Mainframes

1. Mainframes • Contain about 70% of corporate data from operations (accounting, payroll, billing, etc.) • Often the “database server” in web-enabled database applications

2. Mainframes • Dominated by IBM • Mainframe competitors build clones • Called plug-compatible machines

3. Terminal-Host Communication • Traditionally, Just a Terminal, Host, and Transmission Line (Chapter 1) • Poor response time • Poor user interface: sending graphics over a distance is expensive (and lines usually are slow) • Inadequate for production workers who use their terminals hours per day

4. Mainframe Communication • User site has multiple terminal users • 3270 Terminals • High speeds, some color, some graphics User Site 3270 Terminal

5. Mainframe Communication • Cluster Controller at User Site • Supports a cluster of terminals and printers • Provides limited on-screen text editing power to terminals • This elimination of text editing work allows the mainframe to focus on high-value database chores Limited Text Editing Cluster Controller

6. Mainframe Communication • Cluster Controller at User Site • Supports a cluster of terminals and printers • Provides limited on-screen text editing power to terminals • This also reduces response time because editing is done locally Limited Text Editing Cluster Controller

7. Mainframe Communication • Cluster Controller at User Site • Multiplexes transmissions of multiple terminals and printers to the central site • This reduces transmission costs, which are expensive for higher-speed long-distance links A A A A A A B B A Central Site Long- Distance Line B B

8. Mainframe Communication • Transmission Line • Long-distance lines are expensive per bit sent • But 3270 terminals need high speeds • Multiplexes terminal communication onto 56 kbps, 1.544 Mbps or faster line to give high speed but keep cost reasonable Central Site Long- Distance Line

9. Mainframe Communication • Central Site • Communications Controller • Handles multiplexing to reduce transmission cost • Handles detailed interactions with cluster controllers, freeing mainframe to deal with database processing Communications Controller

10. Mainframe Communication • Mainframe • Handles high-value database work • Must be freed of low-value communications processing work to be economically efficient Mainframe

11. Mainframe Communication • Reducing Response Time • Text editing work is done locally • Still delay for heavy database work on mainframe • Reducing Transmission Costs • Multiplexing, and • Cluster controller provides limited local screen editing, so fewer bits need to be transmitted to and from the mainframe

12. Mainframe Communication • Reducing Work the Mainframe Needs to Do, so that it can Focus on High-Value Database Processing • Cluster controller handles most text-editing chores freeing mainframe from having to support this work, and • Communications controller handles details of communication with cluster controllers, freeing mainframe from having to support this work

13. Application Servers • NOT Part of Mainframe Communications • Can act as terminals or cluster controllers • Transparent to mainframe: no need to do anything differently on mainframe system App Server App Server

14. Mainframes • Use SNA Standards Architecture Instead of TCP/IP • Not peer-to-peer control; Master-slave control under a System Services Control Point program on a mainframe • SSCP program governs all sessions among devices SSCP

15. Mainframes • SNA Standards Architecture • Like TCP/IP and OSI, uses layering • Uses OSI standards at the physical and data link layers

16. Mainframes • SNA Standards Architecture • SNA Path Control layer is like TCP/IP internet layer and OSI network layer • SNA Transmission Control layer is like the OSI and TCP/IP transport layer • However, not peer to peer operation; master-slave operation under the control of the SSCP

17. Mainframes • SNA Standards Architecture • Highest layers are like OSI layers • Network Addressable Unit (NAU) Services layer is like OSI session layer • Data Flow Control layer is like OSI presentation layer • However, applications are not standardized within SNA • There is no SNA application layer

18. Mainframes • SNA NAUs • Communication takes place between network addressable units (NAUs) • Unit is a general name for a communicating entity • In networks, communicating entities must have addresses; So they are network addressable units

19. Mainframes • Logical Units • Deal directly with end users • Terminals are logical units! • Connection points on mainframe (not mainframe itself) deal with application programs,which are considered to be end users Application Human User LU6 Connection

20. Mainframes • Physical Units • Do not deal directly with end users • Mainframe, communications controller, cluster controller • Path control network connects cluster controller and communication controller Path Control Network

21. Mainframes • SSCP • Third type of NAU • Program located on the mainframe • In classic SNA, two other NAUs can only be connected under the control of the SSCP

22. Mainframes • Versions of SNA • Classic SNA • All communication under the control of SSCP • Advanced Peer-to-Peer Networking (APPN) • Newer; NAUs can connect directly • High-Performance Routing • Classic SNA and APPN are difficult to route • Newer still; HPR improves routing

23. Mainframes • SNA and Router Networks • To link cluster controllers to communications controller over routed networks • Data Link Switching (DLSw) standard supports SNA transmission through routers • High-Performance Routing (HPR) is better

24. Mainframes • Mainframes and TCP/IP Networks • TN3270E • TN3270E servers communicate with mainframe • Users have PCs with TN3270E client software that emulates 3270 terminals TCP/IP Network PC with TN3270E Client TN3270E Server