Telecommunications and Networks

Chapter 6 – Understanding Technology (Third Edition)

William M. Pegram 2

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. Pegram 3

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. Pegram 4

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 – 64-128K (now made somewhat obsolete by cable and DSL)

William M. Pegram 5

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. Pegram 6

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

802.11 IEEE standards• Bluetooth – Short range (e.g. 15-20 feet)

William M. Pegram 7

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. Pegram 8

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. Pegram 9

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. Pegram 10

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. Pegram 11

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. Pegram 12

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. Pegram 13

Communications Protocols

• Hypertext Transfer Protocol (HTTP)• Simple Mail Transfer Protocol (SMTP) – sends

email between servers• Post Office Protocol (POP) – retrieves email

from server, newest version is POP3• Internet Message Access Protocol (IMAP) –

retrieves email 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. Pegram 14

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. Pegram 15

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. Pegram 16

Wireless Application Protocols

• Internet Protocol (IP)• Wi-Fi (802.11 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. Pegram 17

NVCC Courses

• ITN 100 – Introduction to Telecommunications (required for AS in IT degree)

• ITN 101 – Introduction to Network Concepts