[VoiceOps] TCP Signaling for SIP Signaling

[Alex Balashov]

On Mon, Jul 17, 2017 at 02:30:41PM -0500, John S. Robinson wrote:

> Although SIP registration state and SIP call state can be replicated
> over a pair of SBC's (Acme or Sonus), TCP state cannot be maintained.
> There is way to much going on at the driver level for that to be
> practical.  When switchover occurs, the TCP "transmission control"
> parameters are stale.  So, there will be a TCP RST, and the endpoints
> need to start over with the whole SYN / SYN,ACK "three-way handshake"
> drill.

I am not familiar intimately with the modalities of commercial SBC
vendors' failover options these days, but it had been my understanding
that Acme Packet can, in fact, replicate TCP session state at the OS
network stack level and fail it over "relatively seamlessly". I am not
sure offhand where I learned that or whether it is accurate. 

Regardless, it is certainly not a common denominator within the
industry, and is a difficult problem to solve. 

Moreover, speaking from an open-source vantage point, I think there is a
lot of concern that big, ambitious, capital-intensive investments in
this type of failover may not pay off if the future holds that failover
at that layer be done more commonly by "infrastructure", i.e. at the
hypervisor level. 

-- Alex

-- 
Alex Balashov | Principal | Evariste Systems LLC

Tel: +1-706-510-6800 / +1-800-250-5920 (toll-free) 
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