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4.1 | |
Introduction to Ethernet/802.3 LANs | |
| 4.1.7 | |
Ethernet 10 BASE-T transmission time |
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All networks have what is called bit time or
slot time. Many LAN technologies, such as Ethernet, define bit time as
the basic unit of time in which ONE bit can be sent. In order for the
electronic or optical devices to recognize a binary one or zero, there
must be some minimum duration during which the bit is on or off.
Transmission time equals the number of bits
being sent times the bit time for a given technology. Another way to
think about transmission time is the time it takes a frame to be
transmitted. Small frames take a shorter amount of time. Large frames
take a longer amount of time.
Each 10 Mbps Ethernet bit has a 100 ns transmission window. This is the bit time. A byte equals 8 bits. Therefore, 1 byte takes a minimum of 800 ns to transmit. A 64-byte frame, the smallest 10BASE-T frame allowing CSMA/CD to function properly, takes 51,200 ns ( 51.2 microseconds). Transmission of an entire 1000-byte frame from the source station requires 800 microseconds just to complete the frame. The time at which the frame actually arrives at the destination station depends on the additional latency introduced by the network. This latency can be due to a variety of delays including all of the following:
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