User guide

9: Client Applications — Commands and Responses

DC 900-1338I 165

From the ICP’s perspective, the

attach command establishes a session between the client

application and one of the ICP links. A successful

attach command gives the ICP and the

client application IDs that are unique to the current session with which they can relay

information.

The protocol session identifier is used by the ICP to manage information exchanged

between the client application and a specific link. The protocol session identifier is

requested by the client, then defined and returned by the ICP.

For the

attach command, the fields of the ICP and protocol headers that the ICP receives

contain the following values:

ICP_HDR

count = size of protocol header (16 bytes)

command = DLI_ICP_CMD_ATTACH

status = high bits indicate byte ordering

params[0] = return node number

PROT_HDR

link = link number

After the ICP processes the attach command, it returns these headers with the following

field modifications:

ICP_HDR

status = error code or zero if successful

PROT_HDR

modifier = error code or zero if successful

session = session ID assigned by the ICP

The ICP receives an ICP header containing DLI_ICP_CMD_ATTACH in the command

field and a return node number (assigned by msgmux for the Freeway server or the ICP

driver for the embedded ICP product) in the

params[0] field. It also receives a link num-

ber in the

link field of the protocol header. If the ICP can successfully complete the

attach, it returns a session number in the

session field of the protocol header and a zero

(indicating success) in both the