Home > Articles > Networking > Voice/IP Communications

This chapter is from the book

Introduction to Multiprotocol Label Switching

Multiprotocol Label Switching (MPLS) is a method of switching IP packets through a network by applying simple labels to packets. This allows devices in the network core to switch packets according to these labels with minimal lookup activity. Besides the obvious advantage of faster network transit, MPLS also provides the privacy and quality of service (QoS) advantages of connection-oriented services such as ATM without the complexity of manually creating fully-meshed PVCs.

MPLS integrates the performance and traffic-management capabilities of the data link layer (Layer 2) with the scalability and flexibility of network layer (Layer 3) routing. MPLS is applicable to networks using any Layer 2 switching, but it has particular advantages when applied to ATM networks. It integrates IP routing with ATM switching to offer scalable IP-over-ATM networks.

In contrast to label switching, conventional Layer 3 IP routing is based on the exchange of network reachability information. As a packet traverses the network, each router extracts all the information relevant to forwarding from the Layer 3 header. This information is then used as an index for a routing table lookup to determine the packet's next hop. This is repeated at each router across the network. At each hop in the network, the packet's optimal forwarding must again be determined.

The information in IP packets, such as information on IP Precedence and Virtual Private Network (VPN) membership, is usually not considered when packets are forwarded. To get maximum forwarding performance, typically only the destination address is considered. However, because other fields could be relevant, a complex header analysis must be done at each router the packet meets.

The main concept of MPLS is to include a label on each packet. Packets or cells are assigned short, fixed-length labels. Switching entities perform table lookups based on these simple labels to determine where data should be forwarded.

The label summarizes essential information about routing the packet:

  • Destination

  • Precedence

  • VPN membership

  • QoS information from Resource Reservation Protocol (RSVP)

  • The packet's route, as chosen by traffic engineering (TE)

With label switching, the complete analysis of the Layer 3 header is performed only once: at the edge label switch router (LSR), which is located at each edge of the network. At this location, the Layer 3 header is mapped to a fixed-length label.

At each router across the network, only the label need be examined in the incoming cell or packet in order to send the cell or packet on its way across the network. At the other end of the network, an edge LSR swaps the label out for the appropriate header data linked to that label.

A key result of this arrangement is that forwarding decisions based on some or all of these different sources of information can be achieved by means of a single table lookup from a fixed-length label. For this reason, label switching makes it feasible for routers and switches to make forwarding decisions based on multiple destination addresses.

Label switching integrates switching and routing functions, combining the reachability information provided by the router function with the traffic engineering benefits achieved by the optimizing capabilities of switches.

ATM MPLS Technical and Business Benefits

MPLS, in conjunction with other standard technologies, offers many features that are critical for service providers:

  • MPLS, in combination with the standard IP routing protocols OSPF and IS-IS, provides full, highly scalable support of IP routing within an ATM infrastructure.

  • MPLS, in combination with Border Gateway Protocol (BGP), provides support for highly scalable IP VPN services. IP VPN services are an invaluable development in provider networks, giving enterprise customers a service that meets their needs for private, connectionless delivery of IP services.

  • Service-Level Agreements (SLAs) can be provided in a form suitable for connectionless traffic. Cisco networks assist the process of providing SLAs by supporting MPLS in combination with forthcoming standards. Along with supporting VPNs, the ability to offer SLAs suitable for IP traffic is a critical requirement to meet new demands for IP services.

  • Cisco's implementation of MPLS allows support for harder QoS where required using full ATM switch capabilities.

Cisco IP+ATM networks fully support all relevant IP routing protocols and MPLS while fully supporting traditional ATM services. MPLS and IP routing can readily be introduced into traditional ATM networks by using permanent virtual path (PVP) or PVC tunnels since MPLS-capable switches are continuously being introduced.

Cisco IP+ATM switches allow carriers to continue meeting their existing demands for virtual circuit services while adding optimized support for critically important new services: IP and IP VPNs. Furthermore, Cisco supports all the standards relevant to carrier-class IP services: MPLS, Multiprotocol BGP, other standard routing protocols, and MPLS traffic engineering.

Label Switching Advantages

MPLS offers many advantages over traditional IP over ATM.

When integrated with ATM switches, label switching uses switch hardware optimized to take advantage of the fixed length of ATM cells and to switch the cells at high speeds. For multiservice networks, label switching allows the Cisco WAN switch to provide ATM, Frame Relay, and IP Internet service all on a single platform in a highly scalable way. Support of all these services on a common platform provides operational cost savings and simplifies provisioning for multiservice providers.

For ISPs using ATM switches at the core of their networks, label switching allows the Cisco BPX 8600 series, the 8540 Multiservice Switch Router, MGX 8850-PXM45 (discussed in a moment), and other Cisco ATM switches to provide a more scalable and manageable networking solution than overlaying IP over an ATM network. Label switching avoids the scalability problem of too many router peers and provides support for a hierarchical structure within an ISP's network.

These MPLS benefits are analyzed in greater detail in the following list:

  • Integration—When applied to ATM, MPLS integrates IP and ATM functionality rather than overlaying IP on ATM. This makes the ATM infrastructure visible to IP routing and removes the need for approximate mappings between IP and ATM features. MPLS does not need ATM addressing and routing techniques such as PNNI, although these can be used in parallel if required.

  • Greater reliability—In wide-area networks (WANs) with ATM infrastructures, MPLS is an easy solution for integrating routed protocols with ATM. Traditional IP over ATM involves setting up a mesh of PVCs between routers around an ATM cloud, and the Next-Hop Resolution Protocol (NHRP) achieves a similar result with switched virtual circuits (SVCs). But a number of problems exist with this approach, all arising from the fact that the PVC links between routers are overlaid on the ATM network. This makes the ATM network structure invisible to the routers. A single ATM link failure could make several router-to-router links fail, creating problems with large amounts of routing update traffic and subsequent processing. (See the next section for details.)

  • Better efficiency—Without extensive tuning of routing weights, all PVCs are seen by IP routing as single-hop paths with the same cost. This might lead to inefficient routing in the ATM network.

  • Direct CoS implementation—When used with ATM hardware, MPLS makes use of the ATM queueing and buffering capabilities to provide different classes of service. This allows direct support of IP precedence and CoS on ATM switches without complex translations to the ATM Forum service classes.

  • More elegant support of multicast and RSVP—In contrast to MPLS, overlaying IP on ATM has other disadvantages, particularly in support of advanced IP services such as IP multicast and RSVP. Support of these services entails much time and work in the standards bodies and implementation; the resulting mapping between IP features and ATM features is often approximate.

  • VPN scalability and manageability—MPLS can make IP VPN services highly scalable and very easy to manage. VPN services are an important way to provide enterprises with private IP networks within their infrastructures. When an ISP offers a VPN service, the carrier supports many individual VPNs on a single infrastructure. With an MPLS backbone, VPN information can be processed only at the ingress and exit points, with MPLS labels carrying packets across a shared backbone to their correct exit point. In addition to MPLS, Multiprotocol (BGP) is used to deal with information about the VPNs. The combination of MPLS and Multiprotocol BGP makes MPLS-based VPN services easier to manage, with straightforward operations to manage VPN sites and VPN membership. It also makes MPLS-based VPN services extremely scalable, with one network able to support hundreds of thousands of VPNs.

  • Reduces the load on network cores and is more robust—VPN services demonstrate how MPLS supports a hierarchy of routing knowledge. Additionally, you can isolate Internet routing tables from service provider network cores. Similar to VPN data, MPLS allows access to the Internet routing table only at the ingress and egress points of a service provider network. With MPLS, transit traffic entering at the edge of the provider's autonomous system can be given labels that are associated with specific exit points. As a result, internal transit routers and switches need only process the connectivity with the provider's edge routers, shielding the core devices from the overwhelming routing volume exchanged on the Internet. This separation of interior routes from full Internet routes also provides better fault isolation and improved stability.

  • Traffic engineering capabilities—Other benefits of MPLS include traffic engineering capabilities needed for the efficient use of network resources. Traffic engineering lets you shift the traffic load from overutilized portions of the network to underutilized portions, according to traffic destination, traffic type, traffic load, time of day, and so on.

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.

Overview


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.

Surveys

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.

Newsletters

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.

Security


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

Children


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

Marketing


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.

Choice/Opt-out


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.

Links


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