Specifications

TOKEN RING OVERVIEW
2-4
Physical (Layer One)
This layer interfaces directly to the physical medium and is responsible for
sending and receiving a stream of bits across that medium. It defines the
electrical, mechanical, and signal characteristics to the medium.
Data Link (Layer Two)
This layer controls the flow of information between systems and the next
adjacent system on the path to the final destination. It provides simple
error correction and detection mechanisms to eliminate loss of data and
data corruption. It is also responsible for packaging data into frames ready
for transmission over the network.
Network (Layer Three)
This layer provides a means of establishing a connection between systems.
It enables systems to be connected together, even if they are on different
subnetworks and if the subnetworks are of different types. It controls
networking issues such as routing and flow control.
Transport (Layer Four)
This layer provides the upper layers with guaranteed quality of service in
terms of throughput and reliability. This quality of service is requested by
the Session Layer and is provided irrespective of the speed and reliability
of the underlying communications services. For example, the Transport
Layer can enhance throughput performance by multiplexing or running
several network connections in parallel in order to service a single
transport connection. Similarly, in order to enhance reliability, it may use
error correction and detection schemes.
Session (Layer Five)
This layer provides a means for organized and synchronized exchange of
data between systems. In simple terms, it establishes a framework for
dialogue between systems. For example, when a connection is established,
the Session Layer arranges the way the data should be sent: in one
direction only, in alternate directions, or in both directions at the same
time.
Presentation (Layer Six)
This layer provides a common representation of information while it is in
transit between two cooperating systems. For example, because two end
systems may use different character sets and different codes to represent
symbols, the Presentation Layers of the two systems must agree on a
common representation. Having done so, they can translate the data
which is sent to them from the Application Layer into that common
representation ready for transmission across the network.