Symptom During the interworking between the SIP trunk and PSTN network, subscribers fail to use the fax service. Possible Causes - The SIP fax machine is faulty.
- The data of the SIP fax machine is improperly configured.
- The data of the SoftX3000 is improperly configured.
- The bearer network is faulty.
- The media negotiation is faulty.
- The UMG device is faulty and its configuration is incorrect.
- The access network device is faulty and its configuration is incorrect.
Fault Diagnosis Figure 1 shows the process of troubleshooting the failure to use the fax service by SIP subscribers. Figure 1 Process of troubleshooting the failure to use the fax service by SIP subscribers during the interworking between the SIP trunk and the PSTN network
http://localhost:7890/pages/31184407/11/31184407/11/resources/figure/fig_cn_43_25_0011801.png Procedure Check whether the SIP fax machine runs properly. - Check whether the fax machine is faulty using another SIP fax machine.
- Yes => Replace the fax machine or contact the supplier to repair the fax machine.
- No => 2
Check whether the data of the SIP fax machine is properly configured. - Check whether the fax parameters of the SIP fax machine are properly configured according to the document of the SIP fax machine.
- Yes => 3
- No => Modify the configuration data.
Check whether the data of the SoftX3000 is properly configured. Check whether the data configuration is correct. - Run the LST SIPTG command to check whether the Supported Codec List parameter contains the G.711A, G.711U, or T.38 codec format.
- Yes => 4
- No => Run the MOD SIPTG command to modify the configuration.
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Run the LST MGW command to check whether the configuration of the gateway is correct. http://localhost:7890/pages/31184407/11/31184407/11/resources/public_sys-resources/icon-note.gif NOTE: In the Special Attribute field, V3 fax flow must be selected, and No fax and No modem cannot be selected. The Voice Codec Type field contains G.711A, G.711u, or T.38. - Yes => 5
- No => Run the MOD MGW command to modify the configuration.
Check whether the media negotiation is in normal state. - Open the Broadband Signaling Trace window and enter the IP address of the calling party to trace the SIP messages.
- When switching over to the fax service, check that a 200 OK message is successfully sent to respond to the INVITE message.
- Yes => 7
- No => It indicates that fax negotiation fails. In this case, contact the maintenance engineers of the device that sends the non-200 OK response.
- When switching over to the fax service, check whether the media directions in the INVITE and 200 OK messages are correct.
- Yes => 8
- No => Contact the maintenance engineers of the device that sends an incorrect media direction.
http://localhost:7890/pages/31184407/11/31184407/11/resources/public_sys-resources/icon-note.gif NOTE: During the fax, the media direction should be sendrecv. If the media direction is sendonly, recvonly, or inactive, the fax fails inevitably. (If the SDP does not contain the description of the media direction, the media direction is sendrecv by default.)
- When switching over to the fax service, check whether the fax codec type in the INVITE message is the same as that in the 200 OK response.
- Yes => 9
- No => Contact the maintenance engineers of the device that sends an incorrect media codec.
http://localhost:7890/pages/31184407/11/31184407/11/resources/public_sys-resources/icon-note.gif NOTE: If the fax codec is G.711A or G.711U PassThrough, the media attribute fields in the INVITE and 200 OK messages for switching over to the fax service contain the attribute lines, which are similar to the following ones:
Check whether the UMG device is in normal state and the data configuration is correct. - Check whether the UMG device is in normal state and the data configuration is correct according to the manual of the UMG product.
- Yes => 10
- No => Rectify the fault according to the manual of the UMG product.
Check whether the bearer network is in normal state. - Trace the SIP messages and trace a network segment (HUB or LAN switch) of the media bearer network. You need to trace the two-way RTP stream between two SIP fax machines.
- Yes => 11
- No => Contact the maintenance engineers on the bearer network side to check the bearer network connection.
http://localhost:7890/pages/31184407/11/31184407/11/resources/public_sys-resources/icon-note.gif NOTE: - For the network whose media stream passes through the SBC or firewall, you need to capture the uplink and downlink media stream on the SBC or firewall. Check whether the address and port number of the RTP stream are those determined through media negotiation during the fax. If an address translation device such as SBC or firewall exists, the address and port number are translated.
- When checking the media bearer network, you need to check whether physical connection of the network is in normal state and check the network quality and packet loss rate. Low network quality and high packet loss rate are also the reasons for fax failure.
- When checking the bearer network, you are recommended to work with the engineers on the bearer network side. As bearer network devices or firewalls are of different types, the methods of capturing the RTP stream are different. For details about the methods, see the maintenance configuration manual for the specified product.
- The softswitch only performs signaling negotiation. The sending and receiving of the media are implemented by the fax machines at both ends.
- The address and port number contained in the fax media are the address and port number for sending and receiving the RTP stream on the fax machines at both ends.
- If a device such as SBC or firewall that provides the address translation function exists on the network, you need to check whether the device modifies the address (that is, the address contained in line C of the SDP) and port number (that is, the port number contained in line M of the SDP) of the media in the fax negotiation signaling.
Check whether the access network device is in normal state and the data configuration is correct. - Check whether the access network device is in normal state and the data configuration is correct according to the manual of the access network product.
- Yes => Contact Huawei technical support engineers.
- No => Rectify the fault according to the manual of the access network product.
Related Information As no formal standard is released for the SIP fax currently, device providers understand the SIP fax in different ways, causing various problems about the SIP fax. All the problems about the SIP fax are categorized into two types: - Configuration related problem
- RTP stream related problem
The RTP stream related problem is hard to identify. Up to now, no method of easily and effectively capturing RTP packets is available. - If multiple networks are involved in media processing, you need to capture the RTP stream based on different network segments.
- If a firewall or SBC exists on the network, you need to pay attention to this device because this device probably causes fax failure.
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