FUNDAMENTALS OF NETWORKING CHAPTER 2 INFORMATION TRANSMIISSION
Need For Protocol Architecture • data exchange can involve complex procedures, cf. file transfer example • better if task broken into subtasks • implemented separately in layers in stack • each layer provides functions needed to perform communication for layers above • using functions provided by layers below • peer layers communicate with a protocol
Key Elements of a Protocol • syntax – data block format • semantics - control info. & error handling • timing - speed matching & sequencing
Technical Essentials for Internet Security OSI MODEL The Open System Interconnection Reference Model (OSI Reference Model or OSI Model) is an abstract description for layered communications and computer network protocol design. It divides network architecture into seven layers which, from top to bottom, are the Application, Presentation, Session, Transport, Network, Data Link, and Physical Layers. It is therefore often referred to as the OSI Seven Layer Model.
Technical Essentials for Internet Security Going from layer 1 to 7: Please Do Not Throw Sausage Pizza Away Going from layer 7 to 1: All People Seem To Need Data Processing OSI MODEL
Technical Essentials for Internet Security Layer 1: Physical Layer The Physical Layer defines the electrical and physical specifications for devices. In particular, it defines the relationship between a device and a physical medium. This includes the layout of pin, voltages, cable specification, hubs, repeaters, network adapters, host bus adapters, and more.
Technical Essentials for Internet Security Layer 1: Physical Layer (cont.) • The major functions and services performed by the Physical Layer are: • Establishment and termination of a connection to a communication medium. • Participation in the process whereby the communication resources are effectively shared among multiple users. For example, flow control. • Modulation, or conversion between the representation of digital data in user equipment and the corresponding signals transmitted over a communications channel. These are signals operating over the physical cabling (such as copper and optical fiber) or over a radio link.
Technical Essentials for Internet Security Layer 1: Physical Layer (cont.) • The same applies to local-area networks, such as Ethernet, token ring , FDDI(Fiber Distributed Data Interface), ITU-T( International Telecommunication Union Telecommunication Standardization Sector) G.hn and IEEE802.1I. • Personal area networks such as Bluetooth and IEEE 802.15.4.
Technical Essentials for Internet Security Layer 2: Data Link Layer The Data Link Layer provides the functional and procedural means to transfer data between network entities and to detect and possibly correct errors that may occur in the Physical Layer. Originally, this layer was intended for point-to-point and point-to-multipoint media, characteristic of wide area media in the telephone system. The data link layer is divided into two sub-layers by IEEE.
Technical Essentials for Internet Security Layer 2: Data Link Layer (Cont.) One is Media Access Control (MAC) and another is Logical Link Control (LLC). MAC is lower sub-layer, and it defines the way about the media access transfer, such as CSMA/CD/CA(Carrier Sense Multiple Access/Collision Detection/Collision Avoidance) LLC provides data transmission method in different network. It will re-package date and add a new header.
Technical Essentials for Internet Security Layer 3: Network Layer • The Network Layer provides the functional and procedural means of transferring variable length data sequences from a source to a destination via one or more networks, while maintaining the quality of service requested by the Transport Layer. • The Network Layer performs • network routing functions, • perform fragmentation and reassembly, • report delivery errors. • Routers operate at this layer—sending data throughout the extended network and making the Internet possible.
Technical Essentials for Internet Security Layer 3: Network Layer (Cont.) • The Network Layer performs • network routing functions, • perform fragmentation and reassembly, • report delivery errors. • Routers operate at this layer—sending data throughout the extended network and making the Internet possible.
Technical Essentials for Internet Security Layer 4: Transport Layer The Transport Layer provides transparent transfer of data between end users, providing reliable data transfer services to the upper layers. The Transport Layer controls the reliability of a given link through flow control, segmentation/desegmentation, and error control.
Technical Essentials for Internet Security Layer 5: Session Layer The Session Layer controls the dialogues (connections) between computers. It establishes, manages and terminates the connections between the local and remote application. It provides for full-duplex, half-duplex, or simplex operation, and establishes checkpointing, adjournment, termination, and restart procedures.
Technical Essentials for Internet Security Layer 6: Presentation Layer The presentation layer is responsible for the delivery and formatting of information to the application layer for further processing or display. It relieves the application layer of concern regarding syntactical differences in data representation within the end-user systems. This layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer.
Technical Essentials for Internet Security Layer 7: Application Layer • The application layer is the OSI layer closest to the end user, which means that both the OSI application layer and the user interact directly with the software application. • Application layer functions typically include: • identifying communication partners, • determining resource availability, • synchronizing communication.
Technical Essentials for Internet Security Layer 7: Application Layer (Cont.) • Identifying communication partners • Determines the identity and availability of communication partners for an application with data to transmit. • Determining resource availability • Decide whether sufficient network or the requested communication exist. • Synchronizing communication • All communication between applications requires cooperation that is managed by the application layer.
Technical Essentials for Internet Security Layer 7: Application Layer (Cont.) • Some examples of application layer implementations include • Hypertext Transfer Protocol (HTTP) • File Transfer Protocol (FTP) • Simple Mail Transfer Protocol (SMTP)
TCP/IP Protocol Architecture • developed by US Defense Advanced Research Project Agency (DARPA) • for ARPANET packet switched network • used by the global Internet • protocol suite comprises a large collection of standardized protocols
Technical Essentials for Internet Security Introduction TCP/IP • The Internet Protocol Suite (commonly known as TCP/IP) is the set of communications protocols used for the Internet and other similar networks. • It is named from two of the most important protocols in it: • the Transmission Control Protocol (TCP) and • the Internet Protocol (IP), which were the first two networking protocols defined in this standard.
Technical Essentials for Internet Security TCP/IP Layers
Technical Essentials for Internet Security TCP/IP STACK
Technical Essentials for Internet Security TCP/IP STACK Two Internet hosts connected via two routers and the corresponding layers used at each hop. The application on each host executes read and write operations as if the processes were directly connected to each other by some kind of data pipe. Every other detail of the communication is hidden from each process. The underlying mechanisms that transmit data between the host computers are located in the lower protocol layers.
Technical Essentials for Internet Security TCP/IP Encapsulation
Technical Essentials for Internet Security TCP/IP SOME PROTOCOL
Transmission Terminology • Data transmission occurs over some transmission medium. • Transmission media may be guided or unguided. • A direct link between two devices is a point-to-point link. • More than two devices communicate over a multipoint link. • Transmission may be simplex, half-duplex, or full-duplex.
Time-Domain Concepts • An analog signal is a continuous. • A signal is discrete if it takes on only finite number of values. • A signal is periodic if s(t+T) = s(t) for all t, where T is a constant.
Time-Domain Concepts (cont.) • The amplitude is the instantaneous value of the signal at any time. • The frequency is the number of repetitions of the period per second; f=1/T Hz. • Phase is a measure of the relative position in time within a single period of a signal.
Time-Domain Concepts (cont.) • The wavelength of a signal is the distance occupied by a single cycle. • If n is the velocity of the signal then the wavelength l = nT = n (1/f). • Note: the velocity or propagation speed is often represented as some fraction of the speed of light, c = 3 x 108 meters/second.
Freq. Domain Concepts (cont.) • Bandwidth : range of frequencies • Bandwidth = Highest frequency – lowest frequency
Bit Rate • Bit :binary digit, either 0 or 1 • Bit rate : speed at which binary digits ate transmitted over a network , bit per second (bps) • Ex: 103 = 1000 bits can be transferred from the sending computer to the receiving computer each second.
Analog and Digital Transmission • Analog--continuous time signals. • Digital--discrete time signals. • Three Contexts • Data--entities that convey meaning; signals are electric or electromagnetic encoding of data. • Signaling--the physical propagation of the signal along a suitable medium. • Transmission--the communication of data by the propagation and processing of signals.
Analog and Digital Transmission--Data • Analog data--continuous values on some interval. • Ex.: audio, video, temperature and pressure sensors. • Digital data--discrete values. • Ex.: text, integers. • Encoding using binary patterns: Ex: ASCII.
Analog and Digital Transmission--Signals • Analog signal--a continuously varying electromagnetic wave that may be propagated over a variety of media, depending on bandwidth. • Digital signal--a sequence of voltage pulses that may be transmitted over a wire medium. -Speech and analog signals. -Text input and digital signals.
Analog and Digital Transmission--Signals • Analog data can also be represented by digital signals and digital data can be represented by analog signals. • Digital Data can be represented by analog signals: modem. • Analog Data can be represented by digital signals: codec.
Analog and Digital Transmission--Transmission • Analog transmission--transmission of analog signals without regard to content. • For long distances, amplifiers are used . • Amplifiers boost noise, and are "imperfect". • Analog voice is tolerant of the distortion, but for digital data errors will be introduced.
Analog and Digital Transmission--Transmission • Digital transmission-- transmission of digital data (using either analog or digital signals). • For long distances, repeaters are used. • If spaced properly, the errors are eliminated. • Preferred because of: digital technology, data integrity(error coding), capacity utilization, security, integration (of voice, data and more.)
Advantages of Digital Transmission • High Quality • Digital technology • Low cost LSI/VLSI technology • Data integrity • Longer distances over lower quality lines • High utilization • High bandwidth links economical • High degree of multiplexing easier with digital techniques • Security & Privacy • Encryption • Integration • Can treat analog and digital data similarly