Crackling Voice on SIP Users & SIP nwk (A-470 networked via SIP with Hipath 3800

[srirammig112]

Hello everyone,
Iam very glad that i discovered such a forum exists so i hope it would be very useful and informative. Iam doing an installation of Mitel A-470(ver4.1).The configuration is 130 analog extensions,2 SIP extensions( 6737i and 6873i),one ISDN PRI and SIP networking ports(8nos).The PBX at the other end is Siemens Hipath 3800.The network is up with 8 SIP channels for voice communication Iam facing strange issue(s) which i am explaining below :

1. Calls from Mitel Analog extensions to Mitel SIP extensions and vice versa have disturbances in voice .Analog user reports a cracking voice when he receives a call from SIP user but SIP user can hear the analog user perfectly.
2.Calls from Mitel Analog extensions to Siemens Hipath 3800 extensions too have the same voice disturbances.The Siemens user can hear the voice properly but Mitel analog user gets crackling voice while speaking.
3.Calls from Mitel SIP extensions to PSTN via ISDN PRI too have same voice disturbances.The external party reports crackling voice  whereas their voice is clear on the SIP extension.

As a part of resolving this issue I have isolated both the SIP extensions ie i have disconnected both of them from customer's POE switch and have connected them to LAN1.3 and LAN1.4 in Mitel A-470.I have 2 POE injectors from where i have connected both the SIP phones.I have also removed the customer LAN cable connected to LAN1.2 and i have put both the SIP phones in the same IP series as the Mitel A-470.After that when i tested i found all the calls were working fine(Ana-SIP,SIP-Ana,SIP-PSTN).The only testing that wasn't done was calls between Mitel analog and Siemens as we had removed customer LAN cable.

Now,i request can anyone please help me with LAN port settings or port configuration on either Mitel or Cisco switch that would be needed to make it work.Please note that the switch used here is a Cisco Catalyst 2960-X series.

Thank you in advance

regards
Sriram

*****Help ever hurt Never****************************
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[sarond]

What happens if you connect the Siemens direct to a LAN port on the 470. Does the issue go away?

Also just double check your DSP modules in the 470 to make sure they are seated properly.

What happens if you set the RTP to relay via the server in the SIP trunks on the 470.

[srirammig112]

Hi Sarond,
First of all thank you for replying.Now coming to the issue here is what i did to resolve :

01. MTU Change :
          MTU settings of NICs are 1500.   This is absolutely fine for connectivity over Peer to Peer links.  Considering MTU overhead with standby (IPSEC) connectivity between two sites, reduced MTU to 1400 in both PBX systems.. 

02. Siemens Hipath 3800 Changes :
          SIP trunk changed from SIPQ to SIP Native Trunk
          Number of Channels increased from 8 to 24
          Limited RFC Port Range to 100 ports

03. Mitel A-470 Changes :
          SIP Keep alive enabled (RFC6223)
           RTP ports changed to 29000 - 29007
           Codec set to G.711a

         
Key observation during packet capture is with SIP-Q protocol in Siemens PBX, no RPC response to Mitel PBX after initial SIP session negotiation...   After changing trunk configuration on Siemens from SIPQ to SIP Native Trunk, observed UDP packets exchange between PBX systems.

Thank you so much

Regards
Sriram