Method and apparatus for constructing and operating multipoint communication networks utilizing point-to point hardware and interfaces

• US 4,723,120 A
• Filed: 01/14/1986
• Issued: 02/02/1988
• Est. Priority Date: 01/14/1986
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Petty, John S. Jr.
• Primary Examiner(s): YUSKO, DONALD
• Application Number:
  US06/818,632
• Time in Patent Office: 749 Days
• Field of Search: 340/825.02, 340/825.05, 340/825.52, 370/13-15, 370/86, 375/10
• US Class Current: 370/503
• CPC Class Codes: H04L 12/00 Data switching networks interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units G06F13/00

Abstract

The invention permits multiple secondary stations to be connected in a multipoint communication network to a single primary station utilizing point-to-point interfaces such as the standard RS-232 or V.35 which do not ordinarily support multipoint connections. A primary station is connected to one secondary station or modem through a point-to-point interface utilizing either a straight through or cross over cable depending upon whether a modem is included. Data goes through the secondary station or modem to a second interface which is connected to a different secondary station or modem. This type of connection is referred to as a daisy chain. Data is not buffered in the secondary stations but is transmitted directly through each station. Each station monitors the daisy chain signals for clocking, status and identification of data for itself. Since there is no buffering, only a single set of clocking can be used in the chain. The invention allows the individual station to choose the method of clocking to be used throughout the chain without loss of synchronization between data and clocking. When modems are installed in the chain, they provide clocking and status signals. When no modems are installed, the primary station or one secondary station must provide the clocking and status signals. If the primary station fails to provide clocking, the secondary station at the end of the daisy chain provides the clocking and wraps back status signals using a simple logic network. The chain is self-adjusting to changes in topology and to additions and deletions of modems and/or secondary stations.

Claims

1. A method of providing a chained multipoint communications network utilizing plural point-to-point interface hardware devices, comprising steps of:

receiving at a first communications device at an upstream or downstream standard communications interface port a plurality of control and data signals on specified standard number communication interface pins; and

issuing on downstream or upstream standard communication interface ports said plurality of control and data signals from said upstream or downstream ports, respectively, and;

said signals being issued on differently numbered standard communication interface port signal pins than those on which they were received so that they may be received correctly on the same numbered pins as said first device at the next device in said chain which is connected to said communication ports of said first device with a standard crossover connection cable.

2. A method as described in claim 1, wherein:

said issuing step comprises steps at each said device of connecting the received data input lead at one standard interface port to the transmit data output lead at the other standard interface port of each device.

3. A multipoint communication network comprising:

a plurality of point-to-point standard communication interface communications devices;

a plurality of standard communications crossover connecting cables;

said cables connecting the outputs of a standard communication port of one device to the inputs of a standard communication port of another device to construct a multipoint communications network; and

each said device comprising crossover means to connect data received from a said cable at a said standard communications interface input port receive data pin to a standard interface port transmit data pin at a standard communications interface output port thereof.

4. Apparatus as described in claim 3, wherein:

said crossover means comprises a microprocessor connected to the input and output standard communication interface ports of each communications device for monitoring the activity at said port; and

means controlled by said microprocessor in response to said monitored activity for interconnecting certain of the pins of said standard communications interface input port to certain other pins of a standard communications interface output port in a paired arrangement, said certain pins at least comprising the receive data input pin at a standard communications input port and the transmit data pin at a standard communications output port as one said pair.

5. Apparatus as described in claim 4, wherein:

the roles of input and output port designations reverse when the flow of communication reverses from downstream to upstream or vice versa but the pairing of said interconnections remains unchanged.

6. A method of coordinating communications from a primary or controlling station on a serially chained network of devices that each have a standard interface, said primary or controlling station being located at one end of said serially chain network, comprising steps of:

raising a first signal at said primary station on said serially chained network, said signal being directly connected to the first non-primary station;

transmitting said first signal from said first non-primary station to the next non-primary station and from that said next station to the next station until either a modem or the last station in said network is reached;

returning a second signal from said modem or said last secondary station, whichever is first reached by said first signal, said returned signal being returned to the next station closer to said primary station than said modem or said last station; and

passing said second signal from said next station to the next until said primary station receives said second signal; and

raising a third signal at said primary station in response to the receipt of said second signal;

said third signal being directly connected to said first non-primary station;

transmitting said third signal from said first non-primary station to the next said station and from the next said station to the next until either a modem or the last said station in said network is reached; and

returning a fourth signal from said modem or said last secondary station, whichever is first reached by said third signal, to the station next closer to said primary station or modem than said modem or last station; and

passing said fourth signal from said next station to the next until said primary station receives said fourth signal; and

transmitting data from said primary station to said network upon receipt of said fourth signal.

7. A method as described in claim 6, wherein said coordinating of communications is from a non-controlling station to said primary or controlling station, comprising steps of:

initiating said third signal at said non-controlling station having data to transmit, said signal being directly connected to said station next closer to said primary station on said network than said non-controlling station;

transmitting said third signal from said next station to the next until a modem or said primary station receives it; and

raising said fourth signal at said modem or at said primary station, whichever is first reached by said third signal; and

transmitting said fourth signal to said non-controlling station and, upon receipt thereof at said non-controlling station, sending data therefrom.