13.9 Summary
567
In a ring topology, consecutive nodes are connected by point-to-point links that
are arranged to form a single closed path. Information in the form of data packets is
transmitted from node to node around the ring. The interface at each node is an active
device that has the ability to recognize its own address in a data packet in order to
accept messages. The node forwards those messages that do not contain their own
address on to their next neighbor.
In a star architecture, all nodes are joined at a single point called the central
node or hub. The hub can be an active or a passive device. Using an active hub, all
routing of messages in the network is controlled from the central node. This is useful
when most of the communications are between the central and the outlying nodes,
as opposed to information exchange between the attached stations. In a star network
with a passive central node, a power splitter is used at the hub to divide the incoming
optical signals among all the outgoing lines to the attached stations. Star topologies
are widely used in passive optical networks (PONs) and in active Ethernet networks.
In a mesh network, point-to-point links connect the nodes in an arbitrary fashion
that can vary greatly from one application to another. This topology allows significant network configuration flexibility and offers connection protection in case there
are multiple link or node failures. Link protection is accomplished by means of a
mechanism that first determines where a failure has occurred and then restores the
interrupted services by redirecting the traffic from a failed link or node to travel over
another link in the mesh.
Problems
13.1 Consider an N-node star network in which 0 dBm of optical power is coupled
from any given transmitter into the star. Let the fiber loss be 0.3 dB/km.
Assume the stations are located 2 km from the star, the receiver sensitivity is
−38 dBm, each connector has a 1-dB loss, the excess loss in the star coupler
is 3 dB, and the
link margin is 3 dB.
(a) Show that the maximum number of stations
that can be incorporated on this network is N = 380.
(b) Show that a maximum number of N = 95 stations can be attached if the
receiver sensitivity is −32 dBm.
13.2 A two-story office building has two 10-feet-wide hallways per floor that
connect four rows of offices with eight offices per row as is shown in
Fig. 13.47. Each office is a 15 feet × 15 feet square. The office ceiling
height is 9 feet with a false ceiling hung 1 foot below the actual ceiling. Also,
as shown in Fig. 13.47, there is a wiring room for LAN interconnection and
control equipment in one corner of each floor. Every office has a local-area
network socket on each of the two walls that are perpendicular to the hallway
wall. If the cables can be run only in the walls and in the ceilings, estimate
the length of cable (in feet) that is required for the following configurations:
567
In a ring topology, consecutive nodes are connected by point-to-point links that
are arranged to form a single closed path. Information in the form of data packets is
transmitted from node to node around the ring. The interface at each node is an active
device that has the ability to recognize its own address in a data packet in order to
accept messages. The node forwards those messages that do not contain their own
address on to their next neighbor.
In a star architecture, all nodes are joined at a single point called the central
node or hub. The hub can be an active or a passive device. Using an active hub, all
routing of messages in the network is controlled from the central node. This is useful
when most of the communications are between the central and the outlying nodes,
as opposed to information exchange between the attached stations. In a star network
with a passive central node, a power splitter is used at the hub to divide the incoming
optical signals among all the outgoing lines to the attached stations. Star topologies
are widely used in passive optical networks (PONs) and in active Ethernet networks.
In a mesh network, point-to-point links connect the nodes in an arbitrary fashion
that can vary greatly from one application to another. This topology allows significant network configuration flexibility and offers connection protection in case there
are multiple link or node failures. Link protection is accomplished by means of a
mechanism that first determines where a failure has occurred and then restores the
interrupted services by redirecting the traffic from a failed link or node to travel over
another link in the mesh.
Problems
13.1 Consider an N-node star network in which 0 dBm of optical power is coupled
from any given transmitter into the star. Let the fiber loss be 0.3 dB/km.
Assume the stations are located 2 km from the star, the receiver sensitivity is
−38 dBm, each connector has a 1-dB loss, the excess loss in the star coupler
is 3 dB, and the
link margin is 3 dB.
(a) Show that the maximum number of stations
that can be incorporated on this network is N = 380.
(b) Show that a maximum number of N = 95 stations can be attached if the
receiver sensitivity is −32 dBm.
13.2 A two-story office building has two 10-feet-wide hallways per floor that
connect four rows of offices with eight offices per row as is shown in
Fig. 13.47. Each office is a 15 feet × 15 feet square. The office ceiling
height is 9 feet with a false ceiling hung 1 foot below the actual ceiling. Also,
as shown in Fig. 13.47, there is a wiring room for LAN interconnection and
control equipment in one corner of each floor. Every office has a local-area
network socket on each of the two walls that are perpendicular to the hallway
wall. If the cables can be run only in the walls and in the ceilings, estimate
the length of cable (in feet) that is required for the following configurations: