Multiplex communications – Fault recovery – Bypass an inoperative station
Reexamination Certificate
1999-03-22
2003-07-22
Vu, Huy D. (Department: 2665)
Multiplex communications
Fault recovery
Bypass an inoperative station
C370S225000, C370S242000
Reexamination Certificate
active
06597658
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to telecommunications networks. More particularly, this invention relates to an improved network architecture for more effectively and efficiently 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, usually enters and leaves a network at nodes, and is transported through the network via links and nodes. The overall traffic comprises multiple data streams which may be combined in various ways and sent on common links. Generally, a data stream is a flow of data or information and may comprise multiple component data streams.
Nodes, sometimes termed offices, are devices or structures that direct traffic into, out of, and through the network. They can be implemented electronically, mechanically, optically, or in combinations thereof, and are known in the art. Links connect nodes and transmit data between nodes. A path between any two nodes is a route allowing for data transmission between those two nodes; a path may be one link, or may be comprised of multiple links and nodes and other network elements.
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.
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. A link can become inoperative in a number of ways, but most often becomes inoperative as a result of being cut. This may occur, for example, when excavation severs an underground link, or when an automobile accident or storm damages a utility pole carrying a link.
The volume of traffic transported by a network can be significant. Transfer rates for a fiber-optic link may be 20 gigabits per second or more. 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. Data such as audio telephone conversations may be digitally encoded and then transmitted.
Traffic in networks carrying digital data is often circuit switched—for each transmission between two points, a circuit or channel following a path is set up for that traffic. Traffic on a particular circuit in such networks is often sent in one direction only. Thus traffic requiring information to be both sent and received at the same time—for example a telephone conversation, which requires each participant to be able to talk and thus send audio information at the same time—requires two circuits or channels to be established. The two circuits originate and end at the same two points, but may take different paths. Traffic flow through links may be bi-directional, that is, some traffic may flow upstream through a link while other traffic may flow downstream through the same link simultaneously.
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 quickly 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 resources such as link equipment, processing equipment, multiplexers and cross-connects is also of high priority.
Data is typically transmitted and routed at certain standard levels. For example, one two-way phone conversation requires 64K bits/sec to be transmitted in each direction; this rate is termed DS
0
. A T
1
link carrying a DS
1
signal may transmit approximately 1.5 M bits/sec, the data of 24 DS
0
circuits. Thus 24 DS
0
channels may be combined by a multiplexing device and transmitted as one DS
1
channel. A T
3
link may transmit the data of 28 T
1
links, an OC
1
link carries approximately the same amount of data as a T
3
link, an OC
3
link may transmit the data of 3 OC
1
links, an OC
12
link may transmit the data of 12 OC
1
links, and an OC
48
link may transmit the data of 48 OC
1
links, or approximately 2.5 gigabits per second. Different types of multiplexers are used to add or remove different sized bundles of traffic from larger bundles of traffic. For instance, a digital access cross-connect system (“DACS”) may be used to add (multiplex) or drop (demultiplex) a DS
1
channel to or from a DS
3
channel.
When used herein, multiplexing is meant to include demultiplexing, and multiplexer is meant to include a device having demultiplexing capabilities. Equipment which adds or drops traffic to or from a link may be called termination equipment.
Fiber optic lines transmit data using light, and multiple wavelengths of light may be transmitted on one fiber optic line as separate channels. Typically, one wavelength of light carries one OC48 link in one direction, and a fiber optic line may carry 8 wavelengths. Thus one fiber optic line may carry 250,000 one way telephone conversations simultaneously.
Data is transmitted, and is added or removed (“dropped”) from a data stream, in certain standard units. It is more efficient to transmit, route, add or drop data in larger rather than smaller units. Thus traffic is bundled into the largest unit possible. The size of a bundle, channel or data stream used to transmit data may be termed its granularity—channels of higher capacity have higher granularity.
An add/drop multiplexer (“ADM”) may be used to add or remove a wavelength of light from a link. At each node one ADM is required for add/drop capability for each of the multiple wavelengths that may be carried on a fiber optic cable. Multiplexers with the capability to perform add/drop operations on data flow sizes other than wavelengths may be used at nodes. Cross-connects may be used at nodes to switch traffic from one link to another link.
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.
Depending on the configuration of a network and its traffic routing, each node does not require an ADM for all wavelengths that may be carried on a link. If it is determined that a node does not have to access or route traffic on a certain wavelength or channel, or does not need to route traffic among multiple links, that node does not need extra multiplexers or cross-connects. Traffic which may be termed “express” traffic may pass through a node without being demultiplexed or routed by that node.
In one known network, a central controller monitors and controls traffic flow throughout the network, which is organized as a mesh. Complex traffic routing and recovery algorithms are used to manage traffic flow.
FIG. 1
is a diagram illustrating a simplified portion of a known mesh network. Mesh network
300
comprises nodes (e.g., nodes
304
,
306
,
308
and
310
) connected by links (e.g., links
305
,
307
,
311
,
312
,
314
and
316
). Each node in network
300
communicates with controller
302
, sending status information and receiving instructions for properly routing traffic. Nodes may communicate with controller
302
via satellite (not shown), by a land link separate from links carrying traffic (not shown), by links carrying traffic, or by other methods. Each node is interconnected with other nodes by links. For exam
AT&T Corp.
Ryman Daniel J.
Vu Huy D.
LandOfFree
Hierarchical telecommunications network with fault recovery does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Hierarchical telecommunications network with fault recovery, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hierarchical telecommunications network with fault recovery will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3101422