Specifications

2-3
TOKEN RING OVERVIEW
LOCAL AREA NETWORK STANDARDS
Networking standardization has one goal: to allow systems to
communicate with each other. This is particularly relevant to LANs where
the two primary objectives are to permit common resource sharing and to
allow interconnection of many different systems to the same physical
medium. To achieve this, each system must conform to the same standard
for using the LAN. Proprietary network physical media and topologies
would be workable if only one manufacturer existed. Standards play an
important part in LAN design and implementation and interoperability
between vendor products.
Open Systems Interconnect (OSI) Model
The International Standards Organization (ISO) OSI model is intended to
serve as a common basis for development of system-connection standards
by means of a consistent hierarchy of rules. The OSI model defines where
needed tasks for system interconnection are performed, but not how they
are done. How a task is performed in a network is defined in the protocols,
or rules, written for a network type, but are based, nevertheless, on the
OSI model.
The tasks that are needed to manage and control the network are divided
into functional groups called layers. The layers may be implemented by
hardware, software, or both. Each layer in a network-based OSI model
performs a specific task or group of tasks required for proper system
interconnection.
There are seven layers in the OSI model, as shown in Figure 2-2. A brief
description of each layer follows.
Figure 2-2. OSI Model
7
6
5
4
3
2
1
Application
Presentation
Session
Transport
Network
Data Link
Physical