ALLOCATING COMMUNICATION TRAFFIC

Abstract: Communication traffic is allocated through a network of interconnected nodes (103). A communication path may be established between terminals (101) via a plurality of routes. Parameters are processed for portions of a set of potential routes to determine a notional cost of using each of these routes. An optimal level of traffic is identified for each route portion and a parameter (such as notional route length) is adjusted to make the use of said route more costly if the traffic for that portion exceeds said notional value and, in addition, if said traffic for said portion falls below said optimum value. A route is then selected with reference to route cost comparisons.

Description: ALLOCATING COMMUNICATION TRAFFIC The present invention relates to allocating communication traffic through a network of interconnected nodes. Introduction In data communications and telecommunications environments, greater demands are being made for dedicated data links. Communication paths may be established between remote sites by a dedicated physical communications channel although, in the majority of circumstances, the provision of such a channel would be prohibitively expensive. Dedicated communication channels are also provided by effectively sharing resources within a networked environment. A service provider will establish a network of this type and, for each customer, the provider will guarantee a communication path of a specified bandwidth through the network. As new customers subscribe to the service, the number of paths required through the network will increase and further requirements may be placed on the network as customer traffic demands also increase. It is therefore to the advantage of the network provider to configure a network which will satisfy all customer demands while at the same time optimising the allocation of hardware within the network itself. Systems are known in which route selection is made on the basis of notional costs incurred for implementing a particular route from a plurality of possible routes. Costing of this type tends to be made on the basis that it is undesirable for a particular route portion to become saturated, particularly if other regions within the network are being under-utilized. It is therefore known to increase the notional costs of using a particular route (possibly increasing a notional parameter relating to the portion length) as the amount of traffic using the particular portion increases. However, such an approach assumes that the cost of using a particular route will only increase as traffic usage increases. Thus, an analysis of this type tends to suggest that the most efficient route is one in which no actual traffic is being conveyed at all. This is clearly inconsistent with the practical reality, therefore it can be appreciated that existing models for modifying notional route costs are somewhat flawed. Summary of the Invention According to a first aspect of the present invention, there is provided a method of allocating communication traffic through a network of interconnected nodes, wherein a communications path may be established between terminals via a plurality of routes, comprising steps of processing parameters of portions of a set of potential routes to determine a notional cost of using each of said potential routes; identifying an optimal level of traffic for a route portion; adjusting a parameter to make said route portion more costly if the traffic for that portion exceeds said optimal value; adjusting a parameter to make said route portion more expensive if said traffic for said portion falls below said optimal value; and selecting a particular route with reference to route cost compaπsoπs. In a preferred embodiment, the cost of using a route is measured in terms of its notional length. Preferably, route portions are made more costly by increasing their respective notional length. According to a second aspect of the present invention, there is provided apparatus for allocating communication traffic through a network of interconnecting nodes, wherein a communication path may be established between terminals via a plurality of routes, compπsing processing means for processing parameters for portions of a set of potential routes to determine a notional cost of using each of said potential routes, identifying means for identifying an optimal level of traffic for the route portion; adjusting means for adjusting a parameter to make said route portion more costly if the traffic for that portion exceeds said optimal value and to make said route portion more costly if said traffic for said portion falls below said optimum value; and selecting means for selecting a particular route with reference to route cost compaπsons. Brief Description of the Drawings Figure 1 shows two customer sites interconnected via a distributed network; Figure 2 illustrates procedures for selecting a particular route, including a process for costing route portions; Figure 3 illustrates the effect of particular nodes becoming saturated relative to other nodes; Figure 4 illustrates an interactive approach towards network route selection optimization; Figures 5A, 5B and 5C illustrate relationship models of unit cost shown against traffic density; Figure 6A shows a model adopted by the present invention of unit cost against traffic density and Figure 6B illustrates a similar model for cumulative cost with respect to traffic density; Figures 7A and 7B illustrate model extremes for the relationship illustrated in Figure 6B; and Figure 8 details the route-portion costing-process identified in Figure 2, as embodied by the present invention. Detailed Description of the Preferred Embodiments The invention will now be described by way of example only with reference to the drawings identified previously. A communication environment is shown in Figure 1 in which a first customer, illustrated generally at 101 communicates with a second customer, illustrated generally at 102, via a communications network 103. A network provider, responsible for the network 103, has guaranteed a communication channel between the first customer 101 and the second customer 102 of a predetermined bandwidth. In this particular network, bandwidth is allocated as digital communication channels capable of conveying 64 kilobits per second. Multiple channels of this type may be allocated to customers, thereby providing them with effectively any degree of bandwidth in multiples of 64 kilobits per second. Within the network itself, 64 kilobit channels are multiplexed for transmission at 2 megabits per second and again multiple transmission paths may be provided so as to increase transmission bandwidth where required. The network is configured from a plurality of transmission paths, interconnected by a plurality of switching nodes. At each node switching devices are arranged to receive two megabit per second multiplexes, whereupon time switching within the multiplex and space switching to other multiplexes are provided. The topology of the network is such that it is possible for a plurality of routes to be taken for a particular logical communication channel to be established through the network. Customer 101 has two processing environments with computers being arranged to transmit and receive data through a multiplexing device 104. Each workstation includes a processing device 105, a visual display unit 106 and a manually operable keyboard 107, in addition to other input/output devices as required. Data from the multiplexing device 104 is supplied over a transmission line 108 to a first node 110 within the network. In this example, it may be assumed that transmission line 108 is capable of conveying two 64 kilobit per second data streams and additional data streams are received at node 110 in order to generate efficient 2 megabit transmission multiplexes. A network, similar to network 103, could cover a large geographical area, possibly a whole country, with a total number of possible routes through the network being of the order of 100,000. Network 103, made up of nodes 110, 111 , 112, 113, 114, 115, 116, 117 and 118 is a relatively small network and is shown as an example of network structure in general. Communication paths between nodes convey a plurality of multiplexed channels where each channel within the path may be considered as a route portion, making up a constituent piece of the route as a whole. Similarly, transmission through the nodes may be considered as route portions, with each route portion used for a particular route requiring a finite level of network resource. The aforesaid nodes may be considered as being connected by route portions 120, 121 , 122, 123, 124, 125, 126, 127, 128, 129, 130 and 131. Thus, node 110 may communicate with node 118, to allow customers 101 and 102 to communicate, via a path consisting of link 120, node 111 , link 121 , node 112, link 124, node 115, link 129 and node 118. Altematively, a path may be provided by a link 122, node 113, link 125, node 114, link 128, node 117 and link 131 etc. Thus, for any particular communication nodes, a plurality of routes exist through the network and this plurality of all possible routes may be reduced to a set of practical routes from which a particular selection is made for a specific data transfer. The network shown in Figure 103 may be established as a circuit switched network in which a physical communication channel is established for each particular transmission session. Altematively, the network may operate as a packet-switched network in which data generated by a source customer is transmitted as data packets, including destination headers, wherein said headers are read for each particular packet to determine a particular transmission path for that specific packet. When the network is required to convey additional traffic, decisions must be made either once when the channel is established, on a per session basis as the channel is used, or on a per packet basis for each transmitted packet, to identify a preferred transmission route through the network. Selection is made by identifying a set of possible routes, calculating notional costs for each identified route and selecting the route which involves the least cost. A procedure for making a selection of this type is illustrated in Figure 2. At step 201 a set of possible routes is identified and at step 202 a particular route from said identified set is selected. At step 203 a route portion is selected and at step 204 a cost is determined for the particular portion selected at step 203. At step 205 a question is asked as to whether another route portion is to be considered for the selected route and if answered in the affirmative control is retumed to step 203. When the question asked at step 205 is answered in the negative, control is directed to step 206. At step 206 the portion costs for a particular route determined at step 204 are combined to produce a total cost for the selected route. A question is then asked at step 207 as to whether another route is to be considered and when answered in the affirmative control is retumed to step 202. Eventually, all of the routes will have been considered resulting in the question asked at step 207 being answered in the negative and control being directed to step 208. At step 208 the combined portion costs calculated at step 206 for each of the identified routes are compared and from this comparison a best route is determined, based upon the route which has the lowest resulting overall cost. The costing of routes will tend to be based upon static cost estimates, that is to say the marginal cost for placing an additional communication channel through a particular route portion will remain constant irrespective upon the total route loading. This will tend to result in some nodes conveying substantially more traffic than other nodes. This situation is illustrated in Figure 3 which diagrammatically represents the network 103 as shown in Figure 1. In the example shown in Figure 3, the size of each node has been represented in proportion to the amount of traffic conveyed. Thus, as can be seen from Figure 3, central node 314 will tend to convey more traffic than its surrounding nodes, such as the comer nodes 316 and 312. Such a situation will result in non-ideal utilization of nodal hardware which in turn may lead to overall system inefficiencies. Thus, it should be possible to analyze traffic requirements so as to optimize use of an existing network and also to optimize the upgrading of the network as increased demands are made for traffic capacity. A procedure for optimizing the routing of new traffic through an existing network is illustrated in Figure 4. The network shown in Figure 1 is illustrated at 403. A processing system 404 is provided and arranged to receive information 405 defining the network topology and information 406 relating to observations concerning levels of traffic present within the network. The input information 405 and 406 is processed within the processing environment 404 to produce routing control information to a routing control processor 407. The routing control processor 407 controls the routing of traffic through network 403, as illustrated by feedback loop 408. Thus, the effects of routing control will be reflected in new traffic observation data 406 which in turn will feed through into the processing environment 404. Similarly, if modifications are made to the overall network topology, such modifications will feed through to the network topology data 405. In order for the processing environment 404 to supply meaningful infoπnation to the routing control processor 407, it is necessary for the processing environment 404 to be provided with a model as to how routing control should be affected in response to variations in communication traffic. Routing selection is made in accordance with the procedure shown in Figure 2 in which route portions are costed. In order to introduce route selection on the basis of traffic levels, traffic level information is introduced by modifying route-portion costs in response to traffic density. A first model is illustrated in Figure 5A, in which routing efficiency is assumed to be totally independent of conveyed traffic. Thus, as traffic levels increase the cost per additional unit of traffic remains constant and no modifications are made to routing control in response to a measure of traffic density. Experience has shown that the model shown in Figure 5A does not represent a realistic representation of the relationship between unit cost and traffic density. An alternative model is shown in Figure 5B in which the unit cost is initially relatively constant for a significant period, whereafter the unit cost rises sharply as the portion under consideration starts to saturate. This model is used extensively in routing control systems and is pπmaπly designed to ensure that no network portion becomes so overioaded that it may result in traffic being lost. However, the model assumes that while traffic density is relatively low, the unit cost of traffic transmission does not vary. An alternative model is shown in Figure 5C. In this model the cost per unit starts off being relatively high, representing a situation in which expensive network hardware has been installed for a relatively low level of communications traffic. Consequently, under such circumstances, the real cost per unit of traffic is relatively high, given that the transmission is occurring within a relatively inefficient environment. The model shown in Figure 5B will tend to be adopted when real-time decisions are being made to identify a particular route for a particular data transmission. Within dial-up environments, such a model may be particulariy useful, particulariy given the relatively high level of meshing within such environments, that is to say, many possible paths exist for connecting a source to a destination. A model shown in Figure 5C is useful when considering how actual provision is to be made within a network in order to satisfy customer demand. This situation arises more in dedicated networks where the levei of traffic flow tends to be relatively constant over significant periods of time and a plurality of customers are effectively sharing a resource in order to obtain maximum benefit from it. Under these circumstances, it is highly undesirable for a system resource to be conveying a relatively low level of traffic given that, in many situations, this resource could be used elsewhere to improve the overall perceived capacity of the network. In the present embodiment a communications path may be established between temninals via a plurality of routes. Parameters for portions of a set of potential routes are processed to determine notional costs of using each of the said potential routes. An optimal level of traffic for a route portion is identified which usually will often include a range of optimum levels. Outside these levels, a parameter is adjusted in order to make the route portion more costly. Thus, the parameter is adjusted in order to make the route portion more costly if the traffic for that portion exceeds the optimal value or range of optimal values. This is consistent with the model shown in Figure 5B which will endeavour to make the route portion appear more costly as traffic density increases in order to avoid the portion becoming saturated. However, in addition, a parameter, possibly the same parameter, is also adjusted to make the route portion appear more costly if the traffic for said portion falls below the optimum value or range of optimal values. This constraint is consistent with the model shown in Figure 5C in which the unit cost becomes large if the traffic density is very small. With the costings adjusted in this way, a selection of a particular route is made with reference to route cost comparisons. The resulting new model is shown in Figure 6A in which cost per unit of transmission is shown with respect to traffic density. As shown in Figure 6A there is an optimum position where, for the optimal traffic density, the unit cost is minimized. Consequently, the unit cost is increased if traffic density is reduced or increased beyond the optimal value. This relationship may be considered with reference to cumulative costs, as illustrated in Figure 6B. A curve showing cumulative cost against traffic density will initially have a relatively steep gradient, derived from the relatively high unit cost at low traffic densities. As the traffic density increases, the rate of cost increase will decrease with the optimum value lying within the region of inflection where the cumulative cost is relatively flat. Thereafter, the cumulative cost will rise sharply again as the unit cost becomes large for high traffic densities. The procedure for selecting routes in response to cumulative costs will result in traffic being directed such that the traffic density will be directed towards the flat portion of the curve shown in Figure 6B. In practice, this will result in a concentration of traffic on to efficient links, with inefficient links being provided with additional capacity as they tend to start saturating and with inefficient links conveying low traffic densities being removed from the network, provided that an alternative route can be identified, as would normally be the case. Thus, the network will tend to evolve in response to customer demands with optimal efficient use being made of the network investment. The example shown in Figure 6B represents a moderate relationship between cumulative costs and traffic density. Under some circumstances the shape of the curve shown in Figure 6B will look different, as illustrated in Figures 7A and 7B. In Figure 7A the emphases has been placed on high costs for low traffic densities. Consequently, the cumulative cost rises sharply and then tends to reach a plateau, representing a relatively large optimal range. In Figure 7B the dominant effect is due to high costs for high traffic densities. At low densities the cumulative cost rises moderately up towards an optimal range, whereafter, beyond said range, the cumulative cost rises relatively sharply. The adoption of a preferred model, such as the model illustrated in Figures 6B, 7A and 7B will depend upon dynamic constraints in addition to static topological constraints. Thus, the model will change as traffic demand changes for the network as a whole. Thus, an optimal model will change whether absolute traffic flows are being considered for a portion or whether traffic through this portion is being considered relatively to traffic elsewhere. It is therefore possible to provide a plurality of models such that appropriate model data may be selected in response to identified conditions. The model itself may be calculated, possibly as a polynomial spline or altematively values may be derived from a look-up table. In a further level of sophistication, it is possible for intermediate responses to be generated by inteφolating between precalculated or prestored model responses. Process 204 for costing a particular route portion is detailed in Figure 8. At step 801 a value representing the required additional traffic is added to a value representing the amount of traffic presently being conveyed by the portion under consideration. At step 802 an assessment is made as to the particular cost curve required in order to obtain an optimal measure of the marginal cost. As previously stated, this may consist of selecting data or inteφolating between calculated or selected data. At step 803 the marginal cost for the proposed additional traffic is calculated, with reference to the response model selected at step 802. So far, measurements and costs have been referred to in the abstract and it will be appreciated that many factors may be involved when determining an actual cost, so that costs may be compared meaningfully between different route portions. Cost is often measured in terms of route length, which provides a highly representative measurement, particularly if a similar technology is being used for the transmission of data over each of the route portions. By costing route portions in terms of their lengths, it is then possible to effectively modify notional lengths in order to increase or decrease the cost of using that route. It is then possible to implement known procedures for identifying a best route based on the shortest path between nodes. Such an approach may be particulariy attractive in many environments, whereby the need for finding all possible routes may be avoided, thereby improving the requirement processing capacity. It can be seen that the new procedure has two significant benefits. Firstly, it allows an optimized route to be selected for new traffic to be conveyed within an existing network. Furthermore, it also allows information to be derived as to where new network investment should be made in terms of providing additional transmission capacity for particular sections of the network.

Claims: Claims 1. A method of allocating communication traffic through a network of interconnected nodes, wherein a communications path may be established between terminals via a plurality of routes, comprising steps of processing parameters for portions of a set of potential routes to determine a notional cost of using each of said potential routes; identifying an optimal level of traffic for a route portion; adjusting a parameter to make said route portion more costly if the traffic for that portion exceeds said optimal value; adjusting a parameter to make said route portion more costly if said traffic for said portion falls below said optimal value; and selecting a particular route with reference to route cost comparisons. 2. A method according to claim 1 , wherein the cost of using a route is measured in terms of its notional length. 3. A method according to claim 2, wherein route portions are made more costly by increasing their respective notional lengths. 4. A method according to any of claims 1 to 3, wherein said set of potential routes is derived from a set of all possible routes. 5. A method according to Claim 4, wherein a route is selected from the set of possible routes and a cost value is derived for each route portion of said route. 6. A method according to Claim 5, wherein said cost portions are combined to give a cost value for the route. 7. Apparatus for allocating communication traffic through a network of interconnected nodes, wherein a communication path may be established between terminals via a plurality of routes, comprising processing means for processing parameters for portions of a set of potential routes to determine a notional cost of using each of said potential routes; identifying means for identifying an optimal level of traffic for a route portion; adjusting means for adjusting a parameter to make said route portion more costly if the traffic for that portion exceeds said optimal value and to make said route portion more costly if said traffic for said portion fails below said optimum value; and selecting means for selecting a particular route with reference to route cost comparisons. 8. Apparatus according to claim 7, wherein said processing means is arranged to determine route costs with reference to notional lengths of respective route portions. 9. Apparatus according to claim 8, wherein said processing means is arranged to make said route portions more costly by increasing their notional lengths. 10. Apparatus according to any of claims 7 to 9, wherein said processing means is arranged to select a set of potential routes derived from a set of all possible routes. 11. Apparatus according to Claim 10, wherein said processing means is arranged to select a route from the set of possible routes and to derive a cost value for each route portion of said route. 12. Apparatus according to Claim 11 , wherein said processing means is arranged to combine cost portions to give a cost value for a complete route.

Inventors: JOHNSON DAVID, JOHNSON, DAVID
Applicants: BRITISH TELECOMM, JOHNSON DAVID, BRITISH TELECOMMUNICATIONS PLC, JOHNSON, DAVID
Application year: 1997
Main classification: H04L12
IPC codes: H04L12, H04Q3