ICP DAS USA tGW-700 Series User Manual

Also see for tGW-700 Series: User manual User manual User manual

Contents

ICP DAS USA tGW-700 Series User Manual Manual pdf 61 page image

tGW-700 Series User Manual, Version 1.7, Mar 2013 - 61 -Appendix: Glossary1. ARP (Address Resolution Protocol)Consider two machines A and B that share a physical network. Each has an assigned IPaddress IPA and IPB, and a MAC address, MACA and MACB. The goal is to devise low-levelsoftware that hides MAC addresses and allows higher-level programs to work only with theIP addresses. Ultimately, however, communication must be carried out by the physicalnetworks using whatever MAC address scheme the hardware supplies.Suppose machine A wants to send a packet to machine B across a physical network towhich they are both attached, but A only has the Internet address for B, IPB. The questionarises: how does A map that address to the MAC address for B, MACB?ARP provides a method of dynamically mapping 32-bit IP address to the corresponding 48-bit MAC address. The term dynamic is used since it happens automatically and is normallynot a concern for either the application user or the system administrator.2. Clients and ServersThe client-server paradigm uses the direction of initiation to categorize whether a programis a client or server. In general, an application program that initiates peer-to-peercommunication is called a client. End users usually invoke client programs when they usenetwork services.Most client programs consist of conventional application program development tools. Eachtime a client program is executed, it contacts a server, sends a request and waits for aresponse. When the response arrives, the client program continues processing. Clientprograms are often easier to develop than servers, and usually require no special systemprivileges to operate.By comparison, a server is any program that waits for incoming requests from a clientprogram. The server receives a request from a client, performs the necessary computationand returns the result to the client.