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Practical TCP/IP and Ethernet Networking- P54: 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 | Installing and troubleshooting Ethernet systems 247 PCMCIA host bus adapter HBA . These are hardware specific providing the interface between the host expansion bus EISA PCI Micro Channel etc and the standard interface to the PC card sockets Software Socket services which provide a standard low level software interface for programmers so that the details of the HBA do not need to be known Card services provide a high level software interface for configuration software and a method of allocating system resources to the PC cards PC card enablers or PC card client drivers read the PC card s card information structure CIS which is in non-volatile memory on the card indicating the type of device the resources it requires and configuration options. The enabler then configures the HBA and PC card Configuration Software CIS Hardware Run - Time Software HBA Socket Socket PC Card PC Card Enabler S Card Services Socket Services Figure 16.3 PCMCIA software and hardware relationships After configuration subsequent accesses to the PC card take place directly without using the PCMCIA socket or card services as illustrated above. 16.8 Protocolanalyzers Protocol analyzers enable us to capture data going across the LAN for purposes of analysis. An analyzer inserted into a ring or connected across a bus has the capability of looking at all messages being sent. These messages can be stored in our computer-based protocol analyzer for subsequent analysis. By looking through the captured packet of data we can examine the message and protocol control information at each layer of the software. Protocol analyzers can operate in promiscuous mode where they capture all messages from all nodes or filters can be set so that the analyzer only captures those messages to or from specific nodes or in specific protocols. This is very useful for tracking down intermittent faults so we can leave the analyzer running in the knowledge that it will capture the fault condition along with all other packets
