TCP/IP Layer 4 Protocols

TCP/IP Layer 4 Protocols

1. Features

   • Multiplexing using ports
     • Function that allows receiving hosts to choose the correct application for which the data is destined, based on the port number.
       • IP address,Transport protocol, Port number (10.1.1.2, TCP, port 80)
         • Hosts typically allocate dynamic port numbers starting at 1024 because the ports below 1024 are reserved for well-known applications.
           • 20
             • TCP, FTP data
           • 21
             • TCP,FTP control
           • 22
             • TCP, SSH
           • 23
             • TCP, Telnet
           • 53
             • UDP, TCP, DNS
               • TCP for Zone Transfer UDP for DNS Queries
           • 25
             • TCP, SMTP
           • 67,68
             • UDP, DHCP
               • UDP port 67 for sending data to the server, and UDP port 68 for data to the client
           • 69
             • UDP, TFTP
           • 80
             • TCP, HTTP (WWW)
           • 110
             • TCP, POP3
           • 161
             • UDP, SNMP
           • 443
             • TCP, SSL
   • Error recovery (reliability)
     • Process of numbering and acknowledging data with Sequence and Acknowledgment header fields.
   • Flow control using windowing
     • Process that uses window sizes to protect buffer space and routing devices from being overloaded with traffic.
   • Connection establishment and termination
     • Process used to initialize port numbers and Sequence and Acknowledgment fields.
   • Ordered data transfer and data segmentation
     • Continuous stream of bytes from an upper-layer process that is “segmented” for transmission and delivered to upper-layer processes at the receiving device, with the bytes in the same order.

2. Transmission Control Protocol

   • Provides error recovery
     • Relies on IP for end-to-end delivery of the data, including routing issues
   • using 2 bits inside the flag fields of the TCP header. Called the SYN and ACK flags
     • SYN means “synchronize the sequence numbers”
       • a three-way handshake must complete before data transfer can begin.
         • SYN, DPORT=80, SPORT=1027 SYN, ACK, DPORT=1027, SPORT=80 ACK, DPORT=80, SPORT=1027
         • TCP Connection Termination
           • Four-way termination sequence
   • Connection-oriented protocol
     • Requires an exchange of messages before data transfer begins, or that has a required preestablished correlation between two endpoints

3. User Datagram Protocol

   • Does not perform error recovery
   • Connectionless protocol
     • Does not require an exchange of messages and that does not require a preestablished correlation between two endpoints

4. QoS

   • Bandwidth
     • The volume of bits per second needed for the application to work well
   • Delay
     • The amount of time it takes one IP packet to flow from sender to receiver
   • Jitter
     • The variation in delay
   • Loss
     • The percentage of packets discarded by the network before they reach the destination, which when using TCP, requires a retransmission.