- The
QoS or the quality of service is such a parameter that refers to a number of
aspects of computer networks, telephony etc.
- This parameter allows
transportation of traffic as per some specific requirements.
- Technology has
advanced so much now computer networks can also be doubled up as the telephone
networks for doing audio conversations.
- The technology even supports the
applications which have strict service demands.
- The ITU defines the quality of
service in telephony.
It covers all the requirements concerning all the
connection’s aspects such as the following:
Ø Service
response time
Ø Loss
Ø Signal
– to – noise ratio
Ø Cross
– talk
Ø Echo
Ø Interrupts
Ø Frequency
response
Ø Loudness
levels etc.
- The
GoS (grade of service) requirement is one subset of the QoS and consists of
those aspects of the connection that relate to its coverage as well as
capacity.
- For example, outage probability, maximum blocking probability and so
on.
- In the case of the packet switched telecommunication networks and
computer networking, the resource reservation mechanisms come under the concept
of traffic engineering.
- QoS can be defined as the ability by virtue of which
the different applications, data flows and users can be provided with different
priorities.
- It is important to have QoS guarantees if the capacity of the
network is quite insufficient.
- For example, voice over IP, IP-TV and so on.
- All these services are sensitive to delays, have fixed bit rates and have
limited capacities.
- The protocol or network supporting the QoS might agree up
on some traffic contract with the network node’s reserve capacity and the
software.
- However, the quality of service is not supported by the best effort
services.
-Providing high quality communication over such networks provides a
alternative to the QoS control mechanisms that are complex.
- This happens when
the capacity is over-provisioned so much that it becomes sufficient for the
peak traffic load that has been expected.
- Now since the network congestion
problems have been eliminated, the QoS mechanisms are also not required.
- It
might be sometimes be taken as the level of the service’s quality i.e., the
GoS.
- For example, low bit error probability, low latency, and high bit rate and
so on.
- QoS can also be defined as a metric that reflects up on the experienced
quality of the service.
- It is the cumulative effect that can be accepted.
Certain
types of the network traffic require a defined QoS such as the following:
Ø Streaming
media such as IPTV (internet protocol television), audio over Ethernet, audio
over IP etc.
Ø Voice
over IP
Ø Video
conferencing
Ø Telepresence
Ø iSCSI,
FCoE tec. Storage applications
Ø safety
critical applications
Ø circuit
emulation service
Ø network
operations support systems
Ø industrial
control systems
Ø online
games
- All
the above mentioned services are examples of the inelastic services and a
certain level of latency and bandwidth is required for them to operate
properly. - On the other hand, the opposite
kind of services such as the elastic services can work with any level of
bandwidth and latency.
- An example of these type of services is the bulk file
transfer application based up on TCP.
- A number of factors affect the quality of
service in the packet switched networks.
- These factors can be broadly
classified in to two categories namely technical and the human factors.
The
following factors are counted as the human factors:
Ø reliability
Ø scalability
Ø effectiveness
Ø maintainability
Ø grade
of service and so on.
- ATM
(asynchronous transfer mode) or GSM like voice transmissions in the circuit
switched networks have QoS in their core protocol.
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