Friday, November 09, 2007

The Many Flavors of Ethernet Transport

The availability of Ethernet for MAN (Metropolitan Area Network) and WAN (Wide Area Network) transport is popping up all over. Why? Simply because Ethernet is in demand by IT and telecommunications managers looking to get the most Megabits per second at the lowest price for their companies. Ethernet also offers easier management. Multiple locations can be tied together as a large single network.

The very best situation is a direct fiber optic connection from a competitive carrier's point of presence (POP) to your premises. A large national carrier, such as XO communications, can provide first mile connectivity, transport throughout your metro area, and long haul service across the country. Ethernet over Fiber, or EoF, on a carrier designed for IP transport is highly efficient and results in cost savings far beyond what you may be expecting.

But what if you aren't lucky enough to be in a major office complex located in a metropolitan downtown area, just blocks from carrier facilities and already provisioned or "lit" for fiber optic service? Ah, that's were the creative solutions come in.

Ethernet has been widely implemented as a baseband technology for LAN networks. This means that rather than multiplexing the Ethernet signal on a carrier of any sort, it occupies the entire bandwidth of the cabling that carries it. This is still reflected in terms like 10 Base T or 100 Base T. the word "base" refers to baseband. The Ethernet signal is actually packets of information, each carrying up to 1500 bytes of user data.

Once you want to transport your LAN traffic over longer distances than local area network connections, it needs to be carried by a signal or "carrier" that can travel long distances. Actually, just about any digital communications system can carry the individual Ethernet packets as long as it has enough speed or bandwidth to be worthwhile. That includes the T-Carrier system developed by the phone companies to transport digitized phone calls, SONET (Synchronous Optical NETwork) fiber optic carriers, microwave relay and WiFi radios, and point to point optical lasers.

The T-Carriers are especially useful because they've been deployed all over the country and are a mature technology of the phone companies. T1 is the most familiar of the T-Carriers. It is the defacto standard for PBX telephone, dedicated Internet and point to point data transfers for small and medium sized companies. T1 lines are provisioned on twisted pair copper wire. In other words, phone lines. So, T1 lines go everywhere. Using protocol conversion to get packets to and from T1 frames, T1 lines can carry Ethernet. This is often referred to as Ethernet over T1( EoT1) or Ethernet over DS1 (EoDS1). DS1 is the definition of the Data Signal or framing specification for T1 lines.

A related service is Ethernet over DS3, EoDS3. DS3 is the Data Signal level for T3 lines that is also used for SONET fiber optic service. DS1 offers 1.5 Mbps of bandwidth, just a fraction of standard 10 Mbps Ethernet. DS3, however, offers 45 Mbps of bandwidth, almost half of a 100 Mbps Fast Ethernet signal.

When Ethernet is provisioned on T1 twisted pair or T3 coaxial cable, it may be referred to as EoC or Ethernet over Copper. There are other short distance modulation schemes that offer higher bandwidths using in-place copper wiring for that last mile or few hundred feet of connectivity. The big advantage of copper is that it is likely already in place for phone service. Fiber optic carriers offer higher bandwidths to easily support 10 Mbps, 100 Mbps and 1,000 Mbps Ethernet transport, but the cost of construction may be prohibitive unless you are near a carrier POP or are willing to commit to large bandwidth usage.

Which business bandwidth services make the most sense for your organization? Find out which nearby locations are already provisioned for Ethernet service and let our expert consultants help you find the most cost effective services for your needs.

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