13_megaco_h248

Sangwon Min

([email protected])

CPE Lab

(http://cpe.kw.ac.kr)

Megaco/H.248 Protocol

Sangwon Min

Communication Protocol Engineering Lab.

Dept. of Electronics & Communications Engineering

Kwangwoon University

2/33 Sangwon Min([email protected])

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Contents

Protocol Architecture

Connection model transaction and context

Command and parameters

Procedure Example Simplified version

Detail version


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Our Location in Study Flow for VoIP


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Initiation of megaco/H.248

98 fall ~ Each TIPHONE and IETF accept gateway decomposition

98-99 winter

Th first megaco meeting in the IETF

H.GCP is standardizing in the ITU-T

99 sping ~ the megaco/H.248 was off

A novel connection model by the active design team


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Architecture

Similar to the architecture of MGCP ~ MG and MGC

Based on the transaction ~ request and reply

Message description ~ both a text encoding and a binary encoding

Augmented backus-naur form (ABNF) in RFC 2234

Abstract syntax notation no. 1 (ASN 1) in ITU-T X.380

Connection Model Termination; a logical entity as a source or a sink of a media stream

Physical entity : an analog line or a TDM channel in the trunk

Ephemeral termination ~ transiently exists during of a call or media flows; an RTP session

Context; an association between a number of terminations for sharing media between terminations

A termination can exist in only one context at any time


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MEDIA-GATEWAY-CONTROL DEFINITIONS AUTOMATIC TAGS::= BEGIN

MegacoMessage ::= SEQUENCE

{

authHeader AuthenticationHeader OPTIONAL,

mess Message

}

AuthenticationHeader ::= SEQUENCE

{

secParmIndex SecurityParmIndex,

seqNum SequenceNum,

ad AuthData

}

SecurityParmIndex ::= OCTET STRING(SIZE(4))

SequenceNum ::= OCTET STRING(SIZE(4))

AuthData ::= OCTET STRING (SIZE (12..32))

Message ::= SEQUENCE

{ version INTEGER(0..99),

-- The version of the protocol defined here is equal to 1.

mId MId, -- Name/address of message originator

messageBody CHOICE

{

messageError ErrorDescriptor,

transactions SEQUENCE OF Transaction

},

...

}

MId ::= CHOICE

{

ip4Address IP4Address,

ip6Address IP6Address,

domainName DomainName,

deviceName PathName,

mtpAddress OCTET STRING(SIZE(2)),

-- Addressing structure of mtpAddress:

-- 15 0

-- | PC | NI |

-- 14 bits 2 bits

...

}


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Termination and Context

Termination Specific properties according

to the type ~ a set of descriptors

Identified by a TerminationID

Wildcard ~ * (all), $ (choose)

Root termination

Gateway itself as whole

Context Attribute and topology

Topology; flow of media

Identified by a ContextID

Wildcard, assigned by the MG

Null context with ContextID = -

Contains all terminations that do not exist in any other context


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Format and Example

Call Waiting

Scenario


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Commands and Descriptors

Commands

Descriptors Parameters included in a command and a response


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Types of Descriptors (contd)

Media Descriptor


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Types of Descriptors

DigitMap Descriptor

ServiceChange Descriptor

900 Service restored901 Cold boot902 Warm boot903 MGC-directed change904 Termination malfunction 907 Transmission failure 910 Media capability failure913 Signal capability failure915 State loss916 Package change917 Capability change

Code Commentary


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Types of Descriptors - Error Descriptor

400 Bad request401 Protocol error402 Unauthorized403 Syntax error in transaction410 Incorrect identifier421 Unknown action or illegal combination of actions441 Missing remote descriptor 451 No such event in this package471 Implied add for multiplex failure

500 Internal gateway error501 Not implemented503 Service unavailable 510 Insufficient resources517 Unsupported or invalid mode520 MG does not have a digit map530 Temporary network failure581 Does not exist

4XX

Protocol-related error

5XX

Network-related error


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Types of Descriptors topology Descriptor

Flow direction between terminations in a context

Before commands in an action

T2

T1 T3

T2

T1 T3

T2

T1 T3

T2

T1 T3

T2

T1 T3

T2

T1 T3

1. No Topology Description 2. ( T1, T2 Isolate) 3. ( T3, T2 oneway)

4. ( T2, T3 oneway) 5. ( T2, T3 bothway) 6. ( T1, T2 bothway)


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Command Syntax (contd)


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Command Syntax

TerminationID

[,MediaDescriptor]

[,ModemDescriptor]

[,MuxDescriptor]

[,EventsDescriptor]

[,SignalsDescriptor]

[,DigitMapDescriptor]

[,ObservedEventsDescriptor]

[,EventBufferDescriptor]

[,StatisticsDescriptor]

[,PackagesDescriptor]

AuditValue ( TerminationID

AuditDescriptor

)

TerminationID

[,MediaDescriptor]

[,ModemDescriptor]

[,MuxDescriptor]

[,EventsDescriptor]

[,SignalsDescriptor]

[,DigitMapDescriptor]

[,ObservedEventsDescriptor]

[,EventBufferDescriptor]

[,StatisticsDescriptor]

[,PackagesDescriptor]

AuditCapabilities ( TerminationID

AuditDescriptor

)

Notifiy ( TerminationIDObservedEventDescriptor

[, ErrorDescriptor]

)

TerminationID

[,ServiceChangeDescriptor]

ServiceChange ( TerminationID

ServiceChangeDescriptor

)


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Package

Possible Items for Package Common properties, event and signal can be grouped into packages

Termination realizes a set of package

To define the detail feature of the protocol for a specific application

Components PropertyID, EventID, SignalID, StatisticalID and ParameterID and

procedure

Annex E : 13 basic package Base root package, tone generator/detection package, Analog line

supervision package


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Transport

Reliable transport of transaction between an MGC and MG Both TCP and UDP/ALF

Port number

2944 for text-encoded operation for either UDP or TCP

2945 for binary-encoded operation for either UDP or TCP

Security IPsec [RFC 2401 to RFC 2411] in the IP layer

Interim solution : AH header option


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Next Topics

Protocol Architecture

Connection model transaction and context

Command and parameters

Procedure Example Simplified version

Detail version


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Example of Call Procedure


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Procedure Simplified Version (1/4)

MG1 MG2MGC

(MG registration with MGC)

ServiceChange

MEGACO/1 [124.124.124.222]ROOT Method = Restart ServiceChangeAddress=5555 Profile=ResGW/1

Reply

TerminationID = A4444 StreamID = 1 mode=SendReceive SDP Events=2222(al/of)

Modify

(Programs a Termination in the NULL Context)

Reply

Registration proceduresame as MG1

TerminationID = A5555

124.124.124.222 123.123.123.4 125.125.125.111

MEGACO/1 [124.124.124.222]:55555Reply for the ServiceChange services

(Transaction accepted)

SDPv=0c=IN IPV4 $m=audio $ RTP/AVP 0.......


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MG1 MG2MGCUser1 User2

OffHookNotify

(report event to MGC)

Modify(modify termination)

Modify=A4444 Events=2223(al/on,dd/ce{DifitMap=Dialplan0} Signals(cg/dt) DigitMap=Dialplan0 {0|00|[1-7]xxx|8xxxx ...}

- Digits accumulated- Find dialplan match

Notify

- Analyze digits- Determine where to connect

Add

Context $ Add A4444 (TDM Termination) Add $ (RTP Termination) mode =ReceiveOnly SDP

Reply

- New Termination ID and Context ID- SDP Local IP address, UDP port, codec

Event

124.124.124.222 123.123.123.4 125.125.125.111

digits dialed

(Add terminations to a new Context )

(Acknowledges the new Terminationsand fills SDP parameters) )


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Add

Ring

Reply

Modify( Give IPaddress and UDP port of MG2 to MG1)Ring back

Reply

Modify

(Audit the RTP Termination on MG2)

Modify A5555 Event=1235(al/on) Signals { }

Notify

Modify

Modify A4445 Mode=SendReceiveModify A4444 Signals { }

OffHook

Reply

124.124.124.222 123.123.123.4 125.125.125.111

Context $ Add A5555 (TDM Termination) Event=1234(al/of) Signals {al/ri) Add $ (RTP Termination) Mode =SendReceive SDP (local) SDP (remode side)

(Add terminations to a new Contextand rings on User 2)

(Acknowledges the new Terminationsand fills SDP parameters) )

Modify A4445 Remote SDP (IPaddr, UDP port)

Event

(Turn off ringing)

Turn off ringing

Audit

RTP stream


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Substract

Reply

Event

OnHook

Notify

Reply

Substract

Reply

Notify=A5555 ObservedEvent=1235 {19990729T24020002:al/on}

(Report OnHook event)

Subtract = A4444 . Audit (Statistics) Subtract = A4445 Audit (Statistics)

(Subtract Terminations to take down the call)) (Subtract Terminations to take down the call))

Subtract = A5555 . Audit (Statistics) Subtract = A5556 Audit (Statistics)

Reply A5555 . Statistics nt/os=45123 nt/dur=40 A5556 Statistics rtp/ps=1245 nt/os=62345 rtp/pr=780 ........

Termination A4444returns to the null context and isready to detet off-hook event

Termination A5555returns to the null context

124.124.124.222 123.123.123.4 125.125.125.111

RTP stream


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Detail Procedure ( 1/10 )


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MGCMG 1

Internet

MGCP MGCP MG 2

124.124.24.222:55555125.125.125.111:55555

123.123.123.123.4:55555

5 Same procedure as MG1

MEGACO/1 [124.124.124.222]:55555 Transaction = 10000 { Context = - { Notify = A4444

{ObservedEvents =2222 {19990729T22000000:al/of}}

} } }

Hook off

MEGACO/1 [123.123.123.4]:55555 Reply = 10000 { Context = - {Notify = A4444} }

MEGACO/1 [123.123.123.4]:55555 Transaction = 10001 { Context = - { Modify = A4444 { Events = 2223 { al/on, dd/ce {DigitMap=Dialplan0} }, Signals {cg/dt}, DigitMap= Dialplan0{ (0| 00|[1-7]xxx|8xxxxxxx|Fxxxxxxx|Exx|91xxxxxxxxxx|9011x.)} } } }

MEGACO/1 [124.124.124.222]:55555 Reply = 10001 { Context = - {Modify = A4444} }

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MGCMG 1

Internet

MGCP MGCP MG 2

124.124.24.222:55555125.125.125.111:55555

123.123.123.123.4:55555

MEGACO/1 [124.124.124.222]:55555 Transaction = 10002 { Context = - { Notify = A4444 {

ObservedEvents =2223 {19990729T22010001:dd/ce{ds="916135551212",Meth=FM}}}

} }

MGC to MG1: MEGACO/1 [123.123.123.4]:55555 Reply = 10002 { Context = - {Notify = A4444} }

11

11

MEGACO/1 [123.123.123.4]:55555 Transaction = 10003 { Context = $ { Add = A4444, Add = $ { Media { Stream = 1 { LocalControl { Mode = ReceiveOnly, nt/jit=40 }, Local {

v=0c=IN IP4 $ m=audio $ RTP/AVP 4 v=0 c=IN IP4 $ m=audio $ RTP/AVP 0 }

} } } } }

10

10

12

12

MEGACO/1 [124.124.124.222]:55555 Reply = 10003 { Context = 2000 { Add = A4444, Add=A4445{ Media { Stream = 1 { Local {

v=0c=IN IP4 124.124.124.222

m=audio 2222 RTP/AVP 4; RTP profile for G.723 is 4

a=recvonly } } } } } }

1313

Push dial

9-1-613-

555-1212


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MGCMG 1

Internet

MGCP MGCP MG 2

124.124.24.222:55555125.125.125.111:55555

123.123.123.123.4:55555

MEGACO/1 [124.124.124.222]:55555 Reply = 10005 { Context = 2000 {Modify = A4444, Modify = A4445} } 15

MEGACO/1 [123.123.123.4]:55555 Transaction = 10005 { Context = 2000 { Modify = A4444 { Signals {cg/rt}}, Modify = A4445 { Media { Stream = 1 { Remote {

v=0 c=IN IP4 125.125.125.111 m=audio 1111 RTP/AVP 4 }

} } } } }

Ring-back tone16

16

17

17

MEGACO/1 [125.125.125.111]:55555 Transaction = 50005 { Context = 5000 { Notify = A5555 {ObservedEvents =1234 { 19990729T22020002:al/of}} } }

Hook off

MEGACO/1 [123.123.123.4]:55555 Reply = 50005 { Context = - {Notify = A5555} }

MEGACO/1 [123.123.123.4]:55555 Transaction = 50006 { Context = 5000 { Modify = A5555 { Events = 1235 {al/on}, Signals { } ; to turn off ringing } } }

MEGACO/1 [125.125.125.111]:55555 Reply = 50006 { Context = 5000 {Modify = A4445} }

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Detail Procedure ( 10/10)

13_megaco_h248

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