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In simple terms
a computer network is a series of computers and devices appearing
as a single system to the user. Networks have become popular and
useful because of the ability to distribute the computer workload
over several machines and to provide and store information on several
machines.
- LAN
- Local Area Network is used to connect computers and share
data. Local means in the same building or near enough to be connected
by cable. LANs are capable of transmitting data at very high
speeds.
- VLAN - Virtual LAN is a network of computers that behave as if they are connected to the same wire, though they may actually be physically located on different segments of a LAN.
- WAN
-Wide Area Network where connections are made using high
speed phone lines. A good example of a WAN is the Internet.
- WLAN - Wireless Local Area Network where a group of computers and associated devices can communicate with each other wirelessly.
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Protocols are
a set of standards that define how each computer identifies itself
within the network. The protocol also defines the data format
and how the data should be processed once it reaches its destination.
Data is transferred in "packets".
- TCP/IP (Transmission Control Protocol/Internet Protocol).
This is the most common protocol and is used by Unix/Linux/Windows
based machines. The Internet also relies on TCP/IP.
- FTP (File Transmission Protocol), An application for sending files between computers over a TCP/IP network and the Internet.
- HTTP (HyperText Transport Protocol) The communications protocol used to connect to servers on the World Wide Web.
- DHCP (Dynamic Host Configuration Protocol) A protocol that lets one device on a local network, known as a DHCP server, assign dynamic IP addresses to the other network devices, typically computers.
- RTP (Real-time Transport Protocol) A protocol that enables specialized applications, such as Internet phone calls, video and audio, to occur in real time.
- SNMP (Simple Network Management Protocol) A widely used network monitoring and control protocol.
- Telnet A user command and TCP/IP protocol used for accessing remote computers.
-
NetBEUI, created
by Microsoft for Windows, is mainly used in a small peer-to-peer
Windows only network.
- IPX
is used to network Novell servers.
- AppleTalk
used by Apple machines.
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Ethernet
(IEEE 802.3) is the most popular technology used for networks.
Ethernet provides a good balance between speed, price and ease of
installation and is the most popular LAN technology in use today.
It supports speeds up to 10Mbps.
Fast Ethernet (IEEE 802.3u) is replacing Ethernet and support speeds up to 100Mbps.
Gigabit Ethernet (IEEE 802.3z & 802.3ab) supports data transfer rates of 1000Mbps.
Other LAN types are...
- Token
Ring
- FDDI
(Fiber
Distributed Data Interface)
- LocalTalk
Mbps (Megabits per second) represents one million bits per second, a unit of measure for data transmission.
IEEE (Institue of Electrical and Electronics Engineers) An international non-profit, professional organization directed toward the advancement of theory and practice of electrical, electronics, communications and computer engineering. Boy, what a mouthful!
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Topology
is the method in which a network method is configured.
Each device on the network, typically a computer or server, is called a node. Nodes on an Ethernet
network are connected either by Bus or Point-to-Point
topology.
- The Bus
method consists of nodes connected to a long cable in a series.
Any break in the long cable will cause the
entire series to be inoperable.
- The Point-to-Point
topology connects exactly two nodes together.
If a break occurs in a Point-to-Point, only the two node links are
affected, not the entire network. Point-to-Point normally
uses 10BaseT, 100BaseT or 1000BaseT cabling and is the recommended
topology.
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There are four
major types of cable...
- Thickwire
/ 10BASE5
is typically used to join smaller network segments
into one large LAN.
- Can support
up to 100 nodes and a distance of 500m
- Used because
of its immunity to electrical noise.
- Requires
heavy coaxial cable which is expensive and difficult to work
with.
- Each node
must be exactly 2.5m apart and is connected by tapping into
the wire with a special tool.
- Best used
as a backbone for a BUS topology network.
- Thin
Coax / 10BASE2
is thinner, more flexible and cheaper than Thickwire.
- Can support
up to 30 nodes that must be at least 0.5m but no further
than 185m apart.
- Nodes are
connected using a BNC connector.
- Best used
to connect departments or areas to the backbone of a BUS topology
on the network.
- Twisted
Pair / 10BASET / 100BaseT / UTP / Cat5 /
Cat6
is similar to telephone cable and is the most popular
and recommended.
- Inexpensive
- Used with
Point to Point topology and is limited to 100m per each
segment.
- Most
important if you are using a 100BaseT or greater configuration you should
have the cable certified.
- Click here for more information on CAT cables.
- Fiber
Optic / 10BASE-FL
is used basically the same way as Twisted Pair
- More expensive.
- Effectively
insulates the network from lightning strikes and other electric
interference.
- Node connections
can be up to 2km long and can handle higher speeds of
data transmission.
- Should
be used when connecting two buildings or if you have an environment
with large amounts of electromagnetic interference.
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Transceivers, also
referred to as MAUs (Media Attachment Units) provide an AUI (Application
User Interface) connection to the computer. In simple terms, it
is used to convert the connector type from an RJ45 to AUI.
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Repeaters are
used to connect any type of cable. They basically provide extra
signal strength when you exceed the length limits. Data is transmitted
near the speed of light on a network and the timing of transmitted
data is crucial. Because of this, the path between
any two nodes can't contain more than four repeaters.
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Routers and Bridges
are used to split networks that become too large. These devices
differ from repeaters by their capability to store and forward
data to each network when they sense the network is available. Thus
preventing timing problems.
A Bridge connects two different kinds of local networks, such as a wireless network to a wire Ethernet network.
A Router connects multiple networks together, such as a local network and the Internet.
A Gateway interconnects networks with different, incompatible communication protocols.
A Default Gateway is the device that forwards Internet traffic to your internal network
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Switches
Switches are devices that connect computing devices to host computers, allowing a large number of devices to share a limited number of ports.
An unmanaged swtich is a basic switch that works right out of the box and does not allow the user remote network administration capability.
A managed switch has an IP address that lets you monitor and administer your network.
Layer 2 is an OSI (Open Systems Architecture) device, the data link layer; this layer is responsible for moving data across the physical links in a network.
Layer 3 is an OSI device that determines network addresses, routes and quality of service for information transport. A router is a Layer 3 device and switches can also have Layer 3 capability.
QoS (Quality of Sevice) is a mechanism which gives priorities to certain types of traffic to ensure the throughput. For example, streaming multimedia.
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Servers are devices
which allow the use of terminals, printers and modems to be connected
to the network. For example you can connect a Server to a node
along with several terminals or printers. Servers offer the benefit
of data not having to travel over the entire network. If you are printing
to a printer connected to the same server as your terminal, the data
is transmitted within your "domain" or server segment. Thus
reducing the network load.
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Because companies
are adding new locations, have employees in the field or working from
home, the need to talk to the "corporate" computer has
become a necessary requirement.
This article is
going to address the different configurations that are possible and
touch upon some solutions. Because of the complexity, each solution
could be an article in itself, but the intent of this article is to
introduce you to the capabilities and methods.
As
you will see...
- depending on
where you are connecting from
- what you are
connecting to
- what
you want to do once you are connected
- will influence
and dictate what options and methods you will want to use.
There are
three main types of remote connections. There are situations
where a remote connection may require the need of more than one
type of connection.
Character Based
This is
a connection where you are only using a CRT (dumb terminal),
i.e. not a PC, to "log in" or telnet/SSH to a UNIX/Linux
based system. You may already be using this type of connection.
This connection type can only run "character based"
applications and NOT Windows or graphical based applications.
It is possible
to make this type of connection using a dumb terminal emulator
running on a PC. The emulator basically turns your PC back into
a dumb terminal and emulates a specific brand CRT such as Wyse,
TeleVideo, Esprit, etc.
Some examples
of emulators are CROSSTALK, Bitcom, TinyTerm, and
PowerTerm.
Send/Receive
Data Only
This type
of connection is most commonly used to transmit EDI or E-Mail
data. The connection can be made upon demand or on an automated
basis. Customized program scripts, that run behind the scenes
(i.e. background mode) are usually used to automate the
sending and/or receiving of data once the connection is established.
An example
of software tools used in this type of connection are SMTP and FTP. FTP is currently the most common and reliable method.
This connection
type is also used to transmit data files from a PC to, perhaps,
your notebook computer.
Network
Connection
Network
communications can include running "character based"
applications, Windows or graphical applications
or simply transmitting data. Using a browser to access the Internet is an example of a remote network connection.
There are
basically three different types of situations that may require
remote connections. Each of these has their own unique sets of
problems and solutions.
Fixed Site
This situation
is where you have more than one office, plant or warehouse.
The distance could be across town or in another city. Basically
any distance that doesn't allow you to run your own cable, but
requires the use of phone lines. Usually a "dedicated"
connection such as ISDN, DSL or a T1 line.
Mobile Site
This represents
a situation where you are connecting from different locations
each time. An example would be where sales agents are traveling
to different customer sites and making a connection from the
customer's site or a hotel room. A computer, modem or Internet connection and appropriate
software is required to make the connection.
Home Site
This situation
is similar to the "fixed" connection. At the minimum,
it will require a computer and an Internet connection.
Depending
on the type of computer system you are connecting to, different
equipment and software will be required at both ends.
UNIX/Linux System
If you are
connecting to a UNIX system, you are probably using a "character-based"
application. If you are making the connection to run the character-based
application you only need a dumb terminal or a PC using emulator
software and using SSH for a secure connection..
Windows System
If you are
connecting to a computer running Windows, you
will need special communications software at both ends, i.e.
Host and Remote. The computer you are connecting from is the
"Remote". The computer you are connecting to is the
"Host".
Examples
of communication software for this purpose are VNC, pcAnywhere,
Carbon Copy, Citrix and Windows Terminal Server.
Via
Internet
This would
require that your main computer has a dedicated connection to
the Internet.
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Choosing the correct
phone line type depends on the
- Length of the
connection
- How much data
will be transferred
- How fast you
want data transferred.
Basically the
higher the speed that can be transmitted, the higher the cost.
Currently, there
are several methods that one can use to connect to the Internet. The
different options vary in speed, cost, reliability, and availability.
The goal for your company's Internet connection is to obtain
the highest speed at the lowest cost. Seems simple? Well,
not always.
In case the abbreviations
used in this article confuse you, and they will, we have provided
a handy definition list at the end of this
article.
Integrated
Services Digital Network (ISDN)
accommodates speeds at either 64 or 128 Kbps. It works with data,
voice and video signals.
- Method:
Dedicated line with 1 or 2 channels at 56Kbps per channel.
- Speed:
Maximum of 128Kbps with 2 channels.
- Availability:
90% coverage.
- Cost:
$50-$400 to depending on type of service. Can be set at a fixed
rate or variable depending on usage. Can require a 1-year contract.
- Other
Requirements: Router and/or ISDN modem. Account with
an ISP.
- Pros:
Cost, availability, reliability, can
be fixed rate..
- Cons: Operates in half-duplex mode
- Method:
Uses copper pair wiring. sDSL provides the same transfer
speed for uploading or downloading. aDSL provides a faster download
speed but slower upload.
- Speed:
Speeds are quoted as up to a specific
rate. No assurance you will actually get the highest speed. Actual
performance can result in a 70% loss.
- Availability:
Limited
- Cost:
Depending on the speed, $50-$125/month.
- Other
Requirements: Need to be within 18,000 feet of CO, Router.
- Pros:
Faster and cheaper than ISDN, fixed monthly rate, easy set-up.
- Cons: Operates in half-duplex mode
Cable - DSL (Digital Subscriber Line)
Communications
are available over the same cable as used for cable TV. This can
provide a high speed connection. The downside of cable is the
fact that it is a shared line. The more people in your area that
have cable, the slower you connection becomes.
- Method:
Uses the same cable as cable TV.
- Speed:
Maximum is 10,000Kbps for download, 128-256Kbps upload. Because
the cable line is shared with others, speed can vary.
- Availability:
Limited.
- Cost:
$50-$300/month.
- Other
Requirements: Cable modem. (Usually supplied by cable
supplier)
- Pros:
High speed, low cost, fixed rate, easy set-up.
- Cons:
Availability, perhaps slower speeds as more users sign up. May not be able to get a dedicated IP address. Operates in half-duplex mode
- Method:
Dedicated line with up to 24 channels. Each channel provides
64Kbps
- Speed:
1,500-2,000Kbps
- Availability:
Almost everywhere
- Cost:
$375 - 1500+ month
- Other
Requirements: Routers, DSU/CSU
- Pros:
High speed, very reliable, fixed rate. Operates in full-duplex mode
- Cons:
Expensive
Half Duplex: Data transmission that can occur in two directions over a single line, but only one direction at a time.
Full Duplex: Has the capability to receive and transmit data simultaneously.
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If you decide
to discuss options with an ISP or phone company, you will discover
that they speak a strange language. To help you learn this new language;
here are a few commonly used buzz-words.
- Kbps:
Thousand bytes per second.
- POTS:
Plain old telephone service. Standard analog phone line.
- DSL:
Digital Subscriber Line
- sDSL:
Symmetrical Digital Subscriber Line. Same speed both directions.
- ISDN:
Two 64Kbps channels that can be combined for a maximum of 128Kbps.
- ISP:
Internet Service Provider
- CPE:
Customer Premises Equipment. Catch-all term for your connection
equipment.
- CO:
Central Office - Aggregation point for all phone lines in a given
area.
- RBOC:
Regional Bell Operating Company. Monopolies created during the breakup
of the Bell System in 1983.
- ILEC:
Incumbent Local Exchange Carrier. A RBOC that typically owns the
last mile of copper phone line and local exchange.
- CLEC:
Competitive Local Exchange Carrier. A company that competes with
an ILEC by supplying their own network and switching services.
- FCC:
Federal Communications Commission. Busy bodies.
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Glossary
The terms are
listed in a logical manner on how they relate to each other instead
of alphabetically.
Packets
Basically,
when your machine connects to a network, either locally or on
the Internet, data is transmitted in packets. Packets are
groups of information that contain a message and address
information.
Messages
could contain an E-mail message, login and password, web site
address, data, etc.
Address
contents contain destination and source information, i.e. routing
information. The routing information controls who should get
the message, who sent the message and should there be a response.
Visualize a super highway where each vehicle represents a packet
containing information, i.e. messages. The driver knows where
to deliver the message by the address information and what to
do with the message based on routing information.
So that everyone
follows the same methods and so that computers can talk to each other,
protocols or rules have been established.
ICMP (Internet Control Message Protocol) is used to communicate IP
status and error messages between hosts and routers.
ARP (Address
Resolution Protocol) is the protocol used to dynamically map
internet addresses to a physical hardware device.
PPTP (Point to Point Tunneling Protocol) is a VPN protocol that allows Point to Point Protocol to be tunneled through an IP network.
RARP (Reverse Address Resolution Protocol) is used by a host computer
to obtain an IP address based on the address of the host's network
card.
RIP (Routing
Information Protocol) is basically used between main host machines
to re-direct or route traffic to the correct location. Somewhat
like exit ramps on the superhighway.
Hosts:
When you connect to a local server or make a connection on the
Internet, you are connecting to a host computer. Host computers
can be identified or accessed by either a domain name or IP address.
Domain
is a element of the naming hierarchy used on the Internet.
Domain Name is a unique name that identifies a host site,
either on an Internet or local Server site.
An example
of a domain name would be www.AHinc.com
An example of a domain would be AHinc
DNS (Domain
Name Server) is used to translate from the Domain Name to
an IP address. The Domain Name is like your personal name and
the IP address is like your social security number. If there was
a DNS that contained both pieces of information, by providing
your name, your social security number could be found. The main
difference is there are people with the same name, but a Domain
Name has to be unique.
Because passwords
and other confidential data are sent over a network, security methods
must be employed to prevent snoopy people from reading stuff that
doesn't belong to them.
Authentication is a process by which a user's identity is checked within the
network.
Encryption
is a type of network security used to encode data so that only
the intended destination can access or decode the information.
AES (Advanced Encryption Standard) that uses up to 256-bit key encryption to secure data or symmetric 128-bit block data encryption.
DES (Data
Encryption Standard) is a cryptographic algorithm method developed
by the US National Bureau Standards.
SSL (Secure Socket Layer) is an application layer security protocol used to provide authentication and communication privacy of data transmitted over the Internet.
PAP (Password
Authentication Protocol) and CHAP (Challenge Handshake
Authorization) (yep, were back to more protocols) are
used to identify and authenticate a user and their associated
password.
RADIUS (Remote Authentication Dial-in User Service) is a protocol that uses an authentication server to control network access.
VPN (Virtual Private Network) is a security measure to protect data as it leaves one network and goes to another over the Internet.
IPSec (Internet Protocol Security) is a VPN protocol used to implement secure exchange of packets at the IP layer.
ACL (Access Control List) is used within a network security system to allow selective use of services. In the case of NAS usage, an ACL is used to control access to or denial of files or volumes. A list associated with an AFS directory specifies the actions a user or group is permitted to perform on a directory and its files.
Firewall
- A firewall can consist of either a hardware device or software
or combination of both. It is used to divide a network into separate
parts for security reasons. Thus, it won't allow someone beyond
the firewall, i.e. first part of the network, unless they have
authorization. This prevents unauthorized users from gaining access to a computer network or that monitor transfers of information to and from the network.
SPI (Stateful Packet Inspection) is a firewall technology that inspects incoming packets of information before allowing them to enter the network.
DMZ Demilitarized Zone that removes the router's firewall protection from a computer, allowing it to be seen from the Internet.
DoS (Denial of Service) defines a type of attack designed to prevent legitmate users from accessing a resource by overwhelming that resource with useless and malicious traffic.
Intrusion Attack is a type of Internet attack in which an attacker tries to gain access to the information transmitted through the network.
Intrusion Prevention System is a mechanism to detect malicious software, such as Internet worms, Trojan Horses and DoS that can't be detected by a conventional firewall.
Wireless
Access Point is a device that allows wireless-equipped computers and other devices to communicate with each other and with a wired network.
802.11a Wireless network standard with a maximum data transfer rate of 54Mpbs in the frequency range of 5GHz. It has a greater bandwidth that 802.11b but a shorter range.
802.11b Wireless network standard with a maximum data transfer rate of 11Mpbs in the frequency range of 2.4GHz.
802.11g Wireless network standard with a maximum data transfer rate of 54Mpbs in the frequency range of 5GHz and backward compatibility to 802.11b devices.
802.11n Wireless network standard with a maximum data transfer rate of 300Mpbs in the frequency range of of 2.4 or 5GHz and backward compatiblity to 11a, b and g devices.
DTIM (Delivery Traffic Indication Manager) is a message included in data packets that can increase wireless efficiency.
SSID (Service Set Identifier) Your wireless network's name.
WEP (Wired Equivalency Protocol) is a security protocol for wireless networks. WEP aims to provide security by encrypting data over radio waves so that it is protected as it is transmitted from one end point to another. A shared key (similar to a password) is used to allow communication between computers and the router. WEP is fairly easy for hackers to crack and has mainly been replaced by WPA.
Wi-Fi is a brandname of the Wi-Fi Alliance used to describe wireless (WLAN) technology based on the 802.11 standards. Wi-Fi Alliances is a trade group that performs testing, develops specifications, certifies interoperability of products and promotes wireless networking technology, The Wi-Fi Alliances owns the trademark to Wi-Fi.
WPA (Wi-Fi Protected Access) is a security protocol for wireless networks that builds on WEP. It secures wireless data transmission by using akey similar to WEP with the added strength is that key changes dynamically. The changing key makes it much more difficult for a hacker to learn the key and gain access to the network.
WPA2 is the second generation of WPA security and provides a stronger encryption mechanism though AES.
WPA Personal is a version of WPA that uses long and constantly changing encryption keys to make them difficult to decode.
WPA Enterprise is a version of WPA that uses the same dynamic keys as WPA Personal and also requires each wireless device to be authroized according to a master list held in a special authentication server.
Bandwidth is the transmission capacity of a given device or network. Think of as lanes on the highway. The more lanes, the greater the bandwidth and the amount of traffic that can be sent or received.
Broadband is an always-on fast Internet connection.
Cookie is a piece of information sent by a Web site to your Web browser.
Your system saves the piece of information and is expected to
send it back to the server whenever it is requested.
This technique
seems innocent enough at the first look, but can be a source of
getting a virus. I have my browser set to notify me of any cookie
before accepting it. If I am viewing a web site that I am not
familiar with or don't trust, I don't accept the cookie.
Hop
is the data link between two gateways.
MAC (Media Access Control) is an unique address that a manufacturer assigns to each networking device.
NAT (Network Address Translation) os a technology that translates IP addresses of the local area network to a different IP address for the Internet.
PoE (Power over Ethernet) is a technology enabling an Ethernet network cable to deliver both data and power. This elimanates having to plug the unit into a AC power outlet.
Ping (Packet Internet Groper) is an Internet utility to determine whether a particular IP address is online.
Subnet Mask is an address code that determines the size of the network. A common network mask is 255.255.255.0.
VOIP (Voice over Internet Protocol) that enables people to use the Internet to transmit packets of voice data using IP rather than traditional circuit transmissions.
Are your eyes
glazing over yet? Ok, that's enough for today.
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