The communication within the substation in IEC 61850 will typically be based on the sampled value (SV) service, while additional event data can be communicated with GOOSE or by reporting, dependent on its time criticality. Communication to receivers outside a substation can be done either by tunnelling the SV service across some high speed communication network like SDH or SONET, or – if communication delays and delay jitter are not a problem, via IP networks. For the second purpose the current IEC 61850 has to be enhanced by a mapping of samples and probably also GOOSE messages onto an IP based protocol. Due to the basically periodic nature of these services and the usage of multicast addressing UDP is a candidate for this. In the following it is assumed that this new mapping of the SV service will be based on UDP, and therefore shortly be called USV.