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VoIP and DSCP Settings

Updated on April 24, 2012
IP Packets and VoIP QoS
IP Packets and VoIP QoS

QoS for VoIP

VoIP data on the Internet falls into a special category of traffic. Of course, when the Internet first started out almost everything was text. With the emergence of media like audio and video, new management techniques had to be devised to deal with them. For example, buffering allows a device to obtain a certain amount of media information before it starts running what it has so that minor disruptions down the line can be covered up by playing what has already been received. However, VoIP is even more special. This is because unlike other types of traffic, it is real-time. A person listening at one end of a call has to hear what the other person says as soon as possible.There's no space for extensive buffering or traffic management delays. This is why when using VoIP, users need to tell their computer networks to prioritize VoIP data over all others. This can only be achieved using Quality of Service or QoS systems.

This QoS can be implemented in a variety of ways. One technique is called Differentiated Services Code Point or DSCP. This is merely an implementation in the header area of IP packets related to VoIP which allows networks to understand that it's high-priority and needs to be delivered as quickly as possible.

SIP With DSCP Settings

As we have seen before, VoIP traffic using SIP is divided into two types. The first is when the connection is being set up using the SIP protocol involving the standard ports. The second, is when the actual communication takes place using the RTP protocol. These two types of packets have very different purposes and they need to be treated differently as well. The first is a control packet related to signaling and the second relates to media.

DSCP is a protocol which involves placing a number in a specific field in the IP packet that allows network components to recognize what it's meant for and how it has to be treated. A DSCP value of 25 for example lets the network know that the packet is low bandwidth but requires quick travel times. This should be used for control packets like SIP. On the other hand, the DSCP value of 46 implies that it is latency sensitive and networks are meant to provide a Best Effort or BE treatment to them. If you're on a wireless network and Wi-Fi for example, a value of 48 to 63 tells the network that the package is high-priority.

QoS settings for VoIP are very important to ensure that routers and devices recognize the real-time nature of the traffic and deliver it to you as soon as possible. This will help reduce latency, jitter, and lag. SIP account management can also include the setting up of QoS rules on the router and SIP clients. Contact your hosted VoIP system provider to find out what the ideal QoS settings need to be for you.


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