Digital Transmission

Digital Transmission

It is recommended to use 100Mbit Ethernet within buildings. It is fast and widely available, and relatively inexpensive. For small offices and residences, 10Mbit Ethernet is suitable, but due to the small price difference, it is advisable to use 100Mbit Ethernet. 100Mbit Ethernet typically uses twisted pair cables. There are shielded or unshielded cables, with a maximum cable length of 330 feet (100 meters). If longer distances are needed, there are many accessories available at computer stores, such as fiber optic transmitters and wireless networks.

Transmission speed is measured in bits per second. 1 byte equals 8 bits. Transmitting 1 byte requires two additional control bits. This means that transmitting 1 byte requires 10 bits.

• 1 byte/s ~ 10 bits/s
• 1 kbit/s ~ 1,000 bits/s
• 1 Mbit/s ~ 1,000 kbit/s

Bandwidth (kbit/s) = File Size (kB) x Frame Rate (fps) x 10

Many types of transmission can be used to connect to the Internet. The remaining sections of this chapter will discuss different types and modes of transmission.

Telephone Mode, PSTN

Widely used for accessing the outside world. Inexpensive and practical, but not very fast. Transmission errors can occur, requiring data to be resent. The maximum speed when downloading files can reach 56kbit/s, while the maximum speed when uploading files is 33.6 kbit/s. A standard modem can connect a PC directly to a remote camera. The PPP protocol can achieve this.

Telephone Mode, ISDN

Popular in many countries. ISDN mode is generally offered by telephone companies. The maximum speed is 128 kbit/s.

xDSL Mode

Modes such as ADSL, HDSL, IDSL, and VDSL are becoming increasingly popular. Telecom service companies and ISP vendors offer xDSL transmission modes. You can connect to the Internet for a fixed monthly fee. Different companies and standards will have different speeds. Upload and download speeds also differ. Typically, download speeds are around 1Mbit/s, while upload speeds are around 250Kbit/s.

Cable Modem

Cable modem uses cable television cables for transmission. This service is more popular in densely populated urban areas. Speeds vary between different regions and can fluctuate based on how many users are using the service. The general maximum speed is 1 Mbit/s.

T1 Connection

Provided by Internet ISP vendors. You can connect to the Internet as needed for a fixed monthly fee. This line is more popular among businesses or establishments with high line usage, such as internet cafes. The connection speed is 1.5 Mbit/s.

10 Mbit Ethernet

This connection is used within buildings. There are two main standards: 10BaseT using twisted pair cables and 10Base2 using coaxial cables (RG-58). 10Base2 is not commonly used due to its unreliability. If there is a break anywhere in the cable, the entire network will stop working. About 50% of the 10 Mbit/s capacity can be used.

100 Mbit Ethernet

This connection is used within buildings. The main standard is 100BaseT. About 50% of the 100Mbit/s capacity can be used. If a switch is available, up to 100% of the capacity can be utilized.

1000 Mbit (GB) Ethernet

Used in the backbone networks of buildings. The main standard is 1000BaseT. About 50% of the 1000Mbit/s capacity can be used. If a switch is available, up to 100% of the capacity can be utilized.

Mobile Phones, such as GSM, CDMA, CDPD, and TDMA

The mobile phone mode is a good way to connect to remote cameras (such as those used for traffic monitoring). No telephone lines are required. The transmission speed is low, but it meets the needs of static images. The typical communication speed ranges from 5-20Kbit/s. A PC can be directly connected to a remote camera using a standard modem, while the network camera uses a wireless modem.

Wireless Networks, such as IEEE 802.11

Wireless networks are becoming increasingly popular as they do not require cables. There are many standards for high-speed wireless communication. Typically, the maximum communication speed ranges from 1-11Mbit/s, with an actual speed of about 1Mbit/s.

Wireless Networks, Bluetooth

Bluetooth wireless communication is an increasingly popular standard. The maximum speed is 720 Kbit/s, with an actual speed of about 500 Kbit/s.

Which connection method should be chosen?

Here are some recommended options:

• Standard mode for applications that do not require high-speed transmission
• xDSL for offices or home stores
• Mobile phones or wireless networks for remote cameras
• 100Mbit Ethernet is recommended for use within buildings

	Transmission Type	Typical Download Speed	Time Required to Transmit a 25Kbyte Image (seconds)	Maximum Frame Rate When Each Image is 25KB
Transmission to Residential or Building	PSTN	45kbit/s	6	10 frames/minute
	ISDN	120kbit/s	2	0.5
	IDSL	150kbit/s	2	0.6
	ADSL - Low End	768kbit/s	0.3	3
	ADSL - High End	5Mbit/s	0.05	20
	HDSL	1.5Mbit/s	0.2	6
	VDSL	20Mbit/s	0.01	80
	Cable Modem	750kbit/s	0.3	3
	T1	1.5Mbit/s	0.2	6
Transmission Within Residential or Building	10BaseT	5Mbit/s	0.05	20
	100BaseT	50Mbit/s	0.005	200
	1000BaseT	500Mbit/s	0.0005	2000
Wireless Transmission	GSM	9kbit/s	30	2 frames/minute
	802.11	1Mbit/s	0.2	4
	Bluetooth	500kbit/s	0.5	2

This table shows the transmission capabilities of different transmission types. Note that the data in the table is estimated and should be used as a rough reference.

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