ISDN: (Integrated Services Digital Network) A switched digital phone line used for dedicated Internet access up to 128 Kbps. (Switched phone lines use the public telephone network in the same way that voice calls are connected, and are not dedicated/point-to-point circuits.)
DS-0 (64 K): Point-to-point digital telco line used for dedicated Internet access at 56 or 64 Kbps.
T-1 (DS-1): Point-to-point digital telco line used for dedicated Internet access at speeds up to 1.544 Mbps.
T-3 (DS-3): Point-to-point digital telco line used for dedicated Internet access at speeds up to 45 Mbps.
OC-3: Point-to-point digital telco line used for dedicated Internet access at speeds up to 155 Mbps.
Fractional service: a type of Internet access where only part of telco circuit (T-1 or T-3) is activated for use. For example, there are 24 64K channels on a T-1. Service providers offer pricing which is reduced from full T-1 rates for customers who anticipate that their usage will grow over time.
April 1998 Small Business Times, Milwaukee
