Re: [Sipping] Request for Open discussion about SIP mobility

Paul Kyzivat wrote:
> Haruki Izumikawa wrote:
>   
>>  > And related to that - what about non-RTP media?
>>  > This same scenario is applicable to less conventional
>>  > media, such as IM. While technically it is possible
>>  > to follow the pattern you have outlined to establish
>>  > bicast MSRP, the identification of duplicate messages
>>  > will require a different solution.
>>
>> [HI] I think the bicasting solution is needed for realtime multimedia 
>> streams in which re-transmission cannot be acceptable. Therefore, I 
>> don't know some services such as IM or file transfer using MSRP need 
>> bicasting support. In fact, I haven't considered the concern you pointed 
>> out. I'm going to have to weigh this concern more carefully. Thank you 
>> for bringing this matter up.
>>     
>
> I guess it depends on what you mean by "acceptable".
> If you move from wifi to cellular access while IMing, I will not be 
> happy if some IMs from you are dropped or duplicated.
>
> In fact, I think this is more noticable for IM than for voice. With 
> voice a few dropped packets may cause a "glitch" but probably will not 
> create a significant loss of information. But a single dropped IM can be 
> a large loss of information.
>
> And now people are talking about using MSRP for real time text as well.
>
> So while it is perhaps of lower priority and interest, I think media 
> such as MSRP are worthy of some consideration.
>   
I completely agree with Paul, a SIP mobility solution should consider 
also the MSRP and
in general TCP scenario.
In the voice or video scenario (using rtp) a few dropped packets could 
be acceptable even
not noticed at all.
However using MSRP or in general TCP the scenario several issue should 
be considered,
for example:
- the time to setup a new TCP connection (this especially in the 
cellular world takes time several seconds)
- which messages or packets retransmit
- how avoid duplications or even retransmission of the same data

regards
Sal