With increasingly diverse QOS requirements, it is impractical to continue to rely on conventional routing paradigms that emphasize the search for an optimal path based on a predetermined metric, or a particular function of multiple metrics. Modern routing strategies must not only be adaptive to network changes but also offer considerable economy of scope. We consider the problem of routing in networks subject to QOS constraints. After providing an overview of prior routing work, we define various QOS constraints. We present a call architecture that may be used for QOS matching and a connection management mechanism for network resource allocation. We discuss fallback routing, and review some existing routing frameworks. We also present a new rule-based, call-by-call source routing strategy for integrated communication networks. >

Routing subject to quality of service constraints in integrated communication networks

A network management node (10) collects trunk loading data and switch congestion data from switches in a telecommunication system. Path loading vectors (52, 56,) constraint vector (66), and switch congestion vector (76) are calculated and compared to yield potential intermediate switch candidates having the lowest available, trunk traffic loading and switches with the lowest congestion consistent with other constraints associated with intermediate switch selection. Trunk groups with increasing levels of traffic and switches with increasing levels of congestion are incrementally tested in order to yield potential intermediate switch candidates whereby call distribution to the lightest loaded trunks and switches is accomplished.

Network call routing controlled by a management node

A dynamically controlled routing (DCR) telecommunications network is formed by a plurality of network switching elements, each connected to at least one other by at least one circuit group for carrying calls therebetween, and a network processor connected to the network elements by data links. Each network switching element determines, for each call, a neighboring network element to which it should be routed. It does so by accessing a routing table which contains alternate routes to be attempted if a direct route either does not exist or cannot be used. The routing tables are updated periodically by the network controller. The DCR network functions as a group of nodes interconnected by links and routing takes place on a node-to-node basis. At least one of the nodes is a logical entity which does not necessarily have a direct correspondence to a single physical network element but rather corresponds to a group of at least one physical component which may be a network element, a part of a network element, or a plurality of network elements or parts thereof. Likewise, a link to the virtual node does not necessarily correspond to a circuit group but comprises the set of direct circuit groups connecting to the components of the virtual node. DCR networks employing virtual nodes have increased flexibility. For example, final destinations outside the DCR network can be associated with the virtual node ifs an intermediate destination node, thereby allowing a call to exit the DCR network via any of the components of the virtual node rather than via only one Unique Exit Gateway.

Dynamically controlled routing using virtual nodes

An "Intelligent" telecommunications network comprises a plurality of switching units interconnected by links, and connected to a central computer unit by a data communication system. For dynamic routing of a call, a first switching unit responds to a destination address in a call to attempt a direct link to a neighbouring switching unit and, in the event that the attempt is unsuccessful, issues to the central computer unit a message containing the destination address. The central computer unit uses the destination address to identify the unsuccessful link; (ii) updates a routing database to identify the link as unavailable; (iii) determines an alternative route for the call using a tandem node and (iv) compiles a return message including a network address for a tandem switching unit and transmits it to the first switching unit. The latter attempts to route the call via a link to the tandem unit which attempts to complete the call by a direct link to the destination switching unit. The tandem node switching unit also queries the central computer if it cannot complete the call by a direct link to the destination switching unit, whereupon the central computer will set to zero the idleness of the direct link which the tandem unit attempted and then determine an alternate route from the tandem unit to the destination, i.e. with the idleness factors of both direct links set to zero, resulting in an alternate route having three links.

Dynamically controlled routing of calls in intelligent networks

Dynamic routing has been adopted in circuit-switched networks in many parts of the world. Most of the routing algorithms used are least loaded routing (LLR) based for its simplicity and efficiency. Rerouting is the practice of routing calls on alternate paths back to direct paths or to other less congested alternate paths. It allows the continuous redistribution of network loads for the relief of the congestion on direct paths. In this paper, we present an original analysis of an LLR-based rerouting scheme. Through numerical examples and confirmation by computer simulation, the throughput gain of rerouting is established.

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Analysis of rerouting in circuit-switched networks

Dynamic traffic management (DTM) is described. The overall system architecture and data flow, routing, and congestion control are addressed. The main design considerations are reviewed, focusing on the update cycle, protective allowance, multiple alternate routes, congestion-control thresholds, and algorithm extensions. The immediate benefits that automation and near-real-time responsiveness entail in traffic management are outlined. These lie in the areas of capital savings, traffic management automation, and trunk servicing. >

W.H. Cameron

Papers

State-dependent dynamic traffic management for telephone networks

Integrated network operations architecture and its application to network maintenance