Today’s Internet is a packet-based network with an always-on
connection. There are very fundamental differences between circuit-switched connections and packet networks. Circuitswitched
connections require a real time end-to-end session,
whether the transmission is a voice conversation or a data
transfer session. Whatever goes into one end always comes out
the other in the same order. It may be degraded by static or
noise, but its original order is maintained. If there is a loss of
voice or data, a repeat transmission can take place instantly to
guarantee the reliability of the connection.
Internet Protocol (IP) works entirely differently in the
transmission of data, whether using Voice-over-IP (VoIP) or a
binary data file. The data is broken up into small entities called
packets and each one carries a sequence number so that if they
arrive out of sequence, they can be reassembled. They can also
take different paths to the final destination, so there may be
delays in the arrival.
We do not wish to imply that packet is better than circuit
switched. The method selected depends on the application.
HSCSD allows wireless data to be transmitted at up to 38.4
Kbps or more over GSM networks by allocating multiple
time slots to a user. Although this is better than today’s average
data rate over most Wireless Internet access methods, it
will not really support true multimedia content. HSCSD,
however, is well suited for time-sensitive, real-time services
such as large file transfers. Packet is well suited to short file
transfers, messaging, or for longer file transfers where time
is not critical.
IP packet-switched networks operate as distributed networks—
after all, that was the reason for the creation of the
Internet in the beginning. Distributed networks allow for the
decentralized control of key elements required of a network
such as applications, management, and billing. Packet networks
are typically connectionless networks. The path that a
packet takes through the network can vary from packet to packet.
Circuit-switched networks are connection oriented. A connection
is set at the beginning of a session and remains until
the session ends. From a network point of view, connectionless
is a far more efficient use of the network resources because
resources are shared with all users dynamically. Circuitswitched networks use distance, location, and time as yardsticks
to measure the billing rate for sessions. In packet networks,
distance, time, and location are not as important as the
number of packets transferred through the network.
Usage billing becomes far more important in packet networks.
Circuit-switched networks are generally more proprietary,
legacy-based systems, whereas packet networks are much
less complex. Service provisioning is far more difficult for circuitswitched networks.