3. Data Communications
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Transcript of 3. Data Communications
3. Data Communications
3.4 Internet – Internet Connection
Internet/Intranet The development of the Internet The development of IT as a timeline Difference between intranet and the
Internet Functions of a typical school intranet
The development of the Internet
It was conceived by the Advanced Research Projects Agency (ARPA) of the U.S. government in 1969 and was first known as the Advanced Research Projects Agency Network. The original aim was to create a network that would allow users of a research computer at one university to be able to "talk to" research computers at other universities.
Extracted from whatis.com
The development of the Internet
A side benefit of ARPANet's design was that, because messages could be routed or rerouted in more than one direction, the network could continue to function even if parts of it were destroyed in the event of a military attack or other disaster.
Extracted from whatis.com
The development of the Internet
A global network connecting millions of computers. As of 1999, the Internet has more than 200 million users worldwide, and that number is growing rapidly. More than 100 countries are linked into exchanges of data, news and opinions.
Extracted from pcwebopaedia.com
The development of IT as a timeline
Please refer to the following website
spider.georgetowncollege.edu/infoweb/AcademicSupport/classes/ITClass/Powerpoint/it1/sld007.htm
The development of IT as a timeline
1880s 1930s
1840s
Fax
Telephone
TelevisionTelegraph
1800s 1970s
Satellite
Cellular
Fibre Optics
1950s
Computer
1890s
Radio
Intranet Share information Less expensive to build and manage than private
networks A network based on TCP/IP protocols Belong to an organisation, usually a corporation Accessible only by the organisation’s members,
employees or others with authorisation An intranet’s web sites look and act like any other
web sites The firewall surrounding an intranet fends off
unauthorised access
Functions of a typical school intranet
E-mailing Password Chat room Message board Notice board File cabinet Question database Library service
Internet Connection Essential components:
– Dial-up software– Telephone lines– ISP– Leased lines
Connection services:– ISDN– Cable– ADSL
Dial-up softwareMicrosoft Dial-up program
Reference links: www.download.com, tucows.hkstar.com
Telephone lines
www.techweb.com/encyclopedia/
Registered Jack-11 (RJ-11)
ISPs in HK
HKIX
ISPISP ISP
The Internet
ISP – Internet Services ProviderHKIX – Hong Kong Information Exchange
Leased lines a permanent telephone connection between
two points set up by a telecommunications common carrier.
are typically used by businesses to connect geographically distant offices
always active The fee for the connection is a fixed monthly
rate the carrier can assure a given level of quality
Leased lines a T-1 channel is a type of leased line
that provides a maximum transmission speed of 1.544 Mbps
You can divide the connection into different lines for data and voice communication or use the channel for one high speed data circuit
ISDN Integrated Services Digital Network is an
international communications standard for sending voice, video, and data over digital telephone lines or normal telephone wires
ISDN supports data transfer rates of 64 Kbps two lines at once, called B (bearer) channels one for voice and the other for data, or you can
use both lines for data to give you data rates of 128 Kbps
Detailed references: www.webopaedia.com, www.techweb.com/encyclopedia
ISDN
ISDN
Cable modem A modem used to connect a computer to a cable
TV service that provides Internet access. Cable modems can dramatically increase the
bandwidth between the user's computer and the Internet service provider
Cable modems link to the computer via Ethernet, which makes the service online all the time
the speed will vary depending on how many customers on that cable segment are using the Web at the same time
Cable modem
Cable modem
ADSL Asymmetric Digital Subscriber Line, a new
technology that allows more data to be sent over existing copper telephone lines (POTS).
ADSL supports data rates of from 1.5 to 9 Mbps when receiving data (known as the downstream rate) and from 16 to 640 Kbps when sending data (known as the upstream rate).
TCP/IP A protocol is a set of special rules
governing transmitting and receiving of data between end points
TCP – Transmission Control Protocol IP – Internet Protocol Refer to the handouts of chapter 3.2
for the functions of TCP and IP
IP Address An identifier for a computer or device
on a TCP/IP network The format of an IP address is a 32-bit
numeric address written as four numbers separated by periods.
Each number can be zero to 255. For example, 1.160.10.240 could be an IP address.
IP address classes Class A addresses are for large
networks with many devices. Class B addresses are for
medium-sized networks. Class C addresses are for small
networks (fewer than 256 devices). Class D addresses are multicast
addresses.
Class A IP addresses
Class number
Max. networks
Max. hosts
Network ID (bits)
Host ID (bits)
1-127 127 16777214 7 24
0XXXXXXX.xxxxxxxx.xxxxxxxx.xxxxxxxx
Network ID Host ID
Class B IP addresses
Class number
Max. networks
Max. hosts
Network ID (bits)
Host ID (bits)
129-191
16383 65534 14 16
10XXXXXX.XXXXXXXX.xxxxxxxx.xxxxxxxx
Network ID Host ID
Class C IP addresses
Class number
Max. networks
Max. hosts
Network ID (bits)
Host ID (bits)
192-223
2097151 254 21 8
110XXXXX.XXXXXXXX.XXXXXXXX.xxxxxxxx
Network ID Host ID
Class D IP addresses
1110xxxx.xxxxxxxx.xxxxxxxx.xxxxxxxx
Multicast address
Subnet mask The method used for splitting IP networks
into a series of subgroups, or subnets. The mask is a binary pattern that is matched
up with the IP address to turn part of the host ID address field into a field for subnets.
It's called a mask because it can be used to identify the subnet to which an IP address belongs by performing a bitwise AND operation on the mask and the IP address
Subnet maskE.g. with explanations:Subnet mask: 255.255.255.0(11111111.11111111.11111111.00000000)IP address: 150.215.17.9(10010110.11010111.00010001.00001001)Subnet address: 150.215.17.0(10010110.11010111.00010001.00000000)
Subnet maskE.g. with explanations:Subnet mask: 255.255.240.0(11111111.11111111.11110000.00000000)IP address: 150.215.17.9(10010110.11010111.00010001.00001001)Subnet address: 150.215.16.0(10010110.11010111.00010000.00000000)
Default subnet mask numbers
Class Default subnet mask numbers
A 255.0.0.0 (Dec)
B 255.255.0.0 (Dec)
C 255.255.255.0 (Dec)
Reserved IP addresses 127.X.X.X
– Loop back X.X.X.0
– Network X.X.X.255
– Broadcasting
DNS Short for Domain Name System (or Service), an
Internet service that translates domain names into IP addresses
Because domain names are alphabetic, they're easier to remember
The Internet however, is really based on IP addresses Every time you use a domain name, therefore, a DNS
service must translate the name into the corresponding IP address. For example, the domain name www.example.com might translate to 198.105.232.4.
DNS The DNS system is, in fact, its own
network If one DNS server doesn't know how to
translate a particular domain name, it asks another one, and so on, until the correct IP address is returned
Routers A device that forwards data packets from
one local area network (LAN) or wide area network (WAN) to another
Based on routing tables and routing protocols, routers read the network address in each transmitted frame and make a decision on how to send it based on the most expedient route (traffic load, line costs, speed, bad lines, etc.)
Install TCP/IP
Fig. 1Network
Install TCP/IP
Fig. 2
Add
Install TCP/IP
Fig. 3
Protocol
Add
Install TCP/IP
Fig. 4
TCP/IP protocol
Configure TCP/IP
Fig. 5
Dynamic Host Configuration Protocol (DHCP)
Configure TCP/IP
Fig. 6
IP address
Subnet mask
TCP/IP Utilities ping (Packet Inter-Network Groper)
– This is used to test whether the host is reachable or not.
– ping 10.123.48.173– ping www.yahoo.com
TCP/IP Utilities nslookup (name service lookup)
– This is used to find the web address from the IP address or vice and versa
– nslookup 10.123.48.173– nslookup www.yahoo.com
TCP/IP Utilities tracert (trace route)
– This is used to show the path of the packet which has passed through on its way to destination.
– tracert www.koei.co.jp– tracert www.netvigator.com
TCP/IP Utilities netstat (network statistics)
– This is used to view TCP/IP statistics and the current active TCP/IP connections
– netstat
TCP/IP Utilities ipconfig (IP configuration)
– This is used to list the IP configuration of the current computer
– ipconfig– ipconfig /all
TCP/IP Utilities arp (Address Resolution Protocol)
– This is used to displays and modifies the IP-to-Physical address translation tables
– arp -a
Firewall A firewall is special software or
hardware designed to protect a private computer network from unauthorized access. Firewalls are used by corporations, banks and research facilities to keep information private and secure.
Proxy Server A proxy server stores web contents on
local hard disks so that the next visit of the same web addresses will retrieve faster.