Distributed Networks

• Distributed networks are preferred when data is to be transmitted to a group of The transmission distance is relatively short (< 50 km).Examples of distributed networks are – broadcast of video channels over cable TV, telephone and FAX, commonly used topologies for distributed networks are –

1. Hub topology
2. Bus topology

1.      Hub topology

• In hub topology channel distribution takes at hubs or central Hub facilitates the cross-connect switched channels in electrical domain. Fig. 8.5.1 shows hub topology

2.      Linear bus topology

• Linear bus configuration is similar to Ethernet topology using co-axial cable. Fig.8.5.2 shows linear bus configuration.

• A single fiber cable carries the multichannel optical signal throughout the area of service. Distribution is done by using optical taps which divert a small fraction of optical power to each situation.
• A problem with bus topology is that the signal loss increases exponentially with number of taps for stations. This limits the number of stations or subscribers that can be served by a single optical fiber bus.
• Use of optical amplifiers can boost the optical power of bus and therefore large number of stations can be connected to linear bus as long as the effect of fiber dispersion is negligibe.