[ale] OT: DOCSIS Info

gcs8 gcsviii at gmail.com
Wed Jan 18 16:54:36 EST 2012


If that was slimjim100 there is another of his talks from skydogcon 2011
about docsis with me heckeling in the background.
On Jan 18, 2012 4:52 PM, "Matt Rutherford" <matthew.g.rutherford at gmail.com>
wrote:

> Interesting talk - thank you!
>
> -Matt R
>
>
> On Sun, Jan 15, 2012 at 7:40 AM, JD <jdp at algoloma.com> wrote:
>
>> 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
>> >         ______________
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