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2005-05-23Network Database Lab.
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Application layer multimedia multipoint conferences using
Megaco/H.248
Speakers: 戴碧如, 黃仁暐, 戴志華, 林與絜F89921035, F91921025, F92921029, B90901033
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2005-05-23Network Database Lab.
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References‧張任君,應用層多點多媒體會議方法研究與其在Megaco/H.248之應用 Application layer multimedia multipoint conferences using Megaco/H.248,國立臺灣大學電機工程學研究所--碩士論文,民國90年6月。
• Jen-Chun Chang and Wan-Jiun Liao. Application-layer conference trees for multimedia multipoint conferences using Megaco/H.248. In Proc. of IEEE ICME, 2001.
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Outline • Motivation• Previous Works• Overview of Megaco/H.248• Proposed Algorithm• Practical Issues• Experiments• Conclusions
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Motivation • Multimedia conference using Megaco/H.248
– VoIP should offer the same function/service as PSTN– VoIP should provide more attractive services
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Motivation • Multiple control unit (MCU), which centralizes
the control of conference calls– Waste a lot of bandwidth to send replicate data– Inefficient for capability exchanging
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Motivation • Tree topology, rather than a star topology.
– Data destined to the conference goes to the tree in one copy directly from the branch of which the sender is located.
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Outline • Motivation• Previous Works• Overview of Megaco/H.248• Proposed Algorithm• Practical Issues• Experiments• Conclusions
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Previous Works• KMB, which builds a near optimal minimum
spanning trees– Re-build whole tree while any join or leave happens
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Previous Works• Dynamic greedy algorithm
– Join: the joiner connects to the nearest node on the tree using the shortest path
– Leave: mark the node as deleted if it can’t be removed directly; else, remove it
– May waste lots of bandwidth after a series of departure operations
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Previous Works• Join time local optimal algorithm mitigate the
skewed tree problem. – Leave: same with dynamic greedy algorithm– Join: locally reshape the tree while the join step– Increases the join latency– Can not solve the problem of wasting bandwidth
entirely
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Outline • Motivation• Previous Works• Overview of Megaco/H.248• Proposed Algorithm• Practical Issues• Experiments• Conclusions
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System Architecture• Gateway decomposed
– Separate call control from media transcoding• MGC (Media Gateway Controller)• MG (Media Gateway)
– Residential Gateway– Trunking Gateway
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Connection Model (1/3)• Termination and Context
– Termination• Source or destination of media streams
– Context• Association with a collection of Terminations
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Connection Model (2/3)
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Connection Model (3/3)• Descriptors
– Describe properties of Termination of Context– Encapsulated in commands
• Eight important control commands– Add, Modify, Subtract, Move, AuditValue,
AuditCapabilities– Notify– ServiceChange
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Call Processing (1/2)
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Call Processing (2/2)
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Outline • Motivation• Previous Works• Overview of Megaco/H.248• Proposed Algorithm• Practical Issues• Experiments• Conclusions
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Proposed Algorithm• A conference tree is rooted at the root-MG
where the conference initiator is located, and spans all the participating MGs.
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Proposed Algorithm• A multipoint conference tree grows or is
trimmed when members join or leave the conference, respectively.– Conference tree is reshaped using local
reshaping algorithm when a node leaves in order to achieve better performance.
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Conference Operations• Create a multipoint conference• Terminate a multipoint conference• Join a multipoint conference• Leave a multipoint conference
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Create a Multipoint Conference• A conference will be initiated when a
member (i.e., initiator) starts with a Termination in a null Context on the root-MG, with which the initiator connects.
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Example - Create
MG-11 MG-21
MG-12
MGC-1 MGC-2
User1 Null ContextT1
The initial state of the conference
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Create a Multipoint Conference• Each conference is associated with a conference
number.• The initiator dials the conference number to
connect to the root-MG.• On receiving a notified number, an MGC performs
the authentication checking, and informs the root-MG of a success in conference creation.
• The initiator waits until other members join and the conference begins.
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Terminate a Multipoint Conference
• A conference will be terminated when its initiator leaves the conference because the initiator is considered as the host of the conference.
• The initiator’s MG notifies its MGC of a Notify message if the MG is a Residential Gateway, or an REL message if the MG is an SS7 gateway.
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Terminate a Multipoint Conference
• The MGC then forwards the conference message to all the other MGCs involved in the conference.
• Each MGC then in turn sends Subtract commands to the corresponding on-tree MGs to tear down connections and release the resources previously allocated.
• Host change scenario: the conference operates continuously with another host when the initiator leaves.
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Join a Multipoint Conference• A Termination is added to the Context
associated with the conference.• Upon receipt of a joining request from a
user, an MG notifies its MGC of a connection being created.
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Example - Join
MG-11 MG-21
MG-12
MGC-1 MGC-2
Context 1T1User1
Both MGs are in the same MGCUser2
Context 2
T4
T2*
T3*
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Example - Join
MGs are in different MGCs
MG-11 MG-21
MG-12
MGC-1 MGC-2
Context 1T1User1
Context 2
T4User2
T2
T3
*
*
User3
Context 3
T7T5 T6 *
Information Exchange
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Example - Join
Context 3
MG is on-tree
MG-11 MG-21
MG-12
MGC-1 MGC-2
Context 1T1User1
Context 2
T4User2
T2
T3
*
*
T7 User3T5 T6
Information Exchange
User4
*T8
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Leave a Multipoint Conference• Upon detecting a Termination going on-
hook, the Termination’s MG notifies its MGC of the departure of the Termination.
• An MG at which a departing Termination is located is called a departing MG.
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Leave a Multipoint Conference• Case1: Still other Terminations in the Context
when a user departs from its MG– Simply remove the departing Termination.
• Case2: The departure of a leaf MG and no other Terminations in a departing MG – The departing MG just leaves the conference via a
Subtract command to tear down the connection. • Case3: The departure of an intermediate MG
– The MGC applies a local reshaping algorithm to avoid the growth of a skewed tree.
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Local Reshaping Algorithm• To retain the on-going conference activities,
the connection between the departing nodeand its parent node should be torn down only after those connections between the departing node and all its immediate child nodes have been glued back to the tree.
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Local Reshaping Algorithm
2
1
2
3 4
5 6 7 8
Departing MG
(Departing node)
(a)
1
2
3 4
5 6 7 8Rejoin nodes(b)
1
2
3 4
5 6 7 8
Glued back
(c)
1
2
3 4
5 6 7 8
Glued back
(d)
1
3 4
5 6 7 8
(e)
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Context 5
Example - Leave
Conference topology
Context 4
MG-11 MG-21
MG-22
MGC-1 MGC-2
Context 2
Context 3
T6
User3
T7*
User4
MG-23
T14 User6T13 *
Context 1
MG-12
T2
User1
T1T5
*
T8
T12
T4
User2
T3 *T10
T9T11
*User5
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Example - Leave
Case1: Still other Terminations in the Context when departing
Context 5
Context 4
MG-11 MG-21
MG-22
MGC-1 MGC-2
Context 2
Context 3
T6
User3
T7*
User4
MG-23
T14 User6T13 *
Context 1
MG-12
T2
User1
T1T5
*
T8
T12
T4
User2
T3 *T10
T9T11
*User5
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Context 5
Example - Leave
Case1: Still other Terminations in the Context when departing
Context 4
MG-11 MG-21
MG-22
MGC-1 MGC-2
Context 2
Context 3
T6
User3
T7*
MG-23
T14 User6T13 *
Context 1
MG-12
T2
User1
T1T5
*
T8
T12
T4
User2
T3 * T9 T11* User5
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Context 5
Example - Leave
Case2: The departure of a leaf MG and no other Terminations in the departing MG
Context 4
MG-11 MG-21
MG-22
MGC-1 MGC-2
Context 2
Context 3
T6
User3
T7*
MG-23
T14 User6T13 *
Context 1
MG-12
T2
User1
T1T5
*
T8
T12
T4
User2
T3 * T9 T11* User5
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Example - Leave
Case2: The departure of a leaf MG and no other Terminations in the departing MG
Context 4
MG-11 MG-21
MG-22
MGC-1 MGC-2
Context 2
Context 3
T6
User3
T7*
MG-23
Context 1
MG-12
T2
User1
T1T5
*
T8
T4
User2
T3 * T9 T11* User5
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Example - Leave
Case3: The departure of an intermediate MG
Context 4
MG-11 MG-21
MG-22
MGC-1 MGC-2
Context 2
Context 3
T6
User3
T7*
MG-23
Context 1
MG-12
T2
User1
T1T5
*
T8
T4
User2
T3 * T9 T11* User5
Child of MG-22
T15 T16
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Example - Leave
The resultant conference tree after departure
Context 4
MG-11 MG-21
MG-22
MGC-1 MGC-2
Context 2
MG-23
Context 1
MG-12
T2
User1
T1 *
T4
User2
T3 * T11*
User5
T15 T16
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Outline • Motivation• Previous Works• Overview of Megaco/H.248• Proposed Algorithm• Practical Issues• Experiments• Conclusions
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Host Change• Approach
– The same root-MG• Choose another Termination as the new initiator
– A new root-MG• Select a child MG of the root-MG as the new root-
MG
1
2 3
4 5 6 7
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Determination of the Parent MG (1/3)
• Approach– On the same MGC
• Nearest MG under the same MGC
– On another MGC• Nearest MGC from its MGC
2 3
4 5 6 7
1
N
?
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• Network Layer Tree– Shortest path of total distance of all branches
• Application Layer Tree– Simple to implement– Application compatible
Determination of the Parent MG (2/3)
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• Properties– Less Memory– No calculation– Hierarchical topology– May increase the total distance of all branches
Determination of the Parent MG (3/3)
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Outline • Motivation• Previous Works• Overview of Megaco/H.248• Proposed Algorithm• Practical Issues• Experiments• Conclusions
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Experiments• Evaluate the following perspectives
– Join latency– Bandwidth efficiency– Cost effectiveness
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Join Latency• Formal definition
– Time elapsed between when a user joins a conference and when a user has received data
– Including user request time, processing time, and response time
• In this paper– Distance from the member to the MG on the
tree
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Simulation Topology*
*Interested reader can refer to the paper
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Join Latency
Flat topology
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Join Latency
Drop at the point where on-tree MGs is small
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Bandwidth Efficiency• In terms of total number of links required
per approach• Compare the tree approach to the MCU
approach
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Bandwidth Consumption• For tree
– N-1 shortest path to the conference tree, Ci– Require
• For MCU– N-1 shortest path connections between the MCU and all
the other MGs, Bi– Require Bk to send the data to the MCU and then use
to duplicate to all the others– Total
∑−
=
1
1
N
iiCs
∑−
≠=
1
,1
N
kiiiBs
s : time duration to send data
∑−
=
1
1
N
iiBs
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Parameters• The process an MG joining the conference
is a Poisson distribution (1.5s)• The time an MG staying in the conference
is an Exponential distribution (106s)• Data sent by each member is a Poisson
process (20s)• The data length is an exponential
distribution (320Kb)
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N=100, some of them are randomly selected as MG
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Cost Effectiveness• Compare the tree size of dynamic greedy
algorithm and that of KMB to the conference tree
• Run a sequence of 1000 events. – Each may be a Join or Departing– The probability is proportional to the number of
MGs on the tree
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Ratio to dynamic greedy
Conference TreeDynamic Greedy
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Ratio to KMB
XKMB
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Ratio to KMB
XKMB
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Outline • Motivation• Previous Works• Overview of Megaco/H.248• Proposed Algorithm• Practical Issues• Experiments• Conclusions
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Conclusions• Propose a new conference tree structure for
multipoint conferences– Capability exchange for communications is
carried out through the Session Description Protocol in the Megaco/H.248
• Develop an analytical model to evaluate the performance of the proposed approach
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Conclusions• The proposed approach enjoys the
advantages of lower join latency, better bandwidth efficiency and it’s also cost effective.
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References (1/2)‧張任君,應用層多點多媒體會議方法研究與其在Megaco/H.248之應用 Application layer multimedia multipoint conferences using Megaco/H.248,國立臺灣大學電機工程學研究所--碩士論文,民國90年6月。
• Jen-Chun Chang and Wan-Jiun Liao. Application-layer conference trees for multimedia multipoint conferences using Megaco/H.248. In Proc. of IEEE ICME, 2001.
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References (2/2)• L.Kou, G. Markowsky, and L.Berman, “A Fast Algorithm
For Steiner Trees,”Acta Informatica, Vol. 15, pp.141-145, 1981.
• B. M. Waxman, “Routing of Multipoint Connections,”IEEE JSAC, Vol. 6, No. 9, pp. 1617-1622, 1988.
• Yang Ming and Xie Xiren, “A Optimal Dynamic Multicast Routing Algorithm,” Comminications, 1999. APCC/OECC’99. Fifth Asia-Pacific Conference on … and Fourth Optoelectronics and Communications Conference, Volume:2, 1999, Page(s): 1130-1133vol.2.
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Thank You
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Appendix• Message exchange flow chart of each
operation in the proposed conference tree algorithm
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Create a new conference and the second user join the conference with MG (root) that is already on tree
Initiator MG(root) MGC Second user1. Notify
4. Reply
2. Reply3. Modify
Off hook
Dial group #Stop dial tone and collect digits
Analyze digits and do authentication
5. Notify6. Reply
8. Reply7. Modify
WaitOff hook
9. Similar with step 1~6
11. Reply10. Add
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Join an existing conference with MG-new that is not on tree
New user MG-new MGC MG(to be connected)1. Notify
4. Reply
2. Reply3. Modify
Off hook
Dial group #Stop dial tone and collect digits
Analyze digits and do authentication
5. Notify6. Reply
8. Reply7. Add
Ring 12. Reply11. Modify
9. Add10. Reply
Stop Ring 14. Reply13. Modify
Connected
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Leave operation (there are still other users in the MG)
User MG MGC1. Notify
4. Reply
2. Reply3. Subtract
On hook
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Leave operation (there is no other user in the MG and the MG is a leaf MG)
User MG MGC1. Notify
4. Reply
2. Reply3. Subtract
On hookMG-parent
5. Subtract6. Reply
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Leave operation (there is no other user in the MG and the MG is an intermediate MG)
User MG MGC1. Notify
12. Reply
2. Reply
11. Subtract
On hook
MG-child’s-new parent
3. Add4. Reply
MG-parent MG-child
5. Add6. Reply
7. Modify8. Reply
Connection established
9. Subtract10. Reply
14. Reply13. Subtract
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Termination
Root MG (root) MGC1. Notify2. Reply
On hookAll MGs
3. Subtract4. Reply