Where in the SDP RFC I could find why rtpmap is not define when we have just one payload like g711 a

HI Fellows,

I hope you are ok.

I was trying to look for in the SDP RFC following, but I couldn´t find a specific examples of information.

Where in the SDP RFC I could find why rtpmap is not defined when we have just one payload like g711 and just another dynamic payload?

For example:

Here you can see that SDP define the attribute for 8, 0 and 101,

v=0

o=sbc-1 1770824913 490353005 IN IP4 172.1.1.1

s=sip call

c=IN IP4 172.1.1.1

t=0 0

m=audio 21158 RTP/AVP 8 0 101

a=rtpmap:8 PCMA/8000

a=rtpmap:0 PCMU/8000

a=sendrecv

a=ptime:20

a=rtpmap:101 telephone-event/8000

a=fmtp:101 0-15,16

But here the SDP just defines rtpamp attribute for 101.