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Steffen – This is really somewhat off topic for the SG, and getting into implementations, but you raise a problem I have seen a few times over the years. Several times over the years it has come up that the echo cancelled PHY world has implicitly assumed that the link segment response is linear. However, surge protectors may contain nonlinear devices. SPMDs actually aren’t the only source
of nonlinearity, for example, an ill-fitting oxidizing connection can do the same thing. For traditional, low-rate systems, particularly non-echo-cancelled ones, this really only shows up as insertion loss, and the nonlinear echo doesn’t matter. However,
in my experience, the nonlinear echo can have performance-limiting impacts on echo-cancelled systems, creating a residual echo floor for any system using linear echo cancellation. It shows up mainly at long reach, but, is an UNSPECIFIED impairment. In the
cases I dealt with it in the past, the protection devices were within the equipment (we would say on the PMA side of the MDI – although these weren’t Ethernet), and therefore at least the near-end was completely under control of the equipment manufacturer.
However, if we put surge protectors into the link segment, we probably need a linearity specification on the reflected component. This will ultimately relate to powering voltages and other implementation-specific effects, but may need work in 802.3. My question for you is: 1) have you seen this effect? (it would show up on very long links as some surge protectors causing reach loss greater than their insertion loss would indicate) and 2) do you have thoughts on specifying such an
impairment. If so, we may wish to consider a specific objective for compatibility with surge protection practices in the link segment. (I’m trying to write it general – I expect that we can’t be compatible with all) -george From: stds-802-3-spep2p@xxxxxxxxxxxxxxxxx <stds-802-3-spep2p@xxxxxxxxxxxxxxxxx>
On Behalf Of Steffen Graber Hi Peter, I agree with what David said in his response about surge protection and thanks David for your detailed explanations on this.
Related to the inline connectors, they are typically not equally spread across the length of the cable, but several may concentrate at the beginning or end of the segment, e.g.:
Power Switch in cabinet – 1-3 m Cable – Surge Protector in bottom area of cabinet – 30 cm Cable – Inline Connector (IC) at bottom of cabinet – 10-20 m Cable – IC in Marshalling Rack – 100 m Cable – IC in intermediate Fieldbox – 275 m –
IC in intermediate Fieldbox – 100 m – IC at Entry of Field Box – 30 cm – Surge Protector – 30 cm – Field Switch.
Depending on the installation, mostly the power switches (these who provide data and power to an Ethernet-APL Segment) will be located in a large cabinet, typically up to 3 m in height and 1 top 1.5 m in width. In such installations, typically
the power supplies for the switches are in the top rows, then the switches will come and at the bottom of the cabinet, there will be an (optional) row for the surge protectors and often an intermediate connector row, where it goes out of the cabinet (the layout
within the cabinet could be different, but for preinstalled cabinets, there is typically such a common connection point for all the cables going in). The background for having this intermediate connector row is, that in this case, the complete cabinet can
be pre-mounted before delivery to the construction side and that then just the cables coming from the field have to be hooked up all at the same point, which eases installation.
Then depending on how the plant is designed, there might be a further Marshalling Rack, especially in brown-field applications, where e.g. fieldbus or 4-20 mA applications should be replaced. This are racks, where the cables can be physically
routed between the switch cabinets and the cable bulks going out into the field. These racks are typically some meters (e.g. 10-20 m cable distance away from the other cabinets, in the same control room or in a neighbored room.
From there it goes the larger distance into the field, where the field box including the field switch(es) are.
At the destination point, typically the cable again goes to a pre-mounted field box, where there is an intermediate connector where the cable is connected to the complete box, then there might be an (optional) surge protection and from
that point it goes to the trunk input of the field switch. Above example shows, that, even if only 2 intermediate connectors are really needed in this example to handle the long distance run, in total up to 5 ICs + 2 for the surge protection devices are needed to build the segment.
This might be optimized (e.g. by removing the marshalling cabinet, which in new installations typically will not be there to remove the number of needed connectors by one, but will still be needed when upgrading older installations).
Regards, Steffen To unsubscribe from the STDS-802-3-SPEP2P list, click the following link:
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