Table of Contents
Advertisement
1.3.1 Statistical Multiplexing
The DECmux II unit and MUXserver 100 use a statistical multiplexing tech-
nique for communication that allocates time to each data channel in relation to
how much time the channel needs. Unlike the simplest form of time division
multiplexing, where time slots are allocated to channels irrespective of whether
data is ready for transmission or not, with statistical multiplexing, no time
slots go empty unless all communications are complete.
A typical transmission from terminals connected to a DECmux II unit to a
computer system on the LAN is as follows.
1.
At random intervals, data from the terminals arrive at the asynchro-
nous ports of the DECmux II unit. The data words may be at various
baud rates, and may have odd, even, or no parity bits.
2.
The DECmux II unit receives the characters., discards all the start,
stop, and parity bits, and stores the data in a buffer.
3.
Using a protocol that is understood by the DECmux II unit and
MUXserver 100, the DECmux II unit determines how much data to
take from each incoming data channel.
4.
The DECmux II unit places the data into the information field of a
high level data link control (HDLC) frame, as specified by HDLC (see
Figure 1-2).
'
5.
The DECmux II unit sends the HDLC frame over the communi-
cations line to the MUXserver 100 connected to the LAN.
6.
The MUXserver 100 recovers the data from the HDLC frames (that
is, demultiplexes it) and transfers it to the appropriate node on the
LAN using the CSMA/CD Ethernet Protocol.
OPENING
FLAG( F)
01111110
ADDRESS
FIELD(A)
I
CONTROL
FIELD(C)
8 BITS
8 BITS
INFORMATION
FIELD(I)
VARIABLE LENGTH
(ONLY IN I FRAME)
FRAME CHECK
SEQUENCE
(FCS)
16 BITS
Figure 1-2 HDLC Frame Format
4
CHAPTER 1 THE MUXserver 100 ENVIRONMENT
CLOSING
FLAG(F)
01111110
C5-5361
Advertisement
Table of Contents
