Call legs with different codecs

Boyan Sotirov · ‎04-10-2012

The situation is like this. I've got one router (HQ-1) which has one C7965G IP phone registered. This router is connected over E1 line to another router (PSTN) which simulates PSTN-like connectivity. There's also another C7965G IP phone registered to the PSTN router.

I've configured one of the phones to use iLBC as prefered codec. So it works, but when I use these two commands:

HQ-1#show voice call status

CallID CID ccVdb Port Slot/DSP:Ch Called # Codec MLPP Dial-peers

0x3C 1285 0x4B1893A8 50/0/1.0 112 ilbc 20005/112

0x3D 1285 0x49C710B4 0/2/0:15.8 0/1:1 *112 ilbc 112/20005

1 active call found

PSTN#show voice call status

CallID CID ccVdb Port Slot/DSP:Ch Called # Codec MLPP Dial-peers

0xF3 1222 0x488478D0 0/0/0:15.8 0/1:1 19016 g711ulaw 1120/20006

0xF4 1222 0x48844C78 50/0/6.0 *19016 g711ulaw 20006/1120

1 active call found

So it appears to me that I've got one input call leg (from the 7965G phone to the HQ-1 router) and another outgoing call leg (from the HQ-1 router to the PSTN router over the E1 line). Which is perfectly fine.

What confuses me is the second output from the PSTN router. Because it shows one input call leg that is using g711 and another call leg to the 7965G phone.

From my understanding the outgoing call leg from HQ-1 to PSTN should be the input call leg to the PSTN router. Shouldn't it use than the same codec, iLBC in this case? In that case where the transcoding takes place?

Am I interpreting the outputs correctly?

Here're also the outputs from "show voice dsp"

HQ-1# show voice dsp

DSP DSP DSPWARE CURR BOOT PAK TX/RX

TYPE NUM CH CODEC VERSION STATE STATE RST AI VOICEPORT TS ABORT PACK COUNT

==== === == ======== ========== ===== ======= === == ========= == ===== ============

edsp 0001 01 ilbc 0.1 busy 50/0/1.1

edsp 0002 02 ilbc 0.1 IDLE 50/0/1.2

edsp 0003 01 g711ulaw 0.1 IDLE 50/0/2.1

edsp 0004 02 g729r8 p 0.1 IDLE 50/0/2.2

----------------------------FLEX VOICE CARD 0 -----------------------

-------

*DSP VOICE CHANNELS*

CURR STATE : (busy)inuse (b-out)busy out (bpend)busyout pending

LEGEND : (bad)bad (shut)shutdown (dpend)download pending

DSP DSP DSPWARE CURR BOOT PAK TX/RX

TYPE NUM CH CODEC VERSION STATE STATE RST AI VOICEPORT TS ABRT PACK COUNT

====== === == ========= ========== ===== ======= === == ========= == ==== ============

C5510 001 01 ilbc 27.3.3 busy idle 0 0 0/2/0:15 08 0 78343/78355

*DSP SIGNALING CHANNELS*

DSP DSP DSPWARE CURR BOOT PAK TX/RX

TYPE NUM CH CODEC VERSION STATE STATE RST AI VOICEPORT TS ABRT PACK COUNT

====== === == ========= ========== ===== ======= === == ========= == ==== ============

------------------------END OF FLEX VOICE CARD 0 ----------------------------

PSTN#show voice dsp

DSP DSP DSPWARE CURR BOOT PAK TX/RX

TYPE NUM CH CODEC VERSION STATE STATE RST AI VOICEPORT TS ABORT PACK COUNT

==== === == ======== ========== ===== ======= === == ========= == ===== ============

edsp 0001 01 g711ulaw 0.1 IDLE 50/0/1.1

edsp 0002 02 g711ulaw 0.1 IDLE 50/0/1.2

edsp 0003 01 g711ulaw 0.1 IDLE 50/0/2.1

edsp 0004 02 g729r8 p 0.1 IDLE 50/0/2.2

edsp 0005 01 g711ulaw 0.1 IDLE 50/0/3.1

edsp 0006 02 g729r8 p 0.1 IDLE 50/0/3.2

edsp 0007 01 g711ulaw 0.1 IDLE 50/0/4.1

edsp 0008 02 g729r8 p 0.1 IDLE 50/0/4.2

edsp 0009 01 g711ulaw 0.1 IDLE 50/0/5.1

edsp 0010 02 g729r8 p 0.1 IDLE 50/0/5.2

edsp 0011 01 g711ulaw 0.1 busy 50/0/6.1

edsp 0012 02 g729r8 p 0.1 IDLE 50/0/6.2

edsp 0013 01 g711ulaw 0.1 IDLE 50/0/7.1

edsp 0014 02 g711ulaw 0.1 IDLE 50/0/7.2

edsp 0015 01 g711ulaw 0.1 IDLE 50/0/8.1

edsp 0016 02 g729r8 p 0.1 IDLE 50/0/8.2

edsp 0017 01 g711ulaw 0.1 IDLE 50/0/9.1

edsp 0018 02 g729r8 p 0.1 IDLE 50/0/9.2

edsp 0019 01 g711ulaw 0.1 IDLE 50/0/10.1

edsp 0020 02 g729r8 p 0.1 IDLE 50/0/10.2

edsp 0021 01 g711ulaw 0.1 IDLE 50/0/11.1

edsp 0022 02 g729r8 p 0.1 IDLE 50/0/11.2

edsp 0023 01 g711ulaw 0.1 IDLE 50/0/12.1

edsp 0024 02 g711ulaw 0.1 IDLE 50/0/12.2

----------------------------FLEX VOICE CARD 0 -----------------------

-------

*DSP VOICE CHANNELS*

CURR STATE : (busy)inuse (b-out)busy out (bpend)busyout pending

LEGEND : (bad)bad (shut)shutdown (dpend)download pending

DSP DSP DSPWARE CURR BOOT PAK TX/RX

TYPE NUM CH CODEC VERSION STATE STATE RST AI VOICEPORT TS ABRT PACK COUNT

====== === == ========= ========== ===== ======= === == ========= == ==== ============

C5510 001 01 g711ulaw 27.3.3 busy idle 0 0 0/0/0:15 08 0 86893/86913

*DSP SIGNALING CHANNELS*

DSP DSP DSPWARE CURR BOOT PAK TX/RX

TYPE NUM CH CODEC VERSION STATE STATE RST AI VOICEPORT TS ABRT PACK COUNT

====== === == ========= ========== ===== ======= === == ========= == ==== ============

------------------------END OF FLEX VOICE CARD 0 ----------------------------

paolo bevilacqua · ‎04-10-2012

First of all with CME you should normally use G.711. You can explore the use of other codecs when you have the real necessity.

Second, transcoding doesn't happen unless you configure it.

Boyan Sotirov · ‎04-10-2012

Dear Paolo,

I'm not aware of any restrictions as far as the codecs are concernd when CME is used.

Transcoding isn't configured on neither of the routers in this setup.

What I'm puzzled with in this output is that it appears to me that in one direction of the E1 line (from HQ-1 to PSTN) the codec used is iLBC, and on the reverse direction (from PSTN to HQ-1) it's G.711. This doesn't make any sense to me? And when E1 line is used, shouldn't the codec always be G.711uLaw?

So maybe I'm not interpreting the outputs correctly. That's why I started this discussion...