Industrial > Modems, CSU/DSUs, Muxes

DDS (Digital Data Service) is an AT&T® service that transmits data digitally over dedicated leased lines. DDS lines use four wires, and support speeds up to 56 kbps; however, DDS is actually a 64-kbps circuit with 8 kbps being used for signaling. You can also get 64-kbps (ClearChannel™) service. Since the transmission is digital, no modems are needed. Dedicated digital lines are ideal for point-to-point links in wide-area networks.

T1 is a dedicated transmission line operating at 1.544 Mbps. It’s comprised of 24 DSOs, each supporting speeds of 64 kbps. The user sends data at N x 56 or N x 64 over T1 circuits. T1 operates over twisted-pair cable and is suitable for voice, data, and image transmissions on long-distance networks.

T1 is a digital transmission method for multiplexing multiple voice and data channels over two pairs of wires.

By using a technique called Time-Division Multiplexing (TDM), T1 interleaves both voice and/or LAN data across DS0 subchannels. The primary benefit of T1 is bandwidth—1.544 Mbps—available in 24 easily allocated 64-kbps DS0 subchannels.

T1 sends data in frames made up of 24 eight-bit words (one word for each subchannel) and one framing bit for a total of 193 bits per frame. A T1 channel transmits 8000 frames per second.

The framing bits on successive frames follow a pattern for a superframe format. T1 channel banks check this pattern to make sure synchronization is maintained.

T1 is the most flexible end-to-end digital service option available today. It’s the preferred service for internetworking voice, data, fax, and video signals across an enterprise network. And Black Box is your supplier of T1 hardware with a broad range of solutions for consolidating your global high-speed network management.

Local multiplexors extend the distance between computers and terminals or printers that are connected via customer-installed or telco-supplied cable.

Like line drivers, local multiplexors extend RS-232 communications and must be used in pairs. The difference between the two is that multiplexors merge several transmissions into one transmission over a single channel; line drivers generally transmit data over a single channel.

Local multiplexors operate over ordinary twisted-pair copper cable or fiber optic cable. Copper cable is typically used within buildings while fiber optic cable is the most common choice for connecting buildings in a campus environment. For in-building connections, copper cable is widely used because it’s comparatively inexpensive and easy to install. Your building might even have unshielded twisted-pair cable already in place.

The twisted-pair copper cable used for local multiplexors is run throughout buildings from the wallplates of each office or work area to a central wiring closet within the building. Wiring closets have centrally located punchdown blocks where all cables from the building are terminated. That way, when a connection needs to be changed or a new one needs to be made within the building, wiring can be easily rerouted on the punchdown blocks.

Selecting a local multiplexor.
When selecting a local multiplexor, keep in mind that copper-based multiplexors come in a vast array of types. You’ll find multiplexors available with RJ-11, RJ-45, or terminal block connections for your in-house wiring and with RS-232 connections for your computer equipment. All these multiplexors can be used to link a local device to a remote device within a building.