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UIT - Secteur de la normalisation des télécommunications
ITU - Telecommunication Standardization Sector
UIT - Sector de Normalización de las Telecomunicaciones

Study Period 2001-2004

Commission d' études                                                Contributi on tardive 
                                                                                          
Study Group          16                                             Delayed Contributi on  D.___ (WP 1/16)
Comisión de Estudio 
                                                                    Contribuci ón tardía 

Geneva, 5 – 15 February, 2002
                                                                     Texte disponible seulement en 
                                                                     Text available only in         E
                                                                     Texto disponible solamente en 
Question(s): Q14/16

SOURCE:            Conexant Systems Inc.

TITLE:             MoiP and T.38 switching


   Gateways that support both Facsimile-over-IP (FoIP) and Modem-over-IP (MoIP) require a
common procedure that provides easy selection between a facsimile and data connection calls. This
            contribution describes procedures that may be suitable for this purpose.

* Contact:      Keith Chu                                               Tel:        +1 949 579 4121
                Conexant Systems                                        FAX:        +1 949 579 3667
Attention: This is not an ITU publication made available to the public, but an internal ITU Document intended only for use by the
Member States of the ITU and by its Sector Members and their respective staff and collaborators in their ITU related work. It shall
not be made available to, and used by, any other persons or entities without the prior written consent of the ITU.

1 Introduction
Gateways that support both Facsimile-over-IP (FoIP) and Modem-over-IP (MoIP) need to share a
common procedure that caters for the easy selection between a facsimile or data connection and
allow those gateways to switch transport mechanisms (i.e. T.38 or V.MoIP). This contribution
describes procedures that are suitable for this task. The intent is to show that a common set of
procedures between T.38 and V.MoIP are possible and indicate where the transitions of
responsibilities between T.38 and V.MoIP occur.

2 Procedure Considerations
A principal philosophy used in V.MoIP is to allow end-point terminals and their local gateways to
connect independent from the remote terminal/gateway pair. This general strategy can simplify the
procedures dramatically.

V.MoIP call discrimination is studying how terminal Answer tones should be dealt with. This
contribution leverages some of this work and shows how selection can be achieved between V-
series data modem signals and T.30 Facsimile (both standard G3 fax (G3) and high-speed V.34 hdx
G3 fax (HSG3). This contribution shows the commonality and indicates the point at which T.38
would assume procedural responsibility. Note that this procedure is not intended to supplant the
discrimination and selection procedures that are to be defined for V.MoIP.

3 Proposed procedures
It is important to note that for the existing class of FoIP only gateways, the existing mechanisms are
untouched. The following description is only for dual-mode capable gateways. Figure 1 and 2
illustrate how MoIP/FoIP gateways interact for the G3 and HSG3 modes. Note steps 1 to 5 are
subject to the procedures accepted for use in V.MoIP. They are only included for completeness of
the example.

The procedure is;
   1. After a voice path is established end-to-end between terminals F1 and F2. F2 transmits an Answer
      Tone. Depending whether F2 is G3 or HSG3 this tone will be CED or ANSam.
   2. On detection of a 2100Hz Answer Tone (within 50ms) at the Off-Ramp, the voice path between the
      gateways is broken or made to be silent. It is not necessary to discriminate between CED and
      ANSam for this detection process.
   3. During the silence period of not more than TBD ms, the Off-ramp shall determine if the signal is
      ANSam or not. Other verification task could be performed concurrently to prevent false trigger
   4. Once the Off-Ramp has determined the Answer Tone it sends a message to the On-Ramp informing
      it of the type. This could be done using RFC 2833 or similar. Note no change to the IP transport
      protocol has yet been initiated.
   5. On reception of the Answer Tone type message the On-Ramp regenerates the same signal.

If the call is facsimile, there will be two possible events in an error free case (indicated a and b
below). One is F2 is a G3 responding terminal and the second is if F1 is a HSG3 initiating terminal. G3 Case
   6. For a G3 F2, CED will cease after the appropriate time and V.21 (Channel 2) HDLC formatted
      FLAGS will be transmitted. The detection of FLAGS at the Off-Ramp will initiate a switch to T.38 and
      the selection of UDPTL for the transport protocol. The T.38 procedures as they are defined are now

HSG3 Case
   6. For the case where F1 is a HSG3 terminal, this will only happen if ANSam is transmitted by F2, which
       indicates that it could be a V.34 hdx capable machine (although this is not a guarantee). ANSam
       would be regenerated by the On-Ramp and transmitted to F1.

   7. F1 will respond with a V.8 CM signal indicating with one of the two facsimile calling functions. On
       detection and confirmation of the Call Function, the Gateways switch into the T.38 procedures for
       V.34 hdx operation. A message is then sent to the Off-Ramp containing the relevant information
       contained in the received CM.

                  F1                      G1                                 G2                             F2

                                                 Voice Path Established

                                      CED                                         Detect 2100Hz.
                                    Leakage                                       Initiate Break in voice
                                               Voice Path Broken or Silent
                                                                                  path. Max time to
                                                                                  break is 50ms.
                                                    MSG: ANS(V.25)

                                                                                  Verify not ANSam
                                                                                  and take steps so as
                                                                                  to not false trigger.

                                                 Message to G1
                                                 initates 2100 Hz

                                    AT2100           Note: Max
                                                     duration is 3.3

                                                     Switch to T.38                                          FLAGS


                                    FLAGS                 Proceed with
                                                          Existing T.38

                       Figure 1: Standard G3 T.38 interoperation with V.MoIP
                        Note: The call discrimination procedures are informational only

                           F1                     G1                            G2                              F2

                                                       Voice Path Established

                                                                                          Detect 2100Hz.
                                                                                          Initiate Break in
                                                         Voice Path Broken                voice path. Max
                                                                                          time to break is
                                                          MSG: ANS(V.8)

                                                                                          Verify ANSam and
                                                                                          take steps so as to
                                                         Message to G1                    not false trigger.
                                                         initates ANSam

                                                         Check on CM
                                                         Call function
                                                         indicates that it is
                                                         FAX so do it

                                            ANSam          MSG: CM(fax)
                                                           Switch to T.38


                                                          Based upon the
                                                          CM mesage G2               CM
                                                         builds its own CM


                 Figure 2: Proposed V.34 hdx T.38 interoperation with V.MoIP
                            Note: The call discrimination procedures are informational only

4 Additional Comments
As indicated in step 6b, the detection of a CM call function at the On-Ramp is not a guarantee that
F2 is a HSG3 terminal. It could be a Data/Fax modem that has V.8, V.90 or V.34, but support only
the G3 facsimile modulations. In this case the complete V.8 transaction has to be monitored to
ensure that both ends of the connection link use the same mode of operation. This procedure is
defined in T.30 Appendix VII.

5 Summary
This contribution describes a method as how gateways that support both T.38 (G3 and HSG3) and
V.MoIP can determine when to switch to the T.38 procedures. It is proposed that for a gateway that
is both T.38 (with V.34 hdx) and V.MoIP capable, that after following the appropriate
discrimination procedures as defined in V.MoIP, that CM detected at G1 be used to determine the
criteria by which a gateway allows a transition into T.38 V.34 hdx. If F2 is a G3 terminal, it is the
detection of V.21H modulated HDLC FLAGS that initiates the transition to T.38.