understanding ip phone behavior skinny client control protocol sccp prof. yousif @ valencia...
TRANSCRIPT
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Understanding IP Phone Behavior
Skinny Client Control ProtocolSCCP
Prof. Yousif@
Valencia Community College
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Skinny Protocol
• Skinny Protocol is a lightweight master/slave protocol
• CallManager controls every function of the phone.
• CallManager facilitates call signaling to other devices using different protocols– H.323 for routers– TAPI/JTAPI for Soft Phones/IP Communicator
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Master/Slave Example
• When the Phone goes off-hook, it notifies CM that the user has gone off-hook.
• CM sends a message to the phone notifying it play dial tone.
• The phone can not determine when to play dial tone on its own.
• It is important to understand the roles that both IP phones and CM play when troubleshooting IP phones
• Example: Where do you troubleshoot the problem of delayed dial tone???
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Call Processing Behavior
•The Call Processing Behavior can be best explained by examining The CM trace file
•CM Traces are configured from Cisco Service configuration.
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From the Trace Menu, Select Trace configuration
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Collect the Traces for a Certain Period of Time
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A Sample Trace for a Call Between Two IP Phones
1. IP phones use the Skinny protocol to communicate with CallManager
2. All messages to and from a Skinny device are preceded by either the word StationInit or StationD.
3. StationInit means that an inbound TCP message form a Skinny station reached CallManger.
4. Example:
StationInit: 000000004 OffHook
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TCP Handle
• The TCP handle represents a unique value that identifies a specific IP pone registered to this CM Server.
• With The TCP handle, you can follow every message sent and received from a particular IP phone.
• The TCP handle of a device can also be found by looking up the IP phone’s MAC Address until you find a keep alive message to that phone.
• Example: StationInit - InboundStim - KeepAliveMessage - Send KeepAlive to Device Controller. DeviceName=SEP000F8F59D304, TCPHandle=000000004, IPAddr=192.168.1.128, Port=52952, Device Controller=[1,92,1]|<CLID::StandAloneCluster><NID::192.168.1.140>
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Skinny Protocol
• The OffHook message means that CallManger received a Skinny message indicating the phone went off-hook
• The next message in the trace file is: StationD: 000000004 StationOutputDisplayText=‘ 40000 ‘
• StationD signifies that the CM server is sending a message to the IP phone.
• Notice that the same TCP handle is listed• The number 40000 represents the directory
number of the phone.
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Other Skinny Messages
• StationD: 000000004 StartTone tone=33(InsideDialTone) Tells the IP phone to start plying dial tone.
• CallReference=16777225: The Call reference ID is created by CM for each participant in a call and can be used to track a particular call through a CM Trace
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Other Skinny Messages
• StationInit: 000000004 KeypadButton kpButton=4 • StationD: 000000004 StopTone. • CCM|StationD: 000000004 SelectSoftKeys instance=1
reference=16777225 softKeySetIndex=6 • StationInit: 000000004 KeypadButton kpButton=0• CCM|StationInit: 000000004 KeypadButton kpButton=0.|• StationInit: 000000004 KeypadButton kpButton=0.• StationInit: 000000004 KeypadButton kpButton=4• Note: digit * shows as e and a # shows as f• StationD: 000000004 SelectSoftKeys instance=1
reference=16777225 softKeySetIndex=8
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Other Skinny Messages
• Call Manger is constantly analyzing the digits the user dials, and once it finds an exact match, digit analysis returns the results for the match.
• Now is the time to ring the CIPC phone which is configured with DN 40004.
• The Call Routing Chapter will provide additional details on how digit analysis wok in CM
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Other Skinny Messages
• Because CM has collected all the required digits, it is ready to notify the destination IP phone there is an incoming call.
• StationD: 000000005 CallState callState=4 lineInstance=1
• StationD: 000000005 CallInfo callingPartyName='Wael Yousif' callingParty=40000 cgpnVoiceMailbox= calledPartyName='' calledParty=40004
• callReference=16777226• StationD: 000000005 SetRinger
ringMode=2(InsideRing)• StationD: 000000005 DisplayPriNotify
timeOutValue=10 pri=5 notify='€40000' content='From 40000'
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Other Skinny Messages
• Notice that the CIPC phone has a different TCP handle (was assigned during registration)
• Also, notice that the CIPC phone has a different CallReference ID
• The CIPC phone now starts to ring displaying the calling party name and extension number
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Other Skinny Messages
• The following messages perform two functions: First, the display on the IPP changes to indicate that the call is in progress. Second, the phone is told to play the ringback tone which you hear when you place a call
• StationD: 000000004 CallState callState=12 lineInstance=1
• StationD: 000000004 CallInfo callingPartyName='Wael Yousif' callingParty=40000 cgpnVoiceMailbox= calledPartyName='' calledParty=40004
• StationD: 000000004 StartTone tone=36(AlertingTone),
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The CIPC Answers the Call
• StationInit: 000000005 SoftKeyEvent softKeyEvent=11(Answer) lineInstance=1
• The above message is equivalent to the “StationInit OffHook” message in the case where the called phone is another IPP.
• The preparation is now complete for the actual media connection
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Audio Stream Setup
• Skinny uses Real Time Transport Protocol (RTP) over User Datagram Protocol (UDP) packets to send and receive Voice Over IP samples.
• Each RTP stream is called a logical Channel.• A Logical Channel is a Unidirectional RTP
stream,• To Have a two-way conversation, you must have
two logical channels opened; one from the calling device to the called device and one from the called device to the calling device.
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Audio Stream Setup
• In the following section you can see how CM asks the IP phone to open a connection to receive RTP streams.
• You can also see how that CM asks the IP phone for specific parameters, including the codec and packet size.
• StationD: 000000004 OpenReceiveChannel conferenceID=0 passThruPartyID=1000091 millisecondPacketSize=20 compressionType=4(Media_Payload_G711Ulaw64k) qualifierIn=?. myIP: 8001a8c0 (192.168.1.128)|<CLID::StandAloneCluster><NID::192.168.1.140><CT::1,100
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Audio Stream Setup
• Upon receiving an OpenReceiveChannel message, the I phone selects the UDP port number it wants to use to receive RTP packets and reports this information back to the CM in an OpenReceiveChannelAck message.
• StationInit: 000000004 OpenReceiveChannelAck Status=0, IpAddr=0x8001a8c0, Port=17198
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Audio Stream Setup• The same handshake of “OpenReceiveChannel”
and “OpenReceiveChannelAck” is done at the called phone.
• When CM receives the OpenReceiveChannelAck from the CIPC phone, containing the UDP port number, it forwards this information to the calling phone in a StartMediaTransmission message
• StationInit: 000000005 OpenReceiveChannelAck Status=0, IpAddr=0xf001a8c0, Port=24600
• StationD: 000000004 StartMediaTransmission conferenceID=0 passThruPartyID=1000091 remoteIpAddress=f001a8c0(192.168.1.240) remotePortNumber=24600 milliSecondPacketSize=20 compressType=4(Media_Payload_G711Ulaw64k)
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Audio Stream Setup
• At this point the two phones are sending RTP messages to each other.
• Notice that for the duration of this call, the two phones never have sent nor received any Skinny signaling to or from each other.
• This is because all the signaling goes through CM
• The only time IP phones send packets to each other is for the actual Voice Stream.
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Labs
• CCM Traces
• Challenge Lab: Capture The Call Setup and Media Transport Processes using Ethereal