q Algorithm

Last updated July 9, 2006.

(qPT = q Protocol Type  - example: qAU = q APRS UDP)

All packets
{
    Place into TNC-2 format
    If a q construct is last in the path (no call following the qPT)
        delete the qPT
}

All packets from an inbound connection that would normally be passed per current validation algorithm:
{
    If the packet entered the server from an UDP port:
    {
        if a q construct with a single call exists in the packet
            Replace the q construct with ,qAU,SERVERLOGIN
        else if more than a single call exists after the q construct
            Invalid header, drop packet as error
        else
            Append ,qAU,SERVERLOGIN
        Quit q processing
    }

    If the packet entered the server from an unverified connection AND the FROMCALL equals the client login AND the header has been successfully converted to TCPXX format (per current validation algorithm):
    {
        (All packets not deemed "OK" from an unverified connection should be dropped.)
        if a q construct with a single call exists in the packet
            Replace the q construct with ,qAX,SERVERLOGIN
        else if more than a single call exists after the q construct
            Invalid header, drop packet as error
        else
            Append ,qAX,SERVERLOGIN
        Quit q processing
    }

    If the packet entered the server from a verified client-only connection AND the FROMCALL does not match the login:
    {
        if a q construct exists in the packet
            if the q construct is at the end of the path AND it equals ,qAR,login
                Replace qAR with qAo
        else if the path is terminated with ,I
        {
            if the path is terminated with ,login,I
                Replace ,login,I with qAo,login
            else
                Replace ,VIACALL,I with qAr,VIACALL
        }
        else
            Append ,qAO,login
        Skip to "All packets with q constructs"
    }

    If a q construct exists in the header:
        Skip to "All packets with q constructs"

    If header is terminated with ,I:
    {
        If the VIACALL preceding the ,I matches the login:
            Change from ,VIACALL,I to ,qAR,VIACALL
        Else
            Change from ,VIACALL,I to ,qAr,VIACALL
    }
    Else If the FROMCALL matches the login:
    {
        Append ,qAC,SERVERLOGIN
        Quit q processing
    }
    Else
        Append ,qAS,login
    Skip to "All packets with q constructs"
}

If packet entered the server from an outbound connection (to another server's port 1313, for instance) and no q construct exists in the header:
{
    If header is terminated with ,I:
        Change from ,VIACALL,I to ,qAr,VIACALL
    Else
        Append ,qAS,IPADDR (IPADDR is an 8 character hex representation of the IP address of the remote server)
}

All packets with q constructs:
{
    if ,qAZ, is the q construct:
    {
        Dump to the packet to the reject log
        Quit processing the packet
    }

    If ,SERVERLOGIN is found after the q construct:
    {
        Dump to the loop log with the sender's IP address for identification
        Quit processing the packet
    }

    If a callsign-SSID is found twice in the q construct:
    {
        Dump to the loop log with the sender's IP address for identification
        Quit processing the packet
    }

    If a verified login other than this login is found in the q construct and that login is not allowed to have multiple verified connects (the IPADDR of an outbound connection is considered a verified login):
    {
        Dump to the loop log with the sender's IP address for identification
        Quit processing the packet
    }

    If the packet is from an inbound port and the login is found after the q construct but is not the LAST VIACALL:
    {
        Dump to the loop log with the sender's IP address for identification
        Quit processing the packet
    }

    If trace is on, the q construct is qAI, or the FROMCALL is on the server's trace list:
    {
        If the packet is from a verified port where the login is not found after the q construct:
            Append ,login
        else if the packet is from an outbound connection
            Append ,IPADDR

        Append ,SERVERLOGIN
    }
}