bob@islenet.UUCP (Bob Cunningham) (08/26/86)
While looking around for fiber optic Ethernet repeaters to buy, there seems
to be two distinct flavors:
plain repeaters (about $1,000 per end)
slightly fancier repeaters (about $2,500 per end)
The apparent difference is that for the extra cost, you get preamble
reconstitution, fragment extension and perhaps more careful retiming.
Still...some of the less expensive receivers nonetheless claim to be
IEEE802.3 compatible.
Am I mis-reading spec sheets? Is there really any difference?
--
Bob Cunningham {humu|ihnp4}!{islenet|uhmanoa}!bob
cunninghamr%haw.sdscnet@LLL-MFE.ARPA
Hawaii Institute of Geophysics, University of Hawaiiphil@amdcad.UUCP (Phil Ngai) (09/02/86)
In article <2770@islenet.UUCP> bob@islenet.UUCP (Bob Cunningham) writes: >While looking around for fiber optic Ethernet repeaters to buy, there seems >to be two distinct flavors: > > plain repeaters (about $1,000 per end) > > slightly fancier repeaters (about $2,500 per end) > >The apparent difference is that for the extra cost, you get preamble >reconstitution, fragment extension and perhaps more careful retiming. > >Still...some of the less expensive receivers nonetheless claim to be >IEEE802.3 compatible. As I read the 802.3 spec, all 802.3 compliant repeaters must offer: 1) preamble insertion (section 9.1.2.3) 2) fragment extension (section 9.1.2.5) 3) signal retiming (section 9.1.2.1.3) as well as: 4) signal amplification (section 9.1.2.1.1) 5) signal symmetry (section 9.1.2.1.2) I would be interested in the names of the products you have looked at. -- Rain follows the plow. Phil Ngai +1 408 749 5720 UUCP: {ucbvax,decwrl,ihnp4,allegra}!amdcad!phil ARPA: amdcad!phil@decwrl.dec.com
bob@islenet.UUCP (Bob Cunningham) (09/03/86)
Here's the optic fiber repeaters I've been trying to compare specs on:
DEC's DEREP-RA, costing $2k+.
American Photonics, Inc.'s RL6000-R001, costing about $2k.
Cabletron's "Isolan" repeater, type 1150-0, costing about $2k.
Excelan EXOS 1150-0, costing $2k+.
Canoga Data Systems' CER-802 fiber optic repeater, costing $1k+.
Hewlett-Packard, HP28645A (?), costing $??? [3 weeks & still waiting for
specs & price info, sigh].
I've also heard---2nd hand--of a Codex optic fiber repeater supposedly in
the $1k price range that I'm trying to get some definite info on.
I'm still looking for more info on some of these. It seems that there are
some differences between them, but that's often difficult to get from the
somewhat-sparse spec sheets I've gotten from some of the vendors. Most
explicitly claim 802.3 compliance, others spec sheets seem deliberately
vague...hence my question as to whether or not there are any real
differences between the lower-priced & higher-priced models. Other
noticeable, useful differences include different types of LED indicators,
automatic partitioning features...and lengths of warranties.
Prices are even harder to get ahold of, and seem somewhat negotiable. I've
indicated approximate prices (quantity 2) that I've been quoted...usually
over the phone. "Your mileage may vary" (perhaps considerably).
Minor flame: Having to deal with university procurement procedures, I must
have written price quotes to actually buy anything (and, I have to make an
honest effort to compare prices & features). Despite repeated
requests, several vendors of Ethernet-type equipment (not just repeaters)
just won't give me written price quotes. That's already limited my choices
on some equipment I've been buying...vendors I'd otherwise would have
bought from I'm not, simply because I can't get written price quotes from
them.
--
Bob Cunningham {humu|ihnp4}!{islenet|uhmanoa}!bob
cunninghamr%haw.sdscnet@LLL-MFE.ARPA
Hawaii Institute of Geophysics, University of Hawaiiphil@amdcad.UUCP (Phil Ngai) (09/08/86)
In article <2778@islenet.UUCP> bob@islenet.UUCP (Bob Cunningham) writes: >Here's the optic fiber repeaters I've been trying to compare specs on: > >DEC's DEREP-RA, costing $2k+. > >noticeable, useful differences include different types of LED indicators, >automatic partitioning features...and lengths of warranties. DEC doesn't seem to push their automatic partitioning as much as I think is justified. The goal is to keep your network up in the face of equipment failures. For example, suppose one of the repeater's transceiver taps loosens up and the transceiver starts reporting collisions all the time. Without automatic partitioning your network is down, as the repeater will jam every packet it hears. The DEREP counts consecutive collisions. If this count reaches 64 it concludes something is wrong and segments the colliding side. This means data is transmitted to the bad side but data from the bad side is not repeated to the good side. Also collisions on the bad side are not enforced on the good side. When a packet is transmitted to the bad side without a collision the segmented state is exited and normal operation resumes. While it is better to have some of your network up than none of your network up, it is even better to have the whole network up. This can be done at the cost of doubling your investment in equipment. A repeater and its associated set of transceivers are installed in parallel with the primary repeater. This second repeater is in standby mode. (switch selectable) The standby repeater is normally passive, merely monitoring both coax segments. If data is not repeated for an entire slot time, it enters the active mode and repeats packets. Once the primary repeater is restored, it will start repeating packets. The standby repeater which has been active will then collide with the primary repeater. The standby repeater counts up to 56 consecutive collisions and exits the active mode. As the primary repeater does not segment until 64 consecutive collisions, it remains in the active mode. Incurring 56 collisions is relatively time consuming but only happens when a broken primary repeater is put back into service. I think this feature is a nice one. I wish DEC wouldn't be so shy about telling customers about it. -- Rain follows the plow. Phil Ngai +1 408 749 5720 UUCP: {ucbvax,decwrl,ihnp4,allegra}!amdcad!phil ARPA: amdcad!phil@decwrl.dec.com
bob@islenet.UUCP (Bob Cunningham) (09/11/86)
> >DEC's DEREP-RA, costing $2k+. > > > >noticeable, useful differences include different types of LED indicators, > >automatic partitioning features...and lengths of warranties. > > DEC doesn't seem to push their automatic partitioning as much as I > think is justified... I've just been convinced that automatic partitioning is a very, very good thing to have. Two other repeaters with that feature (there might be others, if so I'd like to hear about those) are: American Photonics' R0001 (with SMA fiber connector) and R002 (with ST connector), priced a bit less than DEC's DEREP-RA. Canoga Data Systems's CER-802 (SMA connector only), priced around $1.3k (recent price reduction from $2k, and the paritioning feature may be fairly new also). I intend to buy one of those three brands for some fiber optic links here at the University of Hawaii, and would appreciate hearing anybody's experiences with those last two. -- Bob Cunningham {humu|ihnp4}!{islenet|uhmanoa}!bob cunninghamr%haw.sdscnet@LLL-MFE.ARPA Hawaii Institute of Geophysics, University of Hawaii