How to code a WAP Push message over SMS

This is a small guide in how to code a WAP Push message over SMS.

The Service indication

This is the message we want to deliver. It's a service indication message, the message will be presented to the user and if the user choose to accept the message the link to the server will be used.

WAP-167 Service Indication

<?xml version="1.0"?>
<!DOCTYPE si PUBLIC "-//WAPFORUM//DTD SI 1.0//EN"
"http://www.wapforum.org/DTD/si.dtd">
<si>
<indication href="http://www.it.kth.se/courses/2g1722/push.wml" >
This is a test.
</indication>
</si>

In order to send this we need to code it in WBXML format. Note that the specifics of how to code a service indication element is found in the end of WAP-167.

WBXML

0x02	WBXML version 1.1
0x05	public identifier for SI 1.0
0x04	charset iso-8859-1
0x00	length of string table
0x45	si with content
0xC6	indication with content and attributes
0x0D	token for "href=http://www."
0x03	inline string follows
....	the string "it.kth.se/courses/2g1722/push.wml"
0x00	end of string
0x01	end of indication attributes
0x03	inline string follows
....	the string "2G1722"
0x01	end of indication
0x01	end of si

Strings are coded in 8-bit octets, nothing funny here.

A WSP push

We now have to construct a WSP Push message.

WAP-251 PushMessage
WAP-230 WSP
WSP content type

0x01	push transaction id, could be anything
0x06	WSP type is Push
0x08	header length
0x01	content type length
0xAE	content type: application/vnd.wap.sic
0xAF	header: x-wap-application-id
0x82	2 - the WML User Agent
0xB4	header:push-flag
0x85	101 - last-push, URI authenticated

Note that when you look for the token values in WAP-230 you will not find "0xAE" but rather "0x2E". When coding small integers the high bit is set.

The WSP message is then put in a WDP packet that is directed to the push destination port.

The WDP

The WDP packet have different structure depending on which link layer we are using. Since we are sending it over a SMS we will code it as a User Data Header. Note that we have two elements one specifying the destination port (2948) and a second indicating that
the rest a concatented message.

WAP-259 WDP
GSM 03.40

0x0B	User Data Header length (not including this byte)
0x05	identifer elements, port addressing
0x04	length of element
0x0B84	push dest port (2948)
0x23F0	push originator port (9200)
0x00	concatenated short message
0x03
length of element
0x01	ref number
0x01	max number of segments
0x01	current segmenet number

The SMS

So we now have a WDP that includes a WSP consisting of a Service indication. This should now all be put in a SMS.

0x41	A SMS-SUBMIT message with a User Header
0x00	This is the message reference but here we let the phone set it.
0x0B	Length of the address, change this if you change the receiver number
0x91	The address type used, in this case international starting with country code
XXXXXXXXXXX	This is the phone number, check the SMS tutorial.
0x00	Protocol identifier.
0x04	Data coding scheme, in this case 8-bit bytes.
0x..	This is the length of the User Data

The whole WDP is now interpreted as a User Header Information. If the terminal can not understand the header it will be ignored.

http://web.it.kth.se/~johanmon/attic/2g1722/laborations/push.html