CMPE 80N - Introduction to Networks and the Internet 1 CMPE 80N Winter 2004 Lecture 14 Introduction to Networks and the Internet

CMPE 80N - Introduction to Networks and the Internet 2 Announcements Quiz 3 on Friday, Discussion session on Thu during Debasree’s office hours. Kiran has office hours just before quiz. Quiz 2 statistics. Grades should be out.

CMPE 80N - Introduction to Networks and the Internet 3 Network Layer: Implementation and Services

CMPE 80N - Introduction to Networks and the Internet 4 Network Layer: Implementation and Services What services the network layer provides to the upper (transport) layer? How are functions implemented at the network layer? –Functions: routing and forwarding.

CMPE 80N - Introduction to Networks and the Internet 5 Circuit versus Packet Switching

CMPE 80N - Introduction to Networks and the Internet 6 Circuit Switching Physical copper connection set up when call is made Switching offices

CMPE 80N - Introduction to Networks and the Internet 7 C DDDD CC A D B C Packet Switching PayloadHeader

CMPE 80N - Introduction to Networks and the Internet 8 Circuit Switching vs Packet Switching Circuit switching Must set up a connection (initial delay). Resources are dedicated –Therefore they may be used inefficiently! But, performance is predictable as resources are reserved. Packet switching Very small set-up delay. Efficient shared use of resources. Possible congestion and consequent packet dropping Performance is unpredictable and is a function of current traffic conditions.

CMPE 80N - Introduction to Networks and the Internet 9 The Internet Example of packet switching network!

CMPE 80N - Introduction to Networks and the Internet 10 Datagram and Virtual Circuit Packet switching networks can provide 2 different types of services to transport layer. –Virtual circuit. –Datagram.

CMPE 80N - Introduction to Networks and the Internet 11 Virtual Circuit Analogy to physical circuits used by telephone networks. At connection establishment time, path from source to destination is selected and used throughout connection lifetime. When connection is over, virtual circuit terminated.

CMPE 80N - Introduction to Networks and the Internet 12 Datagram No logical connection. Each packet (datagram) routed independently; successive packets may follow different routes. More work at intermediate routers, but more robust and adaptive to failures and congestion.

CMPE 80N - Introduction to Networks and the Internet 13 The Internet Datagram network! Datagrams are formed by header and payload. IP Datagrams can have different sizes –Header is fixed (20 bytes) –Data area can contain between 1 byte and 65 KB

CMPE 80N - Introduction to Networks and the Internet 14 Forwarding Datagrams Header contains all information needed to deliver datagrams to destination. –Destination address. –Source address. Router examines header of each datagram and forwards it along path to destination.

CMPE 80N - Introduction to Networks and the Internet 15 Routers For VCs, routers keep a table with (VC number, outgoing interface) entries. –Packets only need to carry VC number. For datagrams, routing table. –(destination, outgoing interface) entries. –Each packet must carry destination address.

CMPE 80N - Introduction to Networks and the Internet 16 Routing Algorithms Routing algorithm: decides which route a packet should take from source to destination. –For router: which interface a packet should be forwarded.

CMPE 80N - Introduction to Networks and the Internet 17 Routing Algorithms (cont’d) If datagram network, decision is made for every packet. If VC, decision is made only once when VC is setup.