1999 (Version 1.0) Summary This white paper gives overview digital mod

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1999 (Version 1.0) Summary This white paper gives overview digital mod

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Xilinx Work Digital Modems
1999 (Version 1.0) Summary This white paper gives overview digital modem technologies Xilinx high volume programmable devices used implement complex system level glue digital modem designs. Xilinx Products XC9500 CPLDs, Spartan FPGAs White Paper
This white paper gives overview digital modem technologies Xilinx high volume programmable devices used implement complex system level glue digital modem designs. Xilinx device families targeted these high volume applications include XC9500 CPLDs Spartan FPGAs. flow this document will start with overview various digital modem technologies factors driving their deployment. will next examine major functional blocks digital modem give overview Application Specific Standard Products (ASSPs) that used each functional block. will then illustrate system level glue functions that needed several different digital modem configurations While this document focuses applications these devices digital modem applications, examples discussed illustrate many issues found other designs; specifically, cost effectively interface complex ASSPs with incompatible interfaces. ASIC vendors have abandoned traditional solution this class problems, small ASIC, they moved towards system chip market. Fortunately system designers, classes cost PLDs such Spartan family have filled this void with devices that replace density ASICs retain time market advantages FPGAs.
Overview
Internet users continuing demand higher bandwidth access net. Both class corporate users services driving this. Corporate users being brought Internet corporations begin move away from their private networks. Many using Internet connect remote offices telecommuters their corporate Local Area Networks (LANs) using Virtual Private Network (VPN) technologies. High bandwidth access corporate resources necessary maintain productivity these remote workers. Internet services coming online also benefit from higher bandwidth connection user. Examples include streaming video that integral part every online news service. Users online shopping services need greater bandwidth support high-resolution images that make online buying decision practical. face this demand analog modem technology road with generation devices. Increasing Internet access bandwidth requires migration digital modem technologies.
1999
www.xilinx.com 1-800-255-7778
Xilinx Work Digital Modems
While there numerous approaches being proposed including wireless satellite technologies, generally accepted that bulk users will their high bandwidth digital Internet access using either cable modem Digital Subscriber Line (DSL) modem technologies. Cable modems offer data rates Mbps with caveat that will described later. technologies offer variety access rates Mbps. ISDN original digital subscriber service. ISDN delivers Kbps bandwidth subscriber supports both digital voice data services simultaneously over same line.
ISDN
Once touted ultimate subscriber technology, ISDN seen slow deployment until recently, lack standardization high cost. Most Regional Bell Operating Companies (RBOCs) deliver ISDN dial-up, metered service. This means that during business hours users charged each minute ISDN connection operating. ISDN also lost appeal analog modems have reached Kbps level. Modem suppliers provide software that lets users modems single Kbps connection, close data rate available from ISDN connection. other spectrum, cable modem services delivering bandwidths that order magnitude greater than ISDN. While ISDN will disappearing time soon, projections indicate that growth ISDN market flattening. expected that ISDN will relegated applications where cable modem service available. Analysts indicate there approximately million ISDN lines deployed This represents approximately 1.1% lines.
Cable Modems
Cable modems same coaxial cable that used deliver cable service provide connection Internet. Digital data modulated transmitted channels reserved data services. There standards cable modems. North America Data Over Cable Service Interface Specification (DOCSIS), developed CableLabs used basis interoperable cable modem equipment. Europe cable modem equipment based specifications developed Digital Audio Video Council (DAVIC). spite higher bandwidth that cable modems appear offer over technologies, there some limitations this technology. First bandwidth shared amongst users neighborhood. This result multidrop configuration cable. This means that homes neighborhood effectively wired together same data. This implications. First Mbps bandwidth that cable modems provide shared amongst users neighborhood. second that unless data encrypted before transmitted, vulnerable interception other users. According Gecko Research, 600,000 users U.S. currently using cable modem services. This represents penetration million households that could subscribe.
Digital Subscriber Loop (DSL) technologies same twisted pair copper wiring that used voice telephone service deliver high speed digital data. fact same line that used service used voice service using standard analog phone. standardization issues services have gotten slow start. According Gecko Research, there currently 50,000 service subscribers U.S. This represents meager .03% million phone lines U.S. However expected that services will rapidly rolled over next years.
1999
www.xilinx.com 1-800-255-7778
Xilinx Work Digital Modems
Technologies Once again, lack unified standard been issue that slowed deployment services. range technologies that have been deployed reflects difficulty problem being solved. Table compares several characteristics more significant variants. Table Technology Comparison Technology HDSL HDSL2 SDSL ADSL VDSL IDSL Pairs Required Upstream data Rate Mbps Mbps Kbps Kbps Mbps Kbps Downstream data rate Mbps Mbps Kbps Mbps Mbps Kbps Reach
Driving high-speed data down copper pairs from central office subscriber's home requires sophisticate digital signal processing technology. problem compounded variances line length, cross talk, wire gauge other factors. response this various technologies that have appeared make different tradeoffs between data rate, distance that data driven complexity line-coding scheme used. Fortunately players have agreed agreed common ADSL technology which described ANSI Standard T1.413, based Discrete Multi Tone (DMT) coding scheme. There variants ADSL standard that described standards G.992.1 G.992.2 G.992.1 original full rate, Mbps, specification. problem with this standard that requires installation "splitter" customer premises support both voice data over same line. G.992.2 (formerly known G.Lite) developed Rockwell eliminate need splitter customer line. tradeoff simplified installation reduced data rate, Mbps.
Digital Modems Versus SOHO Routers
Digital modem technology packaged either traditional modem format Small Office Home Office (SOHO) router. Figure illustrates they typically deployed.
Figure Application Digital Modems SOHO Routers figure left illustrates standard modem. modem interfaces: Wide Area Network (WAN) interface, connected phone line, host interface that connected computer. Traditionally host interface serial interface such RS-232 case internal modem host interface computers bus, usually bus. case function modem modulate demodulate (hence term modem) data transmission across interface.
1999
www.xilinx.com 1-800-255-7778
Xilinx Work Digital Modems
explosive growth Local Area Networking created class devices, targeted SOHO applications that combine modem with Access Router. access router used determine whether traffic local segment needs forwarded WAN. SOHO routers also network firewall; that they used keep hackers from accessing local systems Internet connection. SOHO routers typically look like external modems with Ethernet connection rather than host connection. fact 3Com markets their SOHO access router products under name "LAN Modem". advantage SOHO router over standard modem that lets multiple users share single Internet connection. increasing interest home technology expected increase demand this class product.
Digital Modem Architecture
Whether product cable modem, modem, SOHO router these digital modem products share common functional blocks shown Figure
Figure Digital Modem Architecture functional blocks that make system are: interface containing modem functions. complex consisting plus ROM, responsible configuring managing system. Host Interface used connect modem host computer Interface used connect SOHO router
Each these blocks typically implemented small number ASSPs. most cases there mismatches between ASSPs used implement each these blocks. system level glue needed interface these blocks where opportunities Xilinx high volume FPGA CPLD products. following will examine each these functional blocks implemented. Digital Modem Interfaces interfaces implemented with specialized signal processing ASSPs, each which been targeted specific application. While there talk multifunction interfaces based general-purpose programmable technology, each interface currently requires specialized chipset. Functions that included these interfaces include: Data encoding decoding Driving data high speed over long lines requires sophisticated line coding schemes. Clock recovery high-speed data transmission schemes synchronous nature part line coding function encoding extraction clock information with data.
1999
www.xilinx.com 1-800-255-7778
Xilinx Work Digital Modems
Adaptive equalization range line lengths that these interfaces must support forces adaptive equalization schemes deal with line reflections. Error Detection Correction Even with most sophisticated coding schemes line noise will result data errors. result most high speed transmission technologies include error detection correction functions Transmission Convergence These functions include framing Acell delineation included simplify interface rest system.
told, range complexity these functions require large quantities million gates) highspeed logic, much which arithmetic nature. These factors make FPGA implementations these functions cost effective production. ASSP Providers Alcatel dominates market ASSPs with greater than market share. This result fact that Alcatel also leading supplier ADSL equipment. Manufacturers ASSPs fiercely competing this rapidly growing market. players working next generation, cost reduced chipsets keep most product information under NDA. T1.413 compliant solutions available available from Alcatel, Analog Devices, Motorola, Lucent. these devices with exception Lucent offering used either modem central office applications. Lucent WildWire chipset targeted card market supports only G.992.2 (G.Lite) operation. Table summarizes available T1.413 compliant solutions. Table ASSPs Supplier Alcatel Chipset Name MTK-20131 Components MTC-20136 ADSL Transceiver Controller (ARM CPU) MTC-20135 modem AFramer MTC-20134 Analog Front TNETD2100 Digital Interface TNETD2200 ADSL Transceiver TNETD2011 Codec THS6002 Line Driver ADSP 218x AD6435 Digital Interface Controller AD6436 Engine AD6437 Analog Front MC145650 ADSL Transceiver MC03AX1456 ADSL Line Driver DSP1690 ADSL T7780 ADSL line interface Interface Utopia
TNETD2000
Utopia
AD20msp910
Proprietary
Motorola Lucent
CopperGold WildWire
Proprietary
1999
www.xilinx.com 1-800-255-7778
Xilinx Work Digital Modems
Cable Modem ASSP Providers Broadcom dominates market cable modem ASSPs. only significant competition horizon form Conexant CN9414 DOCSIS cable modem. This device includes only modem functions, also RISC microprocessor, USB, Ethernet interfaces. Table Cable Modem ASSPs Supplier Broadcom Conexant Components BCM6010 DOCSIS Cable Modem CN9414 DOCSIS Cable Modem Interface Utopia Single Chip Comments Market leader CPU, Ethernet,
Interfaces
interfaces used local side SOHO router. This interface gives users access connection. most popular interface this application Ethernet; usually Mbps twisted pair version (10BASET). also expect products being introduced that support Phone Networking Alliance (PNA) version Ethernet. technology supports Mbps Ethernet networking over existing phone wiring. Better yet, technology supports simultaneous same wiring phone service. Another network interface that been used first generation modems Mbps ATM. Ethernet will likely replace this interface next generation products. Token-Ring interfaces found only products targeted corporate markets. Interface ASSP Providers interface ASSPs targeted adapter card market. result virtually include host interface. addition software support comes form drivers operating systems. Currently complete Ethernet interface solution consists chips; interface controller commonly referred term Medium Access Controller (MAC) physical layer device (PHY). Intel just introduced controller that integrates both functions into single chip, this intensely price competitive market expect other vendors introduce equivalent products soon. Table illustrates offering available from market leaders Intel AMD. There numerous second tier vendors, including several from Taiwan, offering products this space. Table ASSPs Supplier Intel Components 82559 Fast Ethernet Controller 21145 Phoneline/Ethernet Controller Am79C972 PCnet-FAST+ Controller Am79C978 1/10 Mbps Home Networking Controller 100BASE-TX None PNA, 10BASE-T
1999
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Xilinx Work Digital Modems
Host Interfaces
Host interfaces used local side modem. This interface used connect modem server, other networking equipment. internal modem this interface computer, typically PCI. past most popular interface external modems been RS-232. Unfortunately this interface fast enough support data rates provided digital modems. result manufacturers cable modems have move other interfaces. most popular choice designs been Universal Serial (USB). advantage this interface that been incorporated into core logic over year result included standard feature PCs. downside that while data rate Mbps, most vendors have been able more than Mbps from existing implementations. While adequate full rate cable modem applications, this limitation Mbps supported G.Lite which expected make bulk modem shipments. addition, Intel announced which will support data rates excess Mbps. FireWire, which been positioned serial interface peripherals, currently supports data rates Mbps. Unfortunately while built Macintoshes, supporting FireWire requires card most systems. Host Interface ASSP Providers Unlike interface ASSPs which almost exclusively focused adapter card market, host interface ASSPs typically offered versions adapter cards peripheral devices such mice keyboards. Like interface ASSPs host interface ASSPs targeted adapter cards typically include interface. Again software support provided form drivers Microsoft Windows. Host interface ASSPs targeted device applications, such keyboards, typically include eight-bit interface intended connection cost micro controller. Software support normally provided form example source code that targeted wide range processors used these applications. There numerous suppliers ASSPs USB, some which listed here. While most visible supplier products FireWire, they also available from Philips, IBM, Sony. Table Host Interface ASSPs Supplier Lucent National Cypress Components USS-302 PCI-to-USB OpenHCI Host Controller USS-820 General-Purpose Device Controller USBN9602 General-Purpose Device Controller CY7C64011General-Purpose Device Controller Firewire TSB12LV22 OHCI Link Layer Controller TSB41LV03 Mbps Interface Proprietary Proprietary Proprietary Comments
8-bit RISC
1999
www.xilinx.com 1-800-255-7778
Xilinx Work Digital Modems
Modem With ATM25 Early modems typically supported Mbps interface. reason this that simplest ways Acells that typically used transmission
Figure Modem with ATM25 Host Interface Internally configuration simple fact that most Adevices AForum defined Utopia interface transfer Acells. result interfacing chipset Mbps local interface simply consists direct connection between Utopia interface chipset Utopia interface physical layer device. small used initialize ASSPs handle error conditions. connected 8-bit management that supported physical layer vendors. amount glue logic required this minimal most cases. While this approach results simple design does well market expectations. assumes that user Mbps Aadapter installed Since installed base these adapters close zero, this means that user will have install system. This problem since installing adapter cards still creates significant anxiety with most users results large number calls technical support hotline. this reason Alcatel modem supports both Ethernet interface. While providing Ethernet support does increase probability that user already compatible interface installed, does eliminate need most users open their system. Modem Add-In Card users that intimidated opening their computer installing cards, internal modem still most cost-effective solution. case internal modem this means interfacing Utopia chipset bus.
Figure Modem Card past this been accomplished through Adevice called segmentation reassembly controller (SAR). These devices analogous controllers used Ethernet adapter cards like them include interface. These devices relatively expensive. more cost effective versions available; IDT77222 costs volume requires wide pool SRAM job.
1999
www.xilinx.com 1-800-255-7778
Xilinx Work Digital Modems
significant amount complexity resulting cost this interface eliminated transferring functions hosts implementing only interface functions Utopia interface. doing this interface glue functions implemented Spartan device less than $10. Modem With modem that provides interface attractive since only eliminates need users open their systems also provides means supporting non-PC systems such popular iMac. these reasons this popular approach next generation modem designs.
Figure Modem With Host Interface problem designer such product that means gluing together several ASSPs that were designed directly interconnect. system glue must interface Utopia that transfers Acells from chipset, proprietary micro controller interface that provided controller micro controller itself. addition just connecting pins glue logic needs implement functionality that micro controller overwhelmed with transferring data software. There also issue that protocol between modem host system across been standardized. This means that each modem will require driver support from manufacturer. This case with most analog modems, which driver that comes with Windows. Therefore ability update design field compatible with whatever standard that does emerge valuable feature vendors trying products market quickly. Both glue logic complexity lack standardization make this type product ideal candidate FPGA based glue logic. cost sensitive nature this high volume market makes Spartan ideal solution. SOHO Router Designers SOHO routers also face task gluing together system from ASSPs with differing interfaces. Also features that differentiates router from modem, interaction with each packet that passes through also means that higher performance needed interface between network interfaces must more efficient.
Figure SOHO Router
1999
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Xilinx Work Digital Modems
Since interface usually includes Ethernet interface natural approach glue other blocks PCI. case chipset this usually means interfacing Utopia PCI, add-in card example Spartan device provides very cost means accomplishing this. Once again functionality that needed convert Acells into packets that transferred over Ethernet performed with some simple hardware support implemented FPGA. Many embedded RISC controllers come with interfaces built designer chosen that doesn't, then same Spartan device implement host bridge lower cost that off-the-shelf devices designed that purpose. Spartan FPGA also used implement routing specific functions such header parsing, checksum calculation buffer management leverage MIPs more effectively.
Conclusion
Until digital modem ASSP manufacturers deliver more highly integrated solutions designers these products will faced with task interfacing variety devices with incompatible interfaces. Xilinx high volume FPGA CPLD technologies provide system designers with cost effective solutions that retain traditional time market advantage.
1999
www.xilinx.com 1-800-255-7778

1999 (Version 1.0) Summary This white paper gives overview digital mod

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