Cabletron Systems SEHI100TX-22 - Manual (Page 22)

Chapter 3: Installation Requirements and Specifications
3-4 SEHI100TX User’s Guide
Propagation delay (collision delay) is the amount of time it takes data to
travel from the sending device to the receiving device. Total propagation
delay allowed for the entire network is 256 bit times (2.56
µ
s) in one
direction (5.12
µ
s round trip). If the total propagation delay between any
two nodes on the network exceeds 2.56
µ
s, then use bridges or other
devices to further segment the network.
3.2 NETWORK CABLE LENGTHS
This section details the maximum network cable lengths specified by the
IEEE 802.3u standard for a Class I repeater. As stated previously, the
physical size of the network is limited primarily by propagation delay.
The round trip delay cannot exceed 512 bit times or 5.12
µ
s.
A 100BASE-T network might use all UTP links, all fiber links or a
combination of both. Figure 3-1 shows a simplified example of a network
with one Class I repeater. Link segments A and B represent the longest
links in the network. In this case, if both segment A and segment B are
UTP, each segment may be up to 100 meters long for a maximum network
length of 200 meters. If segment A is UTP and segment B is fiber optics,
the maximum length of the network is 263 meters (with a maximum UTP
segment length of 100 meters). If both segments A and B are multimode
fiber optics, the maximum length is 274 meters.
If a buffered uplink (EPIM-100FMB) is used, the collision domain is
stopped at the EPIM slot. This allows a full length fiber optic link of 400
meters to be used as an uplink while maintaining 100-meter UTP and
400-meter fiber optic lengths to desktops. So if segment A, shown in
Figure 3-1, is UTP and segment B is fiber optics, the maximum length of
the network is 500 meters. If both segments are fiber optics, the maximum
length is 800 meters.
NOTE
A stack of five SEH hubs or four SEH hubs and one SEHI hub
is equivalent to one repeater.