Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!cwjcc!ukma!david From: david@ms.uky.edu (David Herron -- One of the vertebrae) Newsgroups: comp.dcom.lans Subject: Token Ring (was: Re: Info on LANs) Message-ID: <10777@s.ms.uky.edu> Date: 30 Dec 88 21:52:00 GMT References: <12786@cup.portal.com> <920001@hposdl.HP.COM> Reply-To: david@ms.uky.edu (David Herron -- One of the vertebrae) Organization: U of Kentucky, Mathematical Sciences Lines: 86 Yeah, I just got done reading the current BYTE this morning and was especially intrigued with the token ring article ... but I had a couple of questions.. mainly about assumptions of the author. the style of daisy chaining -- The IBM design (he didn't make it clear if he was talking about just the IBM design or token rings in general at this point) has some sort of central ring off which you have two cables going out to the node. The central ring has, at the point where the cable-going-out-to-the-node (I'm going to call it "drop cable") connects in there's some circuitry which detects whether the node is up or not and if it isn't simply passes packets (frames) along. Why have all this extra cabling? Yeah it's a good idea, if you're going to have a fancy net like token ring, to have some smarts to allow packets to go through when nodes go down or are disconnected. BUT .. I think you could do it without having to use two cables to reach the node ... one should be able to do the job. To guard against nodes being turned off you put some stuff on the board which is somehow always powered. This is the thing that detects when the node is down and starts passing packets along. Or maybe it's not on the board itself but it's in a little box that sits on the floor and the little box even detects when the cable going up to the node is physically disconnected ... Or .. the broadband cabling we have on campus proves that you can have multiple transmitters on a cable all transmitting at the same time. Have the central box transmit on one frequency and have the node transmit on another. Lastly .. it was suggested in the article that we use the normal wiring conduit and closets as we do now for phones and ether cable. I don't think that would work unless these cables are very very very thin. At least not compared to ethernet where we pull just one cable all around the floor to serve all our workstations. only one talker at a time -- I see that this helps to avoid collisions but it seems a big waste of the available bandwidth. Ether also allows only one talker at a time so neither has an advantage over the other in this regard. There should be some way of having more than one packet circling the ring at a time. Or did I misread the article? I'm thinking of something like a node has a packet waiting to go out, it see's a packet go by then looks for some special event following the packet to determine whether or not it can transmit its packet. Perhaps the transmitter always transmits a token after transmitting a packet. Then the next station down the line will pick up the token, transmit it's packet (if it has one) then transmit a token. 'cept we have something like a circular buffer and we have to make sure of not overrunning it. size limits -- He said a few things about token rings not being as size limited as ethernets. First off if you were to have a ring of any appreciable number of stations and each station were the maximum distance apart the delays for the one-packet-at-a-time to go around the ring would be very hideous, at least in computer terms. This implies that you'd want to split a token ring into two far earlier than you normally do on ethernets. (We have 40-50 hosts on our ether doing NFS all the time (few of them are diskless suns fortunately, so we don't see much swapping over ether) and aren't thinking of splitting our ether and probably won't think about it until we double in size again). Ethernets are very cheaply split what with LANbridge type boxes being about $1000-$2000 a crack. broadcast packets -- how do you do one? Off hand I'd think you could do it much as now, put a special TO-ADDR (all one's?) and your own FROM-ADDR ... all the nodes around the ring see the packet and actually receive it but don't set that special bit saying it was received. Eventually the original transmittor will receive it again and set the special bit and pass it on. extra overhead beyond normal ethernets .. both the extra cabling and also the two watchdog boxes. -- As I think it over I just see all this extra stuff tossed in that makes it more expensive than ether. And you're not gaining anything in speed. OOooh AAaah, they've raised the speed up to 16Mbps ... that's still the same ball-park as ether. Yet there were articles in Network World all concerned with whether people will be able to find something to do with all that extra bandwidth! Gimme a break! -- <-- David Herron; an MMDF guy <-- ska: David le casse\*' {rutgers,uunet}!ukma!david, david@UKMA.BITNET <-- Now I know how Zonker felt when he graduated ... <-- Stop! Wait! I didn't mean to!