A P P E N D I X B |
After you calculate values for each network device in the path, use these values to determine the PDV for all paths in your network. If your path delays exceed 512 bit times, your network may suffer from late collisions or cyclic redundancy check (CRC) errors.
To calculate the worst case PDV, follow these steps:
1.Determine the delay value for each link segment (LSDV), including inter repeater links.
The LSDV is a delay value associated with a particular network segment. LSDV is similar to the segment delay value (SDV) used in calculating PDV for
LSDV = 2 (round trip delay) x segment length (in meters) x cable delay (in bit times per meter) for the segment
To determine the total segment length, use the following formula: Segment length = sum of all cable lengths between the physical layer interfaces at the repeater and the farthest DTE for end segments + sum of the cable lengths between the physical layer interfaces for inter repeater links. Use meters for measurements. Use the DTE delay values shown with step 4 to find the round trip delay value in bit times per meter (bt/m) for the type of cable used for a particular segment. That table also provides the round trip delay value in bit times. You can use this value if you do not know the actual cable lengths or propagation delays for each link segment. However, because the round trip delay value of 412 bit times for fiber optic cables will not apply to most applications, delays for fiber optic cables should always be calculated.
Cable type | Round trip delay Round trip delay value | |
| value in bit | in bit times |
| times per meter |
|
|
|
|
Category 3 UTP | 1.14 bt/m |
Category 4 UTP | 1.14 bt/m |
Category 5 UTP | 1.112 bt/m |
STP | 1.112 bt/m |
Fiber optic | 1.0 bt/m |
114 bit times (100 meters)
114 bit times (100 meters)
111.2bit times(100 meters)
111.2bit times (100 meters) 412 bit times (412 meters)
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