Compare and Contrast Transport Protocols

quizlet

Objectives

  • 1.1 Compare and contrast the Open Systems Interconnection (OSI) model layers and encapsulation concepts.
  • 1.5 Explain common ports and protocols, their application, and encrypted alternatives.

Transport Layer Ports and Connections

Ports

Port numbers 0 through 1,023 are preassigned by the Internet Assigned Numbers Authority (IANA) to “well-known” server applications. Other server applications have been registered in the port range 1,024 through 49,151. The remaining ports (up to 65,535) are designated for private or dynamic use.

Sockets

  • The port number is used in conjunction with the source IP address to form a socket.
  • Each socket is bound to a software process. Only one process can operate a socket at any one time.

Transmission Control Protocol (TCP)

Transmission Control Protocol is a “slower” protocol of the two between it and UDP, but is more reliable to ensure missing critical information reaches its destination.

TCP Port Fields

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TCP Handshake Breakdown

A three way handshake is made to establish a connection for TCP

  1. Client sends a SYN TCP Flag and enteres SYN-SENT state with a randomly generated sequence number
  2. Server receives the SYN and enters the SYN-RECEIVED state. It then responds with a SYN/ACK TCP flag of it’s own back to the client with a randomly generated sequence number.
  3. Client responds with an ACK segment and assumes the connection has been established.
  4. Server opens up the connection and enters the Established state.

While a connection has been established the client sends packets to the server. If the client doesn’t receive an ACK for the packets sent then the client resends the packet.

TCP Connection Teardown

  1. Client sends a FIN segment and the client enters a FIN-WAIT1 state
  2. Server responds with ACK segment and enters CLOSE-WAIT state
  3. Client receives the ACK segment and enters the FIN-WAIT2 state
  4. The server sends it’s own FIN segment to the client and goes to LAST-ACK state
  5. Client sends an ACK and enters the TIME-AWAIT state. After a time of period the client closes the connection.
  6. Server closes the connection when it receives the ACK

User Datagram Protocol (UDP)

UDP is “connectionless” meaning that there is no guarantee of a successful packet delivery occuring or a retransmission request occuring.

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Review Activity:

  1. How many port numbers are required to establish a connection at the Transport layer?

Two—a server port and a client port.

  1. What is the purpose of the window field in a TCP segment?

It is used for flow control. The window indicates the amount of data that the host can receive before sending another acknowledgement.

  1. What are the sizes of TCP and UDP headers?

TCP is 20 bytes (or more) while UDP is 8 bytes.

  1. True or False? User Datagram Protocol (UDP), like TCP, uses flow control in the sending of data packets.

False.

  1. What port and protocol does TFTP use at the Transport layer?

UDP/69