Token/FDDI/Gig Eth (spidey)

[shadow]

<< To the other question - Token Ring is a fabulous LAN topology with large frame sizes and equal distribution of bandwidth. Depending on the application it CAN run faster then Fast Ethernet.

Would I ever design any network with token ring today? NO.
Too expensive and hard for beginners to troubleshoot. I haven't recommended a shared media LAN in over 2 years save for FDDI on a backup/backbone when gig enet can't work. >>



ok spidey - I'm interested in the last statement &quot;when gig enet can't work&quot; what are these situations?

where do you have or judge it to be necessary to jump to FDDI from gig enet?

thx.

 

[Phokus]

If it's used as a backbone, FDDI is better because it's a ring technology... if part of the ring goes down, the other part is used as a backup.

 

[spidey07]

Several factors could make FDDI attractive.

1) Distance limitations of GigEnet
2) Phokus has a good point, self healing rings mean no spanning-tree issues
3) Political concerns of IT staff, they might not be comfortable with gig
4) FDDI is great at tranfering HUGE amounts of data quickly (large frame size plus multiple tokens) makes for a good data backup network. Fewer frames for same amount of data moved = less processing overhead on end station.
5) Previous install base of FDDI. Making the translation (frame wise) between ethernet and FDDI is a bear for a router. Frames are TOTALLY different. Fragmentation creeps in.
6) FDDI doesn't have the tremendous overhead that gig does. Remeber that gig enet frame sizes have to be at least 512 bytes due to the carrier extension process. This is a LOT of wasted bandwidth. On a 64 byte frame that is 800% overhead. JESUS!!!!

Jumping from GigEnet to FDDI? That would be a hard sell and I can't justify that one.

BUT, as much as I'm hyping FDDI there would still have to be some pretty good reasons for me to use this instead of GIG. GIG is fast, cheap, and melds great with existing ethernet networks. You just gotta do your design of spanning tree religiously.

Don't get me started on GIG vs. ATM vs. POS vs. FDDI\

Hope this helps.
Cheers

 

[shadow]

can you expound on #3?



<< Don't get me started on GIG vs. ATM vs. POS vs. FDDI\ >>



I just might

 

[spidey07]

Soap box on ---

A large campus (40 closet) network may already be based on a token ring distribution model with an FDDI backbone. This company has a couple of knowledable network engineers who run the network quite well and a pretty happy with it.

Now I come in and recommend replacing everything with switched 10/100 with 2-4 gig enet links between buildings for a cost of 5 million dollars. The net engineers are going to pound me on the pitfalls of ethernet and spanning-tree just like the ATM bigots did with PNNI vs Spanning-Tree. I kindly show them the light but the bulb doesn't quite light in their heads.

I'm not saying FDDI is a god send, it's been around for some 10 years. It simply has its place. That place being a very small and dark corner that I would rather not touch unless I have to. I can do gig with literally 100 times the capacity for half the cost.

soap box off ---

spidey

 

[shadow]

I see, thx alot mate

 

[R0b0tN1k]

Token ring based topologies are the best for backbone connections mainly because of their line access method. Ethernet will transfer whenever it sees an empty line, and it can slow things down when the line is frequently busy. Token passing topologies allow every device an equal opportunity to send it's data and is very efficient as a result. FDDI's fault tolerance comes from its dual-ring design...standard token ring dies whenever it's broken. FDDI can also be found in speeds greater than gig ethernet.