Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-07-26
2003-10-21
Nguyen, Chau (Department: 2663)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S401000
Reexamination Certificate
active
06636512
ABSTRACT:
FIELD OF INVENTION
This invention relates to a fully transparent method for optimizing link bandwidth occupation in high speed digital networks, and a system for implementing said method which is particularly adapted to conventional Frame Relay networks. This method is transparent to conventionally existing user's equipment and enables network interoperability.
BACKGROUND ART
Modern communication facilities are made to operate over different transmission media and interconnect, upon request, a very large number of users and applications through complex digital communication networks.
Due to the variety of users' profiles and distributed applications, the corresponding traffic is becoming more and more bandwidth consuming, non-deterministic and requiring more connectivity. This has driven the emergence of fast packet switching network architectures in which data, voice and video information are digitally encoded, chopped into fixed or variable length packets and transmitted through a common set of nodes and links interconnected to constitute the network communication facilities.
An efficient transport of mixed traffic streams on very high speed lines (herein also designated as links or trunks), for these new network architectures, generates a set of requirements in terms of performance and resource consumption including a very high throughput and a very short packet processing time, flexibility to support a wide range of connectivity options, efficient flow and congestion control. Congestion resulting in network performance degrades due to saturation of network resources such as communication links bandwidth, processor cycles, memory buffers, etc.
One basic advantage of packet switching techniques (as opposed to so-called circuit switching techniques) is to allow statistical multiplexing of the different types of data over a line which optimizes the transmission bandwidth. The drawback, however, is that packet switching introduces delays and jitter which might be detrimental for transmission of isochronous data, like video or voice. This is why methods have been proposed to control the network in such a way that delays and jitter are bounded for every new connection that is set up across the packet switched network.
These methods have been described, for instance in a European Application published with number 0000706297 (Method for operating traffic congestion control in a data communication network and system for implementing said method). Said methods include, for any source end-user attached to the network requesting its data to be transported over the network toward a destination end-user also attached to said network, establishing a path through the network high speed lines (links or trunks) and nodes via an entry node port of said network to an indicated destination node using an optimal amount of the available bandwidth of the network.
Due to the very nature of any given source of traffic, a discrimination has to be made among said traffic natures by assigning different priorities. In other words, qualities of service (QoS) are specified in terms of maximum delay (T_max) and packet loss probability (P_loss) upon a source equipment requesting being connected to a destination equipment via the network (i.e., at call set-up time) and based on the nature of the traffic provided by said involved source.
To that end, the QoS and traffic characteristics (e.g. peak rate, mean rate, average packet length) specified and agreed upon by both parties (source owner and network management) are used to compute the amount of bandwidth. For instance, this amount may be equal to the equivalent capacity (Ceq) of the connection to be reserved on every line on the route or path assigned to the traffic between source equipment and destination equipment in order to guarantee a packet loss probability which is smaller than the loss probability (P_loss) that has been specified for the connection. In operation, the network traffic must be controlled dynamically requiring that some packets be dropped within the network to avoid traffic jamming. These packets are flagged as discardable packets through use of a so-called Discardable Eligibility (DE) identifier bit.
In practice, it is common to reserve bandwidth for high priority packets, (e.g. so-called Real Time (RT) traffic) derived from committed QoS traffic, which are transmitted in preference to lower priority packets derived from discardable traffic (e.g. Non Real Time (NRT) traffic or more particularly Non Reserved (NR) traffic). Accordingly, lower priority traffic, (e.g. NR traffic or NRT traffic) sent at a higher rate than their declared rate, is managed to dynamically take advantage of any bandwidth remaining after all the higher priority traffic has been served. This remaining bandwidth can vary widely depending on the actual activity of the high priority traffic sources. It is therefore of considerable importance to manage the low priority traffic so as to optimize the use of the widely varying left-over bandwidth in the network while avoiding any congestion which would reduce network throughput. This requires providing the network (and eventually also the sources) with congestion detection and flow control facilities.
In the domain of flow control mechanisms for non-reserved (NR) traffic, various solutions have already been proposed.
Several mechanisms have been implemented with flow control which can be used on ATM or PTM traffic, the latter providing variable length packets as used in the so-called Frame Relay network (FR) operation, both offering good performance.
One of these mechanisms was disclosed in U.S. Pat. No. 5,313,454 which made the system transparent to the user (source) by providing an internal congestion avoidance method. To that end, congestion is identified throughout the network forward path and identified by setting an indicator in the packet header. Such an indicator is sometimes referred to as a Forward Explicit Congestion Notification (FECN) indicator. Congestion status indicators are used in the destination node either to generate therein a rate control message which is then fed back to the entry node, or to simply notify the traffic originating entry node with a so-called Backward Explicit Congestion Notification (BECN) indicator. This method can generate important overhead in the feedback flow if smooth and flexible congestion control is desired, otherwise the flow regulation would be quite rigid and basic.
In any case, network/link bandwidth occupation should be optimized. To fully appreciate this requirement, one may consider the current link leasing price rates. For instance, the prices in Europe for so-called OC3/STM1 links may be on the order of $100K per 100 Km per month.
Accordingly, any method and means which would enable increased link bandwidth occupation in a high speed digital communication network would be most welcomed.
More particularly, multiplexing techniques enable connecting of several end users on a common physical link by defining so-called Virtual Channels (VC). For instance, switched networks such as Frame Relay (FR) networks and Asynchronous Transfer Mode (ATM) networks are becoming the standard way of networking within Wide Area Networks. One defines as many end-to-end full duplex virtual channels as there are end-to-end connections via the network. Customers find it economically attractive to suppress Internet Protocol network layer (so-called layer
3
) regional concentration points (e.g. 3745/NCP), instead choosing to define many small channels between any given central site (host) and local terminals that are located in branches. One problem associated with this new topology is that bandwidth is now allocated and controlled by a very large number of very small channels. This burdens the network nodes/switches and results in an underutilisation of bandwidth and increased costs as the carriers charge by the number of virtual channels. One solution currently used to save bandwidth is using concentrators to concentrate several small channels into a common channel. This obvious
Lorrain Jean
Marce Jean-Pierre
Thubert Pascal
George Keith M.
Nguyen Chau
Voigt, Jr. Robert A.
Winstead Sechrest & Minick
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