WO2004112322A1

WO2004112322A1 - Method for the use of parallel links in packet-oriented networks with multipath routing

Info

Publication number: WO2004112322A1
Application number: PCT/EP2004/051129
Authority: WO
Inventors: Gero Schollmeier; Christian Winkler
Original assignee: Siemens Aktiengesellschaft
Priority date: 2003-06-18
Filing date: 2004-06-16
Publication date: 2004-12-23

Abstract

The invention relates to a method for the use of parallel links in a packet-oriented network with multipath routing. According to said method, the parallel links are treated as one (logical) link on fixing a distributed line and as multiple logical links on an error reaction. It can thus be guaranteed that the determination of paths through the network can be disjunctive and on a drop-out of one of the parallel links the others may be used for the distribution of the load.

Description

description

Procedure for using parallel links in packet-oriented networks with multi-way routing

The invention relates to a method for using parallel links in a packet-oriented network with multipath routing formed with nodes and links.

The improvement or optimization of packet-oriented networks, especially with regard to real-time traffic, is currently an important field of work for switching technicians, network specialists and Internet experts.

Currently, intensive work is being carried out on packet-oriented networks and in particular the Internet based on the Internet protocol (IP) for the transmission of real-time traffic, such as. B. to further develop voice or video data. For the acceptance of a real-time service by the service user, it is crucial that certain so-called quality of service characteristics can be adhered to. In English, the term "Quality of Service" - QoS for short - is common for this property. In addition to approaches to strict control of the bandwidth used by the user, for example by means of path switching (MPLS: Multi Protocol Label Switching) in connection with bandwidth reservations ( RSVP: Resource Reservation Protocol) there are complementary or alternative efforts to improve the functioning of the conventional Internet.

In the conventional Internet, routing takes place within network domains or autonomous systems, for example using the OSPF (Open Shortest Path First) protocol. A metric, ie fixed routing criteria, is usually used to determine an optimal path for packets routed through the routing domain, and the routing tables of the individual nodes of the network in accordance with these determined paths (often using so-called link-state messages as part of linked-state routing). In a routing table there is then usually an address for the next hop or the next station or the next for a specific destination, which is given by the destination address of the packet

Jump assigned. A router that receives a packet evaluates the address destination information integrated in the packet header, determines the address for the next hop and forwards the packet to the corresponding router or node. In this way, the packets are conveyed hop-by-hop through the network or the routing domain.

An important approach to improve routing within packet-oriented networks is the so-called multipath routing, which is often also referred to as "multipath routing". It is intended to send packets along two or more paths within a routing domain to a destination. Multipath routing brings This is an important improvement on conventional routing in two respects: On the one hand, the distribution of packets in several different ways can achieve a better and more efficient utilization of the network, the bottlenecks that often occur due to uneven loads, which lead to delays and discarding of packets on the other hand, multi-way routing can also be used for a quick reaction to faults or failures within the network. In normal operation, a node distributes the traffic towards a destination evenly or according to a certain distribution weight on the available compartments. A path fan is given by links starting from the node - also referred to as edges in the German-language literature - to which packets of a flow are distributed. If a link fails, the node removes the affected route from the route fan and redistributes the traffic accordingly over the remaining routes. For quality traffic, an acceptance check with suitably calculated acceptance thresholds can ensure that there is only so much quality traffic in the network it is left that the way fan remaining after an error can actually carry this traffic. The network thus offers a planned reserve, which takes over the traffic in the event of a fault while maintaining the promised quality of service (and which can be used in normal operation by lower priority traffic classes - eg best effort traffic).

For IP networks, the second version of the OSPF protocol (see RFCs 2328, 2178, 1583, 1247, 1131) intended to transport protocols along several paths that have the same length in terms of a metric. This protocol extension is known in the trade under the acronym ECMP (Equal Cost Multi Path). Within the framework of this concept there is an equal distribution on the different routes, which is also suggested by the same length or the same costs.

The object of the invention is to improve multi-way routing within packet-oriented networks.

The invention is solved by claim 1.

A packet-based network with multi-way routing is assumed, the nodes of which are usually available route alternatives or distribution compartments for the distribution of traffic. As far as possible, the route alternatives (specifically the "next hops") for a node should be determined in such a way that they use disjoint links via different neighboring nodes in order to ensure a low susceptibility to interference.

Now, in practical networks, there are often parallel links between neighboring nodes that are coupled, for example, to increase capacity, i.e. operate logically like a link with a correspondingly higher capacity (the parallel links of a distribution subject are also referred to below as bundles net). This can be, for example, multiple physical links or multiple wavelengths in a WDM system (WDM: Wave Length Division Multiplexing) or multiple channels in a TDM system (TDM: Time Division Multiplexing).

The invention is based on the finding that bundled links in the course of the definition of route compartments for a multi-way routing should not be included individually like normal links in the route compartments and its traffic distribution, because they usually do not offer the disjointness required for failure protection (the reason is that parallel "links" are often routed along the same route, with WDM even over the same fiber. They also end at the same neighboring node, ie the failure of a node affects all links of a bundle).

It is therefore proposed according to the invention to treat links of a bundle as a link for determining a route fan for distributing packets.

The advantage of the specified invention is that parallel links, which are often used in networks to increase capacity, can be operated as a bundle by this method, and yet mechanisms for increasing reliability, which are based on the existence of (disjoint) alternative routes, can be used.

According to an advantageous further development, links of a bundle in the case of error reactions (e.g. fast rerouting of packets, redefinition of distribution weights, redefinition of limits for a traffic control-related admissibility check) are separated, i.e. treated as different links.

The further training has a positive effect, for example, in the event of error reactions based on a redefinition of traffic distributions weights and / or based on acceptance thresholds for the admission of prioritized traffic in the network. The necessary scope for changing the distribution weights or reducing the permitted traffic also depends on whether packets will be distributed over the other links in the bundle if a link in the bundle breaks.

The following case should be noted in particular: It is technically possible that only one "link" or "channel" of such a bundle fails, e.g. if the laser diode fails for a certain wavelength in a WDM system. Connectivity is preserved in this case, but the usable capacity of the bundle is reduced. If a link in a bundle fails selectively, it is particularly beneficial if the other links in the bundle are treated as properly functioning links in the course of the error response. The extent of the traffic redistribution to be carried out as part of the error reaction is significantly reduced by the availability of the other links in the bundle.

In the case of multipath routing algorithms with a logical network view, which contains nodes and links, a treatment of parallel links according to the invention can also be described as follows:

The multipath routing algorithms calculate e.g. N disjoint "next-hops" for a node to a specific destination (N need not be the same for all nodes). According to the invention, it is proposed to have adjacent nodes at points with P which are to be operated as a bundle:

1. Pass the bundle as a single link between neighboring nodes in the logical network view to the multipath routing algorithms, so that they include this link and, in addition, NI to the bundle and disjoint links among themselves in the route compartments. 2. Then, however, to look at and operate the fan at this node with P + (NI) separate links for error detection and the local error reaction.

This fan then has more than N ways. The links are operated individually and individually subjected to error protection and reaction. If a single link in the bundle fails, the local error reaction can redistribute the traffic over the remaining (P + (N-I)) -1 routes.

Of course, all existing parallel links between two nodes do not have to be included in a particular bundle. So the operator can decide how many and which of the existing links should be included in the set P.

The existing algorithms for determining the traffic distribution weights and the acceptance thresholds can be applied to the logical network view of the multi-route route (bundle = one link) as well as to the physical network view (bundle = P separate links).

The method according to the invention can of course also be applied to several bundles in a node, e.g. P parallel links to neighboring nodes A and Q parallel links to neighboring nodes B. Each bundle P and Q then forms a link when defining the routing compartments.

The subject matter of the invention is explained in more detail below in the context of an exemplary embodiment with reference to figures. Show it:

Fig. 1: a network section with physical links, three of which run in parallel,

Fig. 2: the logical representation of the network section when determining distribution subjects, 3: the logical representation of a distribution fan intended for node A, and

4: the physical representation of the distribution fan from FIG. 3 intended for node A.

FIGS. 1 to 4 show an example of the treatment of parallel links according to the invention when determining distribution subjects. Figure 1 shows a section of a physical network, e.g. an IP (Internet protocol) network with three parallel links from node A to node C. FIG. 2 shows the logical network view transferred to the multipath routing algorithm for determining a distribution fan. The three parallel links are treated as a logical link when defining alternative routes or distribution subjects. This ensures that there are disjoint routes for routing. It is avoided that a distribution fan consists only of links of a bundle. This would e.g. if the destination node C of the parallel links fails, the consequence is that there are no longer any alternative routes within the distribution fan. Instead, the invention ensures that there are at least links to two different nodes in the distribution compartments.

The multipath routing algorithm may determine AN = 2 paths for nodes. Figure 3 then shows the logical distribution fan at node A. It contains two paths. In Figure 4 the logical view is mapped again to the physical one. Now the path fan from node A comprises four further "next hops" or next jumps, namely the three parallel links to C and the one link to D. In this example, all existing parallel links were included in the bundle with P = 3 If one of the three links fails, the remaining two are treated as still intact, as an alternative for the redistribution of traffic For example, it does this by changing the distribution weights for the intact links so that the traffic routed regularly via the failed link is redirected to the other links. As a rule, the node C for the three different parallel links is addressed by three different addresses (eg IP addresses).

Claims

claims

1. Method for the use of parallel links in a packet-oriented network with multipath routing formed with nodes and links, accordingly

- Two or more physically different parallel links are treated as a single link in the determination of a distribution fan for the distribution of data packets by a node in at least two different ways.

2. The method according to claim 1, characterized in that

- the parallel links are treated as separate links in the event of an error reaction.

3. The method according to claim 2, characterized in that

- the error caused by the failure of a network element, e.g. one of the parallel links is given.

4. The method according to any one of the preceding claims, characterized in that

- In the case of parallel links, the physical difference is given by spatial separation or by different electromagnetic carriers.

5. The method according to claim 4, characterized in that - the physically different parallel links are given by multiple physical links, multiple wavelengths in a WDM (Wave Length Division Multiplexing) system or multiple channels in a TDM (Time Division Multiplexing) system.

6. The method according to any one of the preceding claims, dadu rch ge mark ei chne t, since ss - If the traffic weights are readjusted as part of an error response, the physically different parallel links are treated separately.

7. The method according to any one of the preceding claims, characterized in that

- When redefining the limits for traffic within the network as part of an error response, the physically different parallel links are treated separately.

8. The method according to any one of the preceding claims, characterized in that

the method is applied to more than one bundle of parallel links leading away from the node.

9. Network node with means for performing a method according to one of the preceding claims.