How MPLS worksMPLS – or Multiprotocol Label Switching – has been one of the big tech success stories of the past decade.

SAN FRANCISCO - The IETF Thursday threw a birthday party for one of its most successful standards: Multi-Protocol Label Switching.

The Internet’s leading standards body hosted a panel discussion outlining the reasons why the 12-year-old protocol has been so widely deployed and such a big moneymaker for carriers.

"MPLS is one of our wildly successful protocol suites," said Loa Andersson, co-chair of the IETF’s MPLS Working Group and the principal networking architect at the Swedish Research Institute, Acreo AB. Andersson served as moderator for the panel, which was hosted by the Internet Architecture Board, a sister organization to the IETF.

"The major applications that are making money on the Internet are on MPLS," said George Swallow, a Distinguished Engineer at Cisco and the MPLS Working Group Co-Chair.

With MPLS, the IETF integrated the label-switching capabilities of Asynchronous Transfer Mode with the packet orientation of the Internet Protocol. The IETF formed its MPLS Working Group in January 1997, and protocol specifications began trickling out a few years later.

In reviewing the history of the MPLS, the panelists outlined several reasons why MPLS has been so successful. These reasons are a roadmap for anyone trying to develop a successful Internet technology.

Here are the seven reasons why MPLS has proven so popular:

1. MPLS embraced IP

In the early 1990s, the telecom industry was pinning all of its hopes on ATM as the network backbone technology of the future. But in 1995, the Internet exploded, and carriers had to quickly refocus their efforts in a different direction. By 1996, IETF researchers were looking for ways to make circuit-oriented ATM technology run over IP. ATM proponents jumped aboard the MPLS bandwagon in 1997, when the IETF formed its MPLS Working Group. Swallow says the MPLS team was wise to embrace—rather than fight—IP.

2. MPLS is flexible

MPLS has built-in flexibility in several ways, Swallow says. The control plane and the data plane are separate, which allows for many control planes and many forwarding controls. That independence creates a lot of flexibility, Swallow says. Loose semantics allow for flexible control, as does the fact that MPLS supports a label stack of undetermined size. MPLS designers also figured out a simple but flexible way to handle unicast forwarding.

3. MPLS is protocol neutral

MPLS was designed to work in a multiple protocol environment. That allowed MPLS to work with ATM, Frame Relay, Sonet or Ethernet at the core. As backbone network technologies evolved, MPLS was able to evolve, too. MPLS also played a key role in supporting both legacy network technologies and the latest IP-based technology. Today, MPLS is being used to support metro-Ethernet services, mobile communications back-haul communications and video distribution.

4. MPLS is pragmatic

Juniper Fellow Kireeti Kompella says MPLS is "a study in pragmatism." He says the architecture created only two new protocols – Label Distribution Protocol (LDP) and Link Management Protocol (LMP) – and that everything else incorporated existing protocols. Another feature of MPLS that was pragmatic is that many MPLS specs came in competing pairs, and these pairs forced each other to improve. Although it required duplicative work for vendors, Kompella says this strategy "did a lot for the winning spec."

5. MPLS is adaptable

MPLS has been able to evolve over time to support new applications and services, including Layer 2 and Layer 3 VPNs, Ethernet services and traffic engineering. Tom Bechly, a network engineer with Verizon, says MPLS has been successful for service providers because it allowed them to grow networks quickly, add new services and reduce costs. Kompella says the MPLS protocol spec has "lots of wiggle room" which gave the MPLS Working Group room for extensibility. This was key because the reasons why carriers deployed MPLS changed between when the protocol was envisioned and when it was deployed, Kompella says.

6. MPLS supports metrics

The best network technologies have a measurable return on investment. Carriers love the fact that MPLS allows them to gather a wide range of statistics that they can use for network traffic trend analysis and planning. With MPLS, it’s possible to measure traffic volume, latency and delay between two routers. Carriers also can measure traffic between

hubs, metros and regions. Bechly says the ability to gather these statistics using MPLS is more important than path control.

7. MPLS scales

Successful Internet technologies need to be able to scale quickly, and MPLS was able to do that. Verizon uses MPLS for several global networks including its public and private IP networks as well as the vBNS network that supports the U.S. research community. Verizon’s Public IP network, for example, spans 410 points of presence on six continents and spans more than 150 countries. Bechly says these massive networks showed that "MPLS did work, and that it worked on a significant scale."

Read more about lans & wans in Network World's LANs & WANs section.

The Seven Virtues of MPLS

Usually when I blog I try not to wave the Sprint flag too vigorously. But this time, I just have to brag a little about our MPLS VPN product line. What prompts this is a recent event marking the 12th anniversary of Multi-protocol Label Switching (MPLS), about which Network World did a fine article regarding the protocol’s seven reasons for success.

Although Sprint was in the wilderness regarding ATM for a while (Sprint ION, anyone?), once that was fixed, we embraced IP stronger than any of the “traditional” wireline providers. While others were still hyping the benefits of traditional TDM phones and private lines to build “networks,” we stepped up and made the bet-the-company decisions that have led to our success today. Those decisions allowed Sprint to experience above-market growth rates for our IP products for the last three years, to become the fifth largest local phone provider, run a global MPLS network that spans five continents, and win more than our fair share of the IP/MPLS business from enterprise and government customers. Oh yeah, and it also supports the third-largest wireless provider in the U.S. enabling the largest (you guessed it) mobile Internet footprint.

Of all of the work I have done here at Sprint, helping develop Sprint’s Global MPLS product line is my badge of honor (and one that every Sprint person involved with this product and platform should be proud of). Its success dovetails with the seven reasons for MPLS’ success that Network World detailed. Specifically:

1. MPLS embraced IP. Most providers don’t talk about this, but virtually all the original MPLS networks used an ATM core (and often frame relay access). In fact, the initial deployments of MPLS were really solving “carrier problems” rather than customer problems. While these solutions worked fine, they didn’t make the leap in capability until service providers embraced IP. But Sprint started with an IP architecture and never used ATM for our backbone or access. We could have built an MPLS solution on ATM, but we didn’t because ATM was too restrictive and our IP backbone was far more capable of meeting customer needs.

2. MPLS is flexible. No argument here. If Sprint’s Global MPLS network can serve everyone, from Sprint wireless and cable VoIP all the way down to a three-branch community bank, the product has to be flexible. With flexible class of service settings, support for multiple VRFs (sub-VPNs), managed and network-only options, support for multiple protocols, native multicasting, network-based remote access support, and more, it’s clearly a product line to fit any need.

3. MPLS is protocol neutral. MPLS really did provide the flexible “glue” to overcome challenges of legacy technologies. To #1 above…MPLS solved all sorts of issues and has become the Kleenex of VPN network technologies. In other words, MPLS is the de facto standard for VPNs.

4. MPLS is pragmatic. The joke goes that when you put two engineers in a room, they come out with three opinions, each of which is the only correct one. MPLS broke down the engineering “religion” into something everyone could agree on.

5. MPLS is adaptable. Adaptability is the key to meeting customer needs. When the protocol was developed, few would have thought that MPLS (much less IP) could be used to support all of the things we do today, from local voice services to wireless services, real-time HD video, high availability applications, and more.  MPLS showed that IP wasn’t such a “scary” idea and that the technology could really solve practical enterprise problems.

6. MPLS supports metrics. One of the best parts of MPLS was that it allowed a carrier to really understand network performance. Being able to measure how the network performed gave us an incredibly detailed view of what the network was capable of doing. Support one VoIP customer? Sure. But millions? That’s a question you need to answer before telling a customer to fire their LEC for cable VoIP. This network understanding also allowed us to provide great SLAs for customers, SLAs that are end-to-end and commit to a certain experience between any two points and for all traffic. To prove it, we even created the Compass portal to let customers look within our MPLS cloud to view the actual performance of their network.

7. MPLS scales. Honestly, I still have not seen an enterprise network that Sprint’s MPLS product can’t support. Not every situation is right for MPLS VPNs, but regardless of size, complexity, product demands, etc., if the needs are properly qualified I know that our Global MPLS solution can meet your needs.

Bottom line: MPLS is here to stay, and its future, in my opinion, is as a foundation over which convergence will take place

What's next for MPLS?MPLS widely adopted for WANs; MPLS-TP, integration with LTE and IPv6 loom

Multiprotocol Label Switching has been without a doubt one of the most successful technologies of the past decade.The advantages of MPLS are many: in addition to protocol neutrality, MPLS is highly scalable and can intelligently route time-sensitive voice and video packets through low-latency routes throughout the network. Because of these key features MPLS has been widely adopted by enterprises for their WANs, as the most recent data from Nemertes Research indicates that around 84% of companies are now using MPLS for their WANs.

How MPLS works

But this success doesn't mean that MPLS is finished evolving as a technology, as the Internet Engineering Task Force (IETF) has been working on a number of different improvements to MPLS that will allow it to be applied to transport architecture, mobile backhaul and IPv6.

Perhaps the most important MPLS evolution will be MPLS Transport Profile (MPLS-TP), an MPLS expansion that is tailored for optical and transport networks. Andrew Malis, a member of the IETF's Internet Architecture Board and a principal member of Verizon Communications' technical staff, says that MPLS-TP is basically the same as MPLS but with key new features.

"MPLS-TP can take advantage of features such as Quality of Service and fast reroute and put that into optical and transport networks that have typically been based on TDM only," he says. "It brings the benefit of packet switching to optical and transport networks."

According to a paper as the ability to engineer traffic at a monitored end-to-end performance. Additionally, MPLS-TP can run over any physical layer, from Ethernet to SONET/SDH to OTN.

Mike Capuano, the director of service provider marketing at Cisco, says that some transport service operators have been reluctant to use MPLS over their networks because standard MPLS doesn't give them the level of control they feel they need. With MPLS TP, Capuano says transport operators will have the Operations, Administration and Maintenance (OAM) capabilities necessary for properly managing their network.

"Packet technologies have historically not had the same level of instrumentation that transport technologies like SONET/SDH," he says. "So there's been a lot of attention paid to giving Ethernet and MPLS those same features. In certain circumstances transport operators are more comfortable provisioning point-to-point links rather than using MPLS. With MPLS-TP they'll be able to manually provision MPLS tunnels."

MPLS over IPv6, LTE coming further down the lineWhile MPLS-TP will be the most immediate version of the technology to hit the market, engineers have also been hammering out ways to integrate MPLS with IPv6 networks and with 4G wireless Long Term Evolution networks. On the IPv6 side of things, Malis says that the major technological work is finished and that providers "can use MPLS to carry both IPv4 and IPv6 traffic." But even though MPLS is now compatible with IPv6, it's unlikely that it will become widely used in the near future since IPv6 traffic still only accounts for less than 1% of all Web traffic.

"IPv6 migration is obviously a big issue, but we don't think it impacts MPLS as much," Capuano says. "It's more about service providers moving quickly to get to IPv6 before we run out of IPv4 addresses."

Of more immediate interest is the potential to integrate MPLS with LTE technology and use it for mobile backhaul. InfoNetics analyst Michael Howard says that because LTE is an IP-based mobile data technology that it's a perfect fit for MPLS. Malis echoes Howard's sentiments and thinks that MPLS is an ideal technology to use for 4G mobile backhaul.

"3G networks are mostly based on ATM and 4G networks are based on Ethernet and IP," he says. "LTE is focusing on IP over Ethernet as its standard backhaul technology and MPLS works quite well there."

Malis says that designing an MPLS mobile backhaul system is particularly tricky because engineers have to have both clocking requirements and handoffs between stations. These

features are key for a technology such as LTE, which Malis notes will eventually be relied upon not just for data but for voice and video streaming as well. But once MPLS can be successfully implemented on and LTE network, Malis thinks that it will be a major asset to LTE service quality, particularly when it comes to giving priority to voice and video packets.

"One of the real strengths of MPLS is its ability to do traffic engineering," he says. "It's going to be quite a while where carriers are in the process of transitioning to LTE, and the nice thing about MPLS is that it will give them one common infrastructure that they'll get to use over and over."

Disadvantages of MPLS

Personally, I would set completely different criteria for assigning a praise of "wildly successful." For example:- Has the wide-scale implementation of MPLS resulted in significantly lower carrier/service provider TCO than the technology it replaced?- Has the wide-scale implementation of MPLS resulted in significantly better service level performance than the technology it replaced?- Has the end user/customer realized significantly lower access costs and significantly improved service/availability to integrate into an MPLS network, as compared to the previous technology in use?

Based upon these and other related criteria, as well as my experiences in the enterprise and carrier arenas, IMHO, the "jury is still out" (and deliberation is likely to continue for some time to come).

IETF is in a crisis. MPLS does not provide the data stability that is required for full interactive high resolution video conferencing. MPLS services today provide between 20 and 40 ms of data jitter (latency variance) or worse. That is fine for low resolution video conferencing that can stand 50ms buffer in the code/decode hardware and software. For high resolution video conferencing, consistent data jitter of less than 10ms end to end, with 0ms buffer is required in the code/decode hardware and software.

I tested and reported this information as early as 1999 in the IEEE. I got major argument from the vendors, all claiming that their equipment did not cause data jitter, each pointing at the others' implementations. The problem is not with the vendors, it is with the IETF IP stack. Any stack that alters the original frame, including recalculating the CRC for each new tag, can not help but induce data jitter.

The requirement for low end to end data jitter is one of the reasons that 802.3ah and 802.3ae provided OAM support directly in the Ethernet link stream. The IETF vendors realized that they

would not make as much money off of the IEEE standard so that pushed the IETF standard and only made the IETF standard available to the carriers.

There is good reason that vendors like Cisco, Juniper, and others are involved with MPLS, they make a lot of money off of it. By influencing the carriers to use MPLS as the basis for their services, the vendors have guaranteed themselves a market for their higher cost products, which in turn means higher cost of services from the carriers.

IETF is going to have to come up with an 802.1/802.3 like protocol that allows for multiple levels of routing across divergent path methods. For those that really know protocols, it sounds a lot like extended VLANs (an IEEE standard) over carrier interchanges that pushes the routing to the edges of carrier service clouds.

I haven't even commented on the requirement for EXTREMELY LOW data loss to prevent pixilation. I guess the IETF expects everyone to accept poor quality in their HiRes interactive video?

If you have complaints about MPLS performance, don't blame the IETF, Cisco, Juniper, et al. The standards work very well, as do the vendor implementations in various router and switch products.

You should direct your complaints about performance to the MPLS Service Providers, who are ultimately responsible for the design, engineering, and operation of their MPLS networks. Legacy telco providers who provision last-mile MPLS services over the same tired and deteriorating copper cable plant that they use for voice, private line, frame relay, etc, will provide service that's only as good as that last-mile cable plant.

We credit our MPLS 'performance issues' to ARWATTS...

[A]nother [R]eason [W]hy [ATT] [S]ucks