MSYoung

You are actually comparing apples and oranges here, so lets separate them. NFAS (Non Facility Associated Signaling) and FAS (Facility Associated Signaling) is not related to the trunk group. It does not care what you use and you can mix and match both types in one trunk group. You can even spread them over several trunk groups. NFAS and FAS deals with the T1s themselves and how you order them from the vendor.

Let us say you have ordered five T1s and ordered them with FAS signaling. That means each T1 has a D channel of its' own. Each T1 would have a signal group of its' own, thus you would have five signal groups. Now you put all five circuits in one trunk group giving you a trunk group with 115 members. If one D channel failed, the associated T1 would fail.

Now say the five T1s you ordered came with NFAS signaling and now all five T1s are in one signal group set for NFAS (top of the form). The next lines would be where you indicate primary and secondary D channel. The next part is where you have to pay attention because you must list them in the order the CO is sending them to you. The first T1 would have an interface ID of 0 (that marks it as the primary D channel), the second T1 would have an interface ID of 1 (this marks it as the secondary D channel). The remaining T1s would have interface ID's of 2,3,4. This must match the CO. If you do not have a secondary D channel, the interface IDs would be 0,2,3,4,5.

Now you can build your trunk group with 118 members (you gained three channels by going NFAS). Now if you lose the primary D channel, the secondary will take over immediately and all five T1s will remain up and all calls will remain up.

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