re: the source of network (internet) latency. Raymond, Actually, in today's networks most of the latency is due to layer 3 (routing-layer) processing that occurs. Data link layers in most of today's switched networks(with some exceptions, e.g. cable modems / shared-media access schemes) generally exhibit very deterministic, short latencies regardless of loading. The routers are where you get into trouble, because of processing-intensive nature of routing/packet-handling there, and the associated queuing required. A router processes each packet (protocol operations) serially in a CPU, and when a router gets busy (a lot of traffic coming in on it's ports) often the CPU gets too busy with all the protocol work; thus packets start building up in the router's buffers. When a router is too busy and the buffers are getting full, delays can increase exponentially. This well-known non-linear effect, which makes routers difficult to simulate (predict), is where you get into as much as dozens of milliseconds (and more) of latency, through a network.
That's why you have to really look at the infrastructure your ISP is providing. If it's a "cheap and dirty" ISP, you'll see a lot of packet loss and latency through the network. Regards,
-Steve |
