Transcript Telecommunications and Networks

Telecommunications and
Networks
Chapter 6 – Understanding
Technology (Third Edition)
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
2
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
3
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
4
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
5
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
6
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
7
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
8
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
9
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
10
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
11
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
12
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
13
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
14
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
15
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
16
NVCC Courses
• ITN 100 – Introduction to
Telecommunications (required for AS in IT
degree)
• ITN 101 – Introduction to Network
Concepts
William M. Pegram
17