Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W40/00—Communication routing or communication path finding
  • H04W40/02—Communication route or path selection, e.g. power-based or shortest path routing
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
  • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
  • H04L1/18—Automatic repetition systems, e.g. Van Duuren systems
  • H04L1/1829—Arrangements specially adapted for the receiver end
  • H04L1/1835—Buffer management
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L45/00—Routing or path finding of packets in data switching networks
  • H04L45/22—Alternate routing
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L45/00—Routing or path finding of packets in data switching networks
  • H04L45/28—Routing or path finding of packets in data switching networks using route fault recovery
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
  • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L2001/0092—Error control systems characterised by the topology of the transmission link
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W28/00—Network traffic management; Network resource management
  • H04W28/02—Traffic management, e.g. flow control or congestion control
  • H04W28/10—Flow control between communication endpoints
  • H04W28/14—Flow control between communication endpoints using intermediate storage
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W76/00—Connection management
  • H04W76/10—Connection setup

Definitions

• This invention relates to wireless communication systems and, in particular, to a system and method for reducing data transmission loss when a link or node failure occurs.
• Wireless multi-hop mobile networks characteristically lack a definite infrastructure and, consequently, experience frequent link failures caused by node mobility and interference in wireless links. This poses a problem in ensuring Quality of Service (QoS) in such networks.
• QoS Quality of Service
• end-to-end retransmissions typically can not satisfy deadlines for timely delivery of packets.
• Multi-media transfer in particular, is an example of an application that is adversely affected by loss of data packets.
• Multi-hop wireless networks can be found, for example, in applications for personal area networking, military applications, taxicab networks, networks in conference rooms, and emergency applications including "911 calls" coordinating between groups involved in search and rescue missions, or via a network established between ambulance operators at the scene of an accident and doctors at a remote hospital.
• the network topology of a wireless mobile multi-hop network changes over time where network nodes are mobile and links are established and then terminated. Transient failures in such wireless links are also more probable in comparison to wired networks because wireless links are more susceptible to interference. Routing is therefore a difficult problem in such networks, and a path from a source to a destination can not always be assured for an entire communication session.
• Several research efforts have been undertaken to optimize routing protocols in multi-hop networks. These routing protocols optimize routes from a source node to a destination node in the presence of link failures caused by node mobility or link degradation due to transmission interference.
• Various criteria have been suggested to establish the communication path using such optimization procedures. Some of these criteria include power conservation for mobile systems and congestion reduction.
• adaptations to TCP/UDP have been suggested to transport packets in an multi-hop network.
• Prior research efforts in the area have addressed routing issues without considering localized retransmissions and prioritized delivery of packets.
• the protocols discussed in the relevant art depend on higher layers, such as TCP, to deal with packet loss.
• Such approaches rely on end-to-end retransmission of lost packets and, as such, are not suited for ensuring QoS in a wireless multi-hop network, in which link failure happens frequently, as this results in intolerable delay.
• Such approaches do not provide for prioritization in the delivery of packets because the packets flowing from a source to a destination are handled similarly. This is not the optimal methodology as different micro-flows within a flow may have different delivery deadlines.
• Prioritized delivery in wired networks is known in the relevant art, but delivery on time cannot be assured in a wireless network because of the high probability of transmission error.
• the present invention results from the observation that data loss in wireless networks can be mitigated by network-layer buffering data packets at intermediate nodes in the transmission path, and locally retransmitting lost data packets.
• the wireless network formed using one or more intermediate nodes having internal buffers for continually buffering data passing from source to destination nodes, establishes an alternate path bypassing the failed node and retransmitting lost data packets in response to receipt of an error message. If a connecting node lacks an internal buffer, the error message is transmitted upstream to a node having buffered data packets which can provide the missing data.
• Fig. 1 is a diagrammatical representation of a wireless network showing a communication path formed by connecting nodes
• Fig. 2 is a flow diagram describing data transmission using the wireless network of Fig. 1 ;
• Fig. 3 is a diagram of a connecting node of Fig. 1 showing an internal buffer for buffering data passing through the node;
• Fig 4 is a diagram of a connecting node of Fig. 1 showing high, normal, and low-priority transmission buffers for buffering data passing through the node;
• Fig. 5 is a flow diagram describing in greater detail the process of transmitting undelivered data packets as represented in the flow diagram of Fig. 2;
• Fig. 6 is a diagrammatical representation of a wireless network including a connecting node without internal buffering
• Fig. 7 is a diagrammatical representation of a wireless network including a failed wireless link.
• Fig. 8 is a flow diagram describing data transmission using the wireless network of Fig. 7. DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT
• a simple wireless network 10 including a source node 11 (S) and a destination node 21 (D).
• a user of the wireless network 10 may transmit data by establishing an initial communication path between the source node 11 and the destination node 21 via a series of intermediate connecting nodes.
• the initial communication path may include, for purpose of illustration, path segments from the source node 11 to a first connecting node or intermediate node 13 (N 01 ), to a second intermediate node 15 (N 02 ), to a third intermediate node 17 (N 03 ), to a fourth intermediate node 19 (N 0 ), and then to the destination node 21.
• the initial communication path may be established by a serial combination of: a wireless link 31 between the source node 11 and the first intermediate node 13, a wireless link 33 between the first intermediate node 13 and the second intermediate node 15, a wireless link 35 between the second intermediate node 15 and the third intermediate node 17, a wireless link 37 between the third intermediate node 17 and the fourth intermediate node 19, and a wireless link 39 between the fourth intermediate node 19 and the destination node 21.
• one or more of the intermediate nodes 13-19 may fail. Failure may result, for example, from a cessation of operation of a connecting node (e.g., equipment failure or power-down), from a mobile node moving out of the range of an associated wireless link, or from an adverse propagation environment (e.g., atmospheric precipitation or turbulence) at the affected intermediate node. Accordingly, failure of a intermediate connecting node would cause one or more of the wireless links 31-39 to be lost, resulting in a break to the initial communication path with loss or corruption of data as a consequence. Detection of node failure is well-understood in the relevant art and may utilize a timeout mechanism, for example.
• a data packet stream 29 is configured for transmission in accordance with an appropriate protocol.
• each of the individual data packets in the data packet stream 29 successively passes through each of the intermediate nodes 13-19.
• At least one intermediate node in the initial communication path is configured such that the data packets are buffered for possible local retransmission using priority queuing, at step 57, as described in greater detail below. If the initial communication path remains intact, there is node failure detected, at decision block 59, the system stands by for the next transmission, at step 61, and receives data packets when provided, at step 53.
• an alternative connecting path is established, at step 63, using a method known in the relevant art, and the remaining undelivered data packets are transmitted to the destination node 21 to complete the transmittal of the data packet stream 29, at step 65.
• the third intermediate node 17 fails, the wireless links 35 and 37 are lost, as indicated by dotted lines in Fig. 1, and the initial communication path is thereby broken.
• the second intermediate node 15 is notified of the failure and an alternate path, bypassing the failed third intermediate node 17, is found to the destination node 21.
• Such an alternate path may include, for example, a first alternate connecting node 23 (N ⁇ ) and a second alternate connecting node 25 (N ⁇ ).
• a new wireless link 41 can be formed between the second intermediate node
• step 15 and the first alternate connecting node 23 another new wireless link 43 can be formed between the first alternate connecting node 23 and the second alternate connecting node 25, and a new wireless link 45 can be formed between the second alternate connecting node 25 and the fourth intermediate node 19.
• the remaining undelivered data packets are then transmitted to the destination node 21, at step 67, as described in greater detail below. If the transmission session has not been completed, at decision block 61 in Fig. 2, operation returns to step 53 where the next portion of the data packet stream 29 is configured for transmittal.
• an internal buffer 71 is included for storing a number of data packets.
• the size of the buffer 71 is dependent upon the amount of spare memory available in the second intermediate node 15 for use for this function and is determined by one or more factors, including the bandwidth of the application and mobility rate. If sufficient memory is available, the size of the buffer 71 can be increased to handle relatively higher rates of data transmission through the corresponding connecting node and to accommodate data packets arriving during the period of alternate path discovery.
• the buffer 71 can be implemented as a 'software' buffer comprised of a portion of the memory resident in the second intermediate node 15, or can be provided as a hardware component, such as a RAM, in the second intermediate node 15.
• the software buffer can be implemented by reconfiguring the node kernel to do the buffering. That is, the reconfigured kernel functions to buffer and prioritize the packets, and to respond to retransmission requests. Such requests would be parsed, the packet(s) would be located in the buffer(s), and the packet(s) would be scheduled into an out queue, as is well-known in the relevant art.
• the second intermediate node 15 may include an optional processing unit 79 for controlling the identification, storage, and retransmission of the data packets in the buffer 71.
• the buffer 71 As transmitted data packets 29a, 29b,..., 29n arrive on the wireless link 33 and are routed out on the wireless link 35, the buffer 71 also buffers the most recently-transmitted data packets 29a, 29b,...,29n in memory locations 71a, 71c, and 71e respectively, for example.
• the buffer 71 may follow a first-in-first-out protocol.
• buffering can be implemented on a per-flow basis, in which data packets of a particular flow replace previously-buffered data packets of the same flow.
• the intermediate nodes 13-19 each include three internal buffers, as exemplified by buffers 73-77, as indicated in the diagram of the fourth intermediate node 19 in Fig. 4, the buffers comprising a portion of available memory or a discrete memory chip.
• the three buffers 73-77 can be used for segregating the received data packets 29a, 29b,..., 29n into different transmission priority classes, for example, by providing a high-priority buffer 73, a normal-priority buffer 75, and a low-priority buffer 77.
• data packets in the high-priority buffer 73 may be queued for transmission ahead of data packets in the low-priority buffer 77 using a method known in the relevant art.
• Fig. 5 is a flow diagram providing a more detailed description of the operation performed at step 65 of Fig. 2.
• step 63 the alternate path between intermediate nodes 15 and 19 is established as shown in Fig. 1, for example, by utilizing connecting nodes 15, 23, 25, and 19, at step 81. Data packets which now flow along the alternate path are accordingly, also buffered in the alternate connecting nodes 23 and 25.
• the fourth intermediate node 19 is reconfigured with the establishment of the alternate transmission path. That is, data packets, originally transmitted from the third intermediate node 17 to a port 19a prior to failure of the third intermediate node 17, are instead transmitted from the second alternate connecting node 25 to a port 19b subsequent to the failure of the third intermediate node 17.
• the reconfigured fourth intermediate node 19 is the first downstream node in the new transmission path which lies both in the initial communication path and in the alternate transmission path.
• the fourth intermediate node 19 receives a path establishment message for the same flow (i.e., the data packet stream 29)
• the fourth intermediate node 19 recognizes that the third intermediate node 17 has failed and responds by notifying the second intermediate node 15 as to which data packets have been received by the fourth intermediate node 19, at step 83. This is done to avoid the retransmission of duplicate data packets.
• the data packets 29a and 29n arrived at the fourth intermediate node 19 prior to the failure of the third intermediate node 17.
• the fourth intermediate node 19 recognizes the reconfigured transmission path (i.e., the data packet from the second intermediate node 15 arrives at the port 19b and not 19a)
• a notification is sent to the second intermediate node 15 that data packets 29a and 29n have been received.
• the second intermediate node 15 checks to determine which data packets sent to the third intermediate node 17 were not received by the fourth intermediate node 19 and determines that the data packet 29b was not received by the fourth intermediate node 19.
• step 85 data packets identified as missing are obtained from the nearest upstream node, in the initial communication path, where the target node has the corresponding data buffered.
• the data packet 29b exemplifies a missing data packet, which is then retrieved from the buffer 71 in the second intermediate node 15 and transmitted to the fourth intermediate node 19 by way of the alternate path, at step 87.
• the fourth intermediate node 19 transfers the data packets 29a, 29b, and 29n to the destination node 21. If the applicable transmission protocol requires ordered delivery of data packets, the data packet 29n is transferred to the destination node 21 only after transferal of the data packet 29a. Or, if the applicable transmission protocol does not require ordered delivery, the data packet 29b, if buffered in the high-priority buffer
• the wireless network 10 includes a non-buffered intermediate node 27, where there have not been provided in the intermediate node 27 memory resources for an internal buffer. Consequently, the intermediate node 27 cannot buffer the data packets passing along the transmission path. However, the intermediate node 27 has the capability for passing messages upstream as well as a capability for finding alternate paths in case of node or link failure. If an intermediate node fails as discussed above, for example, the third intermediate node 17, a retransmit message 49 is received by the intermediate node 27.
• the retransmit message 49 is sent upstream to the next intermediate node having internal buffers, such as the first intermediate node 13, for example.
• the missing data packet(s), such as the data packet 29b shown in the illustration, is obtained from any of the buffers 73-77 and provided to the requesting node, here exemplified by the fourth intermediate node 19. If the missing data packet 29b is not present in any of the buffers 73-77 of the first intermediate node 13, the message is transmitted to the source node 11.
• missing data packets are obtained from the source node 11 and transmitted to the requesting node, as described above.
• the wireless link 37 in the wireless network 10 has become degraded or otherwise unreliable, due to interference in the transmission medium for example, as indicated in Fig. 7.
• errors may have been introduced into the packet transmission between the third intermediate node 17 and the fourth intermediate node 19.
• the corrective action can be described with additional reference to the flow diagram of Fig. 8 in which the initial communication path is established, at step 91, and data packets from the data packet stream 29 are received at the intermediate nodes, at step 93, and buffered, at step 95. No retransmission messages are received, at decision block 99, if the wireless links 31-39 remain functional and the system stands by for transmission, at step 101.
• the third intermediate node 17 searches internal buffers 73-77 for the corresponding data packet, at step 103. If the data packet is found in one of the buffers 73-77, at decision block 105, the third intermediate node 17 schedules the data packet for priority retransmission into an out-queue (not shown), at step 97. This transmission scheduling is done in accordance with the transmission priority of the data packet, as described above.
• the next upstream node is checked for the requested replacement data, at step 107. If the requested data is found, at decision block 109, the data is transmitted, at step 97. If the requested data is not found, at decision block 109, a query is made as to whether the source node 11 has been reached, at decision block 111. If the source node 11 has not been reached, operation proceeds to decision block 105.
• an optional error message may be issued to the originator of the data transmission, at step 115, and operation proceeds to standby for the next transmission session, at step 101. If the requested data packet is available, at decision block 113, the data packet is scheduled and prioritized for transmission to the destination node 21, at 97.

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• 2002
  • 2002-06-26 MX MXPA03010849A patent/MXPA03010849A/es unknown
  • 2002-06-26 RU RU2003134626/09A patent/RU2298289C2/ru not_active IP Right Cessation
  • 2002-06-26 JP JP2003511466A patent/JP2004537206A/ja not_active Withdrawn
  • 2002-06-26 AU AU2002311547A patent/AU2002311547B2/en not_active Ceased
  • 2002-06-26 CN CNB028108736A patent/CN100411327C/zh not_active Expired - Fee Related
  • 2002-06-26 WO PCT/IB2002/002432 patent/WO2003005629A1/en active Application Filing
  • 2002-06-26 CA CA002449532A patent/CA2449532A1/en not_active Abandoned
  • 2002-06-26 EP EP02738505A patent/EP1415424A4/en not_active Withdrawn
• 2007
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