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| Can FiOS be Over-subscribed? Not Realistically |
| Written by Dave Burstein |
| Wednesday, 25 May 2011 18:57 |
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Prairesky's question at DSL Reports received 50 responses, several suggesting possible but exceedingly rare issues. So I jumped in with a simple answer: it can, but almost never will.
I've been reporting FiOS since before it had a name and am fairly well acquainted with the design. It absolutely is possible to overload FiOS, as noted. It's unlikely to happen even an hour a year, I believe but can't prove, and even then the effect will be small.
GPON FiOS, for example, supports up to 32 ports with 2.4 gig downstream, less than a 2:1 over-subscription on any likely Verizon node.
The chances that all 32 will be connected and drawing 100 megabits is negligible. In practice, there is little congestion even on heavily used networks at 10:1 oversubscription and it would be vanishingly small at 2:1. The box you're connected to (OLT) is designed with plenty of extra capacity even for peaks. In FiOS and other well-designed networks, all the connections behind, the switches and routers, and the peering point to the net are designed with plenty of extra capacity.
In addition, competent network managers monitor traffic on their networks. If a link comes even close to congestion they upgrade. The rule of thumb is that if you ever are getting to 80%, time to upgrade. Verizon's network manager live up to that standard. Digging trenches, sending a tech to the field, and even answering your phone calls takes people time, which is expensive. Upgrading switches isn't free, but the equipment keeps getting cheaper because of Moore's law. So almost everyone keeps the network running with plenty of capacity. No consumer network is designed to overcome all cable cuts, hurricanes, and World Trade Center type events, although most usually do. On 9/11, I was in Washington and Jennie in New York and the voice lines were overloaded. But I easily reached her by email.
If you're seeing a slow down on FiOS or a similar network, such as U-Verse, the odds are good it's at the server or in your home. |