OPEN SYSTEMS INTERCONNECTION AND TCP/IP PROTOCOL SUITE TCP/IP P Open Systems Interconnection Model An ISO standard that covers all aspects of network communications A layered framework consisting of seven separate layers Purpose: to open communication between different systems without requiring changes to the logic of the underlying hardware and software It is not a protocol.
OSI Reference Model The Upper Layers Responsible for applications communicating between hosts Application Presentation Session
The Lower Layers Define how data is transferred through a physical wire or through networking devices. Transport Network Data Link Physical Functions of the Layers Application: provide user interface Presentation: data representation Session: management of sessions Transport: provides reliable or unreliable delivery Network: moves packets from source to destination Data Link: node to node delivery Physical: transmission of bits between devices
Physical characteristics of interfaces & media Representation of bits Data rate Physical Layer Synchronization of bits Line configuration Physical topology Transmission Mode Data Link Layer Framing Physical Addressing Flow control Error Control Access Control
Data Link Sub Layers (IEEE) Media Access Control (MAC) 802.3 Defines how packets are placed on the media. Defines the physical addressing and logical topologies Responsible for line discipline, error notification and ordered delivery of frames Logical Link Control (LLC) 802.2 Responsible for identifying network layer protocols and then encapsulating them. Provide flow control and sequencing of control bits. Network Layer Logical Addressing Routing
Service-point addressing Segmentation and reassembly Transport Layer Connection control Flow control Error control Dialog control Synchronization Session Layer
Translation Encryption Presentation Layer Compression Network virtual terminal File transfer, access & management Application Layer Mail services Directory services
TCP/IP A protocol suite that defines how all transmissions are exchanged across the Internet A hierarchical protocol made up of different modules, each providing a specific functionality Also made up of layers: Application, Transport, Network, Data Link, Physical Application, Transport, Internet, Network Access Functions of Layers Application layer handles high-level protocols, issues of representation, encoding, and dialog control. Transport Layer provides transport services from the source host to the destination host via a logical connection services include TCP and UDP services
Functions of Layers Internet Layer select the best path through the network for packets to travel. main protocol that functions at this layer is the Internet Protocol (IP). Network Access layer concerned with all of the issues that an IP packet requires to actually make a physical link to the network media Similarities between OSI & TCP/IP Both have layers Both have application layers, though they include very different services Both have comparable transport and network layers Packet-switched, not circuit-switched, technology is assumed Networking professionals need to know both models
Differences between OSI & TCP/IP TCP/IP combines the presentation and session layer into its application layer TCP/IP combines the OSI data link and physical layers into one layer TCP/IP appears simpler because it has fewer layers TCP/IP transport layer using UDP does not always guarantee reliable delivery of packets as the transport layer in the OSI model does OSI & the TCP/IP Model Application Presentation Application Session Transport Network Transport Internet Data Link Physical Network Access
SIGNALS Basic Concepts SIGNALS Information can be in the form of data, voice, picture and so on. Even the 0s and 1s cannot be sent across the network links. For transmission to be possible, information must be transformed into electromagnetic signals. Data can be analog or digital. Signals can be analog or digital (like the information they represent). Analog signals can have any value in a range Digital signals can only have a limited number of values.
Forms of Signals Periodic signal: a signal that completes a pattern within a measurable time frame and repeats over identical subsequent periods Period: amount of time required to complete one cycle. Aperiodic signal: a signal having no repetitive pattern. It has been proved that any aperiodic signal can be decomposed into an infinite number of periodic signals. Analog Signals Sine wave: most fundamental form of a periodic signal. Fundamental characteristics: Amplitude: generally refers to the height of the signal. Period: time needed to complete one cycle. Frequency: refers to the number of periods in one second. Frequency and period are inverses of each other. Phase: describes the position of the waveform relative to time zero (amount of shift forward or backward)
Plots Time-domain plot shows changes in signal amplitude with respect to time. Frequency-domain plot shows the relationship between amplitude and frequency Note: A low-frequency signal in the frequency domain corresponds to a signal with a long period in the time domain and vice versa. A signal that changes rapidly in the time domain corresponds to high frequencies in the frequency domain. Plots Time Domain Plot Frequency Domain Plot
Composite Signals The Fourier series allows us to decompose a composite periodic signal into a possibly infinite series of sine waves, each having a different frequency and phase. The Fourier transform allows us to decompose a composite aperiodic signal into an infinite series of simple sine waves, each having a different frequency and phase. Frequency Spectrum of a Signal the combination of all sine waves that make up the signal. The width of the frequency spectrum is the bandwidth of the signal. Examples: 1. If a periodic signal is decomposed into five sine waves with frequencies 200, 400, 600, 800 and 1000 Hz, what is the bandwidth? Draw the spectrum, assuming all components have maximum amplitude of 10 volts. 2. A signal has a bandwidth of 30 Hz. The highest frequency is 70 Hz. What is the lowest frequency? Draw the spectrum if the signal contains all integral frequencies of the same amplitude.
Digital Signals Most digital signals are aperiodic, thus, frequency or period is not appropriate. bit interval time required to send one single bit bit rate number of bits sent in one second A digital signal can be decomposed into a infinite number of simple sine waves called harmonics, each with a different amplitude, phase and frequency and phase. The significant spectrum of a digital signal is the portion of the signal s spectrum that can adequately reproduce the original signal. Examples: 1. A digital signal has a bit rate of 4000 bps. What is the duration of each bit (bit interval)? 2. A digital signal has a bit interval of 50 microseconds. What is the bit rate?