Broadband Related > Broadband Technology
Upstream in VDSL2
Weaver:
Consider this line, taken from a recent thread.
--- Quote ---xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 0
Last initialization procedure status: 0
Max: Upstream rate = 25970 Kbps, Downstream rate = 86204 Kbps
Bearer: 0, Upstream rate = 19999 Kbps, Downstream rate = 79999 Kbps
Bearer: 1, Upstream rate = 0 Kbps, Downstream rate = 0 Kbps
Link Power State: L0
Mode: VDSL2 Annex B
VDSL2 Profile: Profile 17a
TPS-TC: PTM Mode(0x0)
Trellis: U:ON /D:ON
Line Status: No Defect
Training Status: Showtime
Down Up
SNR (dB): 4.6 15.1
Attn(dB): 13.9 0.0
Pwr(dBm): 13.1 4.3
--- End quote ---
The SNRM upstream is ridiculously high as the line is capped at 20 Mbps upstream.
Q: Why on earth do they do this?
There is clearly a good bit more upstream performance available from this excellent short line.
Iain:
Some of us lucky to be close to the cabinet, if you want another one to ponder over, then here you are:
xdslctl info --stats
xdslctl: ADSL driver and PHY status
Status: Showtime
Last Retrain Reason: 1
Last initialization procedure status: 0
Max: Upstream rate = 25946 Kbps, Downstream rate = 100163 Kbps
Bearer: 0, Upstream rate = 20000 Kbps, Downstream rate = 79987 Kbps
Link Power State: L0
Mode: VDSL2 Annex B
VDSL2 Profile: Profile 17a
TPS-TC: PTM Mode(0x0)
Trellis: U:ON /D:ON
Line Status: No Defect
Training Status: Showtime
Down Up
SNR (dB): 11.3 9.6
Attn(dB): 8.8 0.0
Pwr(dBm): -9.9 -10.0
Weaver:
Why cap it?
In fact, in that latter example, why cap the downstream or the upstream ?
re0:
I do not know the exact reason why Openreach have capped it to 20 Mbps and nor will I pretend to know why. This may be something for the more experienced and Openreach/ex-Openreach people. Though I would guess that it is a mix of the following:
* In the absence of vectoring it may not be possible for many lines to reliably sync at above 20 Mbps on the upstream (lines longer then 300-400m on cabinets with a high degree of subscribers probably wouldn't see much above 20 Mbps).
* It is a technical thing to reduce crosstalk as shorter lines will need less bits loaded and lower power levels to achieve headline speeds.
* It is product consistency since FTTP is also subject to the same upstream speeds on products with the same downstream as with FTTC.You could also apply this to the downstream, too. Not just the upstream.
If you think I've got it wrong, please point it out.
Not so much unlike the stats you have posted for the sake example, my modem believes my line would be capable of quite a bit more than 20 Mbps upstream (~28000 Kbps attainable).
--- Code: ---Max: Upstream rate = 28010 Kbps, Downstream rate = 86204 Kbps
Bearer: 0, Upstream rate = 19999 Kbps, Downstream rate = 79999 Kbps
Bearer: 1, Upstream rate = 0 Kbps, Downstream rate = 0 Kbps
Link Power State: L0
Mode: VDSL2 Annex B
VDSL2 Profile: Profile 17a
TPS-TC: PTM Mode(0x0)
Trellis: U:ON /D:ON
Line Status: No Defect
Training Status: Showtime
Down Up
SNR (dB): 6.8 15.6
Attn(dB): 9.4 0.0
Pwr(dBm): 13.3 -6.9
--- End code ---
It should be noted that VDSL 17a is actually capable of speeds of around 100/50 Mbps (DS/US) with the implementation of G.Vector. It is not unusual to see speeds around that in mainland Europe as Telekom Deutschland has 100/40 Mbps on VDSL which presume to be VDSL 17a G.Vector.
Post edited to remove repeated word.
re0:
I would also like to add that back in the days pre-G.INP and pre-XdB (below 6 dB), attaining the full 80/20 Mbps was even more a rarity. Even some short lines would have been subject to interleaving overheads that would have made it impossible to sync at the full 80/20 (especially with crosstalk on busy cabs). This case still stands with ECI cabinets as you may have noticed as ECI hardware still does not have G.INP or XdB profiles.
Navigation
[0] Message Index
[#] Next page
Go to full version