It's possible to transmit data in ICMP ECHO request and ICMP ECHO reply messages. (Commonly referred to as ICMP Tunneling) Embedding your callsign in a ping packet that is sent out every 10 minutes is a very easy and legal way to identify your reclassified Part 97 wireless network.
Reviewing the Unix ping on-line manual page shows us that the data may be set with: -p (pattern). You may send up to 16 characters (including spaces) per ping packet. This pattern must be specified as hexadecimal digits.
Example looped ID script: #!/bin/sh while true do /bin/ping -c 1 -s 21 -p 574952454C455353204E4F4445 44.92.20.35 # WIRELESS NODE /bin/ping -c 1 -s 24 -p 464343204152532043414C4C5349474E 44.92.20.35 # FCC ARS CALLSIGN /bin/ping -c 1 -s 22 -p 204B42394D575220464F52204944 44.92.20.35 # KB9MWR FOR ID sleep 600 done
This ping identification was one of the first methods I came up with. This was before embedded devices came on the market. This posed a whole new issue, until slightly later when is was discovered that most of them were Linux based.
Early microwave data pioneers such as N6GN, VE3JF and KE5FX employed MAC (machine access control) based identification. At the time this involved custom burring a MAC address translating to ones callsign using the ASCII code to an EEPROM. Fortunately now days we have softmacs, so changing a MAC address can be done on the fly much easier. Many embedded access point devices have an option for MAC cloning which will allow you to change it. To change your devices MAC address, you specify your callsign in hex. For Linux systems 'ifconfig eth1 hw ether 4B:42:39:4D:57:52' will do the trick. Working your callsign in at a MAC layer does seem the best, as it ensures it is always transmitted. Simply pad any unused fields with spaces (hex 20) if you have a short callsign. You can use lower and upper case in the event there are multiple devices on your network that use the same callsign.
Other methods to embed your callsign within the ethernet datagram is to configure your callsign as part of your network name. (Notice how I utilize the 44.x.x.x amateur IP's and my hostname contains my callsign) If you do this, background DNS/ARP traffic will take care of the identification requirement. Another good method to by sending the callsign at least every 10 minutes as part of DHCP address renewal. To accomplish this the client's hostname must be set to their callsign. (see the outernet project)
Wireless ethernet communications are considered as using a specified digital code to communicate because commercial products are available that facilitate the transmission and reception of the communications and the technical characteristics of wireless ethernet are publicly documented.
The rules no longer really specify how you must ID. Using this method, your callsign will be encapsulated inside an ethernet frame. And this conforms with 97.119(b)(3) for specified data emission codes [see 97.309 (3) & (4)] This is a perfectly reasonable and acceptable method, anyone with a sniffer or running dump on the link will be able to see your callsign:
eth1: len 60 4b:42:39:4d:57:52->6b:62:39:6d:77:72 type = IP IP: len 42 44.92.20.38->44.92.20.35 ihl 20 ttl 64 prot ICMP ICMP: type echo request id 54377 seq 0 ��� KB9MWR FOR ID
Keep in mind this is just one example of how to fulfill the identification requirement. You may use any other reasonable method you can come up with or any other method that is publicly documented. (which can be fulfilled by explaining your method on your internet webpage, as I have just done for example.)
An easy way to convert ASCII to hex in bash:
[kb9mwr@localhost]$ echo -n "KB9MWR" |xxd -p
4b42394d5752
�97.309 RTTY and data emission codes.
(a) Where authorized by �97.305(c) and 97.307(f) of this Part, an amateur
station may transmit a RTTY or data emission using the following specified
digital codes:
(3) The 7-unit, International Alphabet No. 5, code defined in
ITU-T Recommendation T.50 (commonly known as "ASCII").
ASCII stands for American Standard Code for Information Interchange. Computers can only understand numbers, so an ASCII code is the numerical representation of a character such as 'a' or '@' or an action of some sort. ASCII was developed a long time ago and now the non-printing characters are rarely used for their original purpose. Below is the printable ASCII character table for reference.
Binary | Oct | Dec | Hex | Char |
---|---|---|---|---|
010 0000 | 040 | 32 | 20 | ␠ (space) |
010 0001 | 041 | 33 | 21 | ! |
010 0010 | 042 | 34 | 22 | " |
010 0011 | 043 | 35 | 23 | # |
010 0100 | 044 | 36 | 24 | $ |
010 0101 | 045 | 37 | 25 | % |
010 0110 | 046 | 38 | 26 | & |
010 0111 | 047 | 39 | 27 | ' |
010 1000 | 050 | 40 | 28 | ( |
010 1001 | 051 | 41 | 29 | ) |
010 1010 | 052 | 42 | 2A | * |
010 1011 | 053 | 43 | 2B | + |
010 1100 | 054 | 44 | 2C | , |
010 1101 | 055 | 45 | 2D | - |
010 1110 | 056 | 46 | 2E | . |
010 1111 | 057 | 47 | 2F | / |
011 0000 | 060 | 48 | 30 | 0 |
011 0001 | 061 | 49 | 31 | 1 |
011 0010 | 062 | 50 | 32 | 2 |
011 0011 | 063 | 51 | 33 | 3 |
011 0100 | 064 | 52 | 34 | 4 |
011 0101 | 065 | 53 | 35 | 5 |
011 0110 | 066 | 54 | 36 | 6 |
011 0111 | 067 | 55 | 37 | 7 |
011 1000 | 070 | 56 | 38 | 8 |
011 1001 | 071 | 57 | 39 | 9 |
011 1010 | 072 | 58 | 3A | : |
011 1011 | 073 | 59 | 3B | ; |
011 1100 | 074 | 60 | 3C | < |
011 1101 | 075 | 61 | 3D | = |
011 1110 | 076 | 62 | 3E | > |
011 1111 | 077 | 63 | 3F | ? |
Binary | Oct | Dec | Hex | Char |
---|---|---|---|---|
100 0000 | 100 | 64 | 40 | @ |
100 0001 | 101 | 65 | 41 | A |
100 0010 | 102 | 66 | 42 | B |
100 0011 | 103 | 67 | 43 | C |
100 0100 | 104 | 68 | 44 | D |
100 0101 | 105 | 69 | 45 | E |
100 0110 | 106 | 70 | 46 | F |
100 0111 | 107 | 71 | 47 | G |
100 1000 | 110 | 72 | 48 | H |
100 1001 | 111 | 73 | 49 | I |
100 1010 | 112 | 74 | 4A | J |
100 1011 | 113 | 75 | 4B | K |
100 1100 | 114 | 76 | 4C | L |
100 1101 | 115 | 77 | 4D | M |
100 1110 | 116 | 78 | 4E | N |
100 1111 | 117 | 79 | 4F | O |
101 0000 | 120 | 80 | 50 | P |
101 0001 | 121 | 81 | 51 | Q |
101 0010 | 122 | 82 | 52 | R |
101 0011 | 123 | 83 | 53 | S |
101 0100 | 124 | 84 | 54 | T |
101 0101 | 125 | 85 | 55 | U |
101 0110 | 126 | 86 | 56 | V |
101 0111 | 127 | 87 | 57 | W |
101 1000 | 130 | 88 | 58 | X |
101 1001 | 131 | 89 | 59 | Y |
101 1010 | 132 | 90 | 5A | Z |
101 1011 | 133 | 91 | 5B | [ |
101 1100 | 134 | 92 | 5C | \ |
101 1101 | 135 | 93 | 5D | ] |
101 1110 | 136 | 94 | 5E | ^ |
101 1111 | 137 | 95 | 5F | _ |
Binary | Oct | Dec | Hex | Char |
---|---|---|---|---|
110 0000 | 140 | 96 | 60 | ` |
110 0001 | 141 | 97 | 61 | a |
110 0010 | 142 | 98 | 62 | b |
110 0011 | 143 | 99 | 63 | c |
110 0100 | 144 | 100 | 64 | d |
110 0101 | 145 | 101 | 65 | e |
110 0110 | 146 | 102 | 66 | f |
110 0111 | 147 | 103 | 67 | g |
110 1000 | 150 | 104 | 68 | h |
110 1001 | 151 | 105 | 69 | i |
110 1010 | 152 | 106 | 6A | j |
110 1011 | 153 | 107 | 6B | k |
110 1100 | 154 | 108 | 6C | l |
110 1101 | 155 | 109 | 6D | m |
110 1110 | 156 | 110 | 6E | n |
110 1111 | 157 | 111 | 6F | o |
111 0000 | 160 | 112 | 70 | p |
111 0001 | 161 | 113 | 71 | q |
111 0010 | 162 | 114 | 72 | r |
111 0011 | 163 | 115 | 73 | s |
111 0100 | 164 | 116 | 74 | t |
111 0101 | 165 | 117 | 75 | u |
111 0110 | 166 | 118 | 76 | v |
111 0111 | 167 | 119 | 77 | w |
111 1000 | 170 | 120 | 78 | x |
111 1001 | 171 | 121 | 79 | y |
111 1010 | 172 | 122 | 7A | z |
111 1011 | 173 | 123 | 7B | { |
111 1100 | 174 | 124 | 7C | | |
111 1101 | 175 | 125 | 7D | } |
111 1110 | 176 | 126 | 7E | ~ |