US 2003O223446A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2003/0223446A1 Lewin et al. (43) Pub. Date: Dec. 4, 2003

(54) SYSTEM FOR ENCAPSULATING (52) U.S. Cl...... 370/419,375/220 FRAMES OVERVERY HIGH SPEED DIGITAL SUBSCRIBER LINES (57) ABSTRACT (75) Inventors: Amit Lewin, Tel Aviv (IL); Opher An apparatus for and method of encapsulating Ethernet Yaron, Tel Aviv (IL); Alon Hurwitz, frame data in Very high speed Ramat Gan (IL); Yuri Poddobny, (VDSL) frames. The VDSL frames are transmitted over a Herzelia (IL) point to point VDSL link where they are subsequently extracted and forwarded as standard Ethernet frames. The Correspondence Address: VDSL facility transport system comprises an Ethernet to Edward K. Runyan VDSL Consumer Premises Equipment (CPE) coupled to a McDonnell Boehnen Hulbert & Berghoff DSL Access Multiplexor (DSLAM) over a VDSL transport 32nd Floor facility. The Ethernet to VDSL CPE functions to receive a 300 S. Wacker Drive 10BaseTEthernet signal and encapsulate the Ethernet frame Chicago, IL 60606 (US) into a VDSL frame for transmission over the VDSL facility. The DSLAM is adapted to receive VDSL frames, extract (73) Assignee: 3COM CORPORATION Ethernet frames therefrom and generate and output a stan dard Ethernet Signal. Ethernet frames are encapsulated (21) Appl. No.: 10/430,480 within VDSL frames and transmitted on the wire pair without regard to the state of the SOC signals. This over (22) Filed: May 6, 2003 comes the problems associated with Syncing the transmis Related U.S. Application Data sion of the Ethernet data with the SOC signals. The present invention also provides a method of providing the receiving (63) Continuation of application No. 09/318,887, filed on station an indication of the start of a VDSL frame. A May 26, 1999, now Pat. No. 6,608,834. preamble having certain desirable characteristics Such as good autocorrelation properties, is used by the receiving Publication Classification station to identify the start of a VDSL frame. To further ensure that a detected Start of frame is valid, the length field (51) Int. Cl...... H04L 12/56 of the VDSL frame is examined for a legal length value.

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SYSTEM FOR ENCAPSULATING ETHERNET 0005. As use of the Internet and online services continues FRAMES OVER WERY HIGH SPEED DIGITAL to spread, So does the use of more complex applications, SUBSCRIBER LINES Such as interactive Video games, telecommuting, business to business communications and Videoconferenceing. These FIELD OF THE INVENTION complex applications place Severe Strains on data networks 0001. The present invention relates generally to data because of the intensive bandwidth required to deliver communication Systems and more particularly relates to a data-rich transmissions. For example, a telecommuter who System for transporting Ethernet frames over Very high requires computer aided design (CAD) Software to be trans ported over the data network requires a high-bandwidth data speed Digital Subscriber Lines (VDSL). pipeline because of the Significant size of CAD files. Simi BACKGROUND OF THE INVENTION larly, a business to business transaction in which large database files containing thousand of customer records are 0002 There is a growing need among both individuals eXchanged also consumes large amounts of bandwidth. The and enterprises for access to a commonly available, cost Same is true for users Seeking entertainment value from Sites effective network that provides Speedy, reliable Services. offering high quality Video and audio. The lack of available There is high demand for a high-Speed data network, one bandwidth in today's data networks is the primary barrier with enough bandwidth to enable complex two-way com preventing many applications from entering mainstream use. munications. Such an application is possible today if, for Just as processing power limited the effectiveness of early example, access is available to a university or a corporation PCs, bandwidth constraints currently limit the capabilities of with sufficient finances to build this type of network. But for the average home computer user or Small business, access to today's modem user. high Speed data networks is expensive or Simply impossible. 0006 Most computer modem users access data through Telephone companies are therefore eager to deliver broad the Standard telephone network, known as plain old tele band Services to meet this current explosion in demand. phone service (POTS). Equipped with today's speediest modems, dial up modems on a POTS network can access 0003. One of the problems is that millions of personal data at a rate of 28.8, 33.6 or 56 Kbps. Dial up modem computers have found their place in the home market. transmission rates have increased significantly over the last Today, PCs can be found in approximately 43% of all United few years, but POTS throughput is ultimately limited to 64 States households and a full 50% of United States teenagers Kbps. While this rate may be acceptable for some limited own computers. Virtually every PC sold today is equipped applications like e-mail, it is a Serious bottleneck for more with a modem, enabling communication with the outside complex transactions, Such as telecommuting, Videoconfer world via commercial data networks and the Internet. Cur enceing or full-motion video viewing. To illustrate, full rently, people use their PCS to Send and receive e-mail, to motion Video compressed, using the Motion Picture Enter access online Services, to participate in electronic commerce tainment Group (MPEG)-2 standard requires a data stream and to browse the Internet. The popularity of the Internet is of approximately 6 Mbps, or roughly 208 times the through Such that there are an estimated 50 million users around the put of a 28.8 Kbps modem. Thus, using today's dial up globe. These figures indicate that in the past few years the modems, it would take more than 17 days to capture two personal computer has fueled a dramatic increase in data hours of Video. AS bandwidth demands continue to grow, communications and the corresponding demands on the data providerS Search for better ways to offer high Speed data networks that carry the traffic. access. Further complicating the problem is the need to 0004. The Internet serves as a good example of the deliver all these complex Services at an affordable price. increased demands that have been placed on data networkS. 0007 Today's most popular data access method is POTS. At first, Internet acceSS consisted of text only data transferS. But as discussed previously, POTS is limited when it comes Recently, with the popularity of the World Wide Web to large data transfers. An alternative to POTS currently (WWW) and the construction of numerous sites with high available is Integrated Services Digital Network (ISDN). In quality content, coupled with the development of Internet the past few years, ISDN has gained momentum as a browsers such as Mosaic, Netscape Navigator and Microsoft high-speed option to POTS. ISDN expands data throughput Explorer, the use of graphics, audio, Video and text has to 64 or 128 Kbps, both from the network to the home and Surged on the Internet. While graphics, audio and Video from the home back to the network, and can be technically make for a much more interesting way to View information made available throughout much of the United States and in as opposed to plain text, bandwidth consumption is signifi many other parts of the globe. Similar to POTS, ISDN is a cantly more. A simple background picture with accompa dedicated Service, meaning that the user has Sole access to nying text requires approximately 10 times the bandwidth the line preventing other ISDN users from sharing the same needed by text alone. Real-time audio and Streaming video bandwidth. ISDN is considered an affordable alternative, typically need even more bandwidth. Because of the and in general, ISDN is a much better Solution for applica increased requirement for bandwidth, activities Such as tions Such as Web browsing and basic telecommuting. browsing home pages or downloading graphics, audio and However, like POTS, it severely limits applications such as Video files can take a frustratingly long period of time. telecommuting with CAD files and full-motion video view Considering that the multimedia rich World Wide Web ing. The latter requires roughly 39 times the throughput than accounts for more than one quarter of all Internet traffic, it that provided by ISDN. Multichannel multipoint distribution is easy to See why the demand for bandwidth has outpaced service (MMDS), a terrestrial microwave wireless delivery the Supply. In addition, the creative community is pushing System, and direct broadcast Satellite (DBS), Such as the envelope by offering audio and full motion video on DirecTV and US Satellite Broadcasting (USSB), are wireless numerous sites to differentiate themselves from the millions networks. They both deliver high bandwidth data steams to of other sites competing for maximum user hits. the home, referred to as downstream data, but neither has a US 2003/0223446 A1 Dec. 4, 2003

return channel through which data is sent back over the 0014. It is intended that the SOC signal be used by the network, referred to as upstream data. Although it is a CPE to synchronize the transmission and reception of the relatively affordable System to deploy for broadcast appli data to and from VDSL modem. In the case of transporting cations, because it requires no cable wires to be laid, it falls Ethernet data over the VDSL facility, a problem arises, Short in interactive acceSS. In order to use a wireleSS System however, when attempting to sync Ethernet frames to VDSL for Something as basic as e-mail, an alternate technology frames. The problem with using these SOC signals is that the Such as a telephone line must be used for the upstream VDSL frame is a fixed number of bytes, e.g., 256 bytes, communications. whereas the Ethernet frame may vary from 64 to 1518 bytes. 0008 Another network delivery system is asymmetric Designing and implementing the circuitry, e.g., State digital subscriber line (ADSL). Offering a downstream machines, timing and framing circuits, etc., to perform the capacity of 6 Mbps or more to the home, ADSL has the protocol matching, i.e., Sync timing between Ethernet downstream capacity to handle the most complex data frames and VDSL frames is very complicated and hence transferS, Such as full motion video, as well as an upstream expensive to implement. capacity of at least 500 Kbps. However, due to its limitation 0015. It is desirable to have a means of transporting of downstream bandwidth capacity, it essentially is a Single Ethernet frame data over a VDSL transport facility that does Service platform. Also, Since it has to overcome the chal not require the complicated circuitry and State machines lenge of reusing Several thousand feet of twisted pair wiring, when utilizing the SOC signals provided by the VDSL the electronics required at each end of the cable are complex, modem. and therefore currently very expensive. 0009) Hybrid fiber coax (HFC), a network solution SUMMARY OF THE INVENTION offered by telephone and cable companies, is yet another option for delivering high bandwidth to consumers known in 0016. The present invention is an apparatus for and the art. However, HFC has limitations. HFC networks method of encapsulating Ethernet frame data in Very high provide a downstream capacity of approximately 30 Mbps, speed Digital Subscriber Line (VDSL) frames. The VDSL which can be shared by up to 500 users. Upstream band frames are transmitted over a point to point VDSL link width is approximately 5 Mbps and also is shared. A where they are Subsequently extracted and forwarded as disadvantage with HFC is that shared bandwidth and limited Standard Ethernet frames. upstream capacity become Serious bottlenecks when hun 0017. A typical VDSL facility transport system com dreds of users are Sending and receiving data on the network, prises an Ethernet to VDSL Consumer Premises Equipment With Service increasingly impaired as each user tries to (CPE) coupled to a DSL Access Multiplexor (DSLAM) over access the network. a VDSL transport facility. The DSLAM is typically located 0010. It is a current trend among telephone companies at the curb or before the last mile in a subscriber loop. The around the World to include existing twisted pair copper Ethernet to VDSL CPE functions to receive a 10BaseT loops in their next generation broadband acceSS networkS. Ethernet Signal and encapsulate the Ethernet frame into a Hybrid Fiber Coax (HFC), a shared access medium well VDSL frame for transmission over the VDSL facility. Like Suited to analog and digital broadcast, comes up short when wise, the Ethernet to VDSL CPE also functions to receive a utilized to carry Voice telephony, interactive Video and high VDSL signal, extract Ethernet frames therefrom and output Speed data communications at the same time. them as standard 10BaseT Ethernet signals. 0011 Fiber to the home (FTTH) is still prohibitively 0018. The DSLAM is adapted to receive VDSL frames, expensive in the marketplace that is Soon to be driven by extract Ethernet frames therefrom and generate and output a competition rather than costs. An alternative is a combina standard Ethernet signal. Likewise, the DSLAM is also tion of fiber cables feeding neighborhood Optical Network adapted to receive Standard Ethernet frames from an Ether Units (ONUs) and last leg premises connections by existing net input signal and encapsulate them in VDSL frames for or new copper. This topology, which can be called fiber to transmission over the VDSL facility. the neighborhood (FTTN), encompasses fiber to the curb 0019. In accordance with the invention, the SOC signals (FTTC) with short drops and fiber to the basement (FTTB), provided by the VDSL are not utilized in transmitting the Serving tall buildings with Vertical drops. Ethernet frame data over the VDSL facility. Ethernet frames 0012. One of the enabling technologies for FTTN is very are encapsulated within VDSL frames and transmitted on the high rate digital subscriber line (VDSL). VDSL is an emerg wire pair without regard to the state of the SOC signals. This ing Standard that is currently undergoing discussion in ANSI overcomes the problems associated with Syncing the trans and ETSI committees. The System transmits high-Speed data mission of the Ethernet data with the SOC signals. over short reaches of twisted pair copper telephone lines, with a range of Speeds depending upon actual line length. 0020. The present invention also provides a method of 0013 The VDSL standard as provided by the VDSL providing the receiving Station an indication of the Start of Draft Specification being drafted by the ANSI T1E1.4 a VDSL frame. A preamble having certain desirable char Technical Subcommittee, provides guidelines for the trans acteristics Such as good autocorrelation properties is used by mitter and receiver within the VDSL modem. The connec the receiving station to identify the start of a VDSL frame. tion between the VDSL modem and the CPE specifies a To further ensure that a detected start of frame is valid, the number of signals including TxData, RxData, RXErr, length field of the VDSL frame is examined. TXCLK, RXCLK and TxSOC and RXSOC. The latter two 0021. The receiving station performs a check to deter signals, i.e., TxSOC and RXSOC, provide an indication of mine whether the preamble pattern detected is actually a the start of the VDSL frame to the CPE for both transmission preamble or is Ethernet data within the payload of the VDSL and reception. frame. The length field contains 16 bits allowing for 65,536 US 2003/0223446 A1 Dec. 4, 2003

combinations but only 1518-64=1454 of them are valid 0027 FIG. 2 is a block diagram illustrating the DSL since the payload of the VDSL frame carries only Ethernet Access Multiplexor (DSLAM) in more detail; frame data which can only range from 64 to 1518 bytes. Thus, the length field is checked to further narrow the 0028 FIG. 3 is a block diagram illustrating the Ethernet chance of a wrong Synchronization. to VDSL CPE in more detail; 0029 FIG. 4 is a diagram illustrating the format of a 0022. There is provided in accordance with the present Standard Ethernet frame; invention a method of transporting Ethernet frames over a Very high speed Digital Subscriber Line (VDSL) transport 0030 FIG. 5 is a diagram illustrating the interframe gap facility coupling a first communication device and a Second between two Ethernet frames; communication device, the method comprising the Steps of 0031 FIG. 6 is a diagram illustrating the format of VDSL receiving an input Ethernet frame data on the first commu frames that are transmitted over the VDSL facility; nication device from a first Ethernet compatible communi cation device coupled thereto, encapsulating the received 0032 FIG. 7 is a timing diagram illustrating the rela Ethernet frame within a VDSL frame, inserting a preamble tionship between the Rx Err, SOC and VDSL data signals; and length field in the VDSL frame, transmitting the VDSL and frame over the VDSL transport facility, receiving VDSL 0033 FIG. 8 is a flow diagram illustrating the receiver frame data on the Second communication device, extracting Synchronization method of the present invention. the Ethernet frame from the received VDSL frame and generating an output Ethernet frame therefrom and trans DETAILED DESCRIPTION OF THE mitting the output Ethernet frame to a Second Ethernet INVENTION compatible communication device coupled to the Second Notation Used Throughout communication device. 0034. The following notation is used throughout this 0023 The step of encapsulating comprises the step of document. stripping off the preamble and start of frame fields from the Ethernet frame before placing the Ethernet frame in the VDSL frame. The length field inserted in the VDSL frame Term Definition represents the length of the Ethernet frame without the ADSL Asymmetric Digital Subscriber Line Ethernet preamble and Ethernet start of frame fields. The ANSI American National Standards Institute Step of generating comprises the Step of adding Ethernet CAD Computer Aided Design preamble and Ethernet start of frame fields to the extracted CAP Carrierless Amplitude Modulation/Phase Modulation Ethernet frame. CPE Consumer Premises Equipment CRC Cyclic Redundancy Check DBS Direct Broadcast Satellite 0024. There is also provided in accordance with the DC Direct Current present invention a method of transporting Ethernet frames DSL Digital Subscriber Loop over a Very high speed Digital Subscriber Line (VDSL) DSLAM DSL Access Multiplexor transport facility connecting a first communication device ETSI European Standards Institute FCS Frame Check Sequence and a Second communication device, the method comprising FDM Frequency Division Multiplexing the Steps of receiving an input Ethernet frame data on the FEXT Far End Crosstalk first communication device from a first Ethernet compatible FTTB Fiber to the Building communication device coupled thereto, generating a multi FTTC Fiber to the Curb FTTCab Fiber to the Cabinet byte preamble field for use by the Second communication FTTEx Fiber to the Exchange device to identify the start of a VDSL frame, generating a FTTH Fiber to the Home length field representing the length of the Ethernet frame to FTTN Fiber to the Node be transmitted over the VDSL transport facility, generating HFC Hybrid Fiber Coax IFG Interframe Gap a data field comprising the Ethernet frame to be transmitted ISDN Integrated Services Digital Network over the VDSL transport facility, assembling the preamble MMDS Multichannel Multipoint Distribution Service field, length field and the data field so as to generate a VDSL MPEG Motion Picture Entertainment Group frame, transmitting the VDSL frame over the VDSL trans NEXT Near End Crosstalk port facility, receiving VDSL frame data on the second PC Personal Computer POTS Plain Old Telephone Service communication device, extracting the Ethernet frame from OAM Quadrature Amplitude Modulation the data field and generating an output Ethernet frame QoS Quality of Service therefrom and transmitting the output Ethernet frame to a RF Radio Frequency Second Ethernet compatible communication device coupled RFI Radio Frequency Interference SNMP Simple Network Management Protocol to the Second communication device. SOC Start of Cell SOF Start of Frame BRIEF DESCRIPTION OF THE DRAWINGS USSB US Satellite Broadcasting UTP Unshielded Twisted Pair 0.025 The invention is herein described, by way of VDSL Very High Speed Digital Subscriber Line example only, with reference to the accompanying drawings, WWW World Wide Web wherein: 0.026 FIG. 1 is a block diagram illustrating an Ethernet General Description to VDSL CPE coupled to a DSLAM over a VDSL transport 0035. The present invention is an apparatus for and facility; method of encapsulating Ethernet frame data in Very high US 2003/0223446 A1 Dec. 4, 2003 speed Digital Subscriber Line (VDSL) frames. The VDSL 0041. The 10BaseS system combines copper access frames are transmitted over a point to point VDSL link transmission technology of Ethernet based Services with where they are Subsequently extracted and forwarded as Quality of Service (QoS) guaranteed by the SRVP protocol Standard Ethernet frames. AS used throughout this docu and is capable of being fully managed through an SNMP ment, the term VDSL frame is intended to denote a frame of agent. The 10BaseS transport facility can deliver symmetri data having a variable length that is transmitted over the cal data at 12.96 Mbps (net 10 Mbps) over unshielded VDSL transport facility. The length of the VDSL frame twisted pair (UTP) telephone wires originally intended for varies in accordance with the length of the Ethernet frame bandwidths of between 300 HZ and 3.4 KHZ. OAM modul encapsulated within. The VDSL frame of the present inven lation and blind equalization are used to achieve a high tion bears no relationship and should not be confused with transmission Speed over existing copper infrastructure. In the VDSL frame having a fixed length of 405 bytes as addition, the System is able to cope with Several Sources of described in the VDSL Draft Specification published by the noise Such as impulse noise, e.g., POTS transients, radio ANSI T1B 1.4 Subcommittee. frequency interference (RFI) noise and crosstalk noise, i.e., 0036) A block diagram illustrating an Ethernet over both near end crosstalk (NEXT) and far end crosstalk VDSL transport facility is shown in FIG. 1. The system, (FEXT). In terms of RF emissions, the system can operate generally referenced 10, comprises an Ethernet to VDSL using underground cabling as well as overhead distribution Consumer Premises Equipment (CPE) 14 coupled to a DSL cabling. Access Multiplexor (DSLAM) 18 over a VDSL transport 0042. The DSLAM 18 will now be described in more facility 16. The Ethernet to VDSL CPE 14 functions to detail. A block diagram illustrating the DSL Access Multi receive a 10BaseT Ethernet Signal 12 and encapsulate the plexor (DSLAM) in more detail is shown in FIG. 2. As Ethernet frame into a VDSL frame for transmission over the described previously, the DSLAM 18 functions to encapsu VDSL facility 16. Likewise, the Ethernet to VDSL CPE 14 late and extract Ethernet frames into and from VDSL frames. also functions to receive a VDSL signal and extract Ethernet The DSLAM typically is adapted to generate a plurality of frames therefrom for output as standard 10BaseT Ethernet VDSL streams to be transmitted over a plurality of VDSL Signals 12. facilities 30 via one or more VDSL transceivers 32 at the 0037. The DSLAM 18 is adapted to receive VDSL front end. The DSLAM comprises a high speed Ethernet frames, extract Ethernet frames therefrom and generate and port at the back end, an Ethernet Switch 36, Ethernet output a standard Ethernet signal. Likewise, the DSLAM 18 encapsulation/extraction circuitry 35 and a plurality of is also adapted to receive Standard Ethernet frames from an VDSL transceivers 32. The transceiver 40 functions to Ethernet input signal 20 and encapsulate them in VDSL receive, for example, a 10BaseT Fast Ethernet Signal 42 and frames for transmission over the VDSL facility 16. provide bidirectional Fast Ethernet communications. 0038. The VDSL facility 16 may comprise any suitable 0043. In the Ethernet to VDSL direction, Ethernet frames transport facility that is capable of transporting 10BaseT are received over the 100BaseT Fast Ethernet port 42 and are Ethernet data from one point to another. Preferably the input to the Fast Ethernet transceiver 40. The Fast Ethernet VDSL facility conforms to the VDSL standard which is Signals are input to an Ethernet Switch 36 capable of currently a draft specification being formulated by the ANSI Switching at Fast Ethernet speeds. The GT48212 Switched TIE 1.4 Technical Subcommittee. Ethernet Controller manufactured by Galileo Technology, 0039. A transport facility suitable for use with the present San Jose, Calif. can be used to construct the Ethernet Switch invention is the 10BaseS transport facility described in detail of the present invention. The Switch 36 is coupled via signal in U.S. application Ser. No. 08/866,831 filed May 30, 1997, lines 34 to circuitry 35 that performs Ethernet encapsulation entitled Ethernet Transport Facility Over Digital Subscriber and extraction. The Ethernet encapsulation/extraction cir Lines, Similarly assigned and incorporated herein by refer cuitry 35 functions to encapsulate the Ethernet frame data ence. Abrief description of this transmission System is given from each of the channels output of the witch 36 into VDSL below. frames and forward them via signal lines 33 to the VDSL 0040. The 10BaseS transport facility is capable of trans transceiver 32 corresponding to that particular channel. The mitting 10 Mbps Ethernet Over existing copper infrastruc VDSL transceivers 32 modulate the VDSL frame data and ture. The System utilizes carrierleSS amplitude and phase generate a VDSL signal Suitable for transmission over the modulation (CAP) which is a version of Suppressed carrier twisted wire pairs 30. Note that the VDSL frames may be quadrature amplitude modulation (QAM). QAM is the most transmitted using the 10BaseS transport facility described commonly used form of high Speed modulation over voice above. telephone lines. The System also utilizes frequency division 0044) In the VDSL to Ethernet direction, VDSL signals, multiplexing (FDM) to separate downstream channels from e.g., 10BaseS signals, are received by one or more VDSL upstream channels. In addition, FDM is also used to Separate transceivers 32 over the twisted pair wires 30. A VDSL both the downstream and the upstream channels from POTS modem suitable for use in constructing the VDSL transceiv and ISDN signals. A Substantial distance in frequency is ers 32 of the present invention comprises the BCM6010 maintained between the lowest data channel and POTS VDSL. Transceiver manufactured by Broadcom, Irvine, frequencies to permit the use of very Simple and cost Calif. or VDSL transceivers manufactured by Savan Com effective POTS splitters, which are actually splitters/com munications Ltd., Netanya, Israel. biners. The upstream channel is placed above the down Stream channel in frequency. The downstream and upstream 0045. Each VDSL transceiver 32 functions to demodulate data channels are separated in frequency from bands used the signal received over the twisted pair wires 30 and output for POTS and ISDN, enabling service providers to overlay VDSL frames via signal lines 33 to Ethernet encapsulation/ 10BaseS on existing Services. extraction circuitry 35. The Ethernet encapsulation/extrac US 2003/0223446 A1 Dec. 4, 2003

tion circuitry 35 functions to extract the Ethernet frame data Signal input to the transceiver and the RXData output of the encapsulated within the VDSL frame and generate Standard transceiver. The Tx and RX SOC signals provide a pulse at Ethernet frames, which are then input via Signal lines 34 to the beginning of the VDSL frame. A VDSL frame comprises the Ethernet, Switch 36. The Switch forwards the Ethernet a fixed number of bytes, e.g., 256, which has no relation to frames to the transceiver 40 for transmission over the the number of bytes in an Ethernet frame. 100BaseT port 42. 0051 AS discussed previously in the Background Section 0046) The Ethernet to VDSL CPE unit will now be of this document, the circuitry required is very complex to described in more detail. A block diagram illustrating the design to synchronize Ethernet frames to the VDSL frames Ethernet to VDSL CPE in more detail is shown in FIG. 3. in accordance with the SOC signals. The present invention The Ethernet to VDSL CPE unit 14 comprises an Ethernet overcomes this problem by Sending and receiving Ethernet transceiver 50, Ethernet encapsulation/extraction circuitry frame data over VDSL asynchronously with respect to the 52 and VDSL transceiver 54. The Ethernet transceiver 50 is Tx or RX SOC signals. The invention functions to transmit adapted to receive and transmit standard 10BaseT Ethernet the Ethernet frame data over the VDSL channel without signals 12. An Ethernet transceiver Suitable for use with the utilizing the Tx or RX SOC signals. This eliminates any present invention comprises the LXT905 10BaseT Ethernet problems associated with Synchronizing the Ethernet data to transceiver manufactured by Level One Communications, the SOC data. Problems include, for example, breaking up Inc., Sacramento, Calif. the Ethernet frame data into multiple sections to fit within 0047 The transceiver 50 communicates with the encap the Smaller VDSL frames (when the Ethernet frame exceeds Sulation/extraction circuitry 52 via Signal lines that comprise 256 bytes) and Subsequently regenerating the Ethernet frame Tx and Rx data lines and a plurality of Tx and Rx control by assembling the multiple Smaller Sections. lines. The Ethernet encapsulation/extraction circuitry 52 0052 A diagram illustrating the format of a standard performs protocol conversion between Ethernet and VDSL Ethernet frame is shown in FIG. 4. A standard Ethernet frame formats. A VDSL modem Suitable for use in con frame, generally referenced 60, comprises a plurality of structing the VDSL transceiver 54 of the present invention fields. The fields include a 7 byte preamble 62 consisting of comprises the BCM6010 VDSL. Transceiver manufactured 0xAA characters, a one byte Start of Frame (SOF) character by Broadcom, Irvine, Calif. or VDSL modems manufactured 64 consisting of OXAB, a 6 byte destination address 66, a by Savan Communications Ltd., Netanya, Israel. 6 byte source address 68, 2 byte type/length 70, 46 to 1500 0048. In the Ethernet to VDSL direction, Ethernet frames byte data field 72 and a 4 byte Frame Check Sequence 74 are received over the 10BaseTEthernet port 12 and are input that comprises a CRC check. The type/length field 70 may to the Ethernet transceiver 50. The Ethernet signals are comprise either type or length data, depending on the variant input, via TX and RX data and control lines, to the Ethernet of Ethernet used. The fields comprising the destination encapsulation/extraction circuitry 52 which functions to address 66, source address 68, type/length 70, data 72 and encapsulate the Ethernet frame data received over the Eth FCS 74 are commonly referred to as the Ethernet frame. ernet port 12 into VDSL frames. The VDSL frames are then Note that the Ethernet frame may comprise from 64 to 1518 forwarded to the VDSL transceiver 54. The VDSL trans bytes depending on the Size of the data field. Data shorter ceiver 54 functions to modulate the VDSL frame data and than 46 bytes is padded to a minimum of 46 bytes. generate a VDSL signal Suitable for transmission over the 0053. In accordance with the 802.3 standard, Ethernet twisted wire pair 16. Note that the VDSL frames may be data is transmitted using Manchester coding whereby an idle transmitted using the 10BaseS transport facility described character is transmitting using DC and a '0' and 1 char above. acters are transmitted having a transition half way through 0049. In the VDSL to Ethernet direction, VDSL signals, the symbol, the transition for a '0' being opposite that for 1. which may comprise 10BaseS Signals, are received by the 0054) A diagram illustrating the interframe gap between VDSL transceiver 54 over the twisted pair wire 16. The two Ethernet frames is shown in FIG. 5. The Ethernet IEEE VDSL transceiver 54 functions to demodulate the signal 802.3 standard provides for a minimum Interframe Gap received over the twisted pair wire 16 and output VDSL (IFG) of 9.6 s between frames to facilitate collision detection frames to the Ethernet encapsulation/extraction circuitry 52. and avoidance. The 9.6 s IFG is equivalent to 12 bytes for The Ethernet encapsulation/extraction circuitry 52 functions 10 Mbps Ethernet. An example is shown whereby two to extract the Ethernet frame data encapsulated within the Ethernet frames 80, 82 are separated by an IFG of 9.6 s. The VDSL frame and generate standard Ethernet frames which IFG is removed by the CPE 14 and is not transmitted over are then forwarded to the Ethernet transceiver 50 for trans the VDSL facility. The IFG is inserted, however, when mission over the 10BaseT port 12. transmitting Ethernet frames constructed from VDSL frame 0050. The VDSL transceiver 54 functions to provide the data received over the VDSL facility. clocking via TxCLK and RXCLK signals for both transmit 0055. A diagram illustrating the format of VDSL frames and receive data Signals TxData, RXData. In addition, the that are transmitted over the VDSL facility (or 10BaseS transceiver 54 provides a RXErr signal that is asserted when facility) is shown in FIG. 6. The VDSL frame, generally an error is detected in the received data. An error condition referenced 90, comprises a 5 byte preamble field 92, a 2 byte may comprise a framing error, loSS of Synchronization of the length field 94 and a data field 96. The preamble 92 receive signal, etc. Further, the transceiver 54 provides a TX comprises any Suitable bit pattern that facilitates reception, and Rx Start of Cell (SOC) signal, TxSOC, RXSOC. The detection and synchronization of the VDSL signal at the SOC signals, as defined in the VDSL draft standard, are receiver. Preferably, the preamble is chosen to have optimal suitable for use in transporting ATM cell data over VDSL but autocorrelation properties. The preamble field is used by the are Suitable also for general use in Synchronizing the TxData receiving station to identify a start of VDSL frame. Note that US 2003/0223446 A1 Dec. 4, 2003

this field should not be confused with the 7 byte preamble field 62 (FIG. 4) of the Ethernet frame itself consisting of -continued OXAA characters. as 10-12 0056. The length field 94 conveys to the receiving station the number bytes in the data field that follows. The data field comprises the encapsulated Ethernet frame that may have a 0061. In accordance with the present invention, the length of 64 to 1518 bytes (excluding the preamble and SOF receiving Station performs a check to determine whether the fields). The entire VDSL frame 90 can have a length, preamble pattern detected is actually a preamble or is including the preamble and length fields, ranging from 71 to Ethernet data within the payload of the VDSL frame. The 1525 bytes. Note that if the IEEE 802.1Q standard is to be length field contains 16 bits allowing for 65,536 combina Supported, the frame may be 4 bytes longer. tions but only 1518-64=1454 of them are valid. Thus, the length field can be checked to further narrow the chance of 0057. It is important to note that in accordance with the a wrong Sync. A flow diagram illustrating the receiver Sync present invention, as described previously, the VDSL frame method is presented below. is transmitted without the use of the Tx or RX SOC signals provided by the VDSL transceiver. In place of the SOC 0062) A flow diagram illustrating the receiver synchro Signals, the preamble performs the role of providing a means nization method of the present invention is shown in FIG. for the receiver in the VDSL transceiver to know when a 8. The first step is to hunt for the preamble (step 110). If the VDSL frame begins. The length field allows the receiver to preamble pattern is detected (step 112), the first two bytes know when the VDSL frame ends. following the preamble are read in (step 114). This is the length field. Since the VDSL frame payload only carries 0.058 A timing diagram illustrating the relationship Ethernet data, the value of the length field must be in the between the RXErr, SOC and VDSL data signals is shown in range of 64 to 1518 bytes. If the value of the length is less FIG. 7. As described previously, the RXErr signal (trace than 64 or more than 1518 (step 116), then the preamble bit 100) is generated by the VDSL transceiver when sync is lost pattern detected was not a preamble indicating the Start of a or any other error occurs in the receiver. The SOC signal VDSL frame. The Rx Err signal is asserted by the VDSL (trace 102) is shown comprising a pulse to Signal the start of transceiver (step 120) and a search of the preamble starts the VDSL frame within the transceiver. The SOC signal, anew (step 110). If the length is legal, the remainder of the however, is not used by the apparatus of the invention. The VDSL frame is read in (step 118). data (trace 104) shown comprises a sequence of VDSL 0.063. Using this Sync method further decreases the prob frames each consisting of a preamble, length and data fields ability of obtaining the wrong Sync by a factor given below. with Zeros inserted during idle times. AS shown, the trans mission of the data is completely independent from the SOC Signal 102. AS an example, a Sync occurs as indicated by the 1 I6 (2) dotted portion 106 of the Rx Err trace 100. The data Pr(length error) = (1518-64). () received during this time may contain one or more errors. as 0.022 0059) As described above, the Ethernet frame data boundaries received from the 10BaseTport 12 (FIG.1) have no correlation with the VDSL frames transmitted over the 0064 Multiplying this Pr(length error) factor by the VDSL facility 16. The Rx Err indication at the receiving Pr(preamble error) yields an overall probability for wrong station, however, does relate to the VDSL data frames. If a Synchronization given by Equation 3 below. VDSL frame is encountered that has errors, i.e., the Rx Err Signal is asserted, the frame can either be forwarded or 0065 Pr(wrong sync)=Pr(preamble error) Pr(length dropped in accordance with an RX Err policy, which may be error) Set by the user. If the policy is to drop frames, and the frame received contained non-idle Ethernet frame data, data will be lost. Note that theoretically, up to four Ethernet frames may Pr(wrong sync) = Pr(preamble error). Pr(length error) (3) reside within a single VDSL frame width, assuming 64 byte 1 40 minimum size Ethernet frames and 256 byte VDSL frames () . O.022 (as specified by the VDSL Draft Standard). s 2.2 x 10 0060. In order to regain synchronization, the receiving Station starts looking for the 5 byte pattern of the predefined preamble code. Note, however, that the Ethernet frame data 0066. This results in a relatively low probability of wrong encapsulated within the payload of the VDSL frame may Synchronization. Even in the event a non preamble is contain the exact bit Sequence of the preamble code pattern. detected due to the bit pattern occurring in the payload of the This would result in the receiver regaining the wrong VDSL frame, the upper layers of the protocol Stack, i.e., the Synchronization. The probability of this happening is given , will detect an error and cause a retransmis by Equation 1 below. Sion or other error recovery Scheme. 0067. While the invention has been described with Pr(preamble error) = ()1 40 (1) respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made. US 2003/0223446 A1 Dec. 4, 2003

What is claimed is: receiving an input Ethernet frame data on Said first 1. A method of transporting Ethernet frames over a Very communication device from a first Ethernet compatible high speed Digital Subscriber Line (VDSL) transport facility communication device coupled thereto; coupling a first communication device and a Second com generating a multibyte preamble field for use by Said munication device, Said method comprising the Steps of: Second communication device to identify the Start of a receiving an input Ethernet frame data on Said first VDSL frame; communication device from a first Ethernet compatible generating a length field representing the length of Said communication device coupled thereto; Ethernet frame to be transmitted over said VDSL encapsulating Said received Ethernet frame within a transport facility; VDSL frame; generating a data field comprising Said Ethernet frame to inserting a preamble and length field in said VDSL frame; be transmitted over said VDSL transport facility; transmitting said VDSL frame over said VDSL transport assembling Said preamble field, length field and Said data facility; field so as to generate a VDSL frame; receiving VDSL frame data on Said Second communica transmitting said VDSL frame over said VDSL transport tion device, facility; extracting said Ethernet frame from said received VDSL receiving VDSL frame data on Said Second communica frame and generating an output Ethernet frame there tion device; from; and extracting the Ethernet frame from Said data field and transmitting Said output Ethernet frame to a Second Eth generating an output Ethernet frame therefrom; and ernet compatible communication device coupled to Said Second communication device. transmitting Said output Ethernet frame to a Second Eth 2. The method according to claim 1, wherein Said Step of ernet compatible communication device coupled to encapsulating comprises the Step of Stripping off the pre Said Second communication device. amble and start of frame fields from said Ethernet frame 6. The method according to claim 5, wherein Said Step of before placing said Ethernet frame in said VDSL frame. encapsulating comprises the Step of Stripping off the pre 3. The method according to claim 1, wherein Said length amble and start of frame fields from said Ethernet frame field inserted in said VDSL frame represents the length of before placing said Ethernet frame in said VDSL frame. said Ethernet frame without the Ethernet preamble and 7. The method according to claim 5, wherein said length Ethernet start of frame fields. field inserted in said VDSL frame represents the length of 4. The method according to claim 1, wherein Said Step of said Ethernet frame without the Ethernet preamble and generating comprises the Step of adding Ethernet preamble Ethernet start of frame fields. and Ethernet start of frame fields to said extracted Ethernet 8. The method according to claim 5, wherein said step of frame. generating comprises the Step of adding Ethernet preamble 5. A method of transporting Ethernet frames over a Very and Ethernet start of frame fields to said extracted Ethernet high speed Digital Subscriber Line (VDSL) transport facility frame. connecting a first communication device and a Second communication device, Said method comprising the Steps of: