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Network Technology and the Internet Unit E Communications Network The combination of hardware, software and connecting links that transport data (which is encoded, sent to it’s destination and decoded) Noise Encoded Data Source Signal Communications Channel Transmitter Decoded Data Receiver Destination Communications Network Source generates data, e.g. a microphone. A signal is the physical representation of a certain information. Signals can be analog or digital. Analog signals can have an infinite number of values in a range; digital signals can have only a limited number of values. Communications Network Transmitter converts the data into electrical signals A communication channel, or link, is the physical path for signal transmission from one point top another. Noise is any polluting signal. Receiver recovers the data. Bandwidth of a channel is the transmission capacity of a communication channel. Example a fiber optic cable can transmit up to 20 trillions of bits per second, or 2 Gbps. Communications Network Communications system = communications network. There are two categories of communications channels: wired and wireless. Data in wired network travels from one device to another over cables. Data in wireless networks travels through the air. Communication Channels Node: each device connected to network Communications channel: physical path for signal transmission from one node to another – Wired – Wireless Wired Communication Channels Twisted-pair cables (phones) – STP: shielded twisted pair – UTP: unshielded twisted pair for small networks UTP is probably the most commonly used transmission medium (or channel) for small networks. Wired Communication Channels Coaxial cable (television) – High capacity Wired Communication Channels Fiber-optic cable :thin tubes of glass that transport light. Wireless Communication Channels RF: radio frequency signals are sent and receive by a transceiver with antenna. RF signals provide data transport for small home networks, campus networks, and business networks. Microwaves – More capacity than radio waves – Need clear path between transmitter and receiver – Cannot penetrate metal objects Bandwidths The transmission capacity of a communications channel measured in bps (bits per second) Low-bandwidth carries less data than high bandwidth – Telephone – Narrowband High-bandwidth – Coaxial cable – DSL lines – Broadband Types of Networks Internet: global, public Internetwork (internet): is a network that is composed of many smaller networks. An Intranet is a private network that provides many of the same services as the Internet, but has to differences; – A intranet is owned by a private business – Typically an intranet does not provide remote access Types of Networks An extranet is similar to an intranet, except that it allows password-protected access by authorized outside users http://webmail.barry.edu/ A WAN (Wide Area Network) covers a large geographical area and may consists of several smaller networks. The Internet is the largest example of a WAN. A MAN (Metropolitan Area Network) is a public high-speed network capable of voice and data transmission within a range of 80 km. A LAN (Local Area Network) is a network that typically connects PCs within a very limited geographical area, usually a single building. Network Topology A physical topology refers to the layout of devices, wires, and cables on a network. A logical topology refers to the way messages flow. 5 common topologies named for their shapes – Star (central connection point) – Ring (connects devices in a circle) – Bus (common backbone) – Mesh (each device connected to others) – Tree (blend of star and bus) Network Topology Star topology Ring topology Network Topology Bus topology Mesh topology Network Topology Tree topology Network Topology Star Bus Ring Interconnecting Networks Two similar networks can be connected by a bridge – Transfers data without regard to format Router – Electronic device that connects 2 or more networks Gateway – A device or software used to join dissimilar networks by making data compatible Network Hardware Overview Network Hardware Server (also called host computer) – Distribute resources to network users – Contains network management software and files Workstation (also called client) – PC on a LAN – Client is software that lets it talk to server Network Hardware Network Interface Card (NIC) – Example: Ethernet card Connection Devices – Modem: converts PC digital signals – Hub: connects nodes on a LAN – Router: decides best way to route data on network – Gateway: entrance to another network – Repeater: amplifies and regenerates signals Network Addresses Physical address: – Every node has one – Built into circuitry of network device Logical address: (Network address) Transporting Data The way data is transported over a network depends on network topology, the packet switching technology, and protocols. Protocols are rules that ensure the orderly and accurate transmission and reception of data. PROTOCOL MAIN USE TCP/IP Internet NetBIOS/NETB Microsoft EUI networks AppleTalk Macintosh networks IPX/SPX Novell networks Transporting Data When you send a file or an e-mail message over a network, the file is actually broken up into small pieces called packets. A packet is a piece of data that is sent across a computer network. Packet Switching Technology determines how data is broken up so that it can be transported over a network. Packet Switching Technology Packet is a parcel of data on network or a file broken into small, equal size pieces Contains – – – – Sender address Destination address Sequence number Data Packet switching: packets sent independently of each other Communications Protocol Allows two devices to negotiate and agree on how data will be transmitted TCP/IP – Transport Control Protocol/Internet Protocol – Most common – TCP: breaks data into packets – IP: addresses packets Controlling Direction of Data Flow Simplex: one direction (TV) Half duplex: can send and receive data, but not at same time (CB radio) Full Duplex: can send and receive data at same time on same channel (Telephone) IP Addresses ISP gives unique IP address to subscriber Series of numbers in 4 parts – 204.127.129.001 Static IP address: permanent, usually servers Dynamic IP address: temporary, for one session Network Technology and the Internet End