134 IBM 9077 SP Switch Router: Get Connected to the SP Switch
these modes. Hosts must pass on the appropriate information for the GRF
media cards and other HIPPI devices to operate in the desired way.
HIPPI offers many configuration options. The ANSI HIPPI standards and
RFCs describe implementation details, that support source routing, logical
addressing, IP routing, and raw (switch) mode operations.
4.5.1.1 Connection Processing
The GRF processes connections; it does not process data. It accepts data
and establishes a connection point to which it can transfer data.
The HIPPI media card establishes connections and transfers packets. A
HIPPI media card processes one HIPPI connection at a time. It does not
begin another process until the first connection completes.
There are two types of connections:
• IP connections
• Raw connections
In internetworking, the main difference between the two connections is that
data from a HIPPI host can be transferred to any other IP-capable media via
IP routing. Raw mode is HIPPI to HIPPI, and is only used to transfer data
from one HIPPI device to another HIPPI device. The HIPPI I-field tells the
media card which type of connection is being requested.
So the toughest step in the configuration of a HIPPI media card is to compose
the correct HIPPI I-field.
4.5.1.2 Starting a HIPPI Connection
The HIPPI standard requires that a HIPPI connection be established between
a HIPPI source and a HIPPI destination before any data is transmitted. Every
connection "request" signal sent to a HIPPI media card is accompanied by a
HIPPI I-field.
The sequence that establishes a HIPPI connection is as follows:
1. The HIPPI source activates the REQUEST line to a destination while at
the same time placing a 32-bit word, (the I-field), on the data lines.
2. The HIPPI destination sees the REQUEST signal, reads the I-field, and
accepts the connection by activating its CONNECT line back to the
source.
Data coming from an external HIPPI I/O channel may be formatted into
standard IP packets. Embedded in the front of each IP packet is an IP