Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!anise!salt.acc.com!lars From: lars@salt.acc.com (Lars J Poulsen) Newsgroups: comp.protocols.iso Subject: Re: DDN X.25 interface Keywords: DDN, X.25, CCITT Message-ID: <810@anise.acc.com> Date: 9 Jun 89 21:27:45 GMT References: <1152@cbnewsh.att.com> Sender: news@anise.acc.com Organization: Advanced Computer Communications, Santa Barbara, California Lines: 33 In article <1152@cbnewsh.att.com> cheng@cbnewsh.ATT.COM (wan-hong.steve.cheng) writes: >Is there any difference between DDN X.25 interface and CCITT X.25 interface >standard (198?) ? I understand there is a certification procedure to pass >before connection to DDN can be done. Does anyone know the details? Thanks >for your information. The DDN (MilNet, APRAnet and clones) is a bona fide CCITT X.25 1984 compliant network (although it does not seem to have a DNIC). Due to the requirements for stability of the applications that run on this network, the owners have instituted a certification program. Most X.25 network operators will not allow connection of customer equipment without prior certification, but the DDN certification procedure is the most rigorous I have seen. (It tests the error detection and error handling capability of the host as well as normal operation). What is special about the DDN is that most of the traffic is known to be TCP/IP, and the network is optimized for TCP/IP traffic. Special ports are available to hosts that speak no X.25 but speak BBN-1822 AHIP (ARPAnet Host-to-Imp-Protocol), and the network performs protocol conversion as needed. In order to be able to exchange traffic with these hosts, most TCP/IP hosts specify "Standard Mode Facility" at call setup time. Also, there is an algorithmic correspondence between physical attachment point (PSN number, port number), IP address and X.25 address. Also, instead of PADs for asynch terminals, DDN has TACs; i.e. dial-up asynch terminal service uses TELENT protocol instead of X.29. / Lars Poulsen (800) 222-7308 or (805) 963-9431 ext 358 ACC Customer Service Affiliation stated for identification only My employer probably would not agree if he knew what I said !!