Good post. One minor correction, the COM21 modems are DOCSIS 1.1 certified.
----- Original Message ----- From: "bergenpeak" To: Sent: Tuesday, March 19, 2002 9:53 AM Subject: Re: Is cable network really a shared medium? [7:38705] > Hi Sam, > > The shared vs non-shared issue DSL providers mention is somewhat > misleading. In any residential cable or DSL network, you will > have stat muxing. In a cable network, this happens on the HFC > network. In a DSL network, this happens at the Agg router (the > one that terminates all of those DSL connections). The Internet > is one big stat mux. In either the DSL or Cable approach, the > customer observed performance will be a result of many factors, > including access network design (how many subs share the cable > or agg router), the behaviors of these other users, the regional > network design, the size and types of peering connections, and > where the users are actually surfing too. > > My house has a long driveway that only I use. Does that mean > I'll get to work faster than the neighbors down the street > which live in an apartment complex and share a driveway with > other folks? > > In both approaches, one can prioritize traffic or partition bandwidth > to certain groups of users. > > The current standard for how IP/ethernet frames are transmitted over > an HFC network is defined via the DOCSIS 1.0 spec. This specification > is available at www.cablelabs.com. This spec defines how to > support best-effort IP transport. > > Support for additional features, include QoS, is defined in the > DOCSIS 1.1 spec. This document is also available at the above > web site. > > > Some details about DOCSIS cable networks: > > * On the HFC network, a single downstream channel can support > ~25-35 Mb/s (depending on the modulation being used). > > * The upstream connection typically can support between 5-10 Mb/s > (depending on modulation and the size of the channel). > > * The cable operator can opt, based on RF combining, how many homes > (fiber nodes) share a downstream or upstream. When service is > initially > launched in an area, an operator might combine several nodes together > and as the take rate increases, reduce the amount of combining > (which effectovely reduces the number of customers who share the > bandwidth). > > * When a cable modem is brought online, it gets an IP address via > DHCP and then is loaded with configuration information (IP, L2, > and L4 filters), network management, etc information. These > filters prevent issues which arise when DHCP servers are > running in a customer's home, prevents my NETBIOS traffic from being > seen by neighbors, etc. > > There are other technologies still deployed by cable operators to > support > HSD (LanCity, Motorola CDLP, Com21, etc.) which may not operate the same > as DOCSIS. > > Hope this helps. > > > > sam sneed wrote: > > > > I just changed services from DSL to cable modem. I have heard from people, > > including verizon, that cable is not as secure as DSL becuase it is over a > > shared medium. I connected to my cable modem and fired up my packet > sniffer. > > I did not see anyone elses traffic on the line so i am assuming the > bandwith > > is shared( a known fact about cable access) but is somehow filtered at the > > cable modem(bridge). Does anyone know if this assumption is true and the > > inside details of the how data is transmitted over the cable network? A > link > > to a whitepaer would be great. > > > > thanks Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=38813&t=38705 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
