h.248 protocol issue2

ISSUEISSUE

Fixed Network Curriculum

Development Section

Fixed Network Curriculum

Development Section

OAA000005

H.248/MeGaCo protocol

OAA000005


2.02.0

2

Objective Objective

� Functions of H.248/MeGaCo protocol

� H.248/MeGaCo commands

� Meanings and usage of parameters in

H.248/MeGaCo commands

� Message interaction process of


After this session, you will learn:

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References References

� Product Manual -- Technical Manual – Signaling and

Protocols -- Chapter 4 H.248 Protocol

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About this session About this session

Section 1 Overview

Section 2 Message Structure

Section 3 Call Flow

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Bearer Control Protocols Bearer Control Protocols

� Bearer control protocols are used for

the communication between Media

Gateway Controller (MGC) and Media

Gateway (MG).

� As the control-layer equipment,

SoftX3000 supports two bearer

control protocols: MGCP and H.248.

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Concept Concept

� H.248 and MeGaCo refer to the same kind of protocol. It is an

achievement from the efforts of both ITU and IETF. It is named H.248 by

ITU-T and MeGaCo by IETF.

� H.248 comes into being on the basis of MGCP and is combined with

features of other media gateway control associated protocols.

� The function structure of H.248 is similar to that of MGCP. In NGN, both

H.248 and MGCP can be used between SoftX and most components.

� MGCP is deficient in its descriptive capability, which restricts its

applications in large gateways. For those large-scaled gateways, H.248

is a much better choice.

� MGCP message transportation depends on UDP packets over IP

network, and H.248 signaling messages may be based on multiple

bearers such as UDP/TCP/SCTP.

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H.248 Implementation in SoftX3000 H.248 Implementation in SoftX3000

PSTN

SoftPhone

TMG8010

MRS

IAD

E-phone E-phone

IP CoreMGCP/SIP/H.323

SS7

E1

Sigtran

H.248

MG

CP

MGCP/H.248

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Terms Terms

� Media Gateway (MG):

� An MG converts media provided in one type of network to the

format required in another type of network.

� Media Gateway Controller (MGC):

� It controls the call state pertaining to connection control of media

channels of MG.

� Termination:

� A Termination is a logical entity on an MG, capable of sending

and/or receiving one or more streams. A Termination is described

by a number of characterizing properties, which are grouped in a

set of descriptors included in commands. One termination belongs

to one and only one context at any time.

� Context: A context is the association among terminations. It

describes topology relationships among terminations and

media-mixed/switched parameters.

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Terms Terms

Termination

SCN Bearer Channel

Termination

SCN Bearer Channel

Termination

RTP Stream

Context

C ontext

Context

M edia Gatew ay

N ull Context

*

Termination

SCN Bearer Channel

Termination

SCN Bearer Channel

Termination

RTP Stream *

Termination

RTP Stream *

Context

� Context: A context is the association among terminations. It

describes topology relationships among terminations and

media-mixed/switched parameters.

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Four Attributes of a Context Four Attributes of a Context

� Context ID: The identifier of a context.

� Topology structure: Who hears/sees whom, flow

direction of media.

� Priority: Providing the prior handling information of a

context.

� Emergency: Providing the emergent handling

information of a context.

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Protocol Stack Protocol Stack

Transport media

H.248

IP

UDP/TCP/SCTP

H.248

MTP3-B

SSCF

SSCOP

AAL5

ATM

Physical layer

(a) IP-based H.248 (b) ATM-based H.248

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Section 1 Overview


Section 3 Call Flow

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Message Mechanism of H.248 Message Mechanism of H.248

MessageMessage

TransactionITransaction

TransactionIDn

ContextID1Context

ContextIDn

CMD1Command

CMDn

Des-nDes-1Descriptor

...

...

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Protocol Message Protocol Message

� The unit of information is message.

� A message can contain multiple transactions.

� A message has a header, which contains the ID of the

sender.

� Each Message has a version number, indicating the

version followed by the protocol message.

� There is no relationship among the transactions in a

message. They are treated independently.

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Message StructureMessage Structure

Megaco/H.248 message

Trans Hdr

Req or Reply Req or Reply Req or Reply

Transaction Transaction Transaction....Header

CommandCtx PropertiesCtx Hdr Command....

Trans Hdr

Action Action....

....Descriptor Descriptor

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Code of Protocol Message Code of Protocol Message

� The code of a protocol message can be in the text format

or the binary format.

� MGC must support both formats, while MG can support

either one.

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Commands Commands

used to move a Termination from one Context to

another.

MGC→→→→MGMove

used to remove a Termination from a Context and

return statistics on the Termination's

participation in the Context. The Subtract

command on the last Termination in a Context

deletes the Context.

MGC→→→→MGSubtract

used to modify the properties, events and signals

of a Termination.

MGC→→→→MGModify

used to add a Termination to a Context. If no

ContextID is specified, a Context will be

generated and then a Termination is added into it.

MGC→→→→MGAdd

DescriptionDirectionCommands

� H.248 protocol defines eight commands, all of which are sent to MG by

MGC except the command “Notify”, which is sent to MGC by MG. The

command “ServiceChange” can be sent by either the MG or the MGC. .

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Commands (cont.)Commands (cont.)

used to allow the MG to notify the MGC

that a Termination or group of

Terminations is about to be taken out of or into service. ServiceChange is

also used by the MG to announce its

availability to an MGC (registration), and used for notification of MGC

suspension and active/standby switchover.

MGC↔MGServiceChange

used to allow MG to notify MGC of the

detected event.

MG→→→→MGCNotify

used to return a collection of

termination capabilities.

MGC→→→→MGAuditCapabilities

used to return the current state of properties, events, signals and

statistics of Terminations.

MGC→→→→MGAuditValue

meaningsDirectionCommands:

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Section 1 Overview


Section 3 Call Flow

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Scenario 1 – Registration Scenario 1 – Registration

SoftX3000MG

SVC_CHG_REQ

SVC_CHG_REPLY

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Scenario 2 – Initiation of MGScenario 2 – Initiation of MG

SoftX3000MG

MOD_REPLY

MOD_REQ

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SoftX3000Termination1UserA Termination2 UserB

Off-hook

1 NTFY_REQ

NTFY_REPLY

2 MOD_REQMOD_REPLYdial-tone

dialing

5 ADD_REQ

ADD_REPLY

RingingRingback tone

8 NTFY_REQ

NTFY_REPLY

Off-hook

3 NTFY_REQ

NTFY_REPLY

4 ADD_REQ

ADD_REPLY

6 MOD_REQ

MOD_REPLY7 MOD_REQ

MOD_REPLY

Scenario 3 – Successful call Scenario 3 – Successful call

9 MOD_REQ

MOD_REPLY

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SoftX3000Termination1UserA Termination2 UserB

Conversation

On-hook

On-hook

10 MOD_REQ

MOD_REPLY

11 NTFY_REQ

NTFY_REPLY

12 MOD_REQ

MOD_REPLY

13 SUB_REQ

SUB_REPLY

15 MOD_REQ

MOD_REPLY

14 MOD_REQ

MOD_REPLY Busy-tone

16 NTFY_REQ

NTFY_REPLY

17 SUB_REQ

SUB_REPLY

18 MOD_REQ

MOD_REPLY

Scenario 3 – Successful call (cont.) Scenario 3 – Successful call (cont.)

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SoftX3000SG AMG UserB

1 ADD_REQ

ADD_REPLY 2 ADD_REQ

ADD_REPLY

Ringing

5 NTFY_REQ

NTFY_REPLY

Off-hook

3 MOD_REQ

MOD_REPLY4 MOD_REQ

MOD_REPLY

6 MOD_REQ

MOD_REPLY7 MOD_REQ

MOD_REPLY

TGIAM

ACM

ANM

Conversation

Scenario 4 – Successful trunk call Scenario 4 – Successful trunk call

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SoftX3000SG AMG UserBTG

8 NTFY_REQ

NTFY_REPLY

On-hook

9 MOD_REQ

MOD_REPLY

10 SUB_REQ

SUB_REPLY

11 SUB_REQ

SUB_REPLY

REL

RLC

Scenario 4 – Successful trunk call (cont.) Scenario 4 – Successful trunk call (cont.)

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Summary Summary

� Concept and function of H.248: As a bearer control protocol,

H.248 is used for communication between MGC and MG. The

protocol communication consists of terminations and

contexts.

� There are multiple concepts for H.248, and the inclusion

relation in ascending order is as follows: descriptor –

command – action – transaction – message.

� There are 6 commands: ADD, MODIFY, SUBSTRACT, MOVE,

AUDITVALUE, AUDITCAPABILLITIES, NOTIFY and

SERVICECHANGE.

� The function of each command in H.248 call flow must be

mastered as the key point.

h.248 protocol issue2

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