Non-SNA X.25 DTEs connect to IBM or Cisco routers using the ITI transport protocol. The routers then propagate the ITI traffic across the TCP/IP network using the XTP or XOT transport protocol. A peer router extracts the encapsulated ITI packets from the XTP or XOT packets and forwards it on to a peer non-SNA X.25 DTE.
For non-SNA X.25 DTEs, there must always be a peer router to extract the ITI packets from the XTP or XOT packets in order to pass them on to the peer non-SNA X.25 DTE.
For non-SNA traffic, the routers do not by themselves provide direct connection to the host. A FEP, with resident NPSI software, is still required (see figure 2 of this document).
______________________________________________________________________ | | | Without X.25 HostNAS | | | | TCP/IP X.25 | | HOST NETWORK ROUTER NETWORK ITI PAD | | _____________ _____________ _______ | | | | | | | | | | ITI | | | | | <-> <----+--->| | <-----> |<---------->| |<-->| | | | | | | | | X | | I | | | | | | | C | V | T | | | T | | T | | | | | I | T | C | | | P | | I | | | | | C | A | P | | | / | | | | | | | S | M | I | | | X | | P | ITI DEVICE | | | | | | P | | |<-->| O | | A | _______ | | | | | | | | | | T | | D | | | | | | | | | | | | | | | | | |<-->| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | ROUTER FEP | | | | _____________ _________ | | | | | | | | ITI | | | | | | | | <-----> |<-------->| <-> |<-->| | | | | | X | | I | | | | | | | | | | T | | T | | N | N | | | | | | | P | | I | | P | C | | | | | | | / | | | | S | P | | | | | | | X | | P | | I | | | | | | | | O | | A | | | | | | | | |<-->| T | | D | | | | | | | | | | | | | | | | | | | | | | | | | | | | NSC/SNA | | | |<------------------------------------------>| | | | | Non-SNA device traffic is carried across the X.25 network in | | ITI packets. IBM or Cisco routers encapsulate the ITI packets | | in XTP or XOT before they are passed to the TCP/IP network. | | The peer router performs the opposite function and passes | | the extracted ITI packets on to a NPSI resident FEP. NPSI | | converts the ITI packets to SNA PIUs and passes them on to | | NCP. NCP then transfers the SNA data to VTAM over its Native | | Subchannel. | | |
Figure 2: Non-SNA traffic in a hybrid X.25-TCP/IP Network
without HNAS
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Last Update - December 12, 2001