Home > Articles > Networking

How Multiprotocol Label Switching Will Benefit the Internet

Learn the who, what, where, and why of multiprotocol label switching. Then learn how MPLS is done. This excerpt also covers the top ten benefits that MPLS will bring to the current and future Internet architecture.
This chapter is from the book

Do not go where the path may lead, go instead where there is no path and leave a trail.A
— Ralph Waldo Emerson

"It's the bandwidth, stupid."

This flip response from your favorite service provider after all of your keyboard pounding, all that excessive mouse clicking, and all of your "What's taking so long?" whining hit close to the mark in the past. The lack of bandwidth—that is, the carrying capacity of the communications channel—was the primary culprit for long delays, low throughput, and even poor reliability problems. The constantly increasing demands on the Internet and its services require planning and technological innovation for its undeniable success to continue and grow. Indeed, there is an increasing requirement for networking technology in general to accommodate and expand to satisfy the seemingly insatiable appetite for bandwidth resulting from more users and the deployment of new bandwidth-intensive applications.

The Internet is flourishing. Traffic is increasing at a dramatic rate as the Internet becomes a vital part of the communications infrastructure used today. The Internet has become the cornerstone of the Information Age, and Internet technologies are used extensively for many types of new, large-scale enterprise and private networks.

The types of traffic that flow on these networks now include dizzying arrays of voice, data, and video applications, each having their own particular set of services and resource demands. There is significant momentum in the convergence of the Internet and Public Switched Telephone Network (PSTN) that is introducing many new design, deployment, and management challenges. The number of users and devices that support and access the Internet is exploding. Also, many new and important networking technologies are being introduced and integrated throughout the Internet, from the core backbones all the way down to the edges and home access devices in "the last mile." Fiber optics and optical-based communications are also being introduced to work with packet-based networks with unprecedented urgency and resolve. The core of the Internet is being upgraded with high-speed glass fiber links that connect optical cross-connects (OXCs), wave division multiplexers (WDMs), and soon, photonic switches (PXCs).

A hallmark of the Internet has always been that packet traffic has been delivered on a "best-effort" basis using the TCP/IP protocol suite. Service level requirements are usually met by over-provisioning more and faster links and connecting more numerous and sophisticated routers and switches while assuring that network utilization does not get too high. Conventional routing protocols such as BGP, OSPF, and Intermediate System-Intermediate System (IS-IS) orchestrate routes for the routers placed throughout the network to facilitate the delivery of data packets from source to destination. The routers use these various routing protocol algorithms and signaling techniques to efficiently direct the traffic flow within the Internet.

The new and increased demands for more and different services with varying requirements are quickly forcing network and Internet service providers (NSPs and ISPs, respectively), and other specialized internetworking service providers, to realize that new technologies, in addition to more and faster equipment, are what is needed to keep pace.

Perhaps in the not-too-distant future, when a frustrated network user is pounding the keyboard and asking why the response time is so slow, a network administrator can update the standard reply with a snappier retort such as: "It's your quality of service, stupid."

MPLS is a new network technology that promises to offer QoS and many other new and timely applications to current best-effort, IP-based internetworking. MPLS is designed to operate with the current set of Internet routers and switching equipment, as well as become an important enabling technology for the next generation of Internet devices such as IP terabit (and soon, petabit!) routers and OCX switches. MPLS is also a vital solution that will allow current Layer 2 transport technologies such as ATM, FR, and Ethernet to seamlessly interoperate and coexist with IP-based networks. By allowing new disruptive technologies and current soon-to-be legacy implementations to coexist, MPLS provides network planners flexibility in migration and replacement tactics for their desired networking strategies. MPLS is often spoken of as the "glue" for next-generation networks because of this fact.

MPLS is a hybrid of a traditional network's Layer 3 routing protocols and Layer 2 switching technologies. The concepts are not new, but the way they are combined in MPLS may offer a fresh spin on evolving the Internet routing architecture. MPLS separates the control functions from the data forwarding functions in a manner that allows for new, flexible, and operational efficiencies. MPLS introduces a single forwarding model that is based on label swapping. It offers a richer model for routing packets based on additional and configurable input parameters. It also allows a stack of labels within a packet that can be used in a hierarchical fashion for several innovative, new applications. MPLS can coexist with many existing Layer 2 and Layer 3 protocols and provide scalability for how these protocols are used in today's networks.

MPLS allows for the rapid deployment of multiservice applications, which will allow service providers and network users to realize revenues in new ways. MPLS may be the enabling technology for the next information "gold rush."

MPLS is being developed within a working group of the IETF as an open and standardized way of doing label switching. The MPLS Working Group (WG) is also responsible for defining how to implement label-switched paths over various link level technologies. MPLS includes procedures and protocols for the distribution of labels between the network devices that do label manipulation and swapping.

MPLS was derived mainly from several proprietary efforts that were being done in the early and mid-1990s to marry switching and routing. This allowed MPLS's direction to be expanded into several new areas. Some view MPLS as an attempt to take the best features of the ATM technology and add them to IP. These include the connection-oriented nature of setting up paths and the ability to offer various levels of QoS to packet traffic. MPLS will also allow the interoperability of IP with ATM and FR in an integrated fashion to create a single manageable network infrastructure. Finally, the MPLS label framework is being expanded as a more general model for routing in optical switching networks and additional physical layer technologies, such as time division multiplexing (TDM) and the spatial switching of incoming fiber to outgoing fiber.

To better introduce MPLS, the "five W's and H"—a long-standing journalistic device that asks: who, what when, where, why, and how—is effective in presenting and summarizing the basics. Because MPLS is integrated as an Internet technology, it is also important to understand the basics of the Internet, its key models, and other closely related topics.

What Is MPLS?

MPLS is an exciting new hybrid technology that integrates the best of the current approaches for delivering packets from their source to their destination across an internetwork1. A formal definition is presented in Figure 1–12:

Figure 1–1 A formal definition of MPLS.

By using existing and newly enhanced Internet routing and control protocols, MPLS provides virtual connection-oriented switching across Internet routes by supporting labels and the label swapping paradigm. MPLS includes the implementation of label-switched paths (LSPs) over the most popular link level technologies. MPLS also provides the necessary procedures and protocols for the distribution of labels between MPLS-enabled routers and switches.

MPLS work is being done under the auspices of the MPLS WG within the IETF.3 MPLS is still a very new development; it just entered the Internet standards track in the RFC format at the beginning of 2001. (An RFC is the specification format that is used to place a protocol on the standards track and allow it to progress from proposed to draft to full Internet standard.) Current MPLS RFCs are described in Chapter 3, "MPLS Documentation and Resources." For a full discussion of Internet standards, see Appendix B, "MPLS-Related RFC Index."

Because they are being actively worked on, many MPLS specifications are still largely in Internet draft (ID) format. As such, the exact specifics of the protocol and other ancillary issues are being regularly discussed, revised, and improved. IDs can advance to RFCs. Note that all IDs carry with them the caveat that they are "draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or cite them other than as "works in progress"." The current MPLS IDs as of this writing are also described in Chapter 3, "MPLS Documentation and Resources."

The MPLS WG arose from a consensus at the Tag Switching Birds of a Feather (BOF)4 meeting held at the 37th IETF meeting in December 1996 in San Jose, California.5 The first official meeting of the MPLS WG was held the following April at the 38th IETF meeting in Memphis, Tennessee, where the acronym MPLS first came into common use. The MPLS WG has been working ever since in continuing its efforts to advance the MPLS specifications on the standards track.

The original MPLS WG charter statement is shown in Figure 1–2. Now that the MPLS architecture and signaling protocols are on the standardization track, the MPLS WG has undertaken additional tasks. These include investigating multicast issues, specifying extensions for authentication, defining and completing SNMP MIB definitions, specifying fault tolerance and recovery mechanisms, and documenting additional encapsulation methods for the latest lower layer technologies.

Figure 1–2 The original MPLS WG charter.B

Using MPLS for switching TDM slots, optical lambdas (wavelengths), and spatial switching (between incoming and outgoing fibers) are some of the latest developments. These efforts are collectively called Generalized MPLS, or GMPLS. GMPLS is discussed in Chapter 10, "Future MPLS Developments and Directions."

The MPLS WG also originally created a list of eight high-level requirements of "should's" and "must's" to further define the "what" of MPLS:

  1. MPLS should work with most data link technologies.

  2. MPLS should be compatible with most network layer routing protocols and other associated Internet technologies.

  3. MPLS must operate independently from any routing protocols.

  4. MPLS should support a wide range of forwarding granularities for any given label.

  5. MPLS should support operation, administration, and maintenance (OAM).

  6. MPLS must contain loop prevention or detection.

  7. MPLS must operate in a hierarchical network.

  8. MPLS should be very scalable.

These eight requirements are the cornerstones for the major development efforts that have ensued since they were defined. The requirements can be traced through the architecture and the additional supporting specifications.

In conjunction with these requirements, the MPLS WG also set forth a set of eight key objectives. These important MPLS aims are:

  1. The specification of standard protocols to maintain and distribute label binding information to support unicast destination-based routing, where the forwarding is done by swapping labels. (Unicast routing specifies exactly one interface; destination-based routing refers to routing based on the final destination of the packet.)

  2. The specification of standard protocols to maintain and distribute label binding information to support multicast destination-based routing, where the forwarding is done by swapping labels. (Multicast routing specifies more than one interface. The work of integrating multicast techniques and MPLS is still in the discussion phase.)

  3. The specification of standard protocols to maintain and distribute label binding information to support a hierarchy of routing knowledge, where the forwarding is done by swapping labels. (A routing hierarchy refers to knowing the topology within an autonomous system (AS), and also between ASs.)

  4. The specification of standard protocols to maintain and distribute label binding information for supporting explicit paths based on label swapping. These paths may be different from the ones calculated by conventional IP routing, which are based on destination-based forwarding. (Explicit paths are the key to the TE applications that are part of MPLS's prime advantage over conventional routing.)

  5. The specification of standardized procedures for carrying label information over different Layer 2 link level technologies. (MPLS link layer encapsulation makes the technology flexible and scalable.)

  6. The specification of a standard way to interoperate with ATM at the user and control planes (an excellent way to have ATM and IP interoperate, and also a migration path to TCP/IP-only networks).

  7. The specification of support for QoS technologies (such as the Resource Reservation Protocol, or RSVP). (QoS is also one of the most important MPLS applications. MPLS QoS will be a important enabler for the derivation of revenues from next-generation networks.)

  8. The specification of standard protocols to allow hosts to utilize MPLS. (Much like ATM, this objective was never met, as MPLS was implemented from the core outward. Host-based MPLS appears not to be feasible due to scalability and performance issues.)

As can be seen, most of these MPLS objectives serve as the basis for creating and designing the major MPLS technologies and protocols discussed in Chapter 4, "Core MPLS Technologies and Protocols," and Chapter 5, "MPLS Signaling and Label Distribution."

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020