Information about VoIP (Voice over IP) - Quality of Voip Phone Service - IP Phone Service
As the networks originally designed for data, VoIP adoption also is needed to ensure that our voice has priority, that because the conversations occur in real time, so it is unacceptable that VoIP packets arrive late or too late or never. To resolve this problem we have created mechanisms to ensure that VoIP packets are prioritized over a network, so-called quality of service (QoS).The factors involved in the voice quality is as follows:
- Codec
- Bandwidth Latency
- (Redardo the arrival of packets)
- Jitter (latency variation)
- Loss Package
It is common that people think that just by increasing the bandwidth to VoIP is to solve your problems, but this is not necessarily true.
Suppose your company is in common use IP phones that integrate two Ethernet ports, so you share a single point in the IP network between your phone and your computer. However, suppose that you need to frequently transfer files between your PC and other network equipment, as well as the transfer is an 'avalanche' of information that tends to consume all available bandwidth on your connection to the network which seriously affects the application performance audio or video.
Most applications have a low priority on the network and tend to be tolerant of delays, for example slight delay while you get the news will not affect your goal of seeing the news, but it would be unacceptable in its communication by VoIP if teleñfonica these affect the voice quality and generating difficulty understanding what you say or what you say.
The ability to allow the packet loss in IP telephony is very low and should be kept below 2% that does not affect the quality markedly. But the problems that actually affect IP telephony are latency, jitter and boring ECO.
Latency
Is defined as the delay between sending and receiving packets, but from a user's point of view is defined as the gap in the conversation generated by the delays accumulated during the transfer delays and packet processing. The latter delays are often overlooked but it should be noted that while the G.711 codec produces a negligible processing delay of the G.729 tends to produce a larger delay due to compression process performed on the voice.
Delays due to compression can be reduced when using the codec G.711 instead of G.729 whenever possible, for example in local area networks where bandwidth is not a constraint, but connections using the Internet is still requires a compressor to reduce the bandwidth used by each call.
Delays due to the network can be measured with various tools (Cacti, Ethereal, etc) and usually can be adjusted to give attention to the physical components of the network that is often overlooked, such as connectors in poor condition, electric fields magnetic or too close (fluorescent lamps that intersect with the data cable), and others.
Jitter
Jitter is the variation in delays in the arrival of packets between the source and destination usually caused by traffic congestion at some point in the network or the difference in transit time of packets when they travel through different routes.
The usual solution is to use a Buffer (Jitter Buffer) to store the packages before delivery to the destination to ensure they all reach the destination in order, although this introduces an additional delay. In applications such as IP Telephony Asterisk can be configured for a jitterbuffer correct this problem.
On the other hand when it comes to Jitter in LAN or WAN are usually corrected by increasing the bandwidth, of course prioritizing packets will always be an alternative.
Eco
When we have latency and jitter in a VoIP communication can produce the phenomenon of Eco what is usually resolved using 'echo canceller', whether software or hardware.
There are 2 common types of echo: a high level and low-delay that is produced locally and a low level and further delay that occurs in the remote end. Both can be removed by the echo canceller, but it is important to understand that usually echo canceller hardware is more efficient than those built by software, that rule applies mainly to applications such as IP Telephony Asterisk Software although recently have been released by Echo Canceller Octasic software (not GPL), which have proved highly effective in the treatment of the echo.
On the other hand sometimes the echo is within the same IP phone by poor acoustic design or by direct influence of the materials that have been built, which can affect the performance of low-cost IP phones that have an even electronics quality sound level are affected by allowing a return of the voice between the headset and microphone. Usually this type of echo can not be solved with external echo canceller to the phone.
Packet Loss
The percentage of packets that do not reach their destination measures the loss of network packets. This loss may occur because of errors in any of the computers that allow the network connectivity or exceed the capacity of a buffer of a computer or application in times of congestion. Typically in applications that do not work in real time can take advantage of the retransmission of packets, but IP telephony operating in real time and packages can not be broadcast.
Classification & Prioritization
QoS Quality of Service is responsible for providing a level of service for different applications using the network can benefit from it in an appropriate manner, and since not all applications have the same standards of network quality service is assigned to each requirement that requires.
To talk about quality of service we must classify the traffic that travels through our network. Some applications may then be identified by the port they use to move their packages while others can use dynamic ports such identification impossible.
The most common ways to classify traffic on a network are:
- Protocol
- Port Number
- IP Header
- RTP header
- Content (eg, URL)
- Velocity and Flow Pattern
- RSVP Signaling
- Tags routing
- Signatures custom applications
Normally, the classification review, the contents of the package such as the IP protocol, port number or destination, this classification can be performed anywhere on the network, either at ends or in the middle of the network.
Today switches are common to prioritize network packets at the extremes and are an appropriate way to ensure that our packages arrive at their destination in the desired conditions, it is also possible to prioritize packets through traffic management equipment, bandwidth or through firewalls.
The routers can prioritize packets in a network environment and is quite common today, but there are usually less aware of traffic at both ends so that the routers are generally classified by size of package, flow velocity, but can also do it for content and direction.
Not usually reliable ranking delegate to end users or the same application and provided better results, leaving the classification system to one that specializes in such work, although the trend is that both SoftPhones as IP gateways play a role important in the QoS of the VoIP network.
