Understanding the network.pdf - Back to Home

utilization performance. To calculate a throughput performance based
on frame size (in bits), use the following formula:
TFSB = TFSb × FPS = T/S
TFSB is the total frame size in bytes. TFSb is the total frame size in
bits, which is multiplied by the FPS frame per rate. The result is the
throughput per second rate (T/S). To derive the actual network
utilization (based on the frame size), calculate the maximum FPS rate
of the frame and compare the two results.
NOTE
nsec = 1 × 10 -9 or .000000001
usec = 1 × 10 -6 or .000001
msec = 1 × 10 -3 or .0001
sec = 1 × 10 1 or 1
To calculate the FPS rate for a given frame size and trasmission rate,
use the following calculations:
Step 1. Take the total frame size in bytes (TFSB) and multiply it by 8.
That converts it to bits (TFSb). (For demonstration purposes, we are
using a 64-byte frame on a 10Mbps Ethernet segment. Because
Ethernet has an 8-byte preamble and a 12-byte IFG, we need to add
an additional 20 bytes to the 64-byte frame.)
TFSB = 64 bytes + 8 bytes (PRE) + 12 bytes (IFG) = 84 bytes
TFSb = TFSB × 8 = 672 bits
Step 2. Multiply the TPSb by the appropriate bit time (bt) to get the
frame transmission time (FTt). The bt value is the transmission time
per bit, and PTt is the transmission time of a single packet. The
following lists the bit times for the various Layer 2 LAN protocol
transmission speeds:
1Mbps bt = 1 usec
4Mbps bt = 250 nsec