Services : Switched Data Service, Leased Lines and Digital Subscriber Line (DSL)

Switched Data Service
Switched data transmission services is the providing of data transmission service between points that are setup by or for the customer. A specific form of switched data transmission service offered in public telephone networks is called switched multi-megabit data service (SMDS). SMDS provides high-speed data connections in metropolitan areas that are often used for LAN-to-LAN connections where there are several interconnection points (ports). Interfaces to the SMDS networks normally range from T-1 (1.544 Mbps) to T-3 (44.736 Mbps) although 56 Kbps and fractional T-1 are offered in some locations.

Figure 1 shows an example of the cost structure of SMDS data transmission services. This diagram shows that the user pays an installation fee, a port fee for each access port to the data transmission network, and a monthly usage fee based on the data transmission rate used by the customer.


Figure 1: Cost of SMDS Data Transmission Service

Leased Lines
Leased lines are telecommunications circuits (either two-wire or four-wire) rented/leased from a telephone company to connect two or more locations on a permanent basis. Leased lines are normally associated with data services or voice PBX tie line services. Leased lines are ordered as either analog or digital circuits. Analog circuits provide a single full duplex (two-way) path between locations. They terminate in either telephone switches/instruments or in modems. Digital leased lines, on the other hand, terminate in customer service units (CSU’s) rather than modems. The cost of leased lines depends on the region of service, specific carrier pricing plan, and on distance (line length). As a result, leased lines often connect the end user to another carrier that interconnects another leased line to allow connection to its destination. As a result, leased line prices are often quoted from the customer’s location to an EO or POP of a carrier.

Figure 2 shows the typical costs involved in pricing of point-to-point leased lines in the United States. This table shows that average leased line costs for 56 kbps lines is approximately $240 per month. For a T1 line, the average cost is approximately $900 per month and the monthly cost for a DS3 (45 Mbps) connection is approximately $4800.


Figure 2: Typical Cost of Leased Line Service in United States

Digital Subscriber Line (DSL)
Digital subscriber line (DSL) service is a data service that offers varying data transmission rates to customer. DSL service usually connects users directly to an Internet service provider (ISP). DSL service is generally lower in cost than leased line cost. The difference between DSL service and leased line service is that DSL service does not usually guarantee a data transmission rate.

Figure 3 shows an example of cost of DSL service for an ADSL line. This table shows that a customer pays an initial DSL connection fee, purchases or leases a data interface (e.g., router), and pays a monthly subscription of approximately $50 per month.


Figure 3: Cost of Digital Subscriber Line Service