The Mission of the Communications Server Staff is to provide highly available connectivity for users, printers, servers and applications to the mainframes.

Introduction

Consistent with any mainframe network redesign effort I have composed this document to describe, define and illustrate the network design for the mainframe upon installation of the mainframes at your company’s data center. This document is arranged according to the OSI model since its audience will be technical.

Summary

The Open System Interconnection (OSI) reference model describes how information from a software application in one computer moves through a network medium to a software application in another computer. The OSI reference model is a conceptual model composed of seven layers, each specifying particular network functions. The model was developed by the International Organization for Standardization (ISO) in 1984, and it is now considered the primary architectural model for inter-computer communications. The OSI model divides the tasks involved with moving information between networked computers into seven smaller, more manageable task groups. A task or group of tasks is then assigned to each of the seven OSI layers. Each layer is reasonably self-contained so that the tasks assigned to each layer can be implemented independently. This enables the solutions offered by one layer to be updated without adversely affecting the other layers.

IBM SNA model has many similarities with the OSI 7 layers model. Likewise, the SNA model also has 7 layers. The physical control layer is assumed to be implemented via other standards such as those in the cluster control units and 3270 terminals.

Characteristics of the OSI Layers

The seven layers of the OSI reference model can be divided into two categories: upper layers and lower layers.

The upper layers of the OSI model deal with application issues and generally are implemented only in software. The highest layer, the application layer, is closest to the end user. Both users and application layer processes interact with software applications that contain a communications component. The term upper layer is sometimes used to refer to any layer above another layer in the OSI model.

The lower layers of the OSI model handle data transport issues. The physical layer and the data link layer are implemented in hardware and software. The lowest layer, the physical layer, is closest to the physical network medium (the network cabling, for example) and is responsible for actually placing information on the medium.

Since the OSI model provides a conceptual framework for communication between computers, we are using this model to define and describe the design for the mainframe network, we are not going to provide a definition of the layers at this point. Such definitions will be provided at the section associated with it in the context of this document.

The IBM SNA Reference Model

The functions of each SNA layer are described as follows:

Data link control (DLC)- Defines several protocols, including the Synchronous Data Link Control (SDLC) protocol for hierarchical communication, and the Token Ring Network communication protocol for LAN communication between peers. SDLC provided a foundation for ISO HDSL and IEEE 802.2.
Path control- Performs many OSI network layer functions, including routing and datagram segmentation and reassembly (SAR)
Transmission control- Provides a reliable end-to-end connection service (similar to TCP), as well as encrypting and decrypting services
Data flow control- Manages request and response processing, determines whose turn it is to communicate, groups messages, and interrupts data flow on request
Presentation services- Specifies data-transformation algorithms that translate data from one format to another, coordinate resource sharing, and synchronize transaction operations

Transaction services- Provides application services in the form of programs that implement distributed processing or management services.

SNA, OSI and TCP/IP side by side

Figure 1-2. SNA and OSI

Objective

It is the objective of the Communications Server Staff to configure the mainframe connectivity in such a manner that the mainframe is perceived as “just another server” on the network to all other network entities while maintaining the quality of service demanded by most Mission Statements.

While figure 1-3 illustrates a good model of the Communications Server Staff, it is a limited representation in that it represents only about half of the LPARs we currently have in production and nothing of the Disaster Recovery facilities we possess. More detailed and accurate drawings are included later. However to the extent that it is representative of the IBM mainframe technology this is a good reference frame.

Figure 1.3. Overview of mainframe connectivity

Requirements

Protocols

The OSI model provides a conceptual framework for communication between computers, but the model itself is not a method of communication. Actual communication is made possible by using communication protocols. In the context of data networking, a protocol is a formal set of rules and conventions that governs how computers exchange information over a network medium. A protocol implements the functions of one or more of the OSI layers.

Communications Server is required to support a wide range of protocols. Some of these protocols include LAN protocols, WAN protocols, network protocols, and routing protocols. LAN protocols operate at the physical and data link layers of the OSI model and define communication over the various LAN media. WAN protocols operate at the lowest three layers of the OSI model and define communication over the various wide-area media. Routing protocols are network layer protocols that are responsible for exchanging information between routers so that the routers can select the proper path for network traffic. Finally, network protocols are the various upper-layer protocols that exist in a given protocol suite. Many protocols rely on others for operation. For example, many routing protocols use network protocols to exchange information between routers. This concept of building upon the layers already in existence is the foundation of the OSI model.

Applications

There are three primary levels of applications that must be supported through the Mainframe Network. These are here identified as peers and are not listed in order of importance. These are the Systems Level Applications, Mainframe Hosted Business Applications and Distributed Applications that interact with the mainframe.

Systems Level Applications includes but is not limited to CICS, TSO, DB2, IDMS, CAOPS, Blockade, Omegamon and others.
Mainframe Hosted Applications includes but is not limited to Crew Call, Realtime, Travel Master, MEMO and others.
Distributed Applications include UTCS, TYES, EDI, Webconnect and others. It is assumed that all Distributed Applications must interact with the Mainframe.

Printers

While the physical printers are the responsibility of the users, PC/LAN and other groups, almost all non-Windows generated print flows through the mainframe. The Mainframe sub-system that controls, services and supports printing is an LRS product called VPS. LRS products are specifically designed for all aspects of Enterprise Output Management. Our solution provides the ability to deliver output from the Mainframe (batch, on-line and distributed applications) to the most appropriate device, such as; Databases, E-mail Systems, Spreadsheets, Web Browser, Report Mining Tools, Electronic Forms, Network Printers, Files and Queues, Data Center Printers and Fax Servers over the Norfolk Southern routed Network.

Users

The term user is defined as:

A person who requires the services of Content Manager. This term generally refers to users of client applications, rather than the developers of applications, who use the Content Manager APIs.
Someone who is a system administrator, application developer, or similar
Any person, organization, process, device, program, protocol, or system that uses the services of a computing system.
In the Information Catalog Center, a person who accesses the information available in the information catalog but who is not an administrator. Some users can also perform object management tasks normally performed by administrators, such as creating and updating objects.

User support is the basis of our existence and we never loose track of that! At any given time the Mainframe is supporting as many as 16,000 Human Machine Interface (HMI) user level sessions, 1700 to 2000 of which are active terminal sessions performing HMI during the time slice of the snapshot, this is not counting printer sessions. This means as many as 16,000 emulator sessions have been launched and are active at some level most holding a TCP socket of those 1700 to 2000 are actively engaged in some level of transaction.

Other user sessions include application level interfaces through APIs, CICS, DB2 and other systems applications. There may be as many as 40 to 50,000 of these in P103 alone! Gateways, portals, server interconnects all must be rebuilt, tested, active and ready before we move the production processes to TDC.

All these users must be supported without an outage to the greatest extent possible.

Design

OSI Model Physical Layer

The physical layer defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between communicating network systems. Physical layer specifications define characteristics such as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, and physical connectors. Physical layer implementations can be categorized as either LAN or WAN specifications. Figures 1-4 illustrates the physical layer connectivity of the mainframes to the Channel Sub-Systems that support the OSA cards in particular.

Figure 1-4 The Mainframe Channel Sub-System for OSA, IBM 1

In this environment there were three physical machines are each logically partitioned (LPAR) into several virtual servers. These LPARs each have there own TCP/IP stack. Each independent TCP/IP stack inherits the physical connection to the physical machine’s channel sub-system through its host LPAR. Within the physical machine’s channel sub-system there are Channel Path Identifiers (CHPid) that direct the physical machine to allocate the Channel Units (CU) to the owning LPAR. The CU is assigned an address (CUA) which in turn is associated with a Device Name that identifies the physical card device to the LPARs. The Device Name is consistent across all LPARs on that physical machine. There is one physical device associated with a given CHPid but there are many potential CUAs associated therewith (16⁶⁴). Further, depending on the type of OSA card being configured the configuration requires from one to three CUAs per connection. Figure 1-7 illustrates an individual CHPid and the associations thereof.

Figure 1-7 CHPid

Graphical representations though, imply there are more physical connection points than there actually are on each of the three Mainframe machines. Figure 1-8 shows actual photos of the connection points on these machines. If you are looking at this in electronic format the pictures are of high enough resolution that you may zoom in on them to see the connections clearly. Both the FICON and Ethernet connections are clearly visible in these photos.

Figure 1-8 The physical connection points of the Mainframe

Figure 1-9 is a series of photos that show the three physical machines currently at subject data center. These devices are of the same base architecture and construction as the machines planned by the Systems group for deployment. These photos have been included to show representatively the current patch panel configuration employed. See Appendix 1 for detailed text representations of the configurations of the IBM 1 and IBM 2 Mainframes.

Figure 1-9 The Mainframe environment

Now that we have covered what we are connecting to the network, it is time to discuss the media that will be used for such connectivity. Our subject configuration of Mainframes has been altered from the current configuration which includes two Gigabit, Fiber OSA cards and four fast Ethernet, RJ45-D attached copper connections. Our new configurations include Six Gigabit fiber connections and four RJ45-D copper connections.

►In order to accommodate the QoS effort of the Network Operations Center we have requested the fiber cards to be provided as multimode fiber. Figure 1-10 is a table of connections and machines showing the number of connections and the expected connection points.

OSA Cards IBM 1 Machine
CHPID	CUA	Type	Device Name	Function
1A	0100-011F	Fiber, Multimode	Q1A100	TCP/IP
1B	0200-021F	Fiber, Multimode	Q1B101	TCP/IP
1C	0300-031F	Fiber, Multimode	Q1C100	TCP/IP
1D	0400-041F	Fiber, Multimode	Q1D101	TCP/IP
1E	0500-051F	Fiber, Multimode	Q1E100	TCP/IP
1F	0600-061F	Fiber, Multimode	Q1F101	TCP/IP
A1	1100-111F	Cat 6 - Copper	LA1100	DLSw
A2	2100-211F	Cat 6 - Copper	LA2101	DLSw
A3	3100-311F	Cat 6 - Copper	ICC	ICC
A4	4100-411F	Cat 6 - Copper	ICC	ICC
OSA Cards IBM 2 Machine
CHPID	CUA	Type	Device Name	Function
2A	0100-011F	Fiber, Multimode	Q2A200	TCP/IP
2B	0200-021F	Fiber, Multimode	Q2B201	TCP/IP
2C	0300-031F	Fiber, Multimode	Q2C200	TCP/IP
2D	0400-041F	Fiber, Multimode	Q2D201	TCP/IP
2E	0500-051F	Fiber, Multimode	Q2E200	TCP/IP
2F	0600-061F	Fiber, Multimode	Q2F201	TCP/IP
B1	1100-111F	Cat 6 - Copper	LB1200	DLSw
B2	2100-211F	Cat 6 - Copper	LB2201	DLSw
B3	3100-311F	Cat 6 - Copper	ICC	ICC
B4	4100-411F	Cat 6 - Copper	ICC	ICC
OSA Cards IBM 3 Machine
CHPID	CUA	Type	Device Name	Function
3A	0100-011F	Fiber, Multimode	Q3A300	TCP/IP
3B	0200-021F	Fiber, Multimode	Q3B301	TCP/IP
3C	0300-031F	Fiber, Multimode	Q3C300	TCP/IP
3D	0400-041F	Fiber, Multimode	Q3D301	TCP/IP
3E	0500-051F	Fiber, Multimode	Q3E300	TCP/IP
3F	0600-061F	Fiber, Multimode	Q3F301	TCP/IP
C1	1100-111F	Cat 6 - Copper	LC1300	DLSw
C2	2100-211F	Cat 6 - Copper	LC2301	DLSw
C3	3100-311F	Cat 6 - Copper	ICC	ICC
C4	4100-411F	Cat 6 - Copper	ICC	ICC

Figure 1-10 Mainframe connections by type and function

OSI Model Data Link Layer

The data link layer provides reliable transit of data across a physical network link. Different data link layer specifications define different network and protocol characteristics, including physical addressing, network topology, error notification, sequencing of frames, and flow control. Physical addressing (as opposed to network addressing) defines how devices are addressed at the data link layer. Network topology consists of the data link layer specifications that often define how devices are to be physically connected, such as in a bus or a ring topology. Error notification alerts upper-layer protocols that a transmission error has occurred, and the sequencing of data frames reorders frames that are transmitted out of sequence. Finally, flow control moderates the transmission of data so that the receiving device is not overwhelmed with more traffic than it can handle at one time.

The Institute of Electrical and Electronics Engineers (IEEE) has subdivided the data link layer into two sublayers: Logical Link Control (LLC) and Media Access Control (MAC). Figure 1-8 illustrates the IEEE sublayers of the data link layer.

Figure 2-1: The Data Link Layer Contains Two Sublayers

The Logical Link Control (LLC) sublayer of the data link layer manages communications between devices over a single link of a network. LLC is defined in the IEEE 802.2 specification and supports both connectionless and connection-oriented services used by higher-layer protocols. IEEE 802.2 defines a number of fields in data link layer frames that enable multiple higher-layer protocols to share a single physical data link. The Media Access Control (MAC) sublayer of the data link layer manages protocol access to the physical network medium. The IEEE MAC specification defines MAC addresses, which enable multiple devices to uniquely identify one another at the data link layer.

OSI Model Network Layer

The network layer defines the network address, which differs from the MAC address. Some network layer implementations, such as the Internet Protocol (IP), define network addresses in a way that route selection can be determined systematically by comparing the source network address with the destination network address and applying the subnet mask. Because this layer defines the logical network layout, routers can use this layer to determine how to forward packets. Because of this, much of the design and configuration work for internetworks happens at Layer 3, the network layer.

OSI Model Transport Layer

The transport layer accepts data from the session layer and segments the data for transport across the network. Generally, the transport layer is responsible for making sure that the data is delivered error-free and in the proper sequence. Flow control generally occurs at the transport layer.

Flow control manages data transmission between devices so that the transmitting device does not send more data than the receiving device can process. Multiplexing enables data from several applications to be transmitted onto a single physical link. Virtual circuits are established, maintained, and terminated by the transport layer. Error checking involves creating various mechanisms for detecting transmission errors, while error recovery involves acting, such as requesting that data be retransmitted, to resolve any errors that occur.

The transport protocols used on the Internet are TCP and UDP.

OSI Model Session Layer

The session layer establishes, manages, and terminates communication sessions. Communication sessions consist of service requests and service responses that occur between applications located in different network devices. These requests and responses are coordinated by protocols implemented at the session layer.

OSI Model Presentation Layer

The presentation layer provides a variety of coding and conversion functions that are applied to application layer data. These functions ensure that information sent from the application layer of one system would be readable by the application layer of another system. Some examples of presentation layer coding and conversion schemes include common data representation formats, conversion of character representation formats, common data compression schemes, and common data encryption schemes.

Common data representation formats, or the use of standard image, sound, and video formats, enable the interchange of application data between different types of computer systems. Conversion schemes are used to exchange information with systems by using different text and data representations, such as EBCDIC and ASCII. Standard data compression schemes enable data that is compressed at the source device to be properly decompressed at the destination. Standard data encryption schemes enable data encrypted at the source device to be properly deciphered at the destination.

Presentation layer implementations are not typically associated with a particular protocol stack. Some well-known standards for video include QuickTime and Motion Picture Experts Group (MPEG). QuickTime is an Apple Computer specification for video and audio, and MPEG is a standard for video compression and coding.

Among the well-known graphic image formats are Graphics Interchange Format (GIF), Joint Photographic Experts Group (JPEG), and Tagged Image File Format (TIFF). GIF is a standard for compressing and coding graphic images. JPEG is another compression and coding standard for graphic images, and TIFF is a standard coding format for graphic images.

OSI Model Application Layer

The application layer is the OSI layer closest to the end user, which means that both the OSI application layer and the user interact directly with the software application.

This layer interacts with software applications that implement a communicating component. Such application programs fall outside the scope of the OSI model. Application layer functions typically include identifying communication partners, determining resource availability, and synchronizing communication.

When identifying communication partners, the application layer determines the identity and availability of communication partners for an application with data to transmit.
When determining resource availability, the application layer must decide whether sufficient network resources for the requested communication exist. In synchronizing communication, all communication between applications requires cooperation that is managed by the application layer.

Some examples of application layer implementations include Telnet, File Transfer Protocol (FTP), and Simple Mail Transfer Protocol (SMTP).

Test Strategy

The Test Strategy is a high-level document which defines how the quality targets of the project will be achieved. Its scope is the entire technical environment of the system: hardware, network, software, documentation. The strategy identifies:

· at which stages testing will be performed

· the tools to be used

· procedures and policies

· levels of testing.

Bibliography:

Text References:

1. IBM Corporation, IBM eServer zSeries 900 OSA-Express Overview, October 2001;

see www-1.ibm.com/servers/eserver/zseries/networking/osax.html.

2. Bill White and August Kaltenmark, zSeries HiperSockets (Redpaper), December

2001; see http://www.redbooks.ibm.com/redpapers/pdfs/redp0160.pdf.

3. IBM Corporation, z/Architecture Principles of Operation, Order No.

SA22-7832-00, December 2000; available through IBM branch offices.

4. Sidnie Feit, TCP/IP Architecture, Protocols, and Implementation, McGraw-Hill

Book Co., Inc., New York, 1993

IBM Publications References:

Title	Order number	Date
TCP/IP Basic Implementation for z/OS	erc8.0
TCP/IP Basic Implementation for z/OS Student Exercises	erc8.1.1
z/OS Communications Server V1R4 IP Books
z/OS Communications Server IP Configuration Guide V1R4	SC31-8775-02	Sep2002
z/OS Communications Server IP Configuration Reference V1R4	SC31-8776-03	Sep2002
z/OS Communications Server IP User's Guide and Commands V1R4	SC31-8780-02	Sep2002
z/OS Communications Server IP System Administrator's Guide V1R4	SC31-8781-01	Sep2002
UNIX System Services
UNIX System Services Planning V1R4	GA22-7800-04	Sep2002
UNIX System Services User’s Guide V1R4	SA22-7801-03	Sep2002
Redbooks
Communications Server for z/OS V1R2 TCP/IP Implementation Guide Vol 1: Base and TN3270 Configuration	SG24-5227-03	Jun 2002
Communications Server for z/OS V1R2 TCP/IP Implementation Guide Vol 2: UNIX Applications	SG24-5228-03	Apr2002
OS/390 eNetwork Communications Server V2R7 TCP/IP Implementation Guide Vol 3: MVS Applications	SG24-5229-01	Apr1999
Communications Server for z/OS V1R2 TCP/IP Implementation Guide Vol 4: Connectivity and Routing	SG24-6516-00	Jun 2002
Communications Server for z/OS V1R2 TCP/IP Implementation Guide Vol 5: Availability, Scalability, and Performance	SG24-6517-00	Aug2002
Communications Server for z/OS V1R2 TCP/IP Implementation Guide Vol 6: Policy and Network Management	SG24-6839-00	Sep2002
Communications Server for z/OS V1R2 TCP/IP Implementation Guide Vol 7: Security	SG24-6840-00	Jul 2002

http://researchweb.watson.ibm.com/journal/rd/464/baskey.txt

http://www.cisco.com/univercd/cc/td/doc/product/iaabu/centri4/user/scf4ap1.htm

Posted: Sat Sep 28 22:56:22 PDT 2002

For additional information on this reference model consult Chapman, D. B., and Elizabeth D. Zurichy, Building Internet Firewalls, Sebastopol:O'Reilly & Associates, Inc., September 1995. (See Appendix B.) or Heywood, D., Networking with Microsoft TCP/IP, Indianapolis: New Riders Publishing, 1996. (See Chapter 1.) Understanding Architectural Models and Protocols. In an architectural model, a layer does not define a single protocol—it defines a data communication function that may be performed by any number of protocols. Because each layer defines a function, it can contain multiple protocols, each of which provides a service suitable to the function of that layer. Every protocol communicates with its peer. A peer is an implementation of the same protocol in the equivalent layer on a remote computer. Peer-level communications are standardized to ensure that successful communications take place. Theoretically, each protocol is only concerned with communicating to its peer—it does not care about the layers above or below it.

Redbooks™/Redpapers

IBM Redbooks/Redpapers are developed and published by the IBM International Technical Support Organization (ITSO). They are intended to develop and deliver skills, technical know-how, and materials to technical professionals of IBM, Business Partners, and customers.

Glossary of Terms

http://www-306.ibm.com/software/globalization/terminology/


zOS TCPIP Basics