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Introduction to TCP/IP. 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.
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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
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
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
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
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
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
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
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
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
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
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
Presentation Layer • Translates data between the format used by the computer and the format used by the network • Character set conversion
Application Layer • Provides network services to the user • Examples of such services: • Database access • E-mail • File transfers
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