[SIPForum-discussion] bandwidth TIAS and AS values

[ashish rawat]

Hello Al1!

Need clarification on
parameter b (bandwidth request) in SDP parameter. I see two values for
parameter b  1. TIAS and 2. AS
 
TIAS  does not
include transport overhead and AS is application dependent includes overhead
, 
 
AS calculated from TIAS
, ( and to know AS value we need to know whats the overhead , if packet is
IPV4/IPV6  or ipsec , etc)
 
AS = TIAS b/w +
Transport overhead [[ this will get from c field whether this is ipv4/ipv6) *
maximum packets rate( pps) .( this we will get from maxptime/maxprate
 field).
 
In that case AS values
should be higher than TIAS irrespective of any topology. But I see both values
are equal in my lab a well as in cu's scenario. I am using Cisco Call Manager :-
 
Snippet from traces
 taken from lab (IP—CCM1----SIP-----CCM2----IP phone):
 
From Phone to CCM1
 
No Bandwidth
request 
v=0
o=Cisco-SIPUA 8728 0 IN
IP4 10.80.124.110
s=SIP Call
t=0 0
m=audio 22704 RTP/AVP 0
8 18 102 116 101
c=IN IP4 10.80.124.110
a=rtpmap:0 PCMU/8000
 
Invite is sent to CUCM2
without SDP
 
 
From CUCM2 to
 CUCM1 over SIP trunk 
 
 
v=0
o=CiscoSystemsCCM-SIP
105385 1 IN IP4 10.122.138.179
s=SIP Call
c=IN IP4 10.80.124.189
b=TIAS:64000
b=AS:64
t=0 0
 
200 from CUCM1 to
Phone 
 
v=0
o=CiscoSystemsCCM-SIP 22561
1 IN IP4 10.122.138.181
s=SIP Call
c=IN IP4 10.80.124.189
b=TIAS:8000
b=AS:8
t=0 0
m=audio 25466 RTP/AVP 18
101

I have following questions:-

1) Shouldn't AS values
should be higher than TIAS irrespective of any topology?
2) Has any one seen AS=TIAS  on other products. If yes what could be the reasoning behind it?

Thanks,
Ashish Rawat
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