Networking on z/OS
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Systems Network Architecture (SNA)

Networking on z/OS

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"Classic" SNA, based on subarea nodes, is the original networking architecture used by mainframe computers. However, with the popularity and growth of TCP/IP, SNA is changing from being a true network architecture to being what could be termed an "application and application access architecture." In other words, there are many applications that still need to communicate in SNA, but the required SNA protocols are carried over the network by IP.

"New" SNA is SNA/APPN (Advanced Peer-to-Peer Networking). This addition to SNA is based on APPN Peer nodes, and is somewhat more dynamic and less deterministic than SNA/Subarea, and usually requires considerably less definition. It is possible to have SNA/APPN traffic travel over an Ethernet LAN network (and even between LANs) using the IEEE 802.2 frame format. The 802.2 frame is referred to as logical link control (LLC).

Similar to an 802.3 frame, the 802.2 frame contains something called a service access point, or SAP. The SAP is used to identify the SNA resource at the receiving host.

SNA is discussed in detail in the section on SNA and SNA/IP implementation on the mainframe.

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