h.248 protocol issue2
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ISSUEISSUE
Fixed Network Curriculum
Development Section
Fixed Network Curriculum
Development Section
OAA000005
H.248/MeGaCo protocol
OAA000005
H.248/MeGaCo protocol
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
H.248/MeGaCo protocol
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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About this session About this session
Section 1 Overview
Section 2 Message Structure
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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About this session About this session
Section 1 Overview
Section 2 Message Structure
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.
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