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136 IBM 9077 SP Switch Router: Get Connected to the SP Switch
01 Logical Address
When PS is set to 01, that is, logical address, the host does not know or want
to specify the actual physical route to the target endpoint. The host supplies a
logical address for the endpoint host. In this case, all switches and the GRF
must be programmed to route the connection.
The structure of the I-field is different when logical addressing is used. The
24-bit destination addresses are divided into two 12-bit fields. The rightmost
12 bits of the I-field contain the logical address of the target endpoint, the
leftmost 12 bits contain the logical address of the source host.
Each switch or router has to look up the destination host’s logical address in
its own tables and decide which of its output slots it will transfer the data to. In
the table, there may be several output slots that could be used in the route.
PS set to 01 specifies that the
first entry
in the list of possible output ports
must
be used.
IP connection:
An I-field containing a
special logical address
and a PS=01 or
PS=11 setting is used to establish an IP connection with a GRF HIPPI card.
In the I-field, the PS bits are set to 01 or 11, and bits 0–11 contain a
designated destination logical address (
0xfc0) that is mapped to slot 64.
After the IP connection is established, the data packets arriving at the GRF
are routed to the appropriate output slot using the default or a site-specified
IP destination logical address. Therefore, data is transferred using a table
based on
IP addresses
rather than
HIPPI addresses
.
IP routing is discussed later in this chapter. Example 2 describes how to
configure logical addresses.
10 Unused
This PS setting is not currently defined for use by the HIPPI-SC standard.
11 Logical Address
The PS=11 setting is the same as the 01 setting, except that the switch or
GRF can choose
any
output slot from a list of valid slots for this logical
address. (Remember, with PS=01, the
first
port in the list is used.)
Again, the host does not know the route and instead supplies a logical
address for the endpoint host. All switches and the GRF must be
programmed to route the connection.