Hi! Burst Rate and Uplink/Downlink questions.

Hi there,

I am new to this forum, and somewhat new to the PMP450 and access points, so I have a few questions.

1. If you have a lower burst rate than the sustained rate, does that just nulify any burst or does it actually hurt the network?

2. The Uplink on a PMP450 - Is that how fast it transmits the data to the Access Points? Also known as the downlink on the access points? So I currently have two PMP450's and there is 130000 kbps available - using a 80/20 ratio as an exampe, the PMP450 Uplink should be the 80 and the PMP450 downlink is the 20? Is this correct?

3. What is the Broadcast Downlink CIR? I can't find documentation on that.

Thanks so  much!

Hello!  Welcome to the PMP 450!

To answer your questions directly:

1)  If you set the Max Burst Rate to something lower than the Sustained Data Rate (MIR), it will act as if it is set to the MIR value.  It will mean that data will be maxed out at the MIR rate and you actually won't really consume any of the Burst Bucket bits and will have no incremental burst rate.

2)  The terms Uplink and Downlink are directional terms relative to the AP -> SM direction.  So, Downlink is traffic from AP *to* the SM, and Uplink is trafic from the SM *to* the AP.  The 130Mbps number is based on what the PMP device is capable of at top modulation (8x) at 20MH channel.  That would be absolute best case, which is why it is the limit value.  So in your example, it depends which direction you wanted the 80M of throughput to go.  If it is from the AP *to* the SM (so a customer downloading at that speed), then you'd do 80M downlink and 20M uplink.

3) Canopy (PMP) scheduling priority follows this order:  1)  High Priority CIR, 2)  Low Priority CIR, 3) Broadcast CIR, 4) remaining High Priority data (above HP CIR), 5) remaining Low Priority data (above LP CIR), 6) remaining broadcast.   PMP uses a shared broadcast channel in the downlink direction so that we don't send copies of packets and wasting airspace for repeated data.  Without setting broadcast CIR, it is possible that broadcast traffic will struggle to get scheduled if there is constant normal data traffic.     Also, the CIR isn't fully "reserved" in a strict sense - meaning, that if there is less data than the CIR requires, the frame will be filled fully continuing with the priorities listing above.  Just want to make clear that setting CIR doesn't mean parts of the frame go unused, it is just used to ensure access if there is proper demand.   Hope that made sense!

Regarding the burst bucket, there is a great whitepaper on this on our website that you can find here:  http://www.cambiumnetworks.com/resources/pmp-450-maxburst/