Post on 29-Mar-2015
Basic Computer Network
Bandwidth
Data rate measured in bits (not bytes) per seconds
Kbps (Kilobits per seconds) 125 chars/sec
Mbps (Megabits per seconds) 1,250 chars/sec
Gbps (Gigabits per seconds) 12,500 chars/sec
Connecting to the Internet
Requirement A computer or PDA or cell phone An account with an ISP (Internet Service Provider) A modem (modulator/demodulator) for dial-up
services or a NIC (Network Interface Card) for DSL/Cable services
Home Network (single machine)
USB/Ethernet Cable
DSL/Cable Modem
Wall Jack
Home Network (multiple machines)
USB/Ethernet Cable
DSL/Cable Modem
Wall Jack
Hub/Switch/Router
Home Network (multiple machines)
Ethernet Cable
DSL/Cable Modem
Wall Jack
Hub/Switch/Router
Home Wireless Network
Ethernet Cable
DSL/Cable Modem
Wall Jack
Hub/Switch/Router
Connection Types
LAN WLAN Dial-up Services Broadband Services WAN
LAN (Local Area Network)
A network of computers that are in the same physical location, such as home or building
Usually connected using Ethernet A standard on how computers communicate over
a shared media (cable)
http://en.wikipedia.org/wiki/Image:Ethernet_RJ45_connector_p1160054.jpghttp://en.wikipedia.org/wiki/Image:BNC_connector.jpg
Old: BNC connector for coaxial cable New: RJ45 for twisted pair cable
LAN (Local Area Network)
Ethernet Standard 10BaseT
10Mbps (Mega bits per second) 100BaseT
100Mbps 1000BaseT
1000Mbps or 1Gbps
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Ethernet
First network to provide CSMA/CD Developed in 1976 by Xerox PARC (Palo Alto
Research Center) in cooperation with DEC and Intel Is a fast and reliable network solution One of the most widely implemented LAN standards Can provide speeds in the range of 10Mbps- 10
Gbps Used with a bus or star topology
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Types of Ethernet LANs
10Base-T Operates at 10 Mbps IEEE 802.3 standard
Fast Ethernet (100Base-T) Operates at 100 Mbps
Gigabit Ethernet Operates at 1 Gbps Uses fiber optic cable
10 Gbps Ethernet Latest development of ethernet Uses fiber optic cable Developed to meet the increasing bandwidth needs of the LAN
market Wireless Ethernet
IEEE 802.11 standard Operates at around 2.4 Gbps
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LAN basics
LAN’s can be either wired or wireless. Twisted pair, coax or fiber optic cable can be used in wired LAN’s
Nodes in a LAN are linked together with a certain topology. These topologies include: Bus Ring Star Branching tree
A node is defined to be any device connected to the network. This could be a computer, a printer, a router, etc.
A Hub is a networking device that connects multiple segments of the network together A Network Interface Card (NIC) is the circuit board that has the networking logic
implemented, and provides a plug for the cable into the computer (unless wireless). In most cases, this is an Ethernet card inserted in a slot of the computer’s motherboard
The Network Operating System (NOS) is the software (typically part of the operating system kernel) that communicates with the NIC, and enables users to share files and hardware and communicate with other computers. Examples of NOS include: Windows XP, Windows NT, Sun Solaris, Linux, etc..
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Star Topology Each node is connected to a device in the center of the
network called a hub The hub simply passes the signal arriving from any node to
the other nodes in the network The hub does not route the data
Hub
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Ring Topology The ring network is like a bus network, but the “end” of the
network is connected to the first node Nodes in the network use tokens to communicate with each
other
Backbone
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Access Control Methods
Two primary access control methods exist for computers to communicate with each other over the network Token based access Carrier Sense Multiple Access with Collision
Detection (CSMA/CD)
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Token based access
Used in bus and ring network topologies (token ring) Each computer in the network can only send its data
if it has the token. This prevents collisions that occur when data is sent at the same time over the network
The token is a special pattern of bits/bit in a frame that is directly detectible by each node in the network
A computer may only transmit information if it is in possession of the token
The message is sent to all other computers in the network
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Operation of token ring
As an example, suppose node # 1 wants to send information to node # 4 over the network
Initially, an empty frame (network packet) circulates in the network
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2
3
45
6
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When node # 1 receives the empty frame, it inserts a token in the token bit part of the frame. This operation may just be an insertion of a “1” bit
The node then inserts the message it wants to send as well as the address of the receiving node in the frame
The frame is then successively received and examined by each node in the network. First it is sent to node #2. Node #2 examines the frame and compares the address in the frame to its own address. Since addresses do not match, it passes the frame onto node #3, which does the same thing
When the frame is received by node #4, the address of the node matches the destination address within the frame. The node copies the message and changes the token bit in the frame to “0”
The frame is then sent over to node #5. This node also compares addresses and sends it to node #6 which does the same procedure
When node #1 receives the frame, it examines the token bit and recognizes that it has been changed to “0”. Node #1 then concludes that the message has been received by the intended node: node #4. Node #1 then empties the frame and releases the empty frame back into the network for circulation
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CSMA/CD
Usually used in a bus topology Used in Ethernet LAN’s Unlike the token ring, all nodes can send whenever they have
data to transmit When a node wants to transmit information, it first “listens” to
the network. If no one is transmitting over the network, the node begins transmission
It is however possible for two nodes to transmit simultaneously thinking that the network is clear
When two nodes transmit at the same time, a collision occurs The first station to detect the collision sends a jam signal into
the network Both nodes back off, wait for a random period of time and then
re-transmit
WLAN (Wireless LAN)
Wi-Fi (Wireless Fidelity) A wireless technology that connects computers without
cables Access Point (AP)
A device (base station) that connects wireless devices together
Usually connected to a wired-network ESSID (Extended Service Set ID)
A “name” for the AP, eg. mobilenet Hotspot
The area covered by wireless access points
WLAN (Wireless LAN)
Standard 802.11b - 11Mbps 802.11g - 54Mbps 802.11a - 54Mbps
Security WEP (Wired Equivalen Privacy) WPA (Wi-Fi Protected Access)
2.4G
5G
Dial-up Services
Modem Modulator/demodulator A device that converts analog signal to digital
(modulation) and vice versa (demodulation) Speed
1200/2400/9600 bps 14.4/28.8/33.6 Kbps 56 Kbps
Dial-up Services
ISDN Integrated Services Digital Network 2 data channel (56K each) 1 voice channel
Broadband Services
xDSL (Digital Subscriber Line) A technology that provides digital data transmission over
unused frequencies on traditional telephone lines For example, ADSL (Asymmetric DSL): DL > UL Speed
Downlink 128Kbps - 4Mbps
Uplink 64Kbps - 800Kbps
Need a DSL modem Splitters are needed to separate the voice and data
signal
Broadband Services
Cable A technology that provides digital data transmission over cable
TV infrastructure Speed
Downlink 128Kbps - 3~5Mbps
Uplink 64Kbps - 128Kbps~1Mbps
Need a cable modem
Broadband Services
Satellite A technology that provide digital data transmission over
satellites Speed
Downlink 500Kbps - 1Mbps
Uplink 50Kbps - 100Kbps
Need a satellite dish
WAN (Wide Area Network)
A LAN spans a large geographic area, such as connections between cities
Usually connected using leased line T1 (1.5Mbps) T3 (45Mbps) OC3 (155Mbps) OC12 (622Mbps) OC48 (2.4Gbps)
Fiber optic lines
Telecommunication lines
Hub/Switch/Router
To connect multiple segments of networks into a larger one
Hub A multiport repeater to enhance signal within the
same LAN Switch
Like hub but with intelligent Better performance
Router Forward packets from one LAN to another
Intranet vs. Internet
Intranet A private network that is contained within an
enterprise Could be LANs and WANs
Internet A public network of networks
Both are using TCP/IP
TCP/IP
A family of protocols that makes the Internet works
The Robustness Principle “Be liberal in what you accept, and conservative in
what you send” - Jon Postel
TCP/IP (cont)Application Layer
Eg. WWW, FTP, IRC, Email, telnet, …
Transport LayerEg. TCP, UDP
Network LayerEg. IP
Link LayerEg. Ethernet, WiFi
Physical LayerEg. Ethernet Cable, fiber-optics
Segments
Packets
Frames
Bits
Data
Packets
A small chunk of data transmitted over the Internet
Alice
The Internet
The Internet
Bob
VPN (Virtual Private Network) A secure tunnel to a private network through
a public network Once established, local node appears to be a
node in the private network in a secure manner
Host & IP Address
“A host is a computer connected directly to the Internet”
Each host needs an IP address IP address
A 32-bit number, arranged in 4 numbers seperated by “.”
Eg. 74.125.19.147 10. 168. and 192. ranges of IP address’s are
reserved for LANs
DNS (Domain Name System)
Domain name to IP address conversion Eg. www.google.com → ??.???.??.??
Domain name or IP address lookup http://cqcounter.com/whois/
Top-level Domains
gTLDs (generic TLDs) .com, .edu, .net, .org, .gov, .mil .aero, .biz, .coop, .info, .museum, .name, .pro
ccTLDs (country code TLDs) .au, .ca, .br, .de, .fi, .fr, .jp, .hk, .cn, .tw, .my, … .us
Second-level Domains
Domains that are directly below a TLD Eg.
ucr.edu google.com sony.co.jp
Must apply to a registrar for the appropriate TLD
Domain Names & Registrars
Profitable domain names CreditCards.com - $2.75M Loans.com – $3M Business.com - $7.5M
Network Solutions, Inc used to monopolize the name registration
Now, ~500 registrars
How To Register A Domain Name? Come up a new name 2 name servers’ IP addresses 1 administrative contact 1 technical contact Register the name to an Internet domain
registrar Eg. www.netsol.com, www.godaddy.com
Used to be done via email or fax, now all web-based!
Policies
AUP (Acceptable Use Policies) A legal document, written to protect the ISP from
unlawful use of its service, and outlines prohibited uses of the service and possible consequences of misuse
Privacy Policies A document describes an ISP’s policy for
protecting users’ information
Conclusion
Described how to get connected to the Internet
Talked about the related network technologies and components