4. The OSI Model Lower Layer connects one node to another Upper Layer directly assist the user 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical Layer Function Network Choosing the next node and the link to it Data Link Controls the flow of messages on the chosen link Physical Connecting to the physical medium that provides the link Layer Function Application Provides services directly to an application program Presentation Presentation of information to user in a format that the user will understand Session Controls the user to user dialogue – its direction and synchronization Transport Raises the quality of service provided by the network to the level required by user
24. Number of IP Addresses 2^8=256 2^21=2,097,152 (2M) Class C 2^16=65535 (64K) 2^14=16384 (16K) Class B 2^24=16,777,216 (16M) 2^7=128 Class A # of host IDs per network ID # of network IDs Class
25. Class A-D addresses 239.255.255.255 224.0.0.0 1111xxxx D 223.255.255.255 192.0.0.0 110xxxxx C 191.255.255.255 128.0.0.0 10xxxxxx B 127.255.255.255 0.0.0.0 0xxxxxx A Finish address Start address Leftmost bits Class