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Ch.4.Networking and the

InternetSec (4.1):Network Fundamentals:

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Network classifications:

1. Local Area Network (LAN)

2. Metropolitan Area Network (MAN)

3. Wide Area Network (WAN)

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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 distance-perhaps in neighboring cities or on opposite sides of the world

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Network classifications:

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

1. a network of former type is called a Open network2. 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

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There are another classification is based on the topology of the network:

1. Ring: in which the machines are connected in a circular fashion

2. Bus: in which the machines are all connected to a common communication line called a bus

3. Star: in which one machine serves as central focal point to which all the others are connected

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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.

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Network topology:

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Network topology:

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It is important to remember that a network's topology might not be obvious from its physical appearanceFor 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

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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

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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

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Protocols: For a network to function reliably, it is important to establish rules by

which network activities are conducted تأسيس المهم من كان بها، الموثوق بالطريقة الشبكة استخدام أجل من

الشبكة على النشاطات بتنظيم تقوم قواعد Let us consider the problem of coordinating the transmission of

messages among computers in a network. شبكة خالل من الرسائل وانتشار بث في التحكم مشكلة على الضوء لنلقي

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

بث على األجهزة تصر أن ممكن االتصال بهذا تتحكم التي القواعد دون فمنبحاجة تكون فعندها الرسائل تحويل في تخطئ أو الوقت نفس في الرسائل

للمساعدة

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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

هناك كان المشكلة هذه هو token ring protocolولحل والذيالحلقة شبكة في مستخدم

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.

واحد اتجاه في الحلقة شبكة عبر الرسائل جميع بإرسال وذلك

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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

علم قد يكون البداية إلى المتنقلة النسخة تصل فعندماثم ومن الهدف الكمبيوتر إلى وصلت قد الرسالة أن

الحلقة من النسخة بحذف يقوم األجهزة بين ما التعاون على يعتمد فهو

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token ring protocol: To solve this problem, a unique bit pattern, called a token, is passed

around the ring بوضع قاموا المشكلة هذه يسمى bit patternولحل ويتمركز tokenوحيد

الحلقة حول Possession of this token gives the machine the authority to transmit

its own message ال هذا به tokenامتالك الخاصة الرسائل لنقل السلطة الجهاز يعطي

Without the token, a machine is only allowed to forward messages. ال هذا غير الرسائل tokenومن على فقط يرد أن له مسموح الجهاز

Normally, each machine merely relays the token in the same manner in which it relays messages.

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token ring protocol: ال على الحصول في يتتابع جهاز كل العادي الوضع tokenفي

ال الجهاز استقبل فإذا الكيفية له tokenبنفس مسموح فيكونال معها تحمل واحدة رسالة الرسالة tokenنقل أكملت فإذا

ال ينتقل الحلقة حول فيستطيع tokenدورتها اآلخر الجهاز إلىإرسال قبل خاصة رسالة نقل أو لديه التي الرسائل على يرد أن

التالي tokenال الجهاز إلى 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:

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Ethernet protocol Another protocol for coordinating message transmission is

used in bus topology networks that are based on the Ethernet protocol collection.

ال في ويستخدم الرسائل لنقل مخصص آخر بروتوكول هناكtopology bus في مكانه ففي Ethernet protocol collectionو

ال تسمى Ethernetنظام الرسائل نقل في تتحكم التي الحلقة)CSMA /CD(

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

نشرت رسالة كل يأمر البروتوكول ال هذا في األجهزة busلكل

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Ethernet protocol Each machine monitors all the messages but keeps only

those addressed to itself الخاصة بالعناوين فقط يحتفظ ولكن الرسائل كل يراقب جهاز كل

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

ال تصبح حتى ينتظر الجهاز رسالة هذا busلنقل وفي هادئةلل المراقبة استمرار مع بالنقل تبدأ busالوقت

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

التصادم يكتشف الجهازين كال بالنقل بدأ آخر جهاز هناك كان إذامرة النقل محاولة قبل عشوائية أوقات إلعطاء لبرهة ويتوقف

أخرى

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Ethernet protocol

Under the CSMA / CD protocol each machine merely tries again

أكثر أو اثنان يقوم عندما يحدث ما بالضبط هذايتوقفان االثنان الوقت، نفس في المحادثة بعملية

في سيستمرون األشخاص أن هنا االختالف ولكنتحت لكن جهاز CSMA / CDاالسترسال كل

جديد من سيبدأ فقط

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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. repeater2. bridges3. 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

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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:

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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:

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router: The result is that each machine in an internet has two

address: اإلنترنت في عنوانين جهاز لكل أصبح الحقيقة ففي

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,

: ألخرى شبكة من كمبيوتر من رسالة لنقل the computer at the origin bundles the destination's

internet address with the message, هو ويكون الهدف الجهاز هو الحزمة نفس في الموجود الجهاز

للـ internet addressالـ الحزمة ويرسل الرسالة نفس معrouter األصلية الشبكة باستخدام

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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 الـ ينظر بقراءة routerثم فيقوم الحزمة داخل إلى

الهدف العنوان translates that address into the address format that

is appropriate for the other network, and forwards the message to its destination

الـ إلى العنوان هذا بنقل والذي address formatويقومللهدف الرسالة يرسل ثم ومن األخرى الشبكة يلزم

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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:

a) Server must be prepared to serve multiple clients at any time

Client Client

Client Client

Server

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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:: والعمالء الخادم شبكة

مميز حاسوب بوجود إلى serverتتميز الشبكية الخدمات يقدمأخرى الـ clientsحواسيب يكون وقد معه محطة serverترتبط

الـ بخدمة ويقوم عمالقا أو كبيرا حاسوبا أو : clientعمل مثل . الـ أنواع ومن التطبيقية والبرمجيات البيانات :serverتخزين

: الملفات :)file server(خادمعلى المشتركة البيانات وملفات البرامج تخزين في يستخدم

تحميل عملية وتسمى كبيرة وسرعته عالية سعته صلب قرصالعميل إلى الخادم من العكس downloadingالملفات أما

uploadingفيسمى : الطابعة :)printer server(خادم

الشبكة في العمل محطات بين المشتركة بالطابعة يتحكم والذي

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client / server network: : االتصاالت :)communication server(خادم

خارج الحواسيب مع باالتصال الشبكة لمستخدمي بالسماح ويقومالـ ووحدات متسلسلة فتحات عبر الشبكة العالية modemنطاق

السرعة. , الواجبات هذه من أكثر أو لواحدة حاسوبا أحيانا الشبكة وتحجز

المتخصص الخادم يسمى الحالة هذه Dedicate serverوفيتمتلك بينما فقط واحدا خادما تمتلك أن الصغيرة للشبكات ويمكن

: , المتخصصة الخوادم ومن خدم عدة الكبيرة الشبكات: الويب الخاص خادم الويب موقع عليه يخزن والذي

: أيضا . وهناك بالمنشأة: البريد وتخزين خادم واستقبال إرسال عن والمسئول

في للعاملين بريدية عناوين وتخصيص اإللكترونية الرسائلالمنشأة

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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

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peer-to-peer network:

: لنظير نظير شبكة متساوية األجهزة كل الشبكات، من النوع هذا في

أو خادما يكون أن الشبكة في جهاز أي بإمكان و ومتكافئة , عن مميز جهاز يوجد ال أنه أي الوقت نفس في عميال

الشبكة في األخرى األجهزة

. وتستخدم والعمالء الخادم شبكة من كلفة أقل وهذهالبسيطة األعمال ذات المنشآت ذات في

Peer Peer

Peer Peer

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Distributed Systems:

Meaning that they consist of software units that execute as processes on different computers