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The Question is: Hi, Can you please tell me if Micro VAX 3100-96 supports full-duplex or half-duplex communication over the network? All I was able to find out so far was that it uses DC541 SGEC chipset. Using "mc latcp" or "anal/system" would not give me such information. Thank you. Nedo The Answer is : Systems do not support communications, systems support controllers and controllers support communications. Your reference to the SGEC (Second Generation Ethernet Controller) is to a ten megabit per second Ethernet controller interface chip, and traditional Ethernet controllers are not typically associated with the full- and half-duplex terminology used with later (and faster) Fast Ethernet controllers. Traditional Ethernet (IEEE 802.3 CSMA/CD) is related to the older ALOHAnet radio network and to other broadcast radio network technologies and experiments, and has just a single shared connection (or frequency, in the case of the radio-based networks) that is used for both transmit and receive. When you hear of collisions and back-off, this is a result of the controller listening for the network carrier before it transmits. If one station is starting to transmit and hears another start, it backs off a random interval and tries to send the packet again later. If two stations start to transmit at the same moment, a collision occurs and each controller involved in the collision deliberately garbles its packet and backs off a random interval for a later retransmission of the packet. That the Ethernet stations must hear each other also means that the shortest packet dictates the longest network segment permitted on an Ethernet segment. To properly detect and handle a collision, the shortest packet permitted must not complete its transmission before another station's transmission of its shortest packet arrives -- the controllers must detect the collision before the complete packet is transmitted. Thus the speed of the transmission of the shortest packet dictates the maximum length of the wiring. This requirement for carrier sensing and for collision detection provides Ethernet with the CSMA/CD acronym: Carrier Sense Multiple Access with Collision Detection. Fast Ethernet has a pair of connections available -- traditional Ethernet is thus inherently a half-duplex protocol, while Fast Ethernet can use one or can use both of the available connections: Fast Ethernet can be half- or full-duplex, in other words, depending on the signaling used and the capabilities of the network controller and the network plant. Short answer: the SGEC is half-duplex ten megabit Ethernet.
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