WO1999002009A2 - Detection de boucles - Google Patents

Detection de boucles Download PDF

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Publication number
WO1999002009A2
WO1999002009A2 PCT/SE1998/001314 SE9801314W WO9902009A2 WO 1999002009 A2 WO1999002009 A2 WO 1999002009A2 SE 9801314 W SE9801314 W SE 9801314W WO 9902009 A2 WO9902009 A2 WO 9902009A2
Authority
WO
WIPO (PCT)
Prior art keywords
loop
connection
network device
source
cell
Prior art date
Application number
PCT/SE1998/001314
Other languages
English (en)
Other versions
WO1999002009A3 (fr
Inventor
Gert Öster
Jörgen AXELL
Göran HÅGÅRD
Loa Andersson
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.)
Filing date
Publication date
Application filed by Telefonaktiebolaget Lm Ericsson (Publ) filed Critical Telefonaktiebolaget Lm Ericsson (Publ)
Priority to GB9930819A priority Critical patent/GB2343085B/en
Priority to JP50703999A priority patent/JP2002510454A/ja
Priority to AU82516/98A priority patent/AU8251698A/en
Priority to CA002294807A priority patent/CA2294807A1/fr
Publication of WO1999002009A2 publication Critical patent/WO1999002009A2/fr
Publication of WO1999002009A3 publication Critical patent/WO1999002009A3/fr

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q11/00—Selecting arrangements for multiplex systems
    • H04Q11/04—Selecting arrangements for multiplex systems for time-division multiplexing
    • H04Q11/0428—Integrated services digital network, i.e. systems for transmission of different types of digitised signals, e.g. speech, data, telecentral, television signals
    • H04Q11/0478—Provisions for broadband connections
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L12/00—Data switching networks
    • H04L12/54—Store-and-forward switching systems 
    • H04L12/56—Packet switching systems
    • H04L12/5601—Transfer mode dependent, e.g. ATM
    • H04L2012/5625—Operations, administration and maintenance [OAM]
    • H04L2012/5627—Fault tolerance and recovery
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L12/00—Data switching networks
    • H04L12/54—Store-and-forward switching systems 
    • H04L12/56—Packet switching systems
    • H04L12/5601—Transfer mode dependent, e.g. ATM
    • H04L2012/5628—Testing
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L12/00—Data switching networks
    • H04L12/54—Store-and-forward switching systems 
    • H04L12/56—Packet switching systems
    • H04L12/5601—Transfer mode dependent, e.g. ATM
    • H04L2012/5638—Services, e.g. multimedia, GOS, QOS
    • H04L2012/5646—Cell characteristics, e.g. loss, delay, jitter, sequence integrity
    • H04L2012/5652—Cell construction, e.g. including header, packetisation, depacketisation, assembly, reassembly

Definitions

  • the present invention relates to a method and a device for traffic-management in networks.
  • the present invention relates to a method for detecting loops in networks, in particular in a connection-oriented networks such as, for example, an Asynchronous Transfer Mode (ATM) networks, and to a device for use in this method.
  • a connection-oriented networks such as, for example, an Asynchronous Transfer Mode (ATM) networks
  • connection-oriented networks There are two major types of networks used for sending information between networks - connection-oriented networks and connection-less networks.
  • connection-oriented networks such as, for example, an Asynchronous Transfer Mode network
  • a message or information stream is transferred between two end systems (such as a computer or a telephone or the like),e.g. A and B, connected to the network by a connection which is established for, and maintained during the transfer.
  • a and B end systems
  • a connection which is established for, and maintained during the transfer.
  • a logical/virtual connection set-up phase must take place.
  • a path through the network is selected, logical channels are allocated on the links between the nodes in the paths, resources are reserved in the links and the nodes, and the logical channels are interconnected in the nodes, which in this type of network comprise switches.
  • the switches register interconnected logical channels in tables so that the information in the subsequent data phase of the connection can be transferred easily, typically by hardware logic, between interconnected logical channels.
  • the information in the connections is sent in the form of cells, each containing 53 bytes of which 5 form a header and 48 are the payload.
  • the header contains the identity of the logical channel for the connection on the current link. This identifier is changed as necessary by the switch as the cell passes through the node and is transmitted on the next link.
  • the payload contains information from the stream or message being transferred by the connection.
  • loops typically can not occur as this is prevented by functions in the network which handle the signalling.
  • a loop back cell contains information in which the source of the loop-back cell and the destination of the cell can be identified. There is also an indicator, called a loop-back indicator, which shows whether the cell is travelling towards or from the loop-back point destination.
  • a loop-back indicator which shows whether the cell is travelling towards or from the loop-back point destination.
  • This field informs the destination switch or node, in this case node B, that it must turn around the cell and send it back to the source.
  • a node upon receiving a loop-back cell, checks the loop-back point/destination field to see if it shall loop the cell back. If it does loop the cell back then it changes the loop-back indicator to show that the cell has been looped. It does not change the source identity or the loop-back identity. There may also be another field in the loop-back cell, called the correlation tag, which remains unchanged. If the route between A and B is functioning correctly then node A will receive back the loop-back cell from B with the loop-back indicator indicating that the cell has been turned around. This event occurs some time after the insertion of the loop-back cell. This time depends on the length of the route and any queuing or other delays present on it.
  • connection set-up procedure takes some time, in the order of tens to hundreds of milliseconds per node traversed, and thus introduces some latency for the end systems.
  • the information can be transferred through the nodes/switches in an efficient way by the switch hardware.
  • the connection is typically broken and a new connection has to be set up. The new connection will then be routed so as to avoid the troubled part of the network.
  • connection-less networks by connection-less it is meant that no fixed communication is set up between communicating devices but that information is sent by the best route available at the time) e.g. the Internet, where information is sent as discrete packets of information between nodes, e.g. A, B, the packets comprise a header i.e. a part which contains information about, amongst other, its identification, where it came from (its source), where it must go (its destination), its length and other useful information.
  • Each node uses a routing protocol to exchange routing information on how to best reach other nodes in a network.
  • this alternative path at some stage contains a link which has a routing information protocol which leads back to this preceding node.
  • the packets are routed from the preceding node via the alternative path back to the preceding node again.
  • a loop is formed. If a loop is formed then system resources are wasted on unnecessarily sending the packets on hops around the loop. Information packages caught in a loop can be considered as being worthless as even if the loop is broken it is unlikely that they can be delivered to their destinations at the correct time.
  • Loops are, however, usually transient problems. This is because the routing information protocols are updated with information on the network status and hence the primary and alternative paths for each node are constantly also being updated. This updating can be performed by, for example, exchanging distance vectors or information on link states between nodes.
  • Distance vectors contain information for each destination in the network, usually one element per destination, on the time, distance or 'cost' of sending a packet from the particular node to that destination.
  • Each node exchanges, by a routing protocol, distance vectors with all its neighbouring nodes. These exchanges take place periodically and ,possibly, also when events occur which lead to changes in the costs.
  • the distance vectors received from neighbours and knowledge about the cost of the links to the neighbours are used by nodes to recalculate its distance vectors. When a packet is received for forwarding to a certain destination the corresponding distance vector states which link should be used to forward the packet at the lowest cost. The path with the lowest cost is then used to route the packet.
  • a node or a link to a node fails in a particular path then its neighbouring nodes note that the cost of using this failed node or link is infinity and therefore an alternative path must be chosen.
  • the information about the failed node is sent to other neighbouring nodes in an updated distance vector. These nodes then update their own distance vectors and send them to other neighbouring nodes and so on. Thus the information on the failed link slowly propagates through the network.
  • Each updated distance vector influences all the neighbouring nodes and it takes a number of exchanges of distance vectors between neighbouring nodes before the distance vectors converge and a new steady-state is re-established.
  • This convergence period it is possible that packages which were sent on the original path are influenced by the changing distance vectors and end up in a loop. This loop naturally ends when the distance vectors have converged. However during the convergence period, which can last up to the order of a minute, scarce processor and bandwidth resources are wasted.
  • Connection-less networks are flexible and messages can be sent quickly as there is no need to establish a reserved connection between source and destination before sending a message. These networks however require considerable processor capacity to determine the destination of each package being transmitted and loops can occur in the system which waste resources.
  • label switching networks also known as “multi-protocol label switching networks”
  • a connection-less device such as a router
  • a connection-oriented device such as a switch in, for example, an ATM network.
  • Each router uses its routing protocol to build up its routing table with destination information which states which is the best route towards each specific destination, i.e. which node, called the downstream node, it must forward traffic to in order to reach the desired destination. It will then request a logical channel number, known generically as a 'label', from that downstream neighbour for the traffic/packet to each destination.
  • the node When the node gets a corresponding request from its upstream neighbours it can order its switch component to interconnect these channels. As this process is being carried out in the nodes in the network, link layer connections from each source to each destination will be established. These connections will follow the same paths as the best paths which have been decided by the routing protocols and distance vectors.
  • a problem with such label switching networks is that the router network can cause a loop which is then superimposed onto the connection-oriented network.
  • the router network can cause a loop which is then superimposed onto the connection-oriented network.
  • connection-less, e.g. router, networks superimposed on connection- oriented, e.g. switch and/or ATM, networks is that the existence of a loop causes a waste of system resources.
  • Present art routing protocols designed for router networks do not provide guarantees against loops. They merely provide conditions in which the protocol rules ensure that the maximum life time of a loop is limited. This means that if a loop occurs then system resources are wasted until the loop reaches its maximum life time or the system undergoes some change which coincidentally breaks the loop.
  • the present invention seeks to reduce the wastage of system resources when a loop occurs by providing active means for detecting loops and for breaking loops in a connection-oriented network, in particular an ATM network, and more especially a network comprising a connection-less network superimposed on a connection- oriented network.
  • a source switch establishes a connection to a destination switch or node in a connection-oriented network it inserts a loop-detecting means, for example a loop-detecting cell, into the route.
  • This loop-detecting cell contains identifying means which can be recognised by the source node if the loop-detecting cell returns to the node. It there is no loop then this cell will continue to the destination point of the route where it will be discarded.
  • the loop-detecting cell will return to the source node. It will be recognised by the source node and this will alert the source node that there is a loop present and action can then be taken to avoid the loop, e.g. the source node can inform an associated network controlling device, e.g. a router, that there is a loop present.
  • an associated network controlling device e.g. a router
  • the loop-detecting means is a loop-back cell in which, in the information fields of the cell, the source node or switch is both the source and destination (i.e. turning point) of the loop-back cell. If there is no loop present then the loop-back cell cannot return to the source node or switch without being (intentionally) looped as it is transmitted on a link which only leads to the destination point of the route. If there is a loop present then a loop-back cell which has the source identity in both the source and destination/loop-back fields will return to the source node or switch. The loop-back indicator shows that the cell is travelling towards the turning/loop-back point.
  • the node or switch detects the loop by realising that it is itself the source and destination of the loop-back cell. It checks if it is the destination for the loop-back cell and if it is not the destination then the cell is transmitted along its logical channel. In order to identify that it is the originator of the loop-back cell it can use the source identity field or the correlation tag, or both. It shall also check that the loop-back indicator shows that the cell is flowing in the direction towards the loop-back point.
  • the source node in order to ensure that packages of information are not sent into a potential looping path, after sending out a loop detection cell the source node can queue incoming traffic until a certain time has elapsed. This time is chosen such that there is a significant probability that if there is indeed a loop then the loop detection cell will return to the source node before the time elapsed.
  • the elapsed time must not be too long as this leads to unacceptable delays in the processing of the packets and requires large buffers. The time is therefore selected dependent on the type of information being sent and the expected length of the route.
  • the node in order to avoid delaying packets unnecessarily the node starts to send packets without delay along the route after the loop detection cell has been sent. This means that an assumption is made that the new route will not cause a loop. This assumption is acceptable in the case that the occurrence of loops is rare and/or it is unacceptable to delay packets.
  • Figure 1 shows a schematic diagram representing one embodiment of a simplified network according to the invention.
  • Figure 2 shows schematically one embodiment of a loop-detecting cell according to the invention.
  • Figure 1 which will be used to illustrate the basic idea of the invention, shows an example of a hypothetical simple connection-less network superimposed on a connection-oriented network consisting of nodes A, B, C, D and E.
  • each node has a connection-less device, shown for the sake of example as routers, AR, BR, CR, DR and ER respectively, and a connection- oriented device, shown for the sake of example as ATM switches AS, BS, CS, DS, and ES respectively.
  • connection-less device shown for the sake of example as routers, AR, BR, CR, DR and ER respectively
  • connection- oriented device shown for the sake of example as ATM switches AS, BS, CS, DS, and ES respectively.
  • Each node A-E has a route determining means, for example in the form of a routing table, resp. RT A , RT B , RT C , RT D , RT E which contains route information means, for example in the form of route information entries E A-B , E A-C , E A-D , E A-E , etc. to E ⁇ . ⁇ (where is the source and Y is the destination node) showing how packets are to be routed from the resp. node to the other nodes in the network.
  • the route table for node A contains info ⁇ nation on how to send information packets from node A to node B, from node A to node C, from node A to node D and from node A to node E.
  • node A can send packets to node E, i.e. via link LI, L3, L4, L5 or via links L2, L4, L5.
  • node A would send packets to node E via links L2, L4, L5 as this gives the shortest and therefore "cheapest" route, (assuming that the cost of using a link is the same for all links in the network) thus the distance E A-E from source node A to destination node E would have a cost of 3. If link L2 is broken then node A would use links LI, L3, L4, L5 instead and the distance from node A to node E would be increased to 4 and the route information entry would be changed to reflect this. Similarly node B has a distance to node E, E B-E , which is 3, if node 3 is intact and which rises to 4 if node 3 fails.
  • router AR-ER use their routing tables to establish connections through their switches AS-ES as described previously.
  • router AR when it wishes to send traffic to E requests a label from node CR, i.e. in the case of ATM a logical channel number, CLEa-c for the traffic to E. Packets destined for E received by A will then be forwarded to C through that channel.
  • Router CR will ask D for a label, CLEc-d, for traffic for E and can then order its switch CS to interconnect CLEa-c with CLEc-d thereby allowing the traffic from A to E to be handled by switch CS and thus bypassing, and saving resources in, router CR.
  • connections established as described above will follow the paths determined by the routing tables RTx in the routers. If some event causes these routers to generate a loop then this will lead to a connection loop.
  • node A will release its channel to C and will instead ask B for a channel to B, CLEa-b for its traffic towards E.
  • BS will interconnect that with the existing channel CLEb-c.
  • C will ask A for a channel CLEc-a for its traffic towards E.
  • Router AR will order switch AS to interconnect CLEc-a with CLEa-b and router CR will order switch CS to interconnect CLEb-c with CLEc-a, thus forming a loop connection.
  • all packets towards E will circulate in the loop and cause a waste of links and switch resources and eventually lead to problems such as overflows in switch buffers and the like.
  • the loop-detection means comprises a specially modified maintenance loop-back cell 20 which is produced and transmitted by a switch whenever it establishes a communication channel to another switch.
  • Cell 20 has a header 18 and a payload 19.
  • This loop detection cell 20 has the originating switch identified both in the source field 21 as the source as well as in the turning point field 22.
  • This cell 20 can also have a loop-back indicator field 23 which shows if the cell has been looped back.
  • switch AS is to establish communication with switch ES it produces a loop detection cell 20 in which the cell will contain AS as the source and AS as the turning point.
  • This cell 20 is then sent on the route which should lead to switch ES and normally it should never come back to switch AS. If switch AS subsequently receives back any cell which contains AS in both source and turning point fields (21, resp. 22) and with the loop-back indicator 23, if present, showing that the cell has not been looped back then it means that a loop has been formed.
  • the source can also be identified by some other source field, for example, a correlation tag 24 as specified in the ITU-T 610 specification.
  • Switch AS can then take appropriate action to prevent the loop being used and/or to break the loop and/or send an alarm out of the network. In this way a loop can be detected in the time it takes the loop- detection cell to hop round the loop in the newly established route. Generally it can be considered that loops contain only a few nodes and links. Thus the time that a loop detection cell takes to hop around the loop generally will be short and a loop will be detected quickly in a method according to the invention.
  • the loop-detecting cell will continue to the destination node and be discarded, or possibly looped back with the loop-back indicator changed to 'looped'.
  • the switch which produces the loop-detecting cell assumes that there will not be any loops present on the route and forwards packets of information on the route after sending the loop-detecting cell. This avoids delaying the packets of information but can lead to some packets being lost if there is indeed a loop.
  • the number of packets lost will, however, owing to the more rapid loop detection enabled by use of a loop-detection cell, be less than the number which would have been lost anyway if no loop- detection cell had been sent.
  • this embodiment leads to an improved transmission performance and no signal delay.
  • the switch which produces the loop-detecting cell assumes that there is a loop present on the route.
  • it has a timer which is set to expire a predetermined time interval after the loop-detection cell has been sent on the alternate route.
  • the length of the timer is chosen to correspond to an appropriate maximum loop length. Such a maximum length could, for example, be chosen to correspond to the time which a packet would take to hop around a loop of an arbitrary number of links, or could be a set number of transmission periods. Packets with a destination on the route are stored until the end of the timer period.
  • a delay may be acceptable in a data transmission which however cannot accept the loss of a few packets of information without suffering a discernible loss of quality, while a telephony conversation may be able to accept a loss of quality but not a transmission delay. It is possible for a node or switch to determine which embodiment to use for each packet it receives: some being transmitted immediately while others are delayed.
  • the loop detection cell is produced at pre-programmed or predetermined intervals.
  • the loop detection cell is not produced each time a route is established but after a route has been established a pre-programmed or predetermined number of times.
  • the invention is naturally not limited to networks having only 5 nodes and 5 links but is adaptable to networks of any size.
  • connection-less network superimposed on a connection-oriented network
  • present invention in purely connection-oriented networks as well as in networks comprising a connection-oriented network or switch.
  • the invention is not limited to loop-detecting means based on a loop-back cell but can use any other cell which can be suitably designed or modified to inform an originating device that a loop exists.

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Data Exchanges In Wide-Area Networks (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Use Of Switch Circuits For Exchanges And Methods Of Control Of Multiplex Exchanges (AREA)

Abstract

La présente invention concerne un dispositif de détection de boucles produit par un commutateur source (AS) lors de l'établissement d'un itinéraire d'acheminement aboutissant à un commutateur de destination (ES). En l'occurrence, le dispositif de détection de boucles est une cellule de rebouclage (20) comportant un commutateur source (AS), non seulement dans la zone source (21), mais aussi dans la zone renvoi (22).
PCT/SE1998/001314 1997-07-04 1998-07-03 Detection de boucles WO1999002009A2 (fr)

Priority Applications (4)

Application Number Priority Date Filing Date Title
GB9930819A GB2343085B (en) 1997-07-04 1998-07-03 Loop detection
JP50703999A JP2002510454A (ja) 1997-07-04 1998-07-03 ループ検出
AU82516/98A AU8251698A (en) 1997-07-04 1998-07-03 Loop detection
CA002294807A CA2294807A1 (fr) 1997-07-04 1998-07-03 Detection de boucles

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE9702604-1 1997-07-04
SE9702604A SE512055C2 (sv) 1997-07-04 1997-07-04 Detektion av slinga

Publications (2)

Publication Number Publication Date
WO1999002009A2 true WO1999002009A2 (fr) 1999-01-14
WO1999002009A3 WO1999002009A3 (fr) 1999-05-06

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/SE1998/001314 WO1999002009A2 (fr) 1997-07-04 1998-07-03 Detection de boucles

Country Status (7)

Country Link
JP (1) JP2002510454A (fr)
CN (1) CN1132493C (fr)
AU (1) AU8251698A (fr)
CA (1) CA2294807A1 (fr)
GB (1) GB2343085B (fr)
SE (1) SE512055C2 (fr)
WO (1) WO1999002009A2 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
TWI469568B (zh) * 2010-04-22 2015-01-11 Hon Hai Prec Ind Co Ltd 交換設備及其環回偵測方法

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN100344116C (zh) * 2004-04-20 2007-10-17 北京润光泰力科技发展有限公司 一种以太网转换器线路侧环回检测的方法和装置
CN1734991B (zh) * 2004-08-13 2010-08-18 中兴通讯股份有限公司 一种检测多业务传送平台设备业务环回的方法
US7706258B2 (en) * 2004-12-22 2010-04-27 Alcatel Lucent System and method for detecting loops in a customer-provider bridge domain
CN100403705C (zh) * 2006-03-30 2008-07-16 华为技术有限公司 Ppp封装接口的环回检测方法
CN102055525B (zh) * 2010-12-17 2016-03-16 北京格林伟迪科技股份有限公司 环路检测和控制方法
CN103220218B (zh) 2013-04-28 2016-03-30 杭州华三通信技术有限公司 纵向堆叠组网中防止环路的方法和装置

Citations (4)

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US5014262A (en) * 1990-01-02 1991-05-07 At&T Bell Laboratories Apparatus and method for detecting and eliminating call looping in a node-by-node routing network
EP0555926A1 (fr) * 1992-02-14 1993-08-18 Koninklijke KPN N.V. Procédé et moyens de détection d'une boucle d'acheminement dans un réseau de télécommunication
WO1995032571A1 (fr) * 1994-05-24 1995-11-30 Nokia Telecommunications Oy Procede permettant d'empecher un acheminement circulaire dans un reseau de telecommunications
EP0777401A1 (fr) * 1995-11-29 1997-06-04 AT&T Corp. Procédé de contrÔle d'un test à rébouclage entre points ATM

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5014262A (en) * 1990-01-02 1991-05-07 At&T Bell Laboratories Apparatus and method for detecting and eliminating call looping in a node-by-node routing network
EP0555926A1 (fr) * 1992-02-14 1993-08-18 Koninklijke KPN N.V. Procédé et moyens de détection d'une boucle d'acheminement dans un réseau de télécommunication
WO1995032571A1 (fr) * 1994-05-24 1995-11-30 Nokia Telecommunications Oy Procede permettant d'empecher un acheminement circulaire dans un reseau de telecommunications
EP0777401A1 (fr) * 1995-11-29 1997-06-04 AT&T Corp. Procédé de contrÔle d'un test à rébouclage entre points ATM

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
TWI469568B (zh) * 2010-04-22 2015-01-11 Hon Hai Prec Ind Co Ltd 交換設備及其環回偵測方法

Also Published As

Publication number Publication date
GB2343085A (en) 2000-04-26
CA2294807A1 (fr) 1999-01-14
SE9702604D0 (sv) 1997-07-04
CN1132493C (zh) 2003-12-24
GB2343085A8 (en) 2000-05-18
JP2002510454A (ja) 2002-04-02
SE512055C2 (sv) 2000-01-17
AU8251698A (en) 1999-01-25
GB2343085B (en) 2002-07-31
CN1269955A (zh) 2000-10-11
SE9702604L (sv) 1999-01-05
WO1999002009A3 (fr) 1999-05-06
GB9930819D0 (en) 2000-02-16

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