Multitech RF500S Uživatelský manuál stáhnout pdf (Strana 16)

5.3 Secondary Lightning Protection

The phone company provides lighting protection as part of the

Network Interface Device. This is primarily designed to safeguard the

network. Electronic devices are somewhat fragile; this is especially

the case with computer equipment because they have multiple

connections, power, phone, DSL and Ethernet. This makes the

equipment susceptible to line surges. Adding secondary protection

minimizes the risk of damage. The best place for lightning protection

is the building entry point. That allows everything to be bonded

together with a low impedance connection. This minimizes voltage

difference between different conductors. Lightning protectors do not

absorb energy they divert it somewhere else. If the diversion path

does not have low impedance a substantial voltage difference is

created. This is what kills electronic gear.

These protectors add very little capacitance to the line. The high

frequencies used by DSL place special demands on protector to not

degrade the signal

Comm-Omni International manufactures secondary protectors. The protector clips to a 66 style split block.

In a split block the four horizontal terminals are split down the middle. The Surge protector clips over a

pair of rows providing a path from left to the right hand side. The left side connects to the Telco wiring.

The right side to internal wiring connects. With the protector remove inside wiring is completely

disconnected from the external conductors. A grounding bar runs down the left side of the block. This is

connected to a high quality earth ground. Excessive voltage is shunted to ground protecting the equipment.

One protector should be used on each telephone line and on any lines that connect to out buildings.

5.4 Modem Access Adapter

If the DSL line fails the router automatically uses the dial the ISP. We wanted

a way for the modem to have access to more then one line and to prevent

interference between the modem and phones. This maximizes the chance of

completing the call while reducing overall cost by eliminating the need for a

dedicated modem line.

The modem access adapter is a purpose built device that is designed to isolate

the data call from the extension phones. When the modem initiates a call the

access adapter detects the off hook condition. The adapter searches for an idle

line. If it finds an idle line it disconnects the phones and connects that line to

the modem. This prevents the phones from interfering with the computer. If all

lines are busy the modem never receives dial tone and retries the connection

attempt later. This prevents the modem from trying to dial when all lines are in

use.

The adapter is connected to the primary personal line and the business line. When the modem attempts to

connect the adapter tests the primary personal line first, if it is busy the business line is checked. The search

order assumes that during the day, when the business line is needed, the modem uses a personal phone line.

Since the two personal use lines are configured as a hunt group when the first line is busy the call is

automatically routed to the second. If the primary home line is busy the data call is placed on the business

line. This is most likely to occur after normal business hours, when home phone usage is heaviest.

Two toggle switches control operation. The left hand switch enables or disables the device. It also controls

whether or not it searches both lines. The switch on the right selects search order; either line can be selected

to search first. The red indicators show which phone lines are in use and which line the modem is

connected to.

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