hello everybody!
I am a newbie in the computer world.
There are some problems with my ssh server...
I set up a ssh server in my office with optical fiber cable¡Aproviding about twenty persons(in the same office) to log in my server to execute a shell script,but a little lag. With optical fiber cable , switches, and Intel 82557 10M/100M NIC ¡AI don't know why it lags. I observe the total volume of flow is less then one-tenth of 10Mbps.
Could somebody help me?
Is it useful to provide telnet service instead of ssh service?
Should I shut down iptables?

thanks

No, it's the reverse actually:
SSH encodes the traffic, telnet does not
SSH allows you to tunnel other protocols inside its connection, telnet does not.

So basically you're saying that it works but extremely slow? Sounds like a duplex mismatch. Make sure your switch's ports and the PCs' NIC and all set to auto-sense. Or eventually all force to 100/full (I suggest auto-sense everywhere). If you force one side (let's say the switch's port) to 100/Full and leave the default (usually auto-sense) on the other (your linux box) then you get the NIC to come up 100/Half and get a load of collision on the LAN. So it works but slooooow...
Just a guess.

hi,jeickal
The reason I want to provide telnet service is less flow. Becouse of extra encoding information compared with telnet, I think it maybe keep more bandwidty if I use telnet as my login server.
And your suggestion is userful for me.I'll check if it is where the problems are.
Thank yoy

You won't see any speed difference. I honestly never look I the different way telnet and SSH are encoding the frames. But I'm not even sure there is a significatif overhead using SSH. Any anyway if you're on a Ethernet LAN, a SSH flow is nothing compare to 10 Mbps and less than nothing compare to 100 Mbps. Furthermore, you can use SSH to compress the traffic if you're going through low bandwifdth link, I think it's "ssh -C" look at the man pages.
I've been using SSH over a 33kbps line and it's only a little less responsive than on a LAN, it's only text you know? Now if you're opening some tunnel and passing other protocol through SSH it's different, but since you are comparing it with telnet I believe you don't need this.
Just a tip to test you LAN responsivness: Transfer a file with FTP from one PC to another over the LAN. FTP is a very effecient protocol that should eat up all the bandwidth. Transfering a 10MB file should take few seconds. if it takes minutes, than you have a problem with you network (switch/hub//NIC config).