Specifications

3-1
Chapter 3
Ethernet LAN Standards
Standards play an important role in modern local area networks. Without standards, users are forced
to buy proprietary networking equipment from a single vendor. Companies come and go, and product
lines are changed or discontinued. This leads to increased network costs to the users, network down
time and network equipment that does not inter-operate if standards are not in place.
Standards allow for easy integration of multiple vendor equipment into a common network. If one
company disappears, a purchaser has the flexibility to purchase another vendor’s product, being
confident that the two standards based products inter-operate.
The Open Systems Interconnect (OSI) Model
The International Organization for Standardization (ISO) Open Systems
Interconnect (OSI) Model provides a framework for the development of
system connection standards by using a consistent hierarchy of rules. The
OSI model defines where the needed tasks for system interconnection are
performed but not how they are performed. How tasks are performed on
a given layer is defined by the protocols, or rules, written for that
particular network based on the OSI model. The layers may be
implemented in hardware, software or both. Each layer in a network
based on the OSI Model performs specific functions required for proper
system interconnection.
As shown in Figure 3-1, there are seven layers in the OSI Model. They
begin with the Application Layer and finish with the Physical Layer.