# Notes on modem connections

The CX 2000C board interface can provide the same grade of connection to high-speed modems (such as V.34 and V.90) as PBXs and telephone office switches. However, the speed of the connections is not guaranteed to be at the highest rates. The following system factors are important in obtaining optimum modem performance:

- Cables from the board to the modem must be short, telephone grade twisted pair. Avoid routing cables near noise sources. Avoid moisture in cables.

- There should be only one 2-wire analog loop connection from the modem to the ISP. Also, there should be at most one analog-to-digital conversion in the link from the modem to the ISP. Digital trunks to the public network are preferred for V.34 and are required by V.90 technology.

- Add loss in the uplink connection to speed up the downlink connection if analog trunks are used. This reduces the echo signal.

Even with these precautions, network impairments such as noise, echo, or distortion can continue to limit modem performance, causing slower transfer speeds than desired. These are limitations of the network and modem technologies.