WO2001063857A1 - Traitement de surcharges dans un systeme de communications - Google Patents

Traitement de surcharges dans un systeme de communications Download PDF

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Publication number
WO2001063857A1
WO2001063857A1 PCT/SE2001/000408 SE0100408W WO0163857A1 WO 2001063857 A1 WO2001063857 A1 WO 2001063857A1 SE 0100408 W SE0100408 W SE 0100408W WO 0163857 A1 WO0163857 A1 WO 0163857A1
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WIPO (PCT)
Prior art keywords
entity
buffer
mac
transmitter
new
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Application number
PCT/SE2001/000408
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English (en)
Inventor
Göran SCHULTZ
Janne Peisa
Toomas Wigell
Reijo Matinmikko
Original Assignee
Telefonaktiebolaget Lm Ericsson (Publ)
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.)
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Application filed by Telefonaktiebolaget Lm Ericsson (Publ) filed Critical Telefonaktiebolaget Lm Ericsson (Publ)
Priority to EP01908562A priority Critical patent/EP1264447A1/fr
Priority to AU2001236304A priority patent/AU2001236304A1/en
Publication of WO2001063857A1 publication Critical patent/WO2001063857A1/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
    • H04W28/14—Flow control between communication endpoints using intermediate storage
    • 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
    • H04L47/30—Flow control; Congestion control in combination with information about buffer occupancy at either end or at transit nodes
    • 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
    • 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
    • H04W28/0231—Traffic management, e.g. flow control or congestion control based on communication conditions
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W84/00—Network topologies
    • H04W84/02—Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
    • H04W84/04—Large scale networks; Deep hierarchical networks

Definitions

  • the present invention relates in general to the field of communications systems, and in particular, by way of example but not limitation, to handling potential buffer overflows resulting from new users overloading a communications system.
  • Description of Related Art Access to and use of wireless networks is becoming increasingly important and popular for business, social, and recreational purposes. Users of wireless networks now rely on them for both voice and data communications. Furthermore, an ever increasing number of users demand both an increasing array of services and capabilities as well as greater bandwidth for activities such as Internet surfing. To address and meet the demands for new services and greater bandwidth, the wireless communications industry constantly strives to improve the number of services and the throughput of their wireless networks. Expanding and improving the infrastructure necessary to provide additional services and higher bandwidth is an expensive and manpower-intensive undertaking.
  • the wireless communications industry intends to continue to improve the capabilities of the technology upon which it relies and that it makes available to its customers by deploying next generation system(s).
  • Protocols for a next-generation standard that is designed to meet the developing needs of wireless customers is being standardized by the 3 rd Generation Partnership Project (3GPP).
  • 3GPP 3 rd Generation Partnership Project
  • the set of protocols is known collectively as the Universal Mobile Telecommunications System (UMTS).
  • UMTS Universal Mobile Telecommunications System
  • FIG. 1 an exemplary wireless communications system with which the present invention may be advantageously employed is illustrated generally at 100.
  • the network 100 includes a core network 120 and a UMTS Terrestrial Radio Access Network (UTRAN) 130.
  • the UTRAN 130 is composed of, at least partially, a number of Radio Network Controllers (RNCs) 140, each of which may be coupled to one or more neighboring Node Bs 150.
  • RNCs Radio Network Controllers
  • the UMTS network 100 also includes multiple user equipments (UEs) 110.
  • UE may include, for example, mobile stations, mobile terminals, laptops/personal digital assistants (PDAs) with wireless links, etc.
  • Methods, systems, and arrangements in accordance with the present invention enable the prevention of common channel overload in a wireless communications network.
  • UMTS Universal Mobile Telecommunications System
  • new Medium Access Control-dedicated (MAC-d) entities are permitted to transmit data segments in an amount equivalent to their initial credit to a MAC-common (MAC-c) entity.
  • MAC-c MAC-common
  • MAC-d entities in UMTS networks are always permitted to transmit at least their initial credit, the buffer in the MAC-c entity may become overloaded, thus preventing the use of the MAC-c entity by any MAC-d entity.
  • the MAC-c entity if the buffer fill level of the MAC-c buffer reaches a predefined fill level, the MAC-c entity is empowered to discard incoming data segments from MAC-d entities of new users.
  • the credits value of each pre-existing, or old, MAC-d entity may also optionally be set equal to zero.
  • the predefined buffer fill level at which, when reached, the MAC-c entity becomes empowered to reject new incoming data segments may be established responsive to the maximum fill level of the buffer of the MAC-c entity, the maximum guaranteed transmission rate of the common channel, and the maximum allowed additional delay.
  • FIG. 1 illustrates an exemplary wireless communications system with which the present invention may be advantageously employed
  • FIG. 2 illustrates a protocol model for an exemplary next-generation system with which the present invention may be advantageously employed;
  • FIG. 3 illustrates a view of an exemplary second layer architecture of an exemplary next-generation system in accordance with the present invention
  • FIG. 4 illustrates an exemplary method in flowchart form for allocating bandwidth resources to data flow streams between entities in the exemplary second layer architecture of FIG. 3;
  • FIG. 5 illustrates another view of the exemplary second layer architecture of an exemplary next-generation system in accordance with the present invention
  • FIG. 6 illustrates yet another view of the exemplary second layer architecture of an exemplary next-generation system in accordance with the present invention
  • FIG. 7 illustrates an exemplary buffer for an entity of an exemplary next- generation system in accordance with the present invention.
  • FIG. 8 illustrates an exemplary method in flowchart form for modulating a fill level of the exemplary buffer of FIG. 7 in accordance with the present invention.
  • a protocol model for an exemplary next-generation system with which the present invention may be advantageously employed is illustrated generally at 200.
  • the "Uu" indicates the interface between
  • Radio Access Bearers RABs
  • a UE 110 is allocated one or more RABs, each of which is capable of carrying a flow of user or signaling data. RABs are mapped onto respective logical channels.
  • MAC Media Access Control
  • MAC-c Media Access Control
  • MAC-d Media Access Control
  • FACH Primary Common Control Physical CHannel
  • RNC 140 acts at least initially as both the serving and the controlling RNC 140 for the UE 110.
  • the serving RNC 140 may subsequently differ from the controlling RNC 140 in a UMTS network 100, but the presence or absence of this condition is not particularly relevant here.
  • the RNC 140 both controls the air interface radio resources and terminates the layer 3 intelligence (e.g., the Radio Resource Control (RRC) protocol), thus routing data associated with the UE 110 directly to and from the core network 120.
  • RRC Radio Resource Control
  • the MAC-c entity in the RNC 140 transfers MAC- c Packet Data Units (PDUs) to the peer MAC-c entity at the UE 110 using the services of the FACH Frame Protocol (FACH FP) entity between the RNC 140 and the Node B 150.
  • the FACH FP entity adds header information to the MAC-c PDUs to form FACH FP PDUs which are transported to the Node B 150 over an AAL2 (or other transport mechanism) connection.
  • An interworking function at the Node B 150 interworks the FACH frame received by the FACH FP entity into the PHY entity.
  • an important task of the MAC-c entity is the scheduling of packets (MAC PDUs) for transmission over the air interface. If it were the case that all packets received by the MAC-c entity were of equal priority (and of the same size), then scheduling would be a simple matter of queuing the received packets and sending them on a first come first served basis (e.g., first-in, first-out (FIFO)).
  • FIFO first-in, first-out
  • UMTS defines a framework in which different Quality of Services (QoSs) may be assigned to different RABs.
  • Packets corresponding to a RAB that has been allocated a high QoS should be transmitted over the air interface at a high priority whilst packets corresponding to a RAB that has been allocated a low QoS should be transmitted over the air interface at a lower priority.
  • Priorities may be determined at the MAC entity (e.g., MAC-c or MAC-d) on the basis of RAB parameters.
  • UMTS deals with the question of priority by providing at the controlling RNC 140 a set of queues for each FACH.
  • the queues may be associated with respective priority levels.
  • TFC includes a transmission time interval, a packet size, and a total transmission size (indicating the number of packets in the transmission) for each FACH.
  • the algorithm should select for the FACHs a TFC which matches one of those present in the TFC set in accordance with UMTS protocols.
  • a packet received at the controlling RNC 140 is placed in a queue
  • the queue corresponds to the priority level attached to the packet as well as to the size of the packet.
  • the FACH is mapped onto a S-CCPCH at a Node B 150 or other corresponding node of the UTRAN 130.
  • the packets for transmission on the FACH are associated with either a Dedicated Control CHannel (DCCH) or to a Dedicated Traffic CHannel
  • each FACH is arranged to carry only one size of packets. However, this is not necessary, and it may be that the packet size that can be carried by a given FACH varies from one transmission time interval to another.
  • the UE 110 may communicate with the core network 120 of the UMTS system 100 via separate serving and controlling (or drift)
  • RNCs 140 within the UTRAN 130 e.g., when the UE 110 moves from an area covered by the original serving RNC 140 into a new area covered by a controlling/drift RNC 140 (not specifically shown).
  • Signaling and user data packets destined for the UE 110 are received at the MAC-d entity of the serving RNC 140 from the core network 120 and are "mapped" onto logical channels, namely a Dedicated Control
  • the MAC- d entity constructs MAC Service Data Units (SDUs), which include a payload section containing logical channel data and a MAC header containing, inter alia, a logical channel identifier.
  • SDUs MAC Service Data Units
  • the MAC-d entity passes the MAC SDUs to the FACH FP entity.
  • This FACH FP entity adds a further FACH FP header to each MAC SDU, where the FACH FP header includes a priority level that has been allocated to the MAC SDU by an RRC entity.
  • the RRC is notified of available priority levels, together with an identification of one or more accepted packet sizes for each priority level, following the entry of a UE 110 into the coverage area of the drift RNC 140.
  • the FACH FP packets are sent to a peer FACH FP entity at the drift RNC 140 over an AAL2 (or other) connection.
  • the peer FACH FP entity decapsulates the
  • each SDU is placed in a queue corresponding to its priority and size. For example, if there are 16 priority levels, there will be 16 queue sets for each FACH, with the number of queues in each of the 16 queue sets depending upon the number of packet sizes accepted for the associated priority. As described hereinabove, SDUs are selected from the queues for a given FACH in accordance with some predefined algorithm (e.g., so as to satisfy the TFC requirements of the physical channel).
  • the scheme described hereinbelow with reference to FIGS. 3 and 4 relates to data transmission in a telecommunications network and in particular, though not necessarily, to data transmission in a UMTS.
  • the 3GPP is currently in the process of standardizing a new set of protocols for mobile telecommunications systems.
  • the set of protocols is known collectively as the UMTS.
  • FIG. 3 a view of an exemplary second layer architecture of an exemplary next-generation system in accordance with the present invention is illustrated generally at 300.
  • the exemplary second layer architecture 300 illustrates a simplified UMTS layer 2 protocol structure which is involved in the communication between mobile stations
  • the RNCs 140 are analogous to the Base Station Controllers (BSCs) of existing GSM mobile telecommunications networks, communicating with the mobile stations via Node Bs 150.
  • BSCs Base Station Controllers
  • the layer 2 structure of the exemplary second layer architecture 300 includes a set of Radio Access Bearers (RABs) 305 that make available radio resources (and services) to user applications. For each mobile station there may be one or several RABs 305. Data flows (e.g., in the form of segments) from the RABs 305 are passed to respective Radio Link Control (RLC) entities 310, which amongst other tasks buffer the received data segments. There is one RLC entity 310 for each RAB 305. In the RLC layer, RABs 305 are mapped onto respective logical channels 315.
  • RLC Radio Link Control
  • MAC entity 320 receives data transmitted in the logical channels 315 and further maps the data from the logical channels 315 onto a set of transport channels 325.
  • the transport channels 325 are finally mapped to a single physical transport channel 330, which has a total bandwidth (e.g., of ⁇ 2Mbits/sec) allocated to it by the network.
  • a physical channel is used exclusively by one mobile station or is shared between many mobile stations, it is referred to as either a "dedicated physical channel" or a "common channel”.
  • a MAC entity connected to a dedicated physical channel is known as MAC-d; there is preferably one MAC-d entity for each mobile station.
  • a MAC entity connected to a common channel is known as MAC-c; there is preferably one MAC-c entity for each cell.
  • the bandwidth of a transport channel 325 is not directly restricted by the capabilities of the physical layer 330, but is rather configured by a Radio Resource Controller (RRC) entity 335 using Transport Formats (TFs).
  • RRC Radio Resource Controller
  • TFs Transport Formats
  • the RRC entity 335 defines one or several Transport Block (TB) sizes.
  • Transport Block size directly corresponds to an allowed MAC Protocol Data
  • TBS Transport Block Set
  • TTI transmission time interval
  • the RRC entity 335 also informs the MAC entity of all possible TFs for a given transport channel.
  • This combination of TFs is called a Transport Format Combination (TFC).
  • TFC Transport Format Combination
  • the MAC entity can choose to transmit one or two PDUs in one TTI on the particular transport channel in question; in both cases, the PDUs have a size of 80 bits.
  • the MAC entity 320 has to decide how much data to transmit on each transport channel 325 connected to it.
  • These transport channels 325 are not independent of one another, and are later multiplexed onto a single physical channel
  • the RRC entity 335 has to ensure that the total transmission capability on all transport channels 325 does not exceed the transmission capability of the underlying physical channel 330. This is accomplished by giving the MAC entity 320 a Transport Format Combination Set (TFCS), which contains the allowed Transport Format Combinations for all transport channels.
  • TFCS Transport Format Combination Set
  • a MAC entity 320 which has two transport channels 325 that are further multiplexed onto a single physical channel 330, which has a transport capacity of 160 bits per transmission time interval (It should be understood that, in practice, the capacity will be much greater than 160).
  • the MAC entity 320 cannot choose to transmit on both transport channels 325 at the same time using TF3 as this would result in the need to transmit 320 bits on the physical channel 330, which has only a capability to transmit 160 bits.
  • the RRC entity 335 has to restrict the total transmission rate by not allowing all combinations of the TFs.
  • An example of this would be a TFCS as follows [ ⁇ (80, 0), (80, 0) ⁇ , ⁇ (80, 0), (80, 80) ⁇ , ⁇ (80, 0), (80, 160) ⁇ , ⁇ (80, 80), (80, 0) ⁇ , ⁇ (80, 80), (80, 80) ⁇ , ⁇ (80, 160), (80, 0) ⁇ ], where the transport format of transport channel "1" is given as the first element of each element pair, and the transport format of transport channel "2" is given as the second element.
  • the MAC entity 320 can only choose one of these allowed transport format combinations from the transport format combination set, it is not possible to exceed the capability of the physical channel 330.
  • TFCI Transport Format Combination Indicator
  • TFCI Transport Format Combination Indicator
  • Asynchronous Transfer Mode (ATM) networks provision is made for allocating resources on a single output channel to multiple input flows.
  • ATM Asynchronous Transfer Mode
  • the algorithms used to share out the resources in such systems are not directly applicable to UMTS where multiple input flows are transmitted on respective logical output channels. Sharing resources between multiple input data flows is referred to as
  • GPS Generalized Processor Sharing
  • WFQ Weighted Fair Queuing
  • GPS involves calculating a GPS weight for each input flow on the basis of certain parameters associated with the flow. The weights calculated for all of the input flows are added together, and the total available output bandwidth is divided amongst the input flows depending upon the weight of each flow as a fraction of the total weight.
  • GPS could be applied to the MAC entity in UMTS, with the weighting for each input flow being determined (by the RRC entity) on the basis of certain RAB parameters, which are allocated to the corresponding RAB by the network.
  • an RAB parameter may equate to a Quality of Service (QoS) or Guaranteed rate allocated to a user for a particular network service.
  • QoS Quality of Service
  • Guaranteed rate allocated to a user for a particular network service.
  • a backlog of unsent data may build up for the input flow. It is an object of the scheme described herein with reference to FIGS. 3 and 4 to overcome, or at least mitigate, the disadvantage noted in the preceding paragraph. This and other objects are achieved at least in part by maintaining a backlog counter which keeps track of the backlog of unsent data for a given input flow to the MAC entity. The backlog is taken into account when determining an appropriate TFC for that input flow for a subsequent frame.
  • MAC Media Access Control
  • UMTS Universal Mobile Telecommunications System
  • TFC TFC from a TFC Set (TFCS) on the basis of the bandwidth share computed for the input flows, where the TFC includes a Transport Format allocated to each input flow; and for each input flow, if the allocated TF results in a data transmission rate which is less than the determined fair distribution, adding the difference to a backlog counter for the input flow, where the value of the backlog counter(s) is taken into account when selecting a TFC for the subsequent frame of the output data flow.
  • Embodiments of this scheme allow the TFC selection process for a subsequent frame to take into account any backlogs which exists for the input flows. The tendency is to adjust the selected TFC to reduce the backlogs. Such a backlog may exist due to the finite number of data transmission possibilities provided for by the TFCS.
  • Nodes at which the method of this scheme may be employed include mobile stations (such as mobile telephones and communicator type devices) (or more generally UEs) and Radio Network Controllers (RNCs).
  • RNCs Radio Network Controllers
  • the input flows to the MAC entity are provided by respective Radio Link Control (RLC) entities.
  • each RLC entity provides buffering for the associated data flow.
  • the step of computing a fair share of resources for an input flow is carried out by a Radio Resource Control (RRC) entity.
  • the step of computing a fair share of resources for an input flow includes the step of determining the weighting given to that flow as a fraction of the sum of the weights given to all of the input flows. The fair share may then be determined by multiplying the total output bandwidth by the determined fraction.
  • this step may involve using the Generalised Processor Sharing (GPS) mechanism.
  • the weighting for a data flow may be defined by one or more Radio Access Bearer (RAB) parameters allocated to a RAB by the UMTS network, where the RAB is associated with each MAC input flow.
  • RAB Radio Access Bearer
  • the method further includes the step of adding the value of the backlog counter to the computed fair share for that flow and selecting a TFC on the basis of the resulting sums for all of the input flows.
  • the difference may be subtracted frora the backlog counter for the input flow.
  • a node of a Universal Mobile Telecommunications System including: a Media Access Control (MAC) entity for receiving a plurality of input data flows; first processor means for computing for each input flow to the MAC entity a fair share of the available output bandwidth of the MAC entity and for selecting a Transport Format Combination (TFC), from a TFC Set (TFCS), on the basis of the bandwidth share computed for the input flows, where the TFC includes a Transport Format allocated to each input flow; second processor means for adding to a backlog counter associated with each input flow the difference between the data transmission rate for the flow resulting from the selected TFC and the determined fair share, if the data transmission rate is less than the determined fair share, where the first processor means is arranged to take into account the value of the backlog counters when selecting a TFC for the subsequent frame of the output data flow.
  • the first and second processor means are provided by a Radio Resource Control (RRC) entity.
  • RRC Radio Resource Control
  • a simplified UMTS layer 2 includes one Radio Resource Control (RRC) entity, a Medium Access Control (MAC) entity for each mobile station, and a Radio Link Control (RLC) entity for each Radio Access Bearer (RAB).
  • RRC Radio Resource Control
  • the MAC entity performs scheduling of outgoing data packets, while the RLC entities provide buffers for respective input flows.
  • the RRC entity sets a limit on the maximum amount of data that can be transmitted from each flow by assigning a set of allowed Transport Format Combinations (TFC) to each MAC (referred to as a TFC Set or TFCS), but each MAC must independently decide how much data is transmitted from each flow by choosing the best available Transport Format Combination (TFC) from the TFCS.
  • TFC Transport Format Combinations
  • the flowchart 400 is a flow diagram of a method of allocating bandwidth resources to, for example, the input flow streams of a MAC entity of the layer 2 of FIG 3.
  • an exemplary method in accordance with the flowchart 400 may follow the following steps. First, input flows are received at RLCs and the data is buffered (step 405). Information on buffer fill levels is passed to the MAC entity (step 410). After the information on buffer fill levels is passed, the fair MAC bandwidth share for each input flow is computed (step 415). The computed fair share of each is then adjusted by adding the contents of an associated backlog counter to the respective computed fair share (step
  • a TFC is selected from the TFC set to most closely match the adjusted fair shares (step 425).
  • the RLC is next instructed to deliver packets to the MAC entity according to the selected TFC (step 430).
  • the MAC entity may also schedule packets in accordance with the selected TFC (step 435).
  • the traffic channels may be transported on the physical channel(s) (step 440). Once packet traffic has been transported, the backlog counters should be updated (step 445). The process may continue (via arrow 450) when new input flows are received at the RLCs, which buffer the data (at step 405).
  • certain embodiment(s) of the scheme operate by calculating at the MAC entity, on a per Transmission Time Interval (TTI) basis, the optimal distribution of available bandwidth using the Generalised Processor Sharing (GPS) approach (See, e.g., the article by A. K. Parekh et al. referenced hereinabove.) and by keeping track of how far behind each flow is from the optimal bandwidth allocation using respective backlog counters.
  • GPS Generalised Processor Sharing
  • the available bandwidth is distributed to flows by using the standard GPS weights, which may be calculated by the RRC using the RAB parameters.
  • the method may first calculate the GPS distribution for the input flows and add to the GPS values the current respective backlogs. This is performed once for each 10ms TTI and results in a fair transmission rate for each flow. However, this rate may not be optimal as it may happen that there is not enough data to be sent in all buffers. In order to achieve optimal throughput as well as fairness, the fair GPS distribution is reduced so as to not exceed the current buffer fill level or the maximum allowed rate for any logical channel. A two step rating process is then carried out.
  • the set of fair rates computed for all of the input flows is compared against possible Transport Format Combinations (TFCs) in turn, with each TFC being scored according to how close it comes to sending out the optimal rate.
  • TFCs Transport Format Combinations
  • this is done by simply counting how much of the fair configuration a TFC fails to send (if a given TFC can send all packets at the fair rate, it is given a score of zero) and then considering only the TFCs which have the lowest scores. The closest match is chosen and used to determine the amount of packets sent from each queue.
  • TFCs having an equal score are given a bonus score according to how many extra bits they can send
  • the final selection is based on a two-level scoring: the TFC with the lowest score is taken. If there are several TFCs with an equal score, the one with the highest bonus score is chosen. This ensures that the rate for each TTI is maximized. Fairness is achieved by checking that if the chosen TFC does not give all flows at least their determined fair rate, the missing bits are added to a backlog counter of the corresponding flow and the selection is repeated for the next TTI. If any of the flows has nothing to transmit, the backlog is set to zero. This algorithm can be shown to provide bandwidth (and, under certain assumptions, delay bounds) that is close to that of GPS.
  • int maxrate int i ; int tfc, tfci, qf, rate, trch; int tfc_to_use;
  • the exemplary second layer architecture 500 includes additional details regarding elements of, and interrelationships between, various aspects of the second layer architecture of, for example, the Universal Mobile Telecommunications System (UMTS).
  • UMTS Universal Mobile Telecommunications System
  • RRC element 505 is connected to one or more Radio Link Controllers (RLCs) 510.
  • RLCs 510 includes at least one RLC Packet Data Unit (PDU) Buffer 515.
  • the RLCs 510 are connected to respective common channel Medium Access Control (MAC-c) element(s)/layer 520 or dedicated channel Medium Access Control (MAC-d) element(s)/layer 525.
  • MAC-c Medium Access Control
  • MAC-d Medium Access Control
  • the MAC-c, MAC-d, and RLC layers of UMTS may be located, for example, in a Radio Network Controller (RNC) 140 (of FIG. 1) of the UTRAN 130.
  • RNC Radio Network Controller
  • MAC-d 525) When a user (MAC-d 525) becomes active (e.g., new data arrives into an RLC buffer 515 that was previously empty), it sends a number of packets to MAC-c 520 (common channels) according to the user's current initial credit.
  • MAC-d 525 When a user (MAC-d 525) becomes active (e.g., new data arrives into an RLC buffer 515 that was previously empty), it sends a number of packets to MAC-c 520 (common channels) according to the user's current initial credit.
  • MAC-c PDU Buffer 530 will rise in an amount equal to the initial credit. Consequently, regardless of how the initial credit is specified, there is always a possibility that the MAC-c PDU Buffer 530 will be overloaded in situations when/where many new users become active at the same time.
  • the number of simultaneous new users e.g., subscribers
  • This significant number of subscribers may disturb the normal operation of the MAC-c node 520. If all of these new users are permitted to subscribe to this MAC-c node 520, then the resulting congestion will prevent everyone from using the MAC-c entity 520.
  • the MAC-c entity 520 rejects connections from MAC-d entities 525 because all MAC-d entities 525 are allowed to transmit at least their initial credit.
  • the present invention advantageously avoids such congestion in the MAC-c node 520 by implementing and utilizing a predefined buffer fill level "Qcrej", which is described in greater detail hereinbelow with reference to FIG. 7. If the MAC-c PDU Buffer 530 reaches this predefined fill level, the MAC-c node 520 discards the incoming packets from new
  • the present invention provides an additional benefit inasmuch as once new MAC-d entities 525 have transmitted their initial credit, they do not transmit new packets until the MAC-c node 520 activates them by sending to them new credit.
  • the UMTS layer 2 protocol structure
  • a UE 110 e.g., a mobile station, a mobile terminal, a mobile telephone, a wireless data communicator such as a PDA, a portable computer with a wireless link, etc.
  • RNCs 140 are analogous to the Base Station Controllers (BSCs) of existing GSM mobile telecommunications networks, so they communicate with UEs
  • BSCs Base Station Controllers
  • FIG. 6 yet another view of the exemplary second layer architecture of an exemplary next-generation system in accordance with the present invention is illustrated generally at 600.
  • the exemplary second layer architecture 600 may be considered as a subset of the exemplary second layer architecture 500 where the focus is on one common channel.
  • the result for the exemplary second layer architecture 600 is a typical star configuration with a number of RLC-d buffers 515 transmitting data towards one MAC-c buffer 530.
  • the data flow between the RLC-d buffers 515 and the MAC-c buffer 530 is controlled by a flow control function/module 605.
  • the layer 2 structures 500 and 600 include a set of Radio Bearers (RBs) 535 that make available radio resources (and services) to user applications.
  • RBs Radio Bearers
  • each UE there may be one or more RBs 535.
  • Data flows, in the form of packets (or more generally segments), from the RBs 535 are passed to respective RLC entities 510, which buffer the received data segments, among other tasks.
  • RLC entities 510 There is preferably one RLC entity 510 for each RB 535.
  • RBs 535 are mapped onto respective logical channels.
  • a MAC entity receives data transmitted in the logical channels and further maps logical channels onto a set of transport channels.
  • Transport channels are further mapped to a single physical channel that has a total bandwidth (e.g., ⁇ 2 Mbits/sec) allocated to it by the network.
  • a physical channel is referred to as either a "dedicated channel” or a “common channel”, respectively.
  • common transport channels may be considered as Forward Access CHannel (FACH) transport channels.
  • FACH Forward Access CHannel
  • a MAC entity connected to a dedicated channel (DCH) is known as "MAC-d" ; there is preferably one
  • MAC-d entity for each UE.
  • a MAC entity connected to a common channel is known as "MAC-c"; there is preferably one MAC-c entity for each cell.
  • the RRC-d 505 When the dedicated channels of a UE are switched on common transport channels, the RRC-d 505 sends a Common Transport Channel Resources Request message to the RRC-c 505. The RRC-c 505 responds with a Common Transport Channel Request message to the RRC-c 505.
  • the Common Transport Channel Resources Response message includes a list of provided common channel characteristics, including: channel priorities, Initial credits, and data frame sizes. Consequently, all dedicated logical channels of different UEs with the same mapping result are routed to the same common channel.
  • the potential overloading of the common channel e.g., the MAC-c PDU Buffer 530
  • the MAC-c PDU Buffer 530 may be avoided by establishing an extra MAC-c PDU Buffer 530 (fill level) threshold.
  • This buffer fill level threshold may cause the rejection of all new users (e.g., the discarding of the data of new users).
  • all new user packets may be dropped and their initial credits may be set to zero.
  • an exemplary buffer for an entity of an exemplary next-generation system in accordance with the present invention is illustrated generally at 700.
  • the exemplary buffer 700 corresponds to, for example, a MAC-c PDU Buffer 530 (of FIGS. 5 and 6).
  • various levels are defined to the left of the MAC-c PDU Buffer 530 and that these levels, at least in part, demarcate various zones as indicated to the right of the MAC-c PDU Buffer 530. Each zone delineates the relevant credit situation given the fill level of the MAC-c PDU Buffer 530.
  • the exemplary buffer 700 includes a "Qcmin” 705 level and a “Qcmax” 710 level.
  • the "Qc” 715 level reflects the current fill level of the exemplary buffer 700.
  • a “Qcopt” 720 level stands for the, e.g., MAC-c buffer 530 optimum level with regard to delay and throughput requirements.
  • the buffer available space, or "Qcdiff ' 725, is shared between users so that each user is allotted a certain number of credits.
  • new credits may be calculated according to the Qcdiff 725 value and the RLC-d 510 buffer fill level.
  • the Qcdiff 725 may be defined to equal Qcopt 720 - Qc 715 (not shown in FIG. 7) in this instance.
  • the number of control messages may be decreased by introducing the Qcmax 710 threshold level.
  • Qcdiff 725 Qcmax 710 - Qc 715, and no new credits are granted when the buffer fill level Qc 715 falls between Qcopt 720 and Qcmax 710.
  • the level(s) below Qcmin 705 may optionally be used to set credits equal to 'unlimited', which implies that an unlimited number of packets from an RLC buffer 515 may be transferred without any control signals.
  • the buffer level rises above Qcmax 710 but is still below Qcrej 730, no new credits are granted except for initial credits.
  • the credits are cleared by the sending of a 'zero' credits to appropriate MAC-d entities 525.
  • a user becomes active (e.g. , new data arrives into an RLC buffer 515 that was previously empty)
  • the corresponding MAC-d entity sends a number of packets to the MAC-c entity according to the initial credit.
  • the MAC-c buffer 530 fill level rises in accordance with this initial credit. If 'n' new users become active before the next Transmission Time Interval (TTI) (when more data may be moved out from the MAC-c buffer 530), then the MAC-c buffer 530 fill level Qc 715 increases by: n*Initial_credits*Packet_size .
  • TTI Transmission Time Interval
  • This additional threshold is termed "Qcrej" 730 in FIG. 7.
  • Qcrej 730 This additional threshold is termed "Qcrej" 730 in FIG. 7.
  • the exceeding of this threshold value Qcrej 730 precipitates the rejection of all new users that try to gain access.
  • the packets (or, more generally, the segments) of these users are discarded, and their associated credits are set to zero.
  • the channel switching function can identify and switch them towards appropriate dedicated transport channels.
  • the threshold level Qcrej 730 may be specified as follows:
  • Qcrej Qcmax + Re * Tad where Tad represents the maximum allowed additional delay, and Re represents the expected mean transmission rate of the common channel (e.g., the rate at which the packets are emptied from the MAC-c buffer 530).
  • FIG. 8 an exemplary method in flowchart form for modulating a fill level of the exemplary buffer of FIG. 7 in accordance with the present invention is illustrated generally at 800.
  • the flowchart 800 illustrates steps involved in certain embodiments of the present invention for ensuring that multiple new users do not overload a telecommunications network with too many data segments from their initial credits by rejecting such new users in certain situation(s).
  • a MAC-d entity determines that a MAC-d entity buffer holds new data for transmission (step 805).
  • the MAC-d entity transmits a number of segments that equate to the value prescribed for initial credit (step 810).
  • the MAC-c entity receives the segments transmitted by the MAC-d entity (step 815).
  • the MAC-c entity may either hold these new segments in another memory (e.g., a cache memory (not specifically shown) for the MAC-c buffer 530 (of FIG. 7)) or initially store them directly into the MAC-c buffer.
  • another memory e.g.,
  • the MAC-c entity After receiving the new segments, the MAC-c entity inspects the MAC-c buffer (step 820) (e.g., the MAC-c buffer fill level is determined). It is next ascertained whether or not the fill level of the MAC-c buffer is greater than a predetermined rejection buffer fill level threshold (step 825). If not, then the MAC-c entity either accepts or keeps (depending on whether the new data segments were initially stored in a cache memory or directly in the MAC-c buffer, respectively) the data segments either into or at the MAC-c buffer of the MAC-c entity (step 830).
  • the MAC-c entity inspects the MAC-c buffer (step 820) (e.g., the MAC-c buffer fill level is determined). It is next ascertained whether or not the fill level of the MAC-c buffer is greater than a predetermined rejection buffer fill level threshold (step 825). If not, then the MAC-c entity either accepts or keeps (depending on whether the new data segments were initially stored

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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 des procédés, des systèmes et dispositifs pour la prévention de la surcharge d'un canal commun dans un réseau de communications sans fil. Dans un environnement (100) de réseau de système universel de télécommunication mobile (UMTS), par exemple, de nouvelles entités spécialisées (525) de contrôle d'accès au support (MAC-d) sont toujours autorisées à émettre des segments de données en quantité correspondant à leur crédit initial à une entité commune (520) de contrôle d'accès au support (MAC-c). En conséquence, le tampon (530) dans l'entité MAC-c peut devenir surchargé si de nombreuses nouvelles entités MAC-d émettent simultanément des segments de données, empêchant ainsi l'utilisation de l'entité MAC-c (520) par une quelconque entité MAC-d (525). Conformément à certains modes de réalisation, si le repère de remplissage du tampon du MAC-c atteint un niveau prédéfini, l'entité MAC-c (520) est habilitée à rejeter les entités MAC-d (525) de nouveaux utilisateurs en supprimant des segments de données qui en proviennent.
PCT/SE2001/000408 2000-02-25 2001-02-23 Traitement de surcharges dans un systeme de communications WO2001063857A1 (fr)

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AU2001236304A AU2001236304A1 (en) 2000-02-25 2001-02-23 Overload handling in a communications system

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EP1770918A1 (fr) * 2005-09-30 2007-04-04 Evolium Sas Contrôle de flux de données sur les interfaces d'un réseau d'accès radio
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WO2013167343A1 (fr) * 2012-05-11 2013-11-14 Nokia Siemens Networks Oy Egalisation de temps de propagation pour liaisons multi-flux inter-site fluctuantes

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