It's All on the Label
MPLS promises unity, faces interoperability conflicts
By Karen Brown
from the June 4, 2001 issue of Broadband Week
In the Internet universe, Multiprotocol Label Switching promises to be a sort of Grand Unification Theory, able to knit together networks of all IP stripes and flow data over them more efficiently.
Ironically, the biggest problem facing the new technology is trying to find unity--agreeing on a consistent set of application standards and getting vendors and network providers to make their systems interoperable.
The Basics
In a sense, MPLS brings old-fashioned dedicated circuits into the mixed up "best efforts" data delivery world of Internet Protocol. It starts with a label switch path, a set route for packets in a particular data transmission. Brainy label switch routers, located in the network core, can create these paths prior to the data transmission or when the packets' flow is detected by the system.
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The Alphabet Soup of MPLS
MPLS -- multiprotocol label switching. A specified framework for routing traffic across multiple IP networks.
SLA -- service level agreement. The contract between a provider and a customer that sets amount of bandwidth and quality of service, among other things.
VPN -- virtual private network. A growing technology that creates secure links between corporate offices and employees working remotely.
LSR -- label switch router. The brains of an MPLS network, LSRs sit at the network core and set the paths for data transmissions. They also create the labels for data packets.
LSP -- label switch path. The set route for MPLS packets. It can be set ahead of time or when the network detects an MPLS packet entering.
LER -- label edge router. The muscle of an MPLS system, these routers at the network edge strip labels from incoming data, swap them with reassigned replacement labels and send them along.
LAN -- Local Area Network. A network that connects individual computers that share a common connection line to the Internet.
MAN -- Metro Area Network. A system of interconnected networks in a metropolitan area.
ATM -- Asynchronous Transfer Mode. A well-established data switching protocol, it relies on creating stable but inflexible dedicated channel paths for data.
SONET -- Synchronous optical network. A standard for synchronous data transfer using optical networks now commonly found in metro-area fiber networks.
IP -- Internet Protocol. A method for transmitting data on the Internet that breaks data into packets. Each packet has a header with source and destination information, followed the data payload itself.
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The label switch routers then assign labels to data packets, which contain information about the destination and the delivery priorities based on service agreements forged between customer and network operator. As the packets travel through the network, label edge routers along the way strip off the labels and swap them with labels assigned by the core routers before firing it off.
Swapping labels at every hop may seem tedious, but it is more efficient than existing IP routing systems that can't forward packets based on their destination alone. Instead, they have to dig into the IP packet header to find the source and destination and then determine the path and level of service.
"You have to look at a lot of information in the IP header before you can determine what level of service you want to apply to the packet--and you have to do it for each packet," says Sujal Das, senior technical marketing manager for IP systems provider Marvell Technology Group's switching products business unit. "With MPLS you don't have to do any of that. All you have to do is pull out one label and push on another one. And you have a table ready in front of you, that tells you if the packet is going to that destination, you just push this label out and swap it with another one and let the packet go, which is significantly less signal processing than a traditional router."
Virtual circuit and point-to-point tunneling protocols also can create a dedicated connection between two points, but the problem there is the bandwidth is fixed. MPLS label switch paths appear only when the packets enter the network, giving the network operator greater bandwidth flexibility, Das adds.
Another important point: MPLS label information is independent from the packet's IP header, so packets can travel through a mix of edge networks. "Today wide area networks are a mix of technologies anywhere from ATM, frame relay, TDM, packet over SONET and what have you," says Sam Halabi, vice president of the IP carrier business development at Extreme Networks and a member of the MPLS Forum board of directors. "So MPLS seems to be the unifier of services across these backbones."
Where's the Market?
That being said, there are limits to MPLS's reach. Because it would be chaotic to assign labels for every packet destination across myriad networks, MPLS won't completely overrun IP packet forwarding for periodic Internet traffic. But for high volume traffic between two constant points--say communication between virtual private networks--it will make the process far more efficient, according to experts.
That is particularly true with Ethernet networks, the ever-popular edge connection protocol. Ethernet is gaining bandwidth and extending from office local area networks to higher-capacity metro-area fiber rings, but its Internet basics can't guarantee packet delivery or quality.
"What makes MPLS work really well from an Ethernet perspective is up to now Ethernet has been a connection that has been a 'we'll do our best to get it through'-type technology--it is not reliable for voice or video," says Ron Mohr, a senior manager of product marketing at Alcatel. "But with MPLS using RSVP and traffic extensions, we can actually reserve bandwidth ahead of time."
"So we now have reliable paths, so we can now send through there using MPLS," he adds.
Current Deployments
MPLS standards may not be set, but activity still is keen among equipment makers. Recently network equipment powerhouse Alcatel added MPLS capabilities to its newest PowerRail distribution router for use in metro area networks.
"MPLS functionality is coming like gangbusters on the markeplace," says Mohr, who is in charge of the PowerRail product line. Among customers "it is expected you are going to be doing MPLS."
Extreme Networks also has added MPLS functions to its Ethernet product line used in Gigabit Ethernet systems in metro loops in Sweden, Italy and New Zealand. The applications tend to focus on extending metro services such as LAN and VPN across wider regional networks.
"While MPLS in theory can deliver a wide range of switching functions, the initial deployments are the basics--using it as a way to connect two label switched path streams between two points," Halabi says. "So we moved away from all of the complexities of MPLS to the basics of MPLS, which is a circuit technology. And it is going to help evolve IP networks starting to look like the old ATM networks that we moved away from."
One Extreme customer stateside is Yipes Communications, which specializes in metro-area Ethernet networks. The San Francisco-based provider is starting to dabble with MPLS applications, says chief technology officer Kamran Sistanizadeh.
"Initially we are looking at MPLS as a traffic engineering and capacity planning tool," Sistanizadeh says. "It's a tool in a sense that we set up the MPLS pad in the core backbone to create differentiated services--possibly from the traffic engineering capabilities."
Despite the enthusiasm among equipment makers, testing and not deployment is the rule for Yipes. It is testing MPLS with limited transmissions between two regional metro-area networks, and also testing customer premisis MPLS systems in the lab. The hope is to have some limited deployment by the end of the third quarter, according to Sistanizadeh.
"I think definitely there is a promise there," he says. "I just don't want be too optimistic about it yet. I'm sure there are lots of areas where it can help us, in terms of differentiation of service and making sure our SLAs (service level agreements) are in good shape and so forth. But it just needs a lot more testing."
Halabi acknowledges MPLS deployment remains limited, but he thinks as metro-area networks continue to develop virtual LAN offerings, it will become a crucial asset for backbone networks to lure business.
"Whoever can offer the service on a larger scale with more geographical reach would have the value advantage," he notes.
Greatest Obstacles
But widescale deployments are well down the road, and most of the potholes have to do with technological democracy in action. For starters, standards are far from gelled. There is no shortage of drafts for proposed MPLS application standards submitted for comment to the Internet Engineering Task Force's MPLS working group.
While some applications such as traffic engineering are taking shape, "some of the applications coming out are based on MPLS as a technology itself," Halabi says. "So as you start changing the knobs, you need cooperation among multiple vendors to get that application up and running."
Without common agreement, there is a danger in trying to do too much, too fast with MPLS, he adds. "If you define the application very well and you don't try to do the A to Z of MPLS, you have immediate deployment of MPLS applications," Halabi says. "The problem that MPLS would face is if you would try to use it for too many things for too many applications at the same time, you end up having to deploy a complex network for a simple solution. This is where MPLS would stumble."
The reason there are some deployments now has to do with the fact basic MPLS switching is handled by hardware, while the applications are governed by software, Marvell's Das says.
"That is the cool thing about MPLS's design," he says. "So unlike past technologies, where there are interoperability issues and you are worried that you are going to have to re-string up your hardware to fix those issues, MPLS is very well laid out. There is hardly any chance you will have to re-string your hardware for interoperability. You will probably have to upgrade your software."
Still, the biggest hurdle for MPLS is interoperability--trying to get vendors and network operators to agree to common applications and label designations.
"We need to definitely emphasize the interoperability issue, and emphasize the fact that just because this works on one vendor machine does not mean that a cloud can talk to another cloud," Yipes' Sistanizadeh points out. "In most of our portfolio of services, we will have multiple clouds talking to each other, and therefore interoperability between major backbone providers is going to be very important."
With multiple schemes to handle MPLS applications--ranging from different tag sizes to varieties of tag assignment methods--getting one MPLS packet from one side of the world to the other over may be problematic for some time, he says.
"We are not going to be able to bring UUNet and Level3 and Yipes and RBOCs and IXC all together and say, 'Lets have one uniform MPLS.' I don't think that's practical," Sistanizadeh says. "But we are going to be working with each of these service providers that we hand off the traffic to, to understand and make sure that the routers accept our tags, for example. It can get very complicated."
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