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The MPLS FAQ - Page 3 of 3:

9. Generalized MPLS

a. What is "Generalized MPLS" or "GMPLS"
From "Generalized Multi-Protocol Label Switching Architecture" "Generalized MPLS extends MPLS to encompass time-division (e.g. SONET ADMs), wavelength (optical lambdas) and spatial switching (e.g. incoming port or fiber to outgoing port or fiber)." 

GMPLS represents a natural extension of MPLS to allow MPLS to be used as the control mechanism for configuring not only packet-based paths, but also paths in non-packet based devices such as optical switches, TDM muxes, and SONET/ADMs.

For an overview of GMPLS, see Generalized Multiprotocol Label Switching: An Overview of Routing and Management Enhancements

b.  What are the components of GMPLS?
GMPLS introduces a new protocol called the "Link Management Protocol" or LMP.  LMP runs between adjacent nodes and is responsible for establishing control channel connectivity as well as failure detection.  LMP also verifies connectivity between channels.

Additionally, the IETF's "Common Control and Measurement Plane" working group (ccamp) is working on defining extensions to interior gateway routing protocols such as OSPF and IS-IS to enable them to support GMPLS operation.

c. What are the features of GMPLS?
GMPLS supports several features including:

  • Link Bundling - the grouping of multiple, independent physical links into a single logical link
  • Link Hierarchy - the issuing of a suite of labels to support the various requirements of physical and logical devices across a given path
  • Unnumbered Links - the ability to configure paths without requiring an IP address on every physical or logical interface
  • Constraint Based Routing - the ability to automatically provision additional bandwidth, or change forwarding behavior based on network conditions such as congestion or demands for additional bandwidth

d. What are the "Peer" and "Overlay" models?
GMPLS supports two methods of operation, peer and overlay.  In the peer model, all devices in a given domain share the same control plane.  This provides true integration between optical switches and routers.  Routers have visibility into the optical topology and routers peer with optical switches.  In the overlay model, the optical and routed (IP) layers are separated, with minimal interaction.  Think of the overlay model as the equivalent of today's ATM and IP networks, where there is no direct connection between the ATM layer and the IP routing layer.

The peer model is inherently simpler and more scalable, but the overlay model provides fault isolation and separate control mechanisms for the physical and routed network layers, which may be more attractive to some network operators.

e. What is the "Optical Internetworking Forum"?
The Optical Internetworking Forum (OIF) is an open industry organization of equipment manufacturers, telecom service providers and end users dedicated to promote the global development of optical internetworking products and foster the development and deployment of interoperable products and services for data switching and routing using optical networking technologies.

An Introduction to the Optical Internetworking Forum White Paper can be found at

f. Where can I get more information on GMPLS?
For information about GMPLS standards development, visit the IETF Common Control and Measurement Plane (CCAMPP) working group web page at as well as the White Papers section of this web site.

10. Voice over MPLS

a. Can voice and video traffic be natively encapsulated into MPLS?
Yes.  The MFA Alliance has released a bearer transport implementation agreement which can be viewed at

11. MPLS Management

a. How are MPLS networks managed?
Currently, most MPLS implementations are managed using CLI.  Tools such as WANDL's NPAT simulator allow MPLS networks to be modeled prior to deployment.

Several companies in the operational support systems product space have introduced tools designed to ease MPLS network management and automatically provision LSPs.  A partial list is available at 

b. What products are available to model and test MPLS networks?
Http:// lists several commercial and shareware modeling & simulation tools.

c. Are there any MPLS-specific MIBs?
Several internet drafts have proposed creating MPLS-specific MIBS.  Please see for a complete list.

d. Is there open source MPLS code I can use to test MPLS?
Several open source implementations of MPLS currently exist.  These are listed on the MPLS Resource Center's "Vendor Info" page under the heading "MPLS Code."

12. MPLS Training

a. What shows and conferences provide information on MPLS?
Several conferences are devoted to, or include presentations on MPLS.  These include:

For a complete listing of upcoming events and shows,  see the "Training and Conferences" page of the MPLS Resource Center. 

13. MPLS Deployment

a. What are some examples of networks that are already running MPLS?
It used to be easy to maintain a list of worldwide MPLS deployments, these days it would be easier to maintain a list of networks that haven't deployed MPLS in one fashion or another. Nearly every global service provider now offers MPLS-based VPN services and many are using MPLS internally for traffic engineering. Maintaining an accurate list of actual service deployments would be nearly impossible.

For more information on MPLS in production environments, contact the MPLS-OPS list, The MPLS & Frame RElay Alliance, or NANOG.

14. MPLS Interoperability Testing

a. Are there any labs that are performing MPLS interoperability testing?
Several groups and organizations conduct MPLS interoperability testing, including:

  • The University of New Hampshire Interoperability Lab has set up a MPLS Consortium for vendors to test the interoperability of their products and to support MPLS standards development.  More information is available on their web site at
  • Isocore in Fairfax, VA conducts interoperability testing and hosts the "MPLS 200x" annual event each fall in Washington D.C.
  • The MFA Forum has conducted several GMPLS interoperability testing events at conferences such as SuperComm and Next Generation Networks.
  • EANTC AG is a vendor-neutral network test center located in Berlin, Germany and conducts independent MPLS interoperability testing
  • Photonic Internet Lab is supported by the Government of Japan and provides testing and simulation efforts for GMPLS development

 15. Acknowledgements

a. Who helped write this thing?
This FAQ is maintained by Irwin Lazar.  

The following individuals have contributed to this FAQ:
Geoff Bennett - Marconi Inc.
Hamid Ould-Brahim - Nortel Networks, Inc.
Rachel Craven
Paul Joseph - Cisco Systems, Inc.
Jeremy Lawrence, Cisco Systems, Inc. 
Roman Puls - EANTC AG
Rakesh Saha - Hewlett-Packard
Bryan Walsh - Marconi Inc.
Darryl Wortham - Cisco Systems, Inc.

b. How do I submit a question to the FAQ?
We're always looking for additional questions to add to the FAQ.  If you have a question that you'd like us to add, please contact us.


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