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What is ADSL? Technologies of ADSL?
<% if faqtype = "1" then %> Frequently Asked Questions on ADSL



What is ADSL?
Asymmetric Digital Subscriber Line. ADSL is a modem technology that transforms ordinary phone lines (also known as "twisted copper pairs") into high-speed digital lines for ultra-fast Internet access. ADSL also enables access to corporate networks for telecommuters, as well as exciting new interactive multimedia applications such as multiplayer gaming, video on demand and video catalogs.

How does ADSL work?
ADSL modems use digital coding techniques to squeeze up to 99% more capacity out of a phone line without interfering with your regular phone services. That means you could be simultaneously talking on the phone or sending a fax - while surfing the World Wide Web.

How fast is ADSL?
ADSL can provide speeds up to 8 Mbps downstream (to the user) and up to 1 Mbps upstream, depending upon line length and loop and line conditions and also on the service package that you have subscribed with your Internet Service Provider.

What are the benefits of ADSL?
- Simultaneous Internet and voice/fax capabilities over a single telephone line
- Uninterrupted, high-speed Internet access that's always on-line
- Cost-effective solution for residential customers, telecommuters and small businesses
- Data Security that exceeds other technologies

What are the applications you use over ADSL?
ADSL enables two general types of applications -- interactive video and high speed data communications. Interactive video includes movies on demand, other video on demand such as delayed TV segments, video games, video catalogs, and video information retrieval. Data communications covers Internet access, telecommuting (remote LAN access), and specialized network access.

Can the Internet keep up with so much speed?
The Internet infrastructure is constantly being upgraded to handle the rapidly increasing use of the Internet. Many servers operate at 56 Kpbs. In addition, the Internet backbone has grown in an unplanned fashion and a connection may see 20 or more routers, creating significant delay, and for TCP connections, bandwidth throttling. However, a great deal of work is underway to (1) increase server access speeds, (2) improve backbone and NAP bandwidth, (3) increase router speeds, and (4) introduce ATM into the backbone for much lower latency. Futhermore, many Internet service providers will implement proxy or cache servers for frequently visited web pages, creating local access at least for these pages. At the very least, ADSL will make many Internet experiences far much better than voice band modems and the resulting market pressures will inevitably lead to capacity increases.

How does ADSL compare to cable modems?
ADSL provides a dedicated service over a single telephone line; cable modems offer a dedicated service over a shared media. While cable modems have greater downstream bandwidth capabilities (up to 30 Mbps), that bandwidth is shared among all users on a line, and will therefore vary, perhaps dramatically, as more users in a neighborhood get online at the same time. Cable modem upstream traffic will in many cases be slower than ADSL, either because the particular cable modem is inherently slower, or because of rate reductions caused by contention for upstream bandwidth slots.

<% elseif faqtype = "2" then %> Technologies of ADSL



Routers
Routers are connectors that are used to link different networks together. Routers can direct, or route, information to the correct destination.

What is Network Firewall
A firewall is a system or group of systems that enforces an access control policy between two networks. Most buildings are constructed with special walls designed to stop or slow the spread of fire through a building. A network firewall follows the same principle. It is designed to prevent unauthorized individuals from accessing a private network.

What is NAT
NAT is an abbreviation for Network Address Translation. It operates as a solution to having multiple, global IP addresses. If you intend to connect your current LAN to The Internet, it is likely that you will use a form of NAT so that each computer does not require a global unique IP address, but instead can use private addressing.
All traffic to and from the Internet goes through one external host - usually a router.
NAT is often built into routers. If router or NAT receives each packet from the internal private network and modifies the IP header to match the global IP address of the router, before transmitting the packet to the Internet. The router stores the internal IP address, destination IP address and port number in a routing table so when a request is returned on the same port, the NAT can match the internal IP address that originated the request, and then modify the IP header to match that of the internal address.
NAT saves on IP allocation. You can use an IP address from one of those in the ranges stated above for all the internal hosts on your LAN, but still connect to the Internet using NAT. Each IP address costs money, so NAT will help reduce costs.

What is VPN?
A VPN (Virtual Private Network) enables a specific group of users to access private network data and resources securely over the Internet or other networks. Although often using public networks, a VPN inherits the characteristics of a private network, hence the abbreviation of "Virtual" Private Network. It's the concurrent use of tunneling, encryption, authentication, and access control over a public network that basically characterizes a VPN.
VPNs may connect an individual machine and a private network (client-to-server) or a remote LAN (Local Area Network) and a private network (server-to-server). To do so VPNs need: a routed network (to transport data packets), optionally a tunnel switch (to increase security and versatility) , and tunnel terminators (acting like virtual cable terminators).
VPNs create "virtual" point-to-point connections using a technique called 'tunneling'. As the name suggests, tunneling acts like a 'pipe' which bores through a network cloud to connect two points. Typically started by a remote user, the tunneling process encapsulates data and encrypts it into standard TCP/IP packets, which can then safely travel across the Internet.

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