[ale] OT: DOCSIS Info

[JD]

A Cisco DOCSIS guy, Biran Wilson, gives talks at the hacker-cons periodically.
Find the OuterZ0ne videos if you're interested in more detailed, organized
information. DOCSIS3 lets channels be mixed for digital cable video and data. It
also allows channel bonding.

See the Brian Wilson talk - Docsis Coolness
2010: http://www.archive.org/details/Outerz0ne2010Videos

I had both residential and business comcast service through 2 different lines to
the house.  It was weird calling for business ISP support during multi-hour
outages using VoIP connected to the residential line not seeing any issues at all.

I love it when my neighbors talk about how DSL doesn't share bandwidth so it is
better. That means they aren't on my cable line.  The fact that DSL is usually
3x slower ALL-THE-TIME for the same price doesn't matter, it is still "better."
ADSL2+ is changing the performance difference a little, but still has other issues.

There is enough hate for telecom and cable companies to go around. They have
most of us by the balls.



On 01/14/2012 10:17 PM, Matt Rutherford wrote:
> Trying not to run on to much but here is an overview of how DOCSIS does dynamic
> bandwidth. I'll leave out the more detailed guts of it. An in-depth of this
> subject is way too OT here. 
> 
> DOCSIS has a feature that allows for burst speed provisioning within a specified
> range when there is bandwidth availability on the server. This can be applied to
> a set amount of a specific transaction, ie: 5MB, 10MB, 20MB, etc. This provides
> the nice bump in initial download/buffer speed on large videos (see Youtube,
> Netflix, etc) and also is quite noticeable on speed test sites since they are
> file-transfer speed based. Also looks great for marketing and advertising in
> comparison to the speeds offered on DSL. This is all handled by the CMTS.
> 
> Typically the burst speed will be set to the around the same level as your
> provisioned speed, though this is not always true. IE: a 22mbps connection will
> burst speeds up to 44mbps (down) for a pre-determined amount of upwards or
> downwards transfer. Since cable speeds are non-synchronous, you may have a 5mbps
> upstream with bursts up to 10mbps. This cannot be relied on however, hence the
> careful use of 'up to (X)mbps' in advertising. 
> 
> Peak usage hours for residential areas for cable internet bandwidth run
> 5pm-midnight as Kirsa said, so I'd add a +1 to the congestion theory. There are
> other causes as well, but tech support should be checking for those symptoms
> anytime you call in (SNR, bad RX/TX, and high levels of error correction to
> packets from the modem). 
> 
> During heavy usage if there is saturation of the bandwidth availability to below
> a specified threshold, protocols kick in to limit users to speeds lower than
> their 'provisioned' default. This is done dynamically since each CMTS has
> multiple RF cards separated into upstream and downstream. You may have a
> non-saturated upstream but a saturated or congested downstream as far as
> bandwidth goes - we rarely saw upstream problems except for military barracks,
> college towns, and other edge cases. There are other layers of bandwidth
> management and bottlenecks that impact speeds which can exist at the node or
> network level, but outside of RF issues the most typical and noticeable change
> in speeds comes from this type of congestion. 
> 
> -Matt R
> 
> 
> On Sat, Jan 14, 2012 at 8:48 PM, Jim Kinney <jim.kinney at gmail.com
> <mailto:jim.kinney at gmail.com>> wrote:
> 
>     All ISPs know the speedtest sites. Comcast is known to privide priority routing.
> 
>     On Jan 14, 2012 7:53 PM, "Drifter" <drifter at oppositelock.org
>     <mailto:drifter at oppositelock.org>> wrote:
> 
>         On Saturday, January 14, 2012 05:36:53 pm Kirsa wrote:
>         > I would not be surprised if you experienced a similar speed issue next
>         > Friday though... On almost any residential cable node Friday 5-12pm is
>         > peak time and has the most utilization of the entire week. So that you
>         > were down to 4mbit/s on Friday evening and 2mbit/s by Friday night
>         > sounds suspiciously like congestion to me, despite the faulty
>         > equipment.
>         [Rest trimmed for brevity.]
> 
>         I had the same speed issues at 9 am Saturday morning. Snail-slow download
>         speeds continued all day Saturday until I replaced the defective hub.
>         Then: BINGO! full speed returned.  In fact, a speed about 19:45 Saturday
>         (Speakeasy's test) returned the rather unbelievable download speed of
>         40.59 mbs! The upload speed was only 4.16. Obviously some sort of burst
>         speed. Does Comcast have some way to know when I access a speed test site
>         and goose the speed for a few seconds?
> 
>         Sean
>         ______________