I have always thought the RFCs got this totally wrong. The Most Significant Bit should have the highest 'bit number', ie in a byte, bit 7 is the MSB. This was how DEC drew diagrams of in memory representations of stuff, control and status registers and so on. We are stuck with suboptimal representations and in my insignificant opinion we are stuck with really awful protocols like SIP/RTP. Yes, I had TELCO background!