CUCM and CUBE - What is carrier-id/cid

[j.a.m.e.s]

I'm seeing a few references to carrier-id and how it could match a dial-peer either outbound or inbound (e.g. Page 12 in BRKCOL-2314).

Could anyone explain please:

1. What is the format of this carrier-id or cid tag? Is it a SIP header inside the INVITE or is it somehow part of the VIA header?

2. Is there any easy way to set this in CUCM such as a LUA script?

It sounds like an obvious way for CUBE to send calls to a carrier based on the intelligence of the downstream system. Incidentally, if there's a better way to indicate outbound CUBE dialpeer from a CUCM calling node, I would be interested to know.

[j.a.m.e.s]

Luckily @Jonathan Schulenberg posted a old Cisco Live slide (shame on Cisco for removing this vital documentation).

Carrier ID takes this format: x-route-tag="cid:carrier@next-hop" and is part of the VIA header.

Example: x-route-tag="cid:colt@10.1.1.1"

[j.a.m.e.s]

Here is a LUA script to add the Carrier ID into the VIA header on CUCM -> CUBE messages:

--[[
 In CUCM, you MUST specify a parameter of "carrier" (e.g. carrier=colt)
 This script will append ;x-route-tag="cid:carrier@next-hop" to the VIA header.
--]]

M = {}
    trace.enable()
    function M.outbound_ANY(msg)

        local carrier = scriptParameters.getValue("carrier")
        local via = msg:getHeader("Via")
        if via and carrier
        then
            -- Derive NextHop from RequestURI:
            local method,ruri,ver = msg:getRequestLine()
            local nexthop = ruri:match("@(%d+%.%d+%.%d+%.%d+)")
            -- Strip Previous CarrierID tag if present:
            local newvia = via:gsub("^(.*);x-route-tag=\"cid:.+\";?(.*)$", "%1%2")
            -- Add new CarrierID tag:
            newvia = newvia:gsub("^(.+)$","%1" .. ";x-route-tag=\"cid:" .. carrier .. "@" .. nexthop .. "\"" ,1)
            if trace.enabled()
            then
                trace.format("LUA VIA: Nexthop is:%s", nexthop)
                trace.format("LUA VIA: Carrier will be:%s", carrier)
                trace.format("LUA VIA: New header is:%s", newvia)
            end
            -- CUCM to amend the header:
            msg:modifyHeader("Via", newvia)

        end
 end

 return M

I haven't tested this in a live environment and I'm surprised it isn't part of a DevNet sample. If anyone could critique this/or tell me why it won't work, I would be very grateful. It's working well on a basic outbound SIP call.