我正在使用VoIP提供商Messagenet，并且看到它将此INVITE发送给我的客户端：
INVITE sip:me@my.ip.address;transport=udp SIP/2.0
Record-Route: <sip:212.97.59.76:5061;r2=on;lr=on;ftag=as2a6c9e96;rpp=np>
Record-Route: <sip:212.97.59.76;r2=on;lr=on;ftag=as2a6c9e96;rpp=np>
Via: SIP/2.0/UDP 212.97.59.76:5061;branch=z9hG4bKb812.a8e25f17.0
Via: SIP/2.0/UDP 193.227.104.21:5060;branch=z9hG4bK1966d0a8
Max-Forwards: 69
From: "fromname" <sip:fromnumber@sip.messagenet.it>;tag=as2a6c9e96
To: <sip:mynumber@212.97.59.76>
Contact: <sip:fromnumber@193.227.104.21:5060>
Call-ID: 46cee45e062a30e3372663265a0be595@sip.messagenet.it
CSeq: 102 INVITE
User-Agent: whisky
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY, INFO, PUBLISH, MESSAGE
Supported: replaces, timer
X-Mnet-InLeg: whisky:1530689207.16483286;NH9HCiZ0TqZGK1ACkkhlvh67g1ig7LPEf+W5lblauyjqYqxgm1B2stIr6Mog/CC6
Content-Type: application/sdp
Content-Length: 377
v=0
o=root 60186075 60186075 IN IP4 193.227.104.23
s=whisky
c=IN IP4 193.227.104.23
t=0 0
m=audio 50216 RTP/AVP 18 8 3 0 97 101
a=rtpmap:18 G729/8000
a=fmtp:18 annexb=no
a=rtpmap:8 PCMA/8000
a=rtpmap:3 GSM/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:97 iLBC/8000
a=fmtp:97 mode=30
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=ptime:20
a=maxptime:150
a=sendrecv
我的问题是：Record-Route标头中的参数 r2 和 rpp 是什么意思？
Record-Route: <sip:212.97.59.76:5061;r2=on;lr=on;ftag=as2a6c9e96;rpp=np>
Record-Route: <sip:212.97.59.76;r2=on;lr=on;ftag=as2a6c9e96;rpp=np>
我正在寻找有关此的一些文档，但是到目前为止我什么都没发现。