Known techniques of transmitting and receiving inbound messages in a multichannel communication system from a plurality of selective call devices on a plurality of inbound channels include a technique of using a scheduled inbound transmission protocol and a technique of using a contention (unscheduled) inbound transmission protocol. An example of a scheduled inbound transmission protocol is a transmission protocol in which at least one predetermined periodic time slot is reserved on at least one predetermined inbound channel for each selective call device which is active in the selective call communication system. Another example of a scheduled inbound transmission protocol is a transmission protocol in which a selective call device is notified of a response time slot to be used for transmitting a long inbound message. The notification is given within an outbound message, which is sent in response to a short inbound message sent by the selective call device informing the communication system of the existence of the long inbound message.
An example of a contention inbound transmission protocol is an ALOHA protocol, which is well known to one of ordinary skill in the art. Inbound messages sent by an ALOHA protocol are typically transmitted as soon as they are generated. When two such messages happen to be transmitted on one channel such that some portions are transmitted simultaneously, one or both messages may not be received correctly. In this event, the messages are not acknowledged by the selective call communication system and each selective call device repeats the message after a random delay.
The communication system may be a wireline or optical or radio communication system. In a wireline system, the inbound channels may be separated by physically different wires, or may be separated (particularly in the case of high-speed wireline systems) by band limited channels, or by both. In optical or radio communication systems, the channels are typically separated by band-limited channels, but may alternatively or additionally be separated by time or code division duplexing.
Some systems that have an outbound signaling protocol that is synchronous are designed so that the selective call devices acquire synchronization to the outbound signaling protocol and use a scheduled inbound transmission protocol, because a scheduled inbound transmission protocol is typically more efficient than a contention inbound transmission protocol for several types of inbound messages, such as demand responses and acknowledgments. However, a contention transmission protocol can typically be more efficient for other types of inbound messages, such as some unsolicited inbound messages. Thus, it can be desirable to provide for both types of inbound transmission protocols.
Prior art systems typically provide for a mix of scheduled and contention inbound transmission protocols by designating some types of messages to be transmitted using an ALOHA protocol and other types of messages to be transmitted using a scheduled transmission protocol. A selective call device then uses the indicated technique on an authorized inbound channel. The authorized inbound channel is typically any one of the inbound channels that the selective call device is designed to use.
In the prior art systems, the selective call device must seek permission and wait an unspecified length of time before it can be granted a channel to send in its response. This method involves several transmissions and retransmissions between the selective call device, the radio frequency controller, and a home terminal before approval can be communicated to the selective call device.
Thus, what is needed is a technique for reducing the number of transmissions and the latency time currently being experienced when a selective call device has a demand response to an outbound message.