Re: [OpenSIPStack] Questions Regarding RTP communication in openSBC

[Joegen E. B. <joe...@gm...>]

Ashish Khare wrote:
> But then in second case
> does it will pose a security threat  ?
> Because anyone can spoof an IP address and sends the RTP from different port
> ?
>
>
>   

Technically yes.  But this can be augmented by checking the ssrc of the 
RTP packet.  OpenSBC can be set to ignore RTP packets if the ssrc has 
changed.


> On 9/5/07, Joegen E. Baclor <joe...@gm...> wrote:
>   
>> Ashish Khare wrote:
>>     
>>> Hi Joegen,
>>>
>>> I have two questions for RTP communication in openSBC.
>>>
>>> 1) clients have to use the same RTP ports to send the RTP packets on
>>>       
>> which
>>     
>>> they recieve RTP packets. So if the client is recieveing RTP packets on
>>>       
>> port
>>     
>>> 8000, Cient will use 8000 only to send the RTP packets?
>>>
>>>       
>> Most implementations do this, yes.  In fact this behavior is needed for
>> OpenSBC NAT traversal to work.
>>
>>
>>     
>>> 2) When natted client initiated the call,  for example Client A which is
>>> behind a NAT, calls B through openSBC, the first RTP packets need to be
>>> recieved from Client A, at openSBC, in order to send the RTP packets
>>>       
>> from
>>     
>>> Client B to Client A. this is because of NAT device, the RTP packets
>>>       
>> from A
>>     
>>> comes from different port than what was said in the SDP offfer and
>>>       
>> therefore
>>     
>>> RTP packets from B need to be send to this new port.  is my
>>>       
>> understanding
>>     
>>> correct. Please clarify.?
>>>
>>> Please reply.
>>>
>>>       
>> Yes, this is exactly how its done in OpenSBC.
>>
>>
>>     
>>> Thanks.
>>>
>>> -Ashish
>>>
>>>       
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