FAST AND EFFICIENT PACKET TRANSMISSION SYSTEM AND METHOD

Abstract: A fast and efficient packet transmission system and method for transmitting and routing packets through a digital communications network (101, 102, 103, 104, 105 and 106) which utilizes both variable length packets and fixed length packets, or cells, for achieving maximum efficiency and minimum delay in the digital communications network. Network efficiency is maximized by using variable length packets to transmit information across transmission lines (102) and network speed is maximized by using cells to route information to their intended destinations.

Description: FAST AND EFFICIENT PACKET TRANSMISSION SYSTEM AND METHOD BACKGROUND OF THE INVENTION I. Field of the Invention The present invention relates to the field of digital communications. More particularly, the present invention relates to a system and method for transmitting and routing packets in a digital communications network which utilizes both variable length packets and fixed length packets for achieving optimum efficiency and speed through the network. II. Description of the Related Art In packet switching networks, information is transmitted in packets, each of which contains a portion (or all for short messages) of the subscriber's information plus some control information. The control information at a minimum includes the destination address of the packet which enables the network to route the packet through the network and deliver it to its intended destination. At each node en route the packet is received, stored briefly, and passed on to the next node. In packet switching networks, network resources are shared by multiple subscribers on an as-needed basis. In other words, a packet is transmitted as it becomes available, but no transmission facilities are held by a source when it has nothing to send. The connection between subscribers is logical rather than physical. A primary advantage of this type of switching network is its optimized use of the network resources by ensuring that needed physical channels are never idle, except in the absence of traffic. In addition, since packet switching operates in a burst-oriented access mode, a single network resource can accommodate multiple subscribers transmitting and receiving information at different or variable data rates. This ability to simultaneously accommodate variable rate information from multiple subscribers allows packet switching networks to achieve maximum bandwidth efficiencies. Since the length of variable length packets are directly proportional to the rate of information being transmitted within a given time period, variable length packets contain a minimum number of "idle bits." This allows variable length packets to utilize the bandwidth capacity of a transmission medium with maximum efficiency. Many of the advantages of variable length packet switching come with a cost, however. As a result of the overhead involved in storing and processing control information, a variable length packet may experience delay times and other overhead inefficiencies during routing that do not meet the low delay requirements of certain types of information such as voice communications. To decrease the delay times involved in processing control information, fixed length packets, or cells (a cell is defined as a packet with a fixed size), may be used to route information through a network. There are two advantages in using cells when compared with using variable length packets to route information. First, cells simplify network routing and /or switch design due to synchronized flow of cells from all inputs through switching elements. Second, cells reduce processing of control information at network nodes because no cell length calculations are required. Both of these advantages allow cells to be transmitted and routed through a communications network with minimal delay making fixed length cells particularly well suited for low-delay communications such as voice communications. Asynchronous Transfer Mode (ATM) has become the accepted standard for cell relay. ATM is a low-delay, high- bandwidth, fixed cell size, packet switching and multiplexing technique. Using cells involves one obvious disadvantage, however. For communication systems transmitting and receiving variable rate information such as voice information, cells do not exhibit the bandwidth efficiencies achieved by variable length packets. The length of variable length packets will vary proportionally with the rate of the variable rate information. Therefore, when using variable length packets, there is a minimum number of "idle bits" for each packet. In contrast, each cell must be long enough to accommodate the fastest variable rate information. Therefore, slower rate information will occupy only a portion of the bit space available on a fixed length cell and the rest of the cell will consist of "idle bits" or "filler bits." Therefore, there is a tradeoff between network efficiency and network speed. Although variable length packets maximize network efficiency they exhibit greater switching and routing delays than that exhibited by cells. Conversely, fixed length cells can be switched and routed much faster than variable length packets but are less efficient because they contain a greater number of "idle bits." Network efficiency is of paramount importance in the communications industry because corresponding to network efficiency is the ability to handle more subscribers simultaneously which equates to more revenues from paying customers. On the other hand, the quality of transmission is very important to the customer. Therefore, minimizing transmission delays is also very important in the communications industry. With these two competing interests in mind (i.e. network efficiency and network speed), it is apparent that there is a need for a digital communications network which will optimally maximize transmission efficiency and minimize transmission delays. SUMMARY OF THE INVENTION The present invention is a novel packet transmission system and method for transmitting packets through a digital communications network. The packet transmission system utilizes both variable length packets and fixed length packets, or cells, for optimally achieving maximum efficiency and minimum delay during the transmission of information through the digital communications network. Network efficiency is maximized by using variable length packets when information is transmitted across transmission lines. Network delay is minimized by converting the variable length packets into cells at the switch or router interface and then routing the cells to their appropriate destination ports in accordance with the destination address of each cell. The present invention can operate in two modes to provide two- way communications between end subscribers. These two modes are referred to as the forward link and the reverse link. On the reverse link, subscriber information signals are received by a first signal processor, routed through the system, and then transmitted by a second signal processor to their next destinations. On the forward link, subscriber information signals are received by the second signal processor, routed through the system, and then transmitted by the first signal processor to their next destinations. In one embodiment of the present invention, on the reverse link, a first signal processor receives subscriber information signals and processes them into a variable length packet format. The variable length packets are then transmitted across a transmission line to a first packet converter which converts the variable length packets into cells. The cells are then routed by a system router which routes each cell to a particular destination port in accordance with the destination address of each cell. The cells may be routed directly to an Asynchronous Transfer Mode (ATM) Network or other network capable of receiving cells, routed back to a first packet converter in the forward link direction (see forward link discussion below), or routed to a second packet converter. At the second packet converter, the cells are converted back into variable length packets. The variable length packets are then processed by a second signal processor into their next transmission formats and transmitted to their next destinations. On the forward link, a second signal processor receives subscriber information signals and processes them to produce variable length packets. The variable length packets are then converted into cells by a second packet converter. The cells are routed by the system router to a first packet converter. At the first packet converter, the cells are converted back into variable length packets. These variable length packets are then transmitted across a transmission line to a first signal processor where they are processed into their next transmission formats and transmitted to their next destinations. The system router may receive cells directly from an Asynchronous Transfer Mode (ATM) network or other fixed length packet source. These cells can then be routed in either the forward link or reverse link direction to their next destinations. As mentioned above, the system router may also transmit cells directly to an ATM Network or other network capable of receiving information signals in a fixed length packet (cell) format. BRIEF DESCRIPTION OF THE DRAWINGS The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters correspond throughout and wherein: FIG. 1 is a schematic overview of an exemplary packet transmission system; and FIG. 2 is a schematic overview of an exemplary Code Division Multiple Access (CDMA) packet transmission system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An exemplary packet transmission system in which the present invention is embodied is illustrated in FIG. 1. The packet transmission system operates in two modes to provide two-way communications between end-subscribers. These two modes are referred to as the forward link and the reverse link. On the reverse link, subscriber information signals are received by a first signal processor, routed through the system, and then transmitted by a second signal processor to their next destinations. On the forward link, subscriber information signals are received by the second signal processor, routed through the system, and then transmitted by the first signal processor to their next destinations. On the reverse link, first signal processors lOla-lOln receive subscriber information signals and process them into a variable length packet format. The variable length packet format may be one of various formats which are known in the prior art (i.e. HDLC, LAPB, LAPD, etc.). The variable length packets are then transmitted across transmission lines 102a-102n. These transmission lines are typically El or Tl lines which are commercial lines with standard bandwidths. However, other types of lines may be used depending on the capacity requirements of the particular system. Variable length packets utilize the maximum bandwidth capacity of the transmission line because such packets contain a minimum number of "idle bits." Therefore, more users can send information over the line simultaneously and line efficiency is maximized. Upon completion of their transit across transmission lines 102a- 102n, the variable length packets are converted into fixed length packets, or cells, by first packet converters 103a-103n. In contrast to variable length packets, the routing of cells does not require time-consuming packet length calculations. Therefore, switching and routing is done using cells which can be switched or routed much faster than variable length packets. After the variable length packets have been converted into cells, a system router 104 routes each cell to its appropriate destination port in accordance with the destination address of each cell. Standard packet switches and routers are relatively inexpensive and do not exhibit the bandwidth limitations inherent in transmission lines. Therefore, achieving bandwidth efficiency at the switch or router is of relatively little concern when compared to achieving the low delay requirements of many types of communications. In addition, since transmission lines are typically leased from local telephone carriers at a considerable cost they must be utilized to their maximum capacities to achieve cost efficiency. The system router, on the other hand, is typically not leased. If one system router cannot handle the amount of information traffic in its area, it may be upgraded or a second router can be built at relatively little long-term cost to handle the additional information traffic. Therefore, achieving bandwidth efficiencies at the system router is not as important as achieving bandwidth efficiencies across leased transmission lines. The main concern of the system router is to route information to their appropriate destinations with minimal delay. The cells may be routed either directly to an Asynchronous Transfer Mode (ATM) Network or other network capable of receiving cells, or back to the first packet converters 103a-103m (see forward link discussion below), or to the second packet converters 105a-105m. The second packet converters 105a-105m convert the cells back into variable length packets. The variable length packets are then processed by second signal processors 106a-106n into their next transmission formats and transmitted to their next destinations. On the forward link, second signal processors 106a-106n receive subscriber information signals and process them into a variable length packet format. The variable length packets are then converted into cells by second packet converters 105a-105m. The cells are then routed by a system router 104 to first packet converters 103a-103n in accordance with the destination address of each cell. The first packet converters 103a-103m then convert the cells back into variable length packets. The variable length packets are then transmitted across transmission lines 102a-102n to first signal processors lOla-lOln where they are processed into their next transmission formats and transmitted to their next destinations. The system router 104 may receive cells directly from an Asynchronous Transfer Mode (ATM) network or other fixed length packet source. These cells can then be routed in either the forward link or reverse link direction to their next destinations. As mentioned above, the system router may also transmit cells directly to an ATM Network or other network capable of receiving information signals in a fixed length packet format. An exemplary Code Division Multiple Access (CDMA) packet transmission system in which the present invention is embodied is illustrated in FIG. 2. The use of CDMA modulation techniques is one of several techniques for facilitating communications in which a large number of system subscribers are present. The use of CDMA techniques in a multiple access communication system is disclosed in U.S. Patent No. 4,901,307, entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING A SATELLITE OR TERRESTRIAL REPEATERS," and assigned to the assignee of the present invention. This disclosure is hereby incorporated by reference. The relevant features of a CDMA packet transmission system (otherwise known as a CDMA Cellular Landbase Network (CCLN)) are shown in FIG. 2. The CDMA packet transmission system is composed of two parts: a number of base station transceiver subsystems (BTS) 201a-201n and a single base station controller (BSC) 200. In a CDMA communications system, CDMA variable rate packets are transmitted over the air between a subscriber and a base station transceiver subsystem 201a- 201n. The base station transceiver subsystems 201a-201n are the links between subscribers and the base station controller 200 and provide the common air interface to the subscribers. The base station controller 200 contains the resources for setting up and maintaining traffic channels and routing information between the base station transceiver subsystems 201a- 201n and other networks such as a public switched telephone network (PSTN). The CDMA packet transmission system operates in two modes to provide two-way communications between end-subscribers. These two modes are referred to as the forward link and the reverse link. On the reverse link, subscriber information signals are received by base station transceiver subsystems 201a-201n, routed through the base station controller 200, and then transmitted by selector bank subsystems (SBS) 206a-206n to their next destinations. On the forward link, subscriber information signals are received by the selector bank subsystems 206a- 206n, routed through the base station controller 200, and then transmitted by the base station transceiver subsystems 201a-201n to their next destinations. On the reverse link, base station transceiver subsystems 201a-201n receive incoming CDMA signals and process them into High-level Data Link Control (HDLC) variable length packets. The HDLC format is a flag synchronization transmission control format in which information having an arbitrary bit length is regarded as a transfer unit called a variable length packet (sometimes called a frame). The HDLC format enables transfer of continuous information in variable length packets. After the base station transceiver subsystems 201a-201n have processed the incoming CDMA signals, the resulting HDLC variable length packets are then transmitted across transmission lines 202a-202n to a base station controller 200. At the base station controller 200, the HDLC packets are received by first packet converters 203a-203m which convert the HDLC variable length packets into Asynchronous Transfer Mode (ATM) cells. ATM is a low delay, high bandwidth, fixed packet size, packet switching and multiplexing technique which has become an accepted standard for cell relay. After the first packet converters 203a-203m convert the HDLC packets to ATM cells, the ATM cells are routed by a system packet router 204 to their appropriate destination ports in accordance with the destination address of each cell. The ATM cells may be routed either directly to an ATM network, back to the first packet converters 203a-203m in the forward link direction, or to the second packet converters 205a- 205m. At the second packet converters 205a-205m, the ATM cells are converted back into HDLC variable length packets. The HDLC packets are then sent to the selector bank subsystems 206a-206n which process the HDLC packets into their next transmission formats and transmit them to their next destinations. The selector bank subsystems 206a-206n are responsible for the call processing requirements of the base station controller 200 and provide an interface between the base station controller 200 and other networks such as the public switched telephone network (PSTN). Typically the HDLC packets will contain voice information and the selector bank subsystems will process the HDLC packets into pulse code modulated (PCM) voice signals which are then time-division multiplexed and sent to the public switched telephone network. Each of the selector bank subsystems 206a- 206n contain a plurality of selector elements which provide the resources for allocating a unique transmission channel, using time division multiplexing techniques, for the individual subscriber information signals transmitted between the selector bank subsystems 206a-206n and a public switched telephone network or other interfacing network. The public switched telephone network is usually a local telephone carrier. In addition to voice communications the selector bank subsystems 206a-206n may process other types of data to interface with a variety of networks. On the forward link, selector bank subsystems 206a-206n receive subscriber information signals and time division multiplex these signals such that each subscriber signal is provided with a unique transmission channel between a selector bank subsystem and the public switched telephone network, or other interfacing network. Typically the subscriber information signals will be pulse code modulated (PCM) voice communications transmitted by the public switched telephone network. However, other types of signals may be received and processed by the selector bank subsystems 206a-206n enabling them to interface with a variety of networks. The selector bank subsystems 206a-206n then process the subscriber information signals into HDLC variable length packets. The HDLC packets are then sent to second packet converters 205a-205m which convert the HDLC packets into ATM cells. The ATM cells are then routed by the system router 204 to their appropriate destination ports in accordance with the destination address of each cell. After the ATM cells have been routed, they are converted back into HDLC variable length packets by the first packet converters 203a-203m. The HDLC packets are then transmitted across transmission lines 202a-202n to the base station transceiver subsystems 201a-201n. The base station transceiver subsystems 201a-201n then process the variable length packets into CDMA signals and transmit them to their next destinations. The system router 204 may receive ATM cells directly from an ATM network, bypassing the selector bank subsystems 206a-206n and the second packet converters 205a-205m. At the system router 204, the ATM cells may then be routed in either the forward link or reverse link directions to their next destinations. The system described above is not limited to either HDLC variable length packet or ATM cell formats. Other types of variable length packet formats and cell formats may be utilized to achieve the advantages of the present invention. The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. The various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. We claim:

Claims: CLAIMS 1. In a digital communications network, a packet transmission system comprising: a first signal processor for processing received subscriber information signals into variable length packets and for processing variable length packets into outgoing subscriber information signals; a transmission line coupled to said first signal processor; a first packet converter, coupled to said transmission line, for converting said variable length packets into cells and for converting cells into variable length packets; and a system router, coupled to said first packet converter, for routing said cells to their next destinations. 2. The packet transmission system of Claim 1 further comprising: a second packet converter, coupled to said system router, for converting cells into variable length packets and for converting variable length packets into cells; and a second signal processor, coupled to said second packet converter, for processing variable length packets into their next transmission formats and for processing received subscriber information signals into variable length packets. 3. The packet transmission system of Claim 2, wherein said variable length packets are High-level Data Link Control variable length packets. 4. The packet transmission system of Claim 3, wherein said cells are Asynchronous Transfer Mode cells. 5. The packet transmission system of Claim 2, wherein said cells are Asynchronous Transfer Mode cells. 6. The packet transmission system of Claim 1 wherein: said first signal processor comprises a base station transceiver subsystem ; and said subscriber information signals received and transmitted by said first signal processor are Code Division Multiple Access spread spectrum signals. 7. The packet transmission system of Claim 2 wherein: said first signal processor comprises a base station transceiver subsystem ; and said subscriber information signals received and transmitted by said first signal processor are Code Division Multiple Access spread spectrum signals. 8. The packet transmission system of Claim 7 wherein: said second signal processor comprises a selector bank subsystem; and said subscriber information signals received and transmitted by said second signal processor are pulse-code-modulated, time-division- multiplexed signals. 9. The packet transmission system of Claim 2 wherein: said second signal processor comprises a selector bank subsystem; and said subscriber information signals received and transmitted by said second signal processor are pulse-code-modulated, time-division- multiplexed signals. 10. A Code Division Multiple Access packet transmission system comprising: a base station transceiver subsystem for transmitting and receiving CDMA signals to and from a plurality of system subscribers, said base station transceiver subsystem further comprising: a CDMA signal processor for processing received CDMA signals into variable length packets and for processing variable length packets into output CDMA signals; a transmission line, coupled to said base station transceiver subsystem; a first packet converter, coupled to said transmission line, for converting variable length packets into cells and for converting cells into variable length packets; a system router, coupled to said first packet converter, for routing said cells; a second packet converter, coupled to said system router, for converting said cells into variable length packets and for converting variable length packets into cells; and a selector bank subsystem, coupled to said second packet converter, wherein said selector bank subsystem comprises: a signal processor for processing variable length packets into their next transmission formats and for processing received subscriber information signals into variable length packets; and a plurality of selector elements each of which provides a unique transmission channel using time division multiplexing (TDM) for each individual subscriber information signal. 11. The CDMA packet transmission system of Claim 10 wherein said variable length packets are High-level Data Link Control variable length packets. 12. The CDMA packet transmission system of Claim 11 wherein said cells are Asynchronous Transfer Mode cells. 13. The CDMA packet transmission system of Claim 10 wherein said cells are Asynchronous Transfer Mode cells. 14. In a digital communications network, a method for transmitting packets comprising the steps of: a) processing received subscriber information signals into variable length packets using a first signal processor; b) transmitting said variable length packets across a transmission line from said first signal processor to a first packet converter; c) converting said variable length packets into cells using said first packet converter; and d) routing said cells to their next destinations using a system router. 15. The method for transmitting packets of Claim 14 further comprising the steps of: a) converting said cells, after they have been routed by said system router, back into variable length packets using a second packet converter; b) processing said variable length packets into their next transmission formats using a second signal processor; and c) transmitting the resulting signals to their next destinations. 16. The method for transmitting packets of Claim 15 further comprising the steps of: a) processing received subscriber information signals into variable length packets using said second signal processor; b) converting said variable length packets into cells using said second packet converter; c) routing said cells to their intended destination ports using said system router; d) converting said cells back into variable length packets using said first packet converter; e) transmitting said variable length packets across a transmission line to a first signal processor; f) processing said variable length packets into their next transmission formats; and g) transmitting the resulting signals to their next destinations. 17. The method for transmitting packets of Claim 16, wherein said variable length packets are High-level Data Link Control variable length packets. 18. The method for transmitting packets of Claim 17, wherein said cells are Asynchronous Transfer Mode cells. 19. The method for transmitting packets of Claim 16, wherein said cells are Asynchronous Transfer Mode cells. 20. The method for transmitting packets of Claim 16 wherein said subscriber information signals received and transmitted by said first signal processor are Code Division Multiple Access spread spectrum signals. 21. The method for transmitting packets of Claim 20 further comprising the step of time-division multiplexing said subscriber information signals received and transmitted by said second signal processor, using a selector bank subsystem as said second signal processor, to provide a unique transmission channel for each individual subscriber information signal. 22. The method for transmitting packets of Claim 16 further comprising the step of time-division multiplexing said subscriber information signals received and transmitted by said second signal processor, using a selector bank subsystem as said second signal processor, to provide a unique transmission channel for each individual subscriber information signal. 23. In a digital communications network, a method for transmitting packets comprising the steps of: a) routing received cells to a first packet converter using a system router; b) converting said cells into variable length packets using said first packet converter; c) transmitting said variable length packets across a transmission line to a first signal processor; d) processing said variable length packets into their next transmission formats using said first signal processor; and e) transmitting the resulting signals to their next destinations. 24. The method for transmitting packets of Claim 23 further comprising the steps of: a) processing received subscriber information signals into variable length packets using a second signal processor; b) converting said variable length packets into cells using a second packet converter; and c) transmitting said cells to said system router.

Inventors: BROCK MICHAEL P, KHATIBI FARROKH, ROBBINS BARRY R, WEAVER LINDSAY A JR, BROCK, MICHAEL, P., KHATIBI, FARROKH, ROBBINS, BARRY, R., WEAVER, LINDSAY, A., JR.
Applicants: QUALCOMM INC, QUALCOMM INCORPORATED
Application year: 1996
Main classification: H04L
IPC codes: H04L12, H04Q7