Transcript Document 763767

Ch.4.
Networking and the
Internet
Sec (4.1):Network Fundamentals:
1
Network classifications:
1.
2.
3.
Local Area Network (LAN)
Metropolitan Area Network (MAN)
Wide Area Network (WAN)
2
Network classifications:



A LAN: normally consists of a collection of
computers in a single building or building
complex, for ex. The computers in the university
campus or those in a manufacturing plant might
be connected by a LAN
A MAN: is a network of intermediate size, such
as one spanning a local community
A WAN: links machines over a greater distanceperhaps in neighboring cities or on opposite
sides of the world
3
Network classifications:

1.
2.


There are another classifying networks is based on
whether the network's internal operation is based
on designs that are in the public domain or on
innovations owned and controlled by a particular
entity such as an individual or a corporation
a network of former type is called a Open network
a network of a latter type is called a Closed or
Proprietary network
an Internet is an open system TCP/IP
Company like Novell Inc. is closed system
4
There are another classification is based
on the topology of the network:
1.
2.
3.
Ring: in which the machines are
connected in a circular fashion
Bus: in which the machines are all
connected to a common communication
line called a bus
Star: in which one machine serves as
central focal point to which all the others
are connected
5
There are another classification is based
on the topology of the network:



the star network is perhaps the oldest, having
evolved from the paradigm of a large central
computer serving many users.
As the simple terminals employed by these
users grew into small computers themselves, a
star network emerged.
Today, however, the bus topology, having been
popularized under the standards known as
Ethernet, is probably the most popular network
topology.
6
Network topology:
7
Network topology:
8
It is important to remember that a
network's topology might not be obvious
from its physical appearance
For instance, a bus network might not appear as a
long bus from which computers are connected
over short links
1. Each computer connected to each other by
central location called Hub



Hub: which are the central location where are the
computers connected in bus network
The hub is little more than a very short bus
All hubs is relay any signal it receives back out to all
the machines connected to it
9
There are difference between stars
and bus network:


the central device in star network is a
computer that receives and often process
messages from the other computers
but the central device in the bus networks
is a hub that merely provides a common
communication path to all the computers
10
It is important to remember that a
network's topology might not be obvious
from its physical appearance
2.
wireless network, using radio broadcast
technology are becoming quite common

hub in many of today's bus networks is
essentially a radio relay station
11
Protocols:
For a network to function reliably, it is important to establish rules by
which network activities are conducted
‫ كان من المهم تأسيس قواعد تقوم بتنظيم النشاطات‬،‫ من أجل استخدام الشبكة بالطريقة الموثوق بها‬
‫على الشبكة‬
 Let us consider the problem of coordinating the transmission of
messages among computers in a network.
‫ لنلقي الضوء على مشكلة التحكم في بث وانتشار الرسائل من خالل شبكة الكمبيوتر‬
 Without rules governing this communication, all the computers might
insist on transmitting messages at the same time or might fail the
relay messages when that assistance is required
‫ فمن دون القواعد التي تتحكم بهذا االتصال ممكن أن تصر األجهزة على بث الرسائل في نفس‬
‫الوقت أو تخطئ في تحويل الرسائل فعندها تكون بحاجة للمساعدة‬

12
token ring protocol:


One approach to solve this problem is the token ring
protocol, which was developed by IBM in the 1970s and
continues to be a popular protocol in network based on
the ring topology
‫ والذي هو مستخدم في‬token ring protocol ‫ ولحل هذه المشكلة كان هناك‬
‫شبكة الحلقة‬
In this protocol, all the machines in the network transmit
messages in only one common direction , meaning that
all messages sent over the network move around the
ring in the same direction by being forwarded from
computer to computer.
‫ وذلك بإرسال جميع الرسائل عبر شبكة الحلقة في اتجاه واحد‬
13
token ring protocol:


and forwards a copy on around the ring, when
the forwarded copy reaches the originating
computer, that machine knows that the message
must have reached its destination and removes
the message from the ring
Of-course, this system depends on inter
machine cooperation
‫ فعندما تصل النسخة المتنقلة إلى البداية يكون قد علم أن الرسالة قد‬
‫وصلت إلى الكمبيوتر الهدف ومن ثم يقوم بحذف النسخة من الحلقة‬
‫ فهو يعتمد على التعاون ما بين األجهزة‬
14
token ring protocol:


To solve this problem, a unique bit pattern, called a token, is passed
around the ring
‫ ويتمركز حول الحلقة‬token ‫ وحيد يسمى‬bit pattern ‫ ولحل هذه المشكلة قاموا بوضع‬
Possession of this token gives the machine the authority to transmit
its own message
‫ يعطي الجهاز السلطة لنقل الرسائل الخاصة به‬token ‫ امتالك هذا ال‬

Without the token, a machine is only allowed to forward messages.
‫ الجهاز مسموح له أن يرد فقط على الرسائل‬token ‫ ومن غير هذا ال‬

Normally, each machine merely relays the token in the same
manner in which it relays messages.
15
token ring protocol:
‫ بنفس الكيفية‬token ‫ في الوضع العادي كل جهاز يتتابع في الحصول على ال‬
‫ فيكون مسموح له نقل رسالة واحدة تحمل معها‬token ‫فإذا استقبل الجهاز ال‬
‫ إلى الجهاز‬token ‫ فإذا أكملت الرسالة دورتها حول الحلقة ينتقل ال‬token ‫ال‬
‫اآلخر فيستطيع أن يرد على الرسائل التي لديه أو نقل رسالة خاصة قبل إرسال‬
‫ إلى الجهاز التالي‬token ‫ال‬
 However, if the machine receiving the token has
messages of its own to introduce to the network, it
transmits one message while holding the token
 When this message has completed its cycle around the
ring, the machine forwards the token to the next machine
in the ring
 When the next machine receives the token it can either
forward the token immediately or transmit its own new
message before sending the token to the next machine
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token ring protocol:
17
Ethernet protocol
Another protocol for coordinating message transmission
is used in bus topology networks that are based on the
Ethernet protocol collection.
topology bus ‫ هناك بروتوكول آخر مخصص لنقل الرسائل ويستخدم في ال‬
Ethernet ‫ ففي نظام ال‬Ethernet protocol collection ‫و مكانه في‬
(CSMA /CD) ‫الحلقة التي تتحكم في نقل الرسائل تسمى‬
 To transmit message is controlled by the protocol known
as Carrier Sense Multiple Access with Collision
Detection (CSMA/CD)
 This protocol dictates that each message be broadcast
to all the machines on the bus
bus ‫ هذا البروتوكول يأمر كل رسالة نشرت لكل األجهزة في ال‬

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Ethernet protocol
Each machine monitors all the messages but keeps only
those addressed to itself
‫ كل جهاز يراقب كل الرسائل ولكن يحتفظ فقط بالعناوين الخاصة به‬
 To transmit a message, a machine waits until the bus is
silent, and at this time it begins transmitting while
continuing to monitor the bus
‫ هادئة وفي هذا الوقت تبدأ بالنقل‬bus ‫ لنقل رسالة الجهاز ينتظر حتى تصبح ال‬
bus ‫مع استمرار المراقبة لل‬
 If another machine also begins transmitting, both
machine detect the clash and pause for a brief random
period of time before trying to transmit again
‫ إذا كان هناك جهاز آخر بدأ بالنقل كال الجهازين يكتشف التصادم ويتوقف لبرهة‬
‫إلعطاء أوقات عشوائية قبل محاولة النقل مرة أخرى‬

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‫‪Ethernet protocol‬‬
‫‪Under the CSMA / CD protocol each‬‬
‫‪machine merely tries again‬‬
‫‪ ‬هذا بالضبط ما يحدث عندما يقوم اثنان أو أكثر بعملية‬
‫المحادثة في نفس الوقت‪ ،‬االثنان يتوقفان‬
‫‪ ‬ولكن االختالف هنا أن األشخاص سيستمرون في االسترسال‬
‫لكن تحت ‪ CSMA / CD‬كل جهاز فقط سيبدأ من جديد‬
‫‪‬‬
‫‪20‬‬
Ethernet protocol
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Combining Networks:

Sometimes it is necessary to connect existing
networks to form an extended communication
system, this can be done by connecting the
networks to form a larger version of the same
type of network. Like bus network based on the
Ethernet protocols, it is often possible to
connect the buses to form a single large bus.
This is done by means of different devices
known as:
1.
2.
3.
repeater
bridges
switches
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1) Repeater:

which is little more than a device that
connects two buses to form a single long
bus. The repeater simply passes signals
back and forth between the two original
buses without considering the meaning
of the signals
23
2) Bridges:



a similar to, but more complex than a repeater. Like a
repeater, it connected two buses, but it dose not
necessarily pass all messages across the connection.
Instead, it looks at the destination address that a
companies each message and forwards a message
across the connection only when that message is
destined for a computer on the other side
A bridge produces more efficient system than that
produced by a repeater
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2) Bridges:
25
3) Switches:




is a bridge with multiple connections, allowing it to
connect several buses rather than just two .
switch produces a network consisting of several buses
extending from the switch as spokes on a wheel
As in the case of a bridge, a switch considers the
destination address of all messages and forwards only
those messages for other spokes.
Each message that is forwarded is relayed only into
the appropriate spoke, thus minimizing the traffic in
each spoke
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internet:




[note that the generic term internet is distinct from the
Internet. The Internet with the capital I refers to a
particular worldwide internet that we will study in the
other section]
In which the original networks maintain their individuality
and continue to function as independent networks
Sometimes, the networks to be connected have
incompatible characteristics ( connected differences
network with several protocol)
for instance, the characteristics of a ring network using
the token ring protocol are not readily compatible with an
Ethernet bus network using CSMA/CD
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router :



it is a machine using to connection between two
networks to form an internet
a router is computer belonging to both networks
that forwards messages in one network into the
other network
note that the task of a router is significantly
greater than that of repeater, bridges and
switches because a router must convert
between the idiosyncrasies of the two original
networks
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router :
for ex.:
 When transferring a message from a network using the
token ring protocol to a network using CSMA/CD, a
router must receive the message using one protocol and
then transmit it to the other network using another
protocol
Another ex.:
 Consider the problem posed when the two networks
being connected use different addressing systems to
identify the computers in the networks.
 When a computer in one network wants to send a
message to a computer in the other
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router :
30
router :

The result is that each machine in an internet has two
address:
‫ففي الحقيقة أصبح لكل جهاز عنوانين في اإلنترنت‬





Original network address
New internet address
To send a message from a computer in one of the
original networks to a computer in the other,
:‫لنقل رسالة من كمبيوتر من شبكة ألخرى‬
the computer at the origin bundles the destination's
internet address with the message,
internet ‫الجهاز الموجود في نفس الحزمة هو الجهاز الهدف ويكون هو الـ‬
‫ باستخدام الشبكة‬router ‫ مع نفس الرسالة ويرسل الحزمة للـ‬address
‫األصلية‬


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router :



and sends the bundle to the router using the
local network's original addressing system
the router looks inside the bundle, find the
internet address of the message's ultimate
destination
‫ إلى داخل الحزمة فيقوم بقراءة العنوان الهدف‬router ‫ثم ينظر الـ‬
translates that address into the address format
that is appropriate for the other network, and
forwards the message to its destination
‫ والذي يلزم‬address format ‫ويقوم بنقل هذا العنوان إلى الـ‬
‫الشبكة األخرى ومن ثم يرسل الرسالة للهدف‬


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Interprocess Communication:




The various activities executing on the different
computers within a network must often communicate
with each other to coordinate their actions and to
perform their designated task. Such communication
between process is called interprocess
communication
A popular convention used for IC is client / server model
Client : which make requests of other processes, or a
server
Server : which satisfies the requests made by clients
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Continue:

In the LAN network there are two types of
networking
 client

/ server network:
Where there is a specific computer called a
server, which servers all common files and
document so that other computers (client) can
use, access, update and manipulate them at the
same time.
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client / server network:
Client
Client
Server
Client
Client
a) Server must be prepared to serve multiple clients at any time
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client / server network:
Other kinds of servers are:
 print server
 communication server
 mail server
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‫‪client / server network:‬‬
‫‪‬‬
‫‪‬‬
‫‪‬‬
‫‪‬‬
‫‪37‬‬
‫شبكة الخادم والعمالء‪:‬‬
‫تتميز بوجود حاسوب مميز ‪ server‬يقدم الخدمات الشبكية إلى حواسيب‬
‫أخرى ‪ clients‬ترتبط معه وقد يكون الـ ‪ server‬محطة عمل أو حاسوبا‬
‫كبيرا أو عمالقا ويقوم بخدمة الـ ‪ client‬مثل‪ :‬تخزين البيانات والبرمجيات‬
‫التطبيقية‪ .‬ومن أنواع الـ ‪: server‬‬
‫خادم الملفات‪: (file server) :‬‬
‫يستخدم في تخزين البرامج وملفات البيانات المشتركة على قرص صلب سعته‬
‫عالية وسرعته كبيرة وتسمى عملية تحميل الملفات من الخادم إلى العميل‬
‫‪ downloading‬أما العكس فيسمى ‪uploading‬‬
‫خادم الطابعة‪: (printer server) :‬‬
‫والذي يتحكم بالطابعة المشتركة بين محطات العمل في الشبكة‬
‫‪client / server network:‬‬
‫‪‬‬
‫خادم االتصاالت‪: (communication server) :‬‬
‫‪ ‬ويقوم بالسماح لمستخدمي الشبكة باالتصال مع الحواسيب خارج نطاق‬
‫الشبكة عبر فتحات متسلسلة ووحدات الـ ‪ modem‬العالية السرعة‪.‬‬
‫‪ ‬وتحجز الشبكة أحيانا حاسوبا لواحدة أو أكثر من هذه الواجبات‪ ,‬وفي هذه‬
‫الحالة يسمى الخادم المتخصص ‪ Dedicate server‬ويمكن للشبكات‬
‫الصغيرة أن تمتلك خادما واحدا فقط بينما تمتلك الشبكات الكبيرة عدة خدم‪,‬‬
‫ومن الخوادم المتخصصة ‪:‬‬
‫‪‬‬
‫‪‬‬
‫‪38‬‬
‫خادم الويب‪ :‬والذي يخزن عليه موقع الويب الخاص بالمنشأة ‪ .‬وهناك‬
‫أيضا‪:‬‬
‫خادم البريد‪ :‬والمسئول عن إرسال واستقبال وتخزين الرسائل‬
‫اإللكترونية وتخصيص عناوين بريدية للعاملين في المنشأة‬
peer-to-peer network:

Does not use a server. Individual computers
share data directly with others computers
Peer
Peer
b) Peers communicate as equals on a one-to-one basis
39
‫‪peer-to-peer network:‬‬
‫‪ ‬شبكة نظير لنظير‪:‬‬
‫‪‬‬
‫‪‬‬
‫‪40‬‬
‫في هذا النوع من الشبكات‪ ،‬كل األجهزة متساوية ومتكافئة و بإمكان أي‬
‫جهاز في الشبكة أن يكون خادما أو عميال في نفس الوقت‪ ,‬أي أنه ال يوجد‬
‫جهاز مميز عن األجهزة األخرى في الشبكة‬
‫‪Peer‬‬
‫‪Peer‬‬
‫‪Peer‬‬
‫‪Peer‬‬
‫وهذه أقل كلفة من شبكة الخادم والعمالء ‪ .‬وتستخدم في ذات المنشآت‬
‫ذات األعمال البسيطة‬
Distributed Systems:

Meaning that they consist of software units
that execute as processes on different
computers
41