Chapter 1

Introduction

1.1 ISO REFERENCE MODEL

The International Standards Organization (ISO) offers a seven-layer model defining network communication. This model allows communication software to be broken into modules. Each layer provides services needed by the next layer in a way that frees the upper layer from concern about how these services are provided. This simplifies the design of each layer.

The ISO model is shown in Figure 1-1.

Figure 1-1 ISO Reference Model

1.2 NETWORK PROTOCOLS ON SUPER-UX

Figure 1-2 shows the SUPER-UX network protocols and how they fit in the ISO model.

Figure 1-2 SUPER-UX Network Protocols

1.2.1 Lower-Layer Protocols

Lower-layer protocols (1 through 4) allow data transmission and transfer as follows.

• Physical Layer (layer 1)
  This layer provides mechanical, electrical, functional, and procedural means to activate and deactivate physical transmission connections between datalinks.
• Datalink Layer (layer 2)
  This layer provides functional and procedural means for connectionless-mode transmission among networks. SUPER-UX supports Ethernet,FDDI,HIPPI and IXS (IXS is one of the Program Products).
• Network Layer (layer 3)
  This layer provides a means of connectionless-mode transmission among transport entities. It makes transport entities independent of routing and relay considerations associated with connectionless-mode transmission. SUPER-UX supports Internet Protocol (IP) for Ethernet and HYPERchannel-DX.
• Transport Layer (layer 4)
  This layer provides transparent data transfer between sessions and relieves them of concern about achieving reliable and cost effective data transfer. SUPER-UX supports Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).

1.2.2 Upper-Layer Protocols

• Session Layer (layer 5)
  This layer provides the services needed by protocols in the presentation layer to organize and synchronize their dialogue and manage data exchange.
• Presentation Layer (layer 6)
  This layer manages the representation of the information that application layer protocols either communicate or reference during communication.
• Application Layer (layer 7)
  This layer serves as the window between corresponding application processes that are exchanging information.

1.3 APPLICATION INTERFACES

• TLI library -- provides interfaces to TCP/UDP.
• SOCKET system call -- provides TCP/UDP/IP/ICMP interfaces.
• STREAMS system call -- provides interfaces for STREAMS on System V.
• PRC/XDR library -- provides RPC/XDR interfaces.
• Xlib/Xt library -- provides X11 interfaces. See the SUPER-UX X Window System Programmer's Guide for more information.