I'm investigating superframes as a means of determining DSL uptime for rs-ux/w, but there seems to be little consistency between Broadcom-based routers on this measure. Some routers report the same value for both upstream and downstream, but others report different values, and it appears that for VDSL2 connections the value isn't reported at all.
The available literature mostly predates ADSL2+, so does it remain the case on all ADSL versions that there are 4000 frames per second, and a superframe consists of 68 normal frames plus one sync frame?
Does the above apply only to downstream, and if so, what is the situation with upstream?
Is there a corresponding figure for VDSL2?
Any information would be much appreciated.
Yes, I think so. With all xDSL standards, the symbol rate remains at 4000/sec, both up and down. But (excepting perhaps 30MHz VDSL2 Profiles with 8kHz channel spacing), it looks like a superframe for VDSL2 contains 256 data frames (plus the sync frame). So 4000/257 gives the superframe period (64.25 msecs).
From G.993.2 12/2011 (VDSL2 ITU-T Recommendations ~ page 77) [1]
10.2 DMT superframe
The transmit PMD function shall use the DMT superframe structure shown in Figure 10-2. Each DMT superframe shall be composed of 256 data frames, numbered from 0 to 255, followed by a single sync frame. The content of the sync frame is dependent on whether timing for on-line reconfiguration is being signalled (see clause 10.5.3). The data frames are modulated onto 256 data symbols, and the sync frame is modulated onto a sync symbol as defined in clause 10.5.1. The sync symbol provides a time marker for on-line reconfiguration (see clause 13).
(https://forum.kitz.co.uk/proxy.php?request=http%3A%2F%2Fwww1.picturepush.com%2Fphoto%2Fa%2F9516094%2F480%2Froseway%2Fsuperframe-10.2.png&hash=317bd0b3b96aa1819d37f601f5aa77c24c058527) (http://picturepush.com/public/9516094)
NOTE – The duration of a superframe depends on the subcarrier spacing and value of the cyclic extension (see clause 10.4). When the subcarrier spacing is 4.3125 kHz and the mandatory cyclic extension value is used (5/64), the duration of a superframe is 64.25 ms.
[1] http://www.itu.int/rec/T-REC-G.993.2-201112-I/en