Metro Ethernet

Metro Ethernet

Disclaimer; this is intended to be an introductory technical article; certain details have been excluded in the interests of space and clarity. Network design examples are presented to illustrate specific technical points and are not intended to fully complete.

Historically WAN’s (Wide Area Networks) and LAN’s (Local Area Networks) have relied on independent technologies. At a physical layer WAN technologies today continue to be based largely on legacy TDM systems that were built initially to support voice, video and early data communications in a reliable fashion. WAN connectivity over distance often requires the use of regenerators and meet points between multiple Telco suppliers that may span the globe. Without strict adherence to standards, these connections would not function. WAN technologies depend on highly complex and expensive equipment, which can guarantee inter-operability and “five 9’s” reliability required to support the millions of paying customers utilizing the network.

Meanwhile, the advent of early PC’s and the recognition of the value in networking devices together gave rise to Local Area Networks. These LAN’s were developed from a business customer perspective, which placed more emphasis on costs and ease of use over reliability. There were a number of different competing LAN technologies, two of the most common being Token Ring (IBM) and Ethernet (everyone else). The triumph of Ethernet in the marketplace, to the extent where it is included in every PC, game console and some refrigerators, provides a consistent and relatively inexpensive way to build internal networks with relative ease.

As the internal PC networks continued to grow and thrive a need to connect disparate facilities together resulted in development of bridges, gateways and ultimately routers for the sole purpose of connecting LANs to other LAN’s located anywhere from several miles to several thousand miles apart. These devices allow disparate interface types to be connected by performing the necessary modifications to the signal and protocols to allow WAN and LAN equipment to understand one another. Because LAN Ethernet and WAN TDM networks were so vastly different in their technical make-up these intermediary devices were needed to allow inter-communication to occur. While the benefits of enterprise connectivity are great, they come at the cost of special hardware, software and application complexity as the speed of the network can change by a factor of 100 between a client and the server (100 Meg bit per second Ethernet to 1.5 Meg bit per second WAN).

The ever increasing speed of LAN technology (Gig Ethernet is now at Best Buy), and in PCs and servers in addition to increasing complexity of applications and the need to exploit the large amount of data that already exists, causes users to require connectivity that is faster, cheaper, and more simple to own and operate. In recognition of these demands the telecomm industry has been working for the past several years to develop common standards, which will allow domestic and international end-to-end Ethernet services to be deployed as easily as T1. Today these standards do not yet exist.

Metro Ethernet is a generic name for a set of services that are used to replace traditional WAN connectivity with Ethernet connectivity. The use of the term Metro is because the normal range of these services is in the 10’s of miles and that is thought of as a Metropolitan area.

There are several drivers for Metro Ethernet. First the low cost of Ethernet hardware. While the cost of an OC-3 (155Mb) ATM interface is in the 1000s of dollars, the cost of a Gigabit Ethernet port in a switch is in the 100s or 10s of dollars. The other enabler is the increased deployment of what are called multiservice networks by the carriers. Multiservice networks are networks that are able to be used for multiple service offerings with the same network infrastructure. The services are voice, Internet access, dial access and so on. Multiservice networks can be implemented on several layers of the ISO model from fiber to SONET to IP depending on the carriers and its base of equipment. Many carriers offer several technologies for multiservice networks.

We are initially using Metro Ethernet to replace SONET based WAN services with Ethernet services the difference can be shown below.

The traditional WAN environment used in extended campus is below

Here a Layer 3 Ethernet switch is connected to a router which is connected to an ATM switch which is connected to the carrier. The router and its associated interfaces is a rather expensive system and costs upward