Digital transmission & system configurations

Subjects covered below:
LAN configurations
T1 connection
DSL connection
Cable TV modems
Standard telephone modems
Cellular phone modems
Wireless networks
Which connection should I choose?

About LANs

Within an office today, computers are most likely connected via an Ethernet network called a Local Area Network (LAN). Ethernet gives a fast network at a reasonable cost. All modern computers come with an Ethernet connection or are prepared for an Ethernet connection card. If you install an Internet connection today (cable modem, DSL etc.) it will most likely have an Ethernet connector.

10 bits/s ~ 1 byte/s
1,000 bits/s ~ 1 kbps (kilobit/s)
1,000 kbps ~ 1 Mbps (megabit/s)

Bandwidth (kbps) = 
File size (kB) x Frame rate (fps) x 10

Ethernet is available in three speeds: 10 Mbps (Megabits per second), 100 Mbps and 1,000 Mbps. For home and office use, 100 Mbps is recommended. (Transmission speed is measured in bits per second. Eight bits equal one byte. But to transfer one byte, approx. 10 bits are required since approx. two extra bits will be used for control.)

100 Mbit Ethernet normally uses twisted pair copper cables. The cables are available shielded or unshielded and the maximum cable length is 100 meters (330 feet). If longer distances are needed, computer stores have a variety of accessories to choose from, e.g. fiber optic transmitters and wireless (radio) network.

To connect to the Internet, many kinds of transmission types and system configurations are possible.

 
Transmission types, modems and configurations

LAN (Local Area Network)
10/100 Mbit Ethernet, e.g. company intranets, offices, industries, warehouse facilities

10 Mbit Ethernet
Used within a building. There are two main standards for this. 10BaseT, which is using twisted pair cables and 10Base2, which is using coax cables. 10Base2 is not very popular as it is a bit unreliable. If there is a break anywhere on the cable, the whole network stops working. About 50% of the 10 Mbps capacity can be used.

100 Mbit Ethernet
Used within a building. The main standard is called 100BaseT. About 50% of the 100 Mbps capacity can be used. With switches, up to 100% of the capacity can be used. 1000 Mbit Ethernet, Gigabit Ethernet used for backbones in buildings. The main standard is called 1000BaseT. About 50% of the 1,000 Mbps capacity can be used. With switches, up to 100% of the capacity can be used.


T1 connection
Available from Internet providers. You pay a fixed fee every month and you can connect to the Internet as much as you want. This standard is popular among large companies. The connection speed is 1.5 Mbps.


 DSL modem connection
Varying transfer speed, e.g. subsidiaries, small businesses, shops, home offices


ADSL, HDSL, IDSL, VDSL etc. modems are getting more and more popular. DSL transmission is available from telephone companies and Internet providers. You pay a fixed fee every month and you can be connected to the Internet as much as you want. The speed will vary from company to company and from standard to standard; check with your local companies. The speed differs for upload and download. Typically the download speed will be about 1 Mbps and the upload speed will be about 250 kbps.


Cable TV modems
Cable TV modems use the cable TV cables for transmission. This service is popular for houses in some areas. The speed varies from area to area and the speed varies depending on how many neighbors are utilizing the service. A typical maximum speed is 1 Mbps.


Standard/telephone modems
Offers limited bandwidth, e.g. small businesses, public transportation, home offices

Telephone modems, PSTN
Widely used for accessing the outside world. They are cheap and practical, but not very fast. Sometimes transmission errors occur and data has to be sent again. When downloading files, the maximum speed can be up to 56 kbps, but for uploading files, the maximum speed is 33.6 kbps. It is possible to connect directly from a PC to a remote camera using standard modems. A protocol (program) called PPP makes this possible.


Telephone modems, ISDN
Popular in many countries. Usually, the telephone companies deliver ISDN modems. The maximum speed is 128 kbps.


Cellular phone modems, e.g. GSM, CDMA, CDPD, TDMA
Offers limited bandwidth, suitable for transferring still images from for ex. construction job sites, remote technical equipment

Using cellular phone modems is a good way to access remote cameras, e.g. cameras for traffic monitoring. No telephone cables are needed. The transmission speed is low, but sufficient for still images. Typical communication speeds range from 5-20 kbps. It is possible to connect directly from a PC to a remote camera using a standard modem for the computer and a radio modem for the network camera.


Wireless network adapter
Mobile applications that require live streaming video at e.g. live events, trade shows, remote locations without Internet connection

Wireless network, e.g. IEEE 802.11
Radio networks are becoming more and more popular as no cables are needed, which are the biggest cost in many installations. There are many different standards for high-speed radio communication. Typical maximum speeds range from 1-11 Mbps. A typical real life speed is 1 Mbps.

Wireless network, Bluetooth
Bluetooth radio communication is a standard which is now getting popular. The maximum speed is 720 kbit/s. A typical real life speed is 500 kbps.


Which connection should I choose?

The following alternatives are recommended:
• Standard modem for applications not requiring high speed
• DSL for offices
• Cellular phone modem or wireless network for remote cameras
• Within a building, the recommended alternative is 100 Mbit Ethernet


The following table shows typical capacity for different transmission types. Note that the data is approximate. Use it as a rough guide.
 

Transmission type Typical download speed Time to transmit a 25 kbyte image 
(in seconds)
Max. frame rate if every image is 25 kbyte (in FPS)
Transmission to a house or a building PSTN 45 kbps 6 10 frames/minute
ISDN 120 kbps 2 0.5
IDSL 150 kbps 2 0.6
ADSL - Low end 768 kbps 0.3 3
ADSL - High end 5 Mbps 0.05 20
HDSL 1.5 Mbps 0.2 6
VDSL 20 Mbps 0.01 80
Cable modem 750 kbps 0.3 3
T1 1.5 Mbps 0.2 6
 
Transmission within a house of a building 10BaseT 5 Mbps 0.05 20
100BaseT 50 Mbps 0.005 200
1000BaseT 500 Mbps 0.0005 2000
 
Wireless radio transmission GSM 9 kbps 30 2 frames/minute
802.11 1 Mbps 0.2 4
Bluetooth 500 kbps 0.5 2