Phone Service Providers

Quality of Service (QOS) is a networks capability to maintain better service and performance of selected network traffic over the various underlying technologies. However, it is not something that is inherent to a network. One must plan for QOS by deploying features that allow for its implementation throughout the network and not just on one area or on a select router. Using QOS technologies for Voice over IP (VOIP) phone service providers enable you to grant a higher priority service to voice, for instance, while servicing other data transmissions with a lesser priority.

QOS features on the VOIP helps one meet the goals for network performance, scalability, availability, and manageability. Optimization techniques used enable faster and better transmission by lowering delay rates and controlling jitter, required by critical business applications. The voice quality in a phone service providers network is only as good as the quality of the weakest network link. Packet loss, delay and delay variation all contribute to degraded voice quality. The QOS mechanisms empower the network to increase voice quality by minimizing both the fixed and variable delays in a given voice connection.

VOIP applications are real time in nature and so they require QOS from the underlying system. Various factors determine the voice quality

1. Choice of codec.

2. Delay

3. Jitter.

4. Packet loss.

With service providers competing for the same customer base and with the same services in offering, QOS has become a key differentiator. Yet, few phone service providers possess the necessary resources to manage QOS, especially with the increasing complexity of today's networks.

Voice traffic is time sensitive and hence it needs higher QOS than data traffic, such as e-mail. The widespread use of IP makes it ideal for emerging end-to-end voice applications used in conjunction with data applications. However, it is this conjunction that makes necessary the use of QOS to appropriately service both kinds of traffic. Networking equipment and end user stations that carry both data and voice, do not normally distinguish between traffic that requires high-priority connections from traffic that does not require priority service. Without QOS, it is impossible to ensure that voice traffic, which is considered critical and time-sensitive, receives a constant and predictable transmission performance across a backbone that is shared by data traffic.

In an enterprise environment, the long distance telephone charges are significantly reduced by transferring voice and video data over the Internet connection. However, rich multimedia applications, converging video, voice and data do contribute significantly in increasing the network traffic. In order to make VOIP a viable business application, the quality of VOIP should be equal to the traditional PSTN/ISDN voice and video services.

Time sensitive applications like VOIP require that they do not suffer from bandwidth contention from less critical applications and other internet traffic. An optimal quality of service (QOS) solution should therefore ensure that voice and video applications receive the bandwidth that they require.QOS allows for network convergence by enabling data, voice and new phone service providers applications to run on the shared network and bandwidth, thereby reducing the cost of the infrastructure. It works by allowing the prioritization of the VOIP by minimizing the delays and jitter.

What can QOS do for VOIP

1. Policing and shaping the n/w traffic.

2. Avoid Congestion.

3. Queuing and scheduling the network traffic by prioritizing.

What QOS does for voice traffic is that it reduces latency. It helps the voice traffic to get out first by prioritizing it. It uses low bandwidth efficiently and avoids VOIP packet loss. OQS works by using various techniques such as RTP (Real-time Transport Protocol) which allows using bandwidth wisely, LFI that is used to reduce latency and PQ-WFQ (Priority Queuing - WFQ) and LLQ (Low Latency Queuing) on all links to prioritize voice.

A network carrying voice traffic also carries data. Voice and data traffic sharing common path through the network may interact with one another in ways that would affect the application performance of each, resulting in network congestion and packet loss. A constant overload of traffic can get manifested in performance degradation and packet loss which is unacceptable in the case of voice traffic delivery. This network congestion, as it is called can be taken care of by deploying strategies that can implement queuing features. This will allow you ensure that time-critical voice traffic receives the priority transmission it requires.

Yet another effective way to avoid excessive delay is to fragment the data packets, which are larger, and interleave them with voice packets, which are smaller. This improves link efficiency by segmenting data packets into sequences of shorter packets called fragments and interleaving low-delay traffic with the resulting smaller packets. These fragments are of a specified size such that a receiving device can reassemble them into the original frame. In large networks, one needs to calculate the voice delay budget. Fragmentation is generally not needed on higher speed links (768kbps or greater). The optimum size of the fragment that one should specify depends upon the queuing delay.

However, one must understand that though QOS can do good things for you, however it cannot do the impossible. QOS is not a cure for an inadequately low bandwidth as VOIP needs its bandwidth too. QOS can help protect critical traffic on occasionally congested lines. Thus QOS isnt needed when there is enough capacity. It works well when the priority cases are a small percentage. It doesn't help when you run out of capacity or have too many of the priority cases. The algorithms that QOS uses for VOIP are specific to situations and technologies. Having complicated QOS techniques can end up slowing the network traffic rather than improving the performance, which would result in demeaning having QOS.

Finally, advances in technologies like priority control and low-delay processing in packet transmission have generated expectations that voice over Inter-net protocol (VOIP) can be achieved at the same level of VOIP Quality as that of fixed-telephone services. This possibility has created a need for quality-design and quality-control phone service providers methods based on the measurement and analysis of network and overall VOIP Quality. QOS techniques and algorithms wisely applied will surely enable VOIP services to match the quality of PSTN.