Transcript NGN 8 - PTCL Training & Development

MGCP
Media Gateway
Control Protocol
(MGCP)
PTCL Training & Development
Media Gateway Control
Protocol (MGCP)
• Used between SoftSwitch and
IAD(integrated access device)/AG (access
gateway)/TMG (trunk media
gateway)/UMG (universal media gateway)
• The Softswitch (MGC) Controls Media
Gateways by means of MGCP
• is a signaling and call control protocol used
within Voice over IP (VoIP) systems that
typically interoperates with the public
switched telephone network (PSTN)
• In essence MGCP is a Master (softswitch)
and Slave(Media Gateways) Protocol
• MGCP uses SDP for media transporting
MGCP Call Flow Scenario
LEGENDS:
IAM- Initial Address Message
ACM- Address Completion Message
CRCX- Create Connection
MDCX – Modify connection (add
video)
RESP – Response to connection
ANM = Answer Message
SG
SG: To establish call b/w PSTN & SS
RESP
SS
LE
LE
RTP/UDP/IP
TMG/UMG 1
TMG/UMG 2
Media Stream
phone
phone
MGCP Messages…….
Command
Direction of Flow and Command itself
Endpoint Configuration MGC to MG
EPCX
Create Connection
MGC to MG
CRCX
Modify Connection
MGC to MG
MDCX
Delete Connection
MGC to MG
DLCX
Notification Request
MGC to MG
RQNT
Notify
MG to MGC
NTFY
Audit Endpoint
MGC to MG
AUEP
Audit connection
MGC to MG
AUCX
Restart In Progress
MG to MGC
RSIP
MGCP Call Flow Scenario
LEX1
MGC
MG1
MG2
MGC
LEX2
Phone
Phone
MGCP
MGCP
OFF Hook
IAM
CRCX
CRCX
IP NEWTORK
RESP
MDCX
RESP
IAM
ACM
Ringing
RESP
ACM
ANM
OFF hook
ANM
MEGACO/H.248, point of origin…
• MEGACO was designed after some
limitations in MGCP like MGCP could
handle low density
• ITU-T developed MDCP whereas IETF
had developed MGCP
• A compromise between the two
originated in the form of MEGACOProtocol or MEGACOP
• ITU-T (SG-16) also developed H.248 in
parallel to MEGACO
• Finally ITU-T & IETF agreed upon that
both MEGACO & H.248 shall be
identical
MEGACO/H.248, functions
• MEGACO defines the rules/protocols for
the Sofswitch to control MGWs
• Typically MEGACO/H.248 provides
support for media streams
• It provides support for VoIP &
multimedia support for PSTN or VoIP
within the IP network
• MEGACO provides base architecture for
controlling MGWs –how MGWs can be
controlled by SS (MGC)
• MEGACO/H.248 works for a distributed
architecture
MEGACO/H.248, workings..
• MEGACO provides:
• Total control over Media Gateways
MGs
• Call admission and billing
• Signaling interface to PSTN
• Translation for H.323 or SIP protocols
The Softswitch (MGController) instructs
MGWs like:
• To sense off-hook condition
• To apply dial-tone & collect dialed
digits
• To ADD any call connection and its
context (coders required)
• To add UDP port numbers etc
MGCP and MEGACO base model
• Two terminologies are used:
– Termination and Context
• Termination:
– A termination is a logical entity that
transmit/receive media stream or control
streams
– For example: Endpoint is a termination
• Context:
-- It is the association between two
Terminations (Endpoints)
For example: between two Endpoints (Local
Call)
between two RTP ports
(Transit Call)
MGCP and MEGACO base model
• MEGACO Terminations and Context
Context
Simple
Context
Voice Call
Termination
Termination
X
Context
Multimedia
Context
(Conference
Call)
Termination
Null
Context
No Connection
Termination
Termination
X
Termination
MGCP and MEGACO base model
• MGCP terms basic constructs as Endpoints &
Connections
Endpoints: source/sink of data
Connections: an association between two
Endpoints
• MGACO terms basic constructs as Terminations
& Contexts
Termination: an entity within a MGW that
source/sinks data
Context: an association between two Terminations
Possible Contexts:
(local call)
(transit call)
Origin & Dest in same MGW
Between two diff MGW
MEGACO and SoftSwitch!
• Sofswitch MGC creates new Context inside
MG by ADD
• MGC adds, subtracts Terminations to a
Context
• MGW NOTIFIES MGC of events (off-hook,
on-hook) inside MG
• MGC audits (checks) Context & Termination
between MGWs
• MGC uses Service Change command (adding
video/data) during a call to inform MGW
MEGACO Packages….
• MEGACO/H.248 define aspects of
signaling as Packages:
– Commonly defined functions like:
• Connectivity, Transfer and Hold etc
• Examples of Packages are:
•
•
•
•
Transactions = Number
Contexts = Number, $
Termination = Identity or $
Package Data = off-hook, on-hook,
port #
• Events, Signals, statistics = ring back
tones, tone itself, time to ring
MEGACO Messages
Messages
Description of Messages
Add
Addition of a Termination to a context. First Add message
creates new context
Modify
Modification of features of termination, dial tone
Subtract
Removal of a termination fro a context (disconnection)
Move
Removal of a termination from context and addition of this
termination to another context (Conference Call)
Audit Value
Requests Information about features, events, signals
When SS learns features like PRI/BRI or any other
Audit Capabilities
Requests Information about all possible features, events,
signals allowed for this termination
Notify
Notification on Events (off-hook, on-hook)
Service Change
Notification of changes of termination like dead, bad