Carrier Services

Network access can be a critical determinant of business reliability, service quality, and — ultimately — profitability. It can also turn out to be the weakest link in the value chain — imposing crippling costs while delivering sub-par performance.

Clearly, then, your choice of a carrier technology is a pivotal business decision, from which consequences will cascade like the waters of the Zambezi. Unfortunately, you face this choice just as a torrent of new carrier technologies arrives to obscure the view. It's thus more important than ever to take a clear and comprehensive look at the field before making a decision that will shape your relationships with suppliers, employees, and customers.

A practical approach
One of the simplest ways to classify carrier technologies — a category generally understood to include access, hosting, and data networking services — is in terms of their practical business uses:

Technologies used to enable inter-office and WAN connections include ATM, Frame Relay, Private Line, and IP-based VPN.
Technologies used for office-to-Internet connectivity include xDSL, T1 and T3, OC-3 and OC-12, Frame Relay, and ATM.
Remote worker and telecommuting connectivity technologies are typically divided into broadband (usually xDSL) and dialup access.
Secure remote access most often involves VPN technologies using a variety of security mechanisms, including SSL and IPSec.
Hosting services include co-location and fully managed dedicated hosting.
Finally, local and long distance voice services can be conventional or via IP telephony.

Here's a look at some of the characteristics of these network access technologies:

ATM (Asynchronous Transfer Mode)
ATM is a dedicated-connection switching technology that organizes digital data into 53-byte cell units and transmits them over a physical medium using digital signal technology. Individually, a cell is processed asynchronously relative to other related cells and is queued before being multiplexed over the transmission path. Because ATM is designed for easy implementation in hardware (rather than software), faster processing and switch speeds are possible.

DSL (Digital Subscriber Line)
DSL is a technology for bringing high-bandwidth information to homes and small businesses over ordinary copper telephone lines. xDSL refers to different variations of DSL, such as ADSL, HDSL, and RADSL. If you're close enough to a phone company central office offering DSL service, you may be able to receive data at rates up to 6.1 megabits (millions of bits) per second (of a theoretical 8.448 megabits per second), enabling continuous transmission of motion video, audio, and 3-D animation. More typically, individual connections will provide from 1.544 Mbps to 512 Kbps downstream and about 128 Kbps upstream. A DSL line can carry both data and voice signals; the data portion of the line is continuously connected.

Frame Relay
Frame relay is a telecommunication service designed for cost-efficient data transmission of intermittent traffic between LANs and between end-points in a WAN. Frame relay puts data in a variable-size unit called a frame and leaves any necessary error correction (retransmission of data) up to the end-points, which speeds up overall data transmission. Since the network (in most cases) provides a permanent virtual circuit, the customer sees a continous, dedicated connection without paying for a full-time leased line.

Synchronous Optical Network (SONET) (OC-3 and OC-12)
The Synchronous Optical Network (SONET) includes a set of signal rate multiples for transmitting digital signals on optical fiber. The base rate (OC-1) is 51.84 Mbps. OC-2 runs at twice the base rate, OC-3 at three times the base rate, and so on. Asynchronous transfer mode (ATM) uses some of the Optical Carrier levels.

T-Carrier (T1 and T3)
The T-carrier system, introduced by the Bell System in the U.S. in the 1960s, was the first successful system to support digitized voice transmission. The original transmission rate (1.544 Mbps) in the T1 line is in common use today in ISP connections to the Internet, as are T3 lines, which provide 44.736 Mbps. Another commonly installed service is a fractional T1, which uses some portion of the 24 channels in a T1 line. The T-carrier system is entirely digital, using pulse code modulation and time-division multiplexing (TDM). The four wires were originally a pair of twisted pair copper wires, but can now also include coaxial cable, optical fiber, digital microwave, and other media.