WO2004086786A1 - Controle de transmission de paquets dans des systemes de communications cellulaires - Google Patents

Controle de transmission de paquets dans des systemes de communications cellulaires Download PDF

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Publication number
WO2004086786A1
WO2004086786A1 PCT/EP2004/050220 EP2004050220W WO2004086786A1 WO 2004086786 A1 WO2004086786 A1 WO 2004086786A1 EP 2004050220 W EP2004050220 W EP 2004050220W WO 2004086786 A1 WO2004086786 A1 WO 2004086786A1
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WO
WIPO (PCT)
Prior art keywords
buffer
packet control
data packets
packets
subscriber unit
Prior art date
Application number
PCT/EP2004/050220
Other languages
English (en)
Inventor
Howard Thomas
Maya Benson
Bohdan Bodnar
Original Assignee
Motorola Inc
Motorola Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Motorola Inc, Motorola Limited filed Critical Motorola Inc
Publication of WO2004086786A1 publication Critical patent/WO2004086786A1/fr

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Classifications

    • 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
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L47/00—Traffic control in data switching networks
    • H04L47/10—Flow control; Congestion control
    • H04L47/26—Flow control; Congestion control using explicit feedback to the source, e.g. choke packets
    • H04L47/263—Rate modification at the source after receiving feedback
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L47/00—Traffic control in data switching networks
    • H04L47/10—Flow control; Congestion control
    • H04L47/32—Flow control; Congestion control by discarding or delaying data units, e.g. packets or frames
    • H04L47/326—Flow control; Congestion control by discarding or delaying data units, e.g. packets or frames with random discard, e.g. random early discard [RED]
    • 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
    • H04W28/0247—Traffic management, e.g. flow control or congestion control based on conditions of the access network or the infrastructure network
    • 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
    • H04W28/0273—Traffic management, e.g. flow control or congestion control adapting protocols for flow control or congestion control to wireless environment, e.g. adapting transmission control protocol [TCP]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/10—Reselecting an access point controller

Definitions

  • the present invention relates to control of data packets, in particular transmission and storage of packets, in packet switched communication systems incorporating one or more cellular communication systems.
  • the present invention relates in particular, but not exclusively, to the following cellular communication systems: Universal Mobile Telecommunications System (UMTS), General Packet Radio Service (GPRS) and Global System for Mobile Telecommunication (GSM) systems.
  • UMTS Universal Mobile Telecommunications System
  • GPRS General Packet Radio Service
  • GSM Global System for Mobile Telecommunication
  • Packet switched communication systems incorporating cellular communication systems are known.
  • a cellular communication system according to the well known standards General Packet Radio Service (GPRS) and Global System for Mobile Telecommunication (GSM) may be connected to the Internet and communicate therewith using the Internet Protocol (IP).
  • IP Internet Protocol
  • IP Internet Protocol
  • Internet connection may be provided to an end user using a subscriber unit such as a mobile telephone, usually referred to as a mobile station (MS) in GSM/GPRS terminology.
  • MS mobile station
  • a cellular communication system may be connected to the Internet and communicate therewith
  • UMTS Universal Mobile Telecommunications System
  • IP Internet Protocol
  • UE user equipment
  • TCP Transmission Control Protocol
  • TCP Transmission Control Protocol
  • TCP controls how many packets are sent and at what rate from a network element over a given route.
  • ACKs TCP acknowledgement signals
  • TCP the network element adjusts how many packets are sent and at what rate, depending on the ACKs it receives back.
  • TCP interprets gaps in service (i.e. a break in receipt of ACKs) as congestion, and, in response, it reduces both the rate at which it sends packets and the number of packets that it will send before receiving an acknowledgement, TCP triggers its re-transmission time out and begins a slow start on a new route. That is only a few packets are transmitted before waiting for an ACK from the far end of the route, which considerably reduces throughput especially when the round trip time on the route is long.
  • gaps in service i.e. a break in receipt of ACKs
  • provision of packet control functionality When the end of the route is a subscriber unit of a cellular communication system, packet control functionality is required in the cellular communication system.
  • provision of packet control functionality usually includes a packet control unit (PCU) included in or added to a GSM-type base station controller (BSC).
  • provision of packet control functionality usually includes providing such functionality as part of a radio network controller (RNC).
  • RNC radio network controller
  • the PCU controls receipt and storage of the packets at the node it is located at. Storage of packets is usually in a buffer, hereinafter termed the PCU buffer.
  • the PCU further controls transmission of the packets to the radio elements of its cellular communication system.
  • Operation of cellular communication systems includes the well known operation of handover or cell re-selection, i.e. the subscriber unit moves from one cell to another and correspondingly service is handed over from one cell to another.
  • handover or cell re-selection i.e. the subscriber unit moves from one cell to another and correspondingly service is handed over from one cell to another.
  • TCP under operation of TCP over a route that includes a cellular mobile radio component, gaps in service caused by cell re- selection ⁇ cell handover in the cellular communication system) are treated in the same way as other gaps in service.
  • the TCP treats handover as if it were congestion. This leads to unnecessary or inappropriate actions being taken under TCP. This can result in major performance degradation.
  • the resulting drop in throughput and slow regain in throughput can have catastrophic results on performance with packets sent and deleted multiple times.
  • Another disadvantageous effect is that billing (charging) anomalies may arise. For example, packets may be billed for multiple times because of
  • packet-billing records are generated when packets are sent from a serving GPRS support node (SGSN) to a PCU. These packets are buf ered at the PCU until they can be sent over the air interface to the subscriber unit. However, if the subscriber unit is transferred to another cell, and these packets are not redirected to the new cell, these packets will be deleted and ultimately will be re-transmitted by the TCP and will be billed for again.
  • SGSN serving GPRS support node
  • RED random early detection
  • IP networks Another known process is called random early detection (RED).
  • RED is a process used in IP networks to avoid buffers carrying TCP information overflowing, deleting the last packets sent, and so triggering multiple TCP sessions to simultaneously attempt retransmissions making the overload situation worse.
  • the process works by determining the amount by which a receiving data buffer is occupied above a first threshold, and in response to that amount, deleting packets. The deleted packets are selected at random. When these packets are found to be missing by the TCP layer, the transmission rate is reduced, so reducing the probability of simultaneous re- transmissions occurring in the network.
  • RED is not responsive to predicted gaps in transmission, and as currently employed and understood in the art does not function to reduce the throughput on a link which is not experiencing a high buffer load condition.
  • the present invention provides a method of controlling data packets, as claimed in claim 1.
  • the present invention provides a storage medium storing processor-implementable instructions, as claimed in claim 12.
  • the present invention provides apparatus for controlling data packets, as claimed in claim 13.
  • the present invention tends to alleviate or lesolve packet control problems, such as those described above, caused by cell handover and other communications interruptions.
  • the present inventors have realised that it may be beneficial to reduce the amount of data in a PCU buffer when a cell handover, or other break in cellular communication, is impending predicted, or suspected to occur.
  • the flow of packets to the PCU buffer is reduced.
  • packets are deleted from the PCU buffer.
  • the packets may be deleted in s me random fashion.
  • the decision to delete packets, and/or the way in which they are randomly selected for deletion, may preferably be implemented using the same or similar techniques as are used in the RED process.
  • the flow of packets to the PCU buffer is reduced and packets are deleted from the PCU buffer.
  • the packets may be deleted in some random fashion.
  • the decision to delete packets, and/or the way in which they are randomly selected for deletion may preferably be implemented using the same or similar techniques as are used in the RED process.
  • FIG. 1 is a schematic illustration of part of a GPRS cellular communication system 1 connected with the Internet;
  • FIG.2 is a process flowchart showing certain steps carried out in a packet control method of a first embodiment of the invention
  • FIG.3 is a process flowchart showing certain steps carried out in a packet control method of a second embodiment of the invention.
  • FIG.4 is a process flowchart showing certain steps carried out in a packet control method of a third embodiment of the invention.
  • the invention is applied to a cellular communications system compliant with, and containing network elements of, GSM and GPRS.
  • the cellular communication system is connected to the Internet.
  • the invention can be applied to other types of cellular system (e.g. UMTS), It is also to be appreciated that the invention can be apphed to packet switching of packets being received or transmitted from networks other than the Internet, or indeed being switched internally within a cellular communication system,
  • FIG. 1 is a schematic illustration of part of a GPRS cellular communication system 1 connected with the Internet.
  • the GPRS cellular communication system 1 comprises a Gateway GPRS Support Node (GGSN) 2, which is arranged to provide a gateway connection with the Internet 4.
  • GGSN Gateway GPRS Support Node
  • the system 1 further comprises a Serving GPRS Support Node (SGSN)
  • SGSN Serving GPRS Support Node
  • the SGSN 6 which is coupled to the GGSN 2.
  • the SGSN 6 performs high level switching, including determining the location of a particular MS by means of accessing location registers (not shown).
  • the SGSN 6 comprises a buffer, hereinafter referred to as the SGSN buffer 8.
  • the SGSN buffer 8 stores data packets which are en-route to MSs.
  • the system 1 further comprises base station controllers (BSCs) 10, 12, and base transceiver stations (BTSs) 22, 24, 26.
  • BSCs base station controllers
  • BTSs base transceiver stations
  • the BTSs transmit and receive radio signals to and f om MSs.
  • BTS 24 is transmitting and receiving radio signals to and from an MS 34.
  • BSCs 10, 12 are coupled to and control the BTSs.
  • BSC 10 is coupled to, and controls, BTS 22 and BTS 24;
  • BSC 12 is coupled to, and controls, BTS 26.
  • BSC 10 comprises a Packet Control Unit (PCU) 14, which operates to control the receipt, storage and transmission of data packets.
  • PCU 14 comprises a buffer, hereinafter referred to as PCU buffer 16, for storing the data packets.
  • BSC 12 comprises a PCU 18, the PCU 18 comprising a PCU buffer 20.
  • the geographical area covered, i.e. served, by a respective BTS 22, 24, 26 forms a respective cell of the cellular radio communication system 1.
  • the BTS 22 serves a cell 28
  • the BTS 24 serves a cell 30
  • the BTS 26 serves a cell 32.
  • MS 34 is presently in cell 30.
  • data packets being routed to MS 34 from the Internet 4 are routed to MS 34 over the following route: Internet 4 - GGSN 2 - SGSN 6 - BSC 10 - BTS 24 - MS 34. During this, the data packets are buffered at the SGSN buffer 8 and the PCU buffer 16.
  • the system 1 as described above corresponds to a typical conventional arrangement and operates in conventional fashion, excep as will now be described below in relation to embodiments of the present invention.
  • PCU 14 has been adapted, by provision of a selective packet reduction module, to offer, and provide for, an improved packet control process involving selective reduction of packets in and/or arriving at PCU buffer 16, as will be described in more detail below.
  • the module may consist of a single discrete entity added to a conventional PCU, or may alternatively be formed by adapting existing parts of a conventional PCU, for example by reprogramming of one or more processors therein.
  • the required adap tation may be implemented in the form of processor-implementable instructions stored on a storage medium, such as a floppy disk, hard disk.
  • the module may be implemented in the form of hardware, firmware, software, or any combination of these.
  • implementation may be at any appropriate switching node such as any other appropriate type of base station, base station controller etc.
  • implementation may be at any appropriate switching node such as any other appropriate type of base station, base station controller etc.
  • RNC radio network controller
  • implementation may be carried out as part of the packet control functionality provided as part of a radio network controller (RNC), and/or as part of a Node-B, since some aspects of RNC functionality may be delegated to this network element.
  • RNC radio network controller
  • PCU 14 monitors the radio link between BTS 24 and MS 34.
  • Any suitable parameter of the radio link may be monitored (including any combination of plural parameters), where the parameter or combination of parameters may usefully indicate or predict that a break in communication, particularly a cell handover, is likely to take place soon.
  • Possible parameters include Received Signal Level (Rvlev), either uplink, downlink or both; Frame Erasure Ratio (PER); Received Signal Quality (Rxqual), either uplink, downlink or both; neighbour cell measurement; and so on.
  • PCU 14 predicts the probability of cell handover occurring.
  • Any suitable algorithm may be used. This will be determined by the skilled person according to the requirements and characteristics of the particular system under consideration. More particularly, the algorithm is written and implemented using knowledge of previous behaviour of the system with respect to the parameter or parameters, and related to how such behaviour has previously been a suitable indicator of likely cell handover. Another possibility is for such an algorithm, developed for one system or part of a system, to be used in a further system, on the assumption that similar behaviour is to be expected. Another possibility is to compare the radio link quality to MS 34 with measurements reported from other cells. In this case, such measurements may be carried out as an additional part of earlier described step s2.
  • step s6 PCU 14 compares the predicted probability of cell handover occurring with a predetermined threshold.
  • the predetermined threshold is set the handover probability is not greater than the threshold, the process moves to step sl6, which will be described later below. However, if the handover probability is greater than the threshold, then the process moves to step s8, as follows.
  • PCU 14 determines a packet processing factor based upon the predicted probability of cell handover. Any suitable algorithm may be employed, according to the requirements of the particular system under consideration.
  • the packet processing factor may be calculated as a function of the value of the predicted probability of cell handover or as a function of the difference between the value of the predicted probability of cell handover and the threshold used in step $6.
  • the function may include one or more separate communication system parameters, such as volume of data traffic, for example.
  • step s8 (and steps slO and s!2 to be described below) is implemented in a corresponding way to which processing is performed in the earlier mentioned RED process.
  • the packet processing factor is determined as a function of the difference between the value of the predicted probability of cell handover and the threshold used in step s6, such that the packet processing f ctor increases in proportion to the predicted likelihood of cell handover.
  • step slQ PCU 14 compares the packet processing factor with a predetermined threshold.
  • This predetermined threshold is set according to the requirements of the particular system under consideration. In effect, step in the earlier mentioned RED process. If the packet processing factor is not greater than the threshold, the process moves to step si 6, which will be described later below. However, if the packet processing factor is greater than the threshold, then the packet processing action to be performed in this embodiment will take place, and hence the process moves to step sl2, as follows.
  • PCU 14 carries out a packet processing action in response to the process so far having determined this is appropriate in view of the likelihood of cell handover.
  • the packet processing operation performed by PCU 14 is deletion of some packets from its PCU buffer 16, i.e. at step sl2, PCU 14 deletes some packets from PCU buffer 16.
  • the process for determining how many packets, and which packets, to delete may be arranged as desired according to the requirements of the particular system under consideration. Also, the packet deletion may be implemented in a variable fashion dependent upon the occupancy of the PCU buffer 16, i.e. more packets are deleted the more full the PCU buffer 16 is.
  • packets are deleted in a pseudo-random fashion implemented in a corresponding way to which processing is performed in the earlier mentioned RED process.
  • the number pf packets deleted is such that TCP is triggered to reduce the rate of packet deliver)' (i.e. in response to ACKs not being received from the deleted packets) but not to trigger radio link time-out (RTO).
  • Step sl6 is also reached when either of decision steps s6 or slO has resulted in a negative (i.e. in effect whether the data session is still in process and, if applicable, that handover has not actually happened yet). If packet flow is indeed continuing, then the process returns to step s2 to be repeated. However, if packet flow is no longer continuing, the process is ended.
  • the size of the PCU buffer 16 is reduced, using an algorithm that is self contained within the PCU 14, ahead of a predicted cell re-selection event.
  • the mechanism employed in this embodiment is an extended version of the RED algorithm that increases the packet deletion probability for a link in proportion to the predicted likelihood of a cell re-selection event (or other break in communication).
  • a cell re-selection event is predicted from analysis of the radio link quality, for example, from the signal level or FER on the serving link, or from comparison of signal level measurements reported by the user terminal lo the network.
  • the packet processing action to be performed in this embodiment is implemented at a new step sl3, as follows.
  • the packet processing operation flow route (BSC 10 - SGSN 6 - GGSN 2) of a flow control message which will lead to reduced flow of packets to the PCU 14.
  • This embodiment is implemented in a GPRS system, and hence this comprises a message reducing the "maximum bucket size" information it sends to the SGSN under the GPRS standard.
  • PCU 14 sends a flow control message to the SGSN 6, more particularly a message instructing the SGSN 6 to reduce the maximum bucket size for the PCU 14.
  • a flow control message may be employed.
  • a flow rate reduction instruction may be sent to the source node in the Internet of the data packets being received at PCU 14- ) This results in less data packets being received and buffered at PCU 14 of BSC 10 just prior to the predicted handover, thus avoiding the need for them to be sent twice, i.e. once before any such handover and again after the handover. If handover does not materialise, the data flow can be returned to the previous rate, by virtue of no flow reduction message being sent the next time the process reaches step sl3.
  • step sl6 is also reached when either of decision steps s6 or slO has resulted in a negative outcome.
  • PCU 14 determines whether packet flow is continuing (i.e. in effect whether the data session is still in process and, if applicable, that handover has not actually happened yet). If packet flow is indeed continuing then the process returns to step s2 to be repeated. However, if packet flow is no longer continuing the process is ended.
  • the process performs per MS flow control dependent on the predicted likelihood of cell re-selection (i.e. the flow control has been performed in response to specific conditions relating to the data transmission to the specific MS 34, in particular the likelihood that this MS will be changing cells.
  • the size of the PCU buffer 16 is reduced, using an algorithm that is self contained within the PCU 14, ahead of a predicted cell re-selection event so that the number of packets that may be lost during a re-selection event is reduced.
  • the cell re-selection event is predicted from analysis of the radio link quality, for example, from the signal level or FER on the serving link, or from comparison of signal level measurements reported by the MS to the cellular communication system.
  • the per mobile flow control mechanism is initiated to reduce the amount of data buffered at the PCU 14 for transmission to that mobile,
  • a further advantage of this embodiment relates to billing (i.e, charging).
  • Billing records are typically generated when packets aie sent from the SGSN 6 to the PCU 14.
  • the reduction of data flow implemented in this second main embodiment reduces the number of data packets that are first sent to PCU 14 then need to be re-sent to the new PCU 18 after handover to the new cell 32.
  • These data packets are billed for twice, thus double-billing is advantageously reduced in this second main embodiment.
  • the packet processing action to be performed in this embodiment is implemented at a new step sl4, as follows.
  • the packet processing operation performed by PCU 14 comprises deletion of some packets from its PCU buffer 16, and the sending back of a flow control message through the packet flow route (BSC 10 - SGSN 6 - GGSN 2), in this example to the SGSN 6.
  • BSC 10 - SGSN 6 - GGSN 2 the packet flow route
  • PCU 14 deletes some packets from PCU buffer 16 and also sends a flow control message to the SGSN 6. Details of the deletion of some packets are as in the first main embodiment, i.e. as described above for step sl2 of FIG.2. Details of the sending of a flow control message are as in the second main embodiment, i.e. as described above for step sl3 of FIG.3.
  • step sl6 is also reached when either of decision steps s6 or slO has resulted in a negative outcome.
  • PCU 14 determines whether packet flow is continuing (i.e. in effect whether the data session is still in process and, if applicable, that handover has not actually happened yet). If packet flow is indeed continuing, then the process returns to step s2 to be repeated. However, if packet flow is no longer continuing, the process is ended.
  • the decision processes, thresholds etc. for determining whether the likelihood of a cell handover event are as described. It will be appreciated that in Other embodiments, other decision processes, thresholds and so on may be employed. For example, operating parameters may be monitored and analysed so as to recognise patterns of behaviours indicative of impending handover. Another possibility is that the location of the MS may be monitored, and this used to predict that handover is likely.
  • the potential communications interruption whose prediction leads to packet processing is cell handover of the MS.
  • the present invention further encompasses applying the packet processing in response to predicting other forms of communications interruption.
  • the present invention may be applied to any type of communications interruption where the packet processing actions would be beneficial compared to allowing the system to respond as if the resulting delay in ACKs was due to congestion.
  • Examples of other types of communication interruption are entering a region where radio signal quality is poor, e.g. in shadow of buildings or tunnels or excessive body loss, entering a region where interference is excessive, entering a region where mobile speed is excessive, entering a region where transmission is prohibited, at a time when mobile battery power is limited (e.g. run down battery or swapping of batteries), in a terminals where movement of terminals leads to a prediction that the communications path may be compromised or break down, perhaps temporarily.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

L'invention concerne un procédé et un appareil permettant de contrôler des paquets de données routés via un dispositif de contrôle de paquets (14) doté d'un tampon (16) jusqu'à une unité d'abonné (34) dans un système de communication cellulaire (1). Ledit procédé consiste à déterminer une probabilité d'interruption dans une route de communication entre le dispositif de contrôle de paquets (14) et l'unité d'abonné (34), et en fonction de la probabilité, à réaliser un processus de contrôle de paquets servant à diminuer le nombre de paquets de données dans le tampon (16). L'étape de réalisation du processus de contrôle de paquets peut être, en outre, dépendante du nombre de paquets de données dans le tampon (16). Ce processus de contrôle de paquets peut également consister à effacer des paquets de données du tampon (16) et/ou à fournir le débit ou le nombre de paquets de données qui sont envoyés au tampon (16) et qui doivent être diminués. Ladite interruption peut être provoquée par le transfert de l'unité d'abonné (34) entre des cellules du système de communication cellulaire (1).
PCT/EP2004/050220 2003-03-28 2004-02-27 Controle de transmission de paquets dans des systemes de communications cellulaires WO2004086786A1 (fr)

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GB0307152A GB2399989B (en) 2003-03-28 2003-03-28 Packet control in cellular communications
GB0307152.9 2003-03-28

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