I have a project in which a user is interesting in interconnecting and deploying ATAs for VoIP services but wants to use private IP addressing on the devices. My initial though is to NAT these devices and allow my SBC to handle NAT traversal for them. This allows the to use their dedicated connection to my network or if that link goes down fail over to moving to connecting across the internet. They are interested in potentially doing a GRE tunnel and keeping the private addressing in place as it traverses that tunnel. I am concerned about encapsulating the VoIP traffic as well as with the fail over options. Does anybody have any experiences with VoIP over GRE tunnels and what type of results and challenges you encountered? Thanks. --BH
What you are describing is similar to the Acme TSM product where sip / rtp are wrapped in a tunnel for nat traversal purposes. It actually has quite a few strengths but all of them depend on the tunneling devices ability to detect failure and re-negotiate. If there are any interfering devices in the middle with ALG's etc it should cut right through them, and as far as overhead goes, as long as you arent doing any crypto its actually pretty light. You will want to be aware of path MTU for signaling traffic since the extra bits of overhead can pad a large sip packet (think invite with custom headers and large-ish SDP) over 1500 bytes which will cause fragmentation issues. Consider going to compact headers to eliminate this and make some overhead room. RTP wont have this issue of course. Will you be doing sip over udp or tcp for this? Who will be managing the GRE tunnel endpoints, and what devices will be doing the tunneling? What is your sip redundancy model right now? On 08/13/2013 07:17 AM, Bob Hancock wrote:
I have a project in which a user is interesting in interconnecting and deploying ATAs for VoIP services but wants to use private IP addressing on the devices. My initial though is to NAT these devices and allow my SBC to handle NAT traversal for them. This allows the to use their dedicated connection to my network or if that link goes down fail over to moving to connecting across the internet. They are interested in potentially doing a GRE tunnel and keeping the private addressing in place as it traverses that tunnel. I am concerned about encapsulating the VoIP traffic as well as with the fail over options. Does anybody have any experiences with VoIP over GRE tunnels and what type of results and challenges you encountered? Thanks.
--BH
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Allow me to discuss your initial assumption a bit more. Is the user part of your organization, as used in rfc1918? If you're not in the same organization as each other, then this sort of sharing of non-routable IP addresses across organization boundaries is not really anticipated by rfc1918. If you can claim that the endpoint devices are part of your organization, then perhaps an argument can be made. But that implies there is no collaborative coordination of IP space, but rather direct control by a controlling authority. This kind of control does happen when an SP like Comcast/twtelecom assigns an rfc1918 IP to the EMTA at a customer premise. The customer has no control at all, and can actually safely reuse any private IP address he wishes without interfering with the SP. Collaboration breaks down if you don't have a unified way to guarantee uniqueness across BOTH organizations. And I've seen this fail. Rfc1918 itself gives examples of the limitations of using private IP address space. If you cannot control the use of the rfc1918 space in both organizations, it's better to use public IPs on the inter-organization interfaces, with ALG or quality NAT on the endpoints.
mark at ecg.co +12293160013 http://ecg.co/lindsey
On Aug 13, 2013, at 10:19, Bob Hancock <bobhancock205 at gmail.com> wrote:
I have a project in which a user is interesting in interconnecting and deploying ATAs for VoIP services but wants to use private IP addressing on the devices.
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