Although we have mentioned H.261 before can be considered the most widely video compression standard used in the field of multimedia conferencing, it has its limitations as far as its suitability for transmission over PSDN. H261 does not map naturally onto hierarchical coding. A few suggestions has been made as to how this can happen but as a standard there is no support of that. H261 resolution is fine for conferencing applications. Once more quality critical video data need to be compressed, the upper limit optional CIF resolution can start showing inadequate.