WO2008128564A1 - Method and apparatus for the determination of multiple spanning trees - Google Patents
Method and apparatus for the determination of multiple spanning trees Download PDFInfo
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- WO2008128564A1 WO2008128564A1 PCT/EP2007/053813 EP2007053813W WO2008128564A1 WO 2008128564 A1 WO2008128564 A1 WO 2008128564A1 EP 2007053813 W EP2007053813 W EP 2007053813W WO 2008128564 A1 WO2008128564 A1 WO 2008128564A1
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- cost
- spanning tree
- communications link
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L45/00—Routing or path finding of packets in data switching networks
- H04L45/22—Alternate routing
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L45/00—Routing or path finding of packets in data switching networks
- H04L45/02—Topology update or discovery
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L45/00—Routing or path finding of packets in data switching networks
- H04L45/48—Routing tree calculation
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L45/00—Routing or path finding of packets in data switching networks
- H04L45/48—Routing tree calculation
- H04L45/484—Routing tree calculation using multiple routing trees
Definitions
- the present invention relates generally to computer networks.
- Computer networks enable the sharing and exchange of information and/or resources.
- a computer network typically comprises a plurality of computer entities (for example workstations, servers, printers and data storage), which are interconnected by means of one or more communications links.
- a computer entity is able to transmit or receive data over a communications link.
- a common type of computer network is a so-called Local Area Network (LAN) in which various computer entities are connected over a particular locality (e.g. within a building or a group of buildings).
- So called Virtual LANs (VLANs) may be formed using intermediate devices, such as Ethernet switches.
- the intermediate devices comprise a data processor and a plurality of ports which enable the segmentation of the overall network of computer entities.
- the switching function comprises receiving data at an input port and transferring that data to an output port.
- the computer entities are connected to respective intermediate devices and the intermediate devices are connected by way of physical communications links
- VLANs By configuring the intermediate devices appropriately the various VLANs can be created. Such networks are more particularly known as Virtual Bridged Local Area Networks. It will be appreciated that a single intermediate device may provide a physical connection for members of different VLANs.
- the VLANs may be arranged in accordance with the Multiple Spanning Tree Protocol in IEEE 802. IQ (which is a standard defining various aspects of VLANs). In such an arrangement each VLAN is determined by a spanning tree instance.
- VLANs which enable multiple spanning tree topologies to be spread simultaneously over the physical network, result in the physical links between individual networks being spread over all of the available physical links and so realising a high resource usage.
- a method of determining multiple spanning trees over a computer network each spanning tree providing a particular arrangement of communication links between the nodes of the computer network, and the method comprising increasing a cost associated with using a particular communications link if said communications link is included in a previously determined spanning tree.
- a method to define automatically a set of multiple spanning tree instances to allow automatic re-routing of traffic in the presence of a fault and to allow good traffic distribution over all the available resources of the network is practical in the sense that it comprises a computationally simple algorithm and does not offer a mathematically optimal solution.
- each spanning tree providing a particular arrangement of communication links between the nodes of the computer network, and the apparatus being configured to increase a cost associated with using a particular communications link if said communications link is included in a previously determined spanning tree.
- FIG. 1 is a schematic representation of a network topology comprising Local Area Networks (LANs) and bridging equipment between the LANs,
- LANs Local Area Networks
- FIG. 2 is a schematic representation of a first determined spanning tree configuration which represents a first Virtual Local Area Network (VLAN), and
- VLAN Virtual Local Area Network
- Figure 3 is a schematic representation of a second determined spanning tree configuration which represents a second VLAN. DESCRIPTION OF VARIOUS EXEMPLARY EMBODIMENTS OF THE INVENTION
- a network comprising a plurality of Local Area Networks (LANs) 200, 201 , 202, 203 and 204, which connected by way of four Ethernet bridges 100, 101 , 102 and 103.
- the LANs provide communications links between the Ethernet bridges.
- Each of the Ethernet bridges has connected thereto one or more computer entities (not illustrated). It is desired to determine a plurality of Virtual Bridged Local Area Networks over the network 1 by way of an initial set-up procedure. It will be appreciated that at least some of the computer entities connected to different Ethernet bridges will be members of the same VLAN.
- Step 1 (Init) Initially, the physical topology is defined, with bridges and the LANs connecting the bridges.
- the LANs are attributed a cost that should reflect the desired LAN utilisation. Cost assignment could be related with the guidelines provided by the relevant IEEE standard, where high capacity LANs have lower costs to encourage their usage. Cost assignment is however an administrative matter and may be achieved on numerous different bases. However a suggested formula is Zb 1 , where the cost c, of the z ' -th LAN is given by an appropriate constant hi divided by the LAN bandwidth capacity b,.
- Step 2 (Init) Then, a known minimal cost spanning tree algorithm (such as Prim's or Kruskal' s algorithm) is run to find a first spanning tree. More sophisticated algorithms can be used to find Minimum Diameter Spanning Trees (MDST) if a higher computational complexity is acceptable.
- MDST Minimum Diameter Spanning Trees
- the spanning tree depends on the administrative costs assigned in Step 1. This spanning tree has a total cost that is a function of the sum of the costs of the LANs, assigned in Step 1.
- Step 3 The cost of each LAN is replaced with a value that is a function of both its initial cost and the number of found spanning trees that include that LAN.
- This function should still encourage the usage of high capacity LANs, and at the same time favour the LANs that are covered by the least number of spanning trees. This will allow an even number of spanning trees to be spread over the entire topology.
- the details of the costs function can be again an administrative matter and may vary according to the policy of traffic allocation. However, an example formula is suggested below.
- Reasonable functions should be monotonic, in that they always increase or leave unchanged the costs of the LANs: if a LAN was used by some spanning tree in the previous iteration its cost increases, otherwise it remains unchanged.
- Step 4 The same minimal cost spanning tree algorithm as used in Step 2 is run on the topology with the new costs computed in Step 3.
- the (j+l)-th spanning tree is found (as the first is the result of Step 2 during init phase).
- This spanning tree has a total cost that is function of the costs computed in Step 3.
- the monotonic property of the cost function of Step 3 implies that also the total cost of subsequent spanning trees increases progressively: the cost of the (j+l)-th spanning tree is higher than the cost of the j-th spanning tree.
- Step 5 (Term) If the cost of the (j+l)-th spanning tree is "much higher" than the cost of j-th one, it means that the last spanning tree is using: either (i) low capacity LANs or (ii) LANs that are already loaded with several spanning trees therefore its contribution would not bring meaningful improvements to the traffic load, the iteration can be terminated and the last spanning tree discarded.
- "much higher” is a condition to be defined according to the needs of a specific situation. Terminating earlier (a low value for "much higher”) will produce a lower number of spanning trees, that means lower configuration load and coarser load balancing. On the contrary, a "very much higher" cost will lead to a higher number of spanning trees, with higher configuration complexity, but the opportunity for a finer traffic distribution. According to the MSTP standard, the procedure must terminate in any case when 64 spanning trees are produced.
- a collection of spanning trees is produced with enough routing diversity/choices to allow a convenient traffic distribution/balancing of the VLANs over the network topology.
- the above procedure defines trees, in terms of all the bridges of the physical topology and - a subset of the LANs of the physical topology.
- the network operator is then able to manually assign each spanning tree instance to form a VLAN.
- Ci j is the cost of the z ' -th LAN at they-th iteration
- max cost is the maximum cost related to the bandwidth of the z ' -th LAN
- min costi is the minimum cost related to the bandwidth of the z ' -th LAN
- tii j is the number of spanning trees using LAN i at iteration j
- max n is the maximum number of spanning trees (that is 64 for MSTP)
- inst curv is the curvature of the cost curve on n,y basis (eg if equal to 1 it's linear).
- the network administrator will use a data processor to determine the various spanning tree instances.
- the administrator will have specified to the data processor an indication of what is an acceptable maximum cost so that no further spanning tree instances are to be determined. The administrator would then be able to
- each of the Ethernet switches (remotely) configure each of the Ethernet switches to complement the various VLANs.
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Abstract
A method of, and apparatus for, determining multiple spanning trees over a computer network (1), each spanning tree providing a particular arrangement of communication links (200, 201, 202, 203, 204) between nodes (100, 101, 102, 103) of the computer network, and the method comprising increasing a cost associated with using a particular communications link if said communications link is included in a previously determined spanning tree.
Description
METHOD AND APPARATUS FOR THE DETERMINATION OF MULTIPLE SPANNING TREES
FIELD OF INVENTION
The present invention relates generally to computer networks.
BACKGROUND
Computer networks enable the sharing and exchange of information and/or resources. A computer network typically comprises a plurality of computer entities (for example workstations, servers, printers and data storage), which are interconnected by means of one or more communications links. A computer entity is able to transmit or receive data over a communications link. A common type of computer network is a so-called Local Area Network (LAN) in which various computer entities are connected over a particular locality (e.g. within a building or a group of buildings). So called Virtual LANs (VLANs) may be formed using intermediate devices, such as Ethernet switches. Typically the intermediate devices comprise a data processor and a plurality of ports which enable the segmentation of the overall network of computer entities. The switching function comprises receiving data at an input port and transferring that data to an output port. The computer entities are connected to respective intermediate devices and the intermediate devices are connected by way of physical communications links
By configuring the intermediate devices appropriately the various VLANs can be created. Such networks are more particularly known as Virtual Bridged Local Area Networks. It will be appreciated that a single intermediate device may provide a physical connection for members of different VLANs. The VLANs may be arranged in accordance with the Multiple Spanning Tree Protocol in IEEE 802. IQ (which is a standard
defining various aspects of VLANs). In such an arrangement each VLAN is determined by a spanning tree instance.
Advantageously use of a spanning tree topology avoids infinite cycling of data frames, which would overwhelm the network. Thus VLANs, which enable multiple spanning tree topologies to be spread simultaneously over the physical network, result in the physical links between individual networks being spread over all of the available physical links and so realising a high resource usage.
However the improvement in network operability introduced by the MSTP comes at the price of an added configuration burden for the network administrator, that is the need to define different active spanning trees that can optimally allocate traffic. We have realised that it would be desirable to define automatically a plurality of spanning trees and consequently derive parameters for the configuration of the standard MSTP in such a way that the spanning tree instances can be implemented with minimum manual intervention. The network administrator needs only then associate the VLANs to the automatically generated MST instances.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided a method of determining multiple spanning trees over a computer network, each spanning tree providing a particular arrangement of communication links between the nodes of the computer network, and the method comprising increasing a cost associated with using a particular communications link if said communications link is included in a previously determined spanning tree.
In a highly preferred embodiment of the invention there is provided a method to define automatically a set of multiple spanning tree instances to
allow automatic re-routing of traffic in the presence of a fault and to allow good traffic distribution over all the available resources of the network. The method is practical in the sense that it comprises a computationally simple algorithm and does not offer a mathematically optimal solution.
According to a second aspect of the invention there is provided apparatus for determining multiple spanning tree instances over a computer network, each spanning tree providing a particular arrangement of communication links between the nodes of the computer network, and the apparatus being configured to increase a cost associated with using a particular communications link if said communications link is included in a previously determined spanning tree.
BRIEF DESCRIPTION OF THE DRAWINGS
Various embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:
Figure 1 is a schematic representation of a network topology comprising Local Area Networks (LANs) and bridging equipment between the LANs,
Figure 2 is a schematic representation of a first determined spanning tree configuration which represents a first Virtual Local Area Network (VLAN), and
Figure 3 is a schematic representation of a second determined spanning tree configuration which represents a second VLAN.
DESCRIPTION OF VARIOUS EXEMPLARY EMBODIMENTS OF THE INVENTION
With reference to Figure 1 there is shown a network comprising a plurality of Local Area Networks (LANs) 200, 201 , 202, 203 and 204, which connected by way of four Ethernet bridges 100, 101 , 102 and 103. The LANs provide communications links between the Ethernet bridges. Each of the Ethernet bridges has connected thereto one or more computer entities (not illustrated). It is desired to determine a plurality of Virtual Bridged Local Area Networks over the network 1 by way of an initial set-up procedure. It will be appreciated that at least some of the computer entities connected to different Ethernet bridges will be members of the same VLAN.
The description of the procedure which follows is in the form of high level steps including initialisation (Init), iteration (Iteration) and termination (Term) phases.
Step 1 (Init) Initially, the physical topology is defined, with bridges and the LANs connecting the bridges. The LANs are attributed a cost that should reflect the desired LAN utilisation. Cost assignment could be related with the guidelines provided by the relevant IEEE standard, where high capacity LANs have lower costs to encourage their usage. Cost assignment is however an administrative matter and may be achieved on numerous different bases. However a suggested formula is
Zb1, where the cost c, of the z'-th LAN is given by an appropriate constant hi divided by the LAN bandwidth capacity b,.
Step 2 (Init) Then, a known minimal cost spanning tree algorithm (such as Prim's or Kruskal' s algorithm) is run to find a first spanning tree. More sophisticated algorithms can be used to find Minimum Diameter Spanning Trees (MDST) if a higher computational complexity is acceptable. Once
the algorithm is chosen, the spanning tree depends on the administrative costs assigned in Step 1. This spanning tree has a total cost that is a function of the sum of the costs of the LANs, assigned in Step 1.
Step 3 (Iteration) The cost of each LAN is replaced with a value that is a function of both its initial cost and the number of found spanning trees that include that LAN. This function should still encourage the usage of high capacity LANs, and at the same time favour the LANs that are covered by the least number of spanning trees. This will allow an even number of spanning trees to be spread over the entire topology. The details of the costs function can be again an administrative matter and may vary according to the policy of traffic allocation. However, an example formula is suggested below. Reasonable functions should be monotonic, in that they always increase or leave unchanged the costs of the LANs: if a LAN was used by some spanning tree in the previous iteration its cost increases, otherwise it remains unchanged.
Step 4 (Iteration) The same minimal cost spanning tree algorithm as used in Step 2 is run on the topology with the new costs computed in Step 3. At the j-th iteration the (j+l)-th spanning tree is found (as the first is the result of Step 2 during init phase). This spanning tree has a total cost that is function of the costs computed in Step 3. The monotonic property of the cost function of Step 3 implies that also the total cost of subsequent spanning trees increases progressively: the cost of the (j+l)-th spanning tree is higher than the cost of the j-th spanning tree.
Step 5 (Term) If the cost of the (j+l)-th spanning tree is "much higher" than the cost of j-th one, it means that the last spanning tree is using: either (i) low capacity LANs or (ii) LANs that are already loaded with several spanning trees therefore its contribution would not bring meaningful improvements to the traffic load, the iteration can be
terminated and the last spanning tree discarded. As noted above, "much higher" is a condition to be defined according to the needs of a specific situation. Terminating earlier (a low value for "much higher") will produce a lower number of spanning trees, that means lower configuration load and coarser load balancing. On the contrary, a "very much higher" cost will lead to a higher number of spanning trees, with higher configuration complexity, but the opportunity for a finer traffic distribution. According to the MSTP standard, the procedure must terminate in any case when 64 spanning trees are produced.
After the completion of the above procedure, a collection of spanning trees is produced with enough routing diversity/choices to allow a convenient traffic distribution/balancing of the VLANs over the network topology. The above procedure defines trees, in terms of all the bridges of the physical topology and - a subset of the LANs of the physical topology.
(Appropriate parameters for each MSTI (MST protocol instance) to be used by the IEEE standard protocols must be derived.)
The network operator is then able to manually assign each spanning tree instance to form a VLAN.
An example of a formula to appropriately increase LAN costs at each iteration as needed in Step 3 is the following:
C1J = (max_cost!- min_cost1) . (n1}/ max_n)ιnst-curv where:
Cij is the cost of the z'-th LAN at they-th iteration, max cost, is the maximum cost related to the bandwidth of the z'-th LAN,
min costi is the minimum cost related to the bandwidth of the z'-th LAN, tiij is the number of spanning trees using LAN i at iteration j, max n is the maximum number of spanning trees (that is 64 for MSTP), inst curv is the curvature of the cost curve on n,y basis (eg if equal to 1 it's linear).
With reference to Figures 2 and 3 there are shown two possible VLANs, each of which corresponds to a calculated spanning tree instance.
It will be appreciated that in practice the network administrator will use a data processor to determine the various spanning tree instances. The administrator will have specified to the data processor an indication of what is an acceptable maximum cost so that no further spanning tree instances are to be determined. The administrator would then be able to
(remotely) configure each of the Ethernet switches to complement the various VLANs.
Claims
1. A method of determining multiple spanning trees over a computer network, each spanning tree providing a particular arrangement of communication links between nodes of the computer network, and the method comprising increasing a cost associated with using a particular communications link if said communications link is included in a previously determined spanning tree.
2. A method as claimed in claim 1 comprising determining the increase of the cost as a function of the number of previously determined spanning trees which include the communications link.
3. A method as claimed in claim 1 or claim 2 in which if the particular communications link is not included in a previously determined spanning tree its cost is unchanged.
4. A method as claimed in any preceding claim comprising determining the cost of the particular communications link in accordance with the formula:
C1J = (max_cost!- min_cost1) . (n1}/ max_n)ιnst-curv where:
Cij is the cost of the z'-th link at they'-th iteration, max costi is the maximum cost related to the bandwidth of the z'-th link, min costi is the minimum cost related to the bandwidth of the z'-th link, tiij is the number of spanning trees using link i at iteration^', max n is the maximum number of spanning trees (that is 64 for MSTP), inst curv is the curvature of the cost curve on n,y basis (eg if equal to 1 it's linear).
5. A method for configuring connections between a plurality of switching devices comprising the method of any of claims 1 to 4.
6. Apparatus for determining multiple spanning tree instances over a computer network, each spanning tree providing a particular arrangement of communication links between nodes of the computer network, and the apparatus being configured to increase a cost associated with using a particular communications link if said communications link is included in a previously determined spanning tree.
7. A method of determining multiple spanning trees substantially as herein described with reference to the accompanying drawings.
8. Apparatus for determining multiple spanning trees substantially as described herein.
Priority Applications (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2010503360A JP2010525638A (en) | 2007-04-19 | 2007-04-19 | Method and apparatus for determination of multiple spanning trees |
| PCT/EP2007/053813 WO2008128564A1 (en) | 2007-04-19 | 2007-04-19 | Method and apparatus for the determination of multiple spanning trees |
| EP07728275A EP2137904A1 (en) | 2007-04-19 | 2007-04-19 | Method and apparatus for the determination of multiple spanning trees |
| US12/596,436 US20100118739A1 (en) | 2007-04-19 | 2007-04-19 | Method and Apparatus for the Determination of Multiple Spanning Trees |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/EP2007/053813 WO2008128564A1 (en) | 2007-04-19 | 2007-04-19 | Method and apparatus for the determination of multiple spanning trees |
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| Publication Number | Publication Date |
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| WO2008128564A1 true WO2008128564A1 (en) | 2008-10-30 |
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| PCT/EP2007/053813 WO2008128564A1 (en) | 2007-04-19 | 2007-04-19 | Method and apparatus for the determination of multiple spanning trees |
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|---|---|
| US (1) | US20100118739A1 (en) |
| EP (1) | EP2137904A1 (en) |
| JP (1) | JP2010525638A (en) |
| WO (1) | WO2008128564A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP5598474B2 (en) * | 2009-08-26 | 2014-10-01 | 日本電気株式会社 | Network design system, network design method, data transfer route determination method, network design program |
| JP5598475B2 (en) * | 2009-08-26 | 2014-10-01 | 日本電気株式会社 | Network operation system, network operation method, and network operation program |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20090257365A1 (en) * | 2008-04-11 | 2009-10-15 | Tae In Hwang | Method of distributing files over network |
| US10581738B2 (en) * | 2018-01-19 | 2020-03-03 | Cisco Technology, Inc. | Efficient inter-VLAN routing in openflow networks |
Citations (1)
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|---|---|---|---|---|
| US20030005149A1 (en) * | 2001-04-25 | 2003-01-02 | Haas Zygmunt J. | Independent-tree ad hoc multicast routing |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE9704784L (en) * | 1997-12-19 | 1999-06-20 | Ericsson Telefon Ab L M | Method and apparatus in a packet switching network |
| US6937576B1 (en) * | 2000-10-17 | 2005-08-30 | Cisco Technology, Inc. | Multiple instance spanning tree protocol |
| JP3956741B2 (en) * | 2002-03-29 | 2007-08-08 | 富士通株式会社 | Multiple spanning tree protocol processing module and multiple spanning tree setting method |
| US7246172B2 (en) * | 2003-06-06 | 2007-07-17 | Matsushita Electric Industrial Co., Ltd. | Static dense multicast path and bandwidth management |
| US7646733B2 (en) * | 2005-09-16 | 2010-01-12 | Cisco Technology, Inc. | System and method for generating symmetrical spanning trees |
-
2007
- 2007-04-19 EP EP07728275A patent/EP2137904A1/en not_active Withdrawn
- 2007-04-19 WO PCT/EP2007/053813 patent/WO2008128564A1/en active Application Filing
- 2007-04-19 US US12/596,436 patent/US20100118739A1/en not_active Abandoned
- 2007-04-19 JP JP2010503360A patent/JP2010525638A/en active Pending
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20030005149A1 (en) * | 2001-04-25 | 2003-01-02 | Haas Zygmunt J. | Independent-tree ad hoc multicast routing |
Non-Patent Citations (1)
| Title |
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| FARKAS J ET AL: "Distributed resilient architecture for ethernet networks", DESIGN OF RELIABLE COMMUNICATION NETWORKS, 2005. (DRCN 2005). PROCEEDINGS.5TH INTERNATIONAL WORKSHOP ON ISLAND OF ISCHIA, ITALY OCT. 16-19, 2005, PISCATAWAY, NJ, USA,IEEE, 16 October 2005 (2005-10-16), pages 515 - 522, XP010868609, ISBN: 0-7803-9439-9 * |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP5598474B2 (en) * | 2009-08-26 | 2014-10-01 | 日本電気株式会社 | Network design system, network design method, data transfer route determination method, network design program |
| JP5598475B2 (en) * | 2009-08-26 | 2014-10-01 | 日本電気株式会社 | Network operation system, network operation method, and network operation program |
| US9197534B2 (en) | 2009-08-26 | 2015-11-24 | Nec Corporation | Network designing system, network designing method, data transfer path determination method and network designing program |
| US9210069B2 (en) | 2009-08-26 | 2015-12-08 | Nec Corporation | Network operation system, network operation method and network operation program |
Also Published As
| Publication number | Publication date |
|---|---|
| JP2010525638A (en) | 2010-07-22 |
| EP2137904A1 (en) | 2009-12-30 |
| US20100118739A1 (en) | 2010-05-13 |
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