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SNA System Network Architecture

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System Network Architecture (SNA) is a networking architecture developed by IBM in the 1970s for their mainframe computer systems. It provides a framework for communication and data exchange between computers and other devices within a network. SNA was widely used in IBM's customer environments and formed the basis for their networking products and protocols.

Here are the key components and concepts of the SNA architecture:

Physical Connectivity:

SNA supports a variety of physical connectivity options, including direct connections, leased lines, and even satellite links. It can operate over different network technologies, such as synchronous or asynchronous communication links.

Logical Structure:

SNA is organized into a hierarchical structure. The main components are:

  • Physical Unit (PU): A PU represents a physical device or node in the network, such as a mainframe computer, terminal, or printer.
  • Logical Unit (LU): An LU is a logical entity within a PU that provides specific services or functions. Each LU is identified by a unique name or address.
  • LU Type: An LU Type defines the specific function or service that an LU provides, such as terminal emulation, printer control, or file transfer.
  • Session: A session represents an active communication connection between two LUs. It enables the exchange of data and control information between them.

SNA Layers:

SNA consists of multiple layers, each responsible for different aspects of network communication:

  • Physical Layer: This layer deals with the physical transmission of data over the network, including encoding, signaling, and electrical characteristics.
  • Data Link Control (DLC) Layer: The DLC layer ensures error-free transmission of data across the network. It handles error detection, retransmission, and flow control.
  • Data Flow and Control (DFC) Layer: The DFC layer manages the flow and sequencing of data between LUs, ensuring reliable delivery.
  • Boundary Control (BC) Layer: The BC layer establishes, maintains, and terminates sessions between LUs.
  • Transmission Control (TC) Layer: The TC layer handles end-to-end error recovery, flow control, and synchronization.

Advanced Program-to-Program Communication (APPC):

APPC is a protocol within SNA that facilitates communication between applications running on different systems. It provides a set of programming interfaces and protocols for application-to-application data exchange.

Security and Management:

SNA includes security mechanisms for authentication, access control, and data privacy. It also provides management capabilities for network administration, monitoring, and troubleshooting.

Evolution and Integration:

time, SNA has evolved and been integrated with other networking technologies, such as TCP/IP, to enable connectivity between SNA-based systems and modern networks. IBM introduced the Systems Network Architecture/Common Communication Support (SNA/CCS) as a bridge between SNA and TCP/IP environments.

It's worth noting that while SNA was widely used in the past, its prominence has diminished with the rise of TCP/IP and the internet. However, some legacy systems and environments still rely on SNA for their networking requirements.