NAME

       dtpc - Delay-Tolerant Payload Conditioning (DTPC) communications library

SYNOPSIS

           #include "dtpc.h"

           [see description for available functions]

DESCRIPTION

       The dtpc library provides functions enabling application software to use Delay-Tolerant Payload
       Conditioning (DTPC) when exchanging information over a delay-tolerant network.  DTPC is an application
       service protocol, running in a layer immediately above Bundle Protocol, that offers delay-tolerant
       support for several end-to-end services to applications that may require them.  These services include
       delivery of application data items in transmission (rather than reception) order; detection of reception
       gaps in the sequence of transmitted application data items, with end-to-end negative acknowledgment of
       the missing data; end-to-end positive acknowledgment of successfully received data; end-to-end
       retransmission of missing data, driven either by negative acknowledgment or timer expiration; suppression
       of duplicate application data items; aggregation of small application data items into large bundle
       payloads, to reduce bundle protocol overhead; and application-controlled elision of redundant data items
       in aggregated payloads, to improve link utiliization.

       int dptc_attach( )
           Attaches the application to DTPC functionality on the local computer.  Returns 0 on success, -1 on
           any error.

       void dptc_detach( )
           Terminates all access to DTPC functionality on the local computer.

       int dtpc_entity_is_started( )
           Returns 1 if the local DTPC entity has been started and not yet stopped, 0 otherwise.

       int dtpc_open(unsigned int topicID, DtpcElisionFn elisionFn, DtpcSAP *dtpcsapPtr)
           Establishes the application as the sole authorized client for posting and receiving application data
           items on topic topicID within the local BP node.  On success, the service access point for posting
           and receiving such data items is placed in *dtpcsapPtr, the elision callback function elisionFn (if
           not NULL) is associated with this topic, and 0 is returned.  Returns -1 on any error.

       int dtpc_send(unsigned int profileID, DtpcSAP sap, char *destEid, unsigned int maxRtx, unsigned int
       aggrSizeLimit, unsigned int aggrTimeLimit, int lifespan, BpExtendedCOS *extendedCOS, unsigned char
       srrFlags, BpCustodySwitch custodySwitch, char *reportToEid, int classOfService, Object item, unsigned int
       length)
           Inserts an application data item into an outbound DTPC application data unit destined for destEid.

           Transmission of that outbound ADU will be subject to the profile identified by profileID, as asserted
           by dtpcadmin(1), if profileID is non-zero.  In that case, maxRtx, aggrSizeLimit, aggrTimeLimit,
           lifespan, extendedCOS, srrFlags, custodySwitch, reportToEid, and classOfService are ignored.

           If profileID is zero then the profile asserted by dtpcadmin(1) that matches maxRtx, aggrSizeLimit,
           aggrTimeLimit, lifespan, extendedCOS, srrFlags, custodySwitch, reportToEid, and classOfService will
           govern transmission of the ADU, unless no such profile has been asserted, in which case dtpc_send()
           returns 0 indicating user error.

           maxRtx is the maximum number of times any single DTPC ADU transmitted subject to the indicated
           profile may be retransmitted by the DTPC entity.  If maxRtx is zero, then the DTPC transport service
           features (in-order delivery, end-to-end acknowledgment, etc.) are disabled for this profile.

           aggrSizeLimit is the size threshold for concluding aggregation of an outbound ADU and requesting
           transmission of that ADU.  If aggrSizeLimit is zero, then the DTPC transmission optimization features
           (aggregation and elision) are disabled for this profile.

           aggrTimeLimit is the time threshold for concluding aggregation of an outbound ADU and requesting
           transmission of that ADU.  If aggrTimeLimit is zero, then the DTPC transmission optimization features
           (aggregation and elision) are disabled for this profile.

           lifespan, extendedCOS, srrFlags, custodySwitch, reportToEid, and classOfService are as defined for
           bp_send (see bp(3)).

           item must be an object allocated within ION's SDR "heap", and length must be the length of that
           object.  The item will be inserted into the outbound ADU's list of data items posted for the topic
           associated with sap, and the elision callback function declared for sap (if any, and if the
           applicable profile does not disable transmission optimization features) will be invoked immediately
           after insertion of the application data item but before DTPC makes any decision on whether or not to
           initiate transmission of the outbound ADU.

           The function returns 1 on success, 0 on any user application error, -1 on any system error.

       int dtpc_receive(DtpcSAP sap, DtpcDelivery *dlvBuffer, int timeoutSeconds)
           Receives a single DTPC application data item, or reports on some failure of DTPC reception activity.

           The "result" field of the dlvBuffer structure will be used to indicate the outcome of the data
           reception activity.

           If at least one application data item on the topic associated with sap has not yet been delivered to
           the SAP, then the payload of the oldest such item will be returned in dlvBuffer->adu and
           dlvBuffer->result will be set to PayloadPresent.  If there is no such item, dtpc_receive() blocks for
           up to timeoutSeconds while waiting for one to arrive.

           If timeoutSeconds is DTPC_POLL (i.e., zero) and no application data item is awaiting delivery, or if
           timeoutSeconds is greater than zero but no item arrives before timeoutSeconds have elapsed, then
           dlvBuffer->result will be set to ReceptionTimedOut.  If timeoutSeconds is DTPC_BLOCKING (i.e., -1)
           then bp_receive() blocks until either an item arrives or the function is interrupted by an invocation
           of dtpc_interrupt().

           dlvBuffer->result will be set to ReceptionInterrupted in the event that the calling process received
           and handled some signal other than SIGALRM while waiting for a bundle.

           dlvBuffer->result will be set to DtpcServiceStopped in the event that DTPC service has been
           terminated on the local node.

           The application data item delivered in the DTPC delivery structure, if any, will be an object
           allocated within ION's SDR "heap"; the length of that object will likewise be provided in the
           DtpcDelivery structure.

           Be sure to call dtpc_release_delivery() after every successful invocation of dtpc_receive().

           The function returns 0 on success, -1 on any error.

       void dtpc_interrupt(DtpcSAP sap)
           Interrupts a dtpc_receive() invocation that is currently blocked.  This function is designed to be
           called from a signal handler; for this purpose, sap may need to be obtained from a static variable.

       void dtpc_release_delivery(DtpcDelivery *dlvBuffer)
           Releases resources allocated to the indicated DTPC delivery.

       void dtpc_close(DtpcSAP sap)
           Removes the application as the sole authorized client for posting and receiving application data
           items on the topic indicated in sap within the local BP node.  The application relinquishes its
           ability to send and receive application data items on the indicated topic.

SEE ALSO

       dtpcadmin(1), dtpcrc(5), bp(3)