How to configure quality of service (QoS) in your VoIP-applications

Voice over Internet Protocol (VoIP) is quickly replacing landlines for delivering telephone calls to homes and businesses. Ordinary residential home VoIP providers include Vonage, Skype and now Google Voice. Businesses are replacing their legacy digital systems with service providers called Hosted PBX, Hosted VoIP, IP PBX, Virtual PBX, and many others. If you have plans to implement or have already implemented VoIP, you should review your network to ensure quality of service (QoS).

VoIP voice quality problems can have many causes. The lack of or prioritization of voice or QoS priorities is a major source of VoIP problems. This article provides information on where QoS needs to be implemented on the network and gives an explanation of what needs to be done.

QoS provides priority to VoIP packets at points in the network. The most common network choke for most homes and businesses is where data traffic is transmitted from a local area network (LAN) to the Internet. A LAN can operate at a speed of 10 MB to 100 MB (one million bits per second) or more. DSL and cable Internet services can have speeds of up to 256Kb (ths. Bits per second) on the Internet. In fact, the data is moving from a 10-meter superhighway to a 1-lane road. Since VoIP is very sensitive to delays, it does not have to wait for its turn to enter the 1-way road, your Internet connection.

QoS is activated by a router that analyzes each packet and sends certain data to the head of the line. QoS can be implemented through virtual local area networks (VLANs) or a differentiated service code point (DSCP) within the Type of service for IPv4 field or traffic class octet in IPv6. For those familiar with 7 layers of the network, the VLAN operates at layer 2, and the DSCP is layer 3.

VLAN

A VLAN is a virtual subnet that creates smaller broadcast domains on a local area network to ensure efficient use of bandwidth. For example, your VoIP phones may be grouped into one VLAN, and your computers into another. Separate voice and VLAN data may protect VoIP traffic from service disruptions caused by viruses or worms, since Ethernet switches may not connect IP traffic between VLANs.

The best priority is given to this VLAN that carries overall traffic to the Internet. Voice VLAN is assigned the highest priority.

DSCP

DSCP relations to packages that are classified and flagged as associated with a particular class. Routers that support DSCP implement Per Hop Behaviors (PHB), which implement packet forwarding mechanisms for each traffic class. DSCP is the main protocol router that uses different levels of service.

Although the network can implement up to 64 different traffic classes, it is recommended to use certain encodings in the DSCP field. Most networks typically use the default PHB defined, fast forwarding (EF), guaranteed forwarding (AF), and class selector. EF PHB is designed for applications that require low latency, low jitter, and low packet loss, making it suitable for VoIP, video, and other real-time services.

The main disadvantage of DSCP is that any application can mark the EF bit and compete with the critical traffic of your network. For example, your company may use a virtual PBX instead of the traditional telephone system. Your calls to the public switched telephone network should broadcast the Internet with low latency, jitter and packet loss. The router between the local network and the Internet provides packets marked with EF priority on the Internet. Your company's employees can use your personal Skype, Google Voice or other video services that can also mark the EF bit and compete with your critical VoIP traffic. This problem is resolved by certain routers that can check each packet and only support the EF bit for packets destined for specific IP addresses.

Although more difficult to implement, VLANs can provide superior voice prioritization if your computers and VoIP phones are different devices. VLANs assign priority to all traffic on the subnet, including call signaling. DSCP is easier to implement, but less accurate. However, quite small networks, such as small businesses and homes, install a router with DSCP traffic control.