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DESCRIPTION
General
The DCB multidrop multiplexer configuration uses an SRX platform at
the host location (called HOST) and an SPL platform for remote units
(called DROPs). The objective of this multidrop configuration is to
provide reasonable performance at the remote sites in those applications
where a dedicated line from the host is not cost justified. Using high
speed digital multidrop service, many distributed site applications can
benefit from this configuration.
Performance
The SRX provides excellent performance for asynchronous interactive
terminals when using multidrop digital lines, especially at a composite
speed of 128 Kbps. The SRX multidrop is engineered to provide a
quarter second or less echo time in typical configurations. This short
echo time gives each terminal the appearance of direct connection to its
computer port.
Single Host Configuration
The SRX multidrop host multiplexer can have up to 32 ports in
increments of 8 ports. Network configuration is set from the front panel
LCD display or via the Network Management port. Network
configuration (mapping) is determined solely by the host multiplexer.
Each host port is mapped internally to a drop port and the host
multiplexer handles all translation between host and drop port
numbers.
Multiple Host Configuration
The SRX multidrop firmware also allows the host site to expand to more
than a single SRX host. Multiple SRX hosts share the line using an
MSU-4 modem sharing unit. A maximum of 64 ports is recommended
to maintain satisfactory performance.
Configuration Planning
The network configuration must be mapped before the system will
operate. If no host port is assigned to a particular drop, that drop is not
polled for input. Host ports must be mapped to drop ports before those
drop ports become active. For this reason, some amount of planning is
necessary before implementing a multidrop network.
