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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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