2 Purpose of the training This training is intend for help to debug T.30 transmit problem over Mindspeed product. It is not for debug fax terminal application. Thus we care about external procedure, signal, timing, handshake. We do not care much about the fax internal theory, message contain, data compress and etc.By understand the T.30 procedure, help to debug Fax issue base on TDM trace and FPT signal wave from IP trace.
3 3.1) Protocol StackWe will focusing on T.30 and mention a little bit of T.4 and HDLCFAX APPLICATIONImage Compression T.4/T.6Handshaking T.30T.30 Protocol StackData Link HDLCDATA PUMP V.27ter, V.29, V.17, V.34
4 3.3) Terms of fax device: Originate/Caller: start the call(Dialer) Answer/Called/Callee: answer the callSender: device send fax page data (may be not the caller)Receiver: device receive fax page
5 3.2) terms of fax signal: Spectra and frequency analyze: Tone: CNG, CED.Low speed for signaling:V.21 (300bps)High speed for Data transmitV.27ter - up to 4800bpsV up to 9600bpsV up to 14400bps
6 4) Time sequence of a facsimile call: A general ideal Fax procedure was been cut into 5 Phase
7 5) Time sequence of a facsimile call(caller automatic operation) . Off hook. DialPhase A. Device identificationPhase B. Capability negotiation. Channel probingPhase C. Fax message exchangePhase D. Post message handshakingPhase E. Disconnect and. On hook
12 Phase A Call establishment Call establishment can be realized manually and/or automatically.(It is very few people in North America are using Manual fax. Automatic fax are more popular)Caller fax send CNDCalled fax send CED (it is optional on manual mode)
16 CED SignalA continuous 2100 Hz ± 15 Hz tone for a duration of not less than 2.6 seconds and not more than 4.0 seconds. A 200ms ahead and 75 ± 20 ms silence after transmitting the CED
17 Phase B – Pre-message Procedure The pre-message procedure consists of the identification of capabilities and the commanding of the chosen conditions as well as the confirmation of acceptable conditions.i.e. Exchange ID; Negotiate transmit protocol and speed; Training(channel probing)DIS-digital identification signal(capabilities identification)DCS-digital command signal(the response of DIS, indicate what capability will been used in the transmit)CFR-confirmation to receive(the training is successful)FTT-failure to train(the training is failed)(CSI)-called subscriber identification(NSF)-non-standard facilities
18 11) preamble + (NSF)+(CSI) + DIS Low speed data. HDLC frame V.21:300bps(FSK).PreambleThe preamble shall precede all binary coded signalling whenever a new transmission of information begins in any direction (i.e. for each line turnaround). This preamble assures that all elements of the communication channel (e.g. echo suppressors) are properly conditioned so that the subsequent data may be passed unimpaired. This preamble shall be a series of flag sequences for 1 s +/- 15%.Flag sequence Format:(in short: 1sec 0x7E)
19 11) preamble + (NSF)+(CSI) + DIS (CSI) - Called Subscriber IdentificationOptional frame (non-terminal) that provides the specific identity of the called subscriber by its international phone number. FCF(Facsimile Control Field) format. FIF(Facsimile Information Field) length - 20 bytes(NSF) -Non-Standard FacilitiesOptional frame (non-terminal) that may be used to identify specific user requirements which are not covered by T.30 number. FCF format. FIF length - min 3 bytes (the only standard portion of NSF)DIS - Digital Identification SignalMandatory frame (terminal frame) that characterizes the capabilities of the called terminal. FCF format:. FIF length - min 3 bytes (basic capabilities), 10 bytes defined as of 1996 (optional enhancements)Each bit or bit combination in the FIF maps over a capability
20 preamble + (NSF)+(CSI) + DIS Low speed signal spectral
25 5.2) Typical Message Exchanged in Fax Session (non-ECM) CallerOff Hook, Dial, CNG, 0.5 s ON at 1100 Hz, 3 s OFFCalleeOff Hook, CED, 3 s ON at 2100 HzPhase ADIS, at V bps containing callee capabilitiesDCS, at V bps containing the call settingsToneTCF, 1.5 s of 0s at the data rate selected by previous DCSLow SpeedFTT, at V bps indicating TCF not properly receivedPhase BHigh SpeedDCS, at V bps containing the call settingsTCF, 1.5 s of 0s at the data rate selected by previous DCSCFR, at V bps indicating that TCF was properly receivedFacsimile Message, at the data rate selected by previous DCSPhase CMPS, at V bps indicating more pages are to be sentMCF, at V bps, previous fax message was properly receivedPhase DFacsimile Message, at the data rate selected by previous DCSPhase CEOP, at V bps indicating no more pages are to be sentMCF, at V bps, previous fax message was properly receivedPhase DDCN, at V bps indicating the and of the call, On HookPhase E
26 Message Exchange for Fax Session (Call Map, ECM no error )
27 Message Exchange for Fax Session(Procedure Detail)
28 Procedure understanding CNG (-->Hello, I am the Calling fax terminal)CED (<==Hi, This is Called fax terminal)(NSF) (<~~I support this private protocol)(CSI) (<~~this is my phone number or ID)DIS (<==And, here is all my capability)(TSI) (~~>this is my ID)(NSS) (~~>response to NSF, the rest procedure not defined by ITU)DCS (==>Hello, let's start from this config: v.29,200x200,A4...)[TCF] (##>Training, can you recognize this speed signal???)CFR (<==Yes, You can send me the page in this speed)(/FTT) (<==No, try lower speed or protocol)[Page] (##>Attention, by the speed you agreed, here is the page!!!)MPS (==>And, I have more page to send to you)MCF (<==Good, I got the page, go on)(/RTP) (<==OK, but please retrain before rest of the page)(/RTN) (<==Sorry, I did not get the page. please retrain and resend the page)EOP (==>It is the last page for you)MCF (<==Good, I got the page)DCN (==>bye bye)(This is just the typical procedure. refer T.30 for some other option for the message)
30 Distinguish each signal and command 6) ReviewDistinguish each signal and command
31 Automatic operation and manual operation Call establishment can be realized manually and/or automatically.(It is very few people in North America are using Manual fax. Automatic fax are more popular)T.30 Call establishment operateing method 1:Manual mode on both endT.30 Call establishment operateing method 2:Calling manual mode, Called auto modeT.30 Call establishment operateing method 3:Calling auto mode, Called manual modeT.30 Call establishment operateing method 4:Auto modemon both endT.30 Call establishment operateing method 4 bis a&b:V.34 fax
32 T.30 Call establishment method 1 CED is optional when called side in on manual mode (mode 1 and mode 3)According to T.30, CNG should always present at least once (But I experience some Fax it will not send CNG if it has detected CED already)
33 TimerT2: (6s +/- 5s)Time-out T2 makes use of the tight control between commands and responses to detect the loss of command/response synchronization. T2 is 6 +/- 1 seconds and begins when initiating a command search (e.g. the first entrance into the "command received" subroutine, reference flow diagram in 5.2). T2 is reset when an HDLC flag is received or when T2 times out.(6s. The time the receiver fax wait for next command after previous command was received. Will disconnect if time out)T3: (10s +/- 5s)Time-out T3 defines the amount of time a terminal will attempt to alert the local operator in response to a procedural interrupt. Failing to achieve operator intervention, the terminal will discontinue this attempt and shall issue other commands or responses. T3 is 10 +/- 5 seconds, begins on the first detection of a procedural interrupt command/response signal (i.e. PIN/PIP or PRI-Q) and is reset when T3 times out or when the operator initiates a line request.(10s. The time wait for the operator to press a bottom or insert a paper or pick up handset)T4 (3s +/- 15%)Defines how long the receiver waits for HDLC command flags. 3s +/- 15% for automatic units and 4.5s +/- 15% for manual units. Begins when first entering in the Response Received routine Reset when an HDLC Flag is received or when it times out.(3s. The time the sender fax wait for the command response after it resent the command)
34 T2, T4 ExampleReceiver Fax will start T2 (6s) timer when receive a command (and responds the command). Will time out after 6 sec if the command doesn’t come. It will disconnect the line.Receiver Fax will start T4 (3s) timer after send DIS to sender. Will time out and resend this message 3 times if time out.Sender Fax will start T4 timer after send command to receiver Fax. Will time out after 3 sec if a response doesn’t come. It will retry 3 times (except DIS) and send DCN to disconnect the line.T.30 assume the telephone line should at least support low speed signal transmit and not generate any error. Otherwise the line is not good enough for a fax transaction.
35 T4 and RTN Example (non-ECM with error) Sender resend MPS after T4 timeout and receiver return RTN indication the page is not acceptable and ask go back to Phase B
37 ECM Error Correction Mode ECM is a transmission mode for fax (receiver) to automaticly inform and (for sender)resend the corrupted page data.Sender set bit 27 in DIS/DTC command to indicate ECM capability. Receiver set bit 27 in DCS command to confirm ECM mode.The method of ECM is to divide the page data to 64 or 256 bytes a frame; packed as HDLC frame format(with sequence number and FCS); combine 256 frame to a Block.Sender send one block every time. Receiver receive and check the contain for the transmit error. And send back information to sender to inform any error frame. Sender resend error frame and receiver to check again. Repeat this procedure up to four(4) times. A data block call a Partial Page.
38 New Command for ECMBy implementing this, some new message for ECM was been added upon non-ECM mode:PPS: Partial Page Signal. End of Partial Page.EOP, MPS, EOM have been replaced with PPS_EOP, PPS_MPS, PPS_EOMPPS_NULL indicate next Partial Page contains a block for the same page imagePPR: Partial Page Request. Request to resend some error.CTC: Continue To Correct. Request to repeat error correction over times.RNR/RR: to buy time for the low end receivers to rebuild the image buffer, decompress and print the imageEOR/ERR signals to decide to drop the transmission of the current block and move to the next one….
39 ECM Challenges Low end machines used to print as the image arrives Low memory was neededLines were decompressed as they arrivedECM, a whole block needs to be received before the device can start printingHigher memory requirementsFaster processing and printing unitDue to the error correction mechanism, on noisy lines the call can take much longer due to retransmissions
40 6.a) A Typical Fax: FaxLab Trace (ECM mode 2page no error) When no error the procedure is almost same with non-ECM mode
41 PPR(Partial Page Request when error) The FIF of PPR signal is 256 bits(32bytes), each bit corresponds to an FCD frame, bit=0: received correctly, bit=1: received incorrectly or not received. This example is for a short page.
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