Telecommunications and Networks Chapter 6 – Understanding Technology (Third Edition)

William M. Pegram2 Data Transmission Characteristics Bandwidth – number of bits per second that can be transferred over a given medium (broadband vs. narrowband) Analog vs. digital – modems convert digital signals into analog form so that an analog medium (such as a telephone line) can carry these signals; at the other end, modems convert the analog signal back into digital form

William M. Pegram3 Data Transmission Characteristics (cont.) Parallel vs. serial transmission – in parallel transmission, bits are transmitted at the same time, one bit per path whereas in serial transmission, the bits are transmitted one after another Universal Serial Bus (USB) is a type of high-speed serial transmission

William M. Pegram4 Wired Communications Media Twisted-pair cable – telephone lines (“dial up”) Coaxial cable – commonly used for VCR and cable television connections – up to 10Mbps (million bits per second) Note that transmission speeds are given in bits whereas file sizes are normally quoted in bytes Integrated Services Digital Network (ISDN) lines – K (now made somewhat obsolete by cable and DSL)

William M. Pegram5 Wired Communications Media (cont.) Digital Subscriber Line (DSL) – 144K-1.56Mbps, uses existing copper telephone lines Fiber optic cable – light transmitted along string of glass – FIOS, offered by Verizon, is offering speeds in some markets up to 10Mbps upload and 50Mbps download T1 line – digital telephone connections up to 1.54Mbps T3 line – up to 44.7 Mbps - used for ISPs connecting to the internet backbone and the backbone itself

William M. Pegram6 Wireless Communications Media Microwave – stations at line-of-sight intervals Satellite – In geosynchronous orbit (which means they are always over the same point on Earth) – 22,236 miles above earth Cellular Infrared – e.g. wireless keyboard, mouse Wi-Fi – Wireless LAN technology based on the IEEE standards Bluetooth – Short range (e.g feet)

William M. Pegram7 Networks Classified by Architecture Client-server – Networked personal computers, workstations, or terminals (clients) send requests and receive services from another computer (server) Peer-to-peer – Computers in the network have equal responsibilities

William M. Pegram8 Networks Classified by Coverage Local Area Networks (LANs) – private networks with computers located in the same area – LAN uses a special computer, called file server, to house all the network resources; Ethernet is the most commonly used LAN technology Wide Area Networks (WANs) – span two or more LANs Virtual Private Network (VPN) – offices can communicate as if they were within the same corporate network, even though they are using the internet to connect with each other

William M. Pegram9 Networks Classified by Users Intranets – internal users; access to intranet is typically protected by a firewall Extranet – external users have access to internal applications and data via the Internet – usernames and passwords

William M. Pegram10 Network Topologies Bus topology – all computers (nodes) are linked via a single line of cable – all communications travel the length of the bus –Terminator is a device that absorbs signals so they do not reflect back down the line Star topology (hub-and-spoke topology) – computers and devices are linked to a central computer called the host Ring topology – Each computer is connected to two other computers in a circular path

William M. Pegram11 Network and Communications Hardware Hub – Electronic device in older LANs to link computers Switch – Similar to hub, but can inspect data packets and forward to the appropriate destination Repeaters (amplifiers) – increase strength of signals and send along the network Router - used in large networks including the internet, used to connect different networks to ensure messages sent to the correct destination

William M. Pegram12 Network and Communications Hardware (cont.) Gateways – hardware or software that allow communication between dissimilar networks Bridge – hardware or software that allows communication between similar networks

William M. Pegram13 Communications Protocols Hypertext Transfer Protocol (HTTP) Simple Mail Transfer Protocol (SMTP) – sends between servers Post Office Protocol (POP) – retrieves from server, newest version is POP3 Internet Message Access Protocol (IMAP) – retrieves from server Transmission Control Protocol/Internet Protocol (TCP/IP) – host computers on internet File Transfer Protocol (FTP) – allows large files to be transferred over the internet

William M. Pegram14 Directional Protocols Simplex – Communications flow in only one direction Half-Duplex – Communications can flow in both directions, but not at the same time Full-Duplex – Simultaneous transmission in both directions is possible

William M. Pegram15 Determining Stop and Start of Transmission Asynchronous transmission – Each byte is surrounded by control bits – start bit and stop bit – also there is an error checking bit called a parity bit Synchronous transmission – Blocks of bytes are wrapped in start and stop bytes

William M. Pegram16 Wireless Application Protocols Internet Protocol (IP) Wi-Fi ( protocol) –802.11b (up to 11MB) – uses the 2.4 GHz band –802.11a (up to 54Mbps if within 60 feet) – uses the 5 GHz band –801.11g (transfer rates similar to a)- uses the 2.4 GHz band and compatible with b devices –802.11n (up to 74MB) – not approved yet but products sold

William M. Pegram17 NVCC Courses ITN 100 – Introduction to Telecommunications (required for AS in IT degree) ITN 101 – Introduction to Network Concepts