2. Differences between Voice and Data Traffic
Telephone networks are basically designed to carry voice traffic & there are some significant
differences in the nature of voice & data traffic. Voice traffic is generally continuous, whereas data
traffic is bursty in nature.
Voice traffic
Data traffic
Continuous
Bursty
Low bandwidth for
long duration
High bandwidth for
short duration
Typical line utilisation
85-95%
Typical line utilisation
5-15%
Half duplex
Half or full duplex
Real time
Non real time or near
real time
Loss acceptable
Loss unacceptable
Error tolerable
Error unacceptable
3. Switching Techniques for Data Transmission
The recognition of the diverse characteristics of voice and data traffic
has led to the development of a switching technique other than the
one used for voice transmission.
This technique is better suited for transmitting data traffic.
Two switching techniques are prevalent for data transmission :
1. Circuit Switching
2. Store & forward (S&F) switching
4. Circuit Switching
In circuit switching, an electrical path is established between the
source and destination before any data transfer takes place.
The electrical path may be realised by physical wires or coaxial
cables or radio or satellite links.
It remains dedicated to the communicating pair for the entire
duration of the transmission irrespective of whether data is actually
transferred or not.
The connection is released only when specifically signalled so by
either of the communicating entities.
It is entirely analogous to the telephonic switching.
9. Circuit Switching Applications
Public Switch Telephone Network (PSTN)
Private Branch Exchanges (PBX)
Private Wide Area Networks (often used to interconnect PBXs in a
single organization)
Data Switch
10. Advantages and Disadvantages of Circuit
Switching
Advantages:
•
The communication channel (once established) is dedicated.
•
Developed for voice traffic (public telephone network) but can also applied to
data traffic.
Disadvantages:
Channel capacity is dedicated for the whole duration of a connection, If no
data, capacity is wasted
• Long initial delay: circuit establishment takes time
•
•
More expensive than any other switching techniques, because a dedicated
path is required for each connection.
•
Inefficient use of the communication channel, because the channel is not
used when the connected systems are not using it.
11. Store and Forward Switching
In store and forward switching, the switching nodes have the ability to store
user messages and forward the same towards the destination when the links
available.
Each node is equipped with a processor and some buffer storage.
No end-to-end link is set up prior to data transmission.
It is analogous to the postal or telegraph system.
13.
S & F switching is of two types:
1. Message switching
2. Packet switching
14. Message Switching
In message switching, a message is transmitted in its
entirety without a break from one node to another.
The node processor receives the full user message
and store the same.
Check the message for data transmission errors and
perform error recovery if required.
Determine the destination address from the user
message.
Choose an appropriate link based on routing
algorithm.
Forward the message to the next node on the
chosen link.
15. Disadvantages of Message Switching
For long message there is a chance of overflow.
If an error occurs during transmission, the entire message may not be
retransmitted.
If a high priority short message arrives while a long message is in
transmission, it will have to wait until the transmission of the long
message ends.
16. Packet Switching
In packet switching, messages are split into a number of packets,
and they are transmitted in S & F fashion.
Messages are split at the source host and reassembled at the
destination host.
Each packet transmission is independent of the others.
Each packet needs to carry the complete information such as
destination id, source id, message id, and packet id.
19. Advantages and Disadvantages of Packet
Switching
Advantages:
•
•
Packet switching offers improved delay characteristics, because there are no long
messages in the queue (maximum packet size is fixed).
•
Packet switching is cost effective, because switching devices do not need massive
amount of secondary storage.
Packet can be rerouted if there is any problem, such as, busy or disabled links.
Disadvantages:
•
Protocols for packet switching are typically more complex.
•
It can add some initial costs in implementation.
•
If packet is lost, sender needs to retransmit the data.
•
Packets of same message may arrive out of sequence at the destination node.
20. Conclusion
Thus, we can conclude that switching technique can be used for transmission of data
traffic. Though there is a dedicated path in circuit switching due to long initial delay we
are going for S & F switching instead of circuit switching. In S & F switching instead of
using message switching we are using packet switching because of improved delay
characteristics and less buffer storage.
