0195136047.pdf

6.4 COMPUTER NETWORKS 323

(a)

(b)

(c)

(d)

(e)

Figure 6.4.2Network topologies.(a)Bus (multidrop)

topology.(b)Star topology.(c)Ring topology.(d)Tree

topology.(e)Distributed (mesh or hybrid) topology.

Hosts

Internet

Physical

nets

Gateways

Figure 6.4.3Structure of typical TCP/IP

Internet.

coaxial cables, and optical-fiber cables, used in most LANs. Unbounded media, such as the
atmosphere, the ocean, and outer space in which the transmission is wireless, use infrared radiation,
lasers, microwave radiation, radio waves, and satellites. Data are transmitted from one node to
another through various transmission media in computer communications networks.
Twisted pairsare used in low-performance and low-cost applications with a data rate of about
1 Mbit per second (Mbps) for a transmission distance of about 1 km.Baseband coaxial cables
used for digital transmission are usually 50-cables with a data rate of about 10 Mbps over a
distance of about 2 km.Broad-band coaxial cablesused for analog transmission (cable TV) are
usually 75-cables with a data rate of about 500 Mbps over a distance of about 10 km. The
lighter and cheaperfiber-optic cablessupport data transmission of about 1 Gbps over a distance
of about 100 km.