r34rv13wm1rr0r wrote: > > No. The collision domain on a hub is shared throughout causing > each port to > listen before transmitting.
No is correct. A hub can't be configured for full-duplex. If it can be, it's been misnamed. It's really a switch. But the explanation is not correct. A hub port doesn't listen before sending. It doesn't do MAC data-link-layer tasks. It simply forward bits that come in one port out all other ports. On a proper-sized network, the sending end hosts will still be monitoring their transmission, notice any collisions, and retransmit. In my new book, Troubleshooting Campus Networks, I have the following relevant paragraphs: "Collisions on Networks with Hubs and Switches A hub is a repeater that simplifies cabling designs, permitting a star configuration with a hub at the center, like the hub in an old hub-and-spoke wheel. Repeaters and hubs have a few other important jobs and characteristics also. Signals going through a repeater are retimed using the repeater’s timing circuitry to prevent the accumulation of signal jitter. A repeater also regenerates the signal to the proper amplitude and symmetry. Another job of a repeater is to rebuild a received preamble to avoid preambles getting shorter as they go through repeaters’ timing circuits. Repeaters also extend any fragments that have resulted from frames that collided and were cut short. The repeater extends the signal so that the total number of bits output equals 96 bits. Fragment extension ensures that short collision fragments survive a trip through a maximum-size network in the correct time frame. Stations receiving the extended fragment discard it and also defer from sending until the collision event is over. One of the most important tasks of a repeater is to enforce collisions on each connected segment. Repeaters enforce collisions by transmitting a collision-enforcement jam signal. Upon detecting a collision on one segment, a repeater transmits a collision enforcement jam signal on that segment and all other connected segments. This ensures that any station trying to send at that moment hears the collision. In this way, a repeater makes sure all stations are in the same collision domain and can react to collisions correctly. When a repeater detects a collision, it sends a 96-bit jam composed of alternating ones and zeros. Switches are replacing hubs in large campus networks. It is a common misconception that switches don’t need to know about CSMA/CD and that collisions don’t occur on switched networks. In fact, each switch port implements the CSMA/CD standard. When sending a frame, a half-duplex switch port senses carrier, defers if necessary, detects collisions, backs off, and retransmits. Whether a collision might occur or not depends on what is connected to the switched port. If a shared medium is connected to the switch, collisions may occur. Ethernet troubleshooters often wonder about cut-through switches and collisions. A cut-through switch outputs bits as soon as the destination address has been received and the destination port determined. What if there is a collision on that port? Should the switch send a collision enforcement jam on the port that received the frame so the original sender knows to try again? Or has the switch cached the frame so that it can do the retransmitting? Some troubleshooters assume that cut-through processing means that the frame was not cached. Vendor implementations may vary, but Cisco cut-through switches cache all frames, even when in cut-through mode. In this way, each port can handle CSMA/CD duties for that port and no other port. A switch retransmits if a collision occurs and does not notify the original sender in any way. Each port truly delimits a collision domain." Priscilla Oppenheimer > A switch on the other had limits > the collision > domains by port therefore allowing the host to transmit at will. > > > ----- Original Message ----- > From: "Saravanan L" > To: > Sent: Tuesday, September 10, 2002 2:59 AM > Subject: A HUB can work in Full-duplex mode? [7:52973] > > > > Just I want to know can a Hub work in full-duplex mode? > > > > Saravanan > > > *************************************************************************** > > This message is proprietary to Future Software Limited (FSL) > > and is intended solely for the use of the individual to whom > it > > is addressed. It may contain privileged or confidential > information > > and should not be circulated or used for any purpose other > than for > > what it is intended. > > > > If you have received this message in error, please notify the > > originator immediately. 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