INTERNET EQUIPMENT: Buyer’s Guide

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.