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Why does WAN speed degrad asymmetrically w distance?

With a business-class symmetric service, why would upload speed degrade more dramatically with route distance than download speed? I am working on a 3Mb "Ethernet Express" service from Cavalier (cavtel.net) originating in D.C. Cavtel's fiber network covers the eastern half of the US. My tested (multiple speed test websites) and actual experience to the CA office is that my upload speed drops to about half my download speed to points on the West Coast. Why does this happen? Shouldn't H.264 devices use the network symmetrically? The type of traffic I'm concerned with is video teleconferencing, VoIP, and corporate VPN between the office on the East and West Coasts.

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Re: Why does WAN speed degrad asymmetrically w distance?

When an end user tries to upload or send data to the Internet at a rate greater than what the DOCSIS configuration file allows, the cable modem itself should stop the excess traffic from traveling over the cable segment to the CMTS. If the cable modem, for some reason, fails to perform upstream rate limiting properly, then the CMTS explicitly forbids the cable modem from transmitting higher than the allowed rate. This behavior on the CMTS is to ensure that even a cable modem with "hacked" characteristics is unable to subvert the service provider assigned upload rate limits.

Refer the below URL:

http://www.cisco.com/en/US/tech/tk86/tk89/technologies_tech_note09186a00800b123c.shtml#potential

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