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

Mainframes Dominated by IBM Mainframe competitors build clones –Called plug-compatible machines

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

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

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 Cluster Controller Limited Text Editing

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 Cluster Controller Limited Text Editing

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 Central Site Central Site Long- Distance Line AAAAAAA B B BB

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

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

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

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

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

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

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

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

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

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

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

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 LU6 Connection Application Human User

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 Path Control Network

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

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

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

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 TCP/IP Network PC with TN3270E Client TN3270E Server