In some countries the allocation is still channelized at present, whereas others have block or band allocations or a mixture. Voice operation is generally in upper sideband (USB) mode to facilitate inter-communication by non-amateur service users if necessary. In the United States and its Dependencies, channelized USB is mandatory. Where channelization is used, the USB suppressed carrier frequency (a.k.a. 'dial' frequency) is normally 1.5 kHz below the quoted channel frequency. For example, 5403.5 kHz is the 'dial' frequency for the channel centered on 5405 kHz. The "center" of the channel is based on the assumption that the bandwidth of SSB transmissions are 3 kHz, at most. Transmitters that are capable of wider SSB bandwidths should be adjusted for 3 kHz bandwidth or less so their emissions stay within the allocated channel.