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NetWare Link/PPP can use any synchronous full-duplex point-to-point leased lines at speeds up to 2.048 Mbps. It also supports the use of switched-circuit lines (such as switched/56 service) and asynchronous communications over Public Switched Telephone Network (PSTN) lines, as well as synchronous communication over ISDN lines. Switched services and PSTNs provide additional flexibility by allowing on-demand and permanent connections. On-demand connections are established by the router when data must be passed to a remote system, and are terminated when idle. On-demand connection management minimizes the costs associated with serial line connectivity.
Character asynchronous and bit synchronous HDLC framing is supported by PSTNs. Device management allowing connection (circuit) establishment and termination over the PSTN is also supported using various modem command sets. Because PSTN access is unrestricted, authentication of the calling party during inbound connection attempts is provided. Because bandwidth available over most PSTNs is less than that of dedicated circuits, both PPP header compression and payload data compression is provided; however, only one compression method can be used per circuit, not both.
Within the United States, Australia, and Japan, T1 is a digital two-way telecommunications medium that operates at a clock rate of 1.544 Mbps. In Europe, E1 is the telecommunications medium and operates at a clock rate of 2.048 Mbps. The T1 data rate of 1.544 Mbps is digital signal level one, otherwise known as DS-1. The term T1 actually refers to the hardware (usually a system of copper wire cables and amplifiers or generators) used to transport data at the DS-1 rate; however, in common use, T1 has come to mean a transmission line or connection running at 1.544 Mbps.
Traditionally, telephone companies have used these high-speed backbone trunk lines to carry long distance and local voice traffic between their central offices. In addition to voice, T1/E1 is used to transmit facsimile, graphics, and other digital data. In recent years, T1/E1 lines have been used increasingly to implement WAN connectivity.
To access T1/E1 links, the router PC or file server that is running NetWare Link/PPP must be connected to a digital service unit/channel service unit (DSU/CSU) that encodes data for transmission over the WAN link. A DSU converts a serial bit stream into a DS-1 signal; a CSU provides an interface between T1 signaling and the local loop, provided by the local telephone company (telco). The WAN board that you install in the router or file server connects to the DSU/CSU multiplexer or modem.
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