By prioritizing Internet traffic and the core network more efficiently, quality of service (QoS) and traffic engineering functions can address the performance issues related to emerging Internet applications such as real-time voice and video streaming. Network equipment manufacturers are constantly developing new solutions that solve many of the problems associated with today's Internet applications. Multiprotocol label switching (MPLS) is one such solution that has been standardized by the Internet Engineering Task Force (IETF).

AN 132: Implementing Multiprotocol Label Switching with Altera PLDs (PDF) contains more information.

MPLS Network

Figure 1 illustrates the flow of a packet through an MPLS-enabled network. The source network is on the left and the destination network on the right. The large cloud in the center is the wide area network (WAN).

Figure 1. MPLS Network Diagram
  1a. Existing routing protocols (open shortest path first (OSPF), intermediate system to intermediate system (IS-IS)) establish the reachability of the destination networks
  1b. Label distribution protocol (LDP) establishes label-to-destination network mappings
  2. Ingress edge label switching router (LSR) receives a packet, performs layer-3 value-added services, and labels the packets
  3. LSR switches the packet using label swapping
  4. Egress edge LSR removes the label and delivers the packet

System Overview with Altera Solutions

Figure 2 shows an MPLS protocol stack. The diagram is separated into two sections: the control plane and the data plane. The control plane can be implemented on an embedded processor while the data plane can be implemented in programmable logic.

Figure 2. MPLS Protocol Stack


  • LDP = Label distribution protocol
  • LIB = Label information base; table of labels mapping input port/label to output port/label
  • CR-LDP = Constraint-based LDP, used for traffic engineering; resource reservation protocol traffic engineering (RSVP-TE) is another signaling mechanism used for traffic engineering
  • Internet protocol (IP) FWD = Next hop forwarding based on IP address; longest match forwarding used
  • TCP = Transmission control protocol
  • MPLS FWD = Label switching based on MPLS label and LIB lookup
  • UDP = User datagram protocol

Altera Advantages

Using Altera® devices and megafunctions for MPLS networks offers advantages in flexibility, time-to-market, a logic/processor solution, and ultimately, an overall cost reduction path.


System designers need flexibility when manufacturing MPLS systems to incorporate new value-added services. Because of the inherent risk that the services will not be adopted or will need modification while in the field, ASICs are not a viable platform for implementing MPLS. Altera’s FPGAs and intellectual property (IP) provide the flexibility to implement new proprietary features and perform remote in-field upgrades.


Many network equipment vendors continue to research and develop MPLS, and are competing to get to market first with an MPLS product that meets the requirements of Internet service providers. Altera provides programmable logic and IP cores for designers who cannot afford the turnaround times of ASICs. Altera's SoC devices, which feature the ARM® processors, and Altera's Nios® embedded processor can provide designers with time-to-market advantages.

Logic/Processor Solution

MPLS requires a fast logic implementation for label swapping. At the same time, label management functions need to be implemented in software. MPLS lends itself to the combination of logic and processor solutions. Altera’s Excalibur devices allow complex algorithms to be implemented in software, and speed-critical operations to be implemented in logic on a single leading-edge FPGA.

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