Multiprotocol Label Switching (MPLS) and Jitter in VoIP

Multiprotocol Label Switching (MPLS)

 

 

MPLS (Multiprotocol Label Switching) allows packets to be forwarded at the Layer 2 (switching) level rather than at the Layer 3 (routing) level. This is important for Quality of Service (QoS).

MPLS is called multiprotocol because it works with the Internet Protocol (IP), Asynchronous Transport Mode (ATM), and frame relay network protocols. The claim to fame of MPLS is "any-to-any" connectivity. This statement generally implies a comparison to permanent virtual circuit (PVC)-based technologies such as frame relay and ATM, where each site has a physical circuit connecting it to the "cloud." Logical circuits are then configured on the physical circuits to create virtual circuits connecting sites together.

Multiprotocol Label Switching (MPLS) is a protocol for speeding up and shaping network traffic flow. This protocol allows most packets to be forwarded at the Layer 2 (switching) level rather than at the Layer 3 (routing) level. Each packet gets labeled at the edge of the service provider's network and that label determines which pre-determined path the packet will follow. The paths, which are called label-switched paths (LSPs), allow service providers to decide ahead of time what will be the best way for certain types of traffic to flow within a private or public network.

MPLS uses a variety of protocols to establish Label Switched Paths (LSPs) and forward IP packets across the network. The first (ingress) router inserts a label (or a stack of them) in front of the IP header and forwards the packet. All the subsequent routing switches ignore the IP headers and perform packet forwarding based on the labels in front of them. Finally, the egress router removes the label and forwards the original IP packet toward its final destination.

Service providers can use MPLS to improve quality of service (QoS) by implementing service level agreements (SLAs) that define acceptable levels of latency, jitter, packet loss and downtime. For example, a network might have three service levels -- one level for voice, one level for time-sensitive traffic and one level for traffic that won't matter if it takes a few extra milliseconds to travel through the network. The protocol also supports traffic separation and the creation of virtual private networks (VPNs), virtual private LAN services (VPLS) and virtual leased lines (VLLs).

MPLS got its name because it works with the Internet Protocol (IP), Asynchronous Transport Mode (ATM) and frame relay network protocols. A common misconception/ Mis understanding is that MPLS is only used on private networks, but the protocol is used for all service provider networks -- including Internet backbones. In present IT market place, Generalized Multi-Protocol Label Switching (GMPLS) extends MPLS to manage time division multiplexing (TDM), lambda switching and other classes of switching technologies beyond packet switching.

 

Jitter in Voice Over IP:

In voice over IP (VoIP), a jitter buffer is a shared data area where voice packets can be collected, stored, and sent to the voice processor in evenly spaced intervals. Variations in packet arrival time, called jitter, can occur because of network congestion, timing drift, or route changes. The jitter buffer, which is located at the receiving end of the voice connection, intentionally delays the arriving packets so that the end user experiences a clear connection with very little sound distortion. There are two kinds of jitter buffers, static and dynamic.

A static jitter buffer is hardware-based and is configured by the manufacturer.

A dynamic jitter buffer is software-based and can be configured by the network administrator to adapt to changes in the network's delay.