Multi-Protocol Over ATM (MPOA)
A Brief Description
The explosive growth of the Internet and corporate Intranets has accelerated the proliferation of routed networks. As sophisticated applications emerge and requirements for interactive multimedia become commonplace, users will continue to crave higher network access speeds and increased performance. Also, the sheer number of global Internet, Intranet and World-Wide Web users will continue to grow at an astonishing pace.The impact of increased user demand on the existing infrastructure has been well documented. A tremendous strain has been placed on the traditional voice and data networks, often resulting in poor performance and costly outages.
As a result, the networking industry is responding to the challenge of increasing the performance and scalability of routed packet networks. Performance is commonly measured twofold, in terms of transit delay and packet loss.
In typical routed networks, packet level processing must be performed at each hop. As routed networks grow; the number of hops increases. Ultimately, the hop by hop processing results in incremental increases in delay and network performance begins to suffer.
There is no question that the multi-protocol routing function forms an essential basis for today's routed networks, perhaps the most notable of which is the Internet. Researchers worldwide have been investigating schemes to optimize the performance of large networks. Undoubtedly the multi-protocol routing function will continue to be essential in this evolution. The solution will need to be interoperable with today's routers and coexist seamlessly in today's Internetworks.
The ATM Forum's Multi-Protocol Over ATM (MPOA) specification is the industry's first standards based solution that allows routed networks to take advantage of the benefits of the ATM network (i.e. lower latency, performance, scalability). It expands on schemes such as LAN Emulation (LANE), Classical IP/ATM (RFC 1577) and the IETF NHRP (Next Hop Resolution Protocol) to create a standardized notion of a virtual router, or routing functionality integrated within a high speed dynamically switched ATM network. Conceptually, MPOA reduces the cumulative latency in a multi-protocol routed network by reducing the number of intermediate points where packet processing must be performed (i.e. hop-by-hop processing). MPOA allows traffic to be forwarded to its destination over an ATM virtual circuit, which incurs the net delay of a single router "hop."
MPOA splits the traditional role of the router into two functions. The first, the host functional group, deals with direct communication to the end user devices. And the second, the edge device functional group, deals with the network services like route determination, VC mapping and cut through packet forwarding. The ability to separate packet forwarding from other router functions allows a more efficient implementation of the two components. The ability to expedite forwarding of packets in this manner is what is known as 'cut-through routing' and is a distinguishing characteristic of MPOA. Through a new protocol called Next Hop Resolution Protocol (NHRP), routing entities within a switching infrastructure can communicate with one another to determine unknown IP-to-ATM address mappings. This enables the host or edge device to establish a shortcut path to the destination. In this manner, hop by hop processing is limited wherever appropriate and overall performance is enhanced.
The MPOA "switched-routing" methodology consists of three components:
Summary
Technologies such as ATM have gained widespread global acceptance due to their inherent capability of delivering Quality of Service (QoS) guarantees as well as graceful support of a broad range of access and trunking interface speeds. Through ATM, end calls are switched through the network using switched virtual circuits (SVCs) which allocate and release bandwidth as appropriate to meet the requirements of each application. This allows users the opportunity to consolidate data, video, voice and multimedia applications over a single facility. Leveraging the benefits of ATM to expedite the forwarding component of the routing function will strive to meet the diverse requirements of each application.
The powerful QoS and dynamic bandwidth reservation attributes of ATM provide a powerful high speed infrastructure for real-time and non real-time applications provides an elegant solution to the scaling and performance issues of routed networks.
Through intense collaborative efforts within the ATM Forum, a comprehensive group of specifications have been ratified. These specifications form a globally accepted basis for interoperable, standards-based ATM solutions and pave the way for service providers and end users to deploy viable multi-vendor ATM networks. As per the Anchorage Accord, a suite of specifications is currently in place that can leverage the benefits of ATM ranging from the physical layer interfaces to SVC signaling and traffic management.
With the MPOA, end users stand to gain significant performance benefits in consolidating their routed data traffic while leveraging many of the existing benefits of ATM.
Although many solutions have recently been promoted within the marketplace for addressing the issue of scaling routed networks, the ATM Forum MPOA specification presents the first standards based solution in the industry. The net result is increased efficiency and performance for large routed networks. Further, MPOA does not limit these gains solely to IP traffic.
In all, MPOA provides end users and equipment providers the confidence to invest in ATM for future-proof, high performance networking solutions. MPOA may well prove to be a critical component in the evolution of routed networks in the years to come.