SGSN:

a. When the user accesses the SGSN, the SGSN initiates the location update procedure to the HLR. The MAP service user sends a MAP OPEN REQ message to the MAP service provider. The message mainly carries the session ID, application context name, and destination address.
b. The SGSN MAP service user sends the MAP service provider a MAP SERVICE REQ message that carries the parameters relevant to the GPRS location update.
c. The SGSN MAP service user sends a MAP DELIMITER REQ message to the MAP service provider to instruct the session to start.

HLR :

d. The SGSN MAP service provider sends a MAP OPEN IND message to the MAP service user to request the session to be started.
e. The MAP service provider sends a MAP SERVICE IND message to the MAP service user.
f. The HLR MAP decides to accept the session and then sends a MAP OPEN RSP message to the MAP service provider.
g. The MAP service user sends the MAP service provider a MAP SERVICE REQ message that carries the inserted subscription data.
h. The SGSN MAP service user sends a MAP DELIMITER REQ message to the MAP service provider to instruct the session to continue.

very useful document for my regular O& M activity. Thanks.

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useful document, thanks