Link quality agent

Details Link quality agent Link quality agent

2001-02-13

2004-01-13

Ton, Dang (Department: 2666)

Multiplex communications

Diagnostic testing

Fault detection

C370S228000, C359S199200

Reexamination Certificate

active

06678251

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to free space optical communication systems and, in particular, to an intelligent agent in a free space optical communication system.
2. Background Information
Optical wireless transmission is way of providing multi-gigabit connectivity between two locations without the use of an optical fiber interconnection. At the transmitting end, an optical wireless system typically consists of an optical laser source, which is being modulated by a data source to produce and optically encoded data signal. The data source typically provides the intelligence or information to be transmitted, such as data, audio, video, messages, etc. An optical amplifier may amplify the optical signal, which is then transmitted into the atmosphere (or free-space) through a transmitting telescope as an optical transmission beam towards a receiving telescope. On the receiving end of an optical wireless system, a receiving telescope collects part of the optical beam and focuses it as a light spot into a receiving optical fiber. The receiving optical fiber is connected to a receiver/regenerator, which converts the optically encoded data signal back into an electrical data signal.
In an optical wireless system, the atmosphere is the propagation medium for the optical transmission beam (sometimes called a light beam). One drawback to using the atmosphere as the transmission medium is the effect that weather conditions have on the optically encoded data signal. For example, fog often causes the optical link to operate marginally, which means that the receiver may receive sufficient small packet handshaking signals, such as open shortest path first (OSPF) “hello” packets, but not enough of the transmitted data in large packets.
Normally, when data is not being received, the system would shift to a backup means to deliver data. In the situation in which the system is marginal, however, the system may not shift to a backup means to deliver the data and much of the data is lost. Alternatively, the system may shift to a backup means when the receiver does not receives sufficient “hello” packets and return to the primary means to deliver data when the receiver does receive sufficient “hello” packets. The term “flapping” describes the condition in which the optical link goes in and out of tolerance numerous times such that the router has to excessively reconfigure the means to deliver data. Flapping consumes a large percentage of bandwidth and therefore must be controlled. Moreover, in this situation, the system experiences high link error rates, which results in the system having to retransmit packets. Retransmission of packets seriously degrades link bandwidth for data.


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