MPLS: Why the fuss?
From ipinfinity.com
<digg/>
The current over-capacity in core networks and the resultant slowdown in the worldwide telecomminications market has caused carriers large and small to re-examine the return on investment from their existing network assets. The near commoditization of bandwidth pricing means that selling on price alone is not a winning strategy: someone else will always be able to sell faster and cheaper bandwidth. The focus is now on satisfying customer needs. And what customers need are IP services and flexible bandwidth. For delivering multiple network services over a shared network infrastructure, Multi-Protocol Label Switching (MPLS) is emerging as the most important technology. MPLS is the key to accelerated service delivery and the glue that ties together both new and old services. In this short white paper, we will provide a business-level overview of MPLS and why it is becoming the lynchpin for profitable service delivery.
Contents |
MPLS: A Brief history
Although MPLS is now beginning to be deployed in networks for service creation, it is not a new technology. Early proprietary predecessors of MPLS date back to the mid-1990s. For example, Cisco’s Tag switching, Ipsilon’s IP switching, and IBM’s ARIS were all originally proposed as methods for traffic engineering. As these proprietary protocols converged and eventually merged into MPLS under the auspices of the IETF, carriers and vendors alike began to examine and realize the full potential of the technology beyond traffic engineering.
MPLS: How does it work?
IP-based networks typically lack the quality-of-service features available in circuit-based networks, such as Frame Relay and ATM, to which businesses are accustomed. MPLS brings the sophistication of a connection-oriented protocol to the connectionless IP world; it is the secret sauce that makes IP networks good for business-grade applications. Based on simple improvements in basic IP routing, MPLS brings performance enhancements and service creation capabilities to the network.
In a traditional IP network, data packets are routed based on the information contained in their headers and on information that each router has regarding the reachability and availability of other routers in the network. In MPLS networks, packets are assigned a label upon entry to the network and forwarded based on the contents of this label only. By enabling routers to make forwarding decisions based on labels, MPLS avoids the process-intensive packet lookup scheme required in traditional routing. Forwarding packets based on labels rather than routing them based on headers results in several important advantages:
- Packets are processed faster because the time to forward a label rather than route a packet header is shorter
- Packets can be assigned a priority label, making Frame Relay and ATM-like quality-of-service guarantees possible
- Packets travel along circuit-like static paths in a public network, which are a foundation for Virtual Private Networks (VPNs)
- Packet payloads are not examined by the forwarding routers, allowing for different levels of traffic encryption and the transport of multiple protocols
Today, MPLS has three primary functions in a network:
- Traffic engineering
- Layer 3 IP VPNs
- Layer 2 tunneling and VPN Services
How MPLS is used in the network
When first deployed in the mid-1990s, MPLS was used for traffic engineering – that is, to set the path that traffic will travel through the network and to establish performance characteristics for different classes of traffic. Most important in networks where multiple parallel or alternate paths are available, MPLS combines the scalability and flexibility of routing with the performance and traffic management properties of Layer 2 switching.
To deliver IP-based services, MPLS is used to map a customer’s private IP network to the carrier’s own public IP network. These are commonly called MPLS BGP VPNs or RFC 2547 VPNs. Any changes in the IP topology of the customer’s network are dynamically communicated across the carrier’s public network to the customer’s other sites. The carrier achieves this by using MPLS to build virtual router tables for each of its customer’s networks and only forwarding data and routing information to the customer’s other network sites.
As standards groups further explored the properties of MPLS, they discovered MPLS could be used to build paths that emulate Layer 2 point-to-point connections, offering an alternative way of forwarding data without the high overhead of BGP VPNs. These are sometimes referred to as Layer 2 tunnels or virtual private lines. As secure as a Frame Relay or ATM virtual circuit, Layer 2 tunnels offer several appealing features. At Layer 2, MPLS can run over nearly any transport medium, including ATM, Frame Relay, Packet over SONET/SDH, and Ethernet, enabling the integration of IP networks with connection-oriented networks. Carriers can leverage MPLS to establish virtual circuits or tunnels across an IP network, laying the groundwork for MPLS VPNs. And carriers that own IP, Frame Relay, and ATM networks can use MPLS to link them into one interconnected cloud, avoiding expensive hardware upgrades both on the customer and service provider side.
How MPLS helps service delivery
The so-called Martini draft specifies how to transport traffic encoded on the network protocol level, or Layer 2, over MPLS-supported infrastructure. As the most ubiquitously deployed draft today, the Martini draft is already a de facto standard, with more than 10 networking vendors supporting it.
Early MPLS implementations required customers to rewrite their application protocols if they weren’t already able to run over a public IP network, an expensive and time-consuming task. To solve the problem, the Martini draft runs MPLS technology on the network and attaches a label to the packet. This way, carriers can encapsulate any type of traffic in a tunnel and send it out over their IP networks.
While the Martini draft is largely accepted in the industry for encapsulating Ethernet and Packet over SONET/SDH traffic, there still remains an intense debate over how to best encapsulate ATM and Frame Relay traffic. Various standards bodies, such as the ITU, the ATM Forum, the IETF, the IEEE, and the MPLS Forum, are currently working to develop a formal standard. Today, however, all implementations are proprietary.
How MPLS helps service migration
As a protocol-agnostic technology, MPLS enables carriers to leverage their access networks (typically Frame Relay) for service delivery by facilitating a seamless integration with IP networks. MPLS offers benefits that on one hand stem from the nature of IP networks and on the other hand are specific to MPLS-enabled IP networks. It has the underlying strength and scalability of IP routing plus circuit switching features such as path optimization and path protection. This allows carriers to design and build networks with the appropriate levels of Quality of Service (QoS) and redundancy depending on the customer’s business requirements.
Once MPLS has been incorporated into the network, carriers can create and deliver new services. It allows carriers to create point-to-point and point-to-multipoint tunnels, which can be used to connect enterprise campuses across the IP backbone. With Layer 2 MPLS tunnels, carriers can deliver virtual private lines, traditionally a private line or fixed copper circuit but now including Ethernet, and Virtual Private LAN Services (VPLS) between customer locations over an IP/MPLS backbone. By delivering Layer 2 MPLS services over their IP networks, service providers can leverage their existing infrastruc- ture while simplifying their network and reducing operating expenses.
How MPLS simplifies service delivery
In short, MPLS enables carriers to build connectionless IP networks that behave like ATM or Frame Relay networks. With virtual circuit-like tunnels, service providers can reap the benefits of ATM’s QoS capabilities by reserving bandwidth for mission-critical applications.
Most importantly, MPLS has altered service delivery and network integration by enabling seamless virtual tunneling on a cost-effective basis, yielding the following benefits:
- A migration strategy from legacy networks to MPLS-enabled networks: As an evolutionary, not
revolutionary, technology, MPLS works as the glue that binds disparate networks. Leveraging MPLS, carriers can extend Ethernet services over their ATM or SONET/SDH networks.
- Profitable new services: By setting up tunnels through the public network, MPLS enables carriers to
link points on their networks with virtual dedicated pipes to deliver Layer 2 and Layer 3 LAN-to-LAN extension services. At Layer 2, by establishing point-to-point tunnels, carriers can offer virtual private lines. Point-to-multipoint tunnels yield Virtual Private LAN Services. At Layer 3, carriers can establish virtual private networks to deliver BGP/IP VPNs.
- Flexible and dynamic services: MPLS offers carriers connection-oriented control over their
networks, enhancing their ability to deliver dynamic services, such as bandwidth on demand, in place of static ones.
Conclusion
Over the last 10 years there has been much talk of the triple threat of voice, video, and data. Combined with talk of building VPNs over public networks, there is a huge impetus building behind MPLS. It is now recognized as the key technology for delivering different types of service to address the widely diverse needs of network users – from small companies using the network to do business with their customers and suppliers to the largest Fortune 500 company building a global VPN. Just as IP is recognized as the common packet format to contain these different elements, so MPLS is now seen as the unified method of forwarding these diverse packets to their correct destinations with the appropriate level of service.
