![]() ![]() If there’s only one bit per symbol, as is the case with binary NRZ, the bit and baud rates remain the same. If the baud rate is 4800 and there are two bits per symbol, the number of symbols is 2 2 = 4. R = baud rate x log 2S = baud rate x 3.32 log 10S If N is the number of bits per symbol, then the number of required symbols is S = 2 N. Normally the number of symbols is some power of two. For example, if the symbol rate is 4800 baud and each symbol represents two bits, that translates into an overall bit rate of 9600 bits/s. Some cable connections even use modulation to increase the data rate, which is referred to as “broadband transmission.”īy using multiple symbols, multiple bits can be transmitted per symbol. Baseband binary signals can’t be transmitted directly rather, the data is modulated on to a radio carrier for transmission. When the transmission medium can’t handle the baseband data, modulation enters the picture. With more than two symbols, data is transmitted using modulation techniques. However, it’s possible to have more than two symbols per transmission interval, whereby each symbol represents multiple bits. ![]() In this case, the baud or symbol rate is the same as the bit rate. NRZ binary has two symbols, one for each bit 0 or 1, that represent voltage levels. ![]() A symbol is one of several voltage, frequency, or phase changes. Baud rate refers to the number of signal or symbol changes that occur per second. The term “baud” originates from the French engineer Emile Baudot, who invented the 5-bit teletype code. The net data rate also is referred to as the throughput, or payload rate, of effective data rate. In a 10-Gbit/s Ethernet system, gross data rate equals 10.3125 Gbits/s to achieve a true data rate of 10 Gbits/s. In One Gigabit Ethernet, the actual line rate is 1.25 Gbits/s to achieve a net payload throughput of 1 Gbit/s. Typically, the actual line rate is stepped up by a factor influenced by the overhead to achieve an actual target net data rate. This relationship is usually expressed as a percentage of the payload size to the maximum frame size, otherwise known as the protocol efficiency: It would be even greater if the payload was anything smaller. With a maximum payload, the overhead is only 42/1542 = 0.027, or about 2.7%. Payload can range from 42 to 1500 octets. In the protocol frame, the data is called the “payload.” Non-data bits are known as the “overhead.” At times, the overhead may be substantial-up to 20% to 50% depending on the total payload bits sent over the channel.įor example, an Ethernet frame can have as many as 1542 bytes or octets, depending on the data payload. Yet for most serial transmissions, the data represents part of a more complex protocol frame or packet format, which includes bits representing source address, destination address, error detection and correction codes, and other information or control bits. Overheadīit rate is typically seen in terms of the actual data rate. This is usually expressed as 100 Mbits/s. If the bit time is 10 ns, the data rate equals: The data rate R is a function of the duration of the bit or bit time (T B) (Fig. The speed of the data is expressed in bits per second (bits/s or bps). 1), the signal never goes to zero as like that of return-to-zero (RZ) formatted signals. In the non-return-to-zero (NRZ) format (Fig. The data switches between two voltage levels, such as +3 V for a binary 1 and +0.2 V for a binary 0. This data signal is often called the baseband signal. Figure 1 typifies the digital-bit pattern from a computer or some other digital circuit. Data bits transmit one at a time over some communications channel, such as an RS-232 cable or a wireless path. Most data communications over networks occurs via serial-data transmission. This article is part of the Communication Series: What’s the Difference: Serial Communications 101 ![]()
0 Comments
Leave a Reply. |