Broad Mainframe Network Connectivity Options

Internal and External Connectivity Options Abound

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Last week, I continued this series on the development and rapid change in systems, networks and applications. My focus was networking and I discussed open systems adapter express (OSA-Express) because it’s the way that IBM mainframes are usually connected to the outside world. You can think of OSA-Express like the network interface card used in Windows and UNIX systems. This week, I will continue the story with an even deeper focus on mainframe connectivity.The IBM Z platform has I/O networks to servers and storage devices that effectively deliver high-performance and secure networking connectivity. Innovation in hardware and TCP/IP networking, such as on the new IBM z15, reinforce the value of IBM Z by providing the nimbleness to easily share across partitions, the security to expand trusted connectivity and the resiliency to deliver continuous operations. The IBM Z Connectivity Handbook is a helpful tool to get the big picture about the variety and scope of the connectivity options that yield these impressive benefits. For this post, let’s explore communications in more detail than last week’s introduction.For internal LAN connectivity, IBM has options that can eliminate physical cabling with multiple options to communicate between virtual servers on a single IBM mainframe. Let’s take a look at HiperSockets, open systems adapter and internal shared memory are discussed below.The HiperSockets function , also known as internal queued direct input/output, is an integrated function of the firmware of the IBM Z central processor complexes. This function provides users with attachment to high-speed logical local area networks with minimal system and network resource usage. HiperSockets provides internal virtual local area networks, which are IP networks in the IBM Z system. Consequently, HiperSockets provides the fastest TCP/IP communication between consolidated Linux, IBM z/VM, IBM z/VSE, and IBM z/OS virtual servers on the same system.The open systems adapter (OSA) is a network controller that you can install in a mainframe I/O cage. The adapter integrates several hardware features and supports many networking transport protocols used in both internal and external networks. The OSA card is the strategic communications device for the IBM Z architecture that integrates the control unit and device into the same hardware. OSA achieves this by placing its functionality on a single card that directly connects to the central processor complex I/O bus.Internal Shared Memory (ISM) is a virtual network adapter that enables direct access to shared virtual memory, thus providing a highly optimized network interconnect for IBM Z intra-communications. Shared memory communications-direct memory access, referred to as SMC-D, uses internal shared memory. SMC-D optimizes OSes communications in a way that’s transparent to socket applications. It also reduces the CPU cost of TCP/IP processing in the data path, which enables highly efficient and application-transparent communications. Interestingly, SMC-D requires no extra physical resources and instead uses LPAR-to-LPAR communication through HiperSockets or an OSA-Express feature for establishing the initial connection. Both z/OS and Linux on IBM Z support SMC-D.For external LAN connectivity, IBM Z gains fast connections across a physical LAN for both IP-based and non-IP-based workloads. Through a discussion of OSA, RoCE Express and SMC-R below, you will see how these adapters can be combined to provide high-speed TCP/IP communications. OSA-Express supports direct attachment to ethernet, token ring and ATM LANs where clients communicate using SNA or TCP/IP. For details on using either OSA or OSA-Express for SNA, see “IBM Open Systems Adapter Connections Between APPN Nodes” and “Connecting Two VTAMs Using an External Communication Adapter.” For details on using either OSA or OSA-Express for TCP/IP, see the z/OS Communications Server: IP Configuration Reference . For TCP/IP, OSA-Express can be configured to use IBM queued direct I/O architecture to eliminate the need for channel control words and interrupts, resulting in accelerated TCP/IP data packet transmission.Remote direct memory access (RDMA) over converged ethernet, called RoCE , is a communication feature that provides fast memory-to-memory communications between two Z platforms. These features are designed to help reduce utilization of CPU resources for applications that use the TCP/IP stack, for example IBM WebSphere accessing a IBM Db2 database. This feature can also help reduce network latency with memory-to-memory transfers by using shared memory communications over RDMA. This is discussed in the paragraph that follows.Shared memory communication over RDMA (SMC-R) is an open protocol that can be used by any platform or OS that implements the protocol. SMC-R is supported by z/OS, AIX and Linux on IBM Z. On the IBM Z-having SMC-R, along with a RoCE express adapter, a solution is available that is designed for both internal and cross-server communications that takes advantage of high-speed protocols and direct memory placement of data for faster communications. Through the use of SMC-R, organizations can transfer huge amounts of data quickly, with low CPU overhead and with low latency. The use of SMC-R is totally transparent to applications and there are no application changes needed.Next post, I’ll continue with this series focused on systems, network and applications. I’ll finish this part on networking by discussing IBM Z storage networks and coupling connectivity.