the ATU-C presents some technical difficulties in standardizing the interface U-R Interface between Loop and POTS Splitter on the premise side U-R2 Interface between POTS splitter and ATU-R. Note that at present ANSI T1.413 does not define such an interface and separating the POTS splitter from the ATU-R presents some technical difficulties in standardizing the interface VA Logical interface between ATU-C and Access Node. As this interface will often be within circuits on a common board, the ADSL Forum does not consider physical VA interfaces. The V interface may contain STM, ATM, or both transfer modes. In the primitive case of point-to- point connection between a switch port and an ATU-C (that is, a case without concentration or multiplexing), then the VA and VC interfaces become identical (alternatively, the VA interface disappears) VC Interface between Access Node and network. May have multiple physical connections (as shown) although may also carry all signals across a single physical connection. A digital carrier facility (e.g., a SONET or SDH extension) may be interposed at the VC interface when the access node and ATU-Cs are located at a remote site. Interface to 27
  28. 28. the PSTN may be a universal tip-ring interface or a multiplexed telephony interface such as specified in Bellcore TR-08 or TR-303. The broadband segment of the VC interface may be STM switching, ATM switching or private line type connections REFERENCES 1. Dale Veeneman, Robert Olshansky. GTE Laboratories Incorporated. ADSL for Video and Data Services. IEEE Communications Conference. 1995. pp. 837-841. 2. Seiichi Yamano. NTT Transmission Systems Laboratories. The Range of HDSLs and ADSLs in NTT's Local Networks. IEEE Communications Conference. 1994. pp. 444-450. 3. Walter Y. Chen, David L. Waring. Bell Communications Research. ADSL Noise Environment and Potential System Performance. IEEE Communications Conference. 1994. pp. 451-455. 28
  29. 29. 4. Peter S. Chow, John M. Cioffi. Amati Communications Corporation. A Multi- drop In-house ADSL Distribution Network. IEEE Communications Conference. 1994. pp. 456-460. 5. ADSL Timescale 29