1 Figure 3-13: Internet Protocol (IP) Basic Characteristics  There were already single networks, and many more would come in the future  Developers needed to make a few assumptions about underlying networks  So they kept IP simple

2 Figure 3-13: Internet Protocol (IP) Connection-Oriented Service and Connectionless Service  Connection-oriented services have distinct starts and closes (telephone calls)  Connectionless services merely send messages (postal letters)  IP is connectionless

3 IP Packet PC Internet Process First Router Internet Process IP Packet Connectionless Packets Sent in Isolation Like Postal Letters Unreliable No Error Correction Discarded by Receiver if Error is Detected Leaves Error Correction to Transport Layer Reduces the Cost of Routers

4 Figure 3-13: Internet Protocol (IP) (Study Figure) IP is Unreliable (Checks for Errors but does not Correct Errors) (Figure 3-14)  Not doing error correction at each hop between switches reduces switch work and so switch cost  Does not even guarantee packets will arrive in order

5 Figure 3-13: Internet Protocol (IP) (Study Figure) Hierarchical IP Addresses  Postal addresses are hierarchical (state, city, postal zone, specific address) Most post offices have to look only at state and city Only the final post offices have to be concerned with specific addresses

6 Figure 3-15: Hierarchical IP Address Network Part (not always 16 bits) Subnet Part (not always 8 bits) Host Part (not always 8 bits) Total always is 32 bits Host CBA Subnet (17) UH Network ( ) The Internet

7 Figure 3-13: Internet Protocol (IP) (Study Figure) Hierarchical IP Addresses  32-bit IP addresses are hierarchical (Figure 3- 15) Network part tells what network host is on Subnet part tells what subnet host is on within the network Host part specifies the host on its subnet Routers have to look only at network or subnet parts, except for the router that delivers the packet to the destination host

8 Figure 3-13: Internet Protocol (IP) (Study Figure) Hierarchical IP Addresses  32-bit IP addresses are hierarchical Total is 32 bits; part sizes vary Network mask tells you the size of the network part (Figure 3-16) Subnet mask tells you the length of the network plus subnet parts combined

9 Figure 3-16: IP Address Masking with Network and Subnet Masks Network MaskingSubnet Masking Mask RepresentsTells the size of the network part Tells the size of the network and the subnet parts combined Eight ones give the decimal value 255 Eight zeros give the decimal value 00 Masking givesIP address bit where the mask value is 1; 0 where the mask bit is 0 IP address bit where the mask value is 1; 0 where mask bit is 0

10 Figure 3-16: IP Address Masking with Network and Subnet Masks Example 1Network MaskingSubnet Masking IP Address Mask Result Meaning16-bit network part is Combined 24-bit network plus subnet part are Example 2 IP Address Mask Result Meaning8-bit network part is 60Combined 16-bit network plus subnet parts are 60.47