Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
1999-07-08
2003-01-14
Nguyen, Chau (Department: 2663)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S509000
Reexamination Certificate
active
06507592
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus such as a cable modem and a method which support two-way communication of data packets between a head-end system and the cable modem in a Time Division Multiplexed System. A communication channel such as a Hybrid Fibre Coaxial (HFC) channel or a microwave link may be utilised by a service provider to transmit information to homes of multiple users and simultaneously provide a narrow band return channel for each user's data to the service provider.
In particular, the present invention relates to an interface unit and method which are capable of supporting a software implemented management of received/transmitted data packets within a cable modem operating in the Time Division Multiplexed System.
BACKGROUND OF THE INVENTION
With the recent rise in popularity of the Internet and other public or dedicated networks for electronic information exchange, many home computer users are using a modem to access e.g. the Internet through a Public Switched Telephone Network (PSTN) using home telephone lines. In this situation, the PSTN provides a dedicated communication path or circuit from the user's modem to a server located at e.g. an Internet Service Provider. The server functions as a gateway to the Internet. However, the bandwidth of typical home telephone lines is relatively small and/or the modems are typically capable of operating only at channel bit rates below approximately 56 Kbit/s, which limits the speed at which information can be received. Other modem technologies based on the PSTN such as ADSL require that the service provider installs a dedicated modem for each connected user, due to the need for a dedicated communication channel to each user's home. As an alternative to using telephone lines, the Internet can be accessed through HFC channels using a cable modem or a set-top box. HFC channels may provide much greater bandwidth than home telephone lines and are widely available to existing cable television subscribers. However, unlike telephone lines, existing HFC channel infrastructure does typically not provide a dedicated path or channel to the home of the users. Instead, multiple users are usually coupled to the same HFC channel leading to a head-end system which may be located at an Internet Service Provider's site. In addition, analogue or digital television signals are also frequently sent on the same HFC channel. Therefore, Internet service providers that use HFC channels must send and receive both data packets that contain information data, and control packets. The control packets provide the cable modem with information needed to send and receive the data packets, such as what carrier frequency outgoing or upstream packets from the cable modem should be transmitted on, what should its transmitter power level be, how many packets may be transmitted, what data packets on the HFC channel are intended for the cable modem, etc. Accordingly, the control packets provide a mechanism that allows a plurality of users organised in a shared-channel type of structure to communicate with the head-end system. The shared structure typically allows as many as one thousand users to simultaneously communicate with a single common modem forming part of the head-end system. Furthermore, the use of the shared channel provides statistical relief for burst traffic typically generated by Internet applications, so to an Internet user, it may appear that the entire downstream and upstream bandwidths are available on request. Accordingly, by utilising cable modem technology, a service provider can deliver cost effective high speed data communication services to thousands of users with a relatively limited investment in modem hardware and by utilising the existing HFC channel infrastructure.
An important class of cable modems are those operating according to the specifications provided by the European Telecommunications Standards Institute (ETSI) in ETS 300 800: Digital Video Broadcast Interaction Channel for Cable TV Distribution Systems. This specification details a Time Division Multiplexed System for two-way data communication between a head-end system in this context denoted an Interactive Network adapter (INA) and multiple cable modems denoted Network Interface Units (NIUs) located at the homes of the users. The upstream transfer of data from the plurality of users allocated to a particular INA may be divided into time slots and each time slot allocated to a particular user of the multiple users, by utilising Time Division Multiple Access (TDMA) techniques. The TDMA protocol specified in the DVB standard utilises a slotting methodology which allows transmit start times of each of the multiple of NIUs to be synchronised to a common clock source provided by the INA. Synchronising the start times increases message throughput of the shared data channel since the transmitted data packets do not overlap during transmission.
According to the DVB standard, control packets are denoted Media Access Control (MAC) packets or frames. Each NIU contains a unique MAC address which may be hard-coded into the NIU. Consequently, dedicated data may be transmitted from the INA to any particular users cable modem or NIU operating in the data transmission network. Synchronisation of upstream data packets is provided by transmitting some MAC frames which contain a specific time indicator for upstream synchronisation of slots. This time indicator contains information that allows a modem CPU or other data processor to calculate the time at which the modem is allowed to transmit an outgoing data frame to the head-end system if the arrival time of the MAC frame containing the indicator is known. A MAC frame containing the time indicator shall be sent at least in every time period of 3 ms according to the DVB standard. Accordingly, the time indicators provide a mechanism that allows NIUs to operate with the same time reference or clock so that the INA can assign time slots to different users' modems so as to avoid collision of data between different users. However, since there is a slightly different propagation delay between the NIUs in the data transmission network, a time base ranging method must be utilised to compensate for this NIU specific delay. Each NIU is provided by a specific delay time value which has been measured by the INA in a communication session comprising transmitting upstream ranging frames.
Prior art cable modems or set-top boxes have traditionally been based on specialised processors and various dedicated circuitry for receiving and processing incoming data packets as well as generating, encoding etc. outgoing data packets. These specialised processors have traditionally been hard-wired so as to apply a dedicated decoding process, i.e. a substantially fixed set of operations, to the received data packets in correspondence with the communication protocol of the network in question. The hardwired processors have typically been manufactured in CMOS technology as standard-cell designs or gate-array designs since these design methods are capable of providing the number of gates and/or gate density required for such complex Application Specific Integrated Circuits (ASICs). The hard-wiring has previously been assumed necessary to accommodate real time requirements for downstream data packet reception and decoding and for upstream data packet generation and encoding imposed by the high data rate of the received/transmitted data packets. In MPEG transport streams, the data rate of received or down stream data packets at the NIU or cable modem is typically about 42-56 Mbit/s while the upstream/transmitted data rate from the NIU to the INA is about 256 Kbit/s-3.088 Mbit/s.
There are several drawbacks related to the use of hardwired processors in cable modems. One drawback is that a substantial time period is required to designing, manufacturing, testing and production preparing a new or upgraded hard-wired processor. Such upgraded processors are often required to implement a new/revised or enhanced communicati
Hurvig Hans
Hvidtfeldt Henrik
Abelson Ron
Beyer Weaver & Thomas LLP
Cisco Cable Products and Solutions A/S (AV)
Nguyen Chau
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