Payload sizes question

Hi ,

Can anyone tell the difference b/w these 4 sizes of payload found in soap header:Allof them look similar in meaning although they have different values....

<SAP:MessageSizePayload>60197</SAP:MessageSizePayload>

<SAP:MessageSizeTotal>72278</SAP:MessageSizeTotal>

<SAP:PayloadSizeRequest>60197</SAP:PayloadSizeRequest>

<SAP:PayloadSizeRequestMap>0</SAP:PayloadSizeRequestMap>

Thanks