There are many types of connections available for modern networks. Network connection types vary widely. Dial-up, broadband, cable, DSL, satellite, ISDN, and cellular (broadband wireless) are the main types of network connections which we describe.
Ethernet Internet connections are becoming more common in homes and businesses, but are not described here.
The original connection type was dial-up. Dial-up uses the public switched telephone network (PSTN) or the plain old telephone service (POTS) to establish a dialed, circuit-switched connection to an Internet service provider via telephone lines.
Computers use a dial-up modem to modulate and demodulate packets as they enter and exit the computer. Modems have a maximum transfer speed of 56 kbs without compression.
A standard dial-up modem is pictured in Figure 16. Factors such as phone noise, caused by cabling and environmental factors, affect the quality of the connection and play a large part in determining connection speeds. A modem uses baseband signaling, meaning it can only carry one data channel at a time.
Figure 16: Dial-Up Modem
The term, broadband, describes two important concepts in networking. The first describes high-bandwidth communication. Cable modem and DSL circuits are the most common broadband connections available to consumers.
The second meaning describes a type of data transmission in which a single medium (fiber or copper wire) carries several channels at once. This is achieved by multiplexing independent channels into one broadband signal for transmission (such as voice, data, and video). See Figure 17.
Figure 17: Broadband Signaling
A digital subscriber line (DSL) is a broadband connection that transmits data over the telephone line. DSL is an always-on technology. A DSL modem reads and splits the data signal from the voice signal allowing one line to use multiple applications at a time. While the modem separates and reads the data signal, each telephone must have a splitter attached to separate the voice signal from the data signal.
DSL may be either:
- Asymmetric DSL (ADSL), meaning it supports greater downstream bandwidth than upstream bandwidth. This is the most common type of DSL installed in homes.
- Symmetric DSL (SDSL), meaning it has the same downstream and upstream bandwidth. This type is used when large amounts of information are both sent and received.
Cable broadband is a technology delivered via the cable television infrastructure. Cable broadband is typically faster than DSL, but the speed is greatly reduced as more people connect in a given neighborhood.
It also uses a modem to split the data and television signals. It uses an F type connector on RG-6 coaxial cable, as in Figure 18, connecting to the cable modem (Figure 19), and an RJ-45 UTP Ethernet cable connecting to a computer or switch. Download speeds are generally twice as high as upload speeds.
Figure 18: F Connector on RG-6 Cable
Figure 19: Cable Modem
Satellite broadband Internet access is a great option for remote geographies. Satellite relies on four primary components to work:
- A geosynchronous satellite in orbit around the earth
- A number of gateways: ground stations that relay the Internet signal to and from the satellite via microwaves
- A dish antenna located at the subscriber’s home or business
- A satellite modem at the user end that translates the signal
Downstream speeds of up to 50 Mbps are possible with geostationary satellites. Upstream use requires dialing in and the upload speed is limited by the dial-up modem.
ISDN (Integrated Services Digital Network)
Integrated Services Digital Network (ISDN) is a legacy digital service based on existing telephone lines. It is faster than dial-up but slower than DSL. It can be very expensive because of per-minute charges for transmission. ISDN was historically used in business as a backup when the primary service failed.
An ISDN Basic Rate Interface (BRI) connection is depicted in Figure 20. ISDN BRI was often used by consumers or small businesses for 128 kbps connections, with 16 kbps reserved for control signaling.
Figure 20: ISDN BRI
Cellular – Broadband Wireless
Cellular or mobile broadband or broadband wireless is wireless Internet access through a pocket modem, mobile phone (see Figure 21), or another mobile device.
Some mobile services allow several devices to be connected to the Internet using a single mobile connection through a process called tethering. Internet access subscriptions are often sold separately from base mobile phone subscriptions.
Several types of devices provide mobile broadband access including:
- PC cards that plug into a USB port
- mobile broadband modems or hotspots
- mobile devices with built-in support for mobile broadband, such as laptop computers, smartphones, and other mobile Internet devices
Figure 21: Broadband Wireless