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) Web: http://www.evaristesys.com/, http://www.csrpswitch.com/