EP1972097A1

EP1972097A1 - Data link management in coaxial media

Info

Publication number: EP1972097A1
Application number: EP07700276A
Authority: EP
Inventors: Timo Heikkonen; Sami Kuusisto; Mika Kouvonen; Arttu Purmonen; Jani Virta; Mikko Saario
Original assignee: Teleste Oyj
Current assignee: Teleste Oyj
Priority date: 2006-01-13
Filing date: 2007-01-12
Publication date: 2008-09-24
Also published as: FI20065019A0; FI119271B; KR20080086973A; FI20065019A; EP1972097A4; JP4913156B2; JP2009523343A; WO2007080229A1

Abstract

A communication system and a node point of a data network for transmitting a baseband data signal between at least one data terminal connected to a communication system comprising a coaxial cable network, and an external data network or server, which node point comprises connection means for connecting the node point to a coaxial cable network. The node point of a data network is arranged to control its receiver to a receiving mode for receiving data from said data terminal; and to send idle data periodically to said data terminal in order to control the data terminal to a listening mode.

Description

DATA LINK MANAGEMENT IN COAXIAL MEDIA

Field of the invention

The invention relates to an arrangement for transmitting a data signal in a coaxial cable network, and particularly to data link management in coaxial media.

Background of the invention

As the use of the Internet is becoming more and more common, the demand of home Internet connections is constantly increasing. Conventional telephone modem connections are relatively slow due to their narrow bandwidth, and they typically engage the telephone line for the time of the Internet connection. A higher transfer rate is available by means of various xDSL and cable modem subscriber lines. Particularly in areas in which a television signal is led to homes via a cable network, the cable network provides an existing transmission path for the transmission of data signals as well.

In a cable television system (CATV, Community Antenna Television) of the DOCSIS (Data-Over-Cable Service Interface Specifications) type, the data signal is modulated to its specific frequency (channel) in the same way as TV signals, wherein the signals can be transmitted in the same cable and be separated from each other in the receiving set. Households will need a particular cable modem (CM) for setting up a data connection to a computer. A disadvantage for homes is that cable modems are relatively expensive. Cable network operators have the problem that expensive network equipment CMTS (Cable Modem Termination System) used for cable modem connections is only capable of offering a limited number of connections. Furthermore, the cable modem connection has the disadvantage that the network is a trunked network, in which the available transmission capacity (for example, the transmission capacity of one branch of the CATV network) is divided between all the subscriber lines used at the same time, wherein the transmission capacity available for a single home may be small. To avoid these disadvantages, a solution has been developed that is described in more detail in patent application EP 1 099 349. EP 1 099 349 describes a method and a device for transmitting an Ethernet signal in a bi-directional manner to a subscriber line of a cable network. Ethernet signals transmitted in two directions in two separate cables are combined by a combining device to form a signal to be transferred in two directions in a single cable, and they are finally combined by a diplexer with a conventional CATV signal. The formed combined signal can be transmitted in the subscriber line of the CATV network. At the receiving end (in the home connection) of the combined signal, respectively, the Ethernet signal and the CATV signal are separated from the combined signal by filters. The transmission directions of the duplex Ethernet signal are separated by means of a splitting device, and the transmission and reception signals are conveyed by separate cables to the computer, typically via a network adapter connection. The CATV signal is led to the television in the normal way.

The purpose of the patent application EP 1 099 349 is to provide inexpensive means for using the CATV network for the transmission of both a CATV signal and, for example, an Ethernet signal to be led to a computer without a cable modem. As the transmission of the baseband data signal does not require modulation/demodulation, it is possible to use passive components for combining and separating the CATV signal and the baseband Ethernet signal.

In practice, the above-described arrangement cannot be used as such for the transmission of the Ethernet signal, because the total reflection attenuation of the presented network structure remains too weak. This, in turn, results in a strong cross-talk between the transmitting and receiving signal. This is especially harmful in detecting Ethernet link pulses. 10BaseT-Ethernet uses full-duplex (FDX) link pulses for checking the operation of a link between two devices. Link pulses that are smaller than payload data in their amplitude are mixed with the interference caused by cross-talk especially when data traffic is strongly unidirectional, which causes the link to be lost. In addition to cross-talk, other signals relayed in a coaxial cable also cause interference, which complicates the faultless transmission of baseband data signal and link pulses. These signals include, for example, low frequency components of radio and TV transmissions and EMC- interferences caused by different electric devices.

Brief description of the invention

Now, an improved arrangement has been developed to reduce the above-mentioned problems. As different aspects of the invention, we present a communication system, a node point of a data network and a computer software product, which are characterized in what will be presented in the independent claims. The dependent claims disclose advantageous embodiments of the invention.

The invention is based on the idea that when the data is transmitted in a coaxial cable network, the link pulse negotiation of the Ethernet system is removed from use at least partly and replaced with a link management procedure better suitable for the above-described system.

Thus, as a first aspect of the invention we present a communication system for transmitting a baseband duplex data signal in a coaxial cable network, which communication system comprises a node point of a data network for transmitting the baseband data signal between said communication system and an external data network or server; a coaxial cable network for transmitting said baseband data signal between said node point of a data network and at least one node point of a data terminal; and connection means for transmitting said baseband data signal further to at least one data terminal. The node point of a data network comprised by the system is arranged to control its receiver to a receiving mode in order to receive data from said at least one data terminal; and to send idle data periodically to said at least one data terminal in order to control said at least one data terminal to listening mode.

According to an embodiment the node point of the data network is arranged to monitor the status of the link formed from said at least one data terminal to the node point on the basis of the integrity of the received data.

According to an embodiment said node point of a data network is an Ethernet switch, which is arranged to switch off the link pulse negotiation according to the Ethernet standard.

According to an embodiment the node point of a data network is arranged to switch on the link pulse negotiation according to the Ethernet standard for a certain period in order to detect new data terminals attempting link formation.

According to an embodiment the node point of a data network is arranged to monitor interferences in the data transmission connection between the node point and said at least one data terminal; and to adjust the time range of sending idle data into optimal according to the interference conditions.

According to an embodiment in the communication system is arranged to be transmitted cable television signal as a combined signal with said baseband duplex data signal, in which case the communication system further comprises a television signal generator for forming a cable television signal; a connector for filtering the cable television signal and the baseband data signal to separate frequencies and for combining them into a combined signal to be transmitted in a coaxial cable network, and a separator for filtering the cable television signal and the baseband data signal from the received combined signal to their separate frequencies and for separating them into separate signals.

By means of the invention and its various embodiments it is possible to attain several advantages. By means of the arrangement according to the invention it is possible to ensure the operation of the link even in difficult cross-talk situations. By using data in both downstream and upstream directions instead of link pulses, in the above-described system it is possible to ensure a more reliable indication of the operation of the links, because data that is double in its amplitude is significantly less sensitive to interference caused by cross-talk than link pulses. In addition, by sending idle data from the node point to the terminal periodically, the receiver of the terminal is continuously woken up at short enough intervals, which is enough for maintaining the link in the downstream direction. Further, because the receiver of the node point concludes the operation mode of the link on the basis of the integrity of the data, a further confirmation on the operation of the link is thus received. A further advantage is that a normal link pulse negotiation according to the Ethernet standard can be used when cross-talk does not significantly interfere the link pulses and the above- described forced control is used only in a situation where the link pulse negotiation is no longer successful due to an increased cross-talk interference.

Another aspect of the invention is a node point of a data network for transmitting a baseband data signal between at least one data terminal connected to a communication system comprising a coaxial cable network and an external data network or a server, which node point comprises connection means for connecting the node point to said coaxial cable network; said node point of a data network is arranged to control its receiver to a receiving mode for receiving data from said at least one data terminal; and to sent idle data periodically to said at least one data terminal in order to control said at least one data terminal to a listening mode.

As a third aspect of the invention we present a computer software product, which is stored in a computer-readable memory means in order to control the above-described node point of the data network. The computer software product comprises a computer software code for controlling the receiver of the node point to a receiving mode and for receiving data from said at least one data terminal; and a computer software code for sending idle data to said at least one data terminal periodically in order to control the receiver of said at least one data terminal to a listening mode. Brief description of the drawings

The invention will now be described in more detail in connection with preferred embodiments with reference to the appended drawings, in which:

Fig. 1a shows a network arrangement of prior art for the transmission of a CATV signal and a baseband duplex data signal;

Fig. 1b illustrates more in detail the data transfer in a network arrangement according to Fig. 1a; and

Fig. 2 shows some embodiments of the invention in a flow chart.

Detailed description of the embodiments

Figure 1 a is a reduced block chart showing a CATV network arrangement of prior art for the transmission of a CATV signal and a baseband duplex data signal as described in patent application EP 1 099 349. The arrangement of Fig. 1a illustrates the CATV network arrangement in the substantial vicinity of home subscriber lines, where the TV signal is introduced as a baseband connection to a distribution point DP₁ typically via an optical fibre or a coaxial cable. From the distribution point DP on, the network is implemented as a coaxial cable network all the way to the home connection point. This coaxial cable part of the network is often called "the last 100 meters" or also "the last mile".

In Fig. 1a, the distribution point 100 is shown as a single logical unit for reasons of illustration, but in practice, the components of the distribution point are separate and they may be located at relatively long distances from each other. The distribution point 100 comprises an analog and/or digital TV signal modulator 102 modulating the video and audio signal to a form suitable for the coaxial cable network. In particular, the TV signal modulator 102 may be located even at a distance of several kilometers from the other components of the distribution point. Furthermore, the network arrangement comprises a server 104 which may be located, for example, in connection with the headend of the coaxial cable network, in which the Ethernet data signal is introduced via a broadband connection 106a, for example a 100BaseT twin cable connection. By using suitable equipment and transmission media 106b, the server 104 transmits the data signal further to an Ethernet switch 108 that comprises several ports 110 (so- called Ethernet multitap), with which the data signal is typically matched for a I OBaseT twin cable connection 112. For the coaxial cable network, the distribution point comprises a combiner 114 implemented primarily by means of filters (in practice, a diplexer) to filter the baseband Ethernet data signal and the CATV signal respectively with its specific low-pass filter 1 16 and high-pass filter 118. These filtered signals are combined to form a combined signal to be transmitted in the coaxial cable network 122. Furthermore, in connection with the twin cable connection 120 there is a branch circuit arrangement for separating the Ethernet signals of the upstream and downstream directions for the twin cable connection 112.

In a corresponding manner, the house subscriber line 124 is provided with a ground isolator 126 to filter off the lowest interference frequencies from the combined signal. The combined signal is further led via the coaxial cable connection 128 to a wall connection 130 ("wall socket") of the home subscriber line, which comprises a separator for performing operations inverse to those of the combiner 114: a low-pass filter 132 and a high-pass filter 134 (corresponding to the filters 116 and 118) are used to separate the baseband Ethernet data signal and the CATV signal from each other. Furthermore, to separate the Ethernet signals of the upstream and downstream directions, the twin cable connector 136 operating as the wall connection comprises a branch circuit arrangement similar to that in the distribution point 100. The Ethernet signal is thus input via the twin cable connector 136 and the twin cable connection 138 to the computer 140. The Ethernet signal of the upstream direction is led via the same connection in the opposite direction, respectively. Further, the CATV signal is input via the wall connection 142 and the coaxial cable 144 to the television set 146. In Fig. 1b the same CATV network arrangement is illustrated especially from the point of view of data transfer by using the same reference numbers as in Fig. 1a, where applicable. The data incoming to and outgoing from the network arrangement travels via a data cable 106b, which advantageously comprises a twin cable connection, where separate conductors have been reserved for data moving in different directions. A data signal directed to a coaxial cable network is brought to an Ethernet switch 108 of an Ethernet multitap, which in Fig. 1 b is further specified into a datapacket handler 108a, a transmitter 108b and a receiver 108c. The output data signal (e.g. payload data, control signals, link pulses) of the transmitter 108b are shown in Fig. 1b by reference S1 and the input signal of the receiver 108c by reference S2. These signals S1 and S2 thus travel in the twin cable media 112 between the Ethernet switch 108 and the connector/separator 114. In the coaxial cable 122 the combined data and CATV signal S3, which thus comprises data signal components S3a and S3b travelling in different directions. In the connector/separator in connection with the Ethernet wall socket of a home subscriber line the baseband Ethernet data signal and the CATV signal are separated from each other and the Ethernet signals S4 and S5 travelling in different directions are separated from each other for a twin cable connection 138. A data processing device 140 connected to the twin cable 138, such as a computer, or more precisely a network adapter of a computer, is in Fig. 1b divided into three blocks for the purpose of simplification, in the same manner as the Ethernet switch 108: a data packet handler 140a, a transmitter 140b and a receiver 140c.

However, serious problems are found when the operation of such a network arrangement in the transmission of the Ethernet signal is examined in more detail. 10BaseT-Ethemet is designed for a twin cable transfer line, which comprises separate transfer channels for sending and receiving. When transferring data signal in a coaxial cable network the sending and receiving share a common coaxial cable media. The nonidealities of the above cause a too weak total reflection attenuation, which causes a strong cross-talk between the sending and receiving. With reference to Fig. 1b, cross-talk takes place especially between signals S1 and S2 and correspondingly between signals S3a and S3b. In addition, the nonidealities of the Ethernet switch 108, the connector/separator 114, the coaxial cable 122, the connector/separator in the wall socket 130, the twin cable 138 and the data processing device cause cross-talk between signals. Further, the low frequency components of the radio and TV transmissions transferred in the coaxial cable causes interference especially to the signals S3a and S3b. In addition, especially the coaxial cable 122 and the twin cable 138 are subjected to different EMC interferences.

As a result of cross-talk caused by weak total reflection attenuation especially the link pulses that monitor and control the operation of link segment and that are smaller in their amplitude than payload data are interfered and the operation of the link cannot be ensured, but the link may switch off, in which case data can no longer be sent with the link.

The present invention provides one solution to this problem. The invention is based on the idea that because the system cannot ensure the transmission of link pulses according to the Ethernet standard, in the network arrangement according to the invention the link pulse negotiation of the Ethernet system is removed from use at least partly and replaced with a link management procedure better suitable for the above-described system.

According to an embodiment the Ethernet switch 108 maintains the data terminals 140 connected to the system in the listening mode by sending periodically idle data, which controls the receivers 140c of the terminals connected to the system to a listening mode, if they are not already receiving data and thus already in the listening mode. Because the receiver of the terminal is continuously active, this is enough to maintain the link in the downstream direction (from the Ethernet switch to the terminals). According to an embodiment the Ethernet switch 108 comprises means for sending idle data in order to control the time range according to the conditions so that optimal operation is created in different environments. The data terminals 140 connected to the system operate, however, according to the Ethernet standard by using, for example, network adapters according to the Ethernet standard. Thus, the data terminals 140 send link pulses according to the Ethernet standard.

According to an embodiment in the link management arrangement the receiver 108c of the Ethernet switch is forced to remain on substantially continuously, in which case when forced into the receiving mode the receiver does not even try to interpret link pulses nor is interfered by the received interfered link pulses. The receiver 108c is arranged to receive data in the upstream direction coming from the terminal, in which case the receiver checks the integrity of the data and concludes the link operating mode according to the data integrity. In the above- described system this ensures a more reliable indication of the operation of the link, because in the system the data is significantly less sensitive to interference caused by cross-talk than link pulses, because the amplitude of the data is double in comparison to link pulses.

Practice has shown that the above-described cross-talk interference is significant especially when a great deal of data is sent to the downstream direction. Thus, according to an embodiment, a normal link pulse negotiation according to the Ethernet standard can be used when cross-talk does not significantly interfere the link pulses (e.g. when traffic in the downstream direction is quiet) and the above- described forced control is used only in a situation where the link pulse negotiation is no longer successful due to an increased cross-talk interference. Correspondingly, if the cross-talk interference decreases, it is possible to move back to normal link pulse negotiation.

According to an embodiment, opening a new link, i.e. forming a connection between the new terminal that aims to connect to the network arrangement and the Ethernet switch is performed advantageously by means of a link pulse negotiation according to a normal Ethernet standard. This is because when forced into the receiving mode the Ethernet switch 108 does not receive information on that a new link should be opened, in which case it cannot open the port necessary for the connection either. Thus, the receiver 108c of the Ethernet switch 108 forced into receiving mode is periodically removed from the receiving mode and set momentarily to a listening mode to listen for the possible link pulses from the new terminals aiming to connect to the network arrangement. This kind of a momentary setting of the receiver 108c of the Ethernet switch 108 into a link pulse listening mode does not substantially interfere the maintenance of the link, because returning to the receiving mode takes place quickly. In addition it is to be noted that interference of the link pulses is not continuous, but occasional, in which case opening a new link can be performed in a situation where cross-talk interference in small, for example in the above-described situation where traffic in the downstream direction is quiet.

Breakdown of an existing link is interpreted as a terminal switched off from a network arrangement. The Ethernet switch 108 advantageously monitors by means of a timer the upstream data coming from the terminal, in which case if the terminal does not send the data within a predetermined time, the Ethernet switch 108 switches the link off and moves to a listening mode. If, in turn, in the listening mode the Ethernet switch detects link pulses from a terminal aiming to connect to the network arrangement, either from the same or new terminals, the port needed for the connection is opened and a new link is formed. Link switch-off can also be detected by the Ethernet switch when the terminal has switched the connection off and closed its port, in which case the data sent from the Ethernet switch to the terminal in question is reflected back to the Ethernet switch. Thus, the Ethernet switch sees its own transmission from its receiving port.

The operation of the Ethernet switch for the part of the above- described embodiments can be described with a flow chart according to Fig. 2. Initially the connection has not been formed to any data terminal and the receiver of the Ethernet switch listens (200) to the link pulses. When link pulses sent by some data terminal are detected from the connection, the link pulse negotiation according to the Ethernet standard is started (202), as a result of which a data transmission link according to the Ethernet standard is formed (204) between the Ethernet switch and at least one data terminal.

When the data transfer link is formed between the Ethernet switch and at least one data terminal, the Ethernet switch moves to a forced control mode (206), where the transmitter of the Ethernet switch is controlled to send idle data periodically to the data terminals that have formed the link, and the receiver of the Ethernet switch is set to a receiving status, where the link pulses are not listened to, but the link operating mode is concluded on the basis of data integrity.

After this the Ethernet switch can advantageously continue in the forced control mode and at the same time monitor the formed links, i.e. whether the terminal is sending data to the Ethernet switch within the predetermined time or whether the Ethernet switch's own transmission is reflected back (208) from the closed receiving port of the data terminal. If the timer measuring the time after the previous data transmission of the terminal has expired, or if an own transmission is seen at the Ethernet switch, the receiver of the Ethernet switch moves to the normal link pulse listening mode (200). If, in turn, the formed link seems flawless, i.e. data is received from the terminal within the set time, the Ethernet switch continues its operation in a forced control mode (206).

It is obvious that the operation of the Ethernet switch according to Fig. 2 comprises some advantageous embodiments, which are not necessary for implementing the basic idea of the invention, but which when implemented create certain advantages for the operation of the system. A person skilled in the art, however, understands on the basis of the above description that in its simplest form the invention can be implemented in such a manner that after the link is formed between the Ethernet switch and at least one terminal, the Ethernet switch is directed to a forced control mode, by means of which said link is managed.

Thus, it is also obvious, that the implementation of the basic idea of the invention does not require network arrangements, where the television signal is combined to the data signal for coaxial cable transmission. Thus, despite the fact that the above invention is described as an example in the CATV network arrangement according to patent application EP 1099349, the basic idea of the invention can, however, be implemented in a simplified manner as a coaxial cable network arrangement, where only baseband duplex data signal is transmitted. The invention is certainly evidently exploitable in the existing CATV networks, in which case it can also be used for eliminating some of the drawbacks of the CATV network arrangement according to the patent application EP 1099349.

The above-described embodiments of the invention can be most advantageously implemented as a computer software SW, which can be loaded in the memory MEM comprised by the Ethernet switch, which software, when executed in the processor CPU of the Ethernet switch makes the Ethernet switch implement tasks according to the invention. The functions of the computer software SW may be distributed in several different software components that communicate with each other. The computer software may be stored in any memory means, for example on the hard drive of a PC, or on a CD-ROM disc, from which it can be loaded in the memory MEM of the Ethernet switch. The computer program can also be loaded through a network, for example by using a TCP/IP protocol stack. It is also possible to use hardware solutions or a combination of hardware and software solutions to implement the inventive means.

It is obvious for a person skilled in the art that the basic idea of the invention can be implemented in various ways, wherein the invention and its embodiments are not restricted to the examples described hereinabove, but they may vary within the scope of the appended claims.

Claims

Claims:

1. A communication system for transmitting a baseband duplex data signal in a coaxial cable network, the communication system comprising a node point of a data network for transmitting the baseband data signal between said communication system and an external data network or a server; a coaxial cable network for transmitting said baseband data signal between said node point of a data network and at least one node point of a data terminal; connector means for transmitting said baseband data signal further to at least one terminal, characterized in that said node point of a data network is arranged to control its receiver to a receiving mode for receiving data from said at least one data terminal; and send idle date periodically to said at least one data terminal for controlling the receiver of said at least one data terminal to a listening mode.

2. The communication system according to claim 1 , characterized in that said node point of a data network is arranged to monitor the mode of the link formed from said at least one data terminal to the node point on the basis of the integrity of the received data.

3. The communication system according to claim 1 or 2, characterized in that said node point of a data network is an Ethernet switch, which is arranged to switch off the link pulse negotiation according to the Ethernet standard.

4. The communication system according to claim 3, characterized in that said node point of a data network is arranged to switch on the link pulse negotiation according to the Ethernet standard for a certain period in order to detect new data terminals attempting link formation.

5. The communication system according to any of the preceding claims, characterized in that said node point of a data network is arranged to monitor interferences in the data transmission connection between the node point and said at least one data terminal; and adjust the time range of sending idle data into optimal according to the interference situation.

6. The communication system according to any of the preceding claims, characterized in that cable television signal is arranged to be transferred in the communication system as a combined signal with said baseband duplex data signal, in which case the communication system further comprises a television signal generator for forming a cable television signal; a combiner for filtering the cable television signal and the baseband data signal to separate frequencies and for combining them as a combined signal to be transmitted in a coaxial data network; and a separator for filtering the cable television signal and the baseband data signal from the received combined signal to their separate frequencies and for separating them into separate signals.

7. A node point of a data network for transmitting baseband data signal between at least one data terminal connected to a communication system comprising a coaxial network, and an external data network or server, which node point comprises connection means for connecting the node point to said coaxial cable network, characterized in that said node point of a data network is arranged to control its receiver to a receiving mode for receiving data from said at least one data terminal; and send periodically idle data to said at least one data terminal for controlling the receiver of said at least one data terminal receiver to a listening mode.

8. The node point of a data network according to claim 7, characterized in that the node point of a data network is arranged to monitor the mode of the link formed from said at least one data terminal to the node point on the basis of the integrity of the received data.

9. The node point of a data network according to claim 7 or 8, characterized in that the node point of a data network is an Ethernet switch, which is arranged to switch off the link pulse negotiation according to the Ethernet standard.

10. The node point of a data network according to claim 9, characterized in that the node point of a data network is arranged to switch on the link pulse negotiation according to the Ethernet standard for a certain period in order to detect new data terminals attempting link formation.

11. The node point of a data network according to any of the claims 7 to 10, characterized in that the node point of a data network is arranged to monitor interferences in the data transmission connection between the node point and said at least one data terminal. adjust the time range of sending idle data into optimal according to the interference situation.

12. The node point of a data network according to any of the claims 7 to 11 , characterized in that said connection means are connected to a filter unit, which comprises filtering means for filtering the cable television signal to be transmitted and a baseband data signal from said node point of a data network to be sent to said at least one data terminal to separate frequencies and for combining them into a combined signal to be transmitted in the coaxial cable network, and for filtering a baseband data signal received from said at least one data terminal from a received combined signal to its own frequency and for separating to a separate signal.

13. A computer software product stored into a computer- readable memory means for controlling a node point of a data network, which node point is arranged for transmitting a baseband data signal between at least one data terminal connected to a communication system comprising a coaxial cable network and an external data network or sever, which node point comprises connection means for connecting the node point to said coaxial cable network; characterized in that the computer software product comprises a computer software code for controlling a receiver of the node point to a receiving mode and for receiving data from said at least one data terminal; and a computer software code for sending idle data to said at least one data terminal periodically for connecting the receiver of said at least one data terminal to the listening mode.