Practical TCP/IP and Ethernet Networking- P53

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Practical TCP/IP and Ethernet Networking- P53: The transmitter encodes the information into a suitable form to be transmitted over the communications channel. The communications channel moves this signal as electromagnetic energy from the source to one or more destination receivers. The channel may convert this energy from one form to another, such as electrical to optical signals, whilst maintaining the integrity of the information so the recipient can understand the message sent by the transmitter....

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Nội dung Text: Practical TCP/IP and Ethernet Networking- P53

242 Practical TCP/IP and Ethernet Networking 15.4.2 TCP/IP based factory automation Schneider Automation: http://www.transparentfactory.com Richard Hirschmann Gmbh: http://www.hirschmann.de Allen-Bradley: http://www.ab.com 15.4.3 Thin servers LANTronix, http://www.lantronix.com 15.4.4 Web compatible SCADA systems WizNet, http://www.conlab.com.au 15.4.5 Java RCS-7 Java, http://www.auspex-inc.com
16 /TYZGRROTM GTJ ZXU[HRKYNUUZOTM +ZNKXTKZ Y_YZKSY 5HPKIZO\KY When you have completed study of this chapter you should be able to: • Define the functions of various types of network driver software • Describe the parameters which need to be set for a network card to function correctly • Determine how network cards are configured under the plug and play and PCMCIA architectures • Specify the uses for a protocol analyzer 4KZ]UXQ JXO\KXY 4KZ]UXQ JXO\KXY The network driver is a program used to provide an interface between the network card and the higher-level protocols. It spans the data link and network layers of the OSI model as shown in Figure 16.1. The network driver needs to match the specific hardware configuration of the network card such as its addresses of I/O ports, control and status registers, etc. Ethernet cards use the same IEEE 802.3 protocol so they can communicate with one another but each needs a unique driver because of the different vendor hardware implementations. )USVGZOHOROZ_ GTJ [YGMK The network driver must also be compatible with the appropriate network operating system protocols in the network, transport and session layers that are used to send data
6XGIZOIGR :)6/6 GTJ +ZNKXTKZ 4KZ]UXQOTM across the network. In early systems changing from one network protocol to another, e.g. TCP/IP to SPX/IPX, generally necessitated changing the network driver. The network operating systems communication protocols and their relationship to the OSI model are shown in Figure 16.1. Figure 16.1 Network operating system drivers/protocols 4KZ]UXQ IGXJJXO\KX IUTLOM[XGZOUT The configuration of the network card must be set at installation to avoid conflict with the other devices installed on your computer. The manufacturers usually provide an installation guide and/or configuration software to help you set the correct options. The main parameters that may need to be set are as follows: /87 INGTTKR The IRQ channel sets a unique interrupt request (IRQ) vector for when the network card needs attention. This must not conflict with existing devices. It needs to be checked in the normal operating environment. For example, with Windows applications the network card configuration software should be run from within the Windows shell. *3'YNGXKJ SKSUX_ The Network card communicates its data to computer using either direct memory access (DMA) or use of a block of shared memory. The base address of the shared memory (usually 64 kilobytes) is defined here. Network cards are designed to be flexibly reconfigurable to accommodate other applications on your computer. 8'3 HGYK GJJXKYY RAM base address defines the beginning of the address space (usually 16 kilobytes) used by the network card. Other devices must not use such address space. For example, extended memory manager software should be set to exclude such memory to avoid conflicts. /5 HGYK GJJXKYY I/O base address defines the beginning of the address space used to communicate with the internal registers on the network card. Avoid conflicts with existing devices.
/TYZGRROTM GTJ ZXU[HRKYNUUZOTM +ZNKXTKZ Y_YZKSY 853 HGYK GJJXKYY GTJ YO`K This is used for systems with an auto-boot ROM to configure diskless workstations. These load their operating systems over the network. Match the base address and EPROM size to the supplied boot ROM. The network card configuration is set on the card using switches or links and/or stored in flash memory (EEPROM) on the card by the configuration software. 4KZ]UXQ JXO\KX OTZKXLGIK YVKIOLOIGZOUT 4*/9 This is a software specification developed by 3COM and Microsoft in 1988 for use mainly in DOS and OS/2 operating systems. This defines a standard interface for communication between the MAC layer and any compatible protocols. This means that the MAC driver in any vendor’s NDIS compatible network cards can pass data to any NDIS compatible protocol. This standardization enables products from various vendors to be interconnected and to provide simultaneous support for multiple protocols. These NDIS drivers can be unloaded from memory to conserve DOS RAM space or allow changes to other drivers. 5VKT JGZG ROTQ OTZKXLGIK 5*/ The ODI architecture provides an alternative to the OSI layering structure that can allow a number of network cards to simultaneously support different protocol stacks such as TCP/IP, SPX/IPX, etc. The ODI architecture makes use of a link support layer (LSL) and a multiple link interface driver (MLID) as shown in Figure 16.2. The MLID corresponds to part of the data link layer and interfaces to the LSL, which covers part of both the data link and network layers. This provides a standard, hardware independent, virtual interface for the network cards. The LSL switches multiple protocol packets to the correct MLID or the correct protocol stack as required. Figure 16.2 ODI architecture
6XGIZOIGR :)6/6 GTJ +ZNKXTKZ 4KZ]UXQOTM 6GIQKZ JXO\KXY The packet driver is the generic interface between the TCP/IP protocol stack and the software responsible for the local area network card hardware. The packet driver hides the hardware specifics from the protocol stacks and likewise hides the protocol issues from the hardware. The packet driver operates at the MAC layer, and its implementation is critically dependent on the specific card hardware. Common driver specifications have evolved to provide standard interfaces to both the protocol stack and the card hardware, thus enabling the protocol to run on top of all network cards, which have that MAC driver specification. A common example is the packet driver developed by FTP Software, Inc, in 1987. The specification defines how the MAC driver loads and operates under DOS and defines a common software interface for various protocol stacks. The network card is independent of the protocol stacks, and one card can simultaneously handle packets destined for multiple protocols. Each protocol uses a software interrupt in the range 60 h–80 h to communicate with the packet driver. 6R[M GTJ VRG_ GXINOZKIZ[XK Modern PC motherboards support the PC/ISA plug and play (PnP) architecture. With this architecture the PC identifies which slot the particular card is inserted into and the BIOS dynamically assigns the resources the card requires e.g. IRQ, DMA channel etc, resolving any resource conflicts. These resource details are registered in the ESCD (extended system configuration data) and stored in flash memory on the motherboard. The data structure defines the resources used by each device and card on the system. When using PnP it is important to register all legacy cards and devices (non PnP), otherwise resource conflicts are likely. 6)3)/' OTZKXLGIK /TZXUJ[IZOUT PCMCIA are the initials of the Personal Computer Memory Card International Association, which was formed in 1989 to promote the standardization and interchangeability of PC cards. As the name indicates initial devices were memory cards implemented as ‘virtual disk drives’ for mobile computer support. PC cards now come in a wide range of memory devices such as RAM, ROM FLASH memory, AT Attachment (ATA) hard drives, and many I/O devices including modems and network interface cards. The interface enables these devices to be powered from the computer and automatically detected by the system as soon as they are installed and then automatically configured. This gives the PC cards the ability to be inserted into a PCMCIA socket after the system has already been powered up. 6)3)/' OTZKXLGIK The PCMCIA interface consists of the following, as shown in Figure 16.3: .GXJ]GXK • The 16-bit PC card, (A 32-bit PC card and socket interface also exists called CardBus) • PCMCIA socket