Microprocessor-based systems

1. Microprocessor-based systems Course 11 Computer networks

2. The need for communication networks • The need for communication (data and program exchange) between computer systems • Shared use of computing resources (computers, storage, peripheral devices) • First networks: • DARPA-NET – network for military purposes • Academic networks (Americans) • CERN – inter-networks • Today: • the network is a communication and cooperation infrastructure for the development of distributed applications • A set of small computers (PCs), plus a network is more powerful than a computer and several terminals

3. Classification of networks • Based on the way it is used: • Point-to-point networks, dedicated connection between two devices • Broadcasting networks: communication medium for more equipment • Unicast - one recipient • Multicast - multiple recipients • Broadcast - all network nodes are addressed • Anycast – at least one node is addressed • After stretching area: • Personal Area Networks (PAN) • Local Area Networks (LAN) • Metropolitan Networks (MAN) • Wide Area Networks (WAN)

4. Personal area networks (PANs) • Have a stretch of 1-2m • Intended for interconnection of equipment at an individual phone, PDA, headphones, MP3 player, etc.. • Examples: Bluetooth, ZigBee • Low speed • Wireless connectivity in the frequency of public

5. Local Area networks (LAN) • Interconnect equipment in the same building • Belong to some organizations • Distances: 10m-1km • Speed: 10-100Mbs, 1Gbs • Standard protocols: • Ethernet (CSMA / CD), • Token Ring, • Token Bus • Low error rate • Communication medium: twisted pair or coaxial electrical cable

6. Metropolitan area networks • Interconnected local networks in the territory of a locality or region • Can be private or public • Example: the metropolitan network of universities in Cluj • Distances: 1-10km • Speed: 100kbs-10Mbs-100Mbs • Standard protocols: • DQDB (Double Queue Doubel bus), • ATM, • Frame Relay • Communication medium: fiber optics

7. Wide Area Networks (WAN) • allow transfer of information from very large and diverse places • internet = network of networks • Distances: thousand miles • Protocol: TCP / IP • Speed: 100kbs-10Mbs – 100 Mbs • Example: • Internet • AOL • Geant • RoEduNet

8. Network communication models • the need for a model: to ensure compatibility between equipment and networks, regardless of manufacturer, type, location • ISO-OSI model - Open Systems Interchange • Separating the functions of communication on several layers of abstraction: • 7 layers

9. The OSI model

10. Packaging the message Header Useful content Footer …….

11. Access to the communication services • Each layer offers a set of communication services • There are layers with one type of service (in the Internet the network layer is only IP), or layers with different types of services (e.g. for transport layer: TCP - connection-oriented service and UDP – service with no connection) • Higher layers access lower layer services through access points (service access points) • Two components of the same layer but from different computers communicate as if they are directly connected - logical connection • A communication travels through the entire protocol stack

12. The TCP/IP model compared with OSI

13. ATM model

14. Protocol layers • Physical layer • Physical layer deals with information transmission at the bit. A physical layer protocol must specify: • the nature of the signals used to encode binary data (eg voltage layers, currents, laser beam, etc..), and acceptance layers • electrical characteristics, mechanical performance and transmission medium (electrical cables, optical, radio) • methods to reduce noise and eliminate the influence of transmission errors • type of connectors used • Physical protocol must ensure efficient use of transmission medium, and a transfer rate as large. • Depending on the nature of transmission medium can use different encryption methods and compaction of binary information. • The transmission media used in digital communication are: a. twisted pair cable - is cheap, with the frequency dependent transmission distance, may be shielded or unshielded (UTP - Unshielded Twisted Pair), twisting the two wires of the cable increases noise immunity. b. The coaxial cable - is high bandwidth and high noise immunity, transmission distance is relatively large, there are two ways of using: the basic band (one channel / cable) or broadband (multi-channel / cable ) c. optical fiber - is a transmission medium with high performance parameters (high bandwidth, low delay) has full immunity to electromagnetic noise, on a single optical wireless can transmit many channels

15. Physical Layer • Communication media: • Twisted pair cable (UTP) • Coaxial cable • Fiber Optic • Radio • IR transmission • Topology: • Star • Ring • Bus • Tree • graph

16. Data Link Layer • Role: • Structuring data within packages • Providing a secure communication channel • Detecting transmission errors • The parity bits, checksum, CRC • Types of services: • unconfirmed service without connection • confirmed service without connection • confirmed the connection-oriented service • Examples: • HDLC protocol (High Data Link Control) • SLIP protocol (Serial Line Internet Protocol) • Unaltered IP packets for transmission (Internet) • PPP (Point-to-Point Protocol)

17. Access mechanisms to the communication environment (MAC – sub-layer) • Layer used for local area networks where the same medium is shared by multiple nodes • Access control: • Centralized • Distributed • Classification of access methods

18. Network layer • Role: routing messages • Solutions: • Circuit switching - phone system • Packet Switched • Routing algorithms: • The shortest path routing • Flooding algorithm (flooding) • Flow-based routing • Vector-distance routing • Hierarchical routing • Network layer on the Internet – IP (Internet protocol) • The network is organized around three hierarchical levels: • high-speed network that makes up the backbone of the system (backbone) • regional networks (Europe, America, Asia, ..) • academic networks, government, companies, ISPs, etc.. • The IP addresses: 4 bytes, 232 possible addresses – not enough

19. Ap1 Ap2 Ap n Transport layer • Role: creates a secure channel of communication on an uncertain environment • It makes a logical connection between remote applications (like a dedicated pipeline for the two applications) • Transport layer on the Internet: • TCP – connection-based transport protocol • UDP - connectionless transport protocol • Operations performed: • reordering messages in order to respect the initial order • re-transmits erroneous messages • eliminates duplicate messages • It uses the message confirmation technique • Packets are numbered to keep track of their order • Connection is done through sockets (Socket) • Socket = port + IP address Ap1 Ap2 Apn Internet

20. Other OSI layers • Session Layer: • responsible for controlling the sequence of dialogue between the two applications that communicate with each • handles authentication dialog between partners by checking the access passwords • Presentation Layer: • It deals with issues concerning coding-decoding for data security • Application level: • offers various models and communication interfaces for user applications: • - Network virtual terminal (eg TELNET) • - File transfer (eg FTP) • - Email (eg SMTP) • - Remote execution of procedures (RPT) • - Network management (eg SNMP) • - Web browsing, etc..

21. Other Application layer protocols - DNS (Domain Name System) - is a service that allows addressing messages based on symbolic names, the protocol allows transformation of symbolic names for network addresses (IP addresses) - NFS (Network File System) - is a mapping service that allows remote file folders in your local directory, this service provides a uniform access to files regardless of their location - NIS (Network Information System) - is a service providing resource information contained in the network, such applications can be identified, gateway services, etc.., Resembles the "yellow pages" published to identify firms and services they provide - RPC (Remote Procedure Call) - is a protocol through which applications can be launched remotely or procedures, the Protocol provides the procedures and appeal mechanisms for transmitting call parameters, many network applications are based on an RPC mechanism - WWW (World Wide Web) - is a distributed information service that allows searching of information through various databases across the network in Internet, information is organized in the form of pages, a page can contain text, pictures, small applications ( applet's) and especially links to other sites containing similar information, search information is through programs of "navigation" (eg Netscape, Internet Explorer, etc.). is writing pages using HTML and protocol HTTP communication is used.