Step 2 is the hard part.

Matt Ginzton writes here.

DSL Disappointments: Annex M Edition

| Comments

Yet another disappointment with the DSL connection and/or modem from Annex M doesn’t seem to do any good at all for upload speeds.

As I wrote in my introductory post on, the whole reason I was willing to consider them (or DSL technology at all) was the promise of decent upload speeds. The last DSL connection I had was only 768kbps upstream, and even ADSL2+ promises only about 1mbps upstream, but offers this Annex M configuration which trades some downstream bandwidth for upstream bandwidth, with upstream speeds theoretically as high as 3.3mbps (Sonic claims 2.5mbps is more typical real-world performance on a good line). Given that Sonic makes it easy to double these speeds by combining two lines together, now we’re talking — a combined 5mbps upstream would compare decently with what I’m getting from Comcast’s DOCSIS 3 technology.

(It’s hard to know exactly what real-world speeds to expect from Annex M. Sonic’s baseline for a single ADSL2+ line under good conditions, using the default Annex A configuration, is 20mbps/1mbps, or 40mbps/2mbps across 2 lines. Annex M should increase upload speeds to as much as 2.5mbps per line, but at at unknown cost to downstream speeds — I haven’t found anyone willing to predict that. It seems a reasonable estimate would be somewhere between the following hypothetical best case and worst case: best case, I added 1.5mbps of upstream, so it should cost me 1.5mbps of downstream; worst case, I multiplied upstreams speed by 2.5, so my downstream speed will be divided by 2.5. Using those as upper and lower bounds, I should expect something between 8mbps and 18mbps remaining downstream per line, or 16-36mbps/5mbps combined, with Annex M. That would compare favorably enough with the 32mbps/7.5mbps I’m getting from Comcast that, given the reliability problems and caps I’m also getting from Comcast, I’d be happy to switch.)

As described in my earlier posts, after two months of asking Sonic to ask AT&T to provide wiring that will sustain a good ADSL2+ signal, I have one line syncing at 18mbps and one line syncing at only 4mbps (downstream speeds, using Annex A). Still, I figured I might as well see the results of the Annex M spectrum reallocation, so last Friday I called Sonic and asked them to enable Annex M on both lines.

Then I went to the modem’s status page to see the effect on sync speeds. (If you followed my recent post on sync speeds vs actual transfer speeds, all tests here were done at the MPOE with no filter, that is, the best case from those earlier tests.)

First annoyance: the modem wouldn’t sync at all, on either line, until I enabled Annex M on both lines. Maybe this is how it’s designed to work, but from earlier reading of Sonic’s site (2 months ago when I first signed up, all excited by Annex M) that’s not the impression I got. Reading again now, the Annex M FAQ doesn’t say one way or the other, but Dane’s post introducing Annex M seems to imply it’s safe to leave it on on the network end and toggle it at will on your end. That would be more convenient, but for my Comtrend 5361 at least, the behavior is: if the network end is set to Annex A and the modem is set to Annex M, it syncs using Annex A (good), but if the network end is set to Annex M and the modem is set to Annex A, it doesn’t sync at all (bad).

Annoying, but not a deal-breaker. Let’s see how the speeds compare. I’ll give numbers even for the broken configurations that didn’t sync, since I did test those combinations and the results are interesting.

All of the following tests are with Annex M enabled for both lines on Sonic’s end, and at my end with the modem plugged directly into the MPOE with no filter. Speed test results are from

Both master and slave lines set to Annex M:

  • Master sync: 2.54/1.08
  • Slave sync: 12.51/1.14
  • Combined sync: 15.06/2.23
  • Speed test: 5.92/1.83

Master on Annex M, slave on Annex A:

  • Master sync: 2.54/1.08
  • Slave sync: no sync
  • Combined sync: 2.54/1.08
  • Speed test: 2.17/0.88

Master on Annex A, slave on Annex M:

  • Master sync: no sync
  • Slave sync: 12.62/1.14
  • Combined sync: 12.62/1.14
  • Speed test: 10.82/0.96

Both master and slave set to Annex A:

  • Master sync: no sync
  • Slave sync: no sync
  • Speed test: N/A

As a comparison point, here are my most recent numbers for a comparable test with Annex A on both ends:

  • Master sync: 4.84/1.08
  • Slave sync: 18.36/1.15
  • Combined sync: 23.12/2.23
  • Speed test: 19.72/1.83

So, two things to note here.

First, Annex M significantly decreases downstream speed without increasing upstream speed at all, for me. Compare the sync speeds above for Annex A and Annex M. The best sync speed I saw for the slow line was 53% of what it was without Annex M; the best sync speed I saw for the fast line was 69% of what it was without Annex M; the combined sync speed was 76% of what it was without Annex M.

Second, Annex M hurt my transfer speeds even more than the claimed sync speeds. Note the oddity that while bonded operation results in a faster sync speed than connecting the fast line only, when I measure the actual transfer speed, it actually got slower. (That’s reminiscent of the earlier bonding experiments I ran with Annex A.). The single-line Annex M tests both transferred data at the 85% of claimed sync speed that I’ve come to expect, but using both lines bonded together, this ratio drops to only 39%.

Again, I’m curious why bonding the lines results in slower operation than one line alone, without this effect being visible in sync speeds or ATM errors. And unless something is completely wrong here, it looks like Annex M does not, for me, bring DSL back into the realm of competitive upload speeds.