PUP address translation XEROX NS IDP DOD Internet protocol (IP) X.75 Internet NBS Internet ECMA Internet Chaosnet X.25 level 3 Address resolution protocol (ARP) XNS compatibility Berkeley trailer 21000 BBN Simnet 24577 DEC MOP dump/load 24578 DEC MOP remote control 24579 DEC DECnet phase IV 24580 DEC LAT 24582 24583 32773 HP probe 32784 Excelan 32821 Reverse ARP 32824 DEC LANBridge 32823 Appletalk Source: Ref.6. refers to the general class of LANs based on CSMA/CD (see Chapter 11 for a discussion of CSMA/CD). Figure 12.4 shows the OSI relationships with TCP/IP working with the IEEE 802 LAN protocol group. Figure 12.5 illustrates an IEEE 802 frame incorporating TCP, IP, and LLC. Often addressing formats are incompatible from one protocol in one network to another protocol in another network. A good example is the mapping of the 32-bit Internet address into a 48-bit IEEE 802 address. This problem is resolved with ARP (address resolution ENTERPRISE NETWORKS II: WIDE AREA NETWORKS OSI layer 5 and above IEEE 802 Physical Physical Figure 12.4 How TCP/IP working with IEEE 802 series of LAN protocols relates to OSI. IEEE 802.3 CSMA/CD Frame Preamble Destination Source LLC Data Octets IP Header TCP Header Octets (minimum) (minimum) Application Layer Information Figure 12.5 A typical IEEE 802 frame showing LLC and TCP/IP functions. protocol). Another interface problem is limited IP datagram length of 576 octets, where with the 802 series, frames have considerably longer length limits (Ref. 7). 12.3.3 IP Routing Algorithm In OSI the network layer functions include routing and switching of a datagram through the telecommunications subnetwork. The IP provides this essential function. It forwards the datagram based upon the network address contained within the IP header. Each datagram is independent and has no relationship with other datagrams. There is no guaranteed delivery of the datagrams from the standpoint of the Internet protocol. However, the next higher layer, the TCP layer, provides for the reliability that the IP la