SIDANG VIDEO

Sidang video (juga dikenali sebagai telepersidangan video atau telekonferens video, singkatan "VTC") merupakan satu set teknologi telekomunikasi interaktif yang membenarkan seseorang di dua atau lebih lokasi berinteraksi melalui penghantaran video dan audio dua-hala secara serentak. Ia juga telah dirujuk sebagai kerjasama dan merupakan sejenis perisian kumpulan. Ia berbeza dari videofon kerana ia direka untuk sesuatu persidangan dan bukan untuk individu.

Sidang video menggunakan telekomunikasi audio dan video untuk menghubungkan orang di beberapa tempat untuk bermesyuarat. Ini boleh memudah perbualan di antara dua orang dalam pejabat persendirian (point-to-point) atau melibatkan beberapa tempat (multi-point) dengan lebih seorang dalam bilik yang lebih besar di setiap tempat. Selain penghantaran audio dan visual aktiviti mesyuarat, sidang video boleh digunakan untuk berkongsi dokumen, maklumat paparan komputer, dan papan putih.

SEJARAH

Sidang video analog ringkas telah wujud hampir seawal penciptaan televisyen. Sistem sidang video ini terdiri dari dua sistem televisyen litar tertutup yang disambungkan menggunakan kabel. Semasa penerbangan angkasa lepas dikendalikan manusia pertama, NASA menggunakan dua sambungan frekuensi radio (UHF atau VHF), satu untuk setiap arah. Saluran TV sering menggunakan sidang video seperti ini apabila melaporkan dari lokasi jauh. Kemudian sambungan bergerak ke satelit menggunakan lori yang dilengkapi peralatan khas menjadi lebih umum.

Teknik ini bagaimanapun amat mahal, dan tidak boleh diterapkan dalam kegunaan biasa, seperti teleperubatan, pendidikan jarak jauh, mesyuarat perniagaan, dan seterusnya, terutamanya apa-apa kegunaan jarak jauh. Percubaan untuk menggunakan rangkaian telefoni biasa untuk menghantar video imbasan perlahan, seperti sistem pertama yang dibangunkan oleh AT&T, selalunya gagal disebabkan oleh kualiti gambar yang teruk dan ketiadaan teknik pemampatan video yang cekap. Lebar jalur 1 MHz dan kadar Picturephone 6 Mbit/s bit yang lebih besar pada 1970-an juga gagal menjayakan perkhidmatan ini.

Cuma pada 1980-an barulah rangkaian penghantaran telefoni digital mampu disediakan, contohnya ISDN, menjamin kadar bit minimum (lazimnya 128 kilobit/s) untuk penghantaran video dan audio termampat. Sistem khusus yang pertama, seperti yang dibuat oleh firma pelopor seperti PictureTel, mula muncul di pasaran apabila rangkaian ISDN mula berkembang di seluruh dunia. Sistem telepersidangan video sepanjang 1990-an berkembang dengan pantas dari peralatan dan perisian proprietari mahal serta keperluan rangkaian yang tertentu, kepada teknologi piawai yang mudah didapati oleh masyarakat umum pada harga yang munasabah. Akhirnya, pada 1990-an, sidang video berasaskan IP (Internet Protocol) mula boleh digunakan, dan teknologi pemampatan video yang lebih cekap dibangunkan, membolehkan sidang video berasaskan komputer meja, atau komputer peribadi (PC). Pada 1992 CU-SeeMe dibangunkan di Cornell oleh Tim Dorcey et al., IVS pula direka di INRIA, membolehkan VTC digunakan ramai. Kini, perisian tertentu atau plugin web, sestengahnya boleh didapati percuma, seperti NetMeeting, MSN Messenger, Yahoo Messenger, SightSpeed dan Skype menyediakan perkhidmatan murah persidangan video, walaupun dengan kualiti agak rendah, kepada semua.

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IP Address

IP Address

An Internet Protocol address (IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing. Its role has been characterized as follows: "A name indicates what we seek. An address indicates where it is. A route indicates how to get there."

The designers of the Internet Protocol defined an IP address as a 32-bit number and this system, known as Internet Protocol Version 4 (IPv4), is still in use today. However, due to the enormous growth of the Internet and the predicted depletion of available addresses, a new addressing system (IPv6), using 128 bits for the address, was developed in 1995, standardized as RFC 2460 in 1998, and its deployment has been ongoing since the mid-2000s.

IP addresses are binary numbers, but they are usually stored in text files and displayed in human-readable notations, such as 172.16.254.1 (for IPv4), and 2001:db8:0:1234:0:567:8:1 (for IPv6).

The Internet Assigned Numbers Authority (IANA) manages the IP address space allocations globally and delegates five regional Internet registries (RIRs) to allocate IP address blocks to local Internet registries (Internet service providers) and other entities.

IP Versions

Two versions of the Internet Protocol (IP) are in use: IP Version 4 and IP Version 6. Each version defines an IP address differently. Because of its prevalence, the generic term IP address typically still refers to the addresses defined by IPv4. The gap in version sequence between IPv4 and IPv6 resulted from the assignment of number 5 to the experimental Internet Stream Protocol in 1979, which however was never referred to as IPv5.

IPv4 address

In IPv4 an address consists of 32 bits which limits the address space to 4294967296 (232) possible unique addresses. IPv4 reserves some addresses for special purposes such as private networks (~18 million addresses) or multicast addresses (~270 million addresses).

IPv4 addresses are canonically represented in dot-decimal notation, which consists of four decimal numbers, each ranging from 0 to 255, separated by dots, e.g., 172.16.254.1. Each part represents a group of 8 bits (octet) of the address. In some cases of technical writing, IPv4 addresses may be presented in various hexadecimal, octal, or binary representations.

IPv4 private addresses

Early network design, when global end-to-end connectivity was envisioned for communications with all Internet hosts, intended that IP addresses be uniquely assigned to a particular computer or device. However, it was found that this was not always necessary as private networks developed and public address space needed to be conserved.

Computers not connected to the Internet, such as factory machines that communicate only with each other via TCP/IP, need not have globally unique IP addresses. Three ranges of IPv4 addresses for private networks were reserved in RFC 1918. These addresses are not routed on the Internet and thus their use need not be coordinated with an IP address registry.

Today, when needed, such private networks typically connect to the Internet through network address translation (NAT).

IANA-reserved private IPv4 network ranges
	Start	End	No. of addresses
24-bit block (/8 prefix, 1 × A)	10.0.0.0	10.255.255.255	16777216
20-bit block (/12 prefix, 16 × B)	172.16.0.0	172.31.255.255	1048576
16-bit block (/16 prefix, 256 × C)	192.168.0.0	192.168.255.255	65536

Any user may use any of the reserved blocks. Typically, a network administrator will divide a block into subnets; for example, many home routers automatically use a default address range of 192.168.0.0 through 192.168.0.255 (192.168.0.0/24).

IPv6 addresses

The rapid exhaustion of IPv4 address space, despite conservation techniques, prompted the Internet Engineering Task Force (IETF) to explore new technologies to expand the Internet's addressing capability. The permanent solution was deemed to be a redesign of the Internet Protocol itself. This next generation of the Internet Protocol, intended to replace IPv4 on the Internet, was eventually named Internet Protocol Version 6(IPv6) in 1995. The address size was increased from 32 to 128 bits or 16octets. This, even with a generous assignment of network blocks, is deemed sufficient for the foreseeable future. Mathematically, the new address space provides the potential for a maximum of 2¹²⁸, or about 3.403×10³⁸ unique addresses.

The new design is not intended to provide a sufficient quantity of addresses on its own, but rather to allow efficient aggregation of subnet routing prefixes to occur at routing nodes. As a result, routing table sizes are smaller, and the smallest possible individual allocation is a subnet for 2⁶⁴ hosts, which is the square of the size of the entire IPv4 Internet. At these levels, actual address utilization rates will be small on any IPv6 network segment. The new design also provides the opportunity to separate the addressing infrastructure of a network segment — that is the local administration of the segment's available space — from the addressing prefix used to route external traffic for a network. IPv6 has facilities that automatically change the routing prefix of entire networks, should the global connectivity or the routing policy change, without requiring internal redesign or renumbering.

The large number of IPv6 addresses allows large blocks to be assigned for specific purposes and, where appropriate, to be aggregated for efficient routing. With a large address space, there is not the need to have complex address conservation methods as used in Classless Inter-Domain Routing (CIDR).

Many modern desktop and enterprise server operating systems include native support for the IPv6 protocol, but it is not yet widely deployed in other devices, such as home networking routers, voice over IP (VoIP) and multimedia equipment, and network peripherals.

IPv6 private addresses

Just as IPv4 reserves addresses for private or internal networks, blocks of addresses are set aside in IPv6 for private addresses. In IPv6, these are referred to as unique local addresses (ULA). RFC 4193 sets aside the routing prefix fc00::/7 for this block which is divided into two /8 blocks with different implied policies The addresses include a 40-bit pseudorandom number that minimizes the risk of address collisions if sites merge or packets are misrouted.

Early designs used a different block for this purpose (fec0::), dubbed site-local addresses. However, the definition of what constituted sites remained unclear and the poorly defined addressing policy created ambiguities for routing. This address range specification was abandoned and must not be used in new systems.

Addresses starting with fe80:, called link-local addresses, are assigned to interfaces for communication on the link only. The addresses are automatically generated by the operating system for each network interface. This provides instant and automatic network connectivity for any IPv6 host and means that if several hosts connect to a common hub or switch, they have a communication path via their link-local IPv6 address. This feature is used in the lower layers of IPv6 network administration (e.g. Neighbor Discovery Protocol).

None of the private address prefixes may be routed on the public Internet.

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The similarities, differences and preventive

The Similarities and Differences Between AntiVirus and AntiSpyware

Antivirus and antispyware programs work pretty much in the same way, the difference being the type of malicious file and pattern the program scans your hard drive (including the system registry) for  and detects. Today some antivirus programs include antispyware protection, and vise versa. While dual purpose and all-in-one software has its advantages, most industry experts still agree that for optimal protection, computer users should invest in both a good antivirus and a good antispyware program. 

Preventative Maintenance Tips

• Always keep your operating system and programs up-to-date.
• Install an antivirus and antispyware program that automatically scans for viruses when the system boots.
• Update the virus/spyware definitions daily to ensure your system is protected against the latest threats.
• Do not download any files from the Internet unless you are certain the source is not transmitting a virus to you, or that the files are spyware-free.
• Do not use any storage media that has been used in another computer unless you are certain the other computer is free of viruses and will not pass the virus on to your system.
• Never open email attachments from people you don't know; and don't open any file attachment that ends in '.exe., All downloaded files should be scanned by your anti-virus application before you run or install it.

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Tips to Combat Viruses, Worms and Trojan Horses on Your Computer

Keep The Operating System Updated

The first step in protecting your computer from any malicious there is to ensure that your operating system (OS) is up-to-date. This is essential if you are running a Microsoft Windows OS. Secondly, you need to have anti-virus software installed on your system and ensure you download updates frequently to ensure your software has the latest fixes for new viruses, worms, and Trojan horses. Additionally, you want to make sure your anti-virus program has the capability to scan e-mail and files as they are downloaded from the Internet, and you also need to run full disk scans periodically. This will help prevent malicious programs from even reaching your computer.

Use a Firewall

You should also install a firewall. A firewall is a system that prevents unauthorized use and access to your computer. A firewall can be either hardware or software. Hardware firewalls provide a strong degree of protection from most forms of attack coming from the outside world and can be purchased as a stand-alone product or in broadband routers. Unfortunately, when battling viruses, worms and Trojans, a hardware firewall may be less effective than a software firewall, as it could possibly ignore embedded worms in out going e-mails and see this as regular network traffic.

For individual home users, the most popular firewall choice is a software firewall.  A good software firewall will protect your computer from outside attempts to control or gain access your computer, and usually provides additional protection against the most common Trojan programs or e-mail worms. The downside to software firewalls is that they will only protect the computer they are installed on, not a network.

It is important to remember that on its own a firewall is not going to rid you of your computer virus problems, but when used in conjunction with regular operating system updates and a good anti-virus scanning software, it will add some extra security and protection for your computer or network. 

Did You Know... CodeRed, a blended threat, launched DoS attacks, defaced Web servers, and its variant, CodeRed II, left Trojan horses behind for later execution. CodeRed was processed in memory — not on a hard disk — allowing it to slip past some anti-virus products. Computer Economics has estimated the worldwide cost of CodeRed at $2.62 billion dollars. [Source:Symantec Web site]

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The Difference Between a Computer Virus, Worm and Trojan Horse

Viruses, worms and Trojan Horses are all malicious programs that can cause damage to your computer, but there are differences among the three.

One common mistake that people make when the topic of a computer virus arises is to refer to a worm or Trojan horse as a virus. While the words Trojan, worm and virus are often used interchangeably, they are not exactly the same thing. Viruses, worms and Trojan Horses are all malicious programs that can cause damage to your computer, but there are differences among the three, and knowing those differences can help you better protect your computer from their often damaging effects.

What Is a Virus?

A computer virus attaches itself to a program or file enabling it to spread from one computer to another, leaving infections as it travels. Like a human virus, a computer virus can range in severity: some may cause only mildly annoying effects while others can damage your hardware, software or files. Almost all viruses are attached to an executable file, which means the virus may exist on your computer but it actually cannot infect your computer unless you run or open the malicious program. It is important to note that a virus cannot be spread without a human action, (such as running an infected program) to keep it going. Because a virus is spread by human action people will unknowingly continue the spread of a computer virus by sharing infecting files or sending emails with viruses asattachments in the email.

What Is a Worm?

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A worm is similar to a virus by design and is considered to be a sub-class of a virus. Worms spread from computer to computer, but unlike a virus, it has the capability to travel without any human action. A worm takes advantage of file or information transport features on your system, which is what allows it to travel unaided.

The biggest danger with a worm is its capability to replicate itself on your system, so rather than your computer sending out a single worm, it could send out hundreds or thousands of copies of itself, creating a huge devastating effect. One example would be for a worm to send a copy of itself to everyone listed in your e-mail address book. Then, the worm replicates and sends itself out to everyone listed in each of the receiver's address book, and the manifest continues on down the line. 

Due to the copying nature of a worm and its capability to travel across networks the end result in most cases is that the worm consumes too much system memory (or network bandwidth), causing Web servers, network servers and individual computers to stop responding. In recent worm attacks such as the much-talked-about Blaster Worm, the worm has been designed to tunnel into your system and allow malicious users to control your computer remotely.

What Is a Trojan horse?

A Trojan Horse is full of as much trickery as the mythological Trojan Horse it was named after. The Trojan Horse, at first glance will appear to be useful software but will actually do damage once installed or run on your computer.  Those on the receiving end of a Trojan Horse are usually tricked into opening them because they appear to be receiving legitimate software or files from a legitimate source.  When a Trojan is activated on your computer, the results can vary. Some Trojans are designed to be more annoying than malicious (like changing your desktop, adding silly active desktop icons) or they can cause serious damage by deleting files and destroying information on your system. Trojans are also known to create abackdoor on your computer that gives malicious users access to your system, possibly allowing confidential or personal information to be compromised. Unlike viruses and worms, Trojans do not reproduce by infecting other files nor do they self-replicate.

What Are Blended Threats?

Added into the mix, we also have what is called a blended threat. A blended threat is a more sophisticated attack that bundles some of the worst aspects of viruses, worms, Trojan horses and malicious code into one single threat. Blended threats can use server and Internet vulnerabilities to initiate, then transmit and also spread an attack. Characteristics of blended threats are that they cause harm to the infected system or network, they propagates using multiple methods, the attack can come from multiple points, and blended threats also exploit vulnerabilities.

To be considered a blended thread, the attack would normally serve to transport multiple attacks in one payload. For example it wouldn't just launch a DoS attack — it would also, for example, install a backdoor and maybe even damage a local system in one shot. Additionally, blended threats are designed to use multiple modes of transport. So, while a worm may travel and spread through e-mail, a single blended threat could use multiple routes including e-mail, IRC and file-sharing sharing networks.

Lastly, rather than a specific attack on predetermined .exe files, a blended thread could do multiple malicious acts, like modify your exe files, HTML files and registry keys at the same time — basically it can cause damage within several areas of your network at one time.

Blended threats are considered to be the worst risk to security since the inception of viruses, as most blended threats also require no human intervention to propagate. 

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Future Communication & Networking (part 3)

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