Near End - Far End

Hi Folks,

Can anyone confirm if I've got this right.

The 'far end' in router statistics are the downstream stats.


Thanks,
John.

Isn't the term relative to the modem? Near end is data path from the modem, far end is data path to the modem.

Thanks, yes that makes sense.

It confuses me a bit because, from the router's perspective, the router sends data to the far end (ie upstream).

John.

This is the "clarification" provided by the g.992-1 spec.

...
3.18 far-end: Far-end means performance of the downstream loop-side received signal at the
input of the ATU-R, where this performance is reported to the ATU-C in upstream indicators (see
Figure 9-4), or performance of the upstream loop-side received signal at the input of the ATU-C,
where this performance is reported to the ATU-R in downstream overhead indicators; this case is a
mirror image of the above (see Figure 9-4).
...
3.23 near-end: Near-end means performance of the loop-side received signal at the input of the
ATU (see Figure 9-4).
...
ATU = ADSL Transceiver Unit
...
ATU-R = customer modem
...
ATU-C = exchange modem
...

I'm glad you put 'clarification' in quotes

I'm trying to sort out what's up and what's down here:

============= NEAR END ===========
FEC   : 0
CRC   : 24
HEC   : 0
============= FAR END ============
FEC   : 0
CRC   : 467483
HEC   : 0

/ # adsl defects
============== NEAR END =============
ES  (Count of errored seconds): 12
SES (Count of Severely errored seconds): 0
LOS (Count of Loss of signal): 0
============== FAR END ==============
ES  (Count of errored seconds): 304210
SES (Count of Severely errored seconds): 67
LOS (Count of Loss of signal): 16

John.

Edited by deleted (Tue 14-Sep-10 17:43:24)

Remember it's part of the ADSL standard that the modems report detected data errors to each other.

Assuming that you got this data from your home modem.

Near end faults are those detected at the exchange in the upstream data.

Far end faults are those detected by your home modem in the downstream data.

It seems that routers don't have any particular standard over this.

This thread would seem to agree with our conclusions here; namely that Far end errors refer to downstream data.

However, the BE Internet DSLAMs are known to have a bug in that they accumulate the Upstream CRC errors, even through a router re-sync. This means that you can reboot the router and it will instantly begin showing the upstream accumulated errors as reported by the DSLAM.

From this, I'm able to tell with near certainty that the Netgear DG834G v5 regards the 'Far End' data as the upstream data. Here's the DG834Gv5 almost immediately after a reboot:

/ # adsl perf
============= NEAR END ===========
FEC : 0
CRC : 467
HEC : 0
============= FAR END ============
FEC : 0
CRC : 496871
HEC : 0


Swapping routers to a DG834v4 doesn't reset the DSLAM. Firing up the v4 shows the Upstream CRC errors as:

Down Up

SF: 277514 279442
SFErr: 5 496903 <-- CRC

So it looks like its a bit hit and miss how each router manufacturer interprets the standard.

John.

Well, it's interesting, just to post an example for you,
this is the way the ZyXEL P-660HW-T1 reports.

near end is my end (downstream) and far end is DSLAM (upstream)

that looks fairly clear from the low error counts on upstream, the line attenuation and noise margin figures and the frequencies being tested (just one line for upstream)

P-660HW-T1v3> perfdata

near-end FEC error fast: 0
near-end FEC error interleaved: 0
near-end CRC error fast: 401
near-end CRC error interleaved: 0
near-end HEC error fast: 384
near-end HEC error interleaved: 0
far-end FEC error fast: 0
far-end FEC error interleaved: 0
far-end CRC error fast: 28
far-end CRC error interleaved: 0
far-end HEC error fast: 12
far-end HEC error interleaved: 0




P-660HW-T1v3> linedata near

noise margin downstream: 11 db
output power upstream: 12 db
attenuation downstream: 29 db
tone   0- 31: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone  32- 63: 00 00 45 67 67 99 9b ab dc cc dc cd dc dc cc dc
tone  64- 95: 0c cc dd cc cc cc cc cc cc cc bb bb bc bb cb bb
tone  96-127: bb bb bb bb bb bb bb bb bb bb bb bb bb bb ab ba
tone 128-159: ba ba aa aa ba aa aa aa aa aa aa ba aa aa aa ba
tone 160-191: 98 aa aa aa aa aa a9 9a aa aa aa a9 9a a9 7a aa
tone 192-223: 99 89 87 46 77 88 99 99 98 95 89 97 99 88 99 98
tone 224-255: 99 99 99 99 98 99 79 99 89 88 48 77 98 88 65 65
tone 256-287: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 288-319: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 320-351: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 352-383: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 384-415: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 416-447: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 448-479: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 480-511: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00




P-660HW-T1v3> linedata far

noise margin upstream: 25 db
output power downstream: 19 db
attenuation upstream: 15 db
tone   0- 31: 00 00 00 02 45 66 77 77 88 77 77 77 66 54 42 00
tone  32- 63: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone  64- 95: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone  96-127: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 128-159: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 160-191: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 192-223: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 224-255: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 256-287: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 288-319: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 320-351: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 352-383: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 384-415: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 416-447: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 448-479: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 480-511: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00




P-660HW-T1v3> chandata
DSL standard: ADSL_G.dmt
near-end interleaved channel bit rate: 0 kbps
near-end fast channel bit rate: 8128 kbps
far-end interleaved channel bit rate: 0 kbps
far-end fast channel bit rate: 448 kbps
P-660HW-T1v3>

Thanks.

Interestingly, the stats you posted highlight another item I have trouble getting my head around:-

P-660HW-T1v3> linedata near

noise margin downstream: 11 db
output power upstream: 12 db
attenuation downstream: 29 db

Namely the output power is relative to the "opposite" end.

John.

Luckily on this ZyXEL modem it's pretty clear which end they're talking about,

These are the definitions that ZyXEL use, taken directly from the P-660HW-Tx v3 'User's Guide'

but i'm not sure why they match the upstream output power with the downstream noise margin/attenuation figures

noise margin downstream is the signal to noise ratio for the downstream part of the connection (coming into the ZyXEL Device from the ISP). It is measured in decibels. The higher the number the more signal and less noise there is.


output power upstream is the amount of power (in decibels) that the ZyXEL Device is using to transmit to the ISP.


attenuation downstream is the reduction in amplitude (in decibels) of the DSL signal coming into the ZyXEL Device from the ISP.