Specifications

Introduction 2-7
Ethernet Features
Contention Star Topology
The contention star is the access method used with Ethernet. Workstations
are connected to a hub or concentrator located in a wiring closet.
Contention rules dictate that only one station can transmit data at any
given time and any station may talk providing the network is quiet. This
access method eliminates the need for polling and vastly improves
throughput and performance. Hubs can be expanded to handle hundreds
of devices without performance degradation. Expansion is easily
accomplished by simply plugging in a connection at the concentrator.
Failure of the hub can bring that section of the network down. Some
manufacturers allow for redundant backup of the hub and multiple load
sharing power supplies to reduce the possibility of hub failure and
minimize the impact of any such failure. The failure of a node will not
normally affect network operation.
Hybrid Network Topology
A hybrid topology is a combination of any of the three major topologies.
Examples include a ring of stars or a bus of stars or trees. Hybrid networks
may use a combination of point-to-point and multi-point connection
techniques.
For any of the above networks to function reliably and to allow multiple
vendors’ equipment to interoperate on the same network, a set of
standards have been developed. The most notable standards
organizations affecting data communications are the International
Organization for Standardization (ISO), the Institute of Electrical and
Electronic Engineers (IEEE), the Telecommunications Industry Association
(TIA), the American National Standards Institute (ANSI), and the
Consultative Committee on International Telegraphy and Telephony
(CCITT). In the following chapter we will look at the ISO standard as well
as the IEEE project 802 standards, specifically 802.3.