by Olivier | Mar 4, 2010 | CUCM, H.323, IOS, Lab, Non classé, Written Theory |
When you are working with H323 configurations, you can experience teh following ringtones issues , let’s see these issues and how to fix it quickly:
- No Ringback tone on an IP Phone when calling a destination in the PSTN : This comes from a mistmatch between the Call Manager and the PSTN. It can be fixed with the following command progress_ind alert enable 8 under the POTS dial-peer.
- No Ringback tone on a phone in the PSTN when calling an IP Phone: The problem is more similar with the previous one but it differs because it is coming from the other side as this time , the setup message received from the PSTN did not include a progress indicator (PI=0). Indeed, the gateway assumes the network is an ISDN end-to-end network so normally the tone must be handled by the PSTN but it is not an end-to-end call , this is why you have to update again the progress-indicator with the command progress_ind setup enable 3 which is setting the tone in-band.
- No Ringback tone from the PSTN Phone which is forwarded from an IP Phone to another IP Phone : in this case, the issue is caused by the fact that the voice gateway is tearing down logical channel when you are transferring the call , so Audio is not sent. To fix this , you need then to change a parameter under the Call Manager setting ToSendH225UserInfoMsg and put it to True
by Olivier | Mar 4, 2010 | H.323, IOS, Lab, Non classé, Written Theory |
Here are the different messages used by the H225 RAS signaling which can occur between endpoints and GK.
- Gatekeeper Discovery : used by endpoints to register
- GRQ : Gatekeeper Request
- GCF : Gatekeeper Confirm
- GRJ: Gatekeeper Reject
- Registration/Unregistration : used by endpoints to register or unregister their address and their zone withtin the GK.
- RRQ : Registration Request
- RCF : Registration Confirm
- RRJ : Registration Reject
- URQ : Unregistration Request
- UCF : Unregistration Confirm
- URJ : Unregistration Reject
- Admission Control : These messages are used for all admission control and bandwidth management
- ARQ : Admission Request
- ACF : Admission Confirm
- ARJ : Admission Reject
- Bandwidth Control : these messages are used if you want to change the amount of bandwidth during a call
- BRQ : Bandwidth Request
- BCF : Bandwidth Confirm
- BRJ : Bandwidth Reject
- Endpoint Location : These messages are used to retrieve contact information ( also with Directory GK)
- LRQ : Location Request
- LCF : Location Confirm
- LRJ : Location Reject
- Status Information : They are used to retrieve a status information
- IRQ : Information Request
- IRR : Information Response Request
H225 call control signaling is on TCP/1720 and uses Q931 messages to establish, maintain and tear down calls. these messages are
- Setup
- Setup Acknowledge
- Call Proceeding
- Progress Alerting
- Connect
- User Information
- Release Complete
- Status Inquiry
- Status
- Information
- Notify
So in general , here is the following reminder: While h225 call control signaling can be used for call setup, H245 must be used to determine a master/slave relationship, exchange terminal capabilities, logical channel signaling and DTMF relay.
by Olivier | Mar 4, 2010 | H.323, IOS, Lab, Non classé, Written Theory |
We have already spoken about Gatekeeper signaling in this previous post but let’ be more general and see what are the common elements of H.323 stack.
We have H225 RAS ( Registration Admission and Status) which is used between the GK and H323 endpoints.
But under normal operation , we have also H225 which is the call control and signaling part of the H323 stack. So we use it to establish connections.
We have also H245 which is the negotiation part of the H323 stack. So it is during this stage that you can exchange capabilities/codecs, establish logical channels. It is in fact all settings for the transmission of the media.
Reminder:
- H225 RAS => UDP/1719
- GK Discovery => UDP/1718
The Multicast GK discovery uses IP Address 224.0.1.41
by Olivier | Mar 4, 2010 | Non classé, SIP, Written Theory |
In SIP , you will find 2 types of SIP Messages, there are:
- Request: A message sent by a client to a server that is used to invoke certains operations or functions.
- Response : A message sent by a server to a client that indicates the status of the request received from the client.
Here are now the request messages which invoke function on the server ( note that these functions are also called methods)
- Invite : When UAC want to initiate a session, it sends an Invite request to a server. When the request is received by the UAS, it process it and sends the appropriate response message.
- Ack : This message is sent in reply to a final response message from a server.
- Bye : Used to terminate a session
- Cancel : a Cancel request is used to terminate a pending request ( a request for which a final response has not yet been received)
- Register : This message is used to register contact information.
- Options : An UA can query another UA or SIP Proxy server about its capabilities using Options request. In this way, a client can find out capabilities such as supported methods, content types, codecs, and so on.
- Info : This is used to carry session-related control information such a ISUP, ISDN signaling information.
Now let’s see the 6 availables types of responses:
- 1XX : Responses in this range are provisional or informational
- 2XX : Responses indicate a success
- 3XX : Responses indicate a redirection
- 4XX : Responses indicate a client error
- 5XX : Responses indicate a server error
- 6xx : Responses indicate a global failure
by Olivier | Mar 4, 2010 | Non classé, SIP, Written Theory |
Here are various elements, definitions of what you can find in SIP world:
- User Agent (UA) : This an endpoint that can act as both an User Agent Client (UAC) and an User Agent Server (UAS), a good example is a SIP IP Phone.
- UAC : This is a logical entity that initiates and sends requests, such as those specifiying the INVITE method. the UAC is a logigal role, so it lasts only for the duration of a SIP transaction.
- UAS : This is an entity that responds to a SIP request by accepting, rejecting, or redirecting the request. The UAS role also lasts only for the duration of the SIP transaction.
- Redirect Server : This an (UA) server that provides address translation and redirects clients to alternative destination addresses. It does this by sending 3XX responses to requests.
- Proxy Server : A SIP proxy server’s primary role is to provide routing, but it can also enforce policies, provide features, and authenticate and authorize users.
- Registrar Server : Users are registering their current location (location service) so Registrar Server uses the information to provide a lookup service that allows SIP UA to be located.
- Location Service : This is created by a registrar server and is populated with bindings of Address-of-records (AOR). It is a kind of user’s profiel address. This service can be used by the proxy or redirect servers to retrieve information relating to a called party’s possible locations.
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