From: Brown, Patrick (NSOC-OCF} (PBrown4@chartercom.com)
Date: Sun Apr 13 2003 - 01:34:48 GMT-3
The upstream direction(your cable modem to CMTS) operates in TDMA, which
provides the access time to your cable modem off of a particular upstream
via minislots, with the upstream defined by the cable plant combining(nodes
to US). Typically there is only 500 customers(IP address) peer upstream, but
there is usually 6 upstream per cable card, with a total of 4 cable cards
per chassis. This is true if you are hanging off a Cisco uBR7246 with 1x6
cards, but the Cisco uBR10000 has allot more upstreams and downstreams. Most
of the time us MSO's bundle cable interfaces so we can use many upstreams to
1 IP address BLOCK. ex: bundle = 6 US x 500 customers = 3000 IP on 1 logical
subnet.
With Ethernet all 3000 host will be on 1 segment using CSMA/CD(not good),
but with DOCSIS(cable) 3000 host will be spread out over 6 different
segments(upstreams) using TDMA which is more efficient than CSMA/CD is some
ways. So even though DOCSIS provide TRANSPARENT 802.1d service from the
customer prospective, it differs greatly from Ethernet. Hope this brought
more incite.
Thanks,
Patrick B
-----Original Message-----
From: phase90 [mailto:phase90@comcast.net]
Sent: Saturday, April 12, 2003 10:56 PM
To: Brown, Patrick (NSOC-OCF}; ccielab
Subject: Re: cable question - OT but should be simple
OK Pat I believe you! What got me wondering was on my subnet COMCAST had an
11-bit host
field - supporting 2,046 hosts which, in my experience with Windows and
broadcasting seems like alot. I don't think a traditional ethernet LAN or
Vlan for that matter would tolerate this many hosts on 1 segment and still
operate efficiently. This design issue just got me wondering a little bit.
Thanks for
all the replies.
Jerry
----- Original Message -----
From: Brown, Patrick (NSOC-OCF} <PBrown4@chartercom.com>
To: 'phase90' <phase90@comcast.net>; ccielab <ccielab@groupstudy.com>
Sent: Saturday, April 12, 2003 11:06 PM
Subject: RE: cable question - OT but should be simple
> How do you get your IP address! DHCP (255.255.255.255/broadcast)
> You can think of DOCSIS operations being the same as 802.1d.
> DOCSIS provides like transparent Ethernet service over the cable plant.
>
> Thanks,
>
> Patrick B
>
> -----Original Message-----
> From: phase90 [mailto:phase90@comcast.net]
> Sent: Saturday, April 12, 2003 7:54 PM
> To: ccielab
> Subject: cable question - OT but should be simple
>
>
> Hello group,
>
> In doing some simple setup of a LNKSYS hub on a
cable-modem
> account, the question occurred to me - Is this cable network considered
> broadcast or non-broadcast? Any takers ? responses most welcome.
>
> From my modest background I speculate non but then I have no hands-on with
> CMTSs. Thanks
>
>
> Jerry
> just wondering on COMCAST.NET
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