LIU also encodes and decodes the analog waveform to and from the Pulse Code Modulation (PCM) used in the PSTN. The line interface unit (LIU) handles the electronic signaling interface to the Public Switched Telephone Network (PSTN) Network. In internal hardware modems, the internal bus of the computer handles this function. With external modems, a physical cable (such as an RS-232 serial interface) connects the computer to the modem. Hardware modems can be external or internal. Hardware modems have historically been the best modems performance-wise, and also the most reliable type.

In a hardware modem, the modem handles LIU, DSP and CP functions. However, you must also have a good understanding of the mix of client modems. You can troubleshoot the circuit and NAS side to ensure that they are functioning correctly.

The number of analog to digital (A/D) conversions in the circuit. The quality of the circuit (end-to-end connection) between the client modem and the NAS. The quality of the modems on the client side as well as on the NAS. The ability of the NAS modem to interoperate with the vast and ever-shifting range of peer modems (of various quality) encountered in the field. General modem and line operational quality is closely tied to many factors such as: These issues can be caused by client-side, Telco or circuit, or network access server (NAS)-side problems. Many Internet Service Providers (ISPs) encounter user complaints about unstable connections, low connect speeds and so on. The three different types of client modem discussed here are: A controller also interprets attention (AT) commands.

The protocols for hardware error correction, hardware data compression, and basic modulation protocols (for example, V.34, X2, or K56 Flex) exist in the controller. Refer to the appropriate modem manufacturer documentation for more detail.Ī datapump that performs the basic modulation/ demodulation tasks for which modems are named.Ī controller that provides the identity for the modem. This document also provides brief descriptions of chipset vendors. With a good insight into the hardware issues with modems, you can adjust the client configuration to achieve improved performance. This document provides a general technical overview of three common types of client modems seen in the field.

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