T1, T3, and Switched 56 Digital Connectivities

The primary reason some people/companies use digital line is because it provides transmission that is nearly 99 percent error free.  Digital lines are available in several forms, including DDS (Digital Data Service), T1, T3, and Switched 56. Because DDS uses digital communication, it does not require modems. Instead, DDS sends data from a bridge or router through a device called a CSU/DSU (Channel Service Unit/Data Service Unit). This device converts the standard digital signals the computer generates into the type of digital signals (bipolar) that are part of the synchronous communication environment. It also contains electronics to protect the DDS service provider's network. T1 T1 is perhaps the most widely used type of digital line at higher data speeds. It is a point-to-point transmission technology that uses two-wire pairs (one pair to send and the other pair to receive) to transmit a full-duplex signal at a rate of 1.544 Mbps. T1 is used to transmit digital voice, data, and video signals. T1 uses technology called multiplexing, or muxing.  Several signals from different sources are collected into a component called a multiplexer and fed into one cable for trasnmission. At the receiving end, the data is de-multiplexed back into its original form.

Network Introduction Network Cabling Wireless Network Network Interface Card OSI Model Protocols Ethernet - Network architecture Token Ring - Network architecture AppleTalk and ArcNet - Network architectures Repeaters, Bridges, Routers, and Gateways E-mail Standards Modem & Async Comm. T1, T3,& Switched 56 Digital Connectivities Packet-Switching Network,Frame Relay and ATM ISDN & FDDI

A T1 channel can carry 1.544 megabits of data per second, the basic of T-Carrier service. T1 divides this into 24 channels and samples each channel 8,000 time a second.

Using this method, T1 can accommodate 24 simultaneous data transmissions over each two-pair wire. Each channel sample incorporates eight bits. Because each channel is sampled 8,000 time a second, each of the 24 channels can transmit at 64 Kbps. This data rate standard is known as DS-0. The 1.544 Mbps rate is known as DS-1.
 

T3

T3 and Fractional T-3 leased line service provides voice and data-grade service from 6 Mbps to 45 Mbps. They are the highest capacity leased line service commonly available today.

T3 and FT-3 are designed for transporting large amount of data at high speed between two fixed points. A T3 line can be used to replace several T1 lines.

Switched 56

Both local and long distance telephone companies offer this LAN-to-LAN digital dial-up service that transmits data at 56 Kbps. Switched 56 is merely a circuit-switched version of a 56 Kbps DDS line.

The advantage of Switched 56 is that it is used on demand, thereby eliminating the cost of a dedicated line. Each computer using this service must be equipped with a CSU/DSU that can dial up another Switched 56.

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