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#159 - 05/22/00 03:04 AM Explanation of PL%

Just a simple question on how to interpret the Pack Loss (%).<br><br>If route has 3 hops, and there is 10% packet loss on the first and second hops, is it safe to assume that that only 81% of the packets are getting through to the final destination.<br><br><br>

#160 - 05/23/00 01:45 PM Re: Explanation of PL%
Pete Ness Offline

Registered: 08/30/99
Posts: 1106
Loc: Boise, Idaho
The packet PL% numbers don't add up downstream. There are several reasons for this and ways this works.<br><br>First off, remember that everything going to hop 3 (and 4 and 5 and beyond) has to go through hop 2. If hop 2 is losing 10% of the packets, then it may also be losing 10% of the packets passed on as well. If you're seeing 10% PL at 2,3,4 and beyond, then it's likely that the problem originates at hop 2 (substitute the hop you're first getting PL for the 2 here).<br><br>Have a look at this picture, for example:<br><br><br><br>Notice how hop 7 and all hops after it have packet loss. It's likely that hop 7 is introducing this packet loss into the system. Another sign that it's a problem at hop 7 is the additional boost in time at hop 7 (that also translates to all other hops downstream). The additional time boost does *NOT* have to be there for hop 7 to be causing packet loss, however.<br><br>The packet loss shown on each hop is the number of packets sent to that hop that don't return. Each number takes into account the full path to that hop and back again. You don't want to add packet loss for 2 hops together - as the internet will already do that for you.<br><br>Here's another somewhat similar, but different example:<br><br><br><br>In this case, the extra time and packet loss does NOT follow downstream, so this isn't affecting your overall connection to your final destination. This could be because the router at hop 7 is configured to prioritize packets routed through, and give lower priority to packets that expire at it.<br><br>Hope this helps!<br><br>


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