Broadband Access Group 0.6August 1999 Texas Instruments (TI) rese

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Broadband Access Group 0.6August 1999 Texas Instruments (TI) rese

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Technical Paper Describing EtherLoop( Technology
Broadband Access Group 0.6August 1999
Texas Instruments (TI) reserves right make changes products discontinue semiconductor product service without notice, advises customers obtain latest version relevant information verify, before placing orders, that information being relied current. warrants performance semiconductor products related software specifications applicable time sale accordance with TI's standard warranty. Testing other quality control techniques utilized extent deems necessary support this warranty. Specific testing parameters each device necessarily performed, except those mandated government requirements. Certain application using semiconductor products involve potential risks death, personal injury, severe property environmental damage ("Critical Applications"). SEMICONDUCTOR PRODUCTS DESIGNED, INTENDED, AUTHORIZED, WARRANTED SUITABLE LIFESUPPORT APPLICATIONS, DEVICES SYSTEMS OTHER CRITICAL APPLICATIONS. Inclusion products such applications understood fully risk customer. products such applications requires written approval appropriate officer. Questions concerning potential risk applications should directed through local sales office. order minimize risks associated with customer's applications, adequate design operating safeguards should provided customer minimize inherent procedural hazards. assumes liability applications assistance, customer product design, software performance, infringement patents services described herein. does warrant represent that license, either express implied, granted under patent right, copyright, mask work right, other intellectual property right covering relating combination, machine, process which such semiconductor products services might used.
Copyright 1999, Texas Instruments Incorporated
DIGITAL THUNDER, THUNDERSWITCH TRADEMARKS TEXAS INSTRUMENTS INCORPORATED.
ETHERLOOP TRADEMARK ELASTIC NETWORKS INCORPORATED.
ETHERNET TRADEMARK XEROX CORPORATION.
Telephone Email
(972) 644-5580 (972) 480-7800 networks@ti.com
Contents
ABSTRACT.5
PRODUCT SUPPORT.9 RELATED DOCUMENTATION WORLD WIDE SUPPORT E-MAIL SUPPORT INTRODUCTION
SIGNALING COMMUNICATIONS.11 ETHERNET Burst Technology Ethernet Standard Disadvantages ETHERLOOP SIGNALING News Good News Signal Modulation QPSK MAXIMUM BANDWIDTH
ETHERLOOP MODEM IMPLEMENTATION WITH DSP.22
Tables
EtherLoop" Technology
EtherLoop" technology developed Elastic Networks Incorporated provide high-speed data access home over plain telephone system (POTS)-standard twisted pair. EtherLoop uses basic concepts digital subscriber line (DSL) technologies, such high data rate subscriber line (HDSL) asymmetrical digital subscriber line (ADSL), applies well-known packet delivery system algorithms executed programmable Texas Instruments (TI") digital signal processor (DSP) platform. This combination provides high-speed solution that overcomes many limitations ADSL HDSL, without sacrificing speed data quality. Through combination programmable hardware, advanced signal modulation, burst delivery technology Ethernet" packet-data protocol, EtherLoop provides solution that simple install, robust over distances 21,000 feet, efficient power consumption. EtherLoop project started Northern Telecom. project goal develop technology that would allow telephone companies compete with cable modems arena high-speed local data access. basic concepts underlying this technology are:
Utilization existing physical plant real-world expectations noise interference Minimal interference with existing services Relatively cost, with equivalent performance
EtherLoop" Technology
Product Support
Related Documentation
following site specifies product names, part numbers, literature numbers corresponding documentation.
World Wide Support
TI's world wide site www.ti.com contains most current product information, revisions, additions. users must register with TI&ME before they access data sheet archive. TI&ME allows users build custom information pages receive automatic product updates email. Specific information regarding Digital Thunder products located
E-mail Support
technical issues clarification switching products, please send detailed e-mail networks@ti.com. Questions receive prompt attention usually answered within business day.
EtherLoop" Technology
Introduction
EtherLoop technology developed Elastic Networks Incorportated (http://www.elastic.com) provide highspeed data access home over POTS-standard twisted pair. EtherLoop uses basic concepts technologies, such HDSL ADSL, applies well-known packet delivery system algorithms executing programmable platform. This combination provides high-speed solution that overcomes many limitations ADSL HDSL, without sacrificing speed data quality. Through combination programmable hardware, advanced signal modulation, burst delivery technology, Ethernet packet-data protocol, EtherLoop provides solution that simple install, robust over distances 21,000 feet, efficient power consumption. basic concepts underlying this technology are: Utilization existing physical plant real-world expectations noise interference Minimal interference with existing services Relatively cost, with equivalent performance Worldwide, there million twisted pair copper subscriber loops1 installed. These loops carry voice traffic from subscriber's premise telco central offices (CO), circuit switching another subscriber. Voice traffic utilizes only "bottom" 4-kilohertz analog bandwidth available copper wire. This extremely small portion actual bandwidth available. amount bandwidth varies with quality loop gauge wire, general, most subscriber copper loops reliably utilize about megahertz bandwidth. made available, this unused bandwidth provides substantial resource telephone companies. This document describes EtherLoop technology from four perspectives: physical nature signaling, devices communicate EtherLoop modem implementation with programmable chipsets from network architectures where EtherLoop being used comparison EtherLoop with competitive high-speed technologies
"Loop" telephone industry term single twisted pair copper suitable voice service.
EtherLoop" Technology
Signaling Communications
EtherLoop designed hybrid service bringing best features services together with best features Ethernet. provides high data rates extended reach over real-world physical plant. Ethernet half-duplex communications model "burst" packet delivery provides capabilities that mitigate some serious side effects highspeed services. understand EtherLoop helps understand features Ethernet.
technology that utilizes additional bandwidth within analog voice-grade twisted pair copper wiring. copper bandwidth divided into frequency bands. lowest band kilohertz) reserved voice traffic. Those frequencies left alone, continue support traditional voice traffic, while higher frequencies "borrowed" support data traffic. There several variants, each which distinct issues regarding installation usability. most prominent variant ADSL. ADSL supports theoretical speeds megabits second continuously direction over short distances, lower continuous rates maximum range 18,000 feet. ADSL provides much larger downstream signal than upstream, thus increasing efficiency reducing interference. HDSL variant that supplies symmetric 1.544 megabit-per-second pipe over pairs copper wire. 1.5-Mbps rate identical standard telephone company data rate standard, although HDSL easier deploy than runs longer distances. HDSL used both data voice applications, although because high-speed bi-directional traffic, there limitations where HDSL deployed.
EtherLoop" Technology
There problems with these high-speed services. Sending high-speed data requires substantial signal levels power. more signal delivered down copper, more signal "leaks out" interferes with other copper lines close proximity. This also known crosstalk (see Figure Copper wires typically stored group 25-50 tightly bundled
Arrows represent incidence high crosstalk.
Figure Sample 25-Pair Binder With 12/13 Pair "Sub-Units" pairs, this bundling cause considerable problems other high-speed data users potentially with other voice services. Typically, twisted pair bundle, there other pair that closely associated with terms cross talk susceptibility. This usually characterized terms decibels number larger than incurs significant crosstalk.
EtherLoop" Technology
services reach their theoretical performance maximums, near-ideal subscriber loop required. real world, however, most subscriber loops from ideal. wire change gauge, ranging from gauge gauge. This causes distortions interference passing signal. also possible have "bridge taps" loop, where wire attached main loop, connected anything end. Unconnected bridge taps cause reflections signal some incoming signal "bounces" backward (see Figure This reflection interferes with original signal, must filtered transmitter/receivers both ends. This requires extremely adaptable echo-cancellation technology, which adds significant cost complexity system. This primarily problem with carrierless amplitude
Incoming signal
Copy signal splits bridge
Copy reaches reflects
Reflection reaches main signal continuously distorts
Figure Bridge Distortion Continuous Network phase (CAP)-based ADSL systems. Discrete multi-tone (DMT) based ADSL works better with bridge taps, other problems.
Loading coils also significant problem. These metallic coils that attached subscriber loops increase usable length wire. This typically used when subscriber kilofeet more away from central office. However, many cases, subscriber closer central office, still possess loading coils loops because wires used over time. Loading coils cause nearly complete degradation higher-level frequencies, which effectively eliminates possibility delivering high-speed services these "loaded" loops.
EtherLoop" Technology
Lastly, ADSL requires continuous power levels deliver signal from client master vice versa when operating. telco2 environment, other "high density" ADSL deployment (ports/cubic foot) heat from multiple modems must dissipated keep components from overheating, which increases both complexity access module (DSLAM), price components.
Ethernet
Ethernet dominant protocol local area network (LAN). packet-data protocol, which works over standard twisted pairs, special configurations. characteristics that make highly desirable high-speed protocol used copper loop. Burst-mode packet delivery system Very mature, well-tested technology
Burst Technology
Data most environments, considered "bursty" i.e., there long periods silence, followed brief flood data packets. Bursty data important advantage over continuous rate services, such xDSL. Burst data allows half-duplex communications (i.e., only ends talks time). This creates advantage when dealing with bridge taps gauge changes. When data signal reflected back sender, sender does care, because they simultaneously receiving. receiver end) able filter weaker secondary signal fairly easily. packet data protocols essentially follow same model: only speak (send signals) when there something say. When there data transmit, they send nothing, worst, very level carrier signal. This, turn, provides bursty data another advantage over continuous protocols power. transmitter nothing say, requires very little power operate. been found that under normal conditions, packet-data system idle almost time. Given this idle time, average power consumption rate significantly lower than maximum power consumption rate.
Ethernet Standard
Products built Ethernet standard readily accepted into majority local area networks. addition, because technology mature, possible purchase extremely inexpensive chips integrate into device provide Ethernet compatibility. Lastly, this mature technology well understood, expertise building installing Ethernet networks relatively easy find.
Telephone company
EtherLoop" Technology
Disadvantages
Ethernet delivers data frames across networks broadcast fashion. broadcast network, possible predict will talk given moment, Ethernet uses collision-detection system determine when remote device talking, avoids talking during same time period. not, however, possible completely avoid collisions half-duplex Ethernet. Each collision requires network devices stop talking wait short time before speaking again, which reduces total bandwidth available data delivery.
EtherLoop
EtherLoop takes best features technology, then utilizes burst technology reduce interference problems uses Ethernet packet-data model reduce cost connecting data network. EtherLoop also manages avoid collision problem Ethernet. Because EtherLoop used point-to-point fashion (between subscriber premises), possible define device "master" other "slave." slave speaks only when master allows, which effectively eliminates collisions. Because subscriber loop generally lower quality terms error rate (BER) than private LAN, EtherLoop also manages frame error checking retransmission, using Ethernet checksum. This typically done LANs since error rate low. however, appropriate action take noisy copper telephone loop. EtherLoop also takes advantage flexible symmetry available half-duplex Ethernet communication link. amount time spent transmitting each direction directly proportional amount traffic being offered each direction. user downloading file, then most time spent transmitting downstream direction. this case, nearly EtherLoop bandwidth used downstream communication, with only small proportion available bandwidth being used transmit acknowledgements upstream. user uploading large file, then nearly available EtherLoop bandwidth used upstream communication. user engaged video conference, then bandwidth split symmetrically. These only examples EtherLoop bandwidth split. combination possible. EtherLoop does impose fixed upstream/downstream bandwidth ratio user, instead allows user traffic dynamically symmetry. Lastly, EtherLoop utilizes unique "Spectrum Management" software that derived from other technology. When transmitter silent, quality signal monitored. Crosstalk interference measured, device constantly change internal frequencies reduce crosstalk avoid interference. This used continuous rate adaptation technique. This rate adaptation allows modem immediately adapt noise receives generates, generally improves quality modem's transmissions, reduces interference with other lines cable bundle.
EtherLoop" Technology
EtherLoop following characteristics: High-speed interface either from subscriber, based data traffic Little interference from reflections caused poor wiring (bridge taps gauge changes) power heat dissipation Collision avoidance Intelligent burst management optimize data bandwidth direction given application Instantaneous frequency adaptation directed firmware-based spectrum management features that ensure maximum data throughput spectral compatibility with other data services telco binder combination signaling technology, burst mode delivery, Ethernet frame technologies gives EtherLoop competitive advantages. technology allows existing telephone infrastructure, Ethernet burst technology reduces interference power consumption provides low-cost interface.
Signaling
high-quality subscriber loops EtherLoop designed range frequencies from approximately MHz. This frequency range divided into overlapping frequency spectra, only which active point time. lowest spectrum total frequency range 62.5 kHz, highest frequency range 1.667 MHz. Historically speaking, Hertz equivalent symbol second, which would give EtherLoop theoretical maximum symbol rate 1.667 megasymbols second. Using standard signal modulation techniques, such binary phase shift keying (BPSK), which support data symbol, this would translate 1.667 megabits second.
News
frequency spectrum, however, used effectively cases, based crosstalk, loop quality, forth. This reduces maximum symbol rate.
Good News
Equalization technology considerably improve rate, shorter distances (less than kilofeet), which have less noise, symbol rate start reach 1.667 megasymbol limit.
EtherLoop" Technology
Amplitude
Frequency
Figure Amplitude Modulation Signal
Figure Out-of-Phase Signal Figure Standard Signal
Signal Modulation
There variety advanced signaling techniques that "squeeze" more than Hertz. Several these techniques have been used within analog modems bring maximum speed modem kilobits second. Other techniques, such 2B1Q CAP, used with integrated service digital networks (ISDN) some versions ADSL. EtherLoop uses related signal modulations techniques: quadrature phased shift keying (QPSK) quadrature amplitude modulation (QAM). Figure represents standard carrier wave. sine wave starts height cycles through fixed maximum minimum amplitude.
Amplitude
Frequency
amplitude modulated signal uses different amplitudes represent different values. amplitude values possible, that represents another that represents then symbol transmitted (see Figure
EtherLoop" Technology
QPSK
QPSK uses phase shifting represent different values. Figure shows carrier that begins degrees phase from unmodulated carrier.
Amplitude
Wave starts (90°) instead
Frequency
EtherLoop" Technology
Figure QPSK
four possible symbols used QPSK carrier with 90(, 180(, 270( phase shift. These four possible symbols represent log2(4)=2 bits. This would allow 1.667 megasymbols second represent 3.33 megabits. These symbols represented different carriers. carrier degrees phase shift, call phase component. other carrier degrees phase shift called quadrature component. four symbols described here rotated degrees give equivalent symbols with phase shifts 45(, 135(, 225(, 315(, then they represented I+Q, -I+Q, -I-Q I-Q. This graphed shown Figure
EtherLoop" Technology
Figure QAM16
possible improve beyond this combining amplitude phase modulation. Quadrature amplitude modulation (QAM16) supports possible symbols. These symbols created allowing possible amplitudes each component, such I+3Q, 3I-3Q. This illustrated Figure possible symbols allow log2(16)=4bits/symbol, giving total 6.666 megabits second EtherLoop link that supports 1.6666 megasymbols/second. This concept extended further, using more possible amplitudes. instance, QAM64 would support log2(64)=6 bits/symbol, corresponding megabits/second 1.667 megasymbols/second. number symbols increases, becomes more difficult distinguish them from each other, less noise tolerated communication channel. This means that QAM64 yields better results than QAM16 relatively short loops. Note: These speeds vary based quality loop, length loop, types services binder, number other factors. realistic expect that every subscriber will receive maximum rate time.
EtherLoop" Technology
Maximum Bandwidth
physical limits ADSL EtherLoop nearly identical. speed that reached with ADSL reached, least approximated, with EtherLoop. EtherLoop advantage over ADSL, however. While ADSL delivers data both directions simultaneously, EtherLoop delivers data only direction time. This allows EtherLoop reach peak bandwidth equivalent upstream downstream bandwidth ADSL link. example, 6-megabit second downstream 1-megabit second upstream ADSL service particular copper wire could become peak 7megabit EtherLoop link either direction that same wire. EtherLoop adaptively divide this megabits/second bandwidth between upstream downstream way, dictated user traffic.
EtherLoop" Technology
Ethernet Datapump Codec Transceiver
Figure Client EtherLoop Modem
EtherLoop Modem Implementation With
Figure shows client EtherLoop modem based Digital Thunder" DSP.
EtherLoop chipset consists following devices: Programmable Digital Thunder Datapump CODEC with integrated filters Transceiver Ethernet data presented directly DSP. executes EtherLoop firmware from local flash memory sends resulting data stream glueless serial interface EtherLoop datapump. datapump sends sample stream EtherLoop CODEC, which directly drives EtherLoop transceiver. system leverages Digital Thunder following ways. Ethernet high-speed serial interfaces integrated within ensure system cost power dissipation. programmable allows modem firmware dynamically reconfigured flash update necessary. This allows EtherLoop firmware Spectrum Management software flexible. programmable allows functional enhancement basic modem (for example, running routing voice over software addition EtherLoop modem firmware). EtherLoop CODEC transceiver integrate programmable filtering gain control functions that reduce system footprint, cost, power consumption. CODEC support connection multiple transceivers central office application. This allows low-cost lowpower system which modem manages data from multiple POTS lines
EtherLoop" Technology
Network Architecture EtherLoop technology purposefully designed follow format Ethernet IEEE 802.3. This dual purpose. First, allows EtherLoop appear like Ethernet natively, which reduces product costs performing protocol conversion. Second, allows EtherLoop devices into existing network almost location where Ethernet device operates. There some limitations, however: EtherLoop appropriate only point-to-point link EtherLoop provides lower peak bandwidth longer/lower-quality loops. EtherLoop more expensive than Ethernet. These limitations severe they might appear. Much existing Ethernet place 10baseT substandard, which requires point-to-point connections between network device hub. Peak bandwidth important, combination technical improvement fundamental issues distance wire quality. Even conservative estimates EtherLoop's capabilities indicate that should reach megabits second 3000 feet majority existing wiring, while simultaneously supporting analog voice channel. expense EtherLoop only factor when network completely within limited (100 meter) ranges where Ethernet operates correctly. Given these limitations, clear that EtherLoop market niche long-range Ethernet network extensions. There five major markets where long-range Ethernet viable product: Residential Internet access SOHO (small office home office) Internet corporate access Hotel/hospitality/lodging Internet access (campus area network) deployment Data replacement (LAN extension)
EtherLoop" Technology
Central Office Configuration EtherLoop configuration relatively straightforward. Each subscriber brought back EtherLoop multiplexer shelf product, which EtherLoop ready. voice data channels separated, voice channel passed public switched telephone network (PSTN) switch. data channel passed ThunderSWITCH Ethernet switch, which then connects standard transmission control protocol/internet protocol (TCP/IP) asynchronous transfer mode (ATM) network. Depending needs customer, multiple networks attached, example, some users wish public Internet, some wish telco's regional broadband network, some wish connect private corporate networks.
Figure user maintains very simple network with connection back central office internet access point. access point provides semi-intelligent connection management, providing different access gateways subscribers different services (for example, competing ISPs, corporate networks, etc.) discrimination service performed Thunderswitch Ethernet switch, which intelligently routes data appropriate remote resource (either Internet, potentially several private networks) based destination. multiplexer shown Figure provides management EtherLoop master modems, first stage Ethernet packet multiplexing.
Figure illustrates many possible network architectures. Ethernet networking well understood, there numerous
Internet Access Router(s)
Figure Basic Access Model
ThunderSwitch Ethernet Switch
ANetwork
Public Switched Telephone Network (PSTN)
Voice Switch
ways that data delivered secure flexible ways.
EtherLoop" Technology
Access Router
Ethernet Switch
1/T3/OC3 links EtherLoop Link
EtherLoop Customer Premise Equipment (CPE) Modem
Figure Residential Internet Access
Residential Access residential access model most straightforward (see Figure 10). user typically only device connected EtherLoop link, which simplifies overall architecture. provides Ethernet switching, deliver data several routing resources, which could connections Internet, private Intranets, ATM/frame relay transport network. home user typically will assigned more static address (addresses that change each time user connects network), alternatively have address provided boot-up per-computer dynamic host configuration protocol (DHCP).
EtherLoop" Technology
SOHO Corporate Access SOHO model differs moderately from residential access model (see Figure 11). Typically, there will more extensive subscriber's home/office than residential user. this case, modems must take additional responsibilities bridging Ethernet traffic, keeping local traffic subscriber premises side link. This capability built into EtherLoop modems. that configuration, external modem more appropriate.
Access Router public Internet Ethernet VLAN Switch Backhaul links EtherLoop Link corporate
Figure SOHO Corporate Access
EtherLoop Modem/Bridge
EtherLoop" Technology
Public Data Network Central Office Corporate Office
Tunneling Network Link Private Corporate Network Link VLAN/PVC/SVC
Figure SOHO Corporate Office Access Resources
SOHO corporate model requires some additional resources typically either VLAN permanent virtual circuit (PVC)enabled ThunderSWITCH Ethernet switches correctly route correct traffic corporate network, tunneling protocol software, encrypt packets that delivered over public network corporate access point shown Figure
Each these secure communications strategies advantages drawbacks, discussion which beyond scope this document. Future EtherLoop products that would enhance this market include EtherLoop/Ethernet switches VLAN switches, EtherLoop-based routers, ATM/Frame Relay interfaces.
EtherLoop" Technology
Phone Lines
Floor
Floor
Wiring Closet Router
Multiplexer
Figure Hospitality Industry Access
Hospitality Industry EtherLoop provides straightforward provide high-quality data every room hotel through existing telephone infrastructure. primary model installs EtherLoop modem into wall each room, providing Ethernet-enabled RJ45 jack adjacent RJ11 telephone jack. modem brings voice data channels back together delivers them wiring closet closet. Here, EtherLoop multiplexer separates voice from data passes data Thunderswitch Ethernet switch router, shown Figure This provides advantage over wiring with Ethernet. Half cost Ethernet installation cost re-wiring, distances typically limited feet. EtherLoop model, because distances limited about 4000 feet Ethernet-grade data rates mbps), amount equipment needed deploy service greatly reduced, decreasing cost improving maintainability. Internet protocol (IP) access wide area network (WAN) provided through another Elastic Networks product Elastic Internet Proxy (InterProxy). discussion InterProxy beyond scope this document. enhancements hospitality model similar others: concentrating modems, built-in Ethernet switches, VLAN capabilities.
EtherLoop" Technology
Campus Networks/T1 Replacement campus downtown environment, EtherLoop used provide data network access corporations, universities, institutions speeds megabits second, over existing voice lines. this environment, rack-mounted EtherLoop data service unit (DSU) installed customer premise, with corresponding connection either central office, nearby site, depending nature copper access regulations (see Figure 14).
Central Office Corporate Office
Phone Line
Figure Campus Networks/TI Replacement
Point Presence (POP)
Competitive Local Exchange Carrier/ Internet Service Provider (CLEC/ISP) Multiplexer
EtherLoop" Technology
Technological Comparisons This section describes basic differences between EtherLoop, ADSL, HDSL, multiple virtual lines (MVL), cable modems. With ever-changing nature high-speed technology, some this information date. Duplex Mode HDSL, ADSL, G.Lite full-duplex services. other words, both customer premises equipment (CPE) modems communicate simultaneously. appears highly adjustable full-duplex service, based described capabilities. Cable modems either full half-duplex services, depending technology used requirements network connection. Most half duplex. EtherLoop half-duplex service. Only devices communicate time. Full duplex provides advantages better link resource utility because side does have wait other communicate. trade-off this, divided bandwidth. Each side must either distinct transmit receive wires, carefully separated upstream downstream spectrum avoid interference. Half duplex provides advantage full bandwidth utilization both directions. While they transmitting, each device entire link itself. However, there turnaround time, which reduces average bandwidth. Half duplex suitable continuous rate services, such broadcast-quality video. However, suitable packet-based video delivery. Privacy HDSL, ADSL, MVL, G.Lite, EtherLoop point-to-point, private services. only eavesdrop point-to-point service physically line. Once signal leaves local loop, this privacy subject nature network which data resides. Cable modems utilize shared network where devices visible other devices cable segment. Privacy important corporate data integrity personal privacy. market shown, however, that most individuals consider privacy unimportant with regard residential Internet access. Business customers, however, value privacy, which provided combination physical security encrypted data streams. Delivery System HDSL, ADSL, G.Lite, continuous data network products. other words, they continuously transmit, whether there data local loop network transmit not. When there data transmit, these devices deliver idle data until they shut down. EtherLoop cable modems both packet data network products. They deliver idle data when there data send.
EtherLoop" Technology
advantage continuous data network quantifiable reliability link. possible provide continuous data services, such voice video, without compromise quality network congestion. Either there enough bandwidth, there not. advantage packet network efficiency. Many network applications require continuous data operate properly, continuous data networks reliability wasted. addition, some continuous data services, such voice traffic, characterized packet data. Voice traffic significant amount silence, which makes "real" data pattern voice call profile high-speed packet network. side effect from only-speak-when-necessary nature packet network reduction power consumption. Because does require high power when idle, packet network uses significantly less power than equivalent bandwidth continuous data network. Protocols
Because continuous data delivery system, HDSL, ADSL, G.Lite adopted fairly easily provide Ainterface. This allows these products take advantage ATM's carefully planned traffic management data delivery systems. Again, continuous data product provide packet data network interface, placing idle data between valid packets. mentioned before, this inefficient power consumption, still possible. Therefore, HDSL, ADSL, G.Lite provide Ethernet other packet-network protocols, with appropriate conversion logic. Cable modems provide Aservices, bandwidth requirements each home/office considerably reduce number users system when compared Ethernet other packet-based cable modem systems. Most cable modem systems Ethernet communications standard because efficiency serving large numbers customers with shared medium. EtherLoop primarily designed operate with Ethernet other packet networks. They many components Ethernet protocols internally, which allows conversion from "true" Ethernet handled very efficiently reliably. EtherLoop should able provide Aservices high rate speed interfaces such frame user network interface (FUNI) used. also possible provide continuous (256-kilobits-per-second) speed, this capability been investigated. Concentration HDSL cannot easily concentrated. designed point-to-point continuous pipe. ADSL G.Lite concentrated, complex data characteristic must "bursty," like data that found packet network, modem processor must significantly faster than modem. possible concentrate continuous data system, unless speed communications link exceeds utility link individual users. example, reliable bandwidth available local loop megabits second, each modem sends receives data megabits second, possible subscribers utilize same modem. Another option pool ADSL modems among several subscribers allowing subscribers begin sessions. This same model used dial-up access, intelligent these resources. Cable modems are, their very nature, concentrating devices. Only device transmits time, `CO' modem head-end) uses exactly same technology individual subscribers. appears capable concentration, based fundamentals. However, service description depends ability offer multiple services line, which compatible with concentration model. EtherLoop provide concentration multiple subscribers because statistical likelihood idle time. This same principle that allows Ethernet work. possible monitor each several subscribers rapid round-robin fashion, detect incoming data, quickly respond data. This system avoids possibility multiple transmissions because modems organized master slave. modem does deliver data until modem permits This allows master device simultaneously support multiple client devices. Distance
EtherLoop" Technology
HDSL designed travel 12,000 feet using pairs copper, depending implementation. ADSL's maximum range certain, although current literature places limit 18,000 feet. Full-duplex cable modems effectively unlimited range. Half-duplex cable modems appear limited approximately 16,000 feet. G.Lite operates 20,000 feet, advertised work 24,000 feet. EtherLoop operates distances 21,000 feet, possible extend that range. distances available EtherLoop are, theory, also available ADSL. distance increases, speed decreases. Speeds HDSL fixed-speed service, rated 1.544 megabits second, both downstream. This accomplished with pairs, with one. single pair version (HDSL2) just finished standarization process, expected deployed quantities until late 1999. Cable modem speeds vary, based quality link equipment used. Currently, best stated maximum seen megabits second, shared among substantial group subscribers. number users increases, amount bandwidth available user decreases considerably. Typical values megabits downstream kilobits upstream. ADSL speeds vary well, also based quality link equipment used. Theoretical maximums megabits downstream megabit upstream stated. practice, however, with real-world loops, equipment placed field typically rates lower than that. G.Lite advertises speeds 1.5-megabit downstream, 384kilobits upstream range. advertises speeds kilobits, either upstream downstream, both. possible divide bandwidth, example, kilobits kilobits down, 384/384. EtherLoop rated speeds megabits second with QAM-64 distances 4000 feet less. Past that, EtherLoop expected fall into same general speed range addition upstream downstream ADSL signal.
EtherLoop" Technology
Conclusion This technical paper shown that EtherLoop "just another DSL." EtherLoop communications architecture that leverages programmable "wring" maximum possible bandwidth twisted pair copper pipe, does this that flexible enough comprehend wide variety data networking needs. long term, based EtherLoop technology will have measurable impact standard methods transmitting packet data over twisted pair copper wiring. Acknowledgment Sherlock author this technical paper.
EtherLoop" Technology

Broadband Access Group 0.6August 1999 Texas Instruments (TI) rese

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