Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
2000-11-09
2004-09-07
Rao, Seema S. (Department: 2666)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S352000, C370S442000, C370S468000
Reexamination Certificate
active
06788664
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a communication system suitable for transmitting circuit switched and packet switched information over a common transmission link. In particular it relates to a system for transmitting circuit switched and packet switched information over a common time division multiplexed or time division multiple access transmission link in a fixed wireless access communication system or to a system in which packet switched information is transmitted across a channelised transmission link.
It is often desirable to transmit both circuit switched information and packet switched information from a first to a second location.
A circuit switched connection is characterised by the presence of a set-up phase, a connection phase during which a fixed amount of transmission capacity is assigned, and a tear down phase. Routing is determined during the set up phase and is constant throughout the connection. The advantage of circuit switching is that once a connection is established, the transmission capacity required for that connection is guaranteed. Thus, latency is both minimised and constant. The disadvantage is that the capacity is taken up by the connection even when no data is being sent. The predominant application for circuit switched connections is voice transmission (eg. telephony). Voice-band dial-up modems depend on circuit switched connections through the PSTN, and these provide a good example of the wasteful aspect of circuit-switching as the telephone call is maintained even when the data equipment has nothing to send.
A packet-switched data transfer is characterised by the division of the data payload to be transmitted into frames or packets, each of which carries a source and destination address. The packets are routed individually and so several data transfers can share a common transmission link using statistical multiplexing. Packet-switched networks can make use of buffering and flow control techniques (eg. Transmission Control Protocol) and can therefore adapt to changes in loading by increasing or decreasing the rate at which packets are transmitted from each source. A packet-switched approach will generally be more efficient than a circuit-switched approach in an application, such as Internet access, where the data sent is sufficiently bursty or intermittent, and where some variation in latency can be tolerated.
Separate transceiver facilities could be used between a first and a second location, one transceiver facility associated with a circuit switched transmission link and one transceiver facility associated with a packet switched transmission, as is described in International Patent Application WO 95/31060. However, this is a high cost option in view of the cost of duplicated transceiver facilities.
It is known to use a single transmission link, such as a time division multiplexed transmission link for transmitting both circuit switched information and packet switched information from a first to a second location. A problem exists with regard to the currently available arrangements for assigning time slots and/or channels on the transmission link to the two types of traffic.
One option is a fixed assignment wherein each type of traffic is permanently assigned to certain channels or circuits. This is undesirable as no provision is made for the different levels of traffic that exist at different times. For example, using a fixed assignment there could be unused or idle channels assigned to the circuit-switched information during times when all the channels assigned to the packet information are busy and there is a backlog of packet information waiting to be transmitted. Also, there could be times where new circuit-switched connections are blocked because all of the channels allocated to circuit switched traffic are in use during times when there is an under utilisation of the channels allocated to packet information.
This problem has been solved by the use of dynamic assignment mechanisms so that time slots in a transmission link are used efficiently. Such a system is described in EP 0236 102. In this system which operates in real time, preference in the use of time slots is normally given to circuit switched information, although packet switched information is assigned a minimum number of time slots so that there is never a total blockage of packet information in times of heavy circuit switched traffic. Dynamically operated control facilities are provided to allocate packet switched information to all time slots not currently allocated to a circuit switched connection and to all idle time slots currently allocated to a circuit switched connection.
The problem with the system proposed in EP 236 102 arises from the actions that are necessary whenever a new circuit-switched connection is required. The terminal control facilities must suspend packet data transfers, revise the channel allocations, and communicate the new channel assignments to a remote terminal, all before setting up the new circuit-switched connection (and restarting packet transfers). This may be acceptable in the point-to-point transmission links referred to in EP 236 102. However, in point-to-multi-point transmission links, it would be necessary to communicate the revised channel assignments to each of the remote terminals, possibly by means of unreliable transmission paths. The resulting delay in establishing a circuit connection would be significant in many applications. In the case of a TDMA fixed wireless access system, the technique described in EP 236 102 would result in an unacceptable delay before establishing a voice-band path between the telephone set and the local exchange. Alternatively, a means could be devised to set up the new circuit-switched connection without co-ordinating the packet assignments, but this would result in lost packets at a rate that would be unacceptable in most applications.
The same problem arises for the system decribed in GB2,301,992 in which channels in a TDMA transmission link are allocated dynamically to circuit switched information and the remaining time slots in the link are allocated dynamically to packet switched information. In this system packet switched information is preferentially allocated to idle time slots in a previously under utilised control channel in order to improve the efficiency with which both types of information are transmitted.
OBJECT OF THE INVENTION
The object of the present invention is to provide a communication system suitable for transmitting circuit switched and packet switched information over a common transmission link in which the capacity of the link is improved without extending the set up time for circuit-switched connections.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided a communication system including:
a transmission link having a number of channels; and
means for transmitting circuit switched and packet switched information over said transmission link;
wherein the system additionally includes a controller device for periodically pre-allocating channels to circuit switched traffic for a set time period dependent on one or more system parameters existing in a previous set time period.
Thus, at all times there are automatically pre-allocated channels for circuit switched traffic and the remainder of the link resource is available for use by packet switched traffic. This simplifies the process of allocating incoming traffic to channels and/or timeslots on the link as compared to the known methods for real time dynamic allocation of link resource. Additionally, this pre-allocation of channels is automatically optimised on a periodic basis in order to make good use of the link resource, as compared to static allocation, while maintaining the required grade of service to circuit traffic. Furthermore, if the peaks for circuit and packet switched traffic are offset in time then the capacity of the link will be increased by the use of the present invention. A further advantage is that the automatic allocation of channels by the contro
Beighton Peter
Johnson Philip N
Thomas Mark K
Moore, Jr. Michael J.
Nortel Networks Limited
Rao Seema S.
LandOfFree
Communication system for circuit switched and packet... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Communication system for circuit switched and packet..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Communication system for circuit switched and packet... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3187460