Roger, This is a sub rate link, as you use a physical rate of 10Mbps with a downstream service of 5Mbps - This means that somewhere down the link (on the SP network) they would be dropping anything above 5Mbps.
Your router does not have any way (except shaping) to know that there is a limit for 5Mbps, and it would be empting anything queued in its egress buffers at a rate of 10Mbps, which would be then dropped by the downstream rate limit at 5Mbps. If you want to be able to control which traffic is dropped or prioritized in case you have bursts or an overload (for example someone uploading a file, while someone else running a VOIP call) you must perform the shaping so that your router would know that it must release packets to the line at a rate not higher than 5Mbps. The result would be that any drops (if any) would be done by your router, which is aware of the child QOS policy, and not on the SP side, which has a flat drop policy for anything above 5Mbps. You need to remember that IP traffic is very bursty, and even if on average (usually 5 minute average, or even 30 seconds average) you see only <5Mbps of upstream traffic, it down not mean that on a sub-second level you do not have full line rate bursts (you have them for sure...) Arie -----Original Message----- From: cisco-nsp-boun...@puck.nether.net [mailto:cisco-nsp-boun...@puck.nether.net] On Behalf Of Roger Wiklund Sent: Saturday, October 09, 2010 17:49 To: Cisco-nsp Subject: [c-nsp] to shape or not to shape I have a question I have been thinking about. Let's say we purchased a 5Mbit Ethernet Link. The physical speed of the link is 10Mbit, so we shape outbound traffic to 5Mbit, like such: class-map ef match ip dscp ef class-map af4 match ip dscp af41, af42, af43 class-map af3 match ip dscp af31, af32, af33 class-map af2 match ip dscp af21, af22, af23 class-map af1 match ip dscp af11, af12, af13 class-map be match ip dscp be policy-map qos class ef priority 1024 class af4 bandwidth remaining percent 40 random detect dscp-based class af3 bandwith remaining percent 30 random detect dscp-based class af2 bandwith remaining percent 20 random detect dscp-based class af1 bandwith remaining percent 9 randon detect dscp-based class be bandwith remanining percent 1 service-policy shape class class-default shape avarage 5000000 policy-map qos interface wan service-policy output shape So, as we shape, as long as we have buffers, we will never see any tail drops, as we will just delay the packets until we send it, correct? Now imagine we have a framed e1. interface wan bandwith 1984 As we have the full bandwith, no need to shape, so I will just apply the qos service policy for outbound traffic. If this e1 is 100% utilized, we will get tail drops when the buffers are full. So my question now, what if the shape the e1 to 1984, we will still have the full speed, but we shape, and thus avoid tail drop, and just delay the packets instead. I'm thinking we avoid TCP restarts etc etc. pros/cons, or am I wrong about the whole thing? :) Appreache any comments, Thanks! /Roger _______________________________________________ cisco-nsp mailing list cisco-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/ _______________________________________________ cisco-nsp mailing list cisco-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/