Packet Switching Layer Models and Protocol Suites Asst

Packet Switching, Layer Models and Protocol Suites Asst. Prof. Chaiporn Jaikaeo, Ph. D. chaiporn. j@ku. ac. th http: //www. cpe. ku. ac. th/~cpj Computer Engineering Department Kasetsart University, Bangkok, Thailand

Outline n n Circuit vs. packet switching Layered tasks Internet protocol suites ISO's OSI model 2

End-to-End Communication n Direct communication n Most basic form of communication TX RX GND Serial Port Internet communication n Communication is performed over the Internet 3 3

Internet Comm. - App's Viewpoint n Two network applications should interact as if they were directly connected write read App A n Internet B But what's going on underneath? n What is inside the "cloud"? 4 4

Circuit vs. Packet Switching n n Dedicated circuits Circuit switching n n Telephone switches establish circuits for communication Packet switching n n n Data are put into packets Each stamped with source and destination addresses Routers know where to forward packets telephone switch Packet Router 6

Layered Tasks n Computer networks are complex systems n n Tasks involve varieties of hardware and software components, and protocols Networking task is divided into several subtasks, or layers 7

Real World Example n Communication between managers of two companies Communicate 8

What Actually Happens n Communication takes place thru many layers Logical communication Secretary: types a letter Delivery boy: drops the letter Secretary: reads and reports the message Delivery boy: takes the letter Postal truck Post office: Processes and routes the letter 9

Internet Layer Model n The Internet Protocol Stack User Application Layer Software Transport Layer Network Layer Data Link Layer Physical Layer Hardware Transmission Medium 12

Application Layer Responsible for providing services to the user n The only layer to interact with user Data Application Layer SMTP Logical communication HTTP Data FTP H 5 to Transport SMTP Data HTTP Data FTP H 5 from Transport 13

Transport Layer Responsible for delivery of a message from one process to another n Duties/services Port addressing n Segmentation and reassembly n Connection control n Flow control (end-to-end) n Error control (end-to-end) n 14

Transport Layer Process … Process PORT # Data Transport Layer … Data 1 H 4 Data 2 H 4 Data 3 H 4 (segments) to Network from Network 15 15

Network Layer Responsible for the delivery of packets from the original source to the destination n Duties/services Logical addressing n Routing n 16

Network Layer from Transport to Transport Data Network Layer Data H 3 (packet) to Data Link from Data Link 17

Network Layer Data 1. 1 5. 7 1. 1, 1. 2, 6. 1, 5. 7, . . . are logical addresses 1. 2 Network 1 R 1 6. 6 Network 6 6. 3 R 2 Router 5. 2 3. 3 5. 7 3. 8 Network 5 Network 3 18

Data Link Layer Responsible for transmitting frames from one node to the next n Duties/services Framing n Physical addressing n Flow control (hop-to-hop) n Error control (hop-to-hop) n Access control n 19

Data Link Layer from Network to Network Data Link Layer T 2 Data H 2 (frame) to Physical from Physical 20

Data Link Layer A 3, 3 B, 82, 9 F, . . . are physical addresses Data 9 F T 2 Data 3 B 9 F 82 A 3 H 2 21

Data Link Layer Data 1. 1 5. 7 1. 1 97 1. 2 32 Data 1. 1 5. 7 97 25 Network 1 25 R 1 B 1 79 12 Network 6 Data 1. 1 5. 7 79 62 6. 6 6. 3 62 R 3 R 2 54 88 3. 3 3. 8 Network 3 Data 1. 1 5. 7 54 74 5. 7 74 Network 5 22

Physical Layer Responsible for transmitting individual bits from one node to the next n Duties/services Physical characteristics of interfaces and media n Representation of bits n Data rate (transmission rate) n Synchronization of bits n 23

Physical Layer from Data Link Physical Layer to Data Link Data 01001011 (bits) Transmission medium 24

The Big Picture L 5 data H 5 5 5 4 4 3 3 H 2 2 2 T 2 0111011010101001 1 1 011101010010101 L 4 data L 3 data T 2 L 2 data H 4 H 3 L 5 data H 5 L 4 data L 3 data L 2 data H 4 H 3 H 2 Transmission medium 25

Internet Model router sender router receiver Application Transport Network Data Link D. L. Data Link Physical P. L. Physical Transmission medium 26 26

Protocol Suites n A set of protocols must be constructed n n n to ensure that the resulting communication system is complete and efficient Each protocol should handle a part of communication not handled by other protocols How can we guarantee that protocols work well together? n Instead of creating each protocol in isolation, protocols are designed in complete, cooperative sets called suites or families 27 27

Internet Protocol Suite Layer Protocols Application HTTP, FTP, Telnet, SMTP, . . . Transport TCP, UDP, SCTP, . . . Network IP (IPv 4), IPv 6, ICMP, IGMP, . . . Data Link Ethernet, Wi-Fi, PPP, . . . Physical RS-232, DSL, 10 Base-T, . . . 28

OSI Model User n 7. Application Layer 6. Presentation Layer n 5. Session Layer OSI – Open Systems Interconnection Developed by the International Standards Organizations (ISO) 4. Transport Layer 3. Network Layer 2. Data Link Layer 1. Physical Layer Transmission Medium n Two additional layers n n Presentation layer Session layer

Session Layer Responsible for establishing, managing and terminating connections between applications n Duties/services n Interaction management Simplex, half-duplex, full-duplex n Session recovery 30

Presentation Layer Responsible for handling differences in data representation to applications n Duties/services Data translation n Encryption n Decryption n Compression n 31

OSI Layers in Real World 7. Manager Handwrites a message 6. Assistant Prepares final version 5. Secretary Provides address and packs letter 4. Driver Delivers letter to post office Withdraws letter from mailbox 3. Postal staff Checks address and sorts letter 2. Postal staff 1. Postal staff Reads the message Summarizes or translates letter Opens letter Packs letters for certain directions Loads on truck transmission medium Unpacks packages Unloads from truck Pictures from Wikipedia 32