Method for operating a packet bus for transmission of asynchronous and pseudo-synchronous signals

• US 4,586,175 A
• Filed: 04/30/1984
• Issued: 04/29/1986
• Est. Priority Date: 04/30/1984
• Status: Expired due to Fees

• Current Assignee: Northern Telecom Limited (Nortel Networks Corporation)
• Original Assignee: Northern Telecom Limited (Nortel Networks Corporation)
• Inventors: Wood, Samuel F., Bedard, Charles J., Jain, Prem C.
• Primary Examiner(s): Olms, Douglas W.
• Application Number:
  US06/605,722
• Time in Patent Office: 729 Days
• Field of Search: 370/94, 370/85, 370/89, 370/90, 370/95, 370/96, 340/825.5, 340/825.51
• US Class Current: 370/449
• CPC Class Codes: H04L 12/64 Hybrid switching systems

Abstract

Data transactions and voice communications are facilitated in a packet switching system including a group of ports each of which is capable of exchanging inter-destined and intra-destined information signals via a packet bus. The packet bus is operated under the direction of a bus controller which communicates with the ports to arbitrate access to the packet bus for packet transmission. Arbitrating access to the packet bus for pseudo-synchronous and asynchronous signal communications includes the steps of polling the ports within a period of time for high and low priority, transmission requirements. In response to each high priority requirement transmission over a predetermined number of consecutive bus cycles is granted by the bus controller within a predetermined period of time for pseudo-synchronous transmission of signals from each of the corresponding ports one after another. In response to each lower priority requirement, transmission over an indefinite number of consecutive bus cycles is granted by the bus controller for asynchronous transmission of signals from at least one of the corresponding ports. The preceding steps are repeated with a frequency such that high priority grants occur at a uniform rate that is consistent with a sampling rate of digitized voice communications being divided by one less than the predetermined number of consecutive bus cycles.

Claims

1. A method of arbitrating access to a packet bus for transmission of signals of both synchronous and asynchronous natures between a plurality of ports connected thereto, comprising the steps of:

(a) defining bus cycles each being of a set time interval for a transmission of a word portion of said signals;

(b) polling each of said plurality of ports one after another for an indication of a transmission requirement of high priority and polling at least some of the ports one after another for an indication of a transmission requirement of lower priority;

(c) in response to each indication of high priority, granting the packet bus for up to and including a predetermined number of consecutively occurring ones of said bus cycles, wherein said predetermined number of bus cycles occur within a predetermined period of time, for transmission of signals from ports indicating a transmission requirement of high priority;

(d) in response to each indication of lower priority, granting the packet bus for an indefinite number of consecutively occurring ones of said bus cycles, said indefinite number of cycles ocurring within said predetermined period of time, for asynchronous transmission of signals from at least one port indicating a transmission requirement of a lower priority; and

(e) repeating steps (a) through (d) at a frequency sufficient to provide transfer of information of a communication in step (c).

2. A method of arbitrating access to a packet bus as defined in claim 1 wherein the step of granting the packet bus is repeated at a rate at least sufficient for digitized voice communication.

3. A method of arbitrating access to a packet bus as defined in claim 2 wherein the number of bus cycles in step (d) is limited to a predetermined maximum.

4. A method of arbitrating access to a packet bus as defined in claim 1 wherein step (c) is performed exclusively for a first group of the ports within a first portion of the predetermined period of time, and wherein step (c) is subsequently performed exclusively for a second group of ports within a second portion of the predetermined period of time,

whereby regularity of pseudo-synchronous signal transmission via the packet bus is enhanced.

5. A method of operating a packet bus to provide asynchronous and pseudo-synchronous information signal transfers in a communication system comprising at least one bus interface unit connected to the packet bus for exchanging information signals between the packet bus and a terminal interface circuit, at least one bus interface unit connected to the packet bus for exchanging information signals between the packet bus and a call processor, and a bus controller connected to the packet bus for regulating transfer occurrences of said information signals, the method comprising the steps of:

in the bus controller, generating periodic frame intervals, each of said intervals being of a predetermined period of time and each of said intervals defining a predetermined number of packet bus cycles, via address and control portions of the packet bus;

firstly, polling all of the bus interface units, one after another, for a high priority pseudo-synchronous information transfer requirement;

secondly, polling in sequence bus interface units one after another for a lower priority asynchronous information transfer requirement;

and thirdly, making a record of the last lower priority polled bus interface unit at the end of the instant frame interval for use as a start point for a continuation of lower priority polling in a subsequent frame interval;

in one of the bus interface units, in response to a polling address corresponding to a unique address of a bus interface unit and a presence of information destined for at least one bus interface unit, said information being of a priority corresponding to a priority of the polling, transmitting a request signal via the control portion of the packet bus to the bus controller;

in the bus controller, transmitting grant signals, consistent with availability of the transfer portion of the packet bus, one after another to all bus interface units which have responded with a high priority request signal, the transmission of each grant signal being within the same frame interval as a corresponding high priority request signal;

thereafter transmitting individual grant signals, consistant with availability of the transfer portion of the packet bus, said availability being indicated by done signals, one after another, from said bus controller to at least some of the bus interface units which have responded with a lower priority request signal, as long as there is time remaining within a current periodic frame interval;

in each of the bus interface units have been polled, requested, and granted, transmitting information signals, said signal being preceded by destination defining address signals, during a series of consecutive bus cycles via the transfer portion of the packet bus, wherein said series consists of a predetermined plurality of bus cycles in the instance of the grant having been a high priority grant and wherein said series consists of a variable number of bus cycles up to a predetermined limit in the instance of the grant having been a lower priority grant;

transmitting a done signal from a bus interface unit during a predetermined bus cycle occurrence before a last bus cycle of the instant information signals transmission;

each of the bus interface units monitoring the transfer portion of the packet bus for an occurrence of a word corresponding to its unique address during a bus cycle of predetermined time relationship with each occurrence of a grant signal, and in response to an occurrence of its unique address during said predetermined time relationship, each bus cycle receiving information signals thereafter from the transfer bus until another occurrence of the grant signal.