This invention relates generally to multi-class digital networks and, in particular, to a multi-class digital network in which network functions are shared by a network control element and node control elements to ensure efficient utilization of network resources.
A multi-class digital network must accommodate traffic having different characteristics, quality of service (QOS) requirements, and transport modes. For example, a multi-class backbone network may be required to support both connection-based traffic and connectionless traffic. Further complication is traffic may include several classes differentiated by their characteristics and service requirements. The traffic classes may require different and possibly conflicting controls in order to satisfy service commitments and ensure acceptable service quality.
Asynchronous Transfer Mode (ATM) switching technology was developed to provide multi-service digital transport. It was assumed that ATM networks would provide the flexibility and quality of service required to satisfy the demand for digital services.
One disadvantage of ATM networks is that they are adapted to transport packets of only one size and format. Consequently, the packets of services which do not use ATM format must be deconstructed on admission to the ATM network by network edge devices and reconstructed by network edge devices on egress from the ATM network. This slows service delivery, increases computational requirements and complicates the structure and functionality of edge device interfaces.
The varying service requirements in a multi-class network are difficult to satisfy without traffic segregation and network partitioning. For example, certain services such as voice and video are somewhat loss tolerant but delay intolerant, while other services such as the exchange of data packets between computers are quite delay tolerant but completely loss intolerant. In accommodating such variations in service, a multi-service network naturally segregates into a plurality of layers or xe2x80x9cbandsxe2x80x9d which respectively serve the requirements of different types of traffic. This natural division of a network into service bands is well understood and has been widely discussed in the relevant literature.
A challenge in network management is designing network routing and admission controls to manage the service bands in a multi-class network to efficiently accommodate fluctuating service demands. It is well understood that while total network traffic may change relatively slowly over time, the traffic mix in a multi-class network may fluctuate rapidly and unpredictably. To date, efficient methods of accommodating rapid and unpredictable fluctuations in traffic service demand have eluded network designers and traffic managers. There therefore exists a need for a multi-service, multi-class digital network and methods for controlling the network which can accommodate the increasing demand for digital services without unreasonable investment in network infrastructure.
It an object of the invention to provide a multi-class digital network which includes a network control element for performing network-wide functions including network topology monitoring and computation and distribution of network traffic routing sets to network nodes in response to changes in network topology.
It is a further object of the invention to provide a multi-class digital network in which node control elements perform distributed traffic admission control, traffic routing and service-rate allocation for each class of service served by an egress link when traffic connections are set up through the egress link.
It is yet a further object of the invention to provide a multi-class digital network in which service-rate controllers are adapted to control egress on an egress link, the service-rate controller receiving service-rate allocations from associated node control elements.
It is yet a further object of the invention to provide a multi-class digital network wherein the network is a multi-service network adapted to transport digital packets that require different transport modes, each transport mode consisting of at least one transport protocol.
It is another object of the invention to provide a multi-class digital network wherein a network control element also performs network sizing computations which produce periodic specifications for inter-nodal link sizes.
The invention therefore provides a multi-class digital network, comprising:
a network control element which periodically receives network traffic and network state information from network nodes, the network control element performing at least the functions of:
a) network topology monitoring; and
b) computing and distributing network traffic routing sets to network nodes as required;
node control elements which perform at least the functions of:
a) traffic admission control;
b) connection routing; and
c) computation of a service rate allocation for a class served by an egress link when a new traffic connection is set up through the egress link; and
a service rate controller adapted to control egress on the egress link, the service rate controller receiving the service rate allocations from an associated node control element after they are computed.
The invention also provides a network control element for a multi-class digital network, comprising:
at least one connection with the network adapted to periodically receive network traffic and network state information from node control elements in the network;
at least one algorithm for maintaining a current network topology using the network state information; and
at least one algorithm for computing routing sets for switching nodes in the network based on the network traffic and network state information.
The multi-class digital network in accordance with the invention distributes the network processing load between a network control element which handles global functions that are best performed at the network level and traffic functions which are best performed in a distributed fashion at the node level of the network. This distribution of functionality minimizes computational effort and maximizes transmission efficiency.
The network control element in accordance with the invention receives traffic intensity and network state information from the nodes in the network which periodically report such information to the network control element. Using the network state information, the network control element maintains a network topology. The network topology and the traffic intensity data are used by the network control element to compute network traffic routing sets which are identified to the nodes along with an order of preference. The computed routing sets are distributed to the network nodes and used by the network nodes in processing traffic admission requests.
The network nodes include node control elements which control traffic admission, traffic routing and the computation of service-rate allocations for classes of traffic served by egress links at the node.
Edge network node control elements receive traffic admission requests from traffic sources. The edge node control elements compute an equivalent bit rate for each traffic admission request based on a novel method in accordance with the invention. In order to minimize further processing when it is necessary to establish a connection across the network, the edge node control element also computes variables which enable subsequent nodes involved in the connection to rapidly compute an approximate equivalent bit rate used in route selection.
The multi-class digital network in accordance with the invention preferably supports a plurality of digital services which may require different transport modes, each transport mode consisting of at least one transport protocol. Since different transport protocols require different packet sizes, a link controller is provided which accommodates variable packet sizes so that packets need not be disassembled and converted to a standard format by edge device interfaces.
The multi-class digital network adopts a service-rate discipline comprising a guaranteed minimum rate per class in order to ensure efficient use of the network while meeting transmission rate and quality of service commitments. In order to minimize computing requirements for routing, high-frequency, low bit-rate traffic is preferably served by paths commonly referred to as direct routes set up through the network. High bit-rate connection-oriented traffic is preferably served by connections set up on demand. Each service type is preferably assigned to at least one class and each class is preferably assigned to a separate band in the network. The bands are dynamically configured and have elastic boundaries which fluctuate with traffic load. Unused time slots accept traffic from any waiting source in a predetermined hierarchical order in which connectionless traffic without a quality of service is served last.