[VoiceOps] TCP Signaling for SIP Signaling

[Alex Balashov]

The use of TCP on the access/customer side of the network is increasing
because of:

1. Growing SIP message sizes and headers, and the UDP fragmentation it
engenders; 

2. WebRTC and concomitant/similar technologies and feature sets, which
use TCP or TCP-encapsulated transports;

3. Growing requirements of TLS/crypto, especially at the "last mile".

That said, TCP is certainly more resource-intensive, just by
definition. There is a lot of connection state to be held by the OS's
network stack. However, this isn't as relevant a consideration as it was
in the days when the guidance about the resource trade-offs was written,
due to the increase in RAM and processing power. 

And, as Peter E. said, there is the problem of replicating / holding
onto TCP state through failover, which has not been satisfactorily
solved at a reasonably universal level.

UDP continues to hold sway not only because of custom, habit and
inertia, but also because of its innate simplicity and resource
economies at large scales of message processing.

It's not necessarily an inappropriate business decision in 2017 to
switch your customers 100% to TCP. It depends on what kind of
business-level trade-offs you are willing to make with regard to
infrastructure, resource consumption and availability. UDP will probably
continue to obtain inside the service provider network core and in
inter-carrier, strictly Class 4 interconnects/trunk interfaces.

-- Alex

-- 
Alex Balashov | Principal | Evariste Systems LLC

Tel: +1-706-510-6800 / +1-800-250-5920 (toll-free) 
Web: http://www.evaristesys.com/, http://www.csrpswitch.com/