SDISC Assembler Call - NetEx

Intertask CommunicationNETEX is a subsystem that provides the application programmer with a means to perform intertask communication.Like other subsystems, users can call upon NETEX to perform services, provided NETEX residesin the host of each task that is communicating.To communicate using the session layer of NETEX, the calling programs must first establish a session connection.Once the session is established, data transfer may take place in a variety of ways, depending on theneeds of the calling programs. One important feature of NETEX is that NETEX uses internal error checkingand error recovery procedures, which are transparent for the user. This means that once NETEX accepts data,the user is assured of its delivery (except in the case of catastrophic failures, for example, a machine goingdown or a major problem with the communication line). Sessions may be terminated by either of the partiesat any time, although this should be done by mutual agreement.The purpose of this section is to explain the concepts of intertask communication using NETEX. The followingparagraphs introduce the session layer requests and the general concept of a session, and then describeestablishing a session, the data transfer process, terminating a session, handling multiple connections, satellitecommunication, error recovery procedures, and code conversion.Session Layer RequestsThere are eight active requests used by calling programs to call NETEX at the Session level. These requestsmust be issued in a logical order according to rules described in the following paragraphs. These eight requestsand a table called the NETEX Request Block (NRB) are the calling program’s interface to NETEX.The NRB is updated by the calling program when the program issues requests (either directly or via NETEX),and it is updated by NETEX when requests are completed by NETEX. The NRB is completely described in“NETEX Request Block”.Session layer requests may be issued in Assembler or FORTRAN. The formats of the requests in these languagesare provided in “H307 Assembler Interface” and “FORTRAN High Level Interface”. However, thefunctions of these requests are the same and are discussed in general terms in this section. Rules for using therequests are also provided in this sectionThe eight active NETEX requests, listed in the approximate order in which they are issued, are as follows.OFFERThis request makes a calling program utilizing NETEX available to another program on either a remotehost or the local host.CONNECTThis requests a session with a calling program that previously issued an OFFER. The program mayinsert values defining characteristics of the upcoming session in the NRB when this request is issued.This request may also write data to the OFFERing program provided the data does not exceed themaximum segment size specified by either the sending or receiving NETEX.CONFIRMThis request specifies the last step to establish the session. The host which initially issued the OFFERreplies to a CONNECT with the CONFIRM request if the characteristics of the session (data blocksize, etc.) specified in the CONNECT are accepted. This request may also write data to the otherprogram provided the data does not exceed the maximum segment size specified by either the sendingor receiving NETEX.Page 8 Intertask Communication MAN-REF-H307IP-04