User guide

26 DC 900-1303C
Freeway Client-Server Interface Control Document
2.1.2 TSI Data Packets
A TSI data packet is a communication between a client and a server that is passed to or
from the next higher level of processing (via
tRead and tWrite calls when using TSI).
Data packets are used after the two TSI applications have “bound” and are ready to
exchange packets that control Freeway sessions and transfer data to and from the ICP
protocol logic. TSI data packets received by the Freeway server are passed to the Freeway
MsgMux task via
tRead calls. TSI data packets are sent by the Freeway server via the
tWrite call. Each TSI data packet contains a TSI header, a Freeway header, and option-
ally, an ICP header, Protocol header, and any ICP data.
After an ACK control packet has been sent in response to a Bind request, the client and
server are ready to exchange data. There are two types of TSI data packets:
• Freeway control packets for opening and closing Freeway sessions (and, in the
future, for session or MsgMux control)
• Freeway data packets for passing data to and from the Freeway ICPs
The following sections describe these two types of data packets.
2.1.2.1 Freeway Control Packets
Freeway control packet requests are issued by the client. Freeway control packet
responses are issued by the Freeway server. The server validates the request. If the packet
is invalid or the server cannot honor the request (for example, because of lack of
resources), the server sends a response indicating the reason the request cannot be hon-
ored. If the packet is valid, the server sends a response indicating acceptance of the
packet. These packets consist of a TSI header and a Freeway header, and optionally, data
immediately following the Freeway header. The following sections describe each Free-
way control packet. Figure 2–3 on page 29 shows an example of packet data flow.