Computer Network | Quality of Service and Multimedia

Quality-of-service (QoS) refers to traffic control mechanisms that seek to differentiate performance based on application or network-operator requirements or provide predictable or guaranteed performance to applications, sessions, or traffic aggregates. The basic phenomenon for QoS is in terms of packet delay and losses of various kinds.

Types of Quality of Service

• Stateless Solutions: Routers maintain no fine-grained state about traffic, one positive factor of it is that it is scalable and robust. But it has weak services as there is no guarantee about the kind of delay or performance in a particular application which we have to encounter.
• Stateful Solutions: Routers maintain a per-flow state as flow is very important in providing the Quality-of-Service i.e. providing powerful services such as guaranteed services and high resource utilization, providing protection, and is much less scalable and robust.

QoS Parameters

• Packet loss: This occurs when network connections get congested, and routers and switches begin losing packets.
• Jitter: This is the result of network congestion, time drift, and routing changes. Too much jitter can reduce the quality of voice and video communication.
• Latency: This is how long it takes a packet to travel from its source to its destination. The latency should be as near to zero as possible.
• Bandwidth: This is a network communications link's ability to transmit the majority of data from one place to another in a specific amount of time.
• Mean opinion score: This is a metric for rating voice quality that uses a five-point scale, with five representing the highest quality.
• Throughput: Actual rate of successful data transfer over a network.
• Error Rate: Frequency of corrupted or lost data packets.

How does QoS Work?

Quality of Service (QoS) ensures the performance of critical applications within limited network capacity.

• Packet Marking: QoS marks packets to identify their service types. For example, it distinguishes between voice, video, and data traffic.
• Virtual Queues: Routers create separate virtual queues for each application based on priority. Critical apps get reserved bandwidth.
• Handling Allocation: QoS assigns the order in which packets are processed, ensuring appropriate bandwidth for each application

Importance of QoS

• Prioritizes Critical Applications: Ensures real-time apps like VoIP, video conferencing, and streaming perform smoothly.
• Reduces Latency and Jitter: Minimizes delays and fluctuations for better user experience.
• Minimizes Packet Loss: Maintains quality for time-sensitive and valuable applications.
• Efficient Bandwidth Usage: Optimizes traffic flow and prevents network congestion.
• Increases Network Reliability: Provides consistent performance even under heavy load.
• Supports SLAs: Meets service guarantees for delay, throughput, and availability.

Implementing QoS

• Planning: The organization should develop an awareness of each department's service needs and requirements, select an appropriate model, and build stakeholder support.
• Design: The organization should then keep track of all key software and hardware changes and modify the chosen QoS model to the characteristics of its network infrastructure.
• Testing: The organization should test QoS settings and policies in a secure, controlled testing environment where faults can be identified.
• Deployment: Policies should be implemented in phases. An organization can choose to deploy rules by network segment or by QoS function (what each policy performs).
• Monitoring and analyzing: Policies should be modified to increase performance based on performance data.

Models to Implement QoS

1. Integrated Services(IntServ)

• An architecture for providing QoS guarantees in IP networks for individual application sessions.
• Relies on resource reservation, and routers need to maintain state information of allocated resources and respond to new call setup requests.
• Network decides whether to admit or deny a new call setup request.

2. IntServ QoS Components

• Resource reservation: call setup signaling, traffic, QoS declaration, per-element admission control.
• QoS-sensitive scheduling e.g WFQ queue discipline.
• QoS-sensitive routing algorithm(QSPF)
• QoS-sensitive packet discard strategy.

3. RSVP-Internet Signaling

• Creates and maintains a distributed reservation state, initiated by the receiver.
• Supports multicast scaling, with reservations maintained as a soft state.
• PATH messages (forward direction) are used to discover the latest paths.
• RESV messages (reverse direction) are used to reserve resources along those paths.

4. Call Admission

• Session must first declare it's QoS requirement and characterize the traffic it will send through the network.
• R-specification: defines the QoS being requested, i.e. what kind of bound we want on the delay, what kind of packet loss is acceptable, etc.
• T-specification: defines the traffic characteristics like bustiness in the traffic.
• A signaling protocol is needed to carry the R-spec and T-spec to the routers where reservation is required.
• Routers will admit calls based on their R-spec, T-spec and based on the current resource allocated at the routers to other calls.

5. Diff-Serv

Differentiated Service is a stateful solution in which each flow doesn't mean a different state. It provides reduced state services i.e. maintaining state only for larger granular flows rather than end-to-end flows tries to achieve the best of both worlds. Intended to address the following difficulties with IntServ and RSVP:

• Flexible Service Models: IntServ has only two classes, want to provide more qualitative service classes: want to provide 'relative' service distinction.
• Simpler signaling: Many applications and users may only want to specify a more qualitative notion of service.

QoS Tools

• Traffic Classification and Marking
• Traffic Shaping and Policing
• Queue Management and Scheduling
• Resource Reservation
• Congestion Management

Multimedia

Multimedia combines “multi” (many) and “media” (means of communication). It refers to the presentation of text, graphics, audio, video, and animation with tools that allow users to navigate, interact, and communicate using a computer.

Components of Multimedia

• Text: Characters forming words and paragraphs; can use different fonts and sizes for presentation.
• Graphics: Digital visuals like photos, charts, or sketches that enhance appeal and clarity.
• Animation: Makes still images move, adding liveliness and engagement to content.
• Video: Moving images with sound, usually 15–30 frames per second, e.g., films or TV.
• Audio: Sounds like music, speech, or effects; used to enrich interaction. Formats include MP3, WMA,