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To: Frank A. Coluccio who wrote (3112)	11/6/1999 12:54:00 AM
From: barry fowler	Read Replies (3) \| Respond to of 15615

>> are always laid on the ocean floor, and never draped between high mountain peaks in deep water. Just imagine the strain on the cable if this were _not_ the case. I'd think that the tension created by underwater currents would be enough to snap a pretty strong cable. That'd be an interesting calculation -- how far could the cable be "dangled" given known currents and not snap? >> You also imply that the present ring which is being used is self-healing I don't think he said "self-healing". I'm also an engineer and work around other engineers that maintain fiber in our facility. Those individuals tell me they have a device they install on one end of the cable which tells them very precisely where the problem is along the cable. So, Mr. Newmann's reply to this part is credible.

To: Frank A. Coluccio who wrote (3112)	11/6/1999 1:40:00 AM
From: D. Newberry	Read Replies (2) \| Respond to of 15615

Hi Frank, Again, my experience was in the pre-fiber days. I worked for AT&T at the time, but not on transoceanic routes. I had the opportunity to tour one of their cable laying ships and ask a lot of questions. I doubt the mechanics of cable laying has changed much since then, although the cable certainly has. The one thing they stressed was the need to know the precise topology of the ocean floor so that the cable was played out appropriately to lay directly on the floor. If laid incorrectly, the cable can be stressed and will eventually stretch. Just like a land line aerial cable, it must be supported. It isn't really all that difficult since they have detailed topology information of the ocean floor. Still, I thought it interesting. Whether they use submersibles for repair now I don't know. Back then, they went out to the failure site and dragged perpendicular to the cable until they snagged it, then literally pulled it up to the ship. Repairs were made, and the cable was dropped back down to the ocean floor. This was a fairly frequent exercise since repeaters were required at regular intervals, which of course failed occasionally (I don't remember the distances, but it was more than the standard 6000 ft T-1 terrestrial spacing). The fiber rings themselves are self healing. Your typical land based sonet rings will automatically switch to the backup path within 50msec of a failure (Fujitsu and Nortel in particular). A few IP packets get retransmitted due to the "hit", but hardly a big deal. I believe I read sometime back that the undersea systems switch within 300msec, but don't quote me. It is in effect a ring, and the same bandwidth is allocated in counter rotating directions on the ring. That is, the same data travels in different directions on the ring to the terminating end point. As such, if the primary path fails, the terminating mux merely needs to detect the failure then switch to the other receive path. Alarms are triggered and appropriate isolation/repair measures are taken, but in the meantime customer service has been restored. This is how it works on the land based systems. I presume it is the same basic approach on the oceanic systems as well, although I have no first hand knowledge beyond terrestrial systems. This is what makes the ring architecture so robust - its' ability to quickly restore from a failure. Qwest uses the same basic topology with self healing rings across the US (and other countries). Regards, DN