1. Introduction to TCP/IP

2. What is TCP/IP? It is a protocol suite Enables computers within a network to communicate with each other Network can be made up of different computers running different operating systems Is used by the Internet Is used in many private computer networks

3. History of TCP/IP Developed in late 1960s by U.S. Department of Defense’s Advanced Research and Projects Administration (ARPA) to be able to link DoD computers together. During the 1970s, the number of computers connected grew and the network became known as ARPANET During the late 1970s/early 1980s, the protocols used were refined and formed the basis of TCP/IP

4. History of TCP/IP Continued BSD 4.2 version of UNIX was released in 1983 Contained a TCP/IP protocol suite Bell licensed the operating system to universities for $150.00 Corporate version was $20,000 This made minicomputers more affordable for universities Resulted in an explosive growth in the use of ARPANET

5. Open System Interconnection (OSI) Model Developed during the 1970s by International Organization for Standards(ISO) This is a model for allowing communication between different types of computers within a network Specific protocols can be developed using this general model Was intended to promote the development of protocols that could cause different types of computer systems to communicate with each other

6. Layers of the OSI Model Communication between two computers is sufficiently complex that it should be broken down into separate units (layers) Each layer is built on top of a lower layer One layer only communicates with layers adjacent to that layer Each layer has speified what is to take place at that layer, but does not specify how that operation is to take place Seven layers are in the OSI model

7. Names of the OSI Layers Layer 7 - Application Layer 6 - Presentation Layer 5 - Session Layer 4 - Transport Layer 3 - Network Layer 2 - Data Link Layer 1 – Physical

8. Physical Layer Responsible for sending bits of data Deals with the physical connection and transmission/reception of of signals You would define physical and electrical details at this layer

9. Data Link Layer Provides for the flow of data over a single link from one device to another It accepts data units from the Network Layer and packages the information into data units called frames to be presented to the Physical Layer CRC error-detection bits are added at this layer This layer can detect when frames are lost and request that those frames be sent again

10. Network Layer Routing decisions are made here Packets are forwarded for devices that are farther away than one single link Logical network addresses are translated into physical machine addresses Large packets are broken into smaller chunks if the packet is larger than the largest data frame the Data Link Layer will accept

11. Transport Layer Ensures that packets are delivered error free, in sequence, and with no losses or duplications Breaks large messages from the Session Layer into packets to be sent to the destination computer and reassembles packets into messages to be presented to the Session Layer

12. Session Layer Allows Applications on separate computers to share a connection called a session Provides services such as name lookup and security to allow two programs to find each other and establish the communication link Provides for data synchronization and checkpointing so that in the event of a network failure, only the data sent after the point of failure need be re-sent Controls who can transmit and who can receive at what point during the communication

13. Presentation Layer Translates data between the format used by the computer and the format used by the network Character set conversion

14. Application Layer Provides network services to the user Examples of such services: –Database access –E-mail –File transfers

15. Back to TCP/IP The designers of TCP/IP chose a simpler model with fewer layers There are only four layers –Application –Transport –Internet –Network Interface See p. xxvii to compare OSI model with DARPA model