First, I apologize to the reflector if this question has been answered multiple times before. Is there a FAQ for this mailing list? IMO, option 1 is absolutely valid. Some apps may not honor the odd/even rule, and if I recall correctly this requirement has been relaxed a bit in H.323 (correct me if I am wrong). It has been suggested in a few occasions that the odd/even rule is an RTP rule and not an H.225.0 despite the fact that it is mentioned in the spec. Also it is not only "+1", rather the following odd number since the "+1" port may be busy. You can specify an RTCP odd address in OLC for RTCP receive reports and once you get the OLC from the remote endpoint, use the same odd RTCP for Tx reports, and use the lower even number for RTP port and that way you will still be fully compliant. Here is an example START_PDU: ============================= START PDU ============================ LAYER: H245 DIRECTION: Sent PDU_TYPE: OpenLogicalChannel Forward Logical Channel Number: 257 Unicast Address: IP, 209.218.18.91 TSAPIdentifier: 1161 END_PDU: ================================ END PDU ============================= START_PDU: ============================= START PDU ============================ LAYER: H245 DIRECTION: Sent PDU_TYPE: OpenLogicalChannelAck Forward Logical Channel Number: 257 frwrdMltplxAckPrmtrs: H2250LCAPs_mdChnnl: Unicast Address: IP, 209.218.18.91 TSAPIdentifier: 1160 H2250LCAPs_mdCntrlChnnl: Unicast Address: IP, 209.218.18.91 TSAPIdentifier: 1161 END_PDU: ================================ END PDU ============================= START_PDU: ============================= START PDU ============================ LAYER: H245 DIRECTION: Received PDU_TYPE: OpenLogicalChannelAck Forward Logical Channel Number: 257 frwrdMltplxAckPrmtrs: H2250LCAPs_mdChnnl: Unicast Address: IP, 209.218.18.82 TSAPIdentifier: 1030 H2250LCAPs_mdCntrlChnnl: Unicast Address: IP, 209.218.18.82 TSAPIdentifier: 1031 END_PDU: ================================ END PDU ============================= START_PDU: ============================= START PDU ============================ LAYER: H245 DIRECTION: Received PDU_TYPE: OpenLogicalChannel Forward Logical Channel Number: 257 H2250LCPs_mdCntrlChnnl: Unicast Address: IP, 209.218.18.82 TSAPIdentifier: 1031 END_PDU: ================================ END PDU ============================= regards, Hani -----Original Message----- From: Mohamed Mustafa [mailto:M.Mustafa@SDXPLC.COM] Sent: Friday, October 22, 1999 6:15 AM To: ITU-SG16@MAILBAG.INTEL.COM <mailto:ITU-SG16@MAILBAG.INTEL.COM> Subject: Re: RTCP port number Hani, Thanks for your reply. There are still a few points I'm not clear on. Your first four points are consistent with my current understanding of the OLC/OLCA messages. I'll elaborate on these points just to try and avoid the ambiguities of my previous email: There are two optional TransportAddress fields (mediaChannel and mediaControlChannel) within the forward logical channel parameters section of the OLC request message. H.245 specifies that the mediaChannel field should not be included in the OLC request when the transport is unicast. The mediaControlChannel field, if present in the OLC request, specifies the address on which the sender of the OLC will be listening for media control messages. If the mediaControlChannel field is not present in the OLC request, this indicates that a control session is not required. The mediaChannel and mediaControlChannel fields are also present in the OLCA response message. The mediaChannel field must be present in a OLCA response when the transport is unicast, and it specifies the address to which the sender of the corresponding OLC must transmit the media. The mediaControlChannel field in the OLCA response specifies the address on which the sender of the OLCA will be listening for media control messages for this session. The mediaControlChannel should only be included in the OLCA response if a media control channel is required (i.e., only if the mediaControlChannel field was present in the corresponding OLC request). Therefore, assuming a control channel is required, each endpoint must transmit and receive three transport address in order to establish a bi-directional media stream; 1) RTCP address in OLC (a1), 2) RTP address in OLCA (a2), and 3) RTCP address in OLCA (a3). To use a single bi-directional RTCP channel, each endpoint must specify the same address in a1 and a3. The +1 rule requires the port numbers in a1 and a3 to be odd, and that a2 and a3 are identical except for the port number where it is one less in a2 compared to a3. My initial question was regarding the case where one of the endpoints supplies a set of addresses where a1 and a2 do not conform to the +1 rule. There are two possibilities in this case: 1) a1 and a3 are the identical - i.e., single bi-directional RTCP channel, but a2 and a3 do not conform to the +1 rule. 2) a2 and a3 conform to the +1 rule - i.e., 2 unidirectional RTCP channels. My original question can be more precisely worded as: Is option 1 valid? Thanks again, Mohamed