What is QoS?
It is Quality of Service.
You would always want a kind of guarantee that--your network would be able to run all those applications that you assign as High-priority applications, as efficiently & reliably as possible. You would want that all the traffic to/from those high-priority applications gets first priority, even if your network is facing any type of limitation, e.g., network congestion. You can achieve this virtual guarantee with QoS - a set of technologies which work in tandem for your network.
QoS technologies accomplish this by providing differentiated handling and capacity allocation to specific flows in network traffic. They allow the network administrator to assign the order in which packets are handled, and the amount of bandwidth afforded to that application or traffic flow.
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What Makes QoS Mandatory In Networks?The application of QoS is particularly mandatory, if your network usually carries traffic for resource-intensive systems/applications. For example, if your network is supposed to perform well when it is expected to deliver to IPTV, Online Gaming, Streaming Media, Live Video-conferencing, Video on Demand, VoIP etc, then you have no choice but to opt for QoS. Here you can see that all these applications have high sensitivity to latency and jitter.
Whenever you are thinking of network performance in terms of traffic, you are basically thinking of 4-parameters:
1. Bandwidth (Throughput)
It is the speed of a link. QoS can tell a router how to use bandwidth. For example, assigning a certain amount of bandwidth to different queues for different traffic types.
2. Latency (Delay)
The time it takes for a packet to go from its source to its end destination. This can often be affected by queuing delay, which occurs during times of congestion and a packet waits in a queue before being transmitted. QoS enables your organization to avoid this by creating a priority queue for certain types of traffic.
3. Jitter (Variance in latency)
The irregularity in the speed of packets on a network as a result of congestion, which can result in packets arriving late and out of sequence. This can cause distortion or gaps in audio and video that is being delivered.
4. Error Rate (Loss of Data-Packets)
The amount of data lost as a result of packet loss, which typically occurs due to network congestion. QoS enables your organization to decide which packets to drop in such events.
If your mission-critical applications do not get the bandwidth they need, then your business-processes would explode and you would be at the epic-center of that. You don't want that...
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How Does QoS Work In The Networks?QoS mechanisms operate by ORDERING the data-packets, and allotting the BANDWIDTH in the optimized manner. In other words, you can say that queuing of packets and bandwidth management are essential to QoS.
Before you go about implementing QoS, you should differentiate your network-traffic...
You can classify network traffic by IP address or port number, but this approach is not suitable for QoS. Instead, you should classify it by APPLICATION or USER(s). If you do that, you will much better classification of data. Right?
Trust me, this right classification of traffic along with a right policy, would allow you to ensure that there is adequate availability of resources for your most important applications.
Next, you would move on to assign some RULES to your queuing and bandwidth management tools. These tools are highly efficient in handling traffic flows, specific to the classification they received, when this type of traffic enters into the network.
Your queuing mechanism would then allow for packets within traffic flows to be stored until your network is ready to process it. Priority Queuing (PQ) is developed to ensure the necessary availability and minimal latency of network performance for the most important batches of applications and traffic by providing an assigned priority and specific bandwidth to them based on their classification.
This way you are ensuring that the most important activities on your network are not starved of bandwidth by activities of lower priority.
Applications, users, and traffic can be batched in up to 8 differentiated queues...
Let us not forget your bandwidth mechanisms here. Bandwidth management measures and controls traffic flow on your network infrastructure. Its job is to ensure that traffic does not exceed capacity and to prevent network congestion.
You would be using TAFFIC SHAPING, a rate-limiting technique that optimizes or guarantees performance and increases usable bandwidth; and SCHEDULING ALGORITHMS, which offer several methods for providing bandwidth to specific traffic flows.
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In the end, I would say that--
QoS is extremely important when you are dealing with applications that require high-bandwidth for real-time traffic.
For example, if your business depends heavily on Video-Conferencing, then the application or platform you are using for it, has clearly specified:
What is the minimum band-width this application require?
(There would be no upper-cap.)
What is the maximum latency this application would afford?
(beyond that packets would be dropped)
By defaults, these have high sensitivity to jitter and latency, such as VoIP and videoconferencing. Lost packets could cause a delay to the stream, which results in the sound and video quality of a videoconference call to become choppy and indecipherable.
QoS is not one single technology by itself, instead it is a set of technologies collaborating together. There are several techniques that you can use to guarantee the high performance of your most critical applications:
1. You can prioritize delay-sensitive VoIP traffic via routers and switches.
2. You can reserve resources using RSVP protocol.
3. You can create Queuing policies with Routers and Switches.
4. You can mark the traffic, using Class of Service (CoS) at layer 2 header and Differentiated Services Code Point (DSCP) at layer 3.
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This Article Was Written & published by Meena R, Senior Manager - IT, at Luminis Consulting Services Pvt. Ltd, India.
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