1. Network and the internet Part eight Introduction to computer, 2nd semester, 2009/2010 Mr.Nael Aburas nras@iugaza.edu.psnras@iugaza.edu.ps Faculty of Information Technology Islamic University of Gaza

2. TCP/IP protocol  TCP/IP protocol is a collection of protocols standards used by the Internet to implement the four-level communication hierarchy implemented in the Internet.  TCP/IP defines a version of the transport layer, we say version because the TCP/IP provides fir more than one way of implementing the transport layer, one of the other options is UDP (user Datagram Protocol).  This means that the application layer might choose to send data via a TCP or UDP version of the transport layer (4.15)

3. Difference between TCP and UDP 1. Before sending a message as requested by the application layer, a transport layer based on TCP sends its own message to the transport layer at the destination telling that a message is bout to be sent, then waits for this message to be acknowledged.( establish a connection before sending a message). A transport layer based on UDP does not establish such a connection, it sends the message to the address and forgets a bout it.

4. Figure 4.15 Choosing between TCP and UDP 4-4

5. Difference between TCP and UDP 2. TCP transport layer at the origin and destination work together by means of acknowledge to assure that all segments of the message are successfully transferred (TCP is called a reliable protocol). UDP doesn't offer such retransmission services (unreliable protocol). 3. TCP provide flow control, meaning that a TCP transport layer at a message’s origin can reduce the rate at which it transmits to keep from overwhelming its counter part at the destination, as well as congestion control, can adjust its transmission rate to alleviate congestion. UDP doesn't support. 4. Transport layer based on UDP is more streamlined that based on TCP

6. Usage of TCP and UDP Usage of UDP: ◦ DNS lookup ◦ VOIP Usage of TCP: ◦ Mail server

7. TCP/IP  IP is the Internet’s standard for implementing the tasks assigned to the network layer  An interesting feature associated with forwarding is that each time an IP network layer at a message’s origin prepares a packet, it appends a value called a hop count, or time to live, t that packet  This value is a limit to the number of times the packet should be forwarded as it tries to find its way through the Internet.