2X rate - question after reading instruction manual

I was reading some details about the canopy link characteristics on the instruction manual. What I wanted to consult with you all, and in case you haven’t read it yourself, is the following paragraph

Competition for Bandwidth

When multiple SMs vie for bandwidth, the AP divides its bandwidth among them,
considering their effective CIR and MIR values. However, 2X operation uses bandwidth
twice as efficiently as 1X, even where MIR values apply. This is because, in 2X
operation, the modules transmit their data in 4-level frequency shift keying (FSK), not
2-level as they would in 1X operation. This moves twice the data per slot. Thus, for the
sum of all bandwidth that 2X-eligible customers use, the bandwidth available to the
remaining customers increases by half of that sum when these eligible customers are
transmitting and receiving in 2X operation.

What de you make of this? Does it mean that having SMs working at 2X also benefits those that only have 1X? Find this kind of confusing. I would appreciate if someone can shed some light on this.

Thank you

Yes it does. You have 7 mbps aggregate in 1x modulation. Lets say you have 7 SM in 2x and they use 1 mbps. That will theoretically leave 3,5 megs free on the AP.

What about if you have a mix of 1x and 2x SMs? Currently my problem is all my APs are 2x enabled. Some of these APs are holding close to 100 SMs and although the max utilization at peak times is around 4.5 Mbps (out of the almost 9 Mbps I should get based on my downlink percentage and other settings), seems like I’m overloading the APs as new customers are not getting more than 200 Kbps. Tower is fiber fed so there is plenty of bandwidth to share

You can hit the max PPS before you hit the theoretical BW limit of the AP.

At 100 subs I would say you are there. You could squeeze more out by switching all the users to 1X and implementing bursting.

Jerry Richardson wrote:
implementing bursting.


How do you do this without prizm?
sivanisky wrote:
What about if you have a mix of 1x and 2x SMs? Currently my problem is all my APs are 2x enabled. Some of these APs are holding close to 100 SMs and although the max utilization at peak times is around 4.5 Mbps (out of the almost 9 Mbps I should get based on my downlink percentage and other settings), seems like I'm overloading the APs as new customers are not getting more than 200 Kbps. Tower is fiber fed so there is plenty of bandwidth to share


You can see on the sessions page at what modulation are your SMs registered. According to manual 30% will be in 2x mode.

Are your SMs set to 2x? P8 can't do 2x.

The PPS like Jerry said could be a problem.

We have a lot of AP with 100+ customers. We can't get more then 9 mbps aggregate out of them. When we hit the limit we get lower speeds and packet loss.

Upgrede your AP and SM to 8.2, you will get more pps.

Based on solarwinds, This one AP is pulling 750 pps on the down, 650 pps on the up, for a total agregated of 1400 pps. All radios in my network are 8.2.

When I started troubleshooting this, I went thru the manual and that paragraph called my attention because it can be interpreted in different ways. In fact, I made several people read it and they all understood different.

9 Mbps with 100 SMs? What is your config like? are all SMs in 2X mode? and if they are, do they all actually get a signal good enough for 2X?

Thank you

100 SMs in 2x mode = 14 mbps aggregate with packet size for all incoming traffic of 1522 bytes.
75 SMs in 2x mode, 25 in 1x mode = 12,25 mbps aggregate with packet size for all incoming traffic of 1522 bytes.
50 SMs in 2x mode, 50 in 1x mode = 10,5 mbps aggregate with packet size for all incoming traffic of 1522 bytes.
25 SMs in 2x mode, 75 in 1x mode = 8.75 mbps aggregate with packet size for all incoming traffic of 1522 bytes.
100 SMs in 1x mode = 7 mbps aggregate with packet size for all incoming traffic of 1522 bytes.

I use sync, transmit frame spreading is off, 15 miles distance, downlink 75%, control slots 3.

Nice explanation Erkan…I just realized that when i had 52 sm 1x and the ap wouldn go for more than 7mbps.
I configured some with 2x, but its not good to enable 2x in all the sm (right?)
pps is about 1500

So, 14 mbps is just a theorical vaue right…? :cry:

The SM allows configuration for sustained and burst values.

Jerry could you elaborate a bit more?

I am guessing here…

If you are using bam, and your rate plan is lets just say 512/512 (easy number for this example!). You set your BAM configuration to 512 sustained up and down, and then your burst would be 1/1?

Is that the idea?

What is the method used to determine what the optimal burst setting is?

moinavery wrote:

I configured some with 2x, but its not good to enable 2x in all the sm (right?)
pps is about 1500

So, 14 mbps is just a theorical vaue right...? :cry:


Enable 2x at all SMs, and then disable it on the SM where you have problems, there will be few. Search the manual, there is explanation when you should use it.

Also consider that 100% link test in 1x is equal to 50% in 2x mode, so all the values above 60% in 2x are OK.

moinavery
I assume you know what your average noise floor is in your area…

It takes 3dB sustained above the noise floor to maintain a 1X link, and 10dB above the noise floor to maintain a 2X link.

Add in your desired fade margin (should be at least 3dB but 6dB is better) to determine the required signal levels.


Example: In my area the noise floor averages around -83 with a +/- swing of about 3dB.

With a maximum noise floor -81dB:
1X = -81dB noise floor + 3dB = -78dB minimum to maintain a link, -75dB with margin
2X = -81dB noise floor + 10dB - -71dB minimum to maintain a link, -68dB with margin


phreak
In the SM, set the desired sustained up/down rate to whatever you want. I have it set to 1/2 of the subscribers speed.

The burst value is not a speed, but rather quantity. The quantity is how much traffic the SM will pass at the maximum possible rate of the radio link before stepping back down to the sustained rate. I usually allow 1-3Mb down and 500k to 1M up.

Using this feature reduces contention and makes the network run faster. Customers barely notice unless they are camped out on speedtest sites, but most are not. As long as pages load fairly quickly and latency is below about 70ms people are going to be happy.

Have anyone implemented the “Broadcast/Multicast data rate”? What is a good number to limit this?

Thanks for all the great tips

I believe the release notes for 8.2 say that 32kbit is a good starting point.

sivanisky wrote:
Have anyone implemented the "Broadcast/Multicast data rate"? What is a good number to limit this?

Thanks for all the great tips


I've done it. Limit was set to 1 kbps and the PPPoE couldn't handle it. Still searching for the magic number for me. But if you use static IP probably 1 is good!