if an upstream channel is being maxed then the latency will go high ..ive tested it on 2 isps, 1 with 128kbps of up and 1 with 256k .. when they are being maxed the ping to the first hop goes from 10ms (not uploading) to 300+ ms (uploading, maxed) -- :: My current desktop ::
More likely the upstream packets are getting "backed up" in the upstream queue. These packets include ACKS to incoming packets. In this case the ping time is including the time the ping was stuck in the outgoing queue. This occurs even without a router.
If the packets were being dropped by the router, the pings would time out. -- "snmp: the standard e-mail protocol on the Internet" - LinkSys user manual (page 17)
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