Non-Facility Associated Signaling(NFAS)

When a group of PRI interfaces are effectively bundled together, one D-channel can be used for the signaling data of all the combined B-channels, while the redundant D-channels can be used for data transmission. NFAS is only possible with a T1 PRI.

ISDN PRI NFAS是一種共用ISDN D channel(64 kb/s)的技術,而且只適用於T1 PRI。在NFAS中至少要設置一個Primary D channel,Backup D channel則是可有可無,如果有的話通常會將Primary & Backup D channel設置於不同的T1 controller上。假設在兩條T1上共有24 * 2 channels,我們可以只使用一條channel當共用的D channel來傳送控制訊號,剩下來的23 + 24 channels就可以當成B channels(64 kb/s)來傳送Data。
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