I am and a new Account executive at a major ISP and I sell T1/T3/OC3's ++. A common question that I get from customers is "What is the difference between fiber and a T1/T3 connection." What are some benefits and disadvantages to both technologies?
These are two different concepts. Fiber is a physical data transport medium that can be used to support many applications (i.e. FDDI, ATM, Gigabit Ethernet, etc.) T1/T3 are local provider defined services. T1 is a leased line with an aggregate speed of 1.54Mbs that can be multiplexed into many channels between locations. T3 is a leased line with an aggregate of 44Mbs that serves a similar function but at a much higher speed and cost.
It is possible that fiber is used in the equation from the provider to supply your T1/T3 line, however, this is transparent to the customer. Generally, fiber is installed by the customer to provide high speed backbone or campus networks. Unlike T1/T3, once installed, there are no recurring monthly charges.
The benefits of fiber are: customer-owned, very high speeds, no recurring costs, and the ability to create a seamless network across several buildings. The disadvantages are: upfront costs, expensive equipment, distance limitations, and the overall cost of labor to connect over long distances.
The benefits of T1/T3 leased lines: high speed (although nowhere near what fiber can provide), no distance limitations (can connect sites anywhere in the world), equipment is much less expensive. The disadvantages are: cost, monthly charges are based on speed and distance. The faster and further you go the more expensive. Reliability -- generally these provider services are pretty reliable, however, they do experience problems that will cause downtime to the customer. To avoid this, it is recommended to have backup lines with alternate routes in case the main line goes down. This can make monthly costs quite high.