WO1997013343A1

WO1997013343A1 - A method for operating a modem in a network and a modem for use in the network

Info

Publication number: WO1997013343A1
Application number: PCT/IE1996/000066
Authority: WO
Inventors: Benjamin Winston Moore; John Francis Griffin; Thomas Coffey
Original assignee: Busicom Limited
Priority date: 1995-10-05
Filing date: 1996-10-04
Publication date: 1997-04-10
Also published as: AU7330196A

Abstract

A power line network (1) comprises a plurality of similar power line modems (2), which connect a plurality of corresponding computer devices (4) into a power line (3) of the network (1) so that a new modem (2) may be connected into the network (1), or a modem (2) may be removed from the network (1) without the need for altering the addresses of the modems (2) in the network (1) or the new modem (2) being connected into the network (1). The network (1) operates on a token passing protocol, and the modems (2) are assigned different numerical address. The token is passed from one modem (2) to its next adjacent modem (2) in increasing order of numerical address. In order to detect the presence of a new modem in the network (1), each modem (2) on receiving the token polls a first address, the value of which lies between the numerical value of its own address and that of its next adjacent modem (2). Initially, each modem (2) polls a first address of value equal to its own address plus one, and in the absence of an acknowledgement the first address is incremented by one.

Description

"A method for operating a modem in a network and a modem for use in the network"

The present invention relates to a method for operating each modem in a network of modems, and in particular, though not limited to a method for operating each power line modem in a power line network of similar power line modems so that a modem may be connected into, or disconnected from the network without the need for altering the addresses of the modems. The invention also relates to a modem, and in particular, though not limited to a power line modem for use in a power line network of similar power line modems, and the invention relates to a network of the modems.

Where it is desired to connect computer devices into a network, for example, a telephone network or a power line network, a modem is required. In the case of connection of a computer device into a power line, a power line modem is required. In general, when a new modem is to be connected into a network, it is necessary to alter the addresses of the modems already in the network, and to give the modem being connected into the network a new address. Likewise, when a modem is being disconnected from the network, it is also necessary to alter the addresses of the remaining modems in the network. This, it will be appreciated is inconvenient, is time consuming, and leads to downtime of the network, as well as confusion.

There is therefore a need for a method for operating each modem in a network which overcomes this problem. There is also a need for a modem for use in the network which overcomes this problem, as well as to a network comprising a plurality of the modems.

The present invention is directed towards providing such a method for operating a modem, a modem and a network comprising the modems.

According to the invention there is provided a method for operating each modem of a plurality of modems in a network wherein the method facilitates the connection of another modem into the network without the need for altering the address of the modem being connected into the network or any of the modems in the network, each modem being assigned a numerical address, the numerical values of the addresses of the respective modems connected into the network and to be connected into the network being different, communication in the network being carried out under a token passing protocol scheme whereby a token is passed around the network from one modem to its next adjacent modem in order of the numerical values of modem addresses, and only the modem in possession of the token may transmit onto the network, the method for operating each modem in the network comprising the steps of: storing the numerical address of its next adjacent modem in numerical order of address, at least on some occasions on being in possession of the token, polling a first numerical address for detecting the connection of a new modem into the network, the numerical value of the first numerical address lying between the numerical value of its own address, and the numerical value of the stored address of its next adjacent modem, on receipt of an acknowledgement of the first numerical address, which indicates the presence of a new modem in the network, transmitting the stored address of its next adjacent modem to the new modem, updating the address of its next adjacent modem to the first numerical address, and passing the token to the new next adjacent modem.

In one embodiment of the invention, the numerical address assigned to each modem is a whole number which may be equal to, greater than or less than zero.

In another embodiment of the invention, in the absence of an acknowledgement of the just polled first numerical address, the token possessing modem generates a new first address which is derived from the just polled first numerical address, the numerical value of the new first address being different to the numerical value of the just polled first address, and lying between the numerical value of the address of the token possessing modem and the numerical value of the stored address of its next adjacent modem.

In another embodiment of the invention the new first address is generated by the token possessing modem for polling the next time the token possessing modem is to poll a first address. The token possessing modem polls the new first address.

Preferably, the numerical value of the new first numerical address generated by each modem is equal to the numerical value of the last polled first address polled by that modem plus or minus one.

Advantageously, each modem sequentially generates and polls new first numerical addresses until the numerical value of the new first address generated is equal to the numerical value of the address of the next adjacent modem to that modem.

In one embodiment of the invention, on the numerical value of the first address generated by each modem being equal to the numerical value of the address of the next adjacent modem to that modem, that modem generates a new first address equal to the numerical value of its own address plus or minus one.

Preferably, each modem generates its own first numerical address to be polled, the first numerical addresses being derived from its own numerical addresses.

Advantageously, the numerical value of the first numerical address initially polled by each modem is equal to the numerical value of its own numerical address plus or minus one. In one embodiment of the invention the token is passed from one modem to its next adjacent modem in increasing order of numerical value of the addresses of the respective modems. Preferably, the numerical value of the first address initially generated by each modem is equal to the numerical value of the address of that modem plus one. Advantageously, the numerical value of the new first addresses generated by each modem is equal to the numerical value of the last polled first address which was polled by that modem plus one.

In another embodiment of the invention each modem which is connected into the network stores the numerical addresses of all the visible modems in the network. Preferably, each modem which is connected into the network comprises a table of stored numerical addresses of all the visible modems in the network. Advantageously, on receiving a numerical address of a new modem which has been connected into the network, each modem in the network updates its stored numerical addresses to include the numerical address of the new modem.

In one embodiment of the invention each new modem on receiving the token after it has been connected into the network transmits its address onto the network for reception by the other modems in the network.

In another embodiment of the invention each modem comprises an associated computer device, and each modem which is connected into the network stores the identity of the respective computer devices associated with the corresponding modems in the network, the identities of the computer devices being cross-referenced with the numerical addresses of their corresponding modems.

Advantageously, each modem when in possession of the token, on detecting a new modem being connected into the network transmits the stored numerical addresses of all the modems in the network and the identities of their associated computer devices to the new mode . Preferably, in the absence of an acknowledgement of a poll of the numerical address of its next adjacent modem, the token possessing modem identifies its next adjacent modem as having been disconnected from the network, and announces the disconnection of its next adjacent modem on the network, the token possessing modem updates the address of its next adjacent modem to the numerical address of the modem which had been the next adjacent modem to the next adjacent modem of the token possessing modem, and passes the token to its new next adjacent modem.

In another embodiment of the invention the modem whose numerical address is of the highest value of the numerical addresses of the modems which are connected into the network generates a first address and new first addresses up to a predetermined maximum value which corresponds to a predetermined maximum number of modems which may be connected into the network, and the next first address or new first address generated by the modem is equal to zero or one.

In a further embodiment of the invention each modem is a power 1 ine modem.

Additionally the invention provides a modem for connecting into a network which comprises a plurality of similar modems, wherein the modem may be connected into the network without the need for altering the address of the modem being connected into the network or any of the modems in the network, the modem and each modem in the network being assigned a numerical address, the numerical value of the addresses of the respective modems connected into the network and to be connected into the network being different, communication in the network being carried out under a token passing protocol scheme whereby a token is passed around the network from one modem to its next adjacent modem in order of numerical values of modem addresses, and only the modem in possession of the token may transmit onto the network, the modem comprising: a first storing means for storing the numerical address of its next adjacent modem in numerical order, a polling means for polling a first numerical address for detecting the connection of a new modem into the network, the numerical value of the first numerical address lying between the numerical value of its own address and the numerical value of the address of its next adjacent modem, a means for transmitting the stored address of its next adjacent modem to the new modem on receipt of an acknowledgement of the first numerical address, a means for updating the first storing means with the address of its new next adjacent modem by entering the first numerical address to which an acknowledgement has been received in the first storing means, and a means for passing the token to the new next adjacent modem.

In one embodiment of the invention the numerical address assigned to the modem is a whole number which may be equal to, greater than or less than zero.

In another embodiment of the invention the modem comprises a reading means for reading and detecting the presence of an acknowledgement in response to a polled first address. Preferably, the modem comprises a generating means for generating the first address. Advantageously, the generating means generates a new first address in the absence of an acknowledgement to the previously polled first address. Ideally, the numerical value of each new first address lies between the numerical value of its own address and the numerical value of the address of its next adjacent modem in the network.

The polling means polls each new first address.

Preferably, the generating means generates each new first address by changing the numerical value of the last polled first address by plus or minus one. Advantageously, the generating means initially generates the first address from the numerical value of its own numerical address by altering the numerical value of its own numerical address by plus or minus one.

In one embodiment of the invention, on the first address or new first address generated by the generating means being equal to the numerical address of the next adjacent modem, the generating means generates a first address, the numerical value of which is equal to its own numerical address plus or minus one.

In another embodiment of the invention the means for passing the token passes the token to the next adjacent modem in increasing order of numerical value of modem address.

Preferably, the generating means generates the first address initially by increasing the numerical value of its own address by plus one, and generates each new first address by increasing the numerical value of the last polled first address by plus one. Advantageously, the generating means on generating a first address or a new first address which is equal to a predetermined maximum value which corresponds to a predetermined maximum number of modems which may be connected into the network, the generating means generates a new first address equal to zero or one.

In one embodiment of the modem comprises a second storing means for storing the numerical addresses of all visible modems in the network. Preferably, a second updating means is provided for updating the second storing means with the numerical address of a new modem which has been connected into the network. Advantageously, the second storing means stores the identity of computer devices which are associated with the respective modems in the network, the identities of the respective computer devices being cross referenced with their corresponding modem addresses in the second storing means. 8

In one embodiment of the invention the modem is a power line modem.

Further, the invention provides a network comprising a plurality of modems, and each modem is a modem according to the invention.

The invention will be more clearly understood from the following description of a preferred embodiment thereof, which is given by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a schematic representation of a power line network according to the invention illustrating a plurality of computer devices connected onto a power line through a plurality of power line modems also according to the invention,

Fig. 2 is a block representation of one of the power line modems of the network of Fig. 1, the other power line modems being similar, and

Fig. 3 is a flow chart of firmware of the power line modem of Fig. 2, the firmware in the other power line modems being similar.

Referring to the drawings, and initially to Figs. 1 and 2 there is illustrated a network according to the invention, which in this case is a power line network, indicated generally by the reference numeral 1. The power line network 1 comprises a plurality of modems, also according to the invention, namely, power line modems 2 which are connected to a power line 3 of the network 1. The power line modems 2 connect respective computer devices 4 into the network 1. In this embodiment of the invention, the computer devices 4 comprise a plurality of personal computers 5, a plotter 6, a printer 7 and a server 8. In the power line network 1, all the computer devices 4 have access to all of the other computer devices 4, and furthermore, the power line modems 2 are arranged to be essentially transparent to their associated computer devices 4 so that it appears to a user of a computer device 4 that communication is being carried out directly with another computer device 4 with which communication is being made. Additionally, the power line modems 2 and their associated computer devices 4 can be readily easily connected onto the power line 3 and disconnected from the power line 3 without the need for making any alterations to any of the modems 2 or computer devices 4 in the power line network 1 on being connected into or disconnected therefrom. On a modem 2 and its associated computer device 4 being connected into or disconnected from the network 1, the other modems 2 and their associated computer devices 4 in the network 1 are made aware of the change to the network 1, and the identity of the modem 2 and its associated computer device 4 which has been connected into or disconnected from the network 1 is also communicated to the modems 2 and their associated computer devices 4 in the network 1.

The power line modems 2 are identical to each other. Each power line modem 2 comprises a data link processor 10 which transmits and receives data between its associated computer device 4 and the power line 3. A first communicating means for communicating the power line modem 2 with its associated computer device 4 comprises a serial interface 11. A second communicating means, namely, a power line interface 12 communicates the power line modem 2 with the power line 3. An analog interface chip 14 communicates between the data link processor 10 and the power line interface 12, and a digital interface chip 15 communicates between the data link processor 10 and the analog interface chip 14. A read-only memory 16 stores the firmware for controlling operation of the data link processor 10. The part of the firmware which is relevant to the invention is described below with reference to the flowchart of Fig. 3. Each power line modem 2 which is connected into the network 1 or which is to be connected into the network 1 is assigned a numerical address as will be described below. The numerical addresses of the respective modems 2 are different to each other. A non-volatile random access memory 17 in each modem 2 stores its own numerical address and also the identity of its associated computer device 4. The identity of the associated computer device is stored in a form in the non-volatile random access memory 17 which permits the identity of the computer device 4 to be displayed in verbal form on a visual display screen.

A random access memory 18 acts as a first storing means for storing the numerical address of the next adjacent modem 2 in the network to that modem 2. The random access memory 18 also acts as a second storing means for storing a table of the numerical addresses of the power line modems 2 which are connected into the network 1 and are visible. The identity of the computer devices 4 associated with the respective modems 2 which are connected into the network 1 and are visible are also stored in the random access memory 18, and are cross-referenced with their respective modem addresses in the table. As will be described below, the table of modem addresses and the identity of the associated computer devices 4 are updated each time a new power line modem 2 is connected into the power line network 1, and each time a power line modem 2 is disconnected from the power line network 1.

In this embodiment of the invention, provision is made in the power line network 1 for a predetermined maximum number of power line modems 2 to be connected into the network 1. The predetermined maximum number in this embodiment of the invention is two hundred and fifty-five power line modems 2, although it will be readily apparent to those skilled in the art that there is no upper or lower limit to the maximum number of power line modems 2 which may be connected into the network 1. The numerical addresses of the power line modems 2 range from one to two hundred and fifty-five, in other words 1 to FF (hex), no two modems 2 having the same numerical address. As will be described below, the power line modems 2 may be connected into the power line network 1 in any order, and any of the power line modems 2 may be connected into or disconnected from the power line, and the connection into and disconnection from the network 1 is communicated to the other power line modems 2 remaining in the network 1 which update their table of power line modems and associated computer devices stored in the random access memory 18.

Communication within the power line network 1 is carried out under a token passing protocol scheme. A token is passed around the network from one power line modem 2 to its next adjacent power line modem 2 by the numerical value of the addresses of the respective power line modems 2. Only the power line modem 2 in possession of the token may transmit onto the power line network

1. In this embodiment of the invention, the token is passed from one power line modem 2 to its next adjacent power line modem 2 in increasing numerical order of addresses up to the modem with the address of highest numerical value in the network 1, which may be the address of numerical value of two hundred and fifty-five or may be an address of lower numerical value. When the power line modem 2 with the address of highest numerical value in the power line network 1 is in possession of the token, and the token is to be passed on, it is passed to its next adjacent power line modem

2, which is the power line modem in the network 1 whose address is of the lowest numerical value, which may be one or greater than one. Each power line modem 2 may retain possession of the token for a predetermined period of time, or until transmission onto the power line 3 has been completed, whichever is the soonest. Should one of the power line modems 2 which does not require to transmit onto the power line 3 receive the token, that power line modem 2 passes on the token to its next adjacent power line modem 2 after it has checked for a new power line modem in the network 1 as will be described below.

So that the presence of a new power line modem which has just been connected into the power line network 1 can be identified and made known to all the other power line modems 2 connected into the network 1, each new power line modem 2 on receiving the token for the first time announces its presence onto the power line network 1 to all the power line modems 2 connected into the network 1, together with its numerical address and the identity of its computer device 4. The power line modems 2 in the network 1 in response to the announcement by the new power line modem 2 update their table of stored addresses of power line modems and identities of the corresponding computer devices.

In order that the token can be passed to a new modem 2 which has just been connected into the power line network 1, its presence in the power line network 1 must be detected. This is carried out as follows. Each power line modem 2 before passing on the token to its next adjacent modem 2 polls a first address in search of a new modem. The numerical values of the first addresses polled lie between the numerical value of the address of the token possessing modem and that of its next adjacent modem, which is stored in the random access memory 18. In this case since the token is being passed around the network 1 in increasing order of numerical values of addresses, the numerical values of the first addresses polled by the token possessing modem 2 are greater than the numerical value of its own address and are less than the numerical value of the address of its next adjacent modem. The first addresses to be polled by the modems 2 are generated by the respective modems 2. Initially, each modem 2 on generating a first address for the first time after being connected into the network 1, generates a first address, the numerical value of which is equal to the value of its own numerical address plus one. In absence of an acknowledgement from a polled first address, each token possessing modem 2 then generates a new first address, the numerical value of which is equal to the numerical value of the last polled first address by that modem plus one. On next coming into possession of the token the modem 2 polls the last generated new first address. Each modem 2 continues to generate new first addresses which are equal to the last polled first address plus one, until an acknowledgement to a first address has been received or until the numerical value of the new first address generated is equal to the numerical value of the address of its next adjacent modem, at which stage the next new first address generated is equal to the numerical value of the address of the modem generating the first address, plus one. Each time a modem 2 takes possession of the token it polls one first address. In the absence of an acknowledgement from the polled first address, the modem 2 generates the next first address as just described, and waits until it next comes into possession of the token at which stage, it polls the already generated new first address.

Should an acknowledgement to one of the polled first addresses be received by the token possessing modem 2, indicating the presence of a new modem 2 in the network 1, the token possessing modem 2 issues a "set next modem address" command to the new modem instructing it to store the address of its next adjacent modem. When issuing the "set next modem address" command the token possessing modem transmits the address of what was the next adjacent modem to itself so that the new modem 2 stores the address of the modem 2 which had been the next adjacent modem 2 to the token possessing modem 2, and which is now the next adjacent modem to the new modem 2. The token possessing modem 2 also transmits the table of stored modem addresses and the identities of the corresponding computer devices 4 to the new modem 2. The token possessing modem 2 updates the address stored of its own next adjacent modem to be equal to the polled first address to which an acknowledgement has been received. In other words, the token possessing modem 2 updates the stored address of its next adjacent modem to being the address of the new modem 2. The token possessing modem 2 then passes the token to the new modem 2 which upon receipt of the token, the new modem 2 announces its own numerical address and the identity of the computer device 4 associated with the new modem 2 onto the network 1 for receipt by all other modems 2 connected to the network 1. All the modems 2 connected into the network 1 at that stage update their respective tables of stored modem addresses and identities of computer devices 4. If the new modem 2 has a message to transmit, it transmits the message, and then passes on the token to its next adjacent modem, the address of which it has already received from the previous token possessing modem 2. For so long as the new modem remains in the network 1, it operates in similar fashion as the other modems 2 in the network 1, and on next receiving the token checks for a new modem 2 between itself and its next adjacent modem.

The disconnection of a power line modem 2 from the network 1 is determined as follows. On a token possessing modem 2 failing to receive an acknowledgement after it attempts to pass on the token to its next adjacent modem 2, it is assumed that its next adjacent modem 2 has been disconnected from the network 1. However, before it is finally determined that its next adjacent modem 2 has been disconnected from the network 1, a number of attempts to poll the next adjacent modem 2 are made by the token possessing modem 2.

On the token possessing modem 2 determining that its next adjacent modem 2 has been disconnected, the token possessing modem 2 updates the stored numerical address of its next adjacent modem to the numerical address of the modem 2 which had been the next adjacent modem to its own next adjacent modem, which has been determined as being disconnected. The token possessing modem then updates its table of stored addresses of power line modems and their associated computer devices 4 which are connected into the network 1 by removing the address of that power line modem 2 from the table, together with the identity of its associated computer device 4. The token possessing modem 2 transmits a "delete command" onto the power line network 1 for reception by the other modems 2 which are connected into the network 1, advising the modems 2 to delete the address of the disconnected modem 2 and the identity of its associated computer device 4 from their respective tables. The token possessing power line modem 2 then passes on the token to its new next adjacent modem. Should the new next adjacent modem fail to acknowledge the attempt to pass the token to it, the token possessing modem 2 goes through a similar routine to establish if the new next adjacent modem has been disconnected. If it is determined that the new next adjacent modem 2 has been disconnected, the token possessing modem continues with the routine just described and again updates its stored next adjacent modem address to the address of the next adjacent modem to the modem of the currently stored next adjacent modem address, and so on. The token possessing modem 2 then also goes through the routine of updating its table of modems connected into the network 1 and their associated computer devices 4, and issues a further delete command onto the network 1, and passes on the token to the further new next adjacent modem.

Referring now to Fig. 3, a flowchart of a subroutine of the firmware stored in the read only memory 16 of each modem 2 for detecting the presence of a new modem 2 in the network 1 will now be described. Block 40 starts the subroutine. The subroutine moves to block 41 which checks if this is the first time the subroutine has been entered, in other words, is this the first time that the modem 2 has checked for a new modem after being connected into the network 1. If so, the subroutine moves to block 42 which generates a first address, which is the address to be polled for checking for a new modem. The numerical value of the first address generated by block 42 is set equal to the numerical value of the address of the token possessing modem plus one. The subroutine then moves to block 43 which polls the first address when the modem comes into possession of the token. In the event that block 41 determines that this is not the first time that the subroutine has been entered, the subroutine moves to block 43, which as just described polls a first address when the modem comes into possession of the token. The first address polled in this case is a first address which had previously been generated by block 45 which will be described below. The subroutine moves from block 43 to block 44 which waits for an acknowledgement from the polled first address. Should block 44 determine that an acknowledgement has not been received, the subroutine moves to block 45 which generates a new first address by incrementing the last polled first address by one. The new first address is polled by the modem the next time the modem comes into possession of the token. Having generated the new first address, the subroutine moves to block 46 which checks if the numerical value of the new first address generated by block 45 is equal to the numerical value of the address of the next adjacent modem. If not, the subroutine moves to block 47, which returns control to the calling routine. The new first address generated by block 45 is stored so that the next time the modem 2 is in possession of the token, it will poll that new first address.

Should block 46 determine that the numerical value of the new first address generated by block 45 is equal to the numerical value of the address of the next adjacent modem, the subroutine moves to block 48 which resets the new first address to being equal to the numerical value of the address of the token possessing modem plus one. This value of the new first address is stored for polling the next time the token possessing modem comes into the possession of the token. The subroutine then moves to block 47, which returns control to the calling routine as already described.

Should block 44 determine that an acknowledgement has been received indicating the presence of a new modem in the network 1, the subroutine moves to block 49, which issues a "set next modem address" command to the new modem and the new modem is commanded to set the address of its next adjacent modem to the address of the modem which had been the next adjacent modem to the token possessing modem. Additionally, block 49 commands the token possessing modem to set its next adjacent modem address to the address of the new modem. Block 49 also commands the token possessing modem to update its table of addresses of modems which are connected into the network 1 along with the identities of their corresponding computer devices 4, to include the address of the new modem and the identity of its associated computer device. Block 49 further commands the token possessing modem to transmit the table of stored modem addresses and the identities of the associated computer devices to the new modem. The routine then moves to block 48 which has already been described.

Operation of the power line network 1 for the transmission of data between computer devices 4 is as follows. On data to be transmitted being received by a power line modem 2 from its associated computer device 4, the power line modem 2 packs the data into data packets. The associated computer device identifies the modem 2 which is associated with the computer device 4 to which the data is to be transmitted. The modem 2 then heads the data packets with the address of the modem 2 of the computer device 4 to which the data is to be transmitted. On the power line modem 2 which wishes to transmit the data receiving the token, the power line modem 2 transmits the data in the packets onto the power line 3 which is received by the addressee modem. The addressee modem then unpacks the data, removes the address and relays the data to its associated computer device 4.

The fact that each power line modem 2 stores a table of all power line modems 2 in the power line network 1 together with the identities of the computer devices 4 cross-referenced to the modem addresses permits each computer device 4 on request from its associated power line modem 2 to obtain the table, and should it be desired, a table of the identities of all the computer devices 4 which are connected into the network 1 may be displayed on a visual display screen of the computer device, or printed out as the case may be. In this way, since the computer devices are identified by verbal identifications, typically, "John's computer", "Tom's computer", "plotter", "printer", etc., a user can readily easily select the identity of the computer device 4 to which data is to be transmitted.

The advantages of the invention are many. By virtue of the fact that each modem when it takes possession of the token checks the network for a new modem with addresses, the numerical values of which lie between the numerical value of the address of the token possessing modem and its next adjacent modem, permits entry of a new power line modem into the network without the need for altering the addresses of any of the modems in the power line network or the address of the new modem. Since each power line modem in the network on receiving an address of a new power line modem which has been connected into the network automatically updates its table of stored addresses of modems and identities of associated computer devices, each modem in the network will always have an up to date table of modems and associated computer devices in the network. Likewise, disconnection of a power line modem from the power line network is accommodated by the respective power line modems updating their table of modem addresses and identities of computer devices on receipt of the delete command.

By virtue of the fact that the modems store the identities of the computer devices associated with the modems in the network, and the identities of the computer devices are cross-referenced with the addresses of the modems, the network operates substantially transparently, and accordingly, it appears to the users of the respective devices in the network that they are communicating directly with the selected computer device without any indication that the communication is through respective modems in the power line network.

While the network described has been described as being a power line network with a plurality of power line modems connected therein, it is envisaged that the network may be any other network, whether power line or otherwise, and in cases where the network is not a power line network, then the modems would be non- power 1 ine modems.

It will be appreciated that in many cases the power line modems may not poll for a new modem each time they receive the token, for example, each modem may only poll for a new modem at predetermined intervals, such as every fifth or tenth time the modem receives the token.

Claims

1. A method for operating each modem of a plurality of modems in a network characterised in that the method facilitates the connection of another modem into the network without the need for altering the address of the modem being connected into the network or any of the modems in the network, each modem being assigned a numerical address, the numerical values of the addresses of the respective modems connected into the network and to be connected into the network being different, communication in the network being carried out under a token passing protocol scheme whereby a token is passed around the network from one modem to its next adjacent modem in order of the numerical values of modem addresses, and only the modem in possession of the token may transmit onto the network, the method for operating each modem in the network comprising the steps of: storing the numerical address of its next adjacent modem in numerical order of address, at least on some occasions on being in possession of the token, polling a first numerical address for detecting the connection of a new modem into the network, the numerical value of the first numerical address lying between the numerical value of its own address, and the numerical value of the stored address of its next adjacent modem, on receipt of an acknowledgement of the first numerical address, which indicates the presence of a new modem in the network, transmitting the stored address of its next adjacent modem to the new modem, updating the address of its next adjacent modem to the first numerical address, and passing the token to the new next adjacent modem.

2. A method as claimed in Claim 1 characterised in that the numerical address assigned to each modem is a whole number which may be equal to, greater than or less than zero.

3. A method as claimed in Claim 1 or 2 characterised in that in the absence of an acknowledgement of the just polled first numerical address, the token possessing modem generates a new first address which is derived from the just polled first numerical address, the numerical value of the new first address being different to the numerical value of the just polled first address, and lying between the numerical value of the address of the token possessing modem and the numerical value of the stored address of its next adjacent modem.

4. A method as claimed in Claim 3 characterised in that the new first address is generated by the token possessing modem for polling the next time the token possessing modem is to poll a first address.

5. A method as claimed in Claim 3 or 4 characterised in that the token possessing modem polls the new first address.

6. A method as claimed in any of Claims 3 to 5 characterised in that the numerical value of the new first numerical address generated by each modem is equal to the numerical value of the last polled first address polled by that modem plus or minus one.

7. A method as claimed in Claim 6 characterised in that each modem sequentially generates and polls new first numerical addresses until the numerical value of the new first address generated is equal to the numerical value of the address of the next adjacent modem to that modem.

8. A method as claimed in Claim 7 characterised in that on the numerical value of the first address generated by each modem being equal to the numerical value of the address of the next adjacent modem to that modem, that modem generates a new first address equal to the numerical value of its own address plus or minus one.

9. A method as claimed in any preceding claim characterised in that each modem generates its own first numerical address to be polled, the first numerical addresses being derived from its own numerical addresses.

10. A method as claimed in any preceding claim characterised in that the numerical value of the first numerical address initially polled by each modem is equal to the numerical value of its own numerical address plus or minus one.

11. A method as claimed in any preceding claim characterised in that the token is passed from one modem to its next adjacent modem in increasing order of numerical value of the addresses of the respective modems.

12. A method as claimed in Claim 11 characterised in that the numerical value of the first address initially generated by each modem is equal to the numerical value of the address of that modem plus one.

13. A method as claimed in Claim 11 or 12 characterised in that the numerical value of the new first addresses generated by each modem is equal to the numerical value of the last polled first address which was polled by that modem plus one.

14. A method as claimed in any preceding claim characterised in that each modem which is connected into the network stores the numerical addresses of all the visible modems in the network.

15. A method as claimed in Claim 14 characterised in that each modem which is connected into the network comprises a table of stored numerical addresses of all the visible modems in the network.

16. A method as claimed in Claim 14 or 15 characterised in that on receiving a numerical address of a new modem which has been connected into the network, each modem in the network updates its stored numerical addresses to include the numerical address of the new modem.

17. A method as claimed in any of Claims 14 to 16 characterised in that each new modem on receiving the token after it has been connected into the network transmits its address onto the network for reception by the other modems in the network.

18. A method as claimed in any of Claims 14 to 17 characterised in that each modem comprises an associated computer device, and each modem which is connected into the network stores the identity of the respective computer devices associated with the corresponding modems in the network, the identities of the computer devices being cross-referenced with the numerical addresses of their corresponding modems.

19. A method as claimed in Claim 18 characterised in that each modem when in possession of the token, on detecting a new modem being connected into the network transmits the stored numerical addresses of all the modems in the network and the identities of their associated computer devices to the new modem.

20. A method as claimed in any preceding claim characterised in that in the absence of an acknowledgement of a poll of the numerical address of its next adjacent modem, the token possessing modem identifies its next adjacent modem as having been disconnected from the network, and announces the disconnection of its next adjacent modem on the network, the token possessing modem updates the address of its next adjacent modem to the numerical address of the modem which had been the next adjacent modem to the next adjacent modem of the token possessing modem, and passes the token to its new next adjacent modem.

21. A method as claimed in any preceding claim characterised in that the modem whose numerical address is of the highest value of the numerical addresses of the modems which are connected into the network generates a first address and new first addresses up to a predetermined maximum value which corresponds to a predetermined maximum number of modems which may be connected into the network, and the next first address or new first address generated by the modem is equal to zero or one.

22. A method as claimed in any preceding claim characterised in that each modem is a power line modem.

23. A modem for connecting into a network which comprises a plurality of similar modems, characterised in that the modem may be connected into the network without the need for altering the address of the modem being connected into the network or any of the modems in the network, the modem and each modem in the network being assigned a numerical address, the numerical value of the addresses of the respective modems connected into the network and to be connected into the network being different, communication in the network being carried out under a token passing protocol scheme whereby a token is passed around the network from one modem to its next adjacent modem in order of numerical values of modem addresses, and only the modem in possession of the token may transmit onto the network, the modem comprising: a first storing means for storing the numerical address of its next adjacent modem in numerical order, a polling means for polling a first numerical address for detecting the connection of a new modem into the network, the numerical value of the first numerical address lying between the numerical value of its own address and the numerical value of the address of its next adjacent modem, a means for transmitting the stored address of its next adjacent modem to the new modem on receipt of an acknowledgement of the first numerical address, a means for updating the first storing means with the address of its new next adjacent modem by entering the first numerical address to which an acknowledgement has been received in the first storing means, and a means for passing the token to the new next adjacent mode .

24. A modem as claimed in Claim 23 characterised in that the numerical address assigned to the modem is a whole number which may be equal to, greater than or less than zero.

25. A modem as claimed in Claim 23 or 24 characterised in that the modem comprises a reading means for reading and detecting the presence of an acknowledgement in response to a polled first address.

26. A modem as claimed in any of Claims 23 to 25 characterised in that the modem comprises a generating means for generating the first address.

27. A modem as claimed in Claim 26 characterised in that the generating means generates a new first address in the absence of an acknowledgement to the previously polled first address.

28. A modem as claimed in Claim 27 characterised in that the numerical value of each new first address lies between the numerical value of its own address and the numerical value of the address of its next adjacent modem in the network.

29. A modem as claimed in Claim 27 or 28 characterised in that the polling means polls each new first address.

30. A modem as claimed in any of Claims 27 to 29 characterised in that the generating means generates each new first address by changing the numerical value of the last polled first address by plus or minus one.

31. A modem as claimed in any of Claims 26 to 30 characterised in that the generating means initially generates the first address from the numerical value of its own numerical address by altering the numerical value of its own numerical address by plus or minus one .

32. A modem as claimed in Claim 30 or 31 characterised in that on the first address or new first address generated by the generating means being equal to the numerical address of the next adjacent modem, the generating means generates a first address, the numerical value of which is equal to its own numerical address plus or minus one.

33. A modem as claimed in any of Claims 23 to 32 characterised in that the means for passing the token passes the token to the next adjacent modem in increasing order of numerical value of modem address.

34. A modem as claimed in Claim 33 characterised in that the generating means generates the first address initially by increasing the numerical value of its own address by plus one, and generates each new first address by increasing the numerical value of the last polled first address by plus one.

35. A modem as claimed in Claim 33 or 34 characterised in that the generating means on generating a first address or a new first address which is equal to a predetermined maximum value which corresponds to a predetermined maximum number of modems which may be connected into the network, the generating means generates a new first address equal to zero to one.

36. A modem as claimed in any of Claims 23 to 35 characterised in that the modem comprises a second storing means for storing the numerical addresses of all visible modems in the network.

37. A modem as claimed in Claim 36 characterised in that a second updating means is provided for updating the second storing means with the numerical address of a new modem which has been connected into the network.

38. A modem as claimed in Claim 36 or 37 characterised in that the second storing means stores the identity of computer devices which are associated with the respective modems in the network, the identities of the respective computer devices being cross referenced with their corresponding modem addresses in the second storing means.

39. A modem as claimed in any of Claims 23 to 38 characterised in that the modem is a power line modem.

40. A network comprising a plurality of modems characterised in that each modem is a modem according to any of Claims 23 to 39.