A few back haul providers comprise the
high-speed backbone of the Internet.
Only a handful of these providers are
capable of handling the massive
amounts of Internet traffic that continues
to grow. Many parts of the back haul
providers overlap with each other, which
improves both the speed and reliability
of the network. 28
IT Certification CCIE,CCNP,CCIP,CCNA,CCSP,Cisco Network Optimization and Security Tips
Web Servers
Web Servers
All web pages are stored on computers
called web servers. Thousands of these
servers can be dedicated servers for
companies, hosting servers that house
many personal pages, or even single
computers housing individual pages.
All web pages are stored on computers
called web servers. Thousands of these
servers can be dedicated servers for
companies, hosting servers that house
many personal pages, or even single
computers housing individual pages.
Domain Name Server (DNS)
This server maps domain names to
their IP addresses. One of the reasons
that the Internet has taken off in use and
popularity is because www.cisco.com
is much easier to remember than
25.156.10.4.
their IP addresses. One of the reasons
that the Internet has taken off in use and
popularity is because www.cisco.com
is much easier to remember than
25.156.10.4.
Access Providers
The web is really made
of many networks connected
in a hierarchy. Local Internet
service providers (ISPs) typically give
residential and small business access
to the Internet. Regional providers
typically connect several local ISPs to
each other and to back haul providers
that connect with other regional
providers.
of many networks connected
in a hierarchy. Local Internet
service providers (ISPs) typically give
residential and small business access
to the Internet. Regional providers
typically connect several local ISPs to
each other and to back haul providers
that connect with other regional
providers.
Extra Layers?
Discussions among technical purists can often lead
to philosophical or budgetary debates that can
quickly derail otherwise-productive meetings.
These discussions are often referred to as Layer 8
(political) and Layer 9 (financial) debates.
Although these layers are not really part of the
OSI model, they are usually the underlying cause
of heated technology arguments.
Another common joke among networking professionals
is the type of networking problem referred
to as a “Layer 8 issue.” Because the network, computers,
and applications stop at Layer 7, Layer 8
sometimes represents the end user actually using
the system. So if you hear your IT person snicker
to his colleagues that your IT trouble ticket is
closed and it was a “Layer 8 issue,” the IT person
is referring to you.
to philosophical or budgetary debates that can
quickly derail otherwise-productive meetings.
These discussions are often referred to as Layer 8
(political) and Layer 9 (financial) debates.
Although these layers are not really part of the
OSI model, they are usually the underlying cause
of heated technology arguments.
Another common joke among networking professionals
is the type of networking problem referred
to as a “Layer 8 issue.” Because the network, computers,
and applications stop at Layer 7, Layer 8
sometimes represents the end user actually using
the system. So if you hear your IT person snicker
to his colleagues that your IT trouble ticket is
closed and it was a “Layer 8 issue,” the IT person
is referring to you.
De-encapsulation
De-encapsulation, the opposite of encapsulation, is
the process of passing information up the stack.
When a layer receives a PDU from the layer below,
it does the following:
1. It reads the control information provided by
the peer source device.
2. The layer strips the control information
(header) from the frame.
3. It processes the data (usually passing it up the
stack).
Each subsequent layer performs this same deencapsulation
process. To continue the preceding
example, when the plane arrives, the box of mail is
removed from the plane. The mailbags are taken
out of the boxes and are sent to the correct post
office. The letters are removed from the mailbags
and are delivered to the correct address. The
intended recipient opens the envelope and reads
the letter.
the process of passing information up the stack.
When a layer receives a PDU from the layer below,
it does the following:
1. It reads the control information provided by
the peer source device.
2. The layer strips the control information
(header) from the frame.
3. It processes the data (usually passing it up the
stack).
Each subsequent layer performs this same deencapsulation
process. To continue the preceding
example, when the plane arrives, the box of mail is
removed from the plane. The mailbags are taken
out of the boxes and are sent to the correct post
office. The letters are removed from the mailbags
and are delivered to the correct address. The
intended recipient opens the envelope and reads
the letter.
Encapsulation
The process of passing data down the stack using
PDUs is called data encapsulation. Encapsulation
works as follows: When a layer receives a PDU
from the layer above it, it encapsulates the PDU
with a header and trailer and then passes the PDU
down to the next layer. The control information
that is added to the PDU is read by the peer layer
on the remote device. Think of this as like putting
a letter in an envelope, which has the destination
address on it. The envelope is then put in a mailbag
with a zip code on it. The bag is then placed in
large box with a city name on it. The box is then
put on a plane for transport to the city.
PDUs is called data encapsulation. Encapsulation
works as follows: When a layer receives a PDU
from the layer above it, it encapsulates the PDU
with a header and trailer and then passes the PDU
down to the next layer. The control information
that is added to the PDU is read by the peer layer
on the remote device. Think of this as like putting
a letter in an envelope, which has the destination
address on it. The envelope is then put in a mailbag
with a zip code on it. The bag is then placed in
large box with a city name on it. The box is then
put on a plane for transport to the city.
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