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Introduction to TCP/IP
Yusuke Matsuoka / Herwin Chan EE201A Spring/2003 UCLA
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OSI and Protocol Stack OSI: Open Systems Interconnect OSI Model TCP/IP Hierarchy Protocols 7th Application Layer 6th Presentation Layer 5th Session Layer 4th Transport Layer 3rd Network Layer 2nd Link Layer 1st Physical Layer Link Layer : includes device driver and network interface card Network Layer : handles the movement of packets, i.e. Routing Transport Layer : provides a reliable flow of data between two hosts Application Layer : handles the details of the particular application
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Packet Encapsulation The data is sent down the protocol stack
Each layer adds to the data by prepending headers 22Bytes 20Bytes 20Bytes 4Bytes 64 to 1500 Bytes
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Ethernet Computer <-> Computer communication on same network
Each device has unique MAC address (48-bit) example: 00-C0-4F Ethernet Packet: Preamble Dest. address Source address Type Data CRC 8bytes 6bytes 6bytes 2bytes bytes 4bytes MAC: Media Access Control
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ARP : Address Resolution Protocol
ARP provides mapping 32bit IP address <-> 48bit MAC address <-> 00-C0-4F ARP cache maintains the recent mappings from IP addresses to MAC addresses Protocol ARP request broadcast on Ethernet Destination host ARP layer responds
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IP: Internet Protocol Unreliable … connectionless datagram delivery service Responsible for routing of data through intermediate networks and computers 0123 4567 11 8901 1111 2345 1111 6789 2222 0123 2222 4567 2233 8901 IP header: 1 :ICMP 6 :TCP 17 :UDP
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IP Routing Routing Table Destination IP address
Source Destination Application Application Transport Router Transport Network Network Network Link Link Link Routing Table Destination IP address IP address of a next-hop router Flags Network interface specification
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ICMP : Internet Control Message Protocol
Used to report problems with delivery of IP Datagrams within an IP network Used by Ping, Tracerout commands Types and Codes Echo Request (type=8, code=0) Echo Reply(type=0, code=0) Destination Unreachable(type=3, code=0) Time Exceeded(type=11, code=0) : Time-to-Live =0 ICMP Message 20bytes 4bytes IP Header ICMP Header ICMP Data Type Code Checksum 1byte 1byte 2bytes
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TCP : Transmission Control Protocol
Connection-Oriented, Reliable, Byte Stream Service Protocol Set up connection Transfer data Close connection TCP Header Format 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Source Port Destination Port Sequence Number Acknowledgement Number Data Offset - Window Checksum Urgent Pointer Options (0 to 10 Words of 32 Bits) TCP Payload Connection connection must be established before data is transferred Reliable Data guaranteed to eventually arrive with no errors
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TCP : State Diagram
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TCP : Connection Establishing a TCP Connection
Client Host Client Host Send SYN seq=x Send FIN seq=x Receive FIN segment Send ACK x+1 Receive SYN segment Send SYN seq=y, ACK x+1 Receive ACK segment Receive SYN +ACK segment Send FIN seq=y, ACK x+1 Receive FIN + ACK segment Send ACK y+1 Send ACK y+1 Receive ACK segment Receive ACK segment Establishing a TCP Connection Closing a TCP Connection
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TCP : Data transfer Timer Timer Client Host Send Packet 1 Start Timer
Packet Lost Packet should arrive ACK should be sent Timer ACK would normally Arrive at this time Time Expires Retransmit Packet1 Start Timer Timer Receive Packet 1 Send AXK 1 Receive ACK 1 Cancel Timer
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HTTP : Hyper Text Transfer Protocol
Stateless Transaction Protocol Each transaction creates a new connection Steps in Transaction Establish connection Request Method <URL> <CR> Response Response Code <Data> <CR> Close connection
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HTTP Common Request Methods GET, PUT, POST Response Categories
Informational :100 Successful :200 Redirection :300 Client Error :400 (eg. 404 Not found) Server Error :500
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Example: Access www.ee.ucla.edu
Client Server Http request GET “ Appl HTTP Appl HTTP Http response 200 “” <CR> <html file in MIME format> Transp TCP Transp TCP Initiate connection (hdshk) Package data (add TCP header) send http request packet Assemble response (break into several packets) Send http response packets Close connection (hdshk) send data to next hop Net IP Net IP Net IP Relay data ARP to provide IP/MAC translation Link ethernet Link ethernet Link ethernet Router(s)
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References “TCP/IP Illustrated, Volume 1 The Protocols “
by W. Richard Stevens ( “Internet Working with TCP/IP Volume 1” by Douglas E. Comer “Sams Teach Yourself TCP/IP in 24 Hours” by Joe Casad. Published by Sams. (
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