مقدمة في تقنية المعلومات د. محمد البرواني

مقدمة عن الشبكات مقدمة عن الشبكات

تصنيف الشبكات : التوزيع الجغرافي 5. Geographical Distribution شبكة محلية Local Area Network - LAN شبكة محلية Local Area Network - LAN شبكة واسعة Wide Area Network – WAN شبكة واسعة Wide Area Network – WAN – شبكة المدينة Metropolitan Area Network – MAN

Local Area Network (LAN) A collection of computers that share hardware, software, and data A collection of computers that share hardware, software, and data –Typically personal computers –Typically within an office or building

LAN Components Network cable Network cable Network interface card (NIC) Network interface card (NIC) Router Router Gateway Gateway

Network Cable Provides a way to connect to network Provides a way to connect to network –Low-cost LANs connected with twisted pair wire –Many connected by coaxial or fiber optic cable –Wireless access point connects to wired network Provides wireless connection to network Provides wireless connection to network

Network Interface Card Connects each computer to wiring in the network Connects each computer to wiring in the network –Handles sending, receiving, and error checking of transmitted data Can be a circuit board or PC card Can be a circuit board or PC card Wireless NIC allows user to connect through wireless access point Wireless NIC allows user to connect through wireless access point

Routers Bridge allows connection of similar networks (those using the same protocol) Bridge allows connection of similar networks (those using the same protocol) Router directs communications traffic when several networks connected together Router directs communications traffic when several networks connected together –If network traffic clogged, router can redirect traffic to another route IP switch used in place of router when networks use the Internet protocol IP switch used in place of router when networks use the Internet protocol –Less expensive and faster than routers

Gateway Lets a node communicate with a computer on another dissimilar network Lets a node communicate with a computer on another dissimilar network –Primary function is converting protocol among networks

LAN Protocols Ethernet Ethernet Token Ring Token Ring

Ethernet إيثرنت Uses either bus or star topology Uses either bus or star topology If two computers transmit at same time, collision occurs If two computers transmit at same time, collision occurs Network detects the collision Network detects the collision Each computer waits random amount of time and retransmits Each computer waits random amount of time and retransmits

Token Ring الشارة الدوارة Uses ring topology Uses ring topology Token (electrical signal) controls which node can send messages Token (electrical signal) controls which node can send messages Only one device can access network at a time Only one device can access network at a time

Wide Area Network (WAN) Can span the world or link computers across town Can span the world or link computers across town –Metropolitan Area Network (MAN) - networks that cover a single city Components Components –Communications services –WAN hardware –WAN software

Communications Services Provided by common carriers Provided by common carriers Two general categories Two general categories –Switched –Dedicated

Switched Service Also called a dial-up connection Also called a dial-up connection –Establishes a temporary connection between two points when call is placed –When call is ended, connection is broken Most common is public telephone system Most common is public telephone system

Dedicated Service Provides permanent connection between two or more locations Provides permanent connection between two or more locations –Companies can build their own (microwave, fiber, etc.) –Can also lease circuits from common carrier Called leased lines Called leased lines –Most common leased lines T1 and T3 high-capacity digital lines T1 and T3 high-capacity digital lines DSL or ISDN lines DSL or ISDN lines

WAN Hardware Normally controlled by one or more host processors (typically mainframe computers) Normally controlled by one or more host processors (typically mainframe computers) Host connectors connect to WAN through front-end processor Host connectors connect to WAN through front-end processor Multiplexer combines data from several slow- speed devices into a single data stream for transmission Multiplexer combines data from several slow- speed devices into a single data stream for transmission

WAN Software Terminal emulation software Terminal emulation software –allows PC to emulate mainframe terminal File transfer (FTP) software File transfer (FTP) software –Allows users to upload/download files –Download - to retrieve a file from another computer –Upload - to send a file to another computer