Understanding TCP: Key Concepts and Functions of the Transmission Control Protocol
This overview delves into the Transmission Control Protocol (TCP), a fundamental component of the transport layer in networking. It covers key standards such as RFC 793, RFC 1122, and RFC 1323, establishing TCP as a connection-oriented, reliable, and full-duplex communication service. The TCP header structure is explored, detailing its critical fields including source and destination ports, sequence and acknowledgment numbers, and flags. Additionally, the functions of TCP, including session establishment via the three-way handshake, byte stream communications, and the use of sliding windows for flow control, are discussed. Troubleshooting tools like Ping are briefly introduced.
Understanding TCP: Key Concepts and Functions of the Transmission Control Protocol
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CPET 355Data Communications & Networking 6. The Transport Layer (Transmission Control Protocol) Paul I-Hai Lin, Professor Electrical and Computer Engineering Technology Purdue University, Fort Wayne Campus Prof. Paul Lin
Transmission Control Protocol (TCP) • Request For Comment Standard • RFC 793 – original • RFC 1122 – revised • RFC 1323 – extension • Connection-oriented service • Accepts user data stream from local process (running program) • Break the up into pieces (< 64 KB, often 1460 bytes) as IP datagram • Using specific port Prof. Paul Lin
Transmission Control Protocol (TCP) • TCP/IP Connections • Full-duplex • Point-to-point • TCP/IP Suites • FTP – file transfer (control port 21, data port 20) • Telnet – remote login terminal service (port 23) • SMTP – E-mail (port 25) • HTTP – HyperText Transfer Protocol (port 80) Prof. Paul Lin
Transmission Control Protocol (TCP) • Transport layer duties: • End-to-end delivery (treat individual packets independently) • Addressing (many-to-many entities called service points) • Reliable delivery (error control, sequence control, loss control, and duplication control) • Flow control • Multiplexing Prof. Paul Lin
The TCP Header From Figure 6-29, Page 537, Computer Networks, 4th Ed, Andrew Tanenbaum, Prentice Hall Prof. Paul Lin
The TCP Segment Header • Max Data Bytes • 20-byte header • 65,495 bytes data = 65535 – 20 bytes (TCP header) – 20 bytes (IP header) Prof. Paul Lin
The TCP Segment Header • Source Port (16-bit) • Destination Port (16-bit) • Sequence Number (32-bit) - specify the sequence position of first data byte in the segment • Ack Number (32-bit) - specify the next sequence number expected by the sender of the segment • TCP Header Length (4-bit) Prof. Paul Lin
The TCP Segment Header(continue) • Reserved (6-bit) • 6 Flags • URG – urgent pointer • ACK – ack is valid or not • PSH – push data for efficiency • RST – reset connection, reject, refuse • SYN – establish connection • FIN – release connection Prof. Paul Lin
TCP Segment Format (continue) • Window Size (16-bit): Buffer space allocated for the connection • Checksum (16-bit): On header and data • Urgent Pointer (16-bit): Points to the end of data in the data field that is considered as urgent and required immediate attention • Options: Variable length, Maximum Segment Size (MMS) could be sent • Padding: Padding on a 32-bit boundary, so that the data offset may correctly pointto it Prof. Paul Lin
The Main Functions of TCP • Session establishment • Byte stream communications • Sliding windows Prof. Paul Lin
The Main Functions of TCPSession Establishment • A TCP Three-way Handshake HOST1SYN. Data HOST2 ACK, SYN. Data ACK Prof. Paul Lin
TCP Byte Stream Communications • Segment sequence number of the first byte in the data field • ACK number for each segment • When TCP sends a segment, it retains a copy of the segment in a queue (transmit window) until an ACK is received • Segments not acknowledged are retransmitted Prof. Paul Lin
TCP Sliding Windows • A Sliding Window = buffer • The size of sliding window can be adjusted • Segments sent may take different routes due to failed or busy links • Data must be buffered on the sending host until remote host has acknowledged it Prof. Paul Lin
TCP/IP Troubleshooting Utilities • Ping (Packet Internet Groper) command • The ping command is design for troubleshooting and tracking a single-point hardware or software failure in the Internet. • Verifies whether a remote host can be reached • Shows statistic about packet loss and delivery time. Prof. Paul Lin
TCP/IP Utilities and Troubleshooting • Ping (Packet Internet Groper) • When called, the ping command sends one datagram per second • Listens for ECHO_RESPONSE returned • Sends 4 transmissions of 32-byte each to verify the network connection by default • Similar to the function of ICMP (Internet Control Messaging Protocol) on the IP layer Prof. Paul Lin
Using Ping – A Linux Example [plin@LinMysql plin]$ ping 149.164.36.5 PING 149.164.36.5 (149.164.36.5) from 149.164.36.5 : 56(84) bytes of data. 64 bytes from 149.164.36.5: icmp_seq=1 ttl=64 time=0.214 ms 64 bytes from 149.164.36.5: icmp_seq=2 ttl=64 time=0.059 ms 64 bytes from 149.164.36.5: icmp_seq=3 ttl=64 time=0.050 ms 64 bytes from 149.164.36.5: icmp_seq=4 ttl=64 time=0.055 ms Prof. Paul Lin
Using Ping – Another Linux Example [plin@LinMysql plin]$ ping -c 10 www.iu.edu PING www.iu.edu (129.79.78.4) from 149.164.36.129 : 56(84) bytes of data. 64 bytes from lux.ucs.indiana.edu (129.79.78.4): icmp_seq=1 ttl=57 time=13.1 ms 64 bytes from lux.ucs.indiana.edu (129.79.78.4): icmp_seq=2 ttl=57 time=12.6 ms 64 bytes from lux.ucs.indiana.edu (129.79.78.4): icmp_seq=3 ttl=57 time=9.65 ms 64 bytes from lux.ucs.indiana.edu (129.79.78.4): icmp_seq=4 ttl=57 time=9.91 ms 64 bytes from lux.ucs.indiana.edu (129.79.78.4): icmp_seq=5 ttl=57 time=9.90 ms Prof. Paul Lin
Using Ping – A MS Windows Example C:\>ping 149.164.36.5 Pinging 149.164.36.5 with 32 bytes of data: Reply from 149.164.36.5: bytes=32 time<10ms TTL=63 Reply from 149.164.36.5: bytes=32 time<10ms TTL=63 Reply from 149.164.36.5: bytes=32 time<10ms TTL=63 Reply from 149.164.36.5: bytes=32 time<10ms TTL=63 Ping statistics for 149.164.36.5: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 0ms, Maximum = 0ms, Average = 0ms Prof. Paul Lin
Using Ping – A MS Windows Example Ping Command C:\>ping /? Usage: ping [-t] [-a] [-n count] [-l size] [-f] [-i TTL] [-v TOS] [-r count] [-s count] [[-j host-list] | [-k host-list]] [-w timeout] destination-list Options: -t Ping the specified host until stopped. To see statistics and continue - type Control-Break; To stop - type Control-C. -a Resolve addresses to hostnames. Prof. Paul Lin
Using Ping – A MS Windows Example (continue) Options: -n count Number of echo requests to send. -l size Send buffer size. -f Set Don't Fragment flag in packet. -i TTL Time To Live. Prof. Paul Lin
Using Ping – A MS Windows Example (continue) Options: -v TOS Type Of Service. -r count Record route for count hops. -s count Timestamp for count hops. -j host-list Loose source route along host-list. -k host-list Strict source route along host-list. -w timeout Timeout in milliseconds to wait for each reply. Prof. Paul Lin
