NETWORK PROGRAMMING. Instructor: Junaid Tariq, Lecturer, Department of Computer Science

Transcription

1 NETWORK PROGRAMMING CSC- 341 Instructor: Junaid Tariq, Lecturer, Department of Computer Science

2 6 Lecture

3 CHAPTER 2: THE TRANSPORT LAYER : TCP AND UDP Contents Introduction UDP: User Datagram Protocol TCP: Transmission Control Protocol TCP Connection Establishment and Termination TIME_WAIT Statet Port Numbers TCP Port Numbers and Concurrent Servers Buffer Sizes and Limitations

4 THE BIG PICTURE IPv4 application AF_INET sockaddr_in{ } IPv6 application AF_INET6 sockaddr_in6{ } m- routed ping appl. appl. appl. appl. tcpdump traceroute traceroute ping API TCP UDP ICMP IGMP IPv4 32- bit addresses 128- bit addresses IPv6 ICMPv 6 ARP, RARP BPF, DLPI datalink Figure 2. 1 Overview of TCP/ IP protocols

5 UDP : USER DATAGRAM PROTOCOL The application writes a datagram to a UDP socket, which is encapsulated as either a IPv4 of a IPv6. UDP provides a: Connectionless service. so Unreliable(no delivery and duplicate protection ti guarantee), but Low overhead and processing makes it useful for some applications (e.g. network management, Voice, Conferencing). Source considers message delivery complete once message placed on network Each UDP datagram has a length and we can consider a datagram as a record. RFC 768[Postel 1980]

6 UDP Very simple structure header simply specifies source(optional) and destination ports length(header and data) checksum(optional): done on entire UDP segment. If not performed, then no error detection is performed on user data for whole process(since IP doesn t check user data)

7 UDP

8 TCP: TRANSMISSION CONTROL PROTOCOL Provides connections between clients and servers. Three-way hand shaking Provides reliability. Acknowledgement Retransmission RTT ( round-trip-time) time) TCP also sequences the data by associating a sequence number with every byte that it sends. TCP provides flow control. window A TCP connection is also full-duplex.

9 TCP HEADER bit source port number 16- bit destination port number 32- bit sequence number 4- bit header length reserved (6bit) U R G 32- bit acknowledgment number A C K P S H R S T S Y N F I N 16- bit window size 16- bit TCP checksum 16- bit urgent pointer 20 bytes option (if any) data (if any) TCP Header

10 TCP Header Format Minimum of 20 Octets long Description of components: Source Port (16 bits): specifies sending user of TCP many common ports assigned special numbers Destination Port (16 bits) specifies receiving user of TCP Sequence Number (32 bits) number of first data octet in this segment octet bound, not segment bound: stream oriented Acknowledgment Number (32 bits) used dfor piggy-back acknowledgment contains sequence # of next octet destination expects to get

11 TCP Header Format Reserved (6 bits): for future use Flags (6 bits) URG: urgent pointer field significant ACK: acknowledge field significant PSH: push function RST: reset the connection SYN: synchronize the sequence numbers FIN: no more data from sender

12 TCP Header Format Window (16 bits) used for flow control credit allocation # of data octets user is willing to accept Checksum (16bits) done on entire segment ensures no data error, and also that address is correct Urgent pointer (16 bits) points to octet following urgent data, so receiver knows how much urgent data is coming Options (variable) only 1 so far: specifies maximum accepted segment size Other parameter aren t in header:they re passed as parameters to IP(precedence, delay, data reliability, security, and data length if necessary)

13 ENCAPSULATION user dt data application Appl header user data TCP TCP header application data TCP segment IP IP header TCP header application data Ethernet header IP header TCP header IP datagram Ethernet frame 46 to 1500 bytes application data Ethernet trailer Ethernet driver Ethernet et Encapsulation of data as it gose down the protocol stacks

14 TCP CONNECTIONS TCP connection setup via 3-way handshake J and K are sequence numbers for messages SYN J client SYN K ACK J+1 server ACK K+1 Hmmm RTT is important!

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