No abstract

No abstract

Modal noise becomes a serious problem in multimode optical fiber systems. It is said that there are two main causes for modal noise, one being the optical source and the other fiber vibration. In this paper, the latter cause is discussed.Firstly the speckle fluctuation due to fiber vibration is expressed by a N-th order orthogonal matrix, and the effect of mode dependent loss at a connection point is expressed by coupling coefficients which are approximated by a geometrical progression, and the calculated results using the geometrical progression are in good agreement with Petermann's results. Using above outlined procedure, a carrier-to-noise ratio (CNR) for modal noise based on our model is formulated and the results calculated by our CNR formula are compared with Hill's results.Next, to investigate validities of this new model and of the modal noise estimation procedure, some experiments are carried out and calculated results are in good agreement with experimental ones. Moreover, the calculated modal noise spectra due to this model are in good agreement with the experimental ones.

Some communication characteristics of an Ethernet were measured and investigated for the purpose of creating a packet-generating model for use in network characteristics simulations. The communication protocols measured were Telnet, X-Window, NetWare, Apple Talk, and so on. The measured results showed some interesting characteristics for the generated packet-length distribution and the packet-generation spacing depending on the communication contents and the terminal types such as Server and Client terminals. Based on the measured data, a variable packet-length generation model for use in network simulations is created. Some simulated results using the model are shown and differences between the variable and the fixed packet-length models are investigated for the throughput characteristics. P I At present, however, local area networks (LANs) are used for various purposes and with various communication modes. Therefore, the packet-generation aspect is complicated [3, 41. Thus, it is somewhat difficult to express the aspect by the generalized method.Traffic situations depend on the communication contents and the communication modes in the LAN. Therefore, we have to give strong consideration to the communication aspects to make a packet-generation model. We can easily predict some differences of those packet-generation aspects between File Access (FA)