Computer Network | Quality of Service and Multimedia

Quality of Service (QoS) is an important concept, particularly when working with multimedia applications. Multimedia applications, such as video conferencing, streaming services, and VoIP (Voice over IP), require certain bandwidth, latency, jitter, and packet loss parameters. QoS methods help ensure that these requirements are satisfied, allowing for seamless and reliable communication.

What is Quality of Service?

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.

QoS Specification

• Delay
• Delay Variation(Jitter)
• Throughput
• Error Rate

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.

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

Benefits of QoS

• Improved Performance for Critical Applications
• Enhanced User Experience
• Efficient Bandwidth Utilization
• Increased Network Reliability
• Compliance with Service Level Agreements (SLAs)
• Reduced Network Costs
• Improved Security
• Better Scalability

Why is QoS Important?

• Video and audio conferencing require a bounded delay and loss rate.
• Video and audio streaming requires a bounded packet loss rate, it may not be so sensitive to delay.
• Time-critical applications (real-time control) in which bounded delay is considered to be an important factor.
• Valuable applications should provide better services than less valuable applications.

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

It creates and maintains distributed reservation state, initiated by the receiver and scales for multicast, which needs to be refreshed otherwise reservation times out as it is in soft state. Latest paths were discovered through "PATH" messages (forward direction) and used by RESV messages (reserve direction).

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

What is Multimedia?

The word multi and media are combined to form the word multimedia. The word “multi” signifies “many.” Multimedia is a type of medium that allows information to be easily transferred from one location to another. Multimedia is the presentation of text, pictures, audio, and video with links and tools that allow the user to navigate, engage, create, and communicate using a computer.

Components of Multimedia

• Text: Characters are used to form words, phrases, and paragraphs in the text. The text can be in a variety of fonts and sizes to match the multimedia software’s professional presentation.
• Graphics: Non-text information, such as a sketch, chart, or photograph, is represented digitally. Graphics add to the appeal of the multimedia application. The use of visuals in multimedia enhances the effectiveness and presentation of the concept. Windows Picture, Internet Explorer, and other similar programs are often used to see visuals.
• Animations: Animation is the process of making a still image appear to move. A presentation can also be made lighter and more appealing by using animation. In multimedia applications, the animation is quite popular. The following are some of the most regularly used animation viewing programs: Fax Viewer, Internet Explorer, etc.
• Video: Photographic images that appear to be in full motion and are played back at speeds of 15 to 30 frames per second. The term video refers to a moving image that is accompanied by sound, such as a television picture.
• Audio: Any sound, whether it’s music, conversation, or something else. Sound is the most serious aspect of multimedia, delivering the joy of music, special effects, and other forms of entertainment. Decibels are a unit of measurement for volume and sound pressure level. Audio files are used as part of the application context as well as to enhance interaction. Audio files must occasionally be distributed using plug-in media players when they appear within online applications and webpages. MP3, WMA, Wave, MIDI, and RealAudio are examples of audio formats. The following programs are widely used to view videos: Real Player, Window Media Player, etc.

Conclusion

QoS is critical for ensuring that multimedia applications run smoothly and effectively across a network. QoS techniques contribute to the quality and reliability of real-time applications by regulating bandwidth, latency, jitter, and packet loss. To fulfill the distinct requirements of various forms of network traffic, QoS is implemented using a combination of categorization, prioritization, resource reservation, and traffic management techniques.