EMI (protocol)
Encyclopedia
External Machine Interface (EMI), an extension to Universal Computer Protocol (UCP), is a protocol
primarily used to connect to short message service centres (SMSCs) for mobile telephones. The protocol was developed by CMG
Wireless Data Solutions, now part of Acision
.
^B01/00045/O/30/66677789///1//////68656C6C6F/CE^C
^B01/00041/R/30/A//66677789:180594141236/F3^C
The start of the packet is signaled by ^B (STX, hex 02) and the end with ^C (ETX, hex 03). Fields within the packet are separated by / characters.
The first four fields form the mandatory header. the third is the operation type (O for operation, R for result), and the fourth is the operation (here 30, "short message transfer").
The subsequent fields are dependent on the operation. In the first line above, '66677789' is the recipient's address (telephone number
) and '68656C6C6F' is the content of the message, in this case the ASCII
string "hello". The second line is the response with a matching transaction reference number, where 'A' indicates that the message was successfully acknowledged by the SMSC, and a timestamp is suffixed to the phone number to show time of delivery.
The final field is the checksum
, calculated simply by summing all bytes in the packet (including slashes) and taking the 8 least significant bit
s from the result.
The full specification is available on the LogicaCMG website developers' forum, but registration is required.
The default alphabet - interesting is that in EMI UCP documentation default alphabet is IRA (eq ASCII on 7bit). In practice default alphabet is GSM-7
, which is almost the same as ASCII on 7 bit, except few characters (for example '_' underline).
Communications protocol
A communications protocol is a system of digital message formats and rules for exchanging those messages in or between computing systems and in telecommunications...
primarily used to connect to short message service centres (SMSCs) for mobile telephones. The protocol was developed by CMG
CMG (company)
CMG was a consulting company focused on telecommunications and computing and based in London, United Kingdom. It was once a constituent of the FTSE 100 Index but was acquired by Logica in 2002.-History:...
Wireless Data Solutions, now part of Acision
Acision
Acision is a privately held mobile communications network infrastructure company specialising in messaging and charging systems that enable popular services such as Short message service , Multimedia Messaging Service , mobile internet browsing, Mobile Broadband and voicemail.-History:Acision's...
.
Syntax
A typical EMI/UCP exchange looks like this :^B01/00045/O/30/66677789///1//////68656C6C6F/CE^C
^B01/00041/R/30/A//66677789:180594141236/F3^C
The start of the packet is signaled by ^B (STX, hex 02) and the end with ^C (ETX, hex 03). Fields within the packet are separated by / characters.
The first four fields form the mandatory header. the third is the operation type (O for operation, R for result), and the fourth is the operation (here 30, "short message transfer").
The subsequent fields are dependent on the operation. In the first line above, '66677789' is the recipient's address (telephone number
Telephone number
A telephone number or phone number is a sequence of digits used to call from one telephone line to another in a public switched telephone network. When telephone numbers were invented, they were short — as few as one, two or three digits — and were given orally to a switchboard operator...
) and '68656C6C6F' is the content of the message, in this case the ASCII
ASCII
The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...
string "hello". The second line is the response with a matching transaction reference number, where 'A' indicates that the message was successfully acknowledged by the SMSC, and a timestamp is suffixed to the phone number to show time of delivery.
The final field is the checksum
Checksum
A checksum or hash sum is a fixed-size datum computed from an arbitrary block of digital data for the purpose of detecting accidental errors that may have been introduced during its transmission or storage. The integrity of the data can be checked at any later time by recomputing the checksum and...
, calculated simply by summing all bytes in the packet (including slashes) and taking the 8 least significant bit
Least significant bit
In computing, the least significant bit is the bit position in a binary integer giving the units value, that is, determining whether the number is even or odd. The lsb is sometimes referred to as the right-most bit, due to the convention in positional notation of writing less significant digits...
s from the result.
The full specification is available on the LogicaCMG website developers' forum, but registration is required.
Technical Limitations
The two digit transaction reference number means that an entity sending text messages can only have 100 outstanding messages (per session); this can limit performance, but only if you have very slow network and incorrectly configure your application on your SMSC (for example one session, with number of window bigger than 100). In practice it does not have any impact on delivery throughput.The default alphabet - interesting is that in EMI UCP documentation default alphabet is IRA (eq ASCII on 7bit). In practice default alphabet is GSM-7
GSM 03.38
In Mobile telephony GSM 03.38 is a character set used in the Short Message Service of GSM based cell phones. It is defined in GSM recommendation 03.38. Messages sent via this encoding can be encoded in the default GSM 7-bit alphabet, the 8-bit data alphabet, and the 16-bit UTF-16 alphabet...
, which is almost the same as ASCII on 7 bit, except few characters (for example '_' underline).
Alternatives
- Short message peer-to-peer protocolShort message peer-to-peer protocolThe Short Message Peer-to-Peer protocol is a telecommunications industry protocol for exchanging SMS messages between SMS peer entities such as short message service centers and/or External Short Messaging Entities. It is often used to allow third parties The Short Message Peer-to-Peer (SMPP)...
(SMPP) also provides SMSShort message serviceShort Message Service is a text messaging service component of phone, web, or mobile communication systems, using standardized communications protocols that allow the exchange of short text messages between fixed line or mobile phone devices...
over TCPTransmission Control ProtocolThe Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol , and therefore the entire suite is commonly referred to as TCP/IP...
/IPInternet ProtocolThe Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
. - Computer Interface for Message Distribution (CIMD)CIMDComputer Interface to Message Distribution is a proprietary short message service centre protocol developed by Nokia for their SMSC .-Syntax:An example CIMD exchange looks like the following:...
developed by NokiaNokiaNokia Corporation is a Finnish multinational communications corporation that is headquartered in Keilaniemi, Espoo, a city neighbouring Finland's capital Helsinki...
External links
- LogicaCMG: Downloads for developers (link no longer active as of 2007-12-24)
- UCP Specification (Vodafone Germany)
- A more detailed UCP Specification
- UCP Perl implementation (for developers)
- Kannel, Open-Source WAP and SMS Gateway with UCP/EMI 4.0 support.