Tải bản đầy đủ

internet service protocol




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.




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.







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 highspeed 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.









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.








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.







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.




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.








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


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,


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







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.






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.
EMI



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.


Tài liệu bạn tìm kiếm đã sẵn sàng tải về

Tải bản đầy đủ ngay

×