computer science

Multiprotocol Label Switching

Multiprotocol Label Switching is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Multiprotocol Label Switching rather than just read about it. In short: Multiprotocol Label Switching (MPLS) is a routing technique in telecommunications networks that directs data from one node to the next based on labels rather than network addresses. Whereas network addresses identify endpoints, MPLS labels identify established paths between endpoints.

Key takeaways

Multiprotocol Label Switching belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Multiprotocol Label Switching to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Multiprotocol Label Switching from memory before moving on to harder problems.

Reference excerpt

Multiprotocol Label Switching (MPLS) is a routing technique in telecommunications networks that directs data from one node to the next based on labels rather than network addresses. Whereas network addresses identify endpoints, MPLS labels identify established paths between endpoints. MPLS can encapsulate packets of various network protocols and supports a range of access technologies, including T1/E1, ATM, Frame Relay, and DSL. MPLS was originally developed to improve packet forwarding by reducing the reliance on complex routing table lookups. With the introduction of hardware-based forwarding engines, forwarding speed is no longer the main reason for deployment, and MPLS today is more often used for traffic engineering, differentiated services quality of service, and BGP/MPLS IP virtual private networks (VPNs). In an MPLS network, packet-forwarding decisions are made solely on the contents of labels, without the need to examine the packet itself. This allows for the creation of end-to-end connections across any type of transport medium, using any protocol. The primary benefit is to eliminate dependence on a particular OSI data link layer technology, and eliminate the need for multiple layer-2 networks to satisfy different types of traffic. Multiprotocol label switching belongs to the family of packet-switched networks. MPLS operates at a layer between traditional definitions of OSI Layer 2 (data link layer) and Layer 3 (network layer), and is often referred to as a layer 2.5 protocol. It was designed to provide a unified data-carrying service for both circuit-based clients and packet-switching clients which provide a datagram service model. It can be used to carry many different kinds of traffic, including IP packets, as well as native Asynchronous Transfer Mode (ATM), Frame Relay, Synchronous Optical Networking (SONET) or Ethernet. MPLS can exist in both an IPv4 and an IPv6 environment, using appropriate routing protocols. The major goal of MPLS development was the increase of routing speed. This goal is no longer relevant because of the usage of newer switching methods such as ASIC, TCAM and CAM-based switching able to forward plain IPv4 as fast as MPLS labeled packets. Now, therefore, the main benefit of MPLS is to implement limited traffic engineering and layer 3 or layer 2 service provider type VPNs over IPv4 networks. MPLS is standardized by the IETF in RFC 3031. It is deployed to connect as few as two facilities to very large deployments. In practice, MPLS is mainly used to forward IP protocol data units and Virtual Private LAN Service (VPLS) Ethernet traffic. Major applications of MPLS are telecommunications traffic engineering and MPLS VPN. MPLS works in conjunction with the Internet Protocol (IP) and its routing protocols, usually interior gateway protocols (IGPs) and supports the creation of dynamic, transparent virtual networks with support for traffic engineering, the ability to transport layer VPNs with overlapping address spaces, and for layer-2 pseudowires that are capable of transporting a variety of transport payloads (IPv4, IPv6, ATM, Frame Relay, etc.).

History In 1996 a group from Ipsilon Networks proposed a flow management protocol. Their IP Switching technology, which was defined only to work over ATM, did not achieve market dominance. Cisco Systems introduced a related proposal, not restricted to ATM transmission, called Tag Switching with its Tag Distribution Protocol (TDP). It was a Cisco proprietary proposal, and was renamed Label Switching. It was handed over to the Internet Engineering Task Force (IETF) for open standardization. The IETF formed the MPLS Working Group in 1997. Work involved proposals from other vendors, and development of a consensus protocol that combined features from several vendors' work. Some time later it was recognized that the work on threaded indices by Girish Chandranmenon and George Varghese had invented the idea of using labels to represent destination prefixes that was central to tag switching. One original motivation was to allow the creation of simple high-speed switches since for a significant length of time it was considered impractical to forward IP packets entirely in hardware. Advances in VLSI and in forwarding algorithms have made hardware forwarding of IP packets possible and common. The current advantages of MPLS primarily revolve around the ability to support multiple service models and perform traffic management. MPLS also offers a robust recovery framework that goes beyond the simple protection rings of synchronous optical networking (SONET/SDH). A number of different technologies were previously deployed with essentially identical goals, such as Frame Relay and ATM. Frame Relay and ATM use labels to move frames or cells through a network. The header of the Frame Relay frame and the ATM cell refers to the virtual circuit that the frame or cell resides on. The similarity between Frame Relay, ATM, and MPLS is that at each hop throughout the network, the label value in the header is changed. This is different from the forwarding of IP packets. MPLS technologies have evolved with the strengths and weaknesses of ATM in mind. MPLS is designed to have lower overhead than ATM while providing connection-oriented services for variable-length frames, and has replaced much use of ATM in the market. MPLS dispenses with the cell-switching and signaling-protocol baggage of ATM. MPLS recognizes that small ATM cells are not needed in the core of modern networks, since modern optical networks are fast enough that even full-length 1500-byte packets do not incur significant real-time queuing delays. At the same time, MPLS attempts to preserve the traffic engineering (TE) and out-of-band control that made Frame Relay and ATM attractive for deploying large-scale networks.

Dates 1994: Toshiba presented Cell Switch Router (CSR) ideas to IETF BOF 1995: George Varghese and Girish Chandranmenon published paper on threaded indices, a form of label switching, at ACM SIGCOMM annual conference 1996: Ipsilon, Cisco and IBM announced label-switching plans 1997: Formation of the IETF MPLS working group 1999: First MPLS VPN (L3VPN) and TE deployments 2000: MPLS Traffic Engineering 2001: First MPLS Request for Comments (RFC) published 2002: AToM (L2VPN) 2004: GMPLS; Large-scale L3VPN 2006: Large-scale TE "Harsh" 2007: Large-scale L2VPN 2009: Label Switching Multicast 2011: MPLS transport profile

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Multiprotocol Label Switching

Start with the simplest possible case. Write down what Multiprotocol Label Switching claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Multiprotocol Label Switching before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Multiprotocol Label Switching ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Multiprotocol Label Switching

In research: Multiprotocol Label Switching appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Multiprotocol Label Switching in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Multiprotocol Label Switching is common in secondary-school and first-year university syllabi. It links to neighbouring topics Internet Standards, MPLS networking, Tunneling protocols, so understanding it makes those chapters shorter.
In everyday life: Look for Multiprotocol Label Switching outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Multiprotocol Label Switching in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Multiprotocol Label Switching means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Multiprotocol Label Switching out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Multiprotocol Label Switching in simple terms?

Why does Multiprotocol Label Switching matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Multiprotocol Label Switching?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Multiprotocol Label Switching.