1. 20.1 Chapter 20 Network Layer: Internet Protocol Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. 20.2 Figure 20.1 Links between two hosts

3. 20.3 Figure 20.2 Network layer in an internetwork: Routing

4. 20.4 Figure 20.3 Network layer at the source, router, and destination (continued)

5. 20.5 Switching Technology Circuit switching ( 회선 교환 ) 전화 교환망 (PSTN) Packet switching ( 패킷 교환 ) Datagram ( 데이터그램 ) 방식 IP Virtual circuit ( 가상 회선 ) 방식 X.25, Frame Relay, ATM

6. 20.6 20-2 IPv4 The Internet Protocol version 4 (IPv4) is the delivery mechanism used by the TCP/IP protocols. Datagram Fragmentation Checksum Options Topics discussed in this section:

7. 20.7 Figure 20.4 Position of IPv4 in TCP/IP protocol suite

8. 20.8 Figure 20.5 IPv4 datagram format

9. 20.9 The type of service field was part of version 4, but never used. Note

10. 20.10 The total length field defines the total length of the datagram including the header. Note

11. 20.11 Figure 20.7 Encapsulation of a small datagram in an Ethernet frame

12. 20.12 Figure 20.8 Protocol field and encapsulated data

13. 20.13 Table 20.4 Protocol values

14. 20.14 Identification (16 bits) It identifies the datagram from a source. Normally it is incremented by 1 every datagram. Time-to-live (8 bits) It is used to control the max. # of hops(routers) visited by the datagram. Normally it starts with 32 or 64. Each router that processes the datagram decrements this number by 1. If the value reaches 0, the router discards this datagram. And the router sends the ICMP message to the source host.

15. 20.15 Figure 20.9 Maximum transfer unit (MTU)

16. 20.16 Table 20.5 MTUs for some networks

17. 20.17 Figure 20.10 Flags used in fragmentation

18. 20.18 Figure 20.11 Fragmentation example

19. 20.19 Figure 20.12 Detailed fragmentation example

20. 20.20 Figure 20.13 Example of checksum calculation in IPv4

21. 20.21 Option Options(variable) It is used for testing and debugging. The following fields are defined. Record route loose source routing strict source routing timestamp