art@ACC.ARPA (01/15/87)
I am trying to obtain information which I think is extremely important for designing and maintaining interface hardware and software which must interconnect to BBN PSNs. Does anyone out there have a detailed understanding of how PSN 6.0 maps between the 1822, X.25 Basic and X.25 Standard services and a description of the underlying packetization performed between PSNs. There doesn't appear to be any publically available documents and BBN seems to be unwilling or unable to communicate any information to us. The original IMPs (PSNs) would take 1822 "messages" of up to roughly 1K and split them up into 128 byte "packets" which were independently shipped throught the IMP network. When all of the "packets" were received and reassembled by the destination IMP and the "message" delivered to the destination host, a Request For Next Message (RFNM - pronounced "ruf num") was sent back to the sending host. For resource control, only 8 messages were allowed to be outstanding to any specific remote host per 1822 "link number". IP datagrams were assigned a specific "link number" to use. Does anyone know whether the current PSNs operate this way for 1822 interfaces? I would like to find out how HDH "packet mode" and HDH "message mode" interacts with the internal PSN transport. I would like to know how DDN Basic mode and DDN Standard mode interacts with the internal PSN transport. Specifically I would like to understand what happens (in DDN Standard Mode) to an IP datagram which is sent as a sequence of X.25 "m-bit" packets and is delivered elsewhere via an 1822 interface. I would like to know how the contents of the X.25 packets are handled and how the X.25 packet window is controlled. My understanding is that PSN 7.0 will change the behavior of X.25 through the PSN network. Anyone have any real information? Art Berggreen <Art@ACC.ARPA> ------