Systems Network Architecture (SNA) is a protocol developed by IBM for networking communications. Introduced in 1974, SNA was designed to allow computer devices to communicate over a structured network environment specifically tailored for IBM computers and applications. This architecture laid the foundation for many subsequent networking innovations.
What is Systems Network Architecture?
Definition and Overview
Systems Network Architecture (SNA) is IBM’s proprietary networking protocol. It was the dominant enterprise networking solution during the 1970s and 1980s and was primarily used for connecting multiple IBM mainframe and midrange systems.
SNA operates at the Network layer of the OSI model and ensures reliable communication between various nodes or logical units (LU). It standardizes communication protocols for IBM’s range of products, from mainframes to PCs, facilitating seamless integration and data exchange.
Historical Context
Introduced in 1974, SNA was a revolutionary networking model tailored for IBM’s suite of hardware and software. At that time, businesses heavily relied on IBM’s mainframe computing power, and SNA facilitated this usage by structuring communication protocols and providing a comprehensive networking framework.
Components of SNA
Physical and Logical Components
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Physical Units (PU):
- PU Type 1: Low-level devices like terminals and printers.
- PU Type 2: Host systems and Controllers.
- PU Type 3: Communications controllers.
- PU Type 4: Front-end processors.
- PU Type 5: Mainframe processors.
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Logical Units (LU):
- LUs enable application processes to communicate within the SNA network.
- LU Type 0 to LU Type 6: Different LUs handle various types of data, such as transactions and file transfers.
Implementation and Applicability
Network Design
SNA networks consist of hierarchical segments, which communicate through designated PUs and LUs. For example, a front-end processor (PU Type 4) can manage communication for multiple LUs, ensuring data transfers are correctly routed and managed.
Benefits and Drawbacks
Benefits
- Highly Reliable: Provides robust error detection and correction mechanisms.
- Structured Protocols: Simplifies communication among IBM devices.
- Scalability: Can be scaled to large enterprise environments.
Drawbacks
- Proprietary: Limited to IBM hardware and software.
- Complexity: Requires specialized knowledge for configuration and management.
- Obsolescence: Declined popularity due to the rise of more versatile protocols like TCP/IP.
Comparison with Other Protocols
SNA vs. TCP/IP
- Scope: SNA is limited to IBM systems, whereas TCP/IP is universally adopted.
- Flexibility: TCP/IP is more adaptable to various hardware and software environments.
- Usage: SNA was dominant in enterprise environments during its prime, but TCP/IP has become the standard for global communication.
FAQs about SNA
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Is SNA still in use today?
- Yes, but primarily in legacy systems that still rely heavily on IBM mainframe infrastructure.
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What replaced SNA in modern networking?
- TCP/IP and other open standards gradually replaced SNA due to their interoperability and flexibility.
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Can SNA and TCP/IP coexist?
- Yes, with the use of gateway solutions, SNA can coexist and communicate with TCP/IP networks.
References
- “IBM Systems Network Architecture (SNA) — Concepts and Products” by IBM.
- “Computer Networks: A Systems Approach” by Larry L. Peterson and Bruce S. Davie.
- RFC 4670 - SNA over IP.
Summary
Systems Network Architecture remains a landmark innovation in the history of computer networking, providing the essential frameworks for reliable, structured communication within IBM’s ecosystem. Though its dominance has waned, its principles continue to influence modern networking protocols and systems.
