Packet switched communication system comprising collision avoidance means

• US 4,514,843 A
• Filed: 12/02/1982
• Issued: 04/30/1985
• Est. Priority Date: 12/02/1982
• Status: Expired due to Term

• Current Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Original Assignee: AT&T, Inc.
• Inventors: Albanese, Andres
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): Chin, Wellington
• Application Number:
  US06/446,191
• Time in Patent Office: 880 Days
• Field of Search: 340/825.5, 340/825.51, 370/93, 370/85, 370/94, 370/86, 455/58
• US Class Current: 370/445
• CPC Class Codes: H04L 12/407 with decentralised control
• CPC Class Codes: H04L 12/44 Star or tree networks

Abstract

The efficiency of packet switching networks is improved by using a collision avoidance technique rather than collision detection. The subscriber links are connected to a common node. A collision avoidance circuit in each link monitors the node to determine whether it is in a busy or idle status. The first message to arrive places the node in a busy status at which time all other, nontransmitting links are disconnected, thereby avoiding a collision. Later arriving messages are stored in buffers at each subscriber location and are transmitted when the node is again idle. In this manner messages are transmitted on a first-come basis, and can be of arbitrary duration regardless of bit rate.

Claims

1. Digital transmission system for controlled transmission of signal packets among a plurality of users, the system comprising a plurality of user links that terminate at a first node, at least one of these user links comprising

(a) a user station comprising signal packet transmitting means;

(b) transmission line means connecting the transmitting means to a first signal-sensing means having at least a "busy" and an "idle" state, the first signal-sensing means being in the busy state whenever a signal packet is arriving at the first signal-sensing means from the transmitting means, and in the idle state otherwise;

(c) second signal-sensing means, connected to the first node, the second signal-sensing means having at least a "busy" and an "idle" state, being in the busy state if the first node carries a signal packet, and in the idle state otherwise;

(d) third means, responsive to the first signal-sensing means and to the second signal-sensing means, for connecting the transmitting means to the first node if the second signal-sensing means are in the idle state when the state of the first signal-sensing means changes from the idle to the busy state upon arrival of a signal packet at the first signal-sensing means from the transmitting means; and

(e) the transmitting means are adapted for transmitting a signal packet to the first signal-sensing means independent of the state of the second signal-sensing means, and for later retransmitting the same signal packet to the first signal-sensing means if the second signal-sensing means were in the busy state when the first signal-sensing means were in the busy state at the time of arrival of the transmitted signal packet at the first signal-sensing means.

2. The system, according to claim 1 wherein each link comprises:

a user interface control unit located at and connected to said node;

and a transmission link connecting said user station to said control unit.

3. The system according to claim 1 wherein said node is a length l of bus, given by

4. The system according to claim 2 wherein each user station includes:

means for storing a digital message;

means for transmitting said message along said transmission link to said control unit;

means for receiving messages from said control unit;

means for comparing received messages with said stored message, and for retransmitting said stored message until a received message is the same as said transmitted message.

5. The system according to claim 2 wherein each control unit includes:

means for receiving messages from said user terminal;

switching means for coupling said receiving means to said node;

said switching means being open in the absence of a message;

said switching means being closed upon receipt of a message when said node is in an "idle" state, but remaining open when said node is in a "busy" state.

6. The system according to claim 5 wherein the transmission link comprises a pair of optical fibers;

and wherein said switch is a switchable optical directional coupler.

7. System of claim 1, wherein each user link that terminates at the first node comprises the elements of (a), (b), (c), (d), and (e) of claim 1.

8. System of claim 1, further comprising

at least one second node remote from the first node;

at least one user link connected to the second node;

interconnecting means comprising first and second node links, the first node link providing a path for transmission of digital signals from the first to the second node, and the second node link providing a path for transmission of digital signals from the second to the first node, each node link comprising;

means for storing a signal to be transmitted from a transmitting node to a receiving node;

means for transmitting the stored signal between the nodes in the appropriate direction along the link;

means for monitoring the status of the receiving node; and

means, responsive to the means for monitoring the status of the receiving node, for causing transmission of the stored signal from the transmitting node to the receiving node if the status of the receiving node is idle.

9. System of claim 8, further comprising means, associated with the transmitting station, for generating a busy burst when a signal packet arrives at the signal storage means from a first user station associated with the transmitting node when the signal storage means are full, the busy burst to be transmitted to at least the first user station.

10. System of claim 1, wherein at least some of the user links comprise optical signal generating means, and optical fiber means for guiding the optical signal.