Editing Systems Network Architecture (section)

==SNA over IP==
As mainframe-based entities looked for alternatives to their 37XX-based networks, IBM partnered with [[Cisco]] in the mid-1990s and together they developed [[Data Link Switching]], or DLSw. DLSw encapsulates SNA packets into IP datagrams, allowing sessions to flow over an IP network. The actual encapsulation and decapsulation takes place in Cisco routers at each end of a DLSw peer connection. At the local, or mainframe site, the router uses Token Ring topology to connect natively to VTAM. At the remote (user) end of the connection, a PU type 2 emulator (such as an SNA gateway server) connects to the peer router via the router's LAN interface. End user terminals are typically PCs with 3270 emulation software that is defined to the SNA gateway. The VTAM/NCP PU type 2 definition becomes a Switched Major Node that can be local to VTAM (without an NCP), and a "Line" connection can be defined using various possible solutions (such as a Token Ring interface on the 3745, a 3172 Lan Channel Station, or a Cisco [[ESCON]]-compatible Channel Interface Processor).