madden@net1.ucsd.edu (Jim Madden) (01/28/89)
UCSD has an extensive broadband cable plant that it uses for terminal connections and as a general purpose ethernet backbone. We are now thinking about attaching new high volume applications to the existing plant and are interested in recommendations and experiences of others with 5 to 10 megabit per second CATV compatible data distribution products such as Applitek's Unilan and Unibridge, Bridge ethernet filters and TCP/IP routers, various MAP/TOP implementations, and ethernet over broadband. We are particularly interested in comments about Applitek equipment and it's ability to use a single 6 Mhz. channel pair and coexist on the same cable plant in channels near broadcast television or other data distribution services. We solicit any other reasonable comments about the project as well. Our immediate need is to connect 10 to 15 TCP/IP workstations in 5 buildings on three different cable legs each of which is about 1,500 meters long. The workstations will use a network file system remote/procedure application that requires them to exchange data among themselves nearly constantly at an aggregate rate of 500,000 bytes per second over several hours at a time. Our current thoughts are that the workstations within each building will be on an isolated ethernet and that the ethernets will be linked together throught the CATV plant via either 802.3 filtering repeaters, although we might instead choose TCP/IP routers to improve building isolation. Any comments? Jim Madden UCSD Network Operations madden@ucsd.edu ucsd!madden Jim Madden UCSD Academic Network Operations, (619)534-2682 madden@ucsd.edu ..!ucsd!madden
ron@ron.rutgers.edu (Ron Natalie) (01/31/89)
We're using Applitek Broadband Bridges. We're also testing out there latest BandMaster broadband unit and have tested the ChipCom EtherModem in the past. We've had some problems with the older Appliteks wedging, but ours are pretty old. We'll let you know how they work. We put them on our busiest link. The Chipcoms worked just fine and they are pretty reliable. Their problem is that they are not frequency agile and they require 12MHz (two channels) and they push their own translator. The Appliteks use a frequency agile 6 MHz channel and can use a regular midsplit translator. They also seem to be a little more expensive list-price wise, but I'm waiting for their University prices. If you've alreadly got a mid-split cable plant in, then using one of these on this net is entirely appropriate. If you were building from scratch, I'd put in fiber. -Ron
kwe@bu-cs.BU.EDU (kwe@bu-it.bu.edu (Kent W. England)) (02/04/89)
In article <1422@ucsd.EDU> madden@ucsd.edu (Jim Madden) writes: >UCSD has an extensive broadband cable plant that it uses for terminal >connections and as a general purpose ethernet backbone. We are now >thinking about attaching new high volume applications to the existing >plant and are interested in recommendations and experiences of others >with 5 to 10 megabit per second CATV compatible data distribution >products such as Applitek's Unilan and Unibridge, Bridge ethernet >filters and TCP/IP routers, >various MAP/TOP implementations, and You might want to be careful about committing to the broadband token bus standard [802.4]. It may not go anywhere in terms of installed base. Ungermann-Bass has dropped support for the broadband token bus medium. They say it is due to lack of market interest. They will be supporting MAP on Ethernet and, I suppose, other IEEE media standards. U-B pioneered MAP support through INI, a joint venture with GE that GE bailed out of a while back. U-B knows the MAP market through INI, so I would take their "advice" seriously and I question whether broadband token bus will ever reach a critical mass of support. Anyway, broadband MAP is looking rather deadend-like. But perhaps broadband token bus has uses outside of MAP. I would be interested to know what other users think and what other vendors already support 802.4. Doesn't someone make a .3-.4 bridge already? Kent England, Boston University
haas@wasatch.UUCP (Walt Haas) (02/04/89)
In article <27676@bu-cs.BU.EDU>, kwe@bu-cs.BU.EDU (kwe@bu-it.bu.edu (Kent W. England)) writes: > You might want to be careful about committing to the broadband > token bus standard [802.4]. It may not go anywhere in terms of > installed base. > Ungermann-Bass has dropped support for the broadband token bus > medium. They say it is due to lack of market interest. The lack of market interest might just be, lack of interest in UB products. > Doesn't someone make a .3-.4 bridge already? Sytek and Concord make bridge products which allow you to encapsulate either Ethernet or 802.3 packets and ship them over 802.4 broadband to a distant Ethernet. Chipcom has a new product that does this, and also has on 802.3<=>802.4 conversion mode so that 802.3 and 802.4 networks can talk to each other. The big advantage that this type of product has over a CSMA/CD on broadband approach is that the distance limits are greater. Our campus is too big for CSMA/CD over broadband products like the Chipcom Ethermodem or Applitek Bandmaster. We chose the 802.4 on broadband bridge approach because of our network diameter. Cheers -- Walt Haas haas@cs.utah.edu utah-cs!haas
smith@cos.com (Steve Smith) (02/09/89)
In article <27676@bu-cs.BU.EDU> kwe@buit13.bu.edu (Kent England) writes: > > You might want to be careful about committing to the broadband >token bus standard [802.4]. It may not go anywhere in terms of >installed base. > Ungermann-Bass has dropped support for the broadband token bus >medium. They say it is due to lack of market interest. They will be >supporting MAP on Ethernet and, I suppose, other IEEE media standards. > U-B pioneered MAP support through INI, a joint venture with GE >that GE bailed out of a while back. U-B knows the MAP market through >INI, so I would take their "advice" seriously and I question whether >broadband token bus will ever reach a critical mass of support. > Anyway, broadband MAP is looking rather deadend-like. But >perhaps broadband token bus has uses outside of MAP. I would be >interested to know what other users think and what other vendors >already support 802.4. Doesn't someone make a .3-.4 bridge already? > > Kent England, Boston University There are a number of manufacturers of 802.4 stuff out there, and I get no impression that they are going to dry up and blow away any time soon. I have seen a couple of 802.3 - 802.4 bridges. They all have the problem that 802.4 allows packets up to 8192 data bytes. If a long packet is routed to an 802.3 network (max length 1500 data bytes), it is simply discarded. They should work fine for 802.3 to 802.4, though. There are several reasons that I see for 802.4 not going anywhere. 1. 802.4 is a very complex protocol. It's only been relatively recently that a single chip controller has been available. Before this, controllers were either custom chip sets or microcoded bitslices. Expensive. 2. While one of the attractions of the broadband medium is that the CATV components are inexpensive and widely available, the headends and modems are *expensive*. The modems by themselves insure that the cost per connection will be at least $1000. 3. 802.4, until the last year or so, has been a moving target. Revisions to the spec have been depressingly frequent. I believe that the current spec is Version K. This might be called "How to Scare Away Chip Manufacturers". 4. 802.4 requires a significant ammount of network management. Unlike Ethernet/802.3, where all of the "operating paramaters" are fixed, 802.4 has a whole bunch of paramaters that must be set in each station, and they must all be the same across the network. The results of screwing up can get gruesome. 5. At least at one time, there were severe interoperability problems between INI's 802.4 stuff and everybody else's. I don't know what the current status of this problem is. 6. *RUMOR ALERT* I have heard that, several years back, INI got a contract to wire up a *big* factory with their 802.4 stuff. Reportedly, it never worked. At all. The company that owned the factory was *not* impressed. This gave 802.4 a really bad reputation. If anybody has any more info on this rumor, I would be interested in hearing about it. DISCLAIMER: These are strictly my own opinions. Any resemblence to any real opinions, public or private, is strictly coincidental. -- -- Steve (smith@cos.com) ({uunet sundc decuac hqda-ai hadron}!cos!smith) "Truth is stranger than fiction because fiction has to make sense."