Ipcf / Ipcf-Mc - Siemens SIMATIC NET SCALANCE W760 Series Configuration Manual

3.3

iPCF / iPCF-MC

The wireless range of an IWLAN system can be expanded by using multiple access points. If
a client moves from the area covered by one access point to the area covered by another
access point, the wireless link is maintained after a short interruption (roaming).
In an industrial environment, there are applications that require a deterministic response
when there are large numbers of nodes and when roaming to another cell require handover
times of less than 100 milliseconds.
● iPCF (industrial Point Coordination Function)
iPCF ensures that the entire data traffic of a cell is ordered, controlled by the access
point. Even with large numbers of nodes, collisions can also be avoided. iPCF also allows
fast cell changes.
You configure iPCF in "iFeatures > iPCF (Page 232)".
● iPCF-MC (industrial Point Coordination Function - Management Channel)
iPCF-MC was developed to make the advantages of iPCF available to fully mobile nodes
that communicate without being dependent on RCoax cable or directional antennas. With
iPCF-MC, the client also searches for potentially suitable access points when it receives
iPCF queries from the access point and the existing connection to an access point is
working problem-free. This means that if a change to a different access point is
necessary, this is achieved extremely quickly. In contrast to iPCF, the handover times for
iPCF-MC are not dependent on the number of wireless channels being used.
You configure iPCF-MC in "iFeatures > iPCF-MC (Page 232)".
iPCF / iPCF-MC - how it works
The access point checks all nodes in the wireless cell cyclically. At the same time, the scan
includes the downlink traffic for this node. In the reply, the node sends the uplink data. The
access point scans a new node at least every 5 ms.
The scan of a node is seen by all other nodes in the cell. This allows a client to detect the
quality of the wireless link to the access point even when it is not communicating with the
access point itself. If the client does not receive any frames from the access point for a
certain time, it starts to search for a new access point.
In iPCF mode, both the search for a new access point and the registration with this access
point have been optimized in terms of time. Handover times significantly below 50 ms are
achieved.
Stable PNIO communication is only possible when a WLAN client is in a cell with more than
60 % (-65 dBm) signal strength at all times. This can be checked by activating and
deactivating the various wireless cells.
This does not mean that the client needs to change when there is a signal strength < 60 %
(< -65 dBm). Make sure that access points are available with adequate signal strength.
SCALANCE W760/W720 to IEEE 802.11n Web Based Management
Configuration Manual, 11/2014, C79000-G8976-C350-03
Technical basics
3.3 iPCF / iPCF-MC
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