Essay: I/O Cage
Essay: I/O Cage
The I/O cage is use to provide a wide range of connectivity option through the use of I/O Cage. Each I/O cage has a number of I/O slots for I/O and cryptographic cards, organized into several domains. Each domain has its own STI link, through an STI multiplexing card, which serves as a linking point between cards in the domain and the CEC Cage where it is connected to one of the books’ MBA fanout cards.
4.2. Self-Time Interface (STI)
The physical connectivity between the I/O cage and the CEC Cage is provided through Self-Timed Interconnect (STI) bus Interface. This interface provides a very high speed link (up to 2.7 GB/s) on each of its connection. Each book in System z9 Mainframe allows for up to 16 STI connections which gives a maximum data transfer speed of 43.2GB/s per book. The STI bus also offers redundancy. It means that if more than one connection exist between the CEC Cage and the I/O Cage, all links acts as backup to each other ( one STI link serves the data needs of two domains).It also offers features such as I/O port balancing and Rebalance features which help in optimizing reliability, availability and serviceability of a Mainframe.
4.3. I/O Cage and STI Connections
The STI connection from the Memory Bus Adapter (MBA) present on the book can be connected either to an STI-MP card (which multiplexes up to 4 secondary STI links to connect other I/O cards), An STI-3 Extender Card (which can provide two ICB-3 links), or, and ICB-4 link (which connects to an STI port directly). More often, STI-MP card is used to provide connectivity between various I/O ports on the I/O cage and the central processing system of the System z9 Mainframe. Each STI-MP provides connectivity to up to four cards in each domain and slots into fixed position in the I/O cage. The speed of this connectivity ranges from 333 MB/s for ESCON to 2GB per second for FICON I/O cards. In the I/O cage a single slot is also reserved for providing Interconnect I/O redundancy, through which a two STI links provided redundancy of I/O as well as processing resource by using an STI mother card.