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Upstream Question

CBR600
Grafter
Posts: 41
Thanks: 1
Registered: 11-08-2015

Upstream Question

Hello Everyone
I'm wondering why my line can't support a better upstream speed ?
Whats the difference between downstream and upstream ? Is it down to the equipment. ?
If you can get a 20Mbps down why can't you get the same or similar up ?
I assume it down to the distance and that modems are powerful enough ?
Just wondering.
Cheers
2 REPLIES
jafreer
Rising Star
Posts: 823
Thanks: 48
Registered: 13-10-2012

Re: Upstream Question

I am no expert but certain frequency bands are allocated for downstream and others for upstream. The attenuation on the line is usually greater at the higher frequencies, so it mostly boils down to how much attenuation there is on your line at the upstream frequencies. Since more frequency bands are allocated to downstream than upstream, it is prioritised more in the sense that more of the available bandwidth is allocated to downstream than upstream.
You asked the following questions...
Whats the difference between downstream and upstream ? Is it down to the equipment. ?
As above, the difference is the frequency bands employed. Since VDSL is rate adaptive, it monitors your line (signal to noise ratio, attenuation etc) and determines what speed it can reliably give you. It can also change other parameters (like interleaving) that may decrease your speed, but improve reliability.
So for the most part, distance from the cabinet has a lot to do with your upstream speed (and downstream of course). How much the signals (upstream and downstream) attenuate is a big factor.
If you can get a 20Mbps down why can't you get the same or similar up ?
Because less bandwidth is allocated to upstream than downstream. If line conditions are such that the max downstream speed you can achieve is 20 Mbps, then it is likely your upstream will also be restricted.
I assume it down to the distance and that modems are powerful enough ?
Distance definitely, but not so much the power of the modem. The design and power level of modems are tightly controlled by standards, so it is not like one modem uses more power than another. However, some people say particular modem chipsets perform better than others (for example, a lot of people say Broadcom chips perform better than Lantiq chipsets on a given line). It is mostly down to what works best for you.
CBR600
Grafter
Posts: 41
Thanks: 1
Registered: 11-08-2015

Re: Upstream Question

Thank you for the explanation.
Appreciate you taking the time.