Page 74 - DCAP406_DCAP_207_Computer Networks

Unit 5: Networking Devices

combinations of shared/dedicated 10/100/1000 Mbps connections. Some E-net switches support Notes
cut-through switching: frame forwarded immediately to destination without awaiting for
assembly of the entire frame in the switch buffer. They significantly increases throughput. They
provide express lane for traffic.

Comparison of Switches and Hubs

Hubs Switches
1 Collision Domain Broadcast Domain
2 All of the parts on a hub are part of the Each part on a switches may be regarded as a
same Ethernet separate Ethernet (but all are part of the same
local area network)
3 All parts on a hub share the same Each part on a switch has its own 10Mb (100 Mb)
10Mb (100 Mb) bandwidth bandwidth

4 Any frame appearing on one port of a A directed frame appearing on one part of a
hub is repeated to all other ports on the switch is forwarded only to the destination port.
hub
5 A sniffer on any hub port can see all of Switched networks are difficult to sniff
the traffic on the network
6 A hub will repeat defective frames

5.5 Hubs

If multiple incoming connections need to be connected with multiple outgoing connections,
then a hub is required. In data communications, a hub is a place of convergence where data
arrives from one or more directions and is forwarded out in one or more other directions. Hubs
are multi-port repeaters, and as such they obey the same rules as rep eaters. They operate at the
OSI Model Physical Layer.
Hubs are used to provide a Physical Star Topology. At the center of the star is the hub, with the
network nodes located on the tips of the star.

Star Topology

The Hub is installed in a central wiring closet, with all the cables extending out to the network
nodes. The advantage of having a central wiring location is that it’s easier to maintain and
troubleshoot large networks. All of the network cables come to the central hub. This way, it is
especially easy to detect and fix cable problems. You can easily move a workstation in - a star
topology - by changing the connection to the hub at the central wiring closet.
The disadvantages to a star topology are given below:
1. Failure of the Hub can disable a major section of the network.

2. The Star Topology requires more cabling than does the ring or the bus topology because
all stations must be connected to the hub, not to the next station.

5.5.1 Hub’s Segment-to-Segment Characteristics

To understand the Ethernet segment-to-segment characteristics of a hub, let us first determine
how the Ethernet Hubs operate. Logically, they appear as a Bus Topology, and physically as a

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