Saturday, June 7, 2014

System Network Architecture

System Network Architecture (SNA) by IBM is a suite of protocols mainly used with IBM mainframe and AS/400 computers. Two SNA protocols are:

     APPC - Advanced Peer-to-Peer Communications provides peer to peer services at the transport and session layer.

     APPN - Advanced Peer-to-Peer Networking supports the computer connections at the network and transport layers.

Microsoft produced the SNA Server so PC networks could connect with SNA networks.

SNA Layers

SNA has its own network model which is:


     Data link - Uses protocols such as token-ring or Synchronous Data Link Control (SDLC).

     Path Control - Performs routing, division, and re-assembly of data packets.

     Transmission - Connection software

     Data flow - Prevents data overflows by monitoring and handling traffic

     Presentation - Handles interfaces to applications

     Transaction - Provides an interface for applications to use network services

SNA Network Devices

     host systems


     Output devices

     Communications controllers

     Cluster controllers - Allow many devices to connect through them. They connect ot a host or communications controller.

SNA Network Categories


     Type 2 - PCs, terminals and printers

     Type 4 - Communications controllers

     type 5 - Host computers used to manage the network

  • Data links - Connection between combinations of hosts, cluster controllers, or nodes. 

Possible SNA communications architectures

     SDLS - Synchronous Data Link Control

     BSC - Binary Synchronous Communication sends bits in frames which are timed sequences of data.





SNA units

NAU - Network Addressable Units

     LU - Logical Units are ports that users use to access network resources

     Type 1 - An interactive batch session

     Type 2 - An IBM 3270 terminal

     Type 3 - An IBM 3270 printer

     Type 6.2 - A program to program session

     Type 7 - An IBM 5250 family session

     PU - Physical Units are a network device used to communicate with hosts.

     Type 2 - Cluster controllers

     Type 3 - Front end process

     Type 5 - Host communications software

SNA software components

     SSCP - Systems Services Control Point manages all resources in the host's domain.

     NCP - Network Control Program performs routing, session management tasks. It runs in the communications controller. 

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