Eicon Networks ISDN NT1 Especificaciones descargar pdf (Pagina 41)

• PC doesn’t answer because the are no programs running that are listening for

incoming calls

However, there is a potential pitfall in this solution. This is because of the restriction that

only one filter can be applied to each setup message.

A fax device, for example, may be configured to accept calls whose bearer capability is

specifically Fax Group 3. However, fax messages which originate within an analogue

network do not come with this very precise call type information. They are simply classified

by ISDN as "generic analogue", just like a voice call.

Therefore, the fax device, which is looking specifically for fax calls, will reject valid fax calls

from fax machines connected to the PSTN.

Similarly, if the fax machine is configured to accept "generic analogue" calls, then a fax

message which originates directly from an ISDN network, and therefore may have the

specific "fax call" type, will be ignored.

Consider the following case:

The fax machine on the analogue network makes a call to the fax machine on the ISDN

network.

The SETUP generated on receipt of the call by the ISDN network specifies the call type is

Generic Analogue. There must be a call type in a SETUP message, but the ISDN cannot

know exactly

what kind of device is causing this SETUP, so it makes a best guess.

In this case, the fax machine in the bottom-right corner will happily answer the incoming

call.

If however, a call is generated by a fax machine on an ISDN line, the SETUP message will

describe the call type as being specifically from a "G3 Fax".

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Eicon Networks ISDN NT1 Especificaciones Pagina 41