SONET is the original fiber protocol developed by the telephone companies to transport large numbers of simultaneous telephone calls between switching centers and internationally. SONET stands for Synchronous Optical NETwork. There is an international version of this protocol called SDH for Synchronous Digital Hierarchy. Together they are often referred to a SONET/SDH.SONET’s origins go back to the initial development of digitized telephone conversations and the transmission of these a groups using trunks known as T1 lines. The larger T3 lines can carry the equivalent of 28 T1 lines or a data bandwidth of 45 Mbps. There are no faster copper telco standards. The next step up is OC-3 at 155 Mbps. That’s enough to transport 3 DS3 circuits and, indeed, the protocol is designed to easily multiplex and demultiplex lower level services. When you order a DS3 today, it will be transported most if not all of the way multiplexed into a OC service. A device called an ADM or Add-Drop Multiplexer gets the service on and off the optical network.
You’ve probably guessed that OC stands for Optical Carrier. There are a number of optical carrier levels that include OC-3 at 155 Mbps, OC-12 at 622 Mbps, OC-24 at 1.24 Gbps, OC-48 at 2.49 Gbps, OC-192 at 9.95 Gbps and OC-768 at 39.8 Gbps. When you hear about 10 Gbps SONET, it is an OC-192 service. The 40 Gbps that many carriers use for long haul transmission is OC-768.
What about intermediate rates? Not all levels between 1 and 768 are defined. Others, such as OC-9, OC-18, OC-36 and OC-96 are standardized but not generally offered in service.
SONET/SDH is set up in ring arrangements with two separate fiber strands for each ring. They are redundant circuits, so if one fails the other can pick up the load within 50 mSec.
Ethernet is a completely different protocol developed by the computer industry rather than the telephone companies. It is based on packets rather than telephone channels. Most LAN connected devices have a NIC or Network Interface Card that supports 10/100/1000 Ethernet. That means the device can run at 10 Mbps, 100 Mbps or 1,000 Mbps (1 Gbps). Corporate LANs may now run at 1 Gbps with some parts of the network using 10 Gbps or 10 GigE.
The equivalent of Ethernet in the LAN for local networks is Ethernet WAN or Wide Area Network. Switched Ethernet used for WAN applications is also called Carrier Ethernet. If the service is local to a particular city or metro area, it is often called Metro Ethernet or Metropolitan Ethernet and the network is referred to as a MAN or Metro Area Network.
Like telco services, Ethernet may be delivered over copper or fiber. Twisted pair copper telephone line can be used up to 100 Mbps. That speed is also available over coaxial copper cable through Cable systems. Beyond that, fiber optic connections can deliver 1 Gbps or 10 Gbps for business applications.
Ethernet is designed to be far more scalable than SONET. Instead of ordering a particular service level, such as OC-24, you order an Ethernet port capable of handling a maximum speed, say 1 Gbps. With the port in place, you can pay for Gigabit Ethernet if you need that much, or you can order 250 Mbps or 500 Mbps Ethernet and upgrade quickly and easily when the need arises.
Which fiber optic service should you order? In general, Ethernet is less expensive per Mbps than SONET. Sometimes the price savings can be dramatic. The one sticking point is that you need to have the service installed in your building. You may have one or the other services now or nothing at all. The cost of construction to bring in the right fiber from the right carrier can outweigh the monthly lease costs. You should know, though, that Ethernet can often be carried on SONET and that competitive carriers are hungry to get new buildings on their networks. These factors can affect the availability and pricing of fiber optic services to your building.
Fiber optic build-outs are progressing rapidly and the demand for high speed bandwidth increases. Even if you went out for bids a year ago, the situation may have changed for the better since then. The best thing to do is get new prices and availability for fiber optic bandwidth services for your particular business location.
Note: Photo of data center servers courtesy of WikimediaCommons
