Method and apparatus for bandwidth reservation

Abstract: A transmitting unit for use in sending data in packets in timeslots within time frames, each packet being sent in a timeslot, the unit comprising means to reserve for uplink transmission in the next uplink time frame a number of timeslots (X), the number of timeslots (X) being determined dependent upon a value which is the number of timeslots (Y) used for uplink transmission in the previous uplink time frame plus the number of packets (Z) remaining for uplink transmission during the last time frame minus the number of time slots (Q) to be used in the present uplink time frame.

Description: Background of the Invention The present invention relates to a transmitting unit for use in sending data in packets in timeslots within time frames and a method of data transmission involving bandwidth reservation, in particular reservation of timeslots. In known time division protocols, a number of time slots per time frame is allocated to a modem to be used for voice or video. The disadvantage is that there must be means to calculate the number of timeslots, and it might allocate too many, causing bandwidth to be wasted, or too few, causing delay in transmission of the packets. In those known systems on the uplink, a packet waits two time intervals for transmission, one interval being for a timeslot to be requested, the second being for allocation of uplink timeslots by the access point of the core network; the access point can be considered as a master modem controlling communications with slave modems. A bandwidth reservation method is disdosed in EP 0 554 975. Summary of the Invention The present invention provides a transmitting unit for use in sending data in packets in timeslots within time frames, each packet being sent in a timeslot, the unit comprising means to reserve for uplink transmission in the next uplink time frame a number of timeslots, the number of timeslots being determined as the number of timeslots used for uplink transmission in the previous uplink time frame plus the number of packets remaining for uplink transmission during the last time frame minus the number of time slots to be used in the present uplink time frame. The present invention in its preferred embodiments advantageously addresses the problem of delay in known time division wireless systems on the uplink. The present invention in its preferred embodiments seeks when possible to effectively eliminate the above-mentioned first interval in which to request a timeslot, and is particularly suitable for voice and/or video data. The present invention in its preferred embodiment has advantages of simple implementation, and low processing power (CPU) and memory requirements. In many cases the delay in packet transmissions on the uplink is cut in half. The present invention in its preferred embodiments is preferably a modem. Advantageously the preferred modem, within three or four time frames, tends to reserve only the same number of time slots as used in the last uplink time frame. The process is adaptive in that the modem "learns" the current bandwidth (number of time slots) and the result of this adaption is reduced packet delay. Preferably the number of time slots (X) reserved is said value. Preferably the number of time slots (X) reserved is the largest of the values determined in a plurality of uplink time frames up to the present uplink time frame and stored in a memory. The present invention also provides a network comprising the transmitting unit, and a receiving unit operative to transmit to the transmitting unit information of time slots allocated in the next uplink frame and to receive the packets sent by the transmitting unit. The present invention also provides a method of sending data in packets in timeslots within time frames, each packet being sent in a timeslot, the method comprising reserving for uplink transmission in the next uplink time frame a number of timeslots (X), the number of timeslots (X) being determined dependent upon a value which is the number of timeslots (Y) used for uplink transmission in the previous uplink time frame plus the number of packets (Z) remaining for uplink transmission during the last time frame minus the number of time slots (Q) to be used in the present uplink time frame. Brief Description of the Drawing Preferred embodiments of the present invention, and a comparitive example, will now be described by way of example and with reference to Figure 1 which is a diagrammatic illustration of a preferred modem. Detailed Description For voice traffic over external wireless data (XWD) systems, delay should be minimised. The inventors realised that, and that a voice call requires approximately constant bandwidth on both uplink and downlink, so it was found possible to use information of the number of timeslots used in the previous uplink timeframe when allocating slots for the next uplink timeframe. System Structure As shown in Figure 1, the system consists of an access point 2 and a modem 4 for time division wireless communication to the access point 2 . The access point is a master modem through which transmissions from the modem 4 are routed, hence it is the access point to the rest of the telecommunications world (also known as the core network). The modem 4 includes a transmitter 6 and receiver 8. The transmitter includes a memory 10 in which unsent packets are queued to be transmitted. The modem 2 includes a controller 12 which controls which timeslots to be used for uplink transmission in each uplink time frame. The controller 12 is informed by the access point 2 which timeslots of each time frame are allocated to the modem 4 for uplink communication. The modem 4 can thus be considered as a slave to the access point 2 in this regard. Let us assume that voice packets are sent in 10 millisecond timeslots in both directions. uplink and downlink, and consider one Wireless Modem (WM) data stream. It will be seen that there is a time frame for downlink followed by a time frame for uplink and so on, i.e. the uplink and downlink time frames alternate. The packets arrive from an Ethernet cable (not shown) and are transmitted by the modem 4 to the access point 2. Two new packets arrive during each time frame. Comparitive Example In each uplink timeframe, the modem 4 is allocated by the access point 2 the full bandwidth, i.e. all the time slots which it requested (reserved) for this timeframe in the previous uplink transmission. In situations where more timeslots are reserved than the number of packets to be transmitted, the extra timeslots are unused (i.e. the bandwidth is wasted) although in some embodiments the wireless modem can use it for other tasks if it has any. The number of time slots M reserved in each (uplink) time frame is the number of packets N remaining for transmission from the previous time frame (before the packets of the current time frame arrive for transmission) minus the number P of packets that are being transmitted in the current time frame. Time Frame Number No. of timeslots RESERVED in this time frame M No. of packets TRANSMITTED in this time frame P Total transmitted packets Total arrived packets No. of Remaining packets No. of Remaining packets of Previous time frame N Time frames in which transmitted packets arrived 1 0 0 0 2 2 2 downlnk downlnk 0 4 4 2 3 4 0 0 6 6 4 4 downlnk downlnk 0 8 8 6 5 4 4 4 10 6 8 1,2 6 downlnk downlnk 4 12 8 6 7 4 4 8 14 6 8 3,4 8 downlnk downlnk 8 16 8 6 9 4 4 12 18 6 8 5,6 10 downlnk downlnk 12 20 8 6 11 4 4 16 22 6 8 7,8 Notes to Table 1: (a) The packets of a time frame arrive after reservation is made so they are not counted in the number of timeslots (packets) reserved in that time frame. (b) The number of packets reserved in a time frame is the Wireless Modem reservation from the access point 2. This is included in the downlink signalling included in each downlink packet (and known as the piggy). (c.) The remaining packets are the number of packets which are left in the to be transmitted queues at the end of the time frame. It will be seen in Table 1 that there is a constant delay of 3 to 4 time frames. The Preferred Scheme A preferred scheme is to reserve for the next uplink time frame a number X of time slots which is the number Y used to transmit in the previous uplink time frame, plus the number of remaining packets Z of the previous downlink time frame, minus the number of timeslots used (packets sent) Q in the present uplink time frame. An example is shown in Table 2 below. It will be seen in Table 2 that from the 7 th time frame onwards there is a delay of only one or two time frames between a packet arriving and being transmitted. In the preferred scheme the pattern of delay between arrival and transmission is not initially constant but becomes constant over a period which includes four to five uplink time frames. This could take about 30 milliseconds. Therefore in a further embodiment of the invention a history is kept of the number of time slots required per time frame longer than just than number used in the last uplink time frame. In the modem according to said further embodiment, each voice packet arriving which is acceptable to be transmitted in the next uplink time frame is counted in a counter. When the modem gets bandwidth i.e. timeslots for uplink transmission in the current time frame, a record of the number of timeslots allocated per time frame is stored in an array holding the latest 8 values, and the counter rezeroed. In each time frame, a check is made whether a poll signal has been received from the access point 2 and if not received, in every even numbered (i.e.downlink) time frame the count is taken to be zero. This mechanism yields a history of the time slot allocations for time frames numbered n to 2n, where n is greater than or equal to 0 and is less than or equal to 8. The maximum number of time slots from the history is included in the reservation request sent to the access point 2. Time Frame Number No. of timeslots RESERVED in this time frame X No. of packets TRANSMITTED in this time frame Q No. of packets TRANSMITTED in PREVIOUS time frame Y Total transmitted packets Total arrived packets No. of Remaining packets No. of Remaining packets of Previous time frame N Time frames in which transmitted packets arrived 1 0 0 0 0 2 2 0 2 downlnk downlnk downlnk 0 4 4 2 3 4 0 0 0 6 6 4 4 downlnk downlnk downlnk 0 8 8 6 5 4 4 0 4 10 6 8 1,2 6 downlnk downlnk downlnk 4 12 8 6 7 8 4 4 8 14 6 8 3,4 8 downlnk downlnk downlnk 8 16 8 6 9 4 8 4 16 18 2 8 5,6,7,8 10 downlnk downlnk downlnk 16 20 4 2 11 8 4 8 20 22 6 4 9,10 12 downlnk downlnk downlnk 20 24 4 6 13 4 4 4 24 26 2 4 11,12 14 downlnk downlnk downlnk 24 28 4 2 15 4 4 4 28 30 2 4 13,14

Claims: A transmitting unit for use in sending data in packets in timeslots within time frames, each packet being sent in a timeslot, the unit comprising means to reserve for uplink transmission in the next uplink time frame a number of timeslots (X) characterized by that the number of timeslots (X) is determined dependent upon a value which is the number of timeslots (Y) used for uplink transmission in the previous uplink time frame plus the number of packets (Z) remaining for uplink transmission during the last time frame minus the number of time slots (Q) to be used in the present uplink time frame. A transmitting unit according to claim 1, in which the number of time slots (X) reserved is said value. A transmitting unit according to claim 1 or claim 2, in which the number of time slots (X) reserved is the largest of the values determined in a plurality of uplink time frames up to the present uplink time frame and stored in a memory. A transmitting unit according to claim 3, in which is the memory holds up to 8 values, one for each of the latest 8 uplink time frames. A transmitting unit according to any preceding claim, which is a modem. A transmitting unit according to claim 5, which is a wireless modem, the packets being sent by radio. A network comprising the transmitting unit according to any preceding claim, and a receiving unit operative to transmit to the transmitting unit information of time slots allocated in the next uplink frame and to receive the packets sent by the transmitting unit. A method of sending data in packets in timeslots within time frames, each packet being sent in a timeslot, the method comprising reserving for uplink transmission in the next uplink time frame a number of timeslots (X) characterized by that the number of timeslots (X) is determined dependent upon a value which is the number of timeslots (Y) used for uplink transmission in the previous uplink time frame plus the number of packets (Z) remaining for uplink transmission during the last time frame minus the number of time slots (Q) to be used in the present uplink time frame.

Inventors: GEVA EREZ, SHAASHUA ODED, ZIV-AV GONEN, GEVA, EREZ, SHAASHUA, ODED, ZIV-AV, GONEN
Applicants: LUCENT TECHNOLOGIES INC, LUCENT TECHNOLOGIES INC.
Application year: 2001
Main classification: H04L12
IPC codes: H04L12