Transcript Before ATM - Politechnika Wrocławska

© Copyright Ezenia Inc, 2000
Multimedia Conferencing Standards
There are two standards associated with Multi media
Conferencing.
H.320 applies to connections across Wide Area Networks.
H.323 applies to connections across Local Area Networks.
Review
Questions
H.323
Standards
H.320
Beginning
Help
1
© Copyright Ezenia Inc, 2000
H.320 Conferences
H.320 is an umbrella standard linking into other standards where
necessary Many standards exist that are relevant to a multimedia
conference.
The H.320 standard defines how a multimedia conference running
over Wide Area (specifically ISDN) should operate. Many of the
individual standards are common to both the WAN and LAN
environments. The major difference is in the area of signalling and
control. WAN environments are connection based; those in the LAN
are connectionless.
Previous
 What other standards are under the H.320 Umbrella?
Beginning
Help
2
© Copyright Ezenia Inc, 2000
H.320 Conferences
H.320
Video
H.261
H.263
Data
T.120
Audio
G.711
G.722
G.728
Multiplexing
H.221
Control
signalling
H.242
H.243
Network
Interfaces
V.xx
X.xx
I.xx
Line
Protocols
I.361
I.363
I.400
Previous
Beginning
Click on the box to find out more about these standards
Help
3
© Copyright Ezenia Inc, 2000
H.323 Standards
H.323 acts as the umbrella standard linking into other
standards where necessary
Release 1 - 1996; Release 2 – 1998 Multimedia conferencing
over IP LANs uses standards from many organisations, some
within ISO and some not, the specific standard H.323 is
predominantly used to identify those standards that are
relevant. Those listed above are not a complete set, but the
ones most likely to be of immediate relevance in configuring
and using the Encounter products.
Previous
 What other standards are under the H.323 Umbrella?
Beginning
Help
4
© Copyright Ezenia Inc, 2000
H.323 Standards
H.323
Video Data Audio Multiplexing Control Security Network Network
H.235
H.261 T.120 G.711
H.222
signalling
Interfaces Protocols
H.263
G.722
H.225
H.225
8802
TCP
G.723
H.244
V.xx
UDP
H.450.x
G.728
X.xx
IP
I.xx
Previous
Beginning
Click on the box to find out more about these standards
Help
5
© Copyright Ezenia Inc, 2000
Video Standards
There are 2 standards for video encoding used for
Multimedia Conferencing. The standards control such
factors as how the signal is compressed and digitised for
transmission, the quality of the picture and how frequently
the screen will be refreshed. The higher the picture quality,
and the more frequent the refresh rate, the higher the
bandwidth requirement.
H.261
H.263
Multimedia
Standards
Beginning
Help
6
© Copyright Ezenia Inc, 2000
H.261
This is the older video encoding standard, but one which is
still widely supported. The choice of refresh rates and
image format allows choices to be made balancing
bandwidth and picture quality. There are two defined image
formats:
Common Intermediate Format (CIF),
which is 352 pixels by 288 lines
Quarter CIF (QCIF), which is 176 pixels by144 lines
H.261 supports the following refresh rates:
Previous
30, 15, 10 and 7.5 times per second
Beginning
This standard is the default for all H.323 traffic and all
Endpoints must be able to support at least this video mode
Help
7
© Copyright Ezenia Inc, 2000
H.263
This is the newer video standard. It offers improved video
coding and decoding, with higher quality options (4CIF has 4
times the picture element count of CIF), and greater refresh
options. There are five defined image formats:
CIF and QCIF (as for H.261)
16CIF - 1408 pixels by 1152 lines
4CIF - 702 pixels by 576 lines
SQCIF - 128 pixels by 96 lines
H.263 supports the following refresh rates:
Previous
30, 15, 10, 7.5, 6, 5, 4, 3, 2, 1 times per second
For some applications a high quality image with very slow
refresh will be desirable, while others would prefer rapid
refresh at the expense of quality.
H.263 is not directly compatible with H.261.
Beginning
Help
8
© Copyright Ezenia Inc, 2000
Audio Standards
G.711
G.722
G.723
G.728
There are more variations of audio standards than
there are of video, but there is only limited flexibility
within each standard. It is possible to interwork these
standards providing a device on the network translates
the codes.
Each encoding standard relies on an analogue to
digital technique called Pulse Coded Modulation
(PCM), of which there are two standard methods of
operating - A-law is used mainly in North America, and
m-law is used mainly in Europe. Some Encoding
standards support both techniques, some only one.
Where both are supported within the standard, the
Endpoints must be compatible with the chosen
technique.
Multimedia
Standards
Beginning
Help
9
© Copyright Ezenia Inc, 2000
G.711
This is the most common audio standards used within both
H.320 and H.323 with G.728 supported in H.320 networks
and G.723 in H.323 networks. It is possible to interwork
these standards providing a device on the network
translates the codes.
G.711 encodes 3.1 KHz audio using pulse code
modulation. G.711 audio is transmitted at 48kbps or
56kbps in H.320, or 64 kbps elsewhere.
Previous
This is the default standard applied to H.323 Endpoints,
regardless of what other standards they can support, they
must support G.711.
Beginning
Help
10
© Copyright Ezenia Inc, 2000
G.722
G.722 encodes 7.0 KHz audio based on sub-bands
(divides the frequency band into higher and lower bands
called sub-bands). It only transmits the change in an input
signal, instead of the whole signal.
G.722 audio is transmitted at 48kbps or 56kbps in H.320,
or 64 kbps elsewhere.
Previous
Beginning
Help
11
© Copyright Ezenia Inc, 2000
G.723
G723 is also known as IP Audio and is often used in H.323
networks. It provides audio quality like the Mobile Phone
standard, and not normal telephone standard sound
quality.
G.723 encodes 3.0 KHz audio and is transmitted at
5.3kbps or 6.3kbps.
Previous
Beginning
Help
12
© Copyright Ezenia Inc, 2000
G.728
G.728 is an audio coding algorithm that takes 128K pulse
code modulated data and transmits it at 16kbps.
It is frequently used in low-speed conferences since it
makes more of the transfer rate bandwidth available for
video.
It is used widely within H.320 networks for this reason.
Previous
Beginning
Help
13
© Copyright Ezenia Inc, 2000
Control Standards
There are two control protocols used within H.323, H225
and H.245.
H.225 is used for control signalling during the initial call set
up between Gatekeeper and Endpoint.
H.245 is then used for control signalling during the
conference itself.
Previous
H.450.x
H.225
H.245
Beginning
Help
14
© Copyright Ezenia Inc, 2000
H.225
H.225 is the principle “language”of the Gatekeeper. A
Gatekeeper has a range of special functions to fulfill,
and so requires a special language of it’s own. H.225
also uses another standard protocol, Q.931.
Previous
H.225 RAS / Q.931
Click here to find out more about these standards
Beginning
Help
15
© Copyright Ezenia Inc, 2000
H.225 RAS
The three prime functions of H.225 are those of
Endpoint Registration, Admission and Status. Each of
these functions is performed as a separate step within
H.225. The Gatekeeper sends “keep alive” messages
to endpoints while it is processing RAS requests.
Registration
Admission
Status
Previous
Beginning
Help
16
© Copyright Ezenia Inc, 2000
Q.931
Q.931is one of the common call signalling protocols used
in Wide Area Networks.
Q.931 is used to establish a connection between an
Endpoint and the Gatekeeper, and between one Endpoint
and another.
Previous
Beginning
Help
17
© Copyright Ezenia Inc, 2000
H.225 Registration
Any Endpoint that wishes to take part in a conference must
Register with a Gatekeeper. When an Endpoint attached to
a LAN is started it will automatically send a message
looking for a Gatekeeper to register with. There can only
be one Gatekeeper that is “allowed” to accept that
registration. Once an Endpoint is registered it will
periodically send an update message to the Gatekeeper to
maintain it’s registration.
Previous
Beginning
 What does the Gatekeeper do
with the registration information?
Help
18
© Copyright Ezenia Inc, 2000
H.225 Registration
The Gatekeeper will use the information gained during
registration to build a “routing” table. This will include
learning the name allocated to each Endpoint as well as it’s
network address.
A gatekeeper can be set to accept any address, or set to
only accept specific addresses. An Endpoint could be set
to register with any gatekeeper, or a specific gatekeeper.
To build a zone (in a multi-gatekeeper system), requires
that one or other device is correctly configured. In a large
network it will be easiest to configure the gatekeepers.
Previous
Beginning
Help
19
© Copyright Ezenia Inc, 2000
H.225 Admission
Before a conference can commence the Gatekeeper will
have to give permission. The originating Endpoint will
request a connection by specifying with whom it wishes to
communicate and the amount of bandwidth it requires.
The Gatekeeper will permit the connection providing
1. Security conditions are satisfied (e.g. valid user,
valid destination, etc.).
2. Sufficient bandwidth exists.
If sufficient bandwidth does not exist, then the Gatekeeper
can negotiate with the Endpoint to attempt to agree a lower
value providing the Endpoint supports such an option.
Previous
Beginning
 How does admission happen?
Help
20
© Copyright Ezenia Inc, 2000
H.225 Admission
Is he allowed to?
Is there enough capacity?
Can we agree on capacity?
Previous
Beginning
Help
21
© Copyright Ezenia Inc, 2000
H.225 Status
The Gatekeeper will monitor the status of all registered
Endpoints and connections, by sending and receiving
“Keep Alive” messages . The prime purpose of this is to
ensure that registered Endpoints remain available. An
Endpoint should de-register when finished, but may not.
To allow for this the Gatekeeper regularly contacts each
Endpoint to see that they are still operational. An Endpoint
that fails to respond is removed from the registered list.
Similarly the Endpoints are required to report periodically to
the Gatekeeper for the duration of a call. If an Endpoint
fails to report for four consecutive times the call is assumed
to have ended and the Gatekeeper will send Disconnect
messages to both Endpoints and release the network
resources.
 How does this happen?
Previous
Beginning
Help
22
© Copyright Ezenia Inc, 2000
H.225 Status
No reply from
Harry, so I’ll
de-register him.
Mary’s still active,
so she can stay
registered
Previous
Beginning
Help
23
© Copyright Ezenia Inc, 2000
H.245
Connections need to be set-up for a specific conference,
monitored to ensure they are functional, and then cleared
at the end of the conference. This is the function of the
H.245 standard.
H.245 Control
Previous
Audio
Beginning
Video
Help
24
© Copyright Ezenia Inc, 2000
Security Standards
H.235 is a security protocol which was introduced into
H.323 at release 2. It provides the following facilities to
ensure that conferences can be more tightly controlled.
By authenticating users, it can control who can join the
conference.
H.235 can enforce Endpoint integrity which forces
Endpoints to be associated with Participants.
It can ensure data stream privacy by using a pseudo
encryption technique.
Using a technique, known as non-repudiation, which
checks that the caller is who they say they are, it can
Previous
ensure that callers are billed correctly.
Beginning
Many endpoints do not currently support H.235.
Help
25
© Copyright Ezenia Inc, 2000
H.450.x
Introduced into H.323 at release 2, H450.x protocols
introduce several supplementary services into the H.323
environment.
H.450.1 is the signalling protocol which controls the
operation of the other protocols.
H.450.2 provides call transfer facilities, which allow callers
to be met by an operator, before joining conference.
Previous
H.450.3 allows calls to be diverted to other endpoints.
Not all endpoints support H.450.x
Beginning
Help
26
© Copyright Ezenia Inc, 2000
Multimedia Conferencing Standards Review Question 1
The H.323 standard is used over Wide Area Networks only.
True
False
Choose your answer
Multimedia
Standards
Beginning
Review that
information again
Move on
to the
next question
Help
27
© Copyright Ezenia Inc, 2000
Wrong Answer
 H.320 is the Multimedia conferencing standard for WANs.
 H.323 is used over any network that uses IP as it’s
transport protocol. This could be a LAN or a WAN network.
Multimedia
Standards
Beginning
Review that
information again
Move on
to the
next question
Help
28
© Copyright Ezenia Inc, 2000
Correct Answer
 Well done
 H.323 is used over any network that uses IP as it’s
transport protocol. This could be a LAN or a WAN network.
Multimedia
Standards
Beginning
Review that
information again
Move on
to the
next question
Help
29
© Copyright Ezenia Inc, 2000
Multimedia Conferencing Standards Review Question 2
Which of the following standards are used for conference control, between
Endpoints,once they have registered with the Gatekeeper.
H.225
H.245
Q.931
RAS
Multimedia
Standards
Choose your answer
Beginning
Review that
information again
Move on
to the
next question
Help
30
© Copyright Ezenia Inc, 2000
Wrong Answer
 H.225 is the protocol used by the Gatekeeper to
communicate with Endpoints.
 H.245 is used to control the conference traffic between
Endpoints.
Multimedia
Standards
Beginning
Review that
information again
Move on
to the
next question
Help
31
© Copyright Ezenia Inc, 2000
Wrong Answer
 Q.931 is part of the H.225 protocol, used by the
Gatekeeper to communicate with Endpoints.
 H.245 is used to control the conference traffic between
Endpoints.
Multimedia
Standards
Beginning
Review that
information again
Move on
to the
next question
Help
32
© Copyright Ezenia Inc, 2000
Wrong Answer
 RAS is part of the H.225 protocol, used by the Gatekeeper
to communicate with Endpoints.
 H.245 is used to control the conference traffic between
Endpoints.
Multimedia
Standards
Beginning
Review that
information again
Move on
to the
next question
Help
33
© Copyright Ezenia Inc, 2000
Correct Answer
 Well done
 H.245 is used to control the conference traffic between
Endpoints.
Multimedia
Standards
Beginning
Review that
information again
Move on
to the
next question
Help
34
© Copyright Ezenia Inc, 2000
Multimedia Conferencing Standards Review Question 3
As a minimum, an H.323 Endpoint must support the H.263 video standard.
True
False
Choose your answer
Multimedia
Standards
Beginning
Review that
information again
Move on
to the
next question
Help
35
© Copyright Ezenia Inc, 2000
Wrong Answer
 H.263 is the newer video Standard, offering more efficient
compression, or higher image quality.
 An H.323 Endpoint must support H.261, as a minimum.
Multimedia
Standards
Beginning
Review that
information again
Move on
to the
next question
Help
36
© Copyright Ezenia Inc, 2000
Correct Answer
 Well done
 An H.323 Endpoint must support H.261, as a minimum.
Multimedia
Standards
Beginning
Review that
information again
Move on
to the
next question
Help
37
© Copyright Ezenia Inc, 2000
Multimedia Conferencing Standards Review Question 4
Which of the following audio standards are most widely used in H.323?
G.711 and G.722
G.711 and G.723
G.711 and G.728
G.723 and G.728
Multimedia
Standards
Choose your answer
Beginning
Review that
information again
Move on
to the
next question
Help
38
© Copyright Ezenia Inc, 2000
Wrong Answer
 G.711 is the most commonly used audio standard in both
H.320 and H.323.
 G.722 is not widely used in H.323.
 G.711 and G.723 are the most commonly used audio
standards in H.323.
Multimedia
Standards
Beginning
Review that
information again
Move on
to the
next question
Help
39
© Copyright Ezenia Inc, 2000
Wrong Answer
 G.711 and G.728 are the most commonly used audio
standards in both H.320.
 G.711 and G.723 are the most commonly used audio
standards in H.323.
Multimedia
Standards
Beginning
Review that
information again
Move on
to the
next question
Help
40
© Copyright Ezenia Inc, 2000
Wrong Answer
 G.723 is widely used in H.323.
 G.728 is widely used in H.320.
 G.711 and G.723 are the most commonly used audio
standards in H.323.
Multimedia
Standards
Beginning
Review that
information again
Move on
to the
next question
Help
41
© Copyright Ezenia Inc, 2000
Correct Answer
 Well done
 G.711 and G.723 are the most commonly used audio
standards in H.323.
Multimedia
Standards
Beginning
Review that
information again
Move on
to the
next question
Help
42
© Copyright Ezenia Inc, 2000
Multimedia Conferencing Standards Review Question 5
Which of the following standards was introduced in Release 2 of the H.323 Standard?
H.225
H.235
H.245
Choose your answer
Multimedia
Standards
Beginning
Review that
information again
Help
43
© Copyright Ezenia Inc, 2000
Wrong Answer
 H.225 is the protocol used by the Gatekeeper, and has
been part of H.323 since release 1 of the standard.
 H.235 was introduced to provide enhanced security in
H.323, release 2.
Multimedia
Standards
Beginning
Review that
information again
Help
44
© Copyright Ezenia Inc, 2000
Wrong Answer
 H.245 is the protocol used by Endpoints for conference
control, once they have registered with the Gatekeeper and
has been part of H.323 since release 1 of the standard.
 H.235 was introduced to provide enhanced security in
H.323, release 2.
Multimedia
Standards
Beginning
Review that
information again
Help
45
© Copyright Ezenia Inc, 2000
Correct Answer
 Well done
 H.235 was introduced to provide enhanced security in
H.323, release 2.
Multimedia
Standards
Beginning
Review that
information again
Help
46