There are two elements that work together to communicate with the processing platform. The means of high-speed communication to the processor can be thought of as the 'pipe' through which the tranasctions will move. And the protocol used to communicate with the processor describes the manner in which information will move through the pipe.
Types of Pipes
Leased Line (not Lease Line) Refers to a phone line that is rented for exclusive 24/7 use from the installation location to another location.
Frame Relay: This can be used when leased line is too expensive or not available. Frame relay uses existing infrastructure.
ISDN: Another type of high speed connectivity using dedicated hardware. (see following)
ISDN turns a regular analog telephone line (copper wire line) into a high-speed digital access line. It supports voice and data communications simultaneously so the telephone and internet can be used at the same time.
- A subscription to an ISDN service through the local telephone company.
- Terminal Adaptor (an external device that is, essentially, a digital modem), purchased from the telephone company.
- A subscription to an ISP
Notes: T-1 is distance sensitive in cost and Frame Relay is not.
T-1 is one option as a pipe for leased line and can be fiber optic or copper.
Frame Relay - http://www.mywanonline.com/frame_relay_explanation.htm
Types of Protocol:
TCP/IP
Other types: IP/SSX and NetBEUI | 
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