SONET provides direct multiplexing of both SONET speeds and current and asynchronous and synchronous services into STS-n Payload.

• Payload types ranges from DS1 and DS3 to OC-3c and OC-12c payloads
• STS-1 supports direct multiplexing of DS-1 and DS-3 clear channel into single or multiple STS-1 envelopes which are called VTs
• Multiple STS-1 envelopes are multiplexed into STS-n signal
• In the method of multiplexing where users 1 through 28 represent individual DS 1, DS 2, DS 1 C and CEPT2 VT user access circuits.
• Below figure shows the method of multiplexing where users 1 through 28 represent individual DS1, DS2, DS1C, and CEPT2 VT user access circuits.
• Each of this input is first adapted to STS- 1 stream.
• These stream are combined with OC-1 and DS3 streams into a SONET multiplexer where they are converted to OC-3 stream
• Finally they are converted to OC-12 trunk and transmitted across the WAN
• It also shows M13 multiplexing 28 DS1s into a single DS3, which the SONET multiplexer converts to OC-n format.
• Five Mbps worth of overhead is bit-stuffed into the signal to boost the contents and meet the STS-1 rate of 51.84 Mbps.