Multiplex communications – Fault recovery
Reexamination Certificate
2001-12-06
2002-09-24
Cheng, Joe H. (Department: 3714)
Multiplex communications
Fault recovery
C370S351000
Reexamination Certificate
active
06456588
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to telecommunications networks. More particularly, this invention relates to an improved network architecture for more effectively routing traffic and recovering from failures.
A telecommunications network transports information from a source to a destination. The source and destination may be in close proximity, such as in an office environment, or thousands of miles apart, such as in a long distance telephone system. The information, which may be, for example, computer data, voice transmissions, or video programming, is known as traffic, and enters a network usually at a node and is transported through the network via links and other nodes until a destination is reached. Nodes are devices or structures that direct traffic; they add new traffic to the network, drop traffic from the network, and route traffic from one portion of the network to another. Links are the transmission paths interconnecting the nodes.
Nodes range in complexity from simple switching or relay devices to entire buildings containing thousands of devices and controls. Nodes can be completely controlled by a central network controller or can be programmed with varying degrees of automated traffic-managing capabilities. The implementation of nodes, which is known in the art, is accomplished either electronically, mechanically, optically, or in combinations thereof.
Links are typically either coaxial cable or fiber-optic cable, but can be any transmission medium capable of transporting traffic. Individual links can vary in length from a few feet to hundreds of miles. Links that are part of a larger network, such as a telephone system, are usually carried on overhead utility poles, in underground conduits, or in combinations of both. Generally, links are either working links or protection links. Working links provide dedicated pathways for transporting traffic, while protection links, which do not regularly transport traffic, provide alternative pathways should a working link become inoperative. A link can become inoperative in a number of ways, but most often, when it is cut. This usually occurs, for example, when excavation severs an underground link, or when a traffic accident or storm damages a utility pole carrying a link.
The volume of traffic transported by a network can be significant. Typical transfer rates for a fiber-optic link can range from 2.5 gigabits per second to 10 gigabits per second. A “gigabit” is a billion bits, and a “bit” is a binary digit (a logical 1 or 0), which is the basic unit of digitized data. Digitized data is a coded sequence of bits, and traffic is typically transported in that form.
Because of the significant volume of traffic typically transported by a network, any disruption in traffic flow can be devastating. Of particular concern are telephone networks, which can transport thousands of individual communications simultaneously. Thus the ability to restore network service should a portion of the network become inoperative is of high priority. Moreover, to ensure that the network is implemented and managed in a cost effective manner, proper allocation of link resources is also of high priority.
Network architecture (the manner in which nodes and links are configured and traffic is controlled) plays a significant role in both the cost-effective implementation and management of a network and the ability of a network to quickly recover from traffic flow disruptions. In one known mesh network, a central controller monitors and controls traffic flow throughout the network. Complex traffic routing and recovery algorithms are used to manage traffic flow. A simplified portion of this network is shown in FIG.
1
. Each node
102
communicates with controller
104
, sending status and receiving instructions for properly routing traffic. Each node is interconnected with other nodes by working links
106
(indicated by solid lines) and selectively placed protection links
108
(indicated by dashed lines). (For clarity, not all nodes and links in
FIG. 1
are identified with reference numerals.)
When a link becomes inoperative, the nodes connected to the inoperative link immediately notify the controller. The controller then determines if an alternative traffic path can be configured with either protection links, spare capacity on working links, or combinations of both. If an alternative path is found, the controller sends appropriate instructions to those nodes that can interconnect the identified links to form the alternative path. Typical recovery time from such a disruption is approximately two seconds. This recovery time was once hailed as a marvel of technology; today, however, it is no longer acceptable. A two-second outage would adversely affect, for example, the transmission of computer data. In fact, an entire computer center could be adversely affected by such an outage.
To improve recovery times, other known mesh networks provide decentralized node control. In these networks, individual nodes, in cooperation with adjacent nodes, routinely route traffic and respond to path failures without significant interaction with the central controller. By communicating locally among themselves, these nodes can, for example, recover from path failures by configuring alternative paths and rerouting traffic to those alternative paths. Decentralized node control has improved recovery times to the millisecond range (thousandths of a second).
Furthermore, restorative capability in these networks has been improved by providing each nodal interconnection with a protection link. This additional protection link coverage increases the likelihood that alternative paths can be configured for most typical path failures.
These improvements, however, have also resulted in several disadvantages. For example, decentralized node control undesirably requires a great deal of inter-nodal communication, which must be supported with increased link capacity and more complex nodes. Nodes must be able to send, receive, analyze, and respond to various inter-nodal traffic management communications, and working link capacity must be increased to transport those communications. Moreover, the additional protection link coverage further increases equipment and maintenance costs. Thus these improvements have undesirably resulted in a more costly network, both in terms of original equipment and the associated maintenance of that equipment.
Networks employing architectures other than mesh configurations are also known. Ring networks, for example, interconnect nodes in a circular fashion to form rings. The rings are then interconnected to form a complete network. Control in this type of network is also decentralized, enabling nodes within each ring to make limited traffic routing decisions. Although the rings are interconnected, each ring operates substantially independently of the others, thus desirably reducing the possibility of a network-wide failure, which a centrally controlled network is susceptible to. Ring networks have further improved recovery times to the microsecond range (millionths of a second). In that short amount of time, telephone customers would not realize that the path carrying their call was cut and rerouted, and transmitted computer data would likely suffer the loss of only a few hundred bits of data, which would simply require retransmission of the lost bits.
A portion of such a ring network is shown in FIG.
2
A. Network
200
includes nodes
202
,
204
,
206
,
208
, and
210
. Each node is connected to working links, indicated by solid lines (such as working link
212
), and protection links, indicated by dashed lines (such as protection link
214
). (For clarity, only the working and protection links of one link pair are identified with reference numerals in
FIG. 2A.
)
A ring recovers from a cut link pair generally as follows: assume the working and protection links between nodes
202
and
204
are cut. Nodes
202
and
204
communicate with adjacent nodes
210
and
206
, respectively, which in turn both communicate with node
208
to swi
AT&T Corp.
Cheng Joe H.
Kenyon & Kenyon
Nguyen Kim T.
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