Section: Information System Operations, Maintenance and Support
Explanation/Reference:
The word INCORRECTLY is the keyword used in the question. You need to find out a statement which is
not valid about packet switching. As in the network switching, packet traverse different path, there will be
always variable delay for each packet to reach to destination.
For your exam you should know below information about WAN message transmission technique:
Message Switching
Message switching is a network switching technique in which data is routed in its entirety from the source
node to the destination node, one hope at a time. During message routing, every intermediate switch in the
network stores the whole message. If the entire network's resources are engaged or the network becomes
blocked, the message-switched network stores and delays the message until ample resources become
available for effective transmission of the message.
Message Switching
Packet Switching
Refers to protocols in which messages are divided into packets before they are sent. Each packet is then
transmitted individually and can even follow different routes to its destination. Once all the packets forming
a message arrive at the destination, they are recompiled into the original message.
Packet Switching
Circuit Switching
Circuit switching is a methodology of implementing a telecommunications network in which two network
nodes establish a dedicated communications channel (circuit) through the network before the nodes may
communicate.
The circuit guarantees the full bandwidth of the channel and remains connected for the duration of the
session. The circuit functions as if the nodes were physically connected similar to an electrical circuit.
The defining example of a circuit-switched network is the early analog telephone network. When a call is
made from one telephone to another, switches within the telephone exchanges create a continuous wire
circuit between the two telephones, for as long as the call lasts.
In circuit switching, the bit delay is constant during a connection, as opposed to packet switching, where
packet queues may cause varying and potentially indefinitely long packet transfer delays. No circuit can be
degraded by competing users because it is protected from use by other callers until the circuit is released
and a new connection is set up. Even if no actual communication is taking place, the channel remains
reserved and protected from competing users.
Circuit Switching
See a table below comparing Circuit Switched versus Packet Switched networks:
Difference between Circuit and packet switching
Virtual circuit
In telecommunications and computer networks, a virtual circuit (VC), synonymous with virtual connection
and virtual channel, is a connection oriented communication service that is delivered by means of packet
mode communication.
After a connection or virtual circuit is established between two nodes or application processes, a bit stream
or byte stream may be delivered between the nodes; a virtual circuit protocol allows higher level protocols
to avoid dealing with the division of data into segments, packets, or frames.
Virtual circuit communication resembles circuit switching, since both are connection oriented, meaning that
in both cases data is delivered in correct order, and signaling overhead is required during a connection
establishment phase. However, circuit switching provides constant bit rate and latency, while these may
vary in a virtual circuit service due to factors such as:
varying packet queue lengths in the network nodes,
varying bit rate generated by the application,
varying load from other users sharing the same network resources by means of statistical multiplexing, etc.
The following were incorrect answers:
The other options presented correctly describes about packet switching.
The following reference(s) were/was used to create this question:
CISA review manual 2014 Page number 265
