Transcript Chapter 4 - CTAE Resource Network

CCNA Discovery
Chapter Four
By
Chief Eng. Amna Ahmed
Institute of Telecommunication
[email protected]
Chapter 4
Explain what the internet is
 Every day millions of people exchange information through the
Internet - but what exactly is the Internet? The Internet is a worldwide
collection of computer networks, cooperating with each other to
exchange information using common standards. Through telephone
wires, fiber optic cables, wireless transmissions and satellite links,
Internet users can exchange information in a variety of forms.
 The Internet is a network of networks that connects users in
every country in the world. There are currently over one billion
Internet users worldwide.
Internet Service
roviders(ISPs)
 Any home, business or organization
that wants to connect to the
Internet must use an Internet Service Provider (ISP). An ISP is a
company that provides the connections and support to access the
Internet. It can also provide additional services such as Email and web
hosting.

ISPs range in size from small to very large and differ in terms of the area
they service. ISPs may provide limited services to a small geographical area
or can have a wide variety of services and support entire countries with
millions of customers. ISPs also differ in the types of connection
technologies and speeds they offer. Examples of well known ISPs include
AOL, EarthLink, and Roadrunner.
The ISPs Relationship With the Internet
 Individual computers and local networks connect to the ISP at a Point of
Presence (POP). A POP is the connection point between the ISP's network
and the particular geographical region that the POP is servicing.
 An ISP may have many Pops depending on its size and the area it
services. Within an ISP, a network of high-speed routers and switches
move data between the various Pops. Multiple links interconnect the Pops
to provide alternate routes for the data should one link fail or become
overloaded with traffic and congested.
 ISPs connect to other ISPs in order to send information beyond the boundaries
of their own network. The Internet is made up of very high-speed data links
that interconnect ISP Pops and ISPs to each other. These interconnections are
part of the very large, high capacity network known as the Internet Backbone.
 Connecting to the ISP at the POP provides users with access to the ISP's
services and the Internet.
Option for connecting to the Isp
 Ps provide a variety of ways to connect to the Internet, depending on location
and desired connection speed.
 In a major city there are typically more choices for ISPs and more connection
options than in a rural area. For example, cable Internet access is only
available in certain metropolitan areas where cable TV service is available.
Remote areas may only have access via dial-up or satellite.
 Each Internet access technology uses a network access device, such as a
modem, in order to connect to the ISP. It may be built in to your computer or
may be provided by the ISP.
The choice of Internet access technologies depends on availability, cost,
access device used, media used and the speed of the connection.
Most of the technologies shown are used for both home and small business.
Leased lines are typically used for business and large organizations, but can be
used to provide high speed connectivity in areas where cable or DSL are not
available
ISP Levels of Service
 Depending on the ISP and the connection technology, various services are
available such as virus scanning, video on demand, and file storage. The
contract with the ISP determines the type and level of services that are
available. Most ISPs offer two different contract levels: home service or
business class service.
 Home service is normally less expensive than business services, and generally
provides scaled-down services such as slower connection speed, reduced web
space storage, and fewer email accounts. A typical home account may include
a minimum of five email addresses with additional addresses being available
for a fee.
When data is transferred, it is either uploaded or downloaded. Downloading
refers to information coming from the Internet to your computer, while uploading
indicates the reverse path, from your computer to the Internet. When the
download transfer rate is different from the upload transfer rate, it is called
asymmetric. When the transfer rate is the same in both directions, it is called
symmetric




Asymmetric:
Most commonly used for the home.
Download speeds are faster than upload
speeds.
Necessary for users that download significantly
more than upload.
Most Internet users, especially those who use
graphics or multimedia intensive web data,
need lots of download bandwidth.
Symmetric:
 Most commonly used for business or individuals
hosting servers on the Internet.
 Used when necessary to upload large amounts of
traffic such as intensive graphics, multimedia, or
video.
 It can carry large amounts of data in both directions
at equal rates.
Importance of the Internet protocol (IP)
 For hosts to communicate on the Internet, they must be running Internet
Protocol (IP) software. The IP protocol is one of a group of protocols that
are collectively referred to as TCP/IP (Transmission Control Protocol /
Internet Protocol). The Internet Protocol (IP) uses packets to carry data

Each IP packet must contain a valid source and destination IP
address. Without valid address information, packets sent will not reach the
destination host. Return packets will not make it back to the original source.
An IP packet has a header at the beginning which contains the source and
destination IP addresses. It also contains control information that describes
the packet to network devices, such as routers, it passes through and also
helps to control its behavior on the network. The IP packet is sometimes
referred to as a datagram.
IP addresses must be unique on the Internet. There are organizations
responsible for controlling the distribution of IP addresses so that there is no
duplication. ISPs obtain blocks of IP addresses from a local, national or
regional Internet registry (RIR). It is the responsibly of the ISPs to manage
these addresses and assign them to end users.
How ISPs Handle packets
Before being sent on the Internet, messages are divided into packets. IP packet size is
between 64 to 1500 bytes for Ethernet networks, and contains mostly user data
Downloading a single 1 MB song would require over 600 packets of 1500 bytes. Each
individual packet must have a source and destination IP address.
When a packet is sent across the Internet, the ISP determines whether the packet is
destined for a local service located on the ISP network, or a remote service located on a
different network.
Every ISP has a control facility for their network, known as the Network Operations
Center (NOC). The NOC usually controls traffic flow and houses services such as emai
and web hosting
Internet Cloud
A diagram that shows all network devices and their interconnections would
be very complex. Additionally, the final routing path between source and
destination is not usually important, only that the source is able to
communicate with the destination. Therefore, in network diagrams a cloud is
often used to represent the Internet or any other complex network,
Device in Internet Cloud
Devices that provide connectivity to end-users must match the technology
used by the end-user to connect to the ISP. For example, if the end-user is
using DSL technology to connect, the ISP must have a DSL Access Multiplexer
(DSLAM) to accept these connections. For cable modems to connect, the ISP
must have a Cable Modem Termination System (CMTS). Some ISPs still accept
analog calls through modems and have banks of modems to support these
users. ISPs that provide wireless access have wireless bridging equipment.
Common Network Cables
Twisted Pair Cables
Coaxial Cable
Fiber Optic Cables
Cabling Standards
 Cabling standards are a set of specifications for the installation and testing of
cables. Standards specify types of cables to use in specific environments,
conductor materials, pinouts, wire sizes, shielding, cable lengths, connector
types and performance limits.
UTP Cables
 Twisted pair cable is most commonly used in network installations. The
TIA/EIA organization defines two different patterns, or wiring scheme, called
T568A and T568B. Each wiring scheme defines the pinout, or order of wire
connections, on the end of the cable.
Identify and describe the cross-over and straight through cable pinouts
and color codes
UTP Cable Termination
UTP and STP cable is usually terminated into an RJ-45
connector
The RJ-45 jack has eight conductors,
and is wired according to either T568A
or T568B. At the patch panel a device
known as a punchdown tool is required
to push the wires into the connector.
The wires should be matched up to the
appropriate insulation displacement
connector (IDC) by color before
punching them down. The punchdown
tool also cuts off any excess wire.
A punchdown tool is not required to
terminate most wall jacks. To terminate
these connectors the cables are
untwisted
and
placed
into
the
appropriate IDC. Placing the cap on the
jack pushes the cables into the IDC and
cuts through the insulation on the
wires.
Describe how to test cable termination and functionality (Cable testing).
Describe how to test cable termination and functionality (Cable testing).
The cable tester is used to perform initial diagnostics. The first test usually is
called a continuity test and it verifies that there is end-to-end connectivity. It can
also detect common cabling faults such as opens and shorts.
 Attenuation, also commonly referred to as insertion loss, is a general term that
refers to the reduction in the strength of a signal. Attenuation is a natural
consequence of signal transmission over any medium. Attenuation limits the
length of network cabling over which a message can be sent.
 Crosstalk is the leakage of signals between pairs. If this is measured near the
transmitting end it is termed near-end crosstalk (NEXT). If measured at the
receiving end of the cable it is termed far-end crosstalk (FEXT). Both forms of
crosstalk degrade network performance and are often caused by untwisting too
much cable when terminating.
Summary
The Internet is a worldwide collection of computer
networks, accessed through ISPs.
Internet Protocol (IP) controls the structure and
addressing of data packets for transport through the
Internet cloud.
ISP Network Operations Centers (NOCs) utilize highend, high-speed devices with redundancy.
Home networks feature multi-function devices which
perform switching and routing.
Networks use physical cabling media which must
conform to standards in construction and termination.
Cabling best practices are designed to reduce
attenuation and crosstalk.