Problems with spotty cable modem connection when connected to 3rd gen Airport Extreme

Question

Hi All, here's my problem:
I've got a 3rd gen airport extreme (AEBS) that I've been using for the last several years and had no issue. Recently, I decided to switch from Verizon DSL to Time Warner Cable, and in order to avoid extra fees, I decided to purchase my own cable modem. Here begins an epic battle with sanity...
- 1st modem Motorolla SB6141: This was the first modem that I bought and it worked like a charm... at first. The first week was like a dream come true, with incredibly fast speeds and very low latency (ping=15ms, dl=30Mbps, ul=5Mbps). The AEBS and the modem got along great, no issues until all the sudden the connection speeds started dropping off. The connection would never fully drop to zero, but close. The bandwidth would hover around 1Mb down, which was about a 1/30 of the speed I was supposed to be getting. I chalked it up to a bad model so I headed back to Best Buy.
- 2nd modem Zoom 5341J: This modem istalled with little issue and worked pretty well. The only problem I encountered with this modem was that it seems to cause a ton of network latency (ping=200ms average), which was way too slow for me. On the first night that I had this modem working, I cycled the power (to try to resolve the latency issue) and it never came back on. there must have been a short in the board or something. Back to Best Buy.
-3rd modem Netgear CMD31T: This modem was an absolute nightmare to get connected to the AEBS. The process involved following a VERY specific order of operations that involved powering down the modem and the AEBS, doing a factory reset on the AEBS, poweing down the AEBS, powering on the modem, plugging the modem into the AEBS, and powering on the AEBS. None of the other modems gave me that much trouble, but when I eventually got it working it was FAST. I was getting the best latency and bandwidth out of all of the modems. Unfortunately, that lasted about 5 minutes, when the bandwidth dropped to 1Mbps and never recovered.
I know what you all are thinking... the problem must be with the AEBS. But here's the kicker, I have an Airport Express that I tested with all three modems and got the same results. Well then (you must be thinking), the problem is obviously with the ISP! But when I connected all three modems directly to my MacBook Pro, they all worked fine, with no connectivity issues. The only time I encounter a problem is when I involve an Apple router. I love my AEBS and my Airport Express, so I'm avoiding buying a different brand router. Does anybody have any suggestions? Thanks for your help!

Answer 1

Well after doing some research, I've figured out that the problem I was encountering had nothing to do with the Airport Extreme or the cable modem! Apparently, my problem was caused my uplink saturation. In other words, my cloud backup service (BackBlaze) was using up all of my upload bandwidth, which meant that ACK packets (acknowledgments) weren't even getting through. This would basically cause any server I was downloading from to stop sending additional packets, making it appear that connection to the internet had been severed. My simple fix was to cap the bandwidth of my BackBlaze backups to about half of my total upload bandwidth. One thing I did learn is that the this issue is usually fixed by using a router with QOS (Quality of Service) capabilities to prioritize ACK packets. Unfortunately, for some reason Apple has neglected to add this feature to even their high end routers.