Convergence Creates An Alphabet Soup

As the convergence of voice and data impacts an increasing number of enterprise customers and systems integrators, companies are finding themselves facing an alphabet soup of acronyms attached to technologies.

DSL is well-known, but what is less familiar are the many flavors of DSL, including ADSL, HDSL, SDSL and VDSL.

Two popular forms of DSL sold to businesses are asymmetric DSL (ADSL) and symmetric DSL (SDSL). HDSL (high bit rate DSL) is a T1 replacement that uses two copper pairs; and VDSL (very high bit rate DSL) is a delivery mechanism for video which requires users to be close to a service provider's central office, said Matthew Davis, senior analyst at The Yankee Group, a Boston-based consulting firm.

There are an exceptional number of DSL varieties because the market evolves so quickly and some of the older DSLs are deployed while new ones are created, said Brad Baldwin, research director at International Data Corp., Framingham, Mass.

Voice-over technologies also have their share of different versions. Voice over IP (VoIP), voice over Frame Relay (VoFR) and Voice over ATM (VoATM) represent the ways to push voice-over packet networks. VoFR relays content from the input port of the switch to the output port. It is used in WANs and across distant LAN-to-LAN connections. VoIP refers to packetized voice transmission over an IP network through a private Internet or WAN.

The major reason for running voice-over packet networks is to save money by avoiding regulatory costs, said David Schwartz, senior analyst at Dataquest, San Jose, Calif. The equipment and administration can be cheaper, and ultimately voice-over packet networks will be more feature-rich, he said.

VoATM and VoFR are prevalent in a carrier's backbone; and VoIP is used mainly in long-distance networks, Schwartz said.

There are multiple flavors of VoATM, said Steve Byers, principal analyst at Current Analysis Inc., Sterling, Va. The hot space right now is Voice over ATM Adaptation Layer 2 (VoAAL2), a variable bit rate format, he said. It is a WAN technology that fills silent pauses with data and does not commit network bandwidth during silent periods, so it is bandwidth-efficient, Byers said.

The VoAAL2 technology is used in SDSL deployment for small- and midsize-business customers, competitive local exchange carriers (CLECs) and independent local exchange carriers (ILECs), Byers said. CRN

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