BUILDING BROADBAND NETWORKS phần 5 ppsx

performance reports for network maintenance. In recognition of DMT capabilities, operational effectiveness, and robustness in noisy local loop environments, ANSI (American National Standards Institute) selected DMT as the basis of the ANSI T1.413 specification developed in 1993. 6.5.2.1 DMT and Discrete Wavelet Multitone Multicarrier (DWMT) Modulation Based on DMT, DWMT (Discrete Wavelet Multitone Multicarrier Modulation) cre- ates more isolation between subchannels than DMT for performance enhancement. 6.5.2.2 DMT Modulation and Carrierless Amplitude and Phase (CAP) Modulation DMT (Discrete Multitone) modulation and CAP (Carrierless Amplitude and Phase) modulation are sophisticated digital signaling processing (DSP) techniques that enable point-to-point transmission over voice-grade telephone lines. DMT is the standard line code for DSL technologies. In addition to serving as the basis for the ANSI (American National Standards Institute) T1.413 specification, DMT modula- tion is also endorsed by the European Telecommunications Standards Institute (ETSI) and the International Telecommunications Union-Telecommunications Stan- dards Sector (ITU-T). DMT manufacturers include Alcatel, Amati, Motorola, Texas Instruments, PairGain, Motorola, Orckit, ADI, and Aware. CAP (Carrierless Amplitude and Phase) modulation is also a version of QAM (Quadrature Amplitude Modulation). In contrast to DMT, CAP is a proprietary technology. As a consequence, CAP chipsets are not always interoperable. None- theless, CAP modems for DSL operations are still in use by vendors such as Nokia. In comparison to CAP, DMT transmissions are adaptable to changing bandwidth and line conditions. Moreover, DMT-supported DSL transmissions are resistant to crosstalk, universal thermal noise, impulse noise generated by electrical appliances, and RFI (Radio Frequency Interference) produced by AM radio band signals. 6.6 DSL STANDARDS ORGANIZATIONS AND ACTIVITIES DSL technologies provide an unprecedented amount of affordable bandwidth over ordinary copper telephone lines. Standards groups in the DSL arena define specifi- cations, procedures, methods, and approaches for supporting DSL equipment com- patibility and interoperability, seamless communications over the local loop, inter- networking operations, and economical and reliable multimedia delivery to the desktop. 6.6.1 C OMMITTEE T1 Accredited by the American National Standards Institute (ANSI) and sponsored by the Alliance for Telecommunications Industry Solutions (ATIS), Committee T1 develops DSL specifications and clarifies approaches for DSL operations. 0889Ch06Frame Page 250 Wednesday, April 17, 2002 3:02 PM © 2002 by CRC Press LLC 6.6.2 DSL F ORUM Established in 1994, the DSL Forum promotes worldwide implementation of resi- dential broadband applications based on DSL technologies. Originally called the ADSL Forum, the DSL Forum contributes to technical advances in DSL technologies. For example, in 2000, the DSL Forum endorsed a set of recommendations supported by the OpenDSL Consortium for enabling automatic configuration of customer premise equipment (CPE). These recommendations provision regular and dependable access to DSL services via a modem linked to an already-configured telephone line. Study Groups and Working Groups sponsored by the DSL Forum explore DSL capabilities in interworking with ATM and IP and develop architectural specifica- tions, interfaces, and procedures fostering DSL implementation and assessment. DSL Forum participants include Aware, Ascend, Cisco Systems, Diamond Lane, Ericsson, Nokia, Philips, Samsung, Sumitomo, 3Com, and Lucent. 6.6.2.1 Testing and Interoperability Working Group Affiliated with the DSL Forum, the Testing and Interoperability Working Group clarifies the capabilities of DSL network configurations, interfaces, operations, and performance by developing tests for verifying DSL equipment interoperability and conformance to DSL standards and specifications. 6.6.2.2 Voice-over-DSL (VoDSL) Working Group A DSL Forum affiliate, the Voice-over-DSL (VoDSL) Working Group sponsors development of voice-over-DSL (VoDSL) specifications. This Working Group con- ducts an extensive review of telephony requirements, including voice quality, reli- ability, and local loop issues, in order to identify VoDSL objectives, deliverables, applications, and service opportunities. Conventional DSL architecture provides one voice channel for telephony service and one large data pipe that supports a larger channel for downstream transmissions and a smaller channel for upstream data transport. Circuit-switched VoDSL solutions convert voice signals into data-like packets that are then interleaved with other data packets and transmitted in a single DSL bitstream via the local loop. Bandwidth is dynamically allocated to various voice and data services on an as-needed basis with voice services receiving priority bandwidth allocations. Packet-switched VoDSL implementations utilize DSL bit- streams of variable length for transporting multiple voice and data packets in an integrated all-packet network environment. The VoDSL Working Group defines parameters for Broadband Loop Emulation Services (BLES) and voice-over-MultiService Data Networks (VoMSDN). This Working Group also delineates network architecture requirements and recommen- dations for enabling interoperable telephony services via a DSL platform that also supports VoIP or IP (Internet Protocol) telephony applications. Based on the VoDSL Working Group’s recommendations, the DSL Forum in 2000 endorsed IP (Internet 0889Ch06Frame Page 251 Wednesday, April 17, 2002 3:02 PM © 2002 by CRC Press LLC Protocol) and ATM specifications that work in concert with DSL for carrying VoDSL traffic. 6.6.3 O PEN DSL C ONSORTIUM AND O PEN DSL I NITIATIVE Sponsored by the OpenDSL Consortium, the OpenDSL initiative streamlines the DSL implementation process and promotes widespread availability of DSL solutions in the marketplace. The OpenDSL initiative establishes a platform for easy instal- lation of interoperable DSL equipment and auto-configuration of network elements, thereby fostering rapid service provisioning of plug-and-play DSL solutions. The OpenDSL Consortium works in concert with the DSL Forum in developing DSL standards and specifications. Moreover, this Consortium also operates an inde- pendent certification program in conjunction with the OpenDSL Certification Lab- oratory for enabling vendors to verify equipment interoperability and standards conformance. Participants in the OpenDSL Consortium include DSL chipset and equipment manufacturers, service providers, and system integrators such as Cisco Systems, Intel, SBC, Efficient Networks, 3Com, Globespan, and Qwest. 6.6.4 I NTERNATIONAL T ELECOMMUNICATIONS U NION -T ELECOMMUNICATIONS S TANDARDS S ECTOR (ITU-T) The International Telecommunications Union-Telecommunications Standards Sector (ITU-T) endorses a series of Recommendations in the DSL domain. For example, the ITU-T G.992.1 Recommendation supports utilization of a filter for splitting data from voiceband signals. This process enables ADSL (Asynchronous Digital Sub- scriber Line) transmissions downstream or from the local telephone exchange to the customer premise at rates of 8 Mbps (Megabits per second). Moreover, the ITU-T G.992.1 Recommendation endorses the use of G.dmt (discrete multitone technology) and defines the interface between ADSL equipment and the local loop. The ITU-T G.996 Recommendation defines methods and procedures for bench- marking performance and interoperability of DSL transceivers. The ITU-T G.997.1 Recommendation describes DSL functions in using SNMP (Simple Network Man- agement Protocol) and DSL Physical Layer or Layer 1 operations. In addition, the ITU-T specifies approaches for enabling seamless DSL symmetric and asymmetric operations, methods for achieving higher DSL transmission rates, and procedures for supporting DSL operations over extended local loops. 6.7 ASYMMETRIC DSL (ADSL) 6.7.1 ADSL F OUNDATIONS ADSL (Asymmetric DSL) is the dominant DSL technology in the present-day DSL environment. Developed in 1994, ADSL technical capabilities are standardized by organizations that include the American National Standards Institute (ANSI), the European Telecommunications Standards Institute (ETSI), and the International 0889Ch06Frame Page 252 Wednesday, April 17, 2002 3:02 PM © 2002 by CRC Press LLC Telecommunications Union-Telecommunications Standards Sector (ITU-T). ADSL technology supports the consolidation of data, video, and voice traffic for transmis- sion over the local loop and provisions QoS (Quality of Service) assurances. ADSL leverages the in-place infrastructure to enable applications such as video security monitoring, interactive television programs, Web exploration, and videocon- ferencing, and concurrently supports the continuation of telephone conversations or fax transmissions. Officially known as full-rate ADSL, this technology is standardized in ITU-T Recommendation G.992.1. Endorsed by the ITU-T in 1998, this specification also supports utilization of a single terminal interface at the subscriber location. 6.7.2 ADSL O PERATIONS ADSL employs a pair of modems or transceivers that are located on either end of the local loop, specifically at the local telephone exchange and at the subscriber site. ATU-R (ADSL Terminal Unit-Remote) refers to ADSL transceivers at subscriber venues. ATU-C (ADSL Terminal Unit-Central Office) refers to ADSL transmission equipment at the local telephone exchange. The ITU-T G.994 Recommendation establishes handshaking procedures for enabling dependable data exchange between ATU-R (ADSL Terminal Unit-Remote) and ATU-C (ADSL Terminal Unit-Central Office) devices. At the subscriber premise, ATU-R (ADSL Terminal Unit-Remote) transceivers such as external and internal ADSL modems perform modulation and demodulation functions for optimizing transmission capabilities of copper wire telephone lines. In addition to ADSL modems, ADSL implementations at subscriber venues require utilization of personal computers (PCs) equipped with Ethernet NICs (Network Interface Cards) and associated wireline connections. ATU-R devices route voice, video, and data traffic to the local telephone exchange and support DSL Physical Layer or Layer 1 operations such as forward error correction and echo cancellation to minimize transmission disruptions in noisy PSTN (Public Switched Telephone Network) environments. ATU-C (ADSL Terminal Unit-Central Office) devices include ADSL transceiv- ers and DSLAMs (DSL Access Multiplexers) at the local telephone exchange. Virtual connections via a DSLAM interface enable connectivity between subscriber venues and the Internet or another network via the local telephone exchange. At the local telephone exchange, ATU-C devices such as hubs, bridges, and routers redirect voice calls to the PSTN (Public Switched Telephone Network) and transmit video, voice, and data to high-speed overlay IP (Internet Protocol) networks that route traffic to the public or commodity Internet or other high-speed backbone networks. Backbone network technologies that work in concert with ADSL include ATM, SONET/SDH, IP, Fibre Channel, Frame Relay, and Gigabit Ethernet. These networks seamlessly transport ADSL frames or packets across local, municipal, and wider area networks to destination addresses. Additionally, telephone service remains available even if the ADSL transceiver at the subscriber premise is incapable of supporting data services. 0889Ch06Frame Page 253 Wednesday, April 17, 2002 3:02 PM © 2002 by CRC Press LLC 6.7.3 DSL A CCESS M ULTIPLEXERS (DSLAM S ) 6.7.3.1 DSLAM Features and Functions ADSL implementation requires the installation of equipment that includes a pair of transceivers (or transmitters and receivers) at the subscriber site and the local tele- phone exchange. This installation serves as the foundation for virtual point-to-point DSL dedicated network connections that provision fast access to high-performance applications via the local loop. At the local telephone exchange, DSL transmissions are redirected to high-speed backbone networking configurations or the public Internet by DSLAMs (DSL Access Multiplexers). DSLAMs also redirect voice calls to and from the PSTN, thereby eliminating the need for time-consuming dial-up operations required by conventional analog telephone modems. In addition to traffic routing and distribution services, DSLAMs support trans- mission of streaming media from the Internet or other high-speed backbone network to designated DSL subscriber venues. DSLAMs enable framing operations for encap- sulation of bit streams into DSL frames or packets for transmission and support basic network monitoring, administrative, and maintenance functions. Advanced DSLAMs also support packet discards, traffic shaping, and traffic prioritization to enable reliable transmission of time-sensitive voice and video appli- cations and data transport. These devices employ advanced protocols such as MPLS (MultiProtocol Label Switching) and work in concert with ATM SVCs (Switched Virtual Circuits) in hybrid ATM-over-ADSL configurations. 6.7.3.2 DSLAM Marketplace Developed by Lucent Technologies and Nortel Networks, next-generation DSLAMs facilitate innovative service combinations such as DSL-over-Frame Relay (DSLoFR) and enable access to high-volume broadband applications such as IP multicasts, VOD (Video-on-Demand), and IVOD (Interactive VOD) with bandwidth assurances. Cisco Systems provisions next-generation DSLAMs that enhance network scal- ability and incorporate network intelligence for enabling communications providers to support guaranteed delivery of high-quality ADSL services. Next-generation DSLAMs from Nokia enable ATM-VoDSL (ATM or Asynchronous Transfer Mode and voice-over ADSL) applications. Available from Paradyne, ReachDSL solutions feature next-generation DSLAMs and long-loop reach technology that enables transmission between 256 and 768 Kbps at distances of 18,000 feet from the local telephone exchange. 6.7.4 POTS (P LAIN O LD T ELEPHONE S ERVICE ) S PLITTER ADSL technology transforms present-day twisted pair telephone lines into virtual com- munications channels to support high-speed multimedia communications. ADSL instal- lations eliminate the need to upgrade the in-place POTS (Plain Old Telephone Service) infrastructure and purchase signal regenerators. However, ADSL implementations require utilization of a POTS splitter that is integrated into the ADSL modem or transceiver at the subscriber location. 0889Ch06Frame Page 254 Wednesday, April 17, 2002 3:02 PM © 2002 by CRC Press LLC Also called a low-pass high-pass filter, a POTS splitter divides available band- width on a telephone line into two virtual channels for separating voice calls from data transmissions at the customer premise. In addition to eliminating signal inter- ference, this process supports development of a virtual channel or circuit between the 300 Hz and 3.4 kHz frequencies for basic telephone service and a virtual channel of higher frequencies for multimedia transmission. In addition, a channel separator divides the virtual multimedia channel into two virtual channels or circuits. The larger channel or circuit supports voice, video, and data transmission downstream as digital pulses in higher frequencies not used for telephone communications. The smaller circuit or channel enables full-duplex oper- ations and information transport upstream. 6.7.5 ADSL T RANSMISSION F UNDAMENTALS ADSL transmits delay-sensitive video, audio, and data traffic and delay-insensitive transmissions as sequences of frames containing variable-length packets. In the downstream path or from the local telephone exchange to the customer site, ADSL technology supports rates ranging from 1.544 Mbps (T-1) to 8 Mbps. For upstream transmission from the customer premise to the local telephone exchange, ADSL technology enables rates ranging from 16 to 640 Kbps. In ADSL transmissions, frames are aggregated into blocks to which error cor- rection codes are affixed. At the customer site, an ADSL modem corrects errors that occur during transmission based on limits previously defined by error correction codes. ADSL systems also employ advanced algorithms for enabling broadband speeds via twisted pair copper lines. ADSL downstream speeds depend on the distance of the subscriber site from the local telephone exchange, wire gauge or thickness, and the condition of the in- place wireline plant. ADSL supports downstream rates reaching 8 Mbps (Megabits per second) at 9,000 feet, 6.312 Mbps at 12,000 feet, 2.048 (E-1) at 16,000 feet, and 1.544 Mbps (T-1) at 18,000 feet or 5.5 kilometers. In parallel with other DSL technologies, ADSL is a high-speed always-on digital switching, routing, and signal processing technology that enables voice calls and fax transmission in RF bands between the 300 Hz and 3.4 kHz frequencies and multimedia transmission in the upper frequency range. Conventional voiceband modems compress voice, video, and data into a narrow range of frequencies for supporting information transmission via PSTN service. By contrast, ADSL employs Digital Signal Processing (DSP) for creating high-speed digital channels to optimize bandwidth capacity of copper telephone lines. Discrete Multitone Technology (DMT) modulation enables asymmetrical infor- mation transport. It also employs a spectral mask that eliminates signal interference. When upstream and downstream frequency bands overlap in ADSL implementations, echo cancellation circuitry is incorporated into ADSL devices for diminishing the effects of signal mismatch and crosstalk. ADSL service to a subscriber premise is provisioned via Unshielded Twisted Pair (UTP). Depending on the ADSL solutions available from the local telephone exchange, a POTS or ISDN channel can be used instead of an ADSL channel for information transport on the return path in the upstream direction. 0889Ch06Frame Page 255 Wednesday, April 17, 2002 3:02 PM © 2002 by CRC Press LLC 6.7.6 ADSL AND ATM The explosion of network traffic and demand for high-speed access to broadband applications contribute to development of ADSL solutions that support interopera- bility with ATM configurations. ATM-over-ADSL services enable multimedia trans- port and applications such as interactive teleconsultations and real-time videocon- ferencing. In ATM-over-ADSL implementations, ATM functions as a Layer 2 or Data-Link Layer protocol over the ADSL access network and ATM cells are encap- sulated in ADSL frames to facilitate transmission over the PSTN infrastructure. ADSL provisions Physical Layer or Layer 1 services. In addition, this hybrid network also supports CoS (Class of Service) with QoS (Quality of Service) assurances. The ANSI T1.415 specification standardizes ATM-over-ADSL operations. 6.7.7 ADSL S TANDARDS O RGANIZATIONS AND A CTIVITIES 6.7.7.1 ANSI (American National Standards Group) T1E1.4 Study Group The ANSI (American National Standards Group) T1E1.4 Study Group develops DSL specifications for enabling nationwide deployment of interoperable ADSL solutions. In 1995, ANSI approved the T1.413 specification describing standardized ADSL operations. This specification also defined a single terminal interface, proto- cols for network operations, and parameters for network management to enable seamless ADSL implementations. An expanded version of the original ANSI specification, the T1.413-1998 stan- dard defines the ADSL interface with the customer premise. In addition, this standard describes enhancements to network performance, endorses ADSL transmission rates at 8 Mbps as opposed to the previously approved 6.1 Mbps rates, and supports ADSL utilization of spectral frequencies that are compatible with ATM operations. More- over, the ANSI T1.413-1998 specification describes ATM-over-ADSL transmission services and delineates ADSL functions that are compatible with the ATM Adapta- tion Layer (AAL) of the ATM protocol stack and with ATM Unspecified Bit Rate (UBR) service. The ANSI T1.413 standard is routinely reviewed, expanded, and updated to reflect technical advances. As an example, the European Telecommunications Stan- dards Institute (ETSI) contributed an Annex to ANSI T1.413-1998 that describes requirements for ADSL implementations in the European Union. In addition, the ITU-T G.992.1 G.dmt (Discrete Multitone) Recommendation and the ITU-T G.992.2 ADSL.Lite Recommendation are based on the ANSI.T1.413-1998 ADSL specifica- tion and the work of ETSI Technical Committees. 6.7.7.2 International Telecommunications Union-Telecommunications Standardization Sector (ITU-T) In 1998, the ITU-T (International Telecommunications Union-Telecommunications Standardization Sector) approved a series of Recommendations that describe ADSL capabilities in supporting high-speed broadband services via the local loop. 0889Ch06Frame Page 256 Wednesday, April 17, 2002 3:02 PM © 2002 by CRC Press LLC 6.7.7.3 DSL Forum and the ATM Forum Standards groups that contribute to the development of ADSL and ATM integrated services and applications include the ATM Forum and the DSL Forum. In addition, the ATM Forum defines an end-to-end ATM system that works in conjunction with ADSL technology for supporting information transport via the local loop. Originally called the ADSL Forum, the DSL Forum defines system configurations and interfaces for supporting transmission of ATM cells via ADSL networks. 6.7.7.3.1 Time-Division Multiplexing (TDM) Protocol Endorsed by the ATM Forum and the DSL Forum, the TDM (Time-Division Mul- tiplexing) protocol enables the encapsulation of ATM cells into ADSL packets and supports seamless information transport in mixed-mode ATM and ADSL configu- rations. In the downstream direction, the access node in an ATM-over-ADSL inter- network provides routing and demultiplexing capabilities. In the upstream direction, this access node performs multiplexing functions. This approach supports secure delivery of basic and sophisticated services; access to applications such as IP multicasts, interactive games, and tele-courses; and multimedia transport with QoS (Quality of Service) guarantees. Transmission of ATM cells over an ADSL platform is consistent with the ITU ANSI T1.413 standard. At the local telephone exchange, the DSLAM functions as an ATM multiplexer to enable hybrid ATM-over-ADSL applications. 6.7.7.3.2 Point-to-Point Protocol (PPP) The DSL Forum supports utilization of Point-to Point-Protocol (PPP) packets for encapsulating ATM cells in ADSL packets for transport via residential broadband access networks. Transmission of PPP frames in ATM-over-ADSL networks elimi- nates the need to run optical fiber to SOHO locations. PPP is a WAN (Wide Area Network) protocol that, in addition to ADSL and ATM, interworks with ISDN, SONET/SDH, Ethernet, Fast Ethernet, Gigabit Ethernet, and Frame Relay technologies. 6.7.8 U.S. ADSL T RIALS AND I MPLEMENTATIONS ADSL implementations require ADSL subscribers to be located within specified distances of the local telephone exchange. As a consequence, independent telephone companies, local exchange carriers, network vendors, and Network Service Providers (NSPs) evaluate ADSL network capabilities and performance in research trials and pilot implementations that are carried out in diverse locations among relatively small numbers of users. As an example, GTE sponsors ADSL trials at Purdue and Duke Universities; 3Com conducts ADSL trials at Princeton University; Verizon sponsors ADSL implementations at Georgetown University; and U.S. West evaluates ADSL capabilities in trials at the University of Wyoming. 6.7.8.1 Cisco Systems Available from Cisco Systems, ATM25 ADSL modems support ATM-over-ADSL solutions that provision connections to Virtual Private Networks (VPNs) and facilitate 0889Ch06Frame Page 257 Wednesday, April 17, 2002 3:02 PM © 2002 by CRC Press LLC Quality of Service (QoS) levels for enabling telecommuting, distance learning, and video broadcast applications at rates of 25 Mbps. 6.7.8.2 GST Telecommunications GST Telecommunications implements full-rate ADSL solutions in San Francisco that facilitate access to the GST Virtual Integrated Transport and Access (VITA) network. The VITA network supports data, voice, and video transmissions via a long-haul fiber optic ATM network that provisions communications services through- out the Western United States. 6.7.9 I NTERNATIONAL ADSL T RIALS AND V ENDOR I MPLEMENTATIONS TeleDanmark, Helsinki Telephone Company, Deutsche Telekom, and France Tele- com provision ADSL service throughout the European Union. In the Middle East, Bezeq, popularly known as Israel Telecom, offers ADSL service in Tel Aviv and Jerusalem. ADSL pilot trials are also conducted in Brazil, Argentina, Taiwan, Japan, Korea, Australia, and New Zealand. 6.7.9.1 Canada 6.7.9.1.1 New Brunswick Telephone (NBTEL) In Canada, the New Brunswick Telephone (NBTEL) Company tests an ATM-over- ADSL solution for enabling access to the Video Active Network. Also known as VIBE, this high-performance network supports access to distance education telepro- grams and facilitates interactive videoconferencing, E-commerce transactions, and home security services. 6.7.9.2 Finland 6.7.9.2.1 University of Tampere In Finland, the University of Tampere conducts trials in conjunction with commu- nications carriers and research institutions to assess the capabilities of ATM-over- ADSL configurations in enabling access to telemedicine and tele-education services and applications. 6.7.9.3 Greece 6.7.9.3.1 Hellenic Telecommunications Organization In Greece, the Hellenic Telecommunications Organization, the National Technical University of Athens, the Aristotle University of Thessaloniki, and the Universities of Athens, Crete, and Patras evaluate ADSL capabilities in enabling access to Web services and delivery of multimedia applications such as video-on-demand (VOD). 6.7.9.4 Netherlands 6.7.9.4.1 Snelnet Project In the Netherlands, the Snelnet Project explores the suitability of an ATM-over- ADSL platform for enabling residential users in Amsterdam and Utrecht to access 0889Ch06Frame Page 258 Wednesday, April 17, 2002 3:02 PM © 2002 by CRC Press LLC music clips, concerts, telecourses, interactive movies, news items, weather-on- demand, film documentaries, cooking courses, simulations, and games. The Snelnet ATM-over-ADSL platform enables rates reaching 2.5 Mbps downstream and 384 Kbps upstream and supports links to SURFnet (National Research and Education Network or NREN of the Netherlands). 6.7.9.5 Singapore 6.7.9.5.1 SingTel (Singapore Telecommunications) Sponsored by the Singapore government and a nationwide industry consortium, SingTel (Singapore Telecommunications) supports utilization of an ATM-over- ADSL platform that enables subscribers at SOHO venues to access Web resources, telebanking and E-commerce services, distance education courses, movies, and entertainment programs. SingTel also provisions links to Singapore ONE or 1-NET (One Network for Everyone), a public Web site featuring broadband applications. 6.7.10 ADSL I MPLEMENTATION CONSIDERATIONS ADSL technology uses sophisticated modulation processes for transporting data, voice, and video traffic over unshielded twisted copper wire pair. This technology provides a constant connection and supports considerably faster transmission rates than a 56 Kbps analog modem. As an example, telecommuters employ ADSL solutions to access an office LAN at relatively the same rate as onsite employees using T-1 (1.544 Mbps) connections. In addition to enabling connectivity to broad- band applications and transforming the way the Public Switched Telephone Network (PSTN) is employed, ADSL also makes lifeline services available via the basic telephone channel in case of emergencies. Designed primarily for residential and SOHO subscribers, ADSL deployment typically involves expenditures for a technician to install a signal splitter at the subscriber site. In addition, ADSL implementation requires the installation of com- patible ATU-R and ATU-C modems or transceivers at the customer premise and the local telephone exchange. DSLAMs at the local telephone exchange play a critical role in enabling fast connections and multimedia transmission. ADSL NSPs gener- ally provision network management services and help-desk support. In contrast to cable modem systems, ADSL networks establish virtual dedicated services that are not shared among multiple users. Factors that contribute to the decision to move forward with ADSL implementation include costs of the upgraded service and application requirements. There are constraints associated with ADSL utilization. ADSL users must be within 18,000 feet of the local telephone exchange to obtain bandwidth benefits associated with this service. Users outside this radius experience degradation in bandwidth capacity and rates supported. ADSL capabilities also depend on the age and state of the local loop architecture and the quality of the telephone line. More- over, load coils originally used to limit noise on telephone lines interfere with the quality of voice signals in upper ADSL frequencies. Power outages, snowstorms, and thunderstorms disrupt the integrity of ADSL transmissions as well. 0889Ch06Frame Page 259 Wednesday, April 17, 2002 3:02 PM © 2002 by CRC Press LLC [...]... access to current and emergent high-speed multimedia broadband services 6.24 OVERVIEW OF POWERLINE NETWORKS As noted, demand for ready access to current and emergent broadband networks and bandwidth-intensive interactive multimedia applications contributes to exploration and assessment of the DSL technologies, satellite services, wireline and wireless cable networks, and ISDN as last-mile solutions for overcoming... attributes and initiatives are reviewed The work of standards organizations in enabling interoperable powerline networks is noted Recent advances in waterway networks are highlighted as well 6. 35 SELECTED WEB SITES Adaptive Networks Powerline Communications Networking Available: http://www.adaptivenetworks.com/ DSL.com Home Page Available: http://www.dsl.com/ DSL Forum Whitepapers Available: http://www.adsl.com/... multimedia applications 6.14.6 .5 Texas Instruments Texas Instruments offers a DSP (Digital Signal Processing) VDSL chipset based on SDMT (Synchronous Discrete Multitone) technology with TDD (Time-Division Duplexing) for enabling high-speed data, video, and voice delivery over ordinary UTP in noisy environments With this technology, downstream speeds at 51 .84 Mbps are enabled 6. 15 6. 15. 1 ISDN DSL (IDSL) IDSL... rates of 1 .54 4 Mbps (T-1) over a single UTP (Unshielded Twisted Pair) at distances up to 12,000 feet With two unshielded twisted copper pairs, wDSL provisions rates at 4 Mbps at distances extending to 12,000 feet With two unshielded twisted copper pairs, wDSL also supports transmissions at 1 .54 4 Mbps (T-1) at distances reaching 18,000 feet 6.16.2 NEWBRIDGE NETWORKS Developed by Newbridge Networks, 3dSL... clusters of adjacent buildings on campus In the absence of FTTB (Fiber-to-the -Building) links, the 1-Meg Modem implementation at CSU is less costly to implement than T-1 leased lines and ISDN installations In addition, capabilities of 1-Meg Modem solutions are also explored at Northern Illinois and Cornell Universities and the University of Michigan 6.16.4 6.16.4.1 NORTEL NETWORKS AND ELASTIC NETWORKS ETHERLOOP... Philadelphia, Pittsburgh, Minneapolis, Denver, Detroit, and Chicago 6.8 .5 INTERNATIONAL ADSL.LITE TRIALS 6.8 .5. 1 AND IMPLEMENTATIONS Germany In Germany, students at the University of Munster and Aachen Technical College participate in a Deutsche Telekom ADSL.Lite initiative Rates at 1 .5 Mbps downstream and 128 Kbps upstream are supported 6.8 .5. 2 Singapore Singapore is the first city in the Asia-Pacific region... powerline networks sponsored by subsidiaries, partners, and affiliates of multiservice utility companies; introduce powerline networking fundamentals, capabilities, and constraints; and review the national and international powerline networking initiatives as well as the work of standards organizations in enabling interoperable powerline networks 6. 25 POWERLINE NETWORK FOUNDATIONS Initially, powerline networks. .. services via in-place private and public powerline networks These standards support equipment interoperability, co-location of powerline networks and residential broadband access configurations based on technologies such as DSL and cable modem within the same in-home environment, and electromagnetic compatibility to avoid interference between powerline networks and other technologies operating in the... powerline networks operate over 220-volt powerlines and support data rates at 1 15 Kbps © 2002 by CRC Press LLC 0889Ch06Frame Page 281 Wednesday, April 17, 2002 3:02 PM 6.29 .5 AMERICAN ELECTRIC POWER One of the largest energy producers in the United States, American Electric Power replaced an aging microwave system with a high-speed fiber optic SONET backbone network This optical fiber network supports broadband. .. Lower Colorado River Authority implements high-speed, high-performance metropolitan networks that use the in-place utility infrastructure for delivery of broadband applications to businesses, hospitals, medical clinics, chambers of commerce, government agencies, and K–12 schools and school districts 6.29. 15 NEWBRIDGE NETWORKS Newbridge Network employs OFDM (Orthogonal Frequency-Division Multiplexing) . of 2 Mbps at 9,000 feet, 6 .5 Mbps at 4 ,50 0 feet, 13 Mbps at 3,000 feet, and 26 Mbps at 1,000 feet are enabled. 6.14 .5 VDSL STANDARDS ORGANIZATIONS AND ACTIVITIES 6.14 .5. 1 DSL Forum The DSL Forum. 0889Ch06Frame Page 255 Wednesday, April 17, 2002 3:02 PM © 2002 by CRC Press LLC 6.7.6 ADSL AND ATM The explosion of network traffic and demand for high-speed access to broadband applications. for encapsulating ATM cells in ADSL packets for transport via residential broadband access networks. Transmission of PPP frames in ATM-over-ADSL networks elimi- nates the need to run optical fiber to SOHO locations.