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Technical Telecom Forum - Telecom Technician - Hardware and Techniques, Help Requests, News and Discussions
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Posted by Atul on May 13, 2005, 3:00 am
hello All
I am reading information about VoIP technology
For that i am concentrating on SIP (Session Initiation Protocol) and
RTP (Real Time Transport Protocol).
I am interested in implementing RTP over TCP
I found that there are some disadvantages of TCP, some are
1) TCP doesn't support multicasting.
2) Through TCP is reliable, it heavily depends on retransmission of
lost or corrupted packets. That increases Delay. Our aim is real time
delivery of packets not reliability.
3) TCP congestion control mechanism decreases the congestion window
when packet losses are detected.
Apart from these flaws i am interested in implementing RTP over TCP
Is it possible ?
What is feasibility of implementing RTP over TCP ?
One more point is What is feasibility of implementing RTP over TCP in
case of NAT (Network Address Translation) is there ?
Need your valuable suggestion.
Thank You !
Atul Thosar
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Posted by Ian on May 15, 2005, 3:51 pm
> hello All
> I am reading information about VoIP technology
> For that i am concentrating on SIP (Session Initiation Protocol) and
> RTP (Real Time Transport Protocol).
> I am interested in implementing RTP over TCP
> I found that there are some disadvantages of TCP, some are
> 1) TCP doesn't support multicasting.
> 2) Through TCP is reliable, it heavily depends on retransmission of
> lost or corrupted packets. That increases Delay. Our aim is real time
> delivery of packets not reliability.
> 3) TCP congestion control mechanism decreases the congestion window
> when packet losses are detected.
> Apart from these flaws i am interested in implementing RTP over TCP
> Is it possible ?
> What is feasibility of implementing RTP over TCP ?
> One more point is What is feasibility of implementing RTP over TCP in
> case of NAT (Network Address Translation) is there ?
> Need your valuable suggestion.
WHY ?
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Posted by Morten Reistad on May 20, 2005, 6:00 pm
Ian <spam"AT"bathfordhill.co.uk> wrote:
>> hello All
>> I am reading information about VoIP technology
>> For that i am concentrating on SIP (Session Initiation Protocol) and
>> RTP (Real Time Transport Protocol).
>> I am interested in implementing RTP over TCP
>> I found that there are some disadvantages of TCP, some are
>> 1) TCP doesn't support multicasting.
>> 2) Through TCP is reliable, it heavily depends on retransmission of
>> lost or corrupted packets. That increases Delay. Our aim is real time
>> delivery of packets not reliability.
Public packet network, reliable delivery, realtime control.
Choose two.
If 1 and 2 is your choice, use TCP.
If 1 and 3 is it, use RTP.
If 2 and 3 is it, go shop for a different network offering.
>> 3) TCP congestion control mechanism decreases the congestion window
>> when packet losses are detected.
>> Apart from these flaws i am interested in implementing RTP over TCP
>> Is it possible ?
>> What is feasibility of implementing RTP over TCP ?
Implementing RTP over TCP correctly is a non-starter. TCP "uses up" your
realtime performance to acheive stream integrity; and use back-off plus
retransmits to acheive it.
>> One more point is What is feasibility of implementing RTP over TCP in
>> case of NAT (Network Address Translation) is there ?
>> Need your valuable suggestion.
There is one reason though. That is firewall penetration. But for
that you cannot implement TCP, just something that is indistiguishable
from TCP as seen from the outside. TCP that just keeps sending at
RTP paces into a huge window, and get acks back; and do retransmits
to keep the intermediate stuff happy.
It could be done well enough for a firewall not to see much difference
unless precise timin analysis were performed. But it would not be TCP.
And you would get better results in the current Internet by faking
DNS packets.
-- mrr
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> I am reading information about VoIP technology
> For that i am concentrating on SIP (Session Initiation Protocol) and
> RTP (Real Time Transport Protocol).
> I am interested in implementing RTP over TCP
> I found that there are some disadvantages of TCP, some are
> 1) TCP doesn't support multicasting.
> 2) Through TCP is reliable, it heavily depends on retransmission of
> lost or corrupted packets. That increases Delay. Our aim is real time
> delivery of packets not reliability.
> 3) TCP congestion control mechanism decreases the congestion window
> when packet losses are detected.
> Apart from these flaws i am interested in implementing RTP over TCP
> Is it possible ?
> What is feasibility of implementing RTP over TCP ?
> One more point is What is feasibility of implementing RTP over TCP in
> case of NAT (Network Address Translation) is there ?
> Need your valuable suggestion.