NETWORK DESIGN TIJ3053Chapter 1 – Overview of Computer Network
Data Communications, Data Networks, and the Internet Thefundamental problem of communication is that of reproducing at one point either exactly or approximately a message selected at another point - The Mathematical Theory of Communication, Claude Shannon
Contemporary Data Comms trends traffic growth at a high & steady rate development of new services advances in technology significant change in requirements emergence of high-speed LANs corporate WAN needs digital electronics
A Communications Model
Communications TasksTransmission system utilization AddressingInterfacing RoutingSignal generation RecoverySynchronization Message formattingExchange management SecurityError detection and correction Network managementFlow control
Data Communications Model
Transmission Medium selection is a basic choice internal use entirely up to business long-distance links made by carrier rapid technology advances change mix fiber optic wireless transmission costs still high hence interest in efficiency improvements
Networking growth of number & power of computers is driving need for interconnection also seeing rapid integration of voice, data, image & video technologies two broad categories of communications networks: Local Area Network (LAN) Wide Area Network (WAN)
Wide Area Networks span a large geographical area cross public rights of way rely in part on common carrier circuits alternative technologies used include: circuit switching packet switching frame relay Asynchronous Transfer Mode (ATM)
Circuit Switching uses a dedicated communications path established for duration of conversation comprising a sequence of physical links with a dedicated logical channel eg. telephone network
Packet Switching datasent out of sequence small chunks (packets) of data at a time packets passed from node to node between source and destination used for terminal to computer and computer to computer communications
Frame Relay packet switching systems have large overheads to compensate for errors modern systems are more reliable errors can be caught in end system Frame Relay provides higher speeds with most error control overhead removed
Asynchronous Transfer Mode ATM evolution of frame relay fixed packet (called cell) length with little overhead for error control anything from 10Mbps to Gbps constant data rate using packet switching technique with multiple virtual circuits
Local Area Networks smaller scope Building or small campus usually owned by same organization as attached devices data rates much higher switched LANs, eg Ethernet wireless LANs
Metropolitan Area Networks MAN middle ground between LAN and WAN private or public network high speed large area
The Internet Internet evolved from ARPANET first operational packet network applied to tactical radio & satellite nets also had a need for interoperability led to standardized TCP/IP protocols
OSI Reference Model & TCP/IP (Comparison) How many layers that OSI & TCP/IP Model? What are differences between OSI & TCP/IP Model? What are similarities among OSI & TCP/IP Model?
Applications – The Interface Between Human and Data Networks Most applications such as web browsers or e-mail clients, incorporate functionality of the OSI layer 5, 6, and 7. Most TCP/IP applications layer protocols were developed before the emergence of personal computer, GUIs and multimedia objects. A comparison of the OSI and TCP/IP model
Applications – The Interface Between Human and Data Networks There are six steps OSI encapsulation process. 3. Software and hardware convert comm to a digital format2. The app layer prepareshuman comm for 4. App layer services initiate the datatransmission over the data transfer 6. The app layernetwork receives data from the1. People create the network and prepares itcommunication for human use. 5. Each layer plays its role
Roles of Transport Layer Provide services to the adjacent layers Prepare application data for transport over network Process network data for use by applications
Transport Layer Functions Primary Functions: 1. Tracking individual communication between applications on sender and receiver 2. Segmenting data and managing each piece 3. Reassembling segments into streams of application data 4. Identifying the different applications 5. Performing flow control between end users 6. Enabling error recovery 7. Initiating a session
OSI network layer OSImodel layer 3 TCP/IP model Internet layer Application HTTP, FTP, Data stream TFTP, SMTP Presentation etc Application Session Transport Segment TCP, UDP Transport Network Packet IP Internet Data link Frame Ethernet, Network Access WAN Physical Bits technologies
Layer 3 protocolA layer 3 protocol such as IP version 4 must: Provide an addressing scheme to identify networks and individual hosts Encapsulate a segment from layer 4 into a packet and include addresses Direct the packet across one or many networks to the destination host Decapsulate (remove the packet header) and give the segment to layer 4.
Data Link Layer – Accessing the Media It provides a means for exchanging data over a common local media. Also links many upper layer services responsible for packaging the data for communication between hosts. Data Link layer to prepare Network layer packets for transmission and to control access to the physical media.
Physical Layer Protocols & Servicesthe binary digits that The role of the OSI Physical layer is to encode represent Data Link layer frames into signals and to transmit and receive these signals across the physical media - copper wires, optical fiber, and wireless - that connect network devices.
Physical Layer Protocols & Services The delivery of frames across the local media requires the following Physical layer elements: a. The physical media and associated connectors b. A representation of bits on the media c. Encoding of data and control information d. Transmitter and receiver circuitry on the network devices
Physical Layer Protocols & Services There are three basic forms of network media on which data is represented: - Copper cable - Fiber - WirelessThe representation of the bits - that is,the type of signal - depends on the typeof media. Copper cable media, the signals arepatterns of electrical pulses. Fiber, the signals are patterns oflight. Wireless media, the signals arepatterns of radio transmissions..
The TCP/IP Concept Use existing network hardware Interconnect networks Add abstractions to hide heterogeneity
TCP/IPTCP/IP is designed to use all types of networks Connection-oriented Connectionless Local Area Network (LAN) Wide Area Network (WAN) Point-to-point link Set of bridged networks
Examples Of Packet Switched Networks Wide Area Nets ARPANET, NSFNET, ANSNET Common carrier services Leased line services Point-to-point connections Local Area Nets Ethernet Wi-Fi
Summary introduced data communications needs communications model defined data communications overview of networks introduce Internet OSI Reference Model & TCP/IP