Transcript H.225 Call Signaling

Store/On-demand Multimedia
Streaming over Wired and
Wireless Networks
[Members]
Chien-Chung Su (蘇建仲)
Yi-Hsiu Liu (劉怡俢)
Outline
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Definition
Characteristics/Requirements
Basic technologies
References
Conclusion
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Definition (1/3)
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Streaming
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Real-time
Multi-user
Streaming protocol
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RTP, RTSP
ITU-T H.323
MMS streaming protocol
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Live shows
Definition (2/3)
Live streaming
MOD system
Subscriber
On-demand streaming
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Definition (3/3)
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MoD (Multimedia-on-Demand) allows users to select
the multimedia they like in their favorite way.
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Any time
Any where
Any contents
Application
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Entertainment
Education
…
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Agenda
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Definition
Characteristics/Requirements
Basic Technologies
References
Conclusion
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Characteristic/Requirement
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Characteristic
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Multimedia stored server
Distributed environment
VCR facilities
Multimedia indexing
Requirement
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Quality of Service
Multimedia on wireless network and 3G network
Multimedia information retrieval
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Agenda
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Definition
Characteristics/Requirements
Basic Technologies
References
Conclusion
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Introduction to H.323
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ITU-T Recommendation H.323
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by Liuyh
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Topics Covered
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What Is H.323?
H.323 Components
H.323 Zone
Protocols Specified by H.323
Terminal Characteristics
Gateway Characteristics
Gatekeeper Characteristics
H.225 Registration, Admission, and Status
H.225 Call Signaling
H.245 Control Signaling
Connection Procedures
Interworking with Other Multimedia Networks
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What Is H.323?
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The H.323 standard is a cornerstone technology for the
transmission of real-time audio, video, and data
communications over packet-based networks
It specifies the components, protocols, and procedures
providing multimedia communication over packet-based
networks
H.323 can be applied in a variety of mechanisms audio
only (IP telephony); audio and video …
H.323 provides myriad services and, therefore, can be
applied in a wide variety of areas consumer, business,
and entertainment applications.
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H.323 in Relation to Other
Standards of the H.32x Family
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The other recommendations of the family specify
multimedia communication services over
different networks:
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H.324 over SCN
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H.320 over integrated services digital networks (ISDN)
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H.321 and H.310 over broadband integrated services
digital networks (B-ISDN)
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H.322 over LANs that provide guaranteed QoS
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One of the primary goals in the development of the
H.323 standard was interoperability with other
multimedia-services networks
This interoperability is achieved through the use of a
gateway
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H.323 Components
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The H.323 standard specifies four kinds
of components
provide the point-to-point and point-tomultipoint multimedia-communication
services:
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terminals
gateways
gatekeepers
multipoint control units (MCUs)
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Terminals
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Used for real-time bidirectional multimedia
communications , running an H.323 and the multimedia
applications
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Because the basic service provided by an H.323 terminal
is audio communications, an H.323 terminal plays a key
role in IP-telephony services
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The primary goal of H.323 is to inter-work with other
multimedia terminals. H.323 terminals are compatible
with H.324 terminals on SCN …
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Gateways
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A gateway connects two dissimilar networks. An H.323
gateway provides connectivity between an H.323
network and a non-H.323 network
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This connectivity of dissimilar networks is achieved by
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translating protocols for call setup and release,
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converting media formats between different networks,
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and transferring information between the networks
connected by the gateway
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A gateway is not required, however, for communication
between two terminals on an H.323 network.
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Gatekeepers
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A gatekeeper can be considered the brain of
the H.323 network. It is the focal point for all
calls within the H.323 network
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Although they are not required, gatekeepers
provide important services such as :
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addressing
authorization
authentication of terminals and gateways
bandwidth management
call-routing services
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Multipoint Control Units
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MCUs provide support for conferences of three or more
H.323 terminals. All terminals participating in the
conference establish a connection with the MCU.
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The MCU manages conference resources, negotiates
between terminals for the purpose of determining the
audio or video coder/decoder (CODEC) to use
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The gatekeepers, gateways, and MCUs are logically
separate components of the H.323 standard but can be
implemented as a single physical device.
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H.323 Zone
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An H.323 zone is a collection of all terminals, gateways, and MCUs managed
by a single gatekeeper (see Figure 2).
A zone includes at least one terminal and may include gateways or MCUs. A
zone has only one gatekeeper.
A zone may be independent of network topology and may be comprised of
multiple network segments that are connected using routers or other devices
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Protocols Specified by H.323
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The protocols specified by H.323 are listed
below. H.323 is independent of the packet
network and the transport protocols over
which it runs and does not specify them.
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audio CODECs
video CODECs
H.225 registration, admission, and status (RAS)
H.225 call signaling
H.245 control signaling
real-time transfer protocol (RTP)
real-time control protocol (RTCP)
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Audio CODEC
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An audio CODEC encodes the audio signal
from the microphone for transmission on the
transmitting H.323 terminal and decodes the
received audio code that is sent to the
speaker on the receiving H.323 terminal.
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Because audio is the minimum service
provided by the H.323 standard, all H.323
terminals must have at least moe audio
CODEC support
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Video CODEC
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A video CODEC encodes video from the
camera for transmission on the transmitting
H.323 terminal and decodes the received
video code tat is sent to the video display on
the receiving H.323 terminal.
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Because H.323 specifies support of video as
optional, the support of video CODECs is
optional as well
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H.225 Registration, Admission,
and Status
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Registration, admission, and status(RAS) is the
protocol between endpoints and gatekeepers.
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The RAS is used to perform registration, admission
control, bandwidth change, status , and disengage
procedures between endpoints and gatekeepers.
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A RAS channel is used to exchange RAS messages.
This signaling channel is opened between an
endpoint and a gatekeeper prior to the
establishment of any other channels
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H.225 Call Signaling
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The H.225 call signaling is used to establish
a connection between two H.323 endpoints.
This is achieved by exchanging H.225
protocol messages on the call-signaling
channel.
The call-signaling channel is opened between
two H.323 endpoints or between an endpoint
and the gatekeeper.
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H.245 Control Signaling
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H.245 control signaling is used to exchange end-toend control messages governing the operation of
the H.323 endpoint.
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These control messages carry information related to
the following:
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Capabilities exchange
Opening and closing of logical channels used to carry
media streams
Flow-control messages
General commands and indications
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Real-Time Transport Protocol
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usage:
RTP provides end-to-end network transport functions suitable for
applications transmitting real-time data
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disadvantage:
RTP does not guarantee quality-of-service for real-time services.
The data transport is augmented by a control protocol (RTCP) to
allow monitoring of the data delivery in a manner scalable to large
multicast networks, and to provide minimal control and
identification functionality.
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conclusion:
RTP and RTCP are designed to be independent of the underlying
transport and network layers. The protocol supports the use of
RTP-level translators and mixers.
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Terminal Characteristics
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H.323 terminals must support the following:
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H.245 for exchanging terminal capabilities and
creation of media channels
H.225 for call signaling and call setup
RAS for registration and other admission control
with a gatekeeper
RTP/RTCP for sequencing audio and video packets
H.323 terminals must also support the G.711
audio CODEC. Optional components in an
H.323 terminal are video CODECs, T.120
data-conferencing protocols, and MCU
capabilities
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Gateway Characteristics
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A gateway provides translation of protocols for call setup
and release, conversion of media formats between different
networks, and the transfer of information between H.323
and non-H.323 networks
An application of the H.323 gateway is in IP telephony,
where the H.323 gateway connects an IP network and SCN
network
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Gateway Characteristics (cont)
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On the H.323 side, a gateway runs H.245 control signaling for
exchanging capabilities…On the SCN side, a gateway runs SCNspecific protocols (e.g., ISDN and SS7 protocols)
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Terminals communicate with gateways using the H.245 controlsignaling protocol and H.225. The gateway translates these protocols
in a transparent fashion to the respective counterparts on the nonH.323 network and vice versa
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Audio and video translation may not be required
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Gatekeepers are aware of which endpoints are gateways because this
is indicated when the terminals and gateways register with the
gatekeeper
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A gateway may be able to support several simultaneous calls between
the H.323 and non-H.323 networks
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Gatekeeper Characteristics
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Gatekeepers provide call-control services for H.323 endpoints, such as
address translation and bandwidth management as defined within
RAS.
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Gatekeepers in H.323 networks are optional. If they are present in a
network, however, terminals and gateways must use their services.
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The H.323 standards both define mandatory services that the
gatekeeper must provide and specify other optional functionality that
it can provide.
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Mandatory Gatekeeper Functions
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Address Translation
Admission Control
Bandwidth Control
Zone Management
Optional Gatekeeper Functions
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Call-Control Signaling
Call Authorization
Call Management
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H.225 Registration, Admission,
and Status
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The H.225 RAS is used between H.323
endpoints (terminals and gateways) and
gatekeepers for the following:
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gatekeeper discovery (GRQ)
endpoint registration
endpoint location
admission control
The RAS messages are carried on a RAS
channel that is unreliable. Hence, RAS
message exchange may be associated with
timeouts and retry counts.
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H.225 Call Signaling
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H.225 call signaling is used to set up connections between H.323
endpoints (terminals and gateways), over which the real-time data
can be transported.
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Call signaling involves the exchange of H.225 protocol messages over
a reliable call-signaling channel.
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H.225 messages are exchanged between the endpoints if there is no
gatekeeper in the H.323 network. When a gatekeeper exists in the
network, the H.225 messages are exchanged either directly between
the endpoints or between the endpoints after being routed through
the gatekeeper.
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The method chosen is decided by the gatekeeper during RAS
admission message exchange.
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Gatekeeper-Routed Call Signaling
Direct Call Signaling
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H.245 Control Signaling
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H.245 control signaling consists of the exchange of endto-end H.245 messages between communicating H.323
endpoints
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The H.245 control channel is the logical channel 0 and is
permanently open, unlike the media channels, a logical
channel is unidirectional
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The messages carried include messages to exchange
capabilities of terminals and to open and close logical
channels.
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Capabilities Exchange
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Logical Channel Signaling
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Connection Procedures
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This module describes
the steps involved in
creating an H.323 call,
establishing media
communication, and
releasing the call.
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Interworking with Other
Multimedia Networks
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The H.323 protocol is specified so that it interoperates with other
networks. The most popular H.323 interworking is IP telephony, when
the underlying network of H.323 is an IP network and the
interoperating network is SCN (see Figure 10).
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Interworking with Other
Multimedia Networks (cont)
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H.323 is compatible with various other H.32x networks. Figure
11 shows an H.323 zone interworking with all H.32x networks.
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Agenda
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Definition
Characteristics/Requirements
Basic Technologies
References
Conclusion
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References
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Multimedia Server
VCR Facilities
Multicast
Wireless
Quality of Services
Others
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Multimedia Server
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Characteristics
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Real-time storage
Large storage space and data transfer rate
How to improve the performance
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Disk scheduling algorithm
Reading and buffering requirement
Admission control
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VCR Facilities
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Bandwidth management
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Hold Bandwidth Delay Scheme
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Release Bandwidth Delay Scheme
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Stop display when waiting for VCR bandwidth
Low waiting time
Loss Scheme
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Continue display when waiting for VCR bandwidth
Reducing quality for smooth VCR-like function
Synchronization
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Multicast (1)
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Heterogeneous network (Internet)
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Multi-rate transmission
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1 Kbs in some cellular networks
Terabytes per second in optical networks
Transmit streams at multiple data rates with
dedicated multicast groups
Layered multicast
Orthogonal layered multicast
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The sum of the rates of all its layers dose not
exceed the rate of the highest resolution signal
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Multicast (2)
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Problem
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Bandwidth is wasted in heterogeneous network with
conventional multicast
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Multicast (3)
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Solution
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Orthogonal layered multicast
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Wireless (1)
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QoS problem is far more challenging in
wireless networks
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Host mobility
Scarcity of bandwidth
Channel fading
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Wireless (2)
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QoS parameters
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Traditional QoS parameters
 Bandwidth
 End-to-end delay
 Jitter
Wireless QoS parameters
 Call Blocking Probability (CBP)
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Call Dropping Probability (CDP)
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The probability of a new connection will be denied
The probability of a existing connection will be forcibly terminated
during a hand-off
Bandwidth utilization
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Wireless (3)
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Three mechanism for handling handoff
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Queuing of hand-off reques
Channel rearrangement
Channel reservation
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Fixed reservation
Statistical reservation
New technique for handling handoff
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Rate-based borrowing scheme
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Wireless (4)
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Rate-based borrowing scheme
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M : desired bandwidth
M : minimum bandwidth
Bandwidth Loss tolerance (BLT)
Actual Borrowable Bandwidth (ABB)
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Quality of Services (1)
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There are many techniques could applied on
QoS management
Three main QoS mechanism
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resource reservation(integrated service)
priority mechanisms(differentiated service)
application control
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Quality of Services (2)
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Integrated service
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Quality of Services (3)
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Differentiated service
Q1
Classifier
Q2
Packets in
Scheduler
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Packets out
Qk
Queuing system
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Quality of Services (4)
機制
描述
優點
缺點
resource
reservation
在建立連線之前，須向所有路徑上的路由器
要求適當的資源
較好的服務品質保證
1.
2.
priority
mechanisms
router會根據封包的優先權給予適當的處理
不會過度浪費網路頻
寬
1.
2.
application control
利用congenstion control和transmission-rate
adaptation來達到QoS的目的
不需要去大幅更動現
有的網路架構
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路徑上的路由器都必須
支援此方法並且具有足
夠的資源
網路頻寬可能被浪費掉
路徑上的所有路由器要
支援此方法
如何訂立好的優先權的
順序是目前許多QoS的
機制仍在探討的問題
如何設計出有效的
congenstion control或
flow conrol機制是主要
的挑戰
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Others
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Proxy server
Compression
Error detection and correction
Synchronization
Multimedia information retrieval
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Agenda
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Definition
Characteristics/Requirements
Basic Technologies
References
Conclusion
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Future works
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Multimedia network will be one part of
humans’ life.
Key points of multimedia development
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Wireless network support multimedia
Multimedia retrieval
Quality of Services
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