/* RTCP code taken directly from the most recent RTP specification: * RFC 3550 * Implementation */ #include "rtcp_from_spec.h" /***** A.7 Computing the RTCP Transmission Interval The following functions implement the RTCP transmission and reception rules described in Section 6.2. These rules are coded in several functions: o rtcp_interval() computes the deterministic calculated interval, measured in seconds. The parameters are defined in Section 6.3. o OnExpire() is called when the RTCP transmission timer expires. o OnReceive() is called whenever an RTCP packet is received. Both OnExpire() and OnReceive() have event e as an argument. This is the next scheduled event for that participant, either an RTCP report or a BYE packet. It is assumed that the following functions are available: o Schedule(time t, event e) schedules an event e to occur at time t. When time t arrives, the function OnExpire is called with e as an argument. o Reschedule(time t, event e) reschedules a previously scheduled event e for time t. o SendRTCPReport(event e) sends an RTCP report. o SendBYEPacket(event e) sends a BYE packet. o TypeOfEvent(event e) returns EVENT_BYE if the event being processed is for a BYE packet to be sent, else it returns EVENT_REPORT. o PacketType(p) returns PACKET_RTCP_REPORT if packet p is an RTCP report (not BYE), PACKET_BYE if its a BYE RTCP packet, and PACKET_RTP if its a regular RTP data packet. o ReceivedPacketSize() and SentPacketSize() return the size of the referenced packet in octets. o NewMember(p) returns a 1 if the participant who sent packet p is not currently in the member list, 0 otherwise. Note this function is not sufficient for a complete implementation because each CSRC identifier in an RTP packet and each SSRC in a BYE packet should be processed. o NewSender(p) returns a 1 if the participant who sent packet p is not currently in the sender sublist of the member list, 0 otherwise. o AddMember() and RemoveMember() to add and remove participants from the member list. o AddSender() and RemoveSender() to add and remove participants from the sender sublist of the member list. *****/ double rtcp_interval(int members, int senders, double rtcp_bw, int we_sent, double avg_rtcp_size, int initial) { /* * Minimum average time between RTCP packets from this site (in * seconds). This time prevents the reports from `clumping' when * sessions are small and the law of large numbers isn't helping * to smooth out the traffic. It also keeps the report interval * from becoming ridiculously small during transient outages like * a network partition. */ double const RTCP_MIN_TIME = 5.; /* * Fraction of the RTCP bandwidth to be shared among active * senders. (This fraction was chosen so that in a typical * session with one or two active senders, the computed report * time would be roughly equal to the minimum report time so that * we don't unnecessarily slow down receiver reports.) The * receiver fraction must be 1 - the sender fraction. */ double const RTCP_SENDER_BW_FRACTION = 0.25; double const RTCP_RCVR_BW_FRACTION = (1-RTCP_SENDER_BW_FRACTION); /* * To compensate for "unconditional reconsideration" converging to a * value below the intended average. */ double const COMPENSATION = 2.71828 - 1.5; double t; /* interval */ double rtcp_min_time = RTCP_MIN_TIME; int n; /* no. of members for computation */ /* * Very first call at application start-up uses half the min * delay for quicker notification while still allowing some time * before reporting for randomization and to learn about other * sources so the report interval will converge to the correct * interval more quickly. */ if (initial) { rtcp_min_time /= 2; } /* * If there were active senders, give them at least a minimum * share of the RTCP bandwidth. Otherwise all participants share * the RTCP bandwidth equally. */ n = members; if (senders > 0 && senders < members * RTCP_SENDER_BW_FRACTION) { if (we_sent) { rtcp_bw *= RTCP_SENDER_BW_FRACTION; n = senders; } else { rtcp_bw *= RTCP_RCVR_BW_FRACTION; n -= senders; } } /* * The effective number of sites times the average packet size is * the total number of octets sent when each site sends a report. * Dividing this by the effective bandwidth gives the time * interval over which those packets must be sent in order to * meet the bandwidth target, with a minimum enforced. In that * time interval we send one report so this time is also our * average time between reports. */ t = avg_rtcp_size * n / rtcp_bw; if (t < rtcp_min_time) t = rtcp_min_time; /* * To avoid traffic bursts from unintended synchronization with * other sites, we then pick our actual next report interval as a * random number uniformly distributed between 0.5*t and 1.5*t. */ t = t * (drand48() + 0.5); t = t / COMPENSATION; return t; } void OnExpire(event e, int members, int senders, double rtcp_bw, int we_sent, double *avg_rtcp_size, int *initial, time_tp tc, time_tp *tp, int *pmembers) { /* This function is responsible for deciding whether to send * an RTCP report or BYE packet now, or to reschedule transmission. * It is also responsible for updating the pmembers, initial, tp, * and avg_rtcp_size state variables. This function should be called * upon expiration of the event timer used by Schedule(). */ double t; /* Interval */ double tn; /* Next transmit time */ /* In the case of a BYE, we use "unconditional reconsideration" to * reschedule the transmission of the BYE if necessary */ if (TypeOfEvent(e) == EVENT_BYE) { t = rtcp_interval(members, senders, rtcp_bw, we_sent, *avg_rtcp_size, *initial); tn = *tp + t; if (tn <= tc) { SendBYEPacket(e); exit(1); } else { Schedule(tn, e); } } else if (TypeOfEvent(e) == EVENT_REPORT) { t = rtcp_interval(members, senders, rtcp_bw, we_sent, *avg_rtcp_size, *initial); tn = *tp + t; if (tn <= tc) { SendRTCPReport(e); *avg_rtcp_size = (1./16.)*SentPacketSize(e) + (15./16.)*(*avg_rtcp_size); *tp = tc; /* We must redraw the interval. Don't reuse the one computed above, since its not actually distributed the same, as we are conditioned on it being small enough to cause a packet to be sent */ t = rtcp_interval(members, senders, rtcp_bw, we_sent, *avg_rtcp_size, *initial); Schedule(t+tc,e); *initial = 0; } else { Schedule(tn, e); } *pmembers = members; } } void OnReceive(packet p, event e, int *members, int *pmembers, int *senders, double *avg_rtcp_size, double *tp, double tc, double tn) { /* What we do depends on whether we have left the group, and * are waiting to send a BYE (TypeOfEvent(e) == EVENT_BYE) or * an RTCP report. p represents the packet that was just received. */ if (PacketType(p) == PACKET_RTCP_REPORT) { if (NewMember(p) && (TypeOfEvent(e) == EVENT_REPORT)) { AddMember(p); *members += 1; } *avg_rtcp_size = (1./16.)*ReceivedPacketSize(p) + (15./16.)*(*avg_rtcp_size); } else if (PacketType(p) == PACKET_RTP) { if (NewMember(p) && (TypeOfEvent(e) == EVENT_REPORT)) { AddMember(p); *members += 1; } if (NewSender(p) && (TypeOfEvent(e) == EVENT_REPORT)) { AddSender(p); *senders += 1; } } else if (PacketType(p) == PACKET_BYE) { *avg_rtcp_size = (1./16.)*ReceivedPacketSize(p) + (15./16.)*(*avg_rtcp_size); if (TypeOfEvent(e) == EVENT_REPORT) { if (NewSender(p) == FALSE) { RemoveSender(p); *senders -= 1; } if (NewMember(p) == FALSE) { RemoveMember(p); *members -= 1; } if(*members < *pmembers) { tn = tc + (((double) *members)/(*pmembers))*(tn - tc); *tp = tc - (((double) *members)/(*pmembers))*(tc - *tp); /* Reschedule the next report for time tn */ Reschedule(tn, e); *pmembers = *members; } } else if (TypeOfEvent(e) == EVENT_BYE) { *members += 1; } } }