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.
by Olivier | Mar 4, 2010 | CUCM, IOS, MGCP, Non classé, Written Theory |
Here are some MGCP messages that you can see in the interaction between the Call Agent and the endpoint:
- EndpointConfiguration (EPCF) : A Call Agent sends this message to a gateway to specify signal encoding that will be received by an endpoint . A good example of these message will be the audio encoding using ulaw or alaw.
- CreateConnection (CRCX) : This command creates a connection between 2 endpoints. the connection is created based on parameters included with the commad such as codec , allowable bandwidth, use of echo cancellation, silence suppression , gain control, and so on.
- ModifyConnection (MDCX) : This is used to modify the parameters associated with a connection that was previously created.
- DeleteConnection (DLCX) : The Call Agent can send this command to inform a gateway that it should terminate a connection, and a gateway can send this command to indicate that a connection can no longer be sutained. In response to a DeleteConnection, an endpoint sends statistics associated with the connection.
- NotificationRequest (RQNT) : This is sent by the Call Agent to instruct a gateway to informit when specific events occur in an endpoint. Example : be on-hook/off-hook, tones,..
- Notify (NTFY) : An endpoint uses this command to inform a Call Agent when requested events occur
- AuditEndpoint (AUEP) : The Call Agent sends the AuditEndpoint command to the gateway to audit the status of an endpoint. The Call Agent can, for example, find out signal status, bearer information, …
- AuditConnection (AUCX) : The Call Agent sends this command to the gateway to find out the status of a connection. Connection status information that can be retrieved using this command includes Call ID, Connection Mode, and connection parameters
- RestartInProgress (RSIP) : The gateway sends this command to the Call Agent to inform the Call Agent that it is taking an endpoint or group of endpoints out of service or is returning an endpoint or group of endpoints to service.
by Olivier | Mar 3, 2010 | CUCM, Non classé, Written Theory |
CDP is a Cisco proprietary protocol that was designed for neighbor discovery. It is a Layer 2 protocol that sends multicast advertisements using SNAP encapsulation. The advertisements are sent by default every 60 seconds, and there is a default hold time of 180 seconds.
CDP advertisements can contain information such as DeviceID, Address, PortID, Capabilities, Version, Platform and native VLAN with much information in ASCII format.
by Olivier | Mar 3, 2010 | CUCM, Non classé, Written Theory |
There are 3 different types of CTI Control devices:
- CTI Ports : Virtual device with virtual lines
- CTI Route Points : These can receive many calls simultaneously for application-controlled redirection
- Cisco IP Phones : These are phones that a CTI application can control
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