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An SMR Based Advance
Resource Reservation
Scheme For Combined
Mobility and QoS
Provisioning
Hao Wang
The University of Edinburgh
WP2, Ubiquitous Service
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Outline
 QoS Provisioning in the Mobile Environment
 A Session-to-Mobility Ratio Based Advance Resource
Reservation Scheme
 Performance Comparison
 Conclusions
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QoS Provisioning in the Mobile
Environment
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Resource ReSerVation Protocol (RSVP)
 RSVP is a network layer protocol which can be used
to reserve resources in the network to guarantee
“hard” QoS provisioning.
 The simplified procedure:



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The sender sends out
the PATH messages
that includes the traffic
profile.
The receiver replies with
the RESV messages
that
reserves
the
resources along the data
path.
Reservation is identified
by the IP addresses and
port numbers.
Sender
PATH
RESV
Receiver
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RSVP in the mobile environment (1/2)
 In the mobile environment, the mobile node has to
changes its IP address after a network layer (L3)
handover.
 Therefore, the mobile
node has to re-establish
the
reservation
after
handover:

Correspondent
for example:
Subnet 2
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Subnet 1
Mobile Node
IP Address 1
IP Address 2
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RSVP in the mobile environment (2/2)
 This resource re-reservation results in two major
problems:
1. reservation delay: the delay of this reservation may be
so long that a delay-sensitive session has to be
terminated.
2. reservation blocking: it is possible that this reservation
request is blocked due to the lack of resources in the
new subnet.
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Solutions of the problems in the literature
 To reduce the reservation delay:

identify the common part of the old and new data path
so that the reservation signalling can be restricted
within the affected part of the network
 To reduce the reservation blocking probability:

make advance resource reservations in the networks
that a mobile node may visit before the handover
 The combination of them would be a good approach
to provide QoS in the mobile environment.
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How to make advance reservation (1/3)
 There are two major types of advance resource
reservation approaches:
1. Agent-based: uses a special agent to make advance
reservation.
2. Multicast-based: takes advantage
of multicast
routing
The active
reservation
protocol.
is actively used for
The passive
communication
reservation is not used
1. Agent-based approach:
butwhich
only reserved
 there is an agent in every subnet
takes charge



of resource reservation.
the mobile node makes active reservation in its current
subnet.
the mobile node makes passive reservations in its
neighbouring subnets.
when the mobile node hands over to a new subnet, it
can uses the passive reservation.
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How to make advance reservation (2/3)
2. Multicast-based schemes:



the current and neighbouring subnets of the mobile
node form a multicasting group, and packets are
delivered using multicasting routing, i.e., the packets
are sent to all the nodes that belong to the group.
similar to the agent-based schemes, the mobile node
makes conventional reservation and predictive
reservations in its current and neighbouring subnets
respectively.
handover of the mobile node is modelled as leaving
and joining the branches of a multicast tree.
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How to make advance reservation (3/3)
 An example showing different types of reservations:
Correspondent
Core Network
Foreign Subnet
Foreign Subnet
Local Subnet
Active/Convensional reservation
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Passive/Predictive reservation
Mobile Node
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Problems of advance resource reservation
1. Making advance reservations in a subnet increases
the blocking probability of new session requests
originating from that subnet.

reduces the Grade of Service (GoS) of the network
2. Since advance reserved resources are not actively
used, they waste network resources from the QoS
traffic’s perspective.


Proposals that allow traffic with lower QoS level to
temporarily borrow the advance reservations is not
reliable.
Only allowing best-effort traffic to use the passive
reservations wastes network resources from the QoS
traffic’s perspective.
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Our solution
 Integrate the call admission control (CAC)
mechanisms into the advance resource reservation
scheme so that the network resource utilisation is
improved.
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A Session-to-Mobility Ratio Based Advance
Resource Reservation Scheme
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Motivation and approach
 Motivation:

to design a scheme which can balance the amount of
active reservations (requested by local mobile nodes)
and passive reservations (requested by foreign mobile
nodes) in a subnet.
 Approach: two CAC mechanisms
1. Passive reservation bounding
2. SMR based replacement
 Modularity:

The detailed signalling procedure is left open and the
scheme can be regarded as a building block of the
proposals that combine MM and QoS
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Passive reservation bounding (1/2)
 Aim:

to restrict the amount of passive reservations in a
subnet.
 We give a higher priority to active reservations by
setting aside resources (e.g. channels) just for them.
 Therefore, there are two types of channels:


dedicated channels: for only active reservations
standard channels: for passive reservations and for
active reservations when there is no free dedicated
channel
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Passive reservation bounding (2/2)
 Needs the help of the bandwidth broker (BB) in each
subnet which takes charge of allocating channels
according to the type of requests:


active reservation –> dedicated or standard channel
passive reservation –> standard channel
 To avoid over-restricting passive reservation, the BB
should try to assign an active reservation to a
dedicated channel first, and then to a standard
channel if no free dedicated channel is available.
 Assume the total number of channels in a subnet is
N and there are S standard channels, then


the maximum number of passive reservations is S, and
at least N-S active reservations can be accepted
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SMR based replacement (1/2)
 Aim:

to efficiently utilise the standard channels of a subnet
since they are scarce resources from the viewpoint of
the foreign mobile nodes.
 The mobile nodes who are most likely to handover
during the session are the most eligible to make
passive reservations.
 This probability can be reflected in the ratio of
session duration to subnet residence time, i.e., the
session-to-mobility ratio (SMR).
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SMR based replacement (2/2)
 The replacement procedure works as follows:
1. If the BB receives a passive reservation request and
finds out there is no free standard channel available,
then:
2. The BB compares the SMR value of the requesting
foreign mobile node (SMR_request) and the smallest of
the SMRs of the foreign mobile nodes that have
already acquired standard channels (SMR_smallest).
3. If SMR_request > SMR_smallest, then the standard
channel is re-allocated to the requesting mobile node.
4. Otherwise, the passive reservation request is rejected.
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Flow chart of the SMR based advance resource
reservation scheme
Yes
Replace that
standard channel.
No
Is there a free
standard channel?
No
Any replaceable
standard channel?
No
Is there a free
standard channel?
No
Block the reservation
request.
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Allocate a dedicated
channel.
Yes
Yes
Is there a free
dedicated channel?
No
Yes
Is it an active
reservation request?
Yes
Allocate a standard
channel.
BB receives a reservation
request.
Allocate a standard
channel.
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About the traffic type
 In our work, the QoS sessions are assumed to be of
the same type. Therefore, a mobile node is more
eligible in the sense that it has a larger SMR value.
 However, in a broader sense, the type of the QoS
sessions should be considered and it is an important
criterion for determining which mobile node is more
suitable for making passive reservations.
 Admission control according to different types of
traffic can be implemented in the “policy control”
module defined in the RSVP protocol.
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About the scheme
1. Although the advance resource reservation scheme
looks similar to the handover prioritised scheme
used in the cellular networks, they are different
majorly in the ways in which resource are reserved.


In handover prioritised schemes, reserved resources
can be used by anyone.
In advance resource reservation schemes, resources
are reserved exclusively and so network utilisation is
deteriorated.
2. The side effects of the scalability problem of RSVP
can be reduced by RSVP aggregation techniques (e.g.
RFC 3175).
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Performance Comparison
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Assumptions in the PEPA models
 Traffic Model:

Two-phase hyper exponential (2P-HE) distribution for
session duration:
 2P-HE is validated by both simulation and
experimental measurements
 Mobility Model

Exponential distribution for the subnet residence time
 What determines the handover behaviour:



cell shape
movement pattern
type of handover
 No proven probability distribution exists.
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Performance metrics
 We investigate the congestion level of the network
form the viewpoint of different types of reservations,
i.e.,
1. Active reservation blocking probability
2. Passive reservation blocking probability
 Tuning parameters are traffic intensity:
1. session arrival rate
2. session holding time
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Active reservation blocking prob. vs. session
arrival rate (mean session holding time = 400s)
2
10
1
Active Reservation Blocking Probability
10
0
10
Ordinary Scheme
SMR Based Scheme
Difference (using division)
-1
10
-2
10
-3
10
SMR based-4 scheme is
10
better because it sets
aside dedicated
channels
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for active 10reservations
50
100
150
200
250
300
350
Mean Session Arrival Interval
400
450
500
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Active reservation blocking prob. vs. session holding
time (mean session arrival interval = 180s)
2
10
Active Reservation Blocking Probability
1
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Ordinary Scheme
SMR Based Scheme
Difference (using division)
0
10
-1
10
-2
10
-3
10
-4
10
150
200
250
300
350
400
Mean Session Holding Time
450
500
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Passive reservation blocking prob. vs. session
arrival rate (mean session holding time = 400s)
1
Passive Reservation Blocking Probability
10
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Ordinary Scheme
SMR Based Scheme
Difference (using division)
0
10
SMR based scheme is
better when the traffic
intensity is high
-1
10
-2
10
due to bounded
resources for passive
-3
reservations
10
50
100
150
200
250
300
350
Mean Session Arrival Interval
400
450
500
27
Passive reservation blocking prob. vs. session
holding time (mean session arrival interval = 180s)
1
Passive Reservation Blocking Probability
10
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0
10
Ordinary Scheme
SMR Based Scheme
Difference (using division)
-1
10
-2
10
-3
10
150
200
250
300
350
400
Mean Session Holding Time
450
500
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Discussion (1/2)
 The reason why SMR based scheme performs better
is because it
1. sets aside dedicated resources for active reservations
2. only allows eligible foreign mobile nodes to make
passive reservations.
 The expense of the SMR based scheme is that

slow mobile nodes have to make reservation requests
after handover
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Discussion (2/2)
 However, the SMR based scheme is still reasonable
because:
1. Blocking passive reservations has no effect on the
foreign mobile node’s ongoing session since it is not
actively used, while an active reservation implies there
is a local mobile node that really needs it.
2. When the foreign mobile node without advance
reservation hands over into the local subnet, its
reservation request is an active one which will benefit
from the passive reservation bounding.
3. The passive reservation brings no revenue whilst
active reservation does.
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Conclusions
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In conclusion
 The SMR based advance resource reservation
scheme can efficiently reduce both active and
passive reservation blocking probabilities.
 The enhancements are achieved by the means of:


setting aside dedicated channels for active reservations,
and
only allowing mobile nodes with large SMR values to
make passive reservations.
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For further information please contact:
Hao Wang
E-mail: [email protected]
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