Operating Systems Internet Addresses Universal Identifiers Universal Communication

Operating Systems

Internet Addresses

Universal Identifiers • Universal Communication Service Communication system which allows any host to communicate with any other host – Name : what an object is – Address : where it is – Route : how to get there

IP Address • Unique 32 -bit address

IP Classes

IP Classes

Layers

TCP/IP vs OSI

Open System Interconnect • The layers of the OSI model provide a framework for understanding networking. • The OSI model is not a protocol, but rather a reference model (abstract structure) that describes the functions and interactions of various data communication protocols.

OSI Stack • Layers 5 through 7, the "higher" layers, are concerned with communication between applications. • Layers 1 through 4, the "lower" layers, are concerned with transmitting raw data between computers.

Physical Layer • The Physical Layer deals with transmitting and receiving bits across a physical medium. • Includes the following types of hardware devices that send and receive signals over each type of physical medium: – – Network interface cards (NICs) Fiber optic transceivers Radio transceivers Modems

Physical Layer (cont. ) • Concerned only with transmitting and receiving physical signals that represent data bits. • Demo • Most error detection and all error correction are the responsibility of higher layers.

Data Link Layer • The Data Link Layer deals with frames over a single physical link. A Data Link Layer address is the unique address built into a NIC. • It uses the signaling services of the Physical Layer below it. • To Layer 3 above, it provides the service of addressing a message to a device located across a single physical transmission path.

Data Link Layer (cont. ) • Network Layer handles data in units called "packets. “ • Network Layer passes a packet to the Data Link Layer, which encapsulates the packet by placing a header and trailer around it (frame). • Frame header includes the unique NIC addresses of the sending and receiving nodes. • Frame trailer contains error-checking information

Data Link Layer (cont. ) • Network Layer handles data in units called "packets. “ • Network Layer passes a packet to the Data Link Layer, which encapsulates the packet by placing a header and trailer around it (frame). • Frame header includes the unique NIC addresses of the sending and receiving nodes. • Frame trailer contains error-checking information

Data Link Layer (cont. ) Transmitting Node • • • Accepts data packets of arbitrary length from the Network Layer. Accepts the address of an adjacent node to which it is to transmit the data. Adds sequence information to the frame in case they get out of sequence during error recovery. Adds error detection and correction codes to the frames. Does not send frames to the Physical Layer at a faster rate than the receiving Data Link Layer process can handle them.

Data Link Layer (cont. ) Receiving Node • • • Receives bits passed up from the Physical Layer and interprets groups of bits as frames. Checks each frame for errors and takes corrective measures if necessary. Handles problems, such as missing frames, through handshaking with its peer process. Puts the frames back in the correct sequence to reconstruct the packet. Passes each decapsulated packet up to the Network Layer. Demo

Network Layer • The Network Layer deals with packets. • Responsible for transmitting data packets between source and destination nodes that may not be connected by the same physical link • Message may pass through an "intermediate node. " Network Layer's job is to use intermediate nodes to transmit a packet to its destination. • Demo

Transport Layer • The Transport Layer carries messages between processes (remember - multitasking). • Transport Layer addresses are process addresses called "port numbers. " • The lowest layer in which peer software processes at either end of a connection carry on a conversation. • Demo

Transport Layer (cont. ) Services • Addressing – deliver data to a specific process within a node. • Connection management – responsible for establishing and releasing connections between processes. – During data transfer, processes on both hosts communicate to verify that data is being received without errors or loss. – When communication is complete, the peer processes terminate the connection to free up resources for other processes. • Flow Control and Buffering – responsible for ensuring that the receiving node has enough memory buffers to store the incoming data – data is not transmitted faster than the receiving node can accept it.

Session Layer • Where a conversation starts and stops • The rules of the conversation are agreed upon. • Facilitates a step-by-step interaction or session between two entities. – Example - an interactive user session begins with a user logging on to the computer and ends with the user logging off.

Session Layer (cont. ) Electronic Conversation • Parties first agree to talk to one another. • They (usually) do not talk simultaneously. • Divide the conversation into parts. • End the conversation in an orderly fashion.

Presentation Layer • The process concerned with how data is presented on the computer and represented inside the computer. • The "representation" layer. – deals with the format of stored computer information. • Three main services: – Data representation – Data security – Data compression

Presentation Layer (cont. ) Services • Data Representation - resolves differences between different types of encoding systems. – – Byte ordering within integers Character coding (EBCDIC and ASCII) Format of floating point numbers Boolean • Data Security - encrypts and decrypts data – Authentication – data encryption • Data Compression - reduces the number of bytes that must be transmitted by translating the data into a more efficient form that requires less storage.

Application Layer • Includes some programs that interact directly with users, and some that provide services to user applications. • E-mail • USENET newsgroups • File transfer and access • Virtual terminals • Web browsers and servers