H.323 study notes

H.323 is a p2p protocol

protocol suite built with:
H.225 – Handles setup/teardown and Q.931 op
H.225 RAS – handles GK signaling
H.245 – feature (codec) negotiaion
H.261 /H.263 Video Conferencing
H.450 – supp services
T.120 – Data Transfer, application sharing

1. Caller-id support on FXO or T1 CAS
2. fractional Pri support
3. widely supported – interoperable (default)
4. many call routing and manipulating options
5. supports voice, video, dara conferencing
6. non-facility associated signalling (NFAS) – single signalling channel for multiple PRI channels
7.H..323 gk support
8.PRI call preservation

1.Call flow CCM and H.323 GW exchange H.225 setup messages (TCP port 1720)
2. CCM and H.323 GW perform H.245 failure negotiation
3. RTP streams sent

H.323 fast start (default) combines H.225 and H.245

debug h225 /245 events


-G.729 Codec (G729r8)
-VAD enabled
-DTMF relay disabled
-Preference 0
-Audio = DSCP EF
Signalling = DSCP AF31
-Huntstop disabled
-RSVP = best effort
-FAX relay disabled
-playout delay = 40 ms

-DID is disabled
-Preference 0
-Digit strip enabled
-register w/gk
-huntstop disabled


Dial-peer voice 2000 voip
dest pattern 2…
session target ipv4:192.xxx

=Voip dial peer and CCM redundancy (h225 timeout) default 30 secs:
#Voice class h323 50 <tag>
#h225 timeout tcp establish 2 (secs)
# dial-peer
#voice-class h323 50

=Multiple codecs per dial-peer (voice class codec)# voice class codec <10>
# codec pref 1
# codec pref 2 g729

#voice-class codec <10>

= Voice Service parameters (allow connections, h323 timers and parameters)

# voice service voip
# allow connections h323 to h323

def: will allow h323 to pots, the above command will allow incomming h323 call to relay another h323 call

SRST mode it will default kick of all connections, to keep active calls active:
– to stop gw detecting cm down
#voice service voip
###no h225 timeout keepalive

to turn off h323 :-)…power switch
#voice service voip
###call service stop

stop fast start, by default the router will combine h225 and h245 into single exchange. some equipment will not support

#voice service voip
###call start slow

|toll bypass config|

dial-peer voip
session target -other router ip-
dest pattern

dial-peer 1000 pots
PORT 0/0/0
dest pattern
no digit strip

by default it will try to connect first DP for 30 secs… reduce timer

|final configuration|

DTMF Relay

all digits dialed are sent in codec b/w. if you are using compressed codec’s; they get scrambled.

#dtmf-relay h245-alpha -for tones but not duration
#dtmf-relay h245-signal + relays length of tone

| Troubleshooting commands    |

Sh dial-peer voice summary
show dialplan number
deb cch323 h225
deb cch323 h245
deb voip ccapi inout **
debug tcp transaction
csim start
show h323 gateway


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