HP OpenVMS Systems

ask the wizard
Content starts here

Ethernet and Duplex Network terminology?

» close window

The Question is:

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.

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.

answer written or last revised on ( 12-JUL-2000 )

» close window