H.323 Call Signaling For the establishment and tear-down of calls - - PowerPoint PPT Presentation
H.323 Call Signaling For the establishment and tear-down of calls Q.931 modified by Rec. H.225.0 Reuse some messages with few modifications A clever use of User-to-User information element Convey all of the extra information
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IP Telephony
Reuse some messages with few modifications A clever use of User-to-User information element
Convey all of the extra information needed in H.323 E.g., H.245 addresses to be used for logical channel
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IP Telephony
The first call-signaling message Bearer Capability
Most of the fields are not used.
Used in the circuit-switched world
It may be used when the call has originated from outside the
A gateway needs to perform the mapping
User-to-User information element
Mandatory: call id, call type, the caller information Optional: source alias, destination alias, H.245 address
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IP Telephony
Optional call-establishment procedures are underway Mandatory
User-to-user information element: destination information
Optional - H.245 address of the called party
The called user is being alerted Indicating specific alerting tone to the calling party
The same parameters as Call Proceeding
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IP Telephony
Sent by a called gateway to indicate call progress in
Conveying in-band tones or announcements (optional)
The called party has accepted the call. Must be sent if the call is to be completed
Call Proceeding and Alerting are optional
User-to-User information
The same as Call Proceeding
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IP Telephony
Terminate a call No Release message
In ISDN, Release and Release Complete
Cause information element, optional
Otherwise, a Release reason in User-to-User information
A call should be redirected Also be used for supplementary services User-to-User contains reason parameter
E.g., routeCallToGatekeeper
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IP Telephony
Between the Setup and Connect messages Immediately after the Connect message Equipment dependent
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IP Telephony
(N) Logical Channels --- Audio Call Signaling Channel (H.225 - Q931) RAS Channel RAS Channel H.323 Internet/PSTN Gateway H.323 Gatekeeper H..323 Terminal PSTN
LAN
T1 or Analog H.245 Control Channel
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IP Telephony
Basic Call without GKs
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IP Telephony
A Basic Call with GKs and Direct Endpoint Call Signaling
Terminal Terminal
a b c f e d h g
Release Complete Setup Alerting Call Proceeding Connect H.245 Establishment Media Exchange H.245 Release
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ARQ ACF ARQ ACF DRQ DRQ DCF DCF GateKeeper GateKeeper
A Basic Call with
ARJ with a cause code of
A Facility with a reason
Terminal Terminal GateKeeper GateKeeper
A B C D E F G H I J K L M N O P Q R S T U V W X y ARQ ACF Setup Call Proceeding Setup Call Proceeding ARQ ARJ Facility Release Complete Setup Call Proceeding Call Proceeding Setup ARQ ACF Connect Connect Connect Release Complete Release Complete Release Complete H.245 Establishment Media Exchange H.245 Release
Optional called-endpoint signaling
LRQ, LCF
Terminal Terminal GateKeeper GateKeeper A B C D E F G H I J K L M N O P Q R S T U ARQ ACF Setup Call Proceeding ARQ ACF Setup Call Proceeding Call Proceeding Setup Connect Connect Connect Release Complete Release Complete Release Complete H.245 establishment Media Exchange H.245 release LRQ LCF
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IP Telephony
Agree on the media formats and bandwidth Multiplexing multiple media streams
E.g., for lip synchronization between audio and video
Not carrying the actual media A generic protocol for the control of media streams
Not dedicated for VoIP
How it works in an H.323 system?
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IP Telephony
Requests
Require the recipient to perform some action and to send
Responses
In reply to Requests
Commands
Require the recipient to perform some action, but no
Indications
Of an informational nature only No action and response is expected.
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IP Telephony
A Logical channel
A unidirectional media path An IP address and port number supporting a particular type of
Has a number that is specified by the sending entity
A two-party conversation
Two logical channels exist Potentially in different formats
An endpoint issues Open Logical Channel
Logical channel number and media information (RTP payload type)
Far endpoint responds with Open Logical Channel Ack
An RTP port
Messages over H.245 Control Channel (channel number 0)
Permanently open as long as the endpoint is involved a call
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IP Telephony
Share information regarding the endpoint’s
Indicate a preference TerminalCabilitySet message
A request message A sequence number plus the types of audio and video
TerminalCapabilitySetAck
with a sequence number
TerminalCapabilitySetReject
With a reason for rejection
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IP Telephony
TerminalCapabilitySetRelease
If no response within a timeout period
SendTerminalCapabilitySet
Request Terminal Capability information A command message that does not requires a specific
The endpoint that receives the messages should
The SendTerminalCapabilitySet message contains two
The sender requests that the far endpoint indicates all its
For confirmation
E.g., there has been a break in communication and one
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IP Telephony
One of the endpoints needs to be the master
Of particular importance for the setup of a multi-party
Compare two pieces of information at each entity
A terminal type value A terminal without an MC: 50 A gateway without an MC: 60 An MCU that supports audio, video and data conferencing: 190 An MCU that is currently managing a conference: 240 (the
A random number (1..16,777,215)
Master-Slave Determination message Master-Slave Determination Ack
A “master” or “slave” indication
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IP Telephony
Terminal Terminal
Open Logical Channel{ Forward Logical Channel Number Data Type Forward Channel Parameters{ Session ID RTP Payload Type. etc.} } Open Logical Channel Ack{ Forward Logical Channel Number Logical Channel Ack Parameters{ Transport Address} } Media Exchange
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IP Telephony
Terminal Terminal
Open Logical Channel{ Forward Logical Channel Number Forward Logical Channel Parameters{ Data Type Session ID RTP Payload Type. etc.} Reverse Logical Channel Parameters { Transport Address Media type RTP Payload Type, etc } } Open Logical Channel Ack{ Forward Logical Channel Number Reverse Logical Channel Parameters{ Reverse Logical Channel Number Transport Address RTP Payload Type, etc. } }
Media Exchange
Open Logical Channel Confirm { Forward Logical Channel Number }
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IP Telephony
CloseLogicalChannel,
Only the initiator can issue Or the receiving end can
A bidirectional channel
Once all logical channels
EndSession, EndSession
Terminal Terminal
Request Channel Close Forward Logical Channel Number Reason Request Channel Close Ack Forward Logical Channel Number Close Logical Channel Forward Logical Channel Number source reason Close Logical Channel Ack Forward Logical Channel Number End Session End Session
a b c d e f
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IP Telephony
Terminal Terminal Gatekeeper Gatekeeper
Plus Capability exchange Master-slave determination
ARQ ACF Setup Call Proceeding ARQ ACF Alerting Connect OLC (bidirectional) OLC Ack OLC Confirm Media Exchange CLC CLC Ack End Session End Session Release Complete DRQ DCF DCF DRQ OLC : Open Logical Channel CLC : Close Logical Channel
s r q p
m l k j i h g f e d c b a
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IP Telephony
Q.931
A faststart element : OpenLogicalChannel requests No H.245 control channel
Terminal Terminal Gatekeeper Gatekeeper
ARQ ACF ARQ ACF DRQ DRQ DCF DCF Setup ( faststart [ logical channel infol ] ) Call Proceeding Alerting Connect ( faststart [ logical channel infol ] ) Media Exchange Release Complete
a b l k i j h g f e d c
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IP Telephony
Set the element h245Tunneling to true The encapsulated data is contained within the
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IP Telephony
Participants call in to a separate MCU through Q.931
Communication Mode command (H.245)
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IP Telephony
Expand an existing two-party call to a conference call
One of the endpoints (or one of the endpoints’ gatekeepers)
Endpoint 3 Endpoint 2
Setup ( CID = N ) Connect ( CID = N ) Capability exchange Master-slave determination Setup ( CID = N ) Connect ( CID = N )
a b l k i j h g f e d c
Endpoint 1 (with MC)
m
Logical Channel Establishment Media Exchange Master-slave determination Logical Channel Establishment Capability exchange Multipoint Conference Multipoint Conference Media Exchange Media Exchange
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IP Telephony
Media Gateway Media Gateway Signaling Gateway Signaling Gateway Control Messaging Control Messaging MGC MGC External Bearer Network External Bearer Network
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IP Telephony
With the same identity, a GSM subscriber can receive
The GSM network remains the same.
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IP Telephony
iGSM Gateway performs the conversion for
GSM MAP and RAS protocol translation GSM/PSTN/IP call setup and release
iGSM Gatekeeper records location information as the
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IP Telephony
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IP Telephony
MSISDN of the MS Transport address of the H.323 terminal (MS resides) Password of the iGSM subscriber HLR address of the iGSM subscriber IMSI of the MS User profile that indicates the service features and
Presence indication
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IP Telephony
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IP Telephony
H.323 Terminal Gatekeeper (new VLR) Gateway HLR
RRQ ( MSISDN , passwd ) IRQ ( UpdateLoc, IMSI, VLR, MSC num ) UPDATE_LOCATE ( IMSI, VLR, MSC number ) INSERT_SUBS_DATA ( user profile ) IRR ( InsSubsData, user profile ) IRQ ( InsSubDataAck ) CANCEL_LOCATION ( IMSI ) CANCEL_LOCATION_ack INSERT_SUBS_DATA_ack INSERT_SUBS_DATA_ack ( HLR number ) IRR ( UpdateLocAck, HLR number ) RCF
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IP Telephony
H.323 Terminal Gatekeeper (old VLR) Gateway HLR
CANCEL_LOCATION ( IMSI ) CANCEL_LOCATION_ack
URQ UCF IRR ( CanLoc, IMSI ) IACK ( CanLocAck )
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IP Telephony
iGSM Gateway Gatekeeper (iGSM VLR)
Gateway MSC Originating Switch
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IP Telephony
Originating Switch GMSC HLR Gateway Gatekeeper VLR H.323 Terminal
I AM SEND_ROUTING_INFORMATION ( MSISDN ) PROVIDE_ROAMING_NO ( IMSI ) LRQ ( RoamNo, IMSI ) LCF ( RoamNoAck, MSRN ) PROVIDE_ROAMING_NO_ack ( MSRN ) SEND_ROUTING_INFORMATION_ack ( MSRN ) I AM ARQ ACF Set-up Call Proceeding ARQ ACF Alerting ACM ACM Connect ANM ANM
Conversation
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IP Telephony
MSC
VLR A HLR GSM VoI P Gateway
GSM MS
VLR B
IP Phone
GSM VoI P Network
p P A
MSC
VLR A HLR GSM VoI P Gateway
GSM MS
VLR B
GSM VoI P Network
P B
MSC
VLR A
HLR
GSM VoI P Gateway
GSM MS
VLR B
GSM VoI P Network
P B
p
p
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IP Telephony