IBM 5500-01E, Руководство по эксплуатации, установке и обслуживанию

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Chapter 6: Twinax Client Cabling Requirements and Problem Solving
90 Planning, Installation, and Maintenance Guide
Dual Mode Function and Express Considerations
The following section describes Dual Mode and Express considerations.
Dual Mode and Multiplexers
Using twinax multiplexers can prevent you from using the full performance
capabilities of the 5500 Control Unit. Multiplexers combine the signals of
multiple ports into a single cable for a long transmission run. The signals are
then demultiplexed back into the separate ports. Because the legacy twinax
workstation controllers gave each port a separate time slice, a multiplexer’s
job was relatively easy. True time domain multiplexing was not necessary
because there was never more than one port active at a time.
You cannot use the old form of eight-port multiplexing (without true time
domain multiplexing) with new workstation controllers (WSC) driving two
ports at the same time (like that in the 5500 Control Unit). The signals from
the two ports would get garbled together, making twinax communication
impossible.
In order to be compatible with these old multiplexers, the Dual Mode
operation of the 5500 Control Unit can be set to disabled. If you do not want
to lose the performance gain associated with this function you can use two
multiplexers instead of one. Multiplex ports 0 through 3 together on one
multiplexer and ports 4 through 7 on the other. The best way is to upgrade the
multiplexer to one that supports the Dual Mode function such as the IBM
7299.
Optimized Mode
Optimized mode streamlines data transmissions to a target device so that
transmission occurs almost twice as fast as in normal transfers. This mode can
be used by enabled devices even though other devices on the same twinax
port do not support the 5250 Express Data Stream. This mode is also
independent of the cabling system being used; it runs on existing cables
without adding new restrictions.
2 Mbps Mode
For 2 Mbps mode to be used, all the devices operating on a given WSC port
must support the 5250 Express Data Stream. When 2 Mbps mode is used,
devices that do not support the 5250 Express Data Stream can be physically
cabled to the port, but they must be turned off or not operating. If any device
that does not support 2 Mbps mode suddenly becomes operational on the port,
Cable information See “Sources for Related Cable
Information” on page 142
Figure 35: Twinax Cabling Schemes