Dial-up Modems

Dial-up modems are used to connect to the Internet using a PSTN dial-up connection. The dial-up modem is connected to the Internet through a normal telephone line. These modems are capable of delivering a bandwidth of up to 56 Kbps under good line conditions. Modems with maximum throughput of 33.6 Kbps are also available and are much cheaper. Internal modem is nothing but a modem card placed in the CPU of a PC. Unlike the case of an external modem, the phone line jack is inserted directly into the slot on the CPU.

If you are using a laptop, a PCMCIA modem card is required. This is typically a 5 mm thick card that fits into the network slot in the laptop. Additionally, a proxy server can be used as a gateway that separates LAN from the outside world. It can also secure the LAN from intrusions as a firewall and act as a cache server that can store and provide local access to downloaded web pages

Cable Modem

In some cities, Internet can now be accessed also through the network of the local television cable operator. There are two ways of access models. Telco-return method, wherein cable modem is used for the return path, and an ordinary dial-up modem is used for the request, which is not prevalent in India. The two-way method uses only a cable modem and uses the cable network for both upload and download.

A cable modem acts as a converter of digital signals to analog signals, a tuner, and a hub. It can come as an external box or an add-in card inside a PC. It can also be integrated into a set-top-box for receiving Internet on a television set. Cable modems are capable of downloading data at about 27 Mbps and uploading at about 2.5 Mbps. However, depending on the kind of bandwidth the cable operator has subscribed and the number of modems connected to his network, users generally enjoy a download speed between 64 Kbps to 1.5 Mbps. What is a must for future operability is that the modem chosen is DOCSIS compliant.

Vendors

• 3Com,
• Com21,
• Motorola (GI),
• Terayon, Viasat (Scientific Atlanta)

SDN Adapter

If one has an ISDN connection, Internet access can be much faster. Using the same copper phone line, ISDN enables data communication up to a speed of 128 Kbps. In the case of an ISDN connection, one needs an ISDN adapter in place of a modem. In the modem model, it converts digital signals from the computer to analog signals and sends it over the analog telephone line. But in the case of ISDN, the telephone line coming in is a digital line. Hence, an ISDN Terminal Adapter (TA) is, as the name suggests, a device that adapts the telephone system with the computer system. The signal from the computer need not be converted to analog. What the TA does is amplify the signal. Also it has provisions for splitting the line into two primary channels—one for Internet access and the other for voice/fax communications.

Vendors

• Ascom,
• Eicon,
• D-Link

Leased Line Modems

A dedicated leased line is essentially a full circuit leased by an user. A pair of leased line modems sets up this dedicated circuit. One of the modems is the "originating" modem while the other is an "answering" modem. These modems come in various speeds and are either two-wire or four-wire in type. One can also use a converter to use a two-wire modem with a four-wire leased line or a four-wire modem with a two-wire leased line.

Vendors

• RAD,
• Motorola,
• Patton,
• Tellabs

SL Modem

Though most of the backbones and cores of today’s telecom networks are digital, a large portion of the last mile is still largely analog twisted-pair copper cables. DSL is a technology that digitizes this large pool of copper for better data communication throughput. DSL modems use different modulation technologies for this purpose. DSL is a rapidly changing technology. Hence, there are many forms of it and many more are on the way. Some DSL modems are asymmetric (different upstream and downstream data rates) while others are symmetric (same upstream/downstream data rates)

Vendors

• Alcatel,
• 3Com,
• D-Link,
• Efficient,
• RAD,
• Ericsson

Satellite Equipment for Internet Access

The set up for Internet access through satellite is basically through a roof-mounted satellite dish and a transceiver (transmitter as well as receiver) that operates in the microwave radio spectrum. The dish can be either of C-band or Ku-band (smaller size). Today’s transceivers are capable of transmitting data at a speed of 50 to 150 Kbps and downloading data at a speed of 150 Kbps and 1.2 Mbps.

In the case of satellite-return access, the uplink is through other traditional links like dial-up, leased line and ISDN.

Vendors

• Gilat,
• Viasat

Router

Routers are used mainly by different networks to communicate with each other using a dedicated communication link leased from a service provider. Also it is used to set up a dedicated connection to the Internet so that the servers that are placed in the public domain in one’s network can be accessed round the clock and the network/server becomes an Internet host.

Another popular use that routers are increasingly being put to is Virtual Private Networks (VPNs), where in the public Internet is used to set up a virtual private link between two networks. With Multi Protocol Label Switching (MPLS) functionalities, routers are able to provide a near-dedicated communication medium through a more reliable VPN than ever. If you want to set up a server and become a host, a router would be necessary. The basic function of a router is to enable two networks (next to each other or miles apart) to communicate with each other. Depending on the type of Internet access, a router can have different interfaces for V.32, Frame Relay, DSL, Cable, and Ethernet connectivity.

Vendors

• Cisco,
• Juniper,
• Unisphere,
• Nortel,
• Lucent

Fixed/Broadband Wireless Radio

Another popular way of accessing the Internet is through wireless radios. The Customer Premises Equipment (CPE) used in this case is a wireless radio with a V.32 or an Ethernet WAN interface. Also, the radio can be a point to point or a point to multipoint radio. This box is connected to a rooftop antenna on one side and a bridge/router on the other. However, the wireless radio can come integrated with a router/bridge. The user has to fix an antenna for this purpose tall enough to have a clear line of sight with the ISP’s antenna.

Vendors

• Cisco,
• P-Com,
• Western Multiplex,
• MRO-Tek.