1. Process-to-Process Delivery:
Chapter 23
Process-to-Process Delivery:
UDP and TCP
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2. 23-1 PROCESS-TO-PROCESS DELIVERY
The transport layer is responsible for process-to-process delivery—the delivery of a packet, part of a message, from one process to another. Two processes communicate in a client/server relationship, as we will see later.

3. The transport layer is responsible for process-to-process delivery.
Note
The transport layer is responsible for process-to-process delivery.

4. Figure 23.1 Types of data deliveries

5. Figure Port numbers

6. Figure 23.3 IP addresses versus port numbers

7. Figure 23.8 Position of UDP, TCP, and SCTP in TCP/IP suite

8. 23-2 USER DATAGRAM PROTOCOL (UDP)
The User Datagram Protocol (UDP) is called a connectionless, unreliable transport protocol. It does not add anything to the services of IP except to provide process-to-process communication instead of host-to-host communication.

9. UDP - User Datagram Protocol
Transport-layer Protocol
Used mainly for one way, short communications
datagrams don’t contain information about other packets
Each packet independent of each other

10. UDP - continued Lack of error control
Checksum is only check, packet is dropped if incorrect
Relies on ICMP for error control
Good alternative for short messages without large communications overhead used by TCP

11. Table 23.1 Well-known ports used with UDP

12. TCP
TCP is a connection-oriented protocol; it creates a virtual connection between two TCPs to send data. In addition, TCP uses flow and error control mechanisms at the transport level.

13. TCP - Transmission Control Protocol
Used where reliable communications is required
Provisions for error control, streaming data, and two way communications
Connections are managed both ways using flags in the TCP packet header

14. Three way handshake TCP
SYN(synchronize) - sent at the beginning of a connection from source host. Contains initialization information.
ACK(acknowledgement) - sent when packet has been received by the destination host
SYN - then sent by destination host
ACK - sent by source host

15. TCP error control Implemented through the ACK flag
Each packet numbered and a timer is started on transmission
Packet is retransmitted if ACK not received before timeout

16. Table 23.2 Well-known ports used by TCP

17. Figure 23.13 Stream delivery

18. Figure 23.14 Sending and receiving buffers

19. At the sending site, the buffer has three types of chambers
At the sending site, the buffer has three types of chambers. The white section contains empty chambers that can be filled by the sending process (producer). The gray area holds bytes that have been sent but not yet acknowledged. TCP keeps these bytes in the buffer until it receives an acknowledgment. The colored area contains bytes to be sent by the sending TCP.

20. Figure TCP segments

21. The numbering starts with a randomly generated number.
Note
The bytes of data being transferred in each connection are numbered by TCP.
The numbering starts with a randomly generated number.