RAD - More

“xDSL” is a generic name for a group of technologies that pass high speed digital transmissions over twisted copper wire pairs, where DSL stands for “digital subscriber line.” Included are standard technologies, such as SHDSL, G.SHDSL.bis, ADSL, and VDSL.

The new G.SHDSL.bis standard enables symmetrical transmission at rates of up to 5.7 Mbps over 2-wires, 11.4 Mbps over 4-wires or 22.2 Mbps over 8-wires, to a range of 2.9 km (1.825 miles). With G.SHDSL.bis technology, a variety of services can be deployed over high bandwidth DSL connections. This compares with SHDSL, which enables symmetrical transmission at data rates up to 2.3 Mbps and symmetrical VDSL, which enables transmission at data rates up to 6, 13 or 26 Mbps for shorter ranges.

Baseband modems

Baseband modems, also known as short haul or short range modems, connect computers, bridges, routers, and other digital communications equipment over relatively short distances, such as inside buildings and campuses or within cities. The modems overcome limitations of digital interfaces and can provide LAN extension when connected to bridges and routers. Many of RAD’s baseband modems support LAN extension using a built-in remote bridge or router, with no need for an external one.

Intelligent modems

Intelligent modems (RAD’s “i” series) are baseband modems with management capabilities. These modems include a management channel that enables the user at the central site to configure the unit at the customer premises, remotely activate diagnostics, and receive real-time alerts on the system status. The management channel can operate in parallel to the data channel over the same wire or fiber link.

Fiber optic technology

Deregulation and demands for increased bandwidth have reduced the price of fiber optic cabling and installation. Fiber is generally superior to copper wires because it provides higher bandwidth over longer distances, is immune to electrical interference and power surges, and provides data security. Fiber optic modems are usually smaller and lighter and consume less power than copper modems.

Fiber optic distance and bandwidth

Distance and bandwidth are determined by fiber type and light source.

Fiber type – There are two types of fiber optic strands: multimode and single mode. Multimode fiber allows propagation of light at various paths, resulting in high attenuation, while single mode fiber allows a single transmission path, which results in lower attenuation and higher speeds.

Light source – Signal attenuation in fiber optics also depends on wavelength. Low attenuation occurs at three different wavelengths: 850 nm, 1310 nm and 1550 nm.

Point-to-point wireless links

License-exempt wireless links provide high bandwidth connectivity over long distances, at a fraction of the cost and time required to deploy fiber optic cables. Businesses can also avoid the cost of leased line service by connecting remote campus locations over wireless links.

The Airmux is RAD’s wireless point-to-point multiplexer. It aggregates E1/T1 circuits and Ethernet traffic over wireless links, extending data/voice transmission for tens of kilometers and miles.

Miniature fiber and short range modems

Miniature short range modems offer the same communications functions as AC-powered modems but with fewer features, such as limited diagnostics capability and no BER tests. Usually they operate over shorter distances at lower rates (normally up to 19.2 kbps). However, certain modems can operate at data rates up to 115.2 kbps in async transmission and up to 128 kbps in sync transmission.

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