Friday, November 6, 2009

Osi (network)

Dear Members,
Kindly check this TOPIC (OSI)

International organization for standardization
Iso has designed a reference model called osi reference model
(open system interconnection). It has 7 layers. It says that
Any n/w for comunication needs 7 layers

1.Application layer
The user uses application layer to send the data. The protocols@ this layer are ftp,http,smtp(e-mail) telenet etc.

2.Presentation layer
Presentation layer takes the data from application layer and presentIn different formats for securing reason. The services offered @This layer areCompression – decompressionCoding – decodingEncryption - decryption

3. Session layer

Establishing the session or the conectivity n/w n/w 1 & n/w 2 is doneBy the session layer.It 1. Establishes a session2. maintains it &3. Terminates it b/w the application

4. Transport layer

End-end connectivity during a session b/w two application is doneBy the transport layer. It also decides the type of connection like tcpor udp i.e. connection oriented or connection less.Services:SequencingFlow ctrl, error detection & correctionTransport layer info + data is called segment

5. Netwrok layer

Logical addressing is done at thenetwork layer i.e. source address &destination address are attached to the data.Protocols @network layerRouted protocols routing protocolsEg: ip,ipx eg: rip,igrp,ospfRouted protocols: they always carry the data along with themRouting protocol: they identify the path for routed protocol tocarry the dataAt this layer routers & layer 3 switches forms packets.

6.Data link layer

It has two Sub layersa)MAC{Media access control } b) LLC {logical link control framing of data}Ip address is lik the pincode & MAC address is like house number.Here layer2 switches are used.Wab protocols used at this layer are PPP,HDLC,FP,X.25 etc.Here error checking CRC bits are added to the packetsDLL info+ packets --> frames

7. physical layer

Takes care of physical connectivity i.e connector,cable etc. hereFrames are converted to bits (1’s & 0’s).The devices like hubs, repeaters,cables & connectors are used atthis layer


Ping: is a computer network tool used to test whether a particular host is reachable across an IP network; it is also used to self test the network interface card of the computer, or as a speed test. It works by sending ICMP “echo request” packets to the target host and listening for ICMP “echo response” replies. Ping does not estimate the round-trip time, as it does not factor in the user's connection speed, but instead is used to record any packet loss, and print a statistical summary when finished.

The word ping is also frequently used as a verb or noun, where it is usually incorrectly used to refer to the round-trip time, or measuring the round-trip time.

History: Mike Muuss wrote the program in December, 1983, as a tool to troubleshoot odd behavior on an IP network. He named it after the pulses of sound made by a sonar, since its operation is analogous to active sonar in submarines, in which an operator issues a pulse of energy at the target, which then bounces from the target and is received by the operator. (The pulse of energy in sonar is analogous to a network packet in ping).

The usefulness of ping in assisting the "diagnosis" of Internet connectivity issues was impaired from late in 2003, when a number of Internet Service Providers began filtering out ICMP Type 8 (echo request) messages at their network boundaries.

This was partly due to the increasing use of ping for target reconnaissance, for example by Internet worms such as Welchia that flood the Internet with ping requests in order to locate new hosts to infect. Not only did the availability of ping responses leak information to an attacker, it added to the overall load on networks, causing problems for routers across the Internet.

Although RFC 1122 prescribes that any host must accept an echo-request and issue an echo-reply in return, this is supposedly a security risk, and thus this standard is frequently not followed on the public Internet.

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ICMP packet
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Generic composition of an ICMP packet

Header (in blue), with Protocol set to 1 and Type of Service set to 0.
Type of ICMP message (8 bits)
Code (8 bits)
Checksum (16 bits), calculated with the ICMP part of the packet (the header is not used)
The ICMP 'Quench' (32 bits) field, which in this case (ICMP echo request and replies), will be composed of identifier (16 bits) and sequence number (16 bits).
Data load for the different kind of answers (Can be an arbitrary length, left to implementation detail. However must be less than the maximum MTU of the network.

Sample with Windows
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Windows appears not to inform the user about duplicated return packets.

Message format
Echo request
The echo request is an ICMP message whose data is expected to be received back in an echo reply ("pong"). The host must respond to all echo requests with an echo reply containing the exact data received in the request message.

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Type must be set to 8.
Code must be set to 0.
The Identifier and Sequence Number can be used by the client to match the reply with the request that caused the reply. In practice, most Linux systems use a unique identifier for every ping process, and sequence number is an increasing number within that process. Windows uses a fixed identifier, which varies between Windows versions, and a sequence number that is only reset at boot time.
The data received by the Echo Request must be entirely included in the Echo Reply.

Echo reply
: The echo reply is an ICMP message generated in response to an echo request, and is mandatory for all hosts and routers.
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Type and code must be set to 0.
The identifier and sequence number can be used by the client to determine which echo requests are associated with the echo replies.
The data received in the echo request must be entirely included in the echo reply.

Payload: The payload of the packet is generally filled with letters of the alphabet as this ASCII tcpdump shows

16:24:47.966461 IP (tos 0x0, ttl 128, id 15103, offset 0, flags [none], proto: ICMP (1), length: 60) > ICMP echo request, id 1, seq 38, length 40

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References: Wikipedia

طريقة استخدام الأمر Ping

طريقة استخدام الأمر

start menu/ run/cmd
ولعمل ping وفحص التوصيل بين جهاز حاسب وآخر أو بين جهاز حاسب وجهاز التحويل (Router) أو مع الخادم (server) فإننا نكتب الأمر كالتالي :
مثال :
حيث xxx هي رقم تعريف الشبكة للجهاز المراد فحص الاتصال معه كما يمكن استخدام اسم النطاق للحاسب DNS مثال
اذا عرض اختبار ping نتيجة الرد فمعنى ذلك أن هناك اتصالاً فعلياً بهذا الجهاز ولكن إذا ظهرت نتيجة الفحص كالتالي :
“Request timed Out"
فهذا يعني عدم وصول رد من الجهاز الذي تم إرسال الحزم له .وهذا يدل على عدة أشياء منها :

الجهاز لايعمل .

-خط التوصيل بين الأجهزة فيه خلل (لايوجد توصيل ).

زمن رد فعل الجهاز الآخر أطول من ثانية.

عدم وجود خط عودة إلى الحاسب الشخصي المستخدم (أي أن التوصيل سليم والجهاز المراد الاتصال به سليم لكن السبب قد يكون في اعدادت الخادم (server) للرد والطريقة المستخدمة للرد.

أمثلة على استخدام
ينبغي مراعاة وضع فراغات بين الأمر ping والمعايير المستخدمة معه وكذلك العنوان المراد الإرسال له .

من النتائج السابقة نستنتج التالي
1-أنه تم إرسال أربعة من حزم البيانات
packets إلى العنوان الوجهة وهو موقع مزاج
2-أن حجم كل
packet مرسل هو 32 bytes وأن كل packet مرسله استغرقت مدة زمنية معينة للوصول إلى الهدف بحيث كان أقصى مدة زمنية استغرقتها إجمالي الـ packets للوصول إلى الهدف هو 1797 ميلي ثانية وأدنى مدة زمنية كانت 1476 ميلي ثانية بينما كان المتوسط لإجمالي الـ packets هو 1639 ميلي ثانية .
3-أن جميع الـ packet أرسلت ولم يُفقد منها شي .

Quality Of Service (Qos)

quality of service (QoS)

refers to resource reservation control mechanisms rather than the achieved service quality. Quality of service is the ability to provide different priority to different applications, users, or data flows, or to guarantee a certain level of performance to a data flow. For example, a required bit rate, delay, jitter, packet dropping probability and/or bit error rate may be guaranteed. Quality of service guarantees are important if the network capacity is insufficient, especially for real-time streaming multimedia applications such as voice over IP, online games and IP-TV, since these often require fixed bit rate and are delay sensitive, and in networks where the capacity is a limited resource, for example in cellular data communication. In the absence of network congestion, QoS mechanisms are not required.

A network or protocol that supports QoS may agree on a traffic contract with the application software and reserve capacity in the network nodes, for example during a session establishment phase. During the session it may monitor the achieved level of performance, for example the data rate and delay, and dynamically control scheduling priorities in the network nodes.

Applications requiring QoS

1. streaming multimedia may require guaranteed throughput to ensure that a minimum level of quality is maintained.
2. IPTV offered as a service from a service provider such as AT&T's U-verse
3. IP telephony or Voice over IP (VOIP) may require strict limits on jitter and delay
4. Video Teleconferencing (VTC) requires low jitter and latency
5. Alarm signalling (e.g., Burglar alarm)
6. dedicated link emulation requires both guaranteed throughput and imposes limits on maximum delay and jitter

شرح مفصل للأمر ping

سنتعرف اليوم على أهم أمر بالشبكات لا بل حتى بالانترنت وهو الأمر

الـ ping اختصار لـ packet Internet Groper وهو أداة معروفة لأغلب مهندسي وخبراء تقنية المعلومات ويعتبر أمر من الأوامر المستخدمة في نظام الدوس وذلك لغرض الفحص والتحقق من الاتصال بمستوى IP مع كمبيوتر آخر أو موجه مسار Router أو طابعة أو أي جهاز آخر يستخدم برتوكول TCP/IP , حيث يرسل الأمر ping مجموعة من حزم البيانات إلى جهاز آخر مشترك في نفس الشبكة ويطلب منه الرد بإشارات معينة على هذه الحزم ثم يعرض النتائج بأكملها على الشاشة كالمثال التالي ,افتح ابدأ ومن قائمة تشغيل اكتبcmd ثم اكتب Ping ومسافة Space ثم رقم IP أو اسم موقع :

الشكل العام للأمر ping :
Ping [-t] [-a] [-n] [-l] [-f] [-i] [-v] [-r] [-s] [-w] [-j] targetname

المعايير المستخدمة مع الامر ping
هنالك بعض المعايير الإختيارية والتي توضع مع الأمر ping وهي :

t- استمر بالإرسال للعنوان المطلوب حتى يتوقف عن الإجابة وإذا أردنا مقاطعة الإحصائيات وعرضها نضغط CTRL+Break , ولمقاطعةping وإنهائه نستخدم CTRL+C .
a- اعرض رقم التعريف للعنوان المحدد.
n- عدد رسائل طلب الارتداد المرسلة (حزم البيانات المرسلة) والافتراضي هو 4.
Reply or request …etc
l- حجم حزمة البيانات المرسلة محدداً بالبايتات bytes و الحجم الافتراضي للحزمة هو 32 والأقصى هو 65.527.
f- عدم تجزئة الحزمة المرسلة (Do not fragment) من قبل أجهزة التوجيه في المسار إلى الوجهة المقصودة.
i- المدة الزمنية بين كل حزمة والثانية مقاسة بالميلي ثانية.
v- نوع الخدمة والافتراضي و هو 0 ويتم تحديده كقيمة عشرية تتراوح
من 0 إلى 255.
r- عدد نقاط التحويل أو القفزات في خط الاتصال بالعنوان وعند استخدام هذا المعيار فقد استخدمت Record Route وذلك لتسجيل المسار المتخذ من قبل رسالة الطلب حتى رسالة الإجابة المتوافقة للطلب.
s- الوقت المسجل عند الوصول لكل قفزة أو تحويله (وقت وصول رسالة طلب الارتداد ورسالة الاجابة المتوافقة).
w- مدة الإنتظار لوصول الرد من العنوان بالميلي ثانية وإن لم يتم استلام رسالة الإجابة يتم عرض رسالة إعلام بالخطأ "انقضاء مهلة الطلب " "Request timed out " والمهلة الافتراضية 4000 (4ثواني ).
j- لتحديد عدد من الوجهات التي تمر بها حزمة البيانات خلال مسارها للوصول إلى المقصد والعدد الأقصى لهذه الوجهات
(Intermediate node ) هو 9 وتكتب قائمة المضيفين بعناوين IP مفصولة بفراغات.

فوائد الأمر

للتعرف على حالة الشبكة وحالة المستضيف موقع ما أو صفحة
2-لتتبع وعزل الأعطال في القطع والبرامج.
3-لإختبار ومعايرة وإدارة الشبكة.
4-يمكن استخدام الأمر ping لعمل فحص ذاتي للحاسب (loopback) وذلك للتأكد من قدرة الحاسب على إرسال واستقبال المعلومات وفي هذه الحالة لايتم إرسال أي شيء للشبكة إنما فقط من الحاسب إلى نفسه وتستخدم هذه الطريقة للتأكد من عمل بطاقة الشبكة المركبة في الحاسب ونستخدم الأمر في هذه الحالة كالتالي
ping local host أو ping
ونحصل على المعلومات التالية في نتيجة الفحص السابق :
1-أنه تم إرسال 4 حزم من البيانات (Packets) ولم يفقد منها شيء.
2-سيتضح الزمن الذي أخذته كل حزمة في الذهاب والعودة بالميلي ثانية.
3-الحجم الأساسي للحزمة الواحدة=32بايت ومدة الإنتظار منذ لحظة الإرسال حتى عودتها هو 1ثانية وعدد الحزم=4 والزمن=صفر لأننا نفحص الحاسب ذاتياً

Universal Serial Bus ( USB )

Universal Serial Bus ( USB )
In information technology, Universal Serial Bus (USB) is a serial bus standard to connect devices to a host computer. USB was designed to allow many peripherals to be connected using a single standardized interface socket and to improve plug and play capabilities by allowing hot swapping; that is, by allowing devices to be connected and disconnected without rebooting the computer or turning off the device. Other convenient features include providing power to low-consumption devices, eliminating the need for an external power supply; and allowing many devices to be used without requiring manufacturer-specific device drivers to be installed.

USB is intended to replace many varieties of serial and parallel ports. USB can connect computer peripherals such as mice, keyboards, PDAs, gamepads and joysticks, scanners, digital cameras, printers, personal media players, flash drives, and external hard drives. For many of those devices, USB has become the standard connection method. USB was designed for personal computers, but it has become commonplace on other devices such as PDAs and video game consoles, and as a power cord between a device and an AC adapter plugged into a wall plug for charging. As of 2008[update], there are about 2 billion USB devices sold per year, and about 6 billion total sold to date.[1]

The design of USB is standardized by the USB Implementers Forum (USB-IF), an industry standards body incorporating leading companies from the computer and electronics industries. Notable members have included Agere (now merged with LSI Corporation), Apple Inc., Hewlett-Packard, Intel, Microsoft and NEC.

The USB 1.0 specification was introduced in 1994. USB was created by the core group of companies that consisted of Intel, Compaq, Microsoft, Digital, IBM, and Northern Telecom. Intel produced the UHCI host controller and open software stack; Microsoft produced a USB software stack for Windows and co-authored the OHCI host controller specification with National Semiconductor and Compaq; Philips produced early USB-Audio; and TI produced the most widely used hub chips. USB was intended to replace the multitude of connectors at the back of PCs, as well as to simplify software configuration of communication devices.

The USB 2.0 specification was released in April 2000 and was standardized by the USB-IF at the end of 2001. Hewlett-Packard, Intel, Lucent (now LSI Corporation since its merger with Lucent spinoff Agere Systems (Lucent has been merged with Alcatel, and became Alcatel-Lucent)), Microsoft, NEC, and Philips jointly led the initiative to develop a higher data transfer rate, 480 Mbit/s, than the 1.0 specification of 12 Mbit/s.

The USB 3.0 specification was released on November 17, 2008 by the USB 3.0 Promoter Group. It has a transfer rate of up to 10 times faster than the USB 2.0 version and has been dubbed the SuperSpeed USB.

Equipment conforming with any version of the standard will also work with devices designed to any previous specification (a property known as backward compatibility).

Device classes
USB defines class codes used to identify a device’s functionality and to load a device driver based on that functionality. This enables a device driver writer to support devices from different manufacturers that comply with a given class code.

Device classes include

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Note class 0: Use class information in the Interface Descriptors. This base class is defined to be used in Device Descriptors to indicate that class information should be determined from the Interface Descriptors in the device.

Types of USB connector

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There are several types of USB connectors, including some that have been added while the specification progressed. The original USB specification detailed Standard-A and Standard-B plugs and receptacles. The first engineering change notice to the USB 2.0 specification added Mini-B plugs and receptacles.

The data connectors in the A - Plug are actually recessed in the plug as compared to the outside power connectors. This permits the power to connect first which prevents data errors by allowing the device to power up first and then transfer the data. Some devices will operate in different modes depending on whether the data connection is made. This difference in connection can be exploited by inserting the connector only partially. For example, some battery-powered MP3 players switch into file transfer mode (and cannot play MP3 files) while a USB plug is fully inserted, but can be operated in MP3 playback mode using USB power by inserting the plug only part way so that the power slots make contact while the data slots do not. This enables those devices to be operated in MP3 playback mode while getting power from the cable

The Standard-A type of USB connector takes on the appearance of a flattened rectangle that plugs into downstream-port sockets on the USB host or a hub and receives power. This kind of connector is most frequently seen on cables that are permanently attached to a device, such as one on a cable that connects a keyboard or mouse to the computer.

Standard-B connectors—which have a square shape with beveled exterior corners—typically plug into upstream sockets on devices that use a removable cable, e.g. between a hub and a printer. Type B plugs deliver power and are therefore analogous to a power socket. This two-connector scheme prevents a user from accidentally creating a loop.

Mini and micro
Various connectors have been used for smaller devices such as PDAs, mobile phones or digital cameras. These include the now-deprecated[12] (but standardized) Mini-A and the current standard Mini-B, Micro-A, and Micro-B connectors. The Mini-A and Mini-B plugs are approximately 3 by 7 mm, while the Micro plugs have a similar width but approximately half the thickness, enabling their integration into thinner portable devices.

The Micro-USB connector was announced by the USB-IF on January 4, 2007 and the Mini-USB connectors were withdrawn[citation needed]. As of February 2009[update], most available devices and cables still use Mini plugs, but the newer Micro connectors are becoming more widely adopted. The thinner Micro connectors are intended to replace the Mini plugs in new devices including smartphones and personal digital assistants. The Micro plug design is rated for 10,000 connect-disconnect cycles. The Universal Serial Bus Micro-USB Cables and Connectors Specification details the mechanical characteristics of Micro-A plugs, Micro-AB receptacles, and Micro-B plugs and receptacles, along with a Standard-A receptacle to Micro-A plug adapter. The carrier-led Open Mobile Terminal Platform (OMTP) group have recently endorsed micro-USB as the standard connector for data and power on mobile devices.[14] These include various types of battery chargers, allowing Micro-USB to be the single external cable link needed by some devices.

USB OTG Sockets: Mini-AB, Micro-AB
Except for special standard-to-Mini-A and standard-to-Micro-A adapters, USB cables always have an A-connector and a B-connector, on opposite ends. A-connectors can always connect to A-sockets; B-connectors can always connect B-sockets. These sockets all come in standard, mini, and micro versions.

For USB On-The-Go (or 'OTG') support for another socket type is defined: the AB, in both mini and micro versions. It can accept both A and B connector, through careful mechanical design. OTG software detects the difference by use of the ID pin, which is grounded in A-connectors and is otherwise floating. When an A-connector is connected to an AB socket, the socket supplies VBUS power to the cable and starts in the host role. When a B-connector is used, the socket consumes VBUS power and starts in the peripheral or device role. OTG allows those two roles to be switched by software, as needed for the task at hand.

Version history
USB 0.7: Released in November 1994.
USB 0.8: Released in December 1994.
USB 0.9: Released in April 1995.
USB 0.99: Released in August 1995.
USB 1.0 Release Candidate: Released in November 1995.

USB 1.0
USB 1.0: Released in January 1996.
Specified data rates of 1.5 Mbit/s (Low-Speed) and 12 Mbit/s (Full-Speed). Does not allow for extension cables or pass-through monitors (due to timing and power limitations). Few such devices actually made it to market.
USB 1.1: Released in September 1998.
Fixed problems identified in 1.0, mostly relating to hubs. Earliest revision to be widely adopted.

USB 2.0
Hi-Speed USB LogoUSB 2.0: Released in April 2000.
Added higher maximum speed of 480 Mbit/s (now called Hi-Speed). Further modifications to the USB specification have been done via Engineering Change Notices (ECN). The most important of these ECNs are included into the USB 2.0 specification package available from
Mini-B Connector ECN: Released in October 2000.
Specifications for Mini-B plug and receptacle. These should not be confused with Micro-B plug and receptacle.
Errata as of December 2000: Released in December 2000.
Pull-up/Pull-down Resistors ECN: Released in May 2002.
Errata as of May 2002: Released in May 2002.
Interface Associations ECN: Released in May 2003.
New standard descriptor was added that allows multiple interfaces to be associated with a single device function.
Rounded Chamfer ECN: Released in October 2003.
A recommended, compatible change to Mini-B plugs that results in longer lasting connectors.
Unicode ECN: Released in February 2005.
This ECN specifies that strings are encoded using UTF-16LE. USB 2.0 did specify that Unicode is to be used but it did not specify the encoding.
Inter-Chip USB Supplement: Released in March 2006.
On-The-Go Supplement 1.3: Released in December 2006.
USB On-The-Go makes it possible for two USB devices to communicate with each other without requiring a separate USB host. In practice, one of the USB devices acts as a host for the other device.
Battery Charging Specification 1.0: Released in March 2007.
Adds support for dedicated chargers (power supplies with USB connectors), host chargers (USB hosts that can act as chargers) and the No Dead Battery provision which allows devices to temporarily draw 100 mA current after they have been attached. If a USB device is connected to dedicated charger, maximum current drawn by the device may be as high as 1.8A. (Note that this document is not distributed with USB 2.0 specification package.)
Micro-USB Cables and Connectors Specification 1.01: Released in April 2007.
Link Power Management Addendum ECN: Released in July 2007.
This adds a new power state between enabled and suspended states. Device in this state is not required to reduce its power consumption. However, switching between enabled and sleep states is much faster than switching between enabled and suspended states, which allows devices to sleep while idle.
High-Speed Inter-Chip USB Electrical Specification Revision 1.0: Released in September 2007.

USB 3.0
On September 18, 2007, Pat Gelsinger demonstrated USB 3.0 at the Intel Developer Forum. The USB 3.0 Promoter Group announced on November 17, 2008, that version 1.0 of the specification has been completed and is transitioned to the USB Implementers Forum (USB-IF), the managing body of USB specifications.[34] This move effectively opens the spec to hardware developers for implementation in future products.


Consumer products are expected to become available in 2010. Commercial controllers are expected to enter into volume production no later than the first quarter of 2010.[38] NEC is aiming to produce its first USB controller in June 2009, initially priced at USD 15.00

Windows 7 drivers are under development but no public releases have been made available as of May 2009. The Linux Kernel supports USB 3.0 as of version 2.6.30.

Reference: Wikipedia

Blu-ray Disc

Blu-ray Disc (also known as Blu-ray or BD) is an optical disc storage medium designed by Sony to supersede the standard DVD format. Its main uses are high-definition video and data storage with 50GB per disc. The disc has the same physical dimensions as standard DVDs and CDs.

The name Blu-ray Disc is derived from the blue laser (violet-colored) used to read and write to this type of disc. In part because of the shorter wavelength (405 nanometres), substantially more data (almost 6 times more) can be stored on a Blu-ray Disc than on a standard DVD, which uses a red (650 nm) laser.

During the format war over high-definition optical discs, Blu-ray Disc competed with the HD DVD format. In February 2008, Toshiba—the main company supporting HD DVD— ceded and effectively ended the format war.

Blu-ray Disc is developed by the Blu-ray Disc Association, a group representing makers of consumer electronics, computer hardware, and motion pictures. As of January 2009, more than 890 Blu-ray disc titles are available in Australia, 720 in Japan, 1,140 in the United Kingdom, and 1,500 in the United States.

Commercial HDTV sets began to appear in the consumer market around 1998, but there was no commonly-accepted, inexpensive way to record or play HD content. In fact, there was no medium with the storage required to accommodate HD codecs, except JVC's Digital VHS and Sony's HDCAM.[6] Nevertheless, it was well known that using lasers with shorter wavelengths would enable optical storage with higher density. When Shuji Nakamura invented practical blue laser diodes, it was a sensation, although a lengthy patent lawsuit delayed commercial introduction.

Blu-ray Disc format finalized
The Blu-ray Disc physical specifications were finished in 2004. In January 2005, TDK announced that they had developed a hard coating polymer for Blu-ray Discs. The cartridges, no longer necessary, were scrapped. The BD-ROM specifications were finalized in early 2006. AACS LA, a consortium founded in 2004, had been developing the DRM platform that could be used to securely distribute movies to consumers. However, the final AACS standard was delayed, and then delayed again when an important member of the Blu-ray Disc group voiced concerns. At the request of the initial hardware manufacturers, including Toshiba, Pioneer and Samsung, an interim standard was published which did not include some features, like managed copy.

Technical specifications
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High-definition video may be stored on Blu-ray ROM discs with up to 1920x1080 pixel resolution at up to 60 frames per second interlaced or 24 frames per second progressive
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Recording speed

On August 8, 2008, Japanese electronics company Buffalo announced that it will ship the first 8x Blu-ray burners in Japan starting from September 2008. On September 22, 2008, Buffalo announced one internal and one external 8x Blu-ray burners for the United States, to be released the same month.[53] The following day Sony announced the BWU-300S, an internal 8x Blu-ray burner for the United States.

** Theoretical

Advanced Access Content System (AACS) is a standard for content distribution and digital rights management. It is developed by AS Licensing Administrator, LLC (AACS LA), a consortium that includes Disney, Intel, Microsoft, Matsushita (Panasonic), Warner Bros., IBM, Toshiba and Sony.

Since appearing in devices in 2006, several successful attacks have been made on the format. The first known attack relied on the trusted client problem. In addition, decryption keys have been extracted from a weakly protected player (WinDVD). Since keys can be revoked in newer releases,[71] this is only a temporary attack and new keys must continually be discovered in order to decrypt the latest discs. This cat-and-mouse game has gone through several cycles and as of August 2008 all current AACS decryption keys are available on the Internet.

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Software standards
The BD-ROM specification mandates certain codec compatibilities for both hardware decoders (players) and the movie-software (content). For video, all players are required to support MPEG-2, H.264/MPEG-4 AVC, and SMPTE VC-1.[55] MPEG-2 is the codec used on regular DVDs, which allows backwards compatibility. MPEG-4 AVC was developed by MPEG and VCEG. VC-1 is a codec that was mainly developed by Microsoft. BD-ROM titles with video must store video using one of the three mandatory codecs. Multiple codecs on a single title are allowed.

The choice of codecs affects the producer's licensing/royalty costs, as well as the title's maximum runtime, due to differences in compression efficiency. Discs encoded in MPEG-2 video typically limit content producers to around two hours of high-definition content on a single-layer (25 GB) BD-ROM. The more advanced video codecs (VC-1 and MPEG-4 AVC) typically achieve a video runtime twice that of MPEG-2, with comparable quality.

MPEG-2 was used by many studios, including Paramount Pictures (which initially used the VC-1 codec for HD DVD releases) for the first series of Blu-ray discs that were launched throughout 2006. Modern releases are now often encoded in either MPEG-4 AVC or VC-1, allowing film studios to place all content on one disc, reducing costs and improving ease of use. Using these codecs will also free many GBs of space for storage of bonus content in HD (1080i/p) as opposed to the SD (480i/p) typically used for most titles. Some studios (such as Warner Bros.) have released bonus content on discs encoded in a different codec than the main feature title; for example the Blu-ray Disc release of Superman Returns uses VC-1 for the feature film and MPEG-2 for bonus content (presumably because it is simply ported from the DVD release).[citation needed]

For audio, BD-ROM players are required to support Dolby Digital, DTS, and linear PCM. Players may optionally support Dolby Digital Plus and DTS-HD High Resolution Audio, as well as lossless formats Dolby TrueHD and DTS-HD Master Audio. BD-ROM titles must use one of the mandatory schemes for the primary soundtrack. A secondary audiotrack, if present, may use any of the mandatory or optional codecs.

For users recording digital television programming, the recordable Blu-ray Disc standard's initial data rate of 36 Mbit/s is more than adequate to record high-definition broadcasts from any source (IPTV, cable/satellite, or terrestrial). BD-Video movies have a maximum data transfer rate of 54 Mbit/s, a maximum AV bitrate of 48 Mbit/s (for both audio and video data), and a maximum video bitrate of 40 Mbit/s. This compares to HD DVD movies which have a maximum data transfer rate of 36 Mbit/s, a maximum AV bitrate of 30.24 Mbit/s, and a maximum video bitrate of 29.4 Mbit/s

References: Wikipedia

Dynamic Host Configuration Protocol (DHCP)

Dynamic Host Configuration Protocol (DHCP) is a protocol used by networked devices (clients) to obtain the information necessary for operation in an Internet Protocol network. This protocol reduces system administration workload, allowing devices to be added to the network with little or no manual intervention.

Dynamic Host Configuration Protocol is a way to manage network parameter assignment from a single DHCP server, or a group of DHCP servers arranged in a fault-tolerant manner. Even in small networks, Dynamic Host Configuration Protocol is useful because it can make it easy to add new machines to the local network.

DHCP is also recommended even in the case of servers whose addresses rarely change, so that if a server needs to be readdressed (RFC 2071), changes can be made in as few places as possible. For devices such as routers and firewalls that should not use DHCP, it can be useful to put Trivial File Transfer Protocol (TFTP) or SSH servers on the same machine that runs DHCP, which also serves to centralize administration.

DHCP can be used to assign addresses directly to servers and desktop machines, and, through a Point-to-Point Protocol (PPP) proxy, to dialup and broadband on-demand hosts, as well as for residential Network address translation (NAT) gateways.

DHCP emerged as a standard-track protocol in October 1993 as defined in RFC 1531, succeeding the BOOTP. The next update, RFC 2131 released in 1997 is the current DHCP definition for IPv4 networks. The extensions of DHCP for IPv6 (DHCPv6) were published as RFC 3315.

Basic protocol operation:
The Dynamic Host Configuration Protocol (DHCP) automates the assignment of IP addresses, subnet masks, default gateway, and other IP parameters.

When a DHCP-configured client (be it a computer or any other network-aware device) connects to a network, the DHCP client sends a broadcast query requesting necessary information from a DHCP server. The DHCP server manages a pool of IP addresses and information about client configuration parameters such as the default gateway, the domain name, the DNS servers, other servers such as time servers, and so forth. Upon receipt of a valid request the server will assign the computer an IP address, a lease (the length of time for which the allocation is valid), and other IP configuration parameters, such as the subnet mask and the default gateway. The query is typically initiated immediately after booting and must be completed before the client can initiate IP-based communication with other hosts.

DHCP provides four modes for allocating IP addresses. The best-known mode is dynamic, in which the client is provided a "lease" on an IP address for a period of time. Depending on the stability of the network, this could range from hours (a wireless network at an airport) to months (for desktops in a wired lab). At any time before the lease expires, the DHCP client can request renewal of the lease on the current IP address. A properly-functioning client will use the renewal mechanism to maintain the same IP address throughout its connection to a single network, otherwise it may risk losing its lease while still connected, thus disrupting network connectivity while it renegotiates with the server for its original or a new IP address.

The other modes for allocation of IP addresses are automatic , in which the address is permanently assigned to a client, and manual, in which the address is selected by the client (manually by the user or any other means) and the DHCP protocol messages are used to inform the server that the address has been allocated.

The automatic and manual methods are generally used when finer-grained control over IP address is required (typical of tight firewall setups), although typically a firewall will allow access to the range of IP addresses that can be dynamically allocated by the DHCP server.

The process of address allocation is known as ROSA. Request, Offer, Send, Accept.

Reference Wikipedia.

Short for Internet Protocol, IP


Short for Internet Protocol, IP is an address of a computer or other network device on a network using IP or TCP/IP . For example, the number "" is an example of such an address. These addresses are similar to addresses used on houses and help data reach its appropriate destination on a network.

There are five classes of available IP ranges: Class A, Class B, Class C, Class D and Class E, while only A, B and C are commonly used. Each class allows for a range of valid IP addresses. Below is a listing of these addresses.

Class Address Range Supports
Class A to Supports 16 million hosts on each of 127 networks.
Class B to Supports 65,000 hosts on each of 16,000 networks.
Class C to Supports 254 hosts on each of 2 million networks.
Class D to Reserved for multicast groups.
Class E to Reserved.

Ranges 127.x.x.x are reserved for loopback tests, for example, Ranges are used to broadcast to all hosts on the local network.

All IP addresses are broken down into 4 sets of octets that break down into binary to represent the actual IP address. The below chart is a basic example of the basic IP
IP: 255. 255. 255. 255.
Binary value: 11111111. 11111111. 11111111. 11111111.
Octet value: 8 8 8 8

If we were to break down the IP "", which is the IP address of Computer Hope, you would get the below value.

166. 70. 10. 23
10100110. 01000110. 00001010. 00010111
128+32+4+2=166 64+4+2=70 8+2=10 16+4+2+1=23

There are several IP addresses used or automatically assigned on a network. For example: 0 is the automatically assigned network address. 1 is the commonly used address used as the gateway. 2 is also a commonly used address used for a gateway. 255 is automatically assigned on most networks as the broadcast address.

Difference between NTFS and FAT32

Difference between NTFS and FAT32


1)allows access local to w2k,w2k3,XP,win NT4 with SP4 & later may get access for somefile.

2)Maximum size of partition is 2 Terabytes & more.

3)Maximum File size is upto 16TB.

4)File & folder Encryption is possible only in NTFS.

FAT 32

1)Fat 32 Allows access to win 95,98,win millenium,win2k,xp on local partition.

2)Maximum size of partition is upto 2 TB.

3)Maximum File size is upto 4 GB.

4)File & folder Encryption is not possible.

Difference between Downstream / upstream



A download involves the receipt of a file copied from a remote network location. Often, a person downloads files to their personal computer from a remote server computer. In Microsoft email networks, for example, people download their email from an Exchange server to their Outlook client.


An upload involves sending a copy of a file to a remote network location. For example, Web publishers upload files to their Web server.
Sending files across a computer network does not necessarily constitute an upload or a download. The terms are more commonly used in client/server networking than in peer-to-peer networking.

From the user's perspective, upstream network traffic flows away from the local computer toward the remote destination.
One way to generate upstream traffic is to upload files to a server or send an email message. Conversely, downloading files and receiving email generate downstream traffic. Typical Internet users create much more downstream than upstream traffic.
Conversely, downstream traffic flows to the user's computer. Traffic on most networks flows in both upstream and downstream directions simultaneously, and often when data flows in one direction, network protocols often send control instructions (generally invisible to the user) in the opposite direction.

Examples: The Web browser sends HTTP requests upstream to the Web server, and the server replies with downstream data usually in the form of HTML pages.

Asymmetric DSL (ADSL) services provides less bandwidth in the upstream direction in order to reserve more bandwidth for downstream traffic.

Measurement Units

Download / upload
Measured by kilo byte

Downstream / Upstream
Measured by kilo bit

So when we look to any ADSL line as an example we will find the following :
1024 kbit is a downstream rate and so if the line works 1:4 this means that it works 1024:256
If we knew that the ADSL line works 1:4 this means that
downstream = upstream*4
As download measured by kilobyte and downstream measured by kilobit , So download rate = downstream \ 8

Examples :
ADSL line with speed 1 m
Downstream = 1024 kbit
Upstream ( If 1:4) = 256 kbit
Download rate = 1024\8 = 128 kbyte
Upload rate = 256\8 = 32 kbyte

What is DNS?

What is DNS?

Domain Name System (DNS) is a database system that translates a computer's fully qualified domain name into an IP address.

Networked computers use IP addresses to locate and connect to each other, but IP addresses can be difficult for people to remember. For example, on the web, it's much easier to remember the domain name than it is to remember its corresponding IP address ( DNS allows you to connect to another networked computer or remote service by using its user-friendly domain name rather than its numerical IP address. Conversely, Reverse DNS (rDNS) translates an IP address into a domain name.

Each organization that maintains a computer network will have at least one server handling DNS queries. That server, called a name server, will hold a list of all the IP addresses within its network, plus a cache of IP addresses for recently accessed computers outside the network. Each computer on each network needs to know the location of only one name server. When your computer requests an IP address, one of three things happens, depending on whether or not the requested IP address is within your local network:

If the requested IP address is registered locally (i.e., it's within your organization's network), you'll receive a response directly from one of the local name servers listed in your workstation configuration. In this case, there usually is little or no wait for a response.

If the requested IP address is not registered locally (i.e., outside your organization's network), but someone within your organization has recently requested the same IP address, then the local name server will retrieve the IP address from its cache. Again, there should be little or no wait for a response.

If the requested IP address is not registered locally, and you are the first person to request information about this system in a certain period of time (ranging from 12 hours to one week), then the local name server will perform a search on behalf of your workstation. This search may involve querying two or more other name servers at potentially very remote locations. These queries can take anywhere from a second or two up to a minute (depending on how well connected you are to the remote network and how many intermediate name servers must be contacted). Sometimes, due to the lightweight protocol used for DNS, you may not receive a response. In these cases, your workstation or client software may continue to repeat the query until a response is received, or you may receive an error message.
When you use an application such as telnet to connect to another computer, you most likely type in the domain name rather than the IP address of that computer. The telnet application takes the domain name and uses one of the above methods to retrieve its corresponding IP address from the name server. A good analogy is to think of DNS as an electronic telephone book for a computer network. If you know the name of the computer in question, the name server will look up its IP address.

الدليل الشامل لكل الفروع شركة تي إي داتا tedata Branches

TE Data Branches

فرع المعادى : 7/2 شارع النصر بجوار سيلانترو كافيه

فرع المهندسين : 32 شارع الرياض متفرع من شارع شهاب

فرع الدقى : 94 شارع التحرير - برج المغربي بلازا - الدقى

فرع المنصورة : 37 شارع حسنى مبارك . ميدان المشاية

فرع الاسكندرية : 25 ميدان فيكتور ايمانويل . سموحة

فرع مدينة نصر :80 شارع مكرم عبيد أمام مسجد الايمان بجوار بنزينة شل

فرع الاقصر : 4 شارع السيد يوسف - الدور الثانى

مواعيد العمل تبدا من التاسعة صباحا حتى التاسعة مساء كل يوم ماعدا الجمعة من الثانية مساء حتى التاسعة مساء

B Tech Branches

بى تك هليوبوليس : 194 شارع النزهة بين ميدان الحجاز وميدان سانت فاتيما ومواعيد العمل تبدا من العاشرة صباحا حتى الثالثة مساء ثم من الخامسة مساء حتى التاسعة والنصف مساء كل
يوم ماعدا يوم الجمعة من الخامسة مساء حتى التاسعة والنصف مساء

بى تك النزهة : 23 شارع جوزيف تيتو بجوار بترو جيت ومواعيد العمل تبدا من الساعة
العاشرة صباحا حتى الساعة الثالثة مساء ثم من الساعة الخامسة مساء حتى الساعة التاسعة والنصف مساء كل يوم ماعدا يوم الجمعة من الخامسة مساء حتى التاسعة والنصف مساء.

بى تك عباس العقاد: 46 شارع عباس العقاد امام شيخ البلد ومواعيد العمل تبدا من العاشرة صباحا حتى الثالثة مساء ثم من الخامسة مساء حتى التاسعة والنصف مساء كل يوم ماعدا يوم الجمعة من الخامسة مساء حتى التاسعة والنصف مساء

بى تك القبة : 127 ا شارع مصر والسودان امام عمر افندى ومواعيد العمل تبدا من الساعة العاشرة صباحا حتى الساعة الثالثة مساء ثم من الساعة الخامسة مساء حتى الساعة التاسعة والنصف مساء كل يوم .

بى تك فيصل : 212 شارع الملك فيصل . محطة الطوابق ومواعيد العمل تبدا من الساعة العاشرة صباحا حتى الساعة الثالثة مساء ثم من الساعة الخامسة مساء حتى الساعة التاسعة والنصف مساء كل يوم ماعدا يوم الجمعة من الخامسة مساء حتى التاسعة والنصف مساء.

بى تك القصر العينى : 101 أ شارع القصر العيتى و مواعيد العمل تبدا من العاشرة صباحا حتى الرابعة مساء ثم من السادسة مساء حتى التاسعة والنصف مساء كل يوم ماعدا يوم الجمعة اجازة.

بى تك امبابة : 81 شارع الوحدة و مواعيد العمل تبدا من الحادية عشر صباحا حتى الثالثة مساء ثم من الخامسة مساء حتى التاسعة والنصف مساء ماعدا يوم الجمعة والسبت اجازة.

بى تك الهرم: 465 شارع نصر الدين و مواعيد العمل تبدا من العاشرة صباحا حتى الثالثة مساء ثم من الخامسة مساء حتى التاسعة والنصف مساء كل يوم ماعدا يوم الجمعة من الساعة الخامسة مساء حتى الساعة التاسعة والنصف مساء.

Branches Inside Exchange

سنترال مصر الجديدة : شارع جسر السويس ومواعيد العمل تبدا من التاسعة صباحا حتى التاسعة مساء كل يوم ماعدا الجمعة من الثانية مساء حتى التاسعة مساء.

سنترال رمسيس : شارع رمسيس ومواعيد العمل تبدا من التاسعة صباحا حتى الرابعة مساء ثم من الخامسة مساء حتى التاسعة مساء كل يوم ماعدا الجمعة من الثانية مساء حتى التاسعة مساء.

سنترال المهندسين : شارع احمد عرابى بجوار عمر افندى ومواعيد العمل تبدا من التاسعة صباحا حتى التاسعة مساء كل يوم ماعدا الجمعة من الثانية مساء حتى التاسعة مساء.

سنترال اكتوبر 2 : ميدان ليلة القدر ومواعيد العمل تبدا من التاسعة صباحا حتى الرابعة مساء ثم من الخامسة مساء حتى التاسعة مساء كل يوم ماعدا الجمعة من الثانية مساء حتى التاسعة مساء.

سنترال شبرا : شارع شبرا بجوار كلية الهندسة ومواعيد العمل تبدا من التاسعة صباحا حتى الرابعة مساء ثم من الخامسة مساء حتى التاسعة مساء كل يوم ماعدا الجمعة من الثانية مساء حتى التاسعة مساء.

سنترال شيراتون : بجوار مسجد صديق ومواعيد العمل تبدا من التاسعة صباحا حتى الخامسة مساء كل يوم ماعدا الجمعة والسبت اجازة.

سنترال الهانوفيل : هانوفيل قبلى بجوار مدرسة حافظة بنت عمر ومواعيد العمل تبدا من التاسعة صباحا حتى الرابعة مساء كل يوم ماعدا الجمعة والسبت اجازة.

سنترال المنشية : شارع سعد زغلول ومواعيد العمل تبدا من التاسعة صباحا حتى التاسعة مساء كل يوم ماعدا الجمعة من الثانية مساء حتى التاسعة مساء.

سنترال ميامى : شارع اسكندر ابراهيم ومواعيد العمل تبدا من التاسعة صباحا حتى التاسعة مساء كل يوم ماعدا الجمعة من الثانية مساء حتى التاسعة مساء.

مركز اتصالات المعادى : بجوار القمر الصناعى ومواعيد العمل تبدا من التاسعة صباحا حتى الخامسة مساء كل يوم ماعدا الجمعة والسبت اجازة.

مركز اتصالات الجيزة : شارع مراد امام مطعم جاد ومواعيد العمل تبدا من التاسعة صباحا حتى الخامسة مساء كل يوم ماعدا الجمعة والسبت اجازة.

سنترال الدقى : اول شارع مصدق بجوار وزارة الزراعة ومواعيد العمل تبدا من التاسعة صباحا حتى الخامسة مساء كل يوم ماعدا الجمعة والسبت اجازة.

سنترال الماظة : تقاطع شارع الثورة مع الميرغنى - القيادة المشتركة - مصر الجديدة. مواعيد العمل تبدا من التاسعة صباحا حتى الثامنة مساء كل يوم ماعدا الجمعة من الثانية مساء حتى الثامنة مساء.