VoIP:

Voice over IP (also called VoIP, IP Telephony, and Internet telephony) is the routing of voice conversations over the Internet or any other IP network. The voice data flows over a general-purpose packet-switched network, instead of the traditional dedicated, circuit-switched voice transmission lines. Protocols used to carry voice signals over the IP network are commonly referred to as Voice over IP or VoIP protocols. Voice over IP traffic may be deployed on any IP network, including ones lacking an Internet connection, for instance on a private building-wide LAN. (Wikipedia | TechEncyclopedia)

T1:

A DS1 circuit is made up of twenty-four 8-bit channels (a.k.a. timeslots and DS0's), each channel being a 64 kbit/s DS0 multiplexed pseudo-circuit. A DS1 is a also a full-duplex circuit, meaning you can (in theory) send 1.536 Mbit/s and receive 1.536 Mbit/s simultaneously. A total of 1.536 Mbit/s of bandwidth is achieved by sampling each of the twenty-four 8-bit DS0's 8000 times per second. This sampling is referred to as 8KHz sampling. An additional 8 kbit/s is obtained from the sampling of a final framing bit, for a total of 1.544 Mbit/s. (Wikipedia | TechEncyclopedia)

DSL:

Digital Subscriber Line, or DSL, is a family of technologies that provide a digital connection over the copper wires of the local telephone network. Older ADSL standards could deliver 8Mbps over about one mile of copper wire. The latest standard ADSL2+ can deliver over 20Mbps per user over similar distances. However many copper lines are longer than one mile reducing the amount of bandwidth that can be transmitted. Modern cable systems, on the other hand, can provide 30Mbps downstream, but this bandwidth is shared between all the users on the cable segment. (Wikipedia | TechEncyclopedia)

OC3:

OC-3 (Optical Carrier 3) is a network line with transmission speed of 155.52Mbit/s (payload 150.336Mbit/s) using fiber optics. (Wikipedia | TechEncyclopedia)

VPN:

A Virtual Private Network, or VPN, is a private communications network usually used within a company, or by several different companies or organizations, communicating over a public network. VPN message traffic is carried on public networking infrastructure (e.g. the Internet) using standard protocols. (Wikipedia | TechEncyclopedia)

DS3:

A Digital Signal 3 (DS3) is a digital signal level 3 T-carrier. The data rate for this type of signal is 44.736 Mbit/s. This level of carrier can transport 28 DS1 level signals within its payload. This level of carrier can transport 672 DS0 level channels within its payload. (Wikipedia | TechEncyclopedia)