Hello,
All the definitions of bandwidth like 1Gbps, OC3 etc give numbers mentioned as bandwidth. Are they birectional? That is if only 500 Mbps in each direction when bidirectional traffic is on.
Thanks,
Harsha
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On synchronous lines like T1, T3, OC1, OC3, etc, the bits per second is more or less the line capacity...meaning on a 1.544mbit T1 someone could be downloading at 1mbit and there would still be about 500kbits left for either more downloading or uploading. There are more factors involved but that's the basic idea.
Ethernet is either full duplex, or half duplex. If you have a 100Mbps line, but you're running in half duplex, then that means that you have 100Mbps available, but only in one direction. Full duplex means that Collision detection is turned off and both ends can send and receive at the same time up to a max theoretical speed of 100Mbps for a COMBINED throughput of 200Mbps but neither send or receive can exceed 100Mbps.
"Full duplex means that Collision detection is turned off" Pseudocyber,, can you exlain this?? from my inderstanding Full duplex means that both of the pairs are used, not just one (so traffic can go in both directions at the same time). But collisions could still occur if 2 hosts tried to use the same line at the same time (hub, not switch used), so CSMA/CD would still have to be on right? I could be wrong. I'm asking more for my own understanding than to prove you wrong.
I can't really explain it, other than to tell you that when you enable full duplex on a connection, this turns off Collision Detection. Which is the problem of allowing the other side to be autonegotiate, because the Auto side cannot negotiate with a side which isn't set to also autonegotiate. So, BY DESIGN, the auto side defaults to half duplex - with collision detection on. So, on the full duplex side it won't detect the collisions which will invariably happen in this scenario and will only be evident to the user as "slowness" but will be evident on a managed switch, or a stack with better error reporting, as CRC errors, alignment errors, giants, and late collision.
A few quotes from google:
The simple solution is to "hard configure" the server's NIC for full duplex operation. This turns off the collision detection, allowing packets to be received during transmission http://www.wildpackets.com
Full duplex is a way of eliminating collisions and deferrals. Simply put it turns off the collision detection hardware so that the network interface can transmit and send simultaneously, there can be no collisions or deferrals. http://members.cox.net/~nd
In addition to CSMA/CD, the 82596 is capable of full-duplex communication. In full-duplexoperation, the 82596 uses the RTS output to enable data transmission through the TEN input of a Intel transceiver. In order for Intel transceivers to operate in full-duplex mode, the transceiver collision detect circuits must be disabled. Collision detection disable is performed through the LEDC pin on the transceiver. http://www.intel.com/desig
Thanks,, the HUBs not being able to go to full duplex that is what was confusing me then and explains it so i understand now. I can't believe ive never noticed that before. Since the switch isn't a bus it will "know" that the line is free. FYI it's the 802.3u standard that defaults it to half duplex if both sides aren't set to auto. So, if one side is set to 100full and the other is set to auto, they will correctly negotiate the speed (100), but not the duplex method b/c the 802.3u standard will put the auto end at half duplex. So one end will be on half and the other will be on Full, obviously causing problems.
yeah i know,,, my admins at my old job did it all the time and then wondered why the users networking speed was slow. My question wasn't about how both ends get to full-duplex, i understood that, but about the collisions. I was misunderstanding that part since Hubs are rarely used anymore and i forgot they can't go int full duplex.
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by: SystmProgPosted on 2005-01-31 at 05:35:19ID: 13182343
it depends on downstream and upstream traffic from and to client networks