Label switching
Encyclopedia
Label switching is a technique of network
relaying to overcome the problems perceived by traditional IP
-table switching (also known as traditional layer 3 hop-by-hop routing). Here, the switching of network packets occurs at a lower level
, namely the data link layer
rather than the traditional network layer
.
Each packet is assigned a label number and the switching takes place after examination of the label assigned to each packet. The switching is much faster than IP-routing
. New technologies such as Multiprotocol Label Switching
(MPLS) use label switching. The established ATM
protocol also uses label switching at its core.
According to RFC 2475 (An Architecture for Differentiated Services, December 1998):
"Examples of the label switching (or virtual circuit) model include Frame Relay, ATM, and MPLS. In this model path forwarding state and traffic management or Quality of Service
(QoS) state is established for traffic streams on each hop along a network path. Traffic aggregates of varying granularity are associated with a label switched path at an ingress node, and packets/cells within each label switched path are marked with a forwarding label that is used to look up the next-hop node, the per-hop forwarding behavior, and the replacement label at each hop. This model permits finer granularity resource allocation to traffic streams, since label values are not globally significant but are only significant on a single link; therefore resources can be reserved for the aggregate of packets/cells received on a link with a particular label, and the label switching semantics govern the next-hop selection, allowing a traffic stream to follow a specially engineered path through the network."
A related topic is "Multilayer Switching," which discusses silicon-based wire-speed routing devices that examine not only layer 3 packet information, but also layer 4 (transport) and layer 7 (application) information.
Computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....
relaying to overcome the problems perceived by traditional IP
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
-table switching (also known as traditional layer 3 hop-by-hop routing). Here, the switching of network packets occurs at a lower level
OSI protocols
The Open Systems Interconnection protocols are a family of information exchange standards developed jointly by the ISO and the ITU-T starting in 1977....
, namely the data link layer
Data link layer
The data link layer is layer 2 of the seven-layer OSI model of computer networking. It corresponds to, or is part of the link layer of the TCP/IP reference model....
rather than the traditional network layer
Network layer
The network layer is layer 3 of the seven-layer OSI model of computer networking.The network layer is responsible for packet forwarding including routing through intermediate routers, whereas the data link layer is responsible for media access control, flow control and error checking.The network...
.
Each packet is assigned a label number and the switching takes place after examination of the label assigned to each packet. The switching is much faster than IP-routing
Routing
Routing is the process of selecting paths in a network along which to send network traffic. Routing is performed for many kinds of networks, including the telephone network , electronic data networks , and transportation networks...
. New technologies such as Multiprotocol Label Switching
Multiprotocol Label Switching
Multiprotocol Label Switching is a mechanism in high-performance telecommunications networks that directs data from one network node to the next based on short path labels rather than long network addresses, avoiding complex lookups in a routing table. The labels identify virtual links between...
(MPLS) use label switching. The established ATM
Asynchronous Transfer Mode
Asynchronous Transfer Mode is a standard switching technique designed to unify telecommunication and computer networks. It uses asynchronous time-division multiplexing, and it encodes data into small, fixed-sized cells. This differs from approaches such as the Internet Protocol or Ethernet that...
protocol also uses label switching at its core.
According to RFC 2475 (An Architecture for Differentiated Services, December 1998):
"Examples of the label switching (or virtual circuit) model include Frame Relay, ATM, and MPLS. In this model path forwarding state and traffic management or Quality of Service
Quality of service
The quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
(QoS) state is established for traffic streams on each hop along a network path. Traffic aggregates of varying granularity are associated with a label switched path at an ingress node, and packets/cells within each label switched path are marked with a forwarding label that is used to look up the next-hop node, the per-hop forwarding behavior, and the replacement label at each hop. This model permits finer granularity resource allocation to traffic streams, since label values are not globally significant but are only significant on a single link; therefore resources can be reserved for the aggregate of packets/cells received on a link with a particular label, and the label switching semantics govern the next-hop selection, allowing a traffic stream to follow a specially engineered path through the network."
A related topic is "Multilayer Switching," which discusses silicon-based wire-speed routing devices that examine not only layer 3 packet information, but also layer 4 (transport) and layer 7 (application) information.