ECE544Lec4DR08

ECE544Lec4DR08 - ECE544: Communication Networks-II, Spring...

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ECE544: Communication Networks-II, Spring 2008 D. Raychaudhuri Lecture 4 Includes teaching materials from L. Peterson
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Today’s Lecture IP basics Routing principles distance vector (RIP) link state (OSPF)
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IP Basics   Best Effort Service  Model Global Addressing  Scheme ARP & DHCP
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IP Internet Concatenation of Networks Protocol Stack R2 R1 H4 H5 H3 H2 H1 Network 2 (Ethernet) Network 1 (Ethernet) H6 Network 3 (FDDI) Network 4 (point-to-point) H7 R3 H8 R1 ETH FDDI IP IP ETH TCP R2 FDDI PPP IP R3 PPP ETH IP H1 IP ETH TCP H8
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Service Model Connectionless (datagram-based) Best-effort delivery (unreliable service) packets are lost packets are delivered out of order duplicate copies of a packet are delivered packets can be delayed for a long time Datagram format Version HLen TOS Length Ident Flags Offset TTL Protocol Checksum SourceAddr DestinationAddr Options (variable) Pad (variable) 0 4 8 16 19 31 Data
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Fragmentation and Reassembly Each network has some MTU Strategy fragment when necessary (MTU < Datagram) try to avoid fragmentation at source host re-fragmentation is possible  fragments are self-contained datagrams use CS-PDU (not cells) for ATM delay reassembly until destination host do not recover from lost fragments 
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Example H1 R1 R2 R3 H8 ETH IP (1400) FDDI IP (1400) PPP IP (512) PPP IP (376) PPP IP (512) ETH IP (512) ETH IP (376) ETH IP (512) Ident = x Offset = 0 Start of header 0 Rest of header 1400 data bytes Ident = x Offset = 0 Start of header 1 Rest of header 512 data bytes Ident = x Offset = 512 Start of header 1 Rest of header 512 data bytes Ident = x Offset = 1024 Start of header 0 Rest of header 376 data bytes
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Global Addresses Properties globally unique hierarchical: network + host Dot Notation 10.3.2.4 128.96.33.81 192.12.69.77 Network Host 7 24 0 A: Network Host 14 16 1 0 B: Network Host 21 8 1 1 0 C:
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Datagram Forwarding Strategy every datagram contains destination’s address if directly connected to destination network, then  forward to host if not directly connected to destination network, then  forward to some router forwarding table maps network number into next hop each host has a default router each router maintains a forwarding table Example (R2)         Network  Number   Next Hop                               1   R3                               2   R1                               3   interface 1                               4   interface 0                        
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Address Translation Map IP addresses into physical  addresses destination host next hop router Techniques encode physical address in host part of IP address table-based ARP table of IP to physical address bindings
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ECE544Lec4DR08 - ECE544: Communication Networks-II, Spring...

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