This chapter expect that you are familiar with RTPS communication architecture described in . Publications can offer multiple reliability policies ranging from best-efforts to strict (blocking) reliability. Subscription can request multiple policies of desired reliability and specify the relative precedence of each policy. Publications will automatically select among the highest precedence requested policy that is offered by the publication. BestEffort: This reliability policy is suitable for data that are sending with a period. There are no message resending when a message is lost. On other hand, this policy offer maximal predictable behaviour. For instance, consider a publication which send data from a sensor (pressure, temperature, ...).

StrictReliable: The ORTE supports the reliable delivery of issues. This kind of communication is used where a publication want to be sure that all data will be delivered to subscriptions. For instance, consider a publication which send commands. Command data flow requires that each instruction in the sequence is delivered reliably once and only once. Commands are often not time critical.

Before creating a Publication or Subscription is necessary to create a domain by using function ORTEDomainAppCreate. The code should looks like: int main(int argc, char *argv[]) { ORTEDomain *d = NULL; ORTEBoolean suspended= ORTE_FALSE; ORTEInit(); d = ORTEDomainAppCreate(ORTE_DEFAUL_DOMAIN, NULL, NULL, suspended); if (!d) { printf("ORTEDomainAppCreate failed\n"); return -1; } } The ORTEDomainAppCreate allocates and initializes resources that are needed for communication. The parameter suspended says if ORTEDomain takes suspend communicating threads. In positive case you have to start threads manually by using ORTEDomainStart. Next step in creation of a application is registration serialization and deserialization routines for the specific type. You can't specify this functions, but the incoming data will be only copied to output buffer. ORTETypeRegisterAdd(d, "HelloMsg", NULL, NULL, 64); To create a publication in specific domain use the function ORTEPublicationCreate. char instance2send[64]; NtpTime persistence, delay; NTPTIME_BUILD(persistence, 3); /* this issue is valid for 3 seconds */ NTPTIME_DELAY(delay, 1); /* a callback function will be called every 1 second */ p = ORTEPublicationCreate( d, "Example HelloMsg", "HelloMsg", &instance2Send, &persistence, 1, sendCallBack, NULL, &delay); The callback function will be then called when a new issue from publisher has to be sent. It's the case when you specify callback routine in ORTEPublicationCreate. When there isn't a routine you have to send data manually by call function ORTEPublicationSend. This option is useful for sending periodic data. void sendCallBack(const ORTESendInfo *info, void *vinstance, void *sendCallBackParam) { char *instance = (char *) vinstance; switch (info->status) { case NEED_DATA: printf("Sending publication, count %d\n", counter); sprintf(instance, "Hello world (%d)", counter++); break; case CQL: //criticalQueueLevel has been reached break; } } Subscribing application needs to create a subscription with publication's Topic and TypeName. A callback function will be then called when a new issue from publisher will be received. ORTESubscription *s; NtpTime deadline, minimumSeparation; NTPTIME_BUILD(deadline, 20); NTPTIME_BUILD(minimumSeparation, 0); p = ORTESubscriptionCreate( d, IMMEDIATE, BEST_EFFORTS, "Example HelloMsg", "HelloMsg", &instance2Recv, &deadline, &minimumSeparation, recvCallBack, NULL); The callback function is shown in the following example: void recvCallBack(const ORTERecvInfo *info, void *vinstance, void *recvCallBackParam) { char *instance = (char *) vinstance; switch (info->status) { case NEW_DATA: printf("%s\n", instance); break; case DEADLINE: //deadline occurred break; } } Similarly examples are located in ORTE subdirectory orte/examples/hello. There are demonstrating programs how to create an application which will publish some data and another application, which will subscribe to this publication.

The reliable communication is used especially in situations where we need guarantee data delivery. The ORTE supports the inorder delivery of issues with built-in retry mechanism The creation of reliable communication starts like besteffort communication. Difference is in creation a subscription. Third parameter is just only changed to STRICT_RELIABLE. ORTESubscription *s; NtpTime deadline, minimumSeparation; NTPTIME_BUILD(deadline, 20); NTPTIME_BUILD(minimumSeparation, 0); p = ORTESubscriptionCreate( d, IMMEDIATE, STRICT_RELIABLE, "Example HelloMsg", "HelloMsg", &instance2Recv, &deadline, &minimumSeparation, recvCallBack, NULL); Note: Strict reliable subscription must set minimumSeparation to zero! The middleware can't guarantee that the data will be delivered on first attempt (retry mechanism). Sending of a data is blocking operation. It's strongly recommended to setup sending queue to higher value. Default value is 1. ORTEPublProp *pp; ORTEPublicationPropertiesGet(publisher,pp); pp->sendQueueSize=10; pp->criticalQueueLevel=8; ORTEPublicationPropertiesSet(publisher,pp); An example of reliable communication is in ORTE subdirectory orte/examples/reliable. There are located a strictreliable subscription and publication.

Actually the ORTE doesn't support any automatic creation of serialization/deserializaction routines. This routines have to be designed manually by the user. In next is shown, how should looks both for the structure BoxType. typedef struct BoxType { int32_t color; int32_t shape; } BoxType; void BoxTypeSerialize(CDR_Codec *cdrCodec, void *instance) { BoxType *boxType=(BoxType*)instance; CDR_put_long(cdrCodec,boxType->color); CDR_put_long(cdrCodec,boxType->shape); } void BoxTypeDeserialize(CDR_Codec *cdrCodec, void *instance) { BoxType *boxType=(BoxType*)instance; CDR_get_long(cdrCodec,&boxType->color); CDR_get_long(cdrCodec,&boxType->shape); } When we have written a serialization/deserialization routine we need to register this routines to midleware by function ORTETypeRegisterAdd ORTETypeRegisterAdd( domain, "BoxType", BoxTypeSerialize, BoxTypeDeserialize, sizeof(BoxType)); The registration must be called before creation a publication or subscription. Normally is ORTETypeRegisterAdd called immediately after creation of a domain (ORTEDomainCreate). All of codes are part of the Shapedemo located in subdirectory orte/contrib/shape.