This article will identify and discuss the primary routing methods utilized by the GFI FAXmaker fax application and many other fax applications on the market today.

CSID – Called Subscriber Identification

CSID is a string which identifies the fax receiving party’s station or number.  This string can be programmed in the fax machine or fax application, and can be a combination of letters and/or numbers.  More frequently, this CSID value will be composed of strictly numbers, as it may help identify the number being sent to.  In addition, CSID is commonly associated with TSID (Transmitting Subscriber Identification), and the two are used almost interchangeably.  The TSID is the string which identifies the fax sending party’s station or number.  The CSID is provided to the sending party in the initial phases of the faxing process.

CSID is one of the more basic routing methods and allows for a fax to be routed based on the CSID/TSID of the sending party.  In order for this routing to occur, the CSID/TSID must match exactly as the number is programmed in the sending party’s device.  Be sure not to confuse CSID with CLID (calling line identification), as many fax applications in an analog environment do not support routing based on CLID.


  • DTMF – Dual-tone multi-frequency

DTMF is a telecommunication signaling technology that utilizes touch-tones for routing over an analog line.  The concept of DTMF routing is similar to DID routing (description found below) except a digital environment is not necessary.  It is still necessary that you purchase a DID block, but the tones may either be supplied by your Telco provider directly, or you may have a gateway device internally that converts a digital to analog signal; the tones may be provided from this device directly if it supports DTMF signaling. Read more on DTMF technology.

  • DID – Direct inward dialing

DID is a feature offered by a Telco provider for use with a customer’s PBX (Private Branch Exchange); additionally, DID may be referred to as DDI (direct dial-in) in European regions.  The DID feature involves the implementation of one or more trunk lines tied to the customer’s PBX, and associated with the line(s) is a range of telephone numbers.  When calls are presented to the PBX, the DNIS (Dialed Number Identification Service) is transmitted, which allows routing to a direct extension.  Typically, the DNIS ranges from four to ten digits, but most commonly it is the last four digits of the number dialed. Read more on DID technology.

Both DTMF and DID routing allow for individual routing to a user without having the overhead of an individual line for each user.  Instead of a one to one relation, both of these technologies focus on bandwidth consumption.  As an example, if you have 500 users who receive faxes, but on average receive twelve faxes consistently, one of these would be a suggested routing method (depending on your telephony environment).

OCR – Optical character recognition

OCR is the technology that allows for the conversion of handwritten or typed printed material to a digital form, to be edited or manipulated by a computer.  In the case of faxing, OCR software may be implemented in combination with faxing software to parse the contents of the received fax job in order to route based on keyword(s) found within the document.  This is a more common routing method in a smaller environment where limited telephony variables are available.  A user may have ten users and only one or two fax lines, but can still perform routing to individual users.


There is no acronym for line routing, as line routing is pretty self-explanatory.  Line routing involves the ability to route one line to one user (or group, in given scenarios).  This may be used more commonly in an environment where all faxes are to go to a general user or mailbox, such as a Human Resource Professional.  These fax jobs may be further analyzed and manually distributed based on the fax contents.

MSN – Multiple Subscriber Number

MSN routing is similar to DID routing, but MSN routing does not require the purchase of DID numbers.  MSN technology relies on ISDN circuitry and allows for tying multiple numbers to one line; these numbers do not have to be contiguous in nature.  Most commonly, MSN technology is used in European regions. Read more on MSN technology.