13-09-2013, 02:23 PM
Switching Principles
Switching Principles[.pdf (Size: 1.17 MB / Downloads: 168)
Circuit Switching – features
• The whole path is reserved for the single pair of end users -
inefficient use of the path if there is bursty traffic
• The delay in transmission of user data is constant,
determined mainly by the signal propagation
Explicit setup and release of a switch setting is needed, the
intention to setup/release a connection must be conveyed
from the initiator to each switch (signaling)
– Time
is needed for both: propagation of the signaling
information and operation of each switch, as well as
propagation of the confirmation of path setting
During the establishing/releasing the path segments can not
be used – but later the resources are assured!!!
Burstiness of data
In many data communication applications, data occur in bursts
separated by idle periods
This type of intermittent data can often be transmitted more
economically by assembling the data into packets (or messages) and
interspersing packets from several channels on one physical
communication path
Message Switching - features
Path capacity is used more efficiently- multiplexing of
different flows (pairs of users) on a single path segment
takes place
Each message must carry a header with routing information.
This header must be processed upon arrival of the message
to the switch.
Usually the store and forward principle is used. Cut-through principle
fairly difficult to implement.
Buffering is needed in the switches in order to avoid
overloading of the output segments - thus variable queuing
delay is enforced in addition to the propagation delay.
• The transmission can start immediately
• Variable data length makes the control (e.g. memory
management) difficult
Why Virtual Circuit Packet Switching
• The idea is to combine the advantages of circuit switching
with the advantages of datagram switching
• Virtual circuit packet switching:
After a small connection setup phase only short (compared to full
addresses) connection identifier are used per packet; this reduces the
addressing overhead per packet
During the setup phase, a table is created stating how to process a
packet with the corresponding connection identifier