Multiprotocol label switching (MPLS) is a protocol designed to get packets of data to their destinations quickly and efficiently. Because it sends data straight to its destination, it is superior to regular Internet Protocol (IP) routing, which bounces data all over the internet before finally sending it to its final destination.
"Multiprotocol" means that the system does not depend on any particular protocol to operate. It is an overlay, which enables it to forward a variety of different types of data, regardless of the protocol used to organize them.
"Label switching" refers to the fact that system routers form a label-switched path (LSP), which is a predetermined path that routes the traffic within the network. This results in better transmission and overall superior quality of service (QoS) when compared to regular IP routing. Some companies have—and continue to use—it, particularly when a strong, uninterrupted connection is critical. It reduces latency and allows companies to execute smoother videoconferences or Voice over Internet Protocol (VoIP) calls, which depend on smooth, uninterrupted streams of data.
These objectives are similar to those of software-defined wide-area networking (SD-WAN). With an SD-WAN-powered connection, data is transferred more efficiently, producing smoother performance. For example, if a company wanted to ensure a smooth videoconference with several satellite offices or remote employees, they could use SD-WAN to make sure each video signal reaches everyone in the conference efficiently. Similar to MPLS, SD-WAN would produce an experience for the end-user with less latency while maintaining a higher resolution.
How an MPLS Network Works
MPLS is not a product or a service. Rather, it is a technique that designates paths to send data between nodes instead of endpoints. As a packet first enters the network, it gets assigned to a forwarding equivalence class (FEC), which dictates how the data packet is forwarded. This is done by appending a bit sequence label to the packet.
The bit sequence label acts like an address on an envelope that tells the data packet where to go. Packets with the same characteristics are associated with the same label and thus get forwarded using the same rules. As the data packet is forwarded from one router to the next, each router contains a table that tells it how to handle those specific types of packets.
In this way, data skips along short path labels instead of long network addresses. This can be done regardless of the underlying network protocols because MPLS is not limited to only handling one specific protocol. It supports whichever access technology is used—T1/E1, frame relay, digital subscriber line (DSL), or asynchronous transfer mode (ATM).
Because each data packet has specific directions as to where it should go, MPLS can allow for lower latency and better quality of service for the end-user.
Traditional IP routing can be compared to the current international airline system. If you want to fly from Belize to Boston, you may have to take one flight from Belize to Houston, Texas, another one to Newark, New Jersey, and yet another flight to Boston. Due to all of the transfers, the total trip can easily take over 24 hours.
With MPLS—and SD-WAN—it is like you are put on a private jet that follows its own, more efficient path. Likely, the jet could go straight from Belize to Boston. If the plane had to stop in the States, it would choose a spot along the way, such as North Carolina, not Houston which is hundreds of miles off course.
When millions of packets of data travel all over the country, some are bound to suffer delays, resulting in latency and poor quality. When data comes with specific directions that send it along a more efficient path, the end-user gets better quality video and audio, as well as faster overall transmissions.
MPLS and the OSI Hierarchy
It is hard to fit MPLS neatly into the Open Systems Interconnection (OSI) seven-layer hierarchy. It fits somewhere between Layer 2 and Layer 3. This is because Layer 2 includes the data link involving devices such as switches, while Layer 3 refers to the network, which includes routers. Because of this, it is sometimes referred to as existing at “Level 2.5” because it is not a device that facilitates a data link (Layer 2), but it is also not a device like a router (Layer 3).
However, like the devices encapsulated in each layer, MPLS does facilitate the transfer of data, so some choose to give it its own layer, “2.5.” It effectively sits “on top of” each node, sending data packets from one to the next, acting much like a unique layer in the hierarchy, moving data from Layer 2 to Layer 3.
Is MPLS an Effective Networking Method?
MPLS, like all networking tools, has distinct advantages and drawbacks. Some of its more compelling benefits can also be experienced using SD-WAN.
- Better performance: MPLS produces better performance than an older technology designed to perform a similar function, ATM. Asynchronous transfer modes first form virtual circuits between two endpoints, and after the circuit has been put in place, the data can be transferred. This worked well over a public switched telephone network (PSTN) and with integrated services digital network (ISDN), but MPLS works better with current IP technology.
- Better traffic management: MPLS ensures traffic on the network is sent to its destination efficiently. While it has an objective similar to that of a frame relay, it is more consistent when it comes to traffic management, resulting in less latency or packet loss.
- Improved security: Even though MPLS does not automatically come with its own security protocol, it is a virtual private network (VPN), which separates it from the public internet. Therefore, threats inherent to the public internet do not affect the system.
- Dependence on a carrier: With MPLS, you need a specific carrier to facilitate the system. If your carrier service disappoints and you decide to switch, your MPLS system may be compromised, requiring a redesign, extra work, and wasted time.
- Expense: MPLS costs far more than other technologies like broadband. If an organization decides to use this approach anyway, they would have to do a detailed cost analysis to make sure the benefits justify the extra expense.
- Lack of comprehensive coverage: An MPLS system is set up to serve a specific area with a limited number of end-users. Expanding the system to include a wider array of users or a broader service area would require an additional expense.