1 Ch.4. Networking and the Internet Sec (4.1):Network Fundamentals:

2 Network classifications: 1. Local Area Network (LAN) 2. Metropolitan Area Network (MAN) 3. Wide Area Network (WAN)

3 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

4 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 network 2. 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

5 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

6 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.

7 Network topology:

8

9 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

10 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

11 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

12 Protocols: For a network to function reliably, it is important to establish rules by which network activities are conducted من أجل استخدام الشبكة بالطريقة الموثوق بها، كان من المهم تأسيس قواعد تقوم بتنظيم النشاطات 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 خلال 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 الاتصال ممكن أن تصر الأجهزة على بث الرسائل في نفس الوقت أو تخطئ في تحويل الرسائل فعندها تكون بحاجة للمساعدة

13 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 ولحل هذه المشكلة كان هناك token ring protocol والذي هو مستخدم في 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

14 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 الأجهزة

15 token ring protocol: To solve this problem, a unique bit pattern, called a token, is passed around the ring ولحل هذه المشكلة قاموا بوضع bit pattern وحيد يسمى token ويتمركز حول الحلقة Possession of this token gives the machine the authority to transmit its own message امتلاك هذا ال token يعطي الجهاز السلطة لنقل الرسائل الخاصة به Without the token, a machine is only allowed to forward messages. ومن غير هذا ال token الجهاز مسموح له أن يرد فقط على الرسائل Normally, each machine merely relays the token in the same manner in which it relays messages.

16 token ring protocol: في الوضع العادي كل جهاز يتتابع في الحصول على ال token بنفس الكيفية فإذا استقبل الجهاز ال token فيكون مسموح له نقل رسالة واحدة تحمل معها ال token فإذا أكملت الرسالة دورتها حول الحلقة ينتقل ال token إلى الجهاز الآخر فيستطيع أن يرد على الرسائل التي لديه أو نقل رسالة خاصة قبل إرسال ال token إلى الجهاز التالي 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

17 token ring protocol:

18 Ethernet protocol Another protocol for coordinating message transmission is used in bus topology networks that are based on the Ethernet protocol collection. هناك بروتوكول آخر مخصص لنقل الرسائل ويستخدم في ال topology bus و مكانه في Ethernet protocol collection ففي نظام ال Ethernet الحلقة التي تتحكم في نقل الرسائل تسمى (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 هذا البروتوكول يأمر كل رسالة نشرت لكل الأجهزة في ال bus

19 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 لنقل رسالة الجهاز ينتظر حتى تصبح ال bus هادئة وفي هذا الوقت تبدأ بالنقل مع استمرار المراقبة لل bus 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 كلا الجهازين يكتشف التصادم ويتوقف لبرهة لإعطاء أوقات عشوائية قبل محاولة النقل مرة أخرى

20 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، الاثنان يتوقفان ولكن الاختلاف هنا أن الأشخاص سيستمرون في الاسترسال لكن تحت CSMA / CD كل جهاز فقط سيبدأ من جديد

21 Ethernet protocol

22 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. repeater 2. bridges 3. switches

23 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

24 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

25 2) Bridges:

26 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

27 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

28 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

29 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

30 router :

31 router : The result is that each machine in an internet has two address: ففي الحقيقة أصبح لكل جهاز عنوانين في الإنترنت  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 لأخرى: the computer at the origin bundles the destination's internet address with the message, الجهاز الموجود في نفس الحزمة هو الجهاز الهدف ويكون هو الـ internet address مع نفس الرسالة ويرسل الحزمة للـ router باستخدام الشبكة الأصلية

32 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 ثم ينظر الـ router إلى داخل الحزمة فيقوم بقراءة العنوان الهدف translates that address into the address format that is appropriate for the other network, and forwards the message to its destination ويقوم بنقل هذا العنوان إلى الـaddress format والذي يلزم الشبكة الأخرى ومن ثم يرسل الرسالة للهدف

33 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

34 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.

35 client / server network: a) Server must be prepared to serve multiple clients at any time Client Server

36 client / server network: Other kinds of servers are: print server communication server mail server

37 client / server network:  شبكة الخادم والعملاء: تتميز بوجود حاسوب مميز server يقدم الخدمات الشبكية إلى حواسيب أخرى clients ترتبط معه وقد يكون الـ server محطة عمل أو حاسوبا كبيرا أو عملاقا ويقوم بخدمة الـ client مثل: 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 downloading أما العكس فيسمى uploading خادم الطابعة: (printer server) : والذي يتحكم بالطابعة المشتركة بين محطات العمل في الشبكة

38 client / server network: خادم الاتصالات: (communication server) :  ويقوم بالسماح لمستخدمي الشبكة بالاتصال مع الحواسيب خارج نطاق الشبكة عبر فتحات متسلسلة ووحدات الـ modem العالية السرعة.  وتحجز الشبكة أحيانا حاسوبا لواحدة أو أكثر من هذه الواجبات, وفي هذه الحالة يسمى الخادم المتخصص Dedicate server ويمكن للشبكات الصغيرة أن تمتلك خادما واحدا فقط بينما تمتلك الشبكات الكبيرة عدة خدم, ومن الخوادم المتخصصة : خادم الويب: والذي يخزن عليه موقع الويب الخاص بالمنشأة. وهناك أيضا: خادم البريد: والمسئول عن إرسال واستقبال وتخزين الرسائل الإلكترونية وتخصيص عناوين بريدية للعاملين في المنشأة

39 peer-to-peer network:  Does not use a server. Individual computers share data directly with others computers Peer b) Peers communicate as equals on a one-to-one basis

40 peer-to-peer network:  شبكة نظير لنظير:  في هذا النوع من الشبكات، كل الأجهزة متساوية ومتكافئة و بإمكان أي جهاز في الشبكة أن يكون خادما أو عميلا في نفس الوقت, أي أنه لا يوجد جهاز مميز عن الأجهزة الأخرى في الشبكة  وهذه أقل كلفة من شبكة الخادم والعملاء. وتستخدم في ذات المنشآت ذات الأعمال البسيطة Peer

41 Distributed Systems: Meaning that they consist of software units that execute as processes on different computers