alan@columbia.UUCP (06/04/87)
In conjunction with the installation of a new phone system at Columbia, a single-cable mid-split broadband system is being installed. No particular means of using the broadband was specified in the phone system RFP -- simply that the cables, amplifiers, splitters, etc. should be installed with the "details" of using the system to be worked out later. Given the time between an initial RFP (a year or two ago) and actual completion of a project this size (about a year from now), this was probably a good idea. We are looking at using the broadband for fast computer networking (10 Mb 802.4?) as well as a (cheaper?) alternative to using the data capabilities of the phone switch for terminal service. The switch is a ROLM CBX 9000AE which will of course require data modules in each phone (around $200+) plus data modules to connect to host CPU ports plus the CPU ports themselves. Obviously having those hosts on the network (most are on ethernet now) with telnet servers will at least save the cost of the host RS-232 ports. Now that I've bored you with the background information, I'd like to solicit descriptions of what you have done with broadband at your site. Pointers to good sources of education (e.g. books, papers, courses) would be greatly appreciated. Also, please do not be shy about saying what it costs. I've heard several times about how expensive broadband modems are. Thanks. Alan Crosswell alan@columbia.edu
ron@topaz.rutgers.edu (Ron Natalie) (06/05/87)
Rutgers, The State University of New Jersey (one of these days I expect
to see Princeton T-shirts that say "not the state university" on them)
has installed a three cable broadband system on the Busch campus (this
campus houses the computer center and most of the engineering/sciences).
Currently only one cable is live (amplifiers in place, on etc...). That
cable is mid-split with the head end located in the main machine room
on campus.
We currently have two data users on the broadband. The first is a GI
point to point RF modem which is not significant. The second is an
Applitek broadband networking system. The Applitek bridges ethernets
in various buildings in a protocol independent way. Since we have had
problems with the Applitek in the past, I have recently been resurveying
the market.
APPLITEK: The Applitek is will bridge ethernets accross the broadband.
It occupies one 6 MHz channel and the RF modems in it are software
frequency selectible. The box plugs into a standard Ethernet transceiver
on the LAN. It provides packet filtering in much the same fashion as
products such as the DEC LANBRIDGE. It has a small amount of monitoring
and control that is accessable via an RS-232 port on the back of the box.
BRIDGE: Bridge makes a similar system. Essentially, this is their ethernet
link level bridge again with broadband modems that come from a company that
they have since bought out. They also occupy a single 6 MHz channel and
provide about 5 MHz of bandwidth. The boxes again filter out packets which
need not travel accross the entire system. The modems are agile across
5 channels. The network may be monitored with the same facility used for
their other products (it is a UDP telnet-like facility that lets you talk
to the processor in each box).
CHIPCOM: Chipcom makes a product called the Ethermodem. This box
simulates a transceiver (actually you can get it with two transceiver
ports) and provides the full ethernet bandwidth over a non-configurable
18 MHz channel. These boxes actually act as true ethernet transceivers
and hence are subject to the normal ethernet distance limitations (unlike
the previous two units) for the entire network. In addition, you will
need a minimum of a Ethernet repeater to interconnect the it to a local
Ethernet although they recommend the DEC LANBRIDGE for packet filtering.
The prices for the three are roughly comparable. Expect to pay about
$6000 for headend equipment and about $10,000 for each Ethernet you
wish to connect to the broadband.
Both the CHIPCOM and BRIDGE products come with good reliability and
performance references. While our Applitek system is pretty solid
now, we did have problems with it in the past. In my investigations
I have found this to be pretty universal, other people had Applitek
systems that used to be bad, I guess that one of the engineering changes
cleared up whatever was causing the reliability problem.
The CHIPCOM and BRIDGE products claim that they require their own
translater/remodulator, which I find unfortunate. The Applitek
seems happy with our existing CATEL (K-TEL?) translator.
I'd be interested in hearing other peoples experiences. I know that
the following people are bridging ethernets on their Broadband network:
University of Maryland
U.S. Army - Dover NJ
Stanford University
University of Wisconsin
Arizona State
MCNC (Research Triangle, NC - I never remember what the acronym
means)michaels@hplabsc.UUCP (Robert Michaels) (06/06/87)
In article <12471@topaz.rutgers.edu>, ron@topaz.rutgers.edu (Ron Natalie) writes: > > I'd be interested in hearing other peoples experiences. I know that > the following people are bridging ethernets on their Broadband network: > We have been using Ungermann-Bass buffered repeaters on our network. These are similar to the BRIDGE box in that it only does 5 Mbits in a 6 Mhz channel. So, it simply buffers incoming traffic on the 10Mbit baseband side into a 256K buffer for retranssmission on the broadband. It will work with most any translator (we use a 3M) and it is frequency agile. We are using 8 units on a system which spans about 3 miles. To reduce the possiblity of overloading the repeaters we isolate them from the baseband ethernets with IP gateways. This makes the broadband logically a subnet of only gateways and from measurements I have made this has quite an effect on total utilzation. The Ungermann-Bass repeaters cost around $3800 each. I have found them to be very reliable, we have yet to have one fail. Our cable system also supports several video channels, some 9.6 Zeta modems, and some Applitek terminal concentrators. From what I can tell the UB repeaters do not effect nor are effected by the other equipment. Ron, I'm curious about your experience with the Chipcomm stuff. I read that it requires 18Mhz bandwidth. Do you need guard bands in addition to that? Also, have you tried using their newly announced modems which only require 12Mhz bandwidth? Robert Michaels HP Labs
sob@academ.UUCP (Stan Barber) (06/08/87)
Baylor College of Medicine is planning to install a broadband
gateway from ethernet into CATV and from CATV to DS2. We have
tentatively chosen BRIDGE as the primary vendor. As soon as things
get more settled, I'll report on what actually happens.
--
Stan uucp:{killer,rice,hoptoad}!academ!sob Opinions expressed here
Olan domain:sob@rice.edu are ONLY mine &
Barber CIS:71565,623 BBS:(713)790-9004 noone else's.page@ulowell.cs.ulowell.edu (Bob Page) (06/24/87)
michaels@hplabsc.UUCP (Robert Michaels) wrote: >I read that [Chipcom] requires 18Mhz bandwidth ... have you tried >using their newly announced modems which only require 12Mhz bandwidth? We are currently using the 18MHz boxes here, and they seem to work well, even though we run them just a little past the distance spec in order to tie two campuses together. We also use them to link ethernets across smaller distances. Our tests on the 12MHz modems are "still in progress," but we haven't found any major problems with them. Of course, you aren't getting something for nothing: although it's nice to have 6MHz back, the 12MHz modems won't allow us to link the two campuses any more. Another note about the new modems is that they use a different part of the band. ..Bob -- Bob Page, U of Lowell CS Dept. page@ulowell.{uucp,edu,csnet}