Re: Internet dies if GPS dies?
Variola wrote... "[If GPS dies] "Internet activity would slow to a crawl, because many backbone operators rely on precise GPS time stamps to route data. " http://www.wired.com/wired/archive/11.05/start.html?pg=6 Sounds like bullshit to me, data clocks should be able to run without being fully synched externally, constantly. Maybe very occasional minor glitches at boundaries of clock domains. Any SONET Gurus wanna comment?" Sure, but I don't know enough about IP to tell you. SONET networks derive their timing from a STRATUM1 clock, which used to be Cesium but which are increasingly GPS-based. If the STRATUM1 clock "dies", the network can look for another high-quality clock. If it doesn't find one, each NE will go into hold-over, and time of of the internal STRATUM (likely 2e) clock until a good clock reappears. But the time stamps for SONET clocks are in the DS1 overhead, so the packets in the (other) DS1s/DS3s, etc...never "see" that timestamp, unless that timestamp is somehow read by a router and then put into the packets. But does a router even GET timing? (ie, is there a BITS interface on a router? I don't think so.) In any event, if the router gets its timing from the SONET network then there's no problem. If they don't get their timing from SONET, I doubt they get it directly from a GPS. So it sounds like bullshit to me. -TD
From: "Major Variola (ret)" <mv@cdc.gov> To: "cypherpunks@lne.com" <cypherpunks@lne.com> Subject: Internet dies if GPS dies? Date: Sun, 20 Apr 2003 21:35:43 -0700
[If GPS dies] "Internet activity would slow to a crawl, because many backbone operators rely on precise GPS time stamps to route data. " http://www.wired.com/wired/archive/11.05/start.html?pg=6
Sounds like bullshit to me, data clocks should be able to run without being fully synched externally, constantly. Maybe very occasional minor glitches at boundaries of clock domains.
Any SONET Gurus wanna comment?
[The article is full of hysterics like this. What it *doesn't* say is that the rockets have been used to launch OsamaSat, HusseinSat, etc., none of which exist of course, no such hardware here]
--- Number theory makes my brain hurt.
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In message <BAY7-F36LCVYl4maEqx0000bfc8@hotmail.com>, "Tyler Durden" <camera_lumina@hotmail.com> wrote:
But the time stamps for SONET clocks are in the DS1 overhead, so the packets in the (other) DS1s/DS3s, etc...never "see" that timestamp, unless that timestamp is somehow read by a router and then put into the packets. But does a router even GET timing? (ie, is there a BITS interface on a router? I don't think so.)
Routers do not have any ability to take input from a frequency standard, even if you have one available. Each interface recovers clocking from the line, or can use an internal clock. Some discussion of this as it applies to routers running PPP over SONET over dark fiber: http://www.cisco.com/en/US/tech/tk713/tk607/technologies_tech_note09186a0080... Those routers will operate independently of any external clock. Routers that are connected to a mux (which includes anything DS3 and below) will recover clock from the mux, which will have its own timing interface or internal clock. I'm not a SONET guru, but my understanding is that even with the internal clocks, you would see at worst an occasional error burst for a few ms. No credible engineer would make a network that fell over without GPS anyway, since it's just too easy for someone to accidentally knock over your antenna while installing another, or nick the cable with a saw, or who knows what. In a nutshell, this isn't something I'd worry about. -- Shields.
participants (2)
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Michael Shields -
Tyler Durden