Embedded Systems September 2000 Vol13_10

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CONNECTING ••. • The result of al l this is a logical con- I* * IP Header *I typedef struct { Il'lT8U INT8U ver_hlen; service; INT16U length; INT16U ident; INT16U fragnent; INT8U INT8U INT16U INT32U INT32U } NetipHdr; Listing 1 continued on p. 72 timetol ive; protocol; checksun; src_addr; dest_addr; I* Header version and length (dwords). */ /* Service type. *I /* Length of datagram (bytes).*/ I* Unique packet identification. */ /* Flags; Fragnent offset. */ /*Packet time to live (in network). */ /* Upper level protocol (UDP, TCP>. */ /* IP header checksun. */ /* Source IP address. */ /* Destination IP address. *I nection between two computers. This connection can be used to send and receive all ki nds of data. For example, the two computers could exchange Web pages via HTTP over TCP, SNMP packets ove r UDP, telnet se ions, voice over IP, or any other type of data that can be sent in a stream of one or more digital packets. Because so many types of da ta can be exchanged ove r IP, th e Inte rne t Protocol is full of features that a re only used by a su bset of co n- nected hosts. In fact, the protocol itself is ove rdue for an upgrade from the curre nt version, called IPv4, to the more capable IPv6. (For more on IPv6 and th e coming changeover, see the a rticle by Stephen Harpste r in this month's Interne t Appli ance Design section.) Sin ce IPv6 is not yet widely deployed and even many of the IPv4 features a re not necessary Y ou Choose the Operating System. You Choose the Single Board Computer. We Do the Rest. at~m 1.888.941.2224 • Now available ... QNX Neutrino, IBM· Visua/Age Micro Edition, IBM MQ Everywhere, US Software Super Task 70 SEPTEMBER 2ooo Embedded Systems Programming - ) ROM DOS 6.22 .__/

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