Is there any documentation, or general rules of thumb, etc. as to how each hop will affect delays and overall throughput?
We live in a rural and very mountainous area, so getting service to some areas requires several hops and relay points, as it is impossible for everyone to see the primary tower. My question is how can I anticipate the possible delays and subsequent decrease in throughput with every hop that I take?
Also, my understanding is that for any given AP, the network speed is only as good as the delay to the furthest SM? Is this correct? So if you have a situation where everyone is 1 mile away, and then you add one SM that is 8 miles away, you are really killing everyone else’s speed because of that one SM?
Also, in regards to hops, I assume that the above issue is not cumulative, right. I mean if a client ends of being 20 miles away, because of all the hops, what effect does that have on the network.
Any info is much appreciated.
etech wrote: Is there any documentation, or general rules of thumb, etc. as to how each hop will affect delays and overall throughput?
We live in a rural and very mountainous area, so getting service to some areas requires several hops and relay points, as it is impossible for everyone to see the primary tower. My question is how can I anticipate the possible delays and subsequent decrease in throughput with every hop that I take?
You add 10 ms to every hop. 5 hops, 50 ms. Nobody will notice that kind of delay.
Also, my understanding is that for any given AP, the network speed is only as good as the delay to the furthest SM? Is this correct? So if you have a situation where everyone is 1 mile away, and then you add one SM that is 8 miles away, you are really killing everyone else's speed because of that one SM?
Not correct if the platform is Canopy. The overall speed of the AP is not affected by distance, it's affected by number of control slots and the distance you have choosed in the AP config menu.
Also, in regards to hops, I assume that the above issue is not cumulative, right. I mean if a client ends of being 20 miles away, because of all the hops, what effect does that have on the network.
No effect except that bandwidth that he consumes.
erkan wrote:
Also, my understanding is that for any given AP, the network speed is only as good as the delay to the furthest SM? Is this correct? So if you have a situation where everyone is 1 mile away, and then you add one SM that is 8 miles away, you are really killing everyone else's speed because of that one SM?
Not correct if the platform is Canopy. The overall speed of the AP is not affected by distance, it's affected by number of control slots and the distance you have choosed in the AP config menu.
OK, so you are saying it does not have to do with the actual physical distance to the AP, but rather the value that I enter in the AP for the distance field. Interesting.
So in effect I am still right to say that the longest distance DOES affect the network, because I have to enter a larger value in the distance field for my furthest client. Also am I to understand from this, that if I put a large value for the distance field, I would be in effect slowing down my network, whether or not there is an SM at that distance?
How accurate is this distance value? Sounds like I should set this to lowest possible value, but how much tolerance is there? I mean how accurately do I need to enter the distance? Should I just use the distance value as displayed on the status page of my furthest SM?
Thank you.
Many things can affect the maximum troughoutput:
1. Uplink/Downlink ratio
2. Number of control slots
3. Maximum distance
4. Packet size
5. Used modulation
6. Interference, retransmition of packets
We use 15 miles for all APs. When you change the max distance on one AP do it on the neighboring also.
Radios waves travel 186k miles/sec. The max distance value does affect throughput and latency, but the value is so small it’s virtually non-existent. We have our AP’s set to 20 miles, with several customers at 18 miles. It’s not an issue.
Set the Max Distance to the lowest value that you think you will need. If you know you will never try to service a customer past 8 miles, then use 10 miles. You will need to set every AP that hear each other to the same max distance, # control slots, and same Downlink Ratio unless you use the Frame Calculator to determine alternate values.
On our network, we have found that if the SM does not have to wait to send it’s frame, the ping time is ~5ms. However as more SM’s request transmit slots, the ping times go up as each SM has to wait it’s turn. Even under heavy usage, we see 17 to 35ms from the SM’s to the AP.
I have a couple of Remote AP’s. The longest one takes the following route over 4 wireless hops:
2.4SM SW Sched --> 2.4AP SW Sched -->900SM --> 900AP --> CMM --> 5.7BHS SW Sched --> 5.7BH SW Sched --> CMM --> Trango 5.7BHM --> Trango BHS --> 2924 Switch --> Server.
Ping statistics for 10.0.30.1:
Packets: Sent = 16, Received = 16, Lost = 0 (0%)
Approximate round trip times in milli-seconds:
Minimum = 17ms, Maximum = 44ms, Average = 25ms
As Erkan mentioned, 50ms is fine as long as it’s consistent. when you start getting wide fluctuations in ping time from 50 ms to >200ms your users will start to notice some lags, particularly gamers.
Interference is a real latency killer as packets get lost and have to be retransmitted adding latency. Also, the amount of traffic goes up due to retries resulting in more lost packets, etc.
Hope that helps.
Thanks for all the info:
We see some wild fluctuations in our network, and I have been trying to figure out what is going on there.
One interesting thing that I was seeing was a client would start an iTunes download and suddenly the delay to all AP’s connected to the same CMM would hit anywhere from 1500-3000ms!!! I tested this with the guy on the phone. He would pause the download and we are back into the 20-80ms range. He would start it up and the delay would sky rocket. Any idea why that would be?
Overall, something is not right in our network. Just today I had someone run some speed test while they were on the phone with me, and I am seeing 6Mbs at our head end and he is seeing 256kbs!
The connection to this particular client is:
5.2SM SW Sched –> 5.2AP SW Sched – . CMM –> 2.4 Wave Wireless 5Mbs SpeedLan 8100 AP Bridge – > 2.4 Wave Wireless 5Mbs SpeedLan 8100 AP Bridge –> 5.2BHS SW Sched –> 5.2BHM SW Sched –> Server (head end)
I have never liked that Wave Wireless AP in there. That unit is discontinued anyway, so it scares me, as it is a major link in our network. We are planning on replacing that with a 5.4 Canopy BH in the next few weeks. Personally I am hoping that it will help things out quite a bit. The delays that I am talking about would not come all the way back to our main server. It would stop at the remote SpeedLan AP. In other words I would be totally unaffected until I would hit the remote AP. So I am not sure if the AP is crapping out, or the CMM or what?
When you say:
You will need to set every AP that hear each other to the same max distance, # control slots, and same Downlink Ratio unless you use the Frame Calculator to determine alternate values.
What exactly does that mean “hearing” each other? So for example all AP’s connected to the same CMM should be set the same way? How about an AP that is downstream and connected via an SM –> AP hop. Is that AP hearing the other AP’s even though it is separated by an SM?
If I have a set up like this:
5.2 AP ----- CMM ----- 5.2 AP –> SM – > 900 AP –> SM’s
Who is considered as “hearing” each other?