Rate Control in Handoff

1
Rate Control in Handoff

• Yi Pan
• Meejeong Lee
• Yuji Imai

2
Problem Statement

• Current handoff techniques
• Single mobile IP binding causes blackout time in
  transmission.
• Handoff causes fluctuation in transmission.
• Standard multicast mobility support doesnt
  provide accurate transmission rate control in
  handoff.

3
Basic Ideas

• Binding multiple mobile IP addresses to a single
  mobile node.
• Using multi-path transmission based on the
  multiple bindings, we eliminate the blackout
  time.
• Two options
• XCAST suitable for rate and QoS sensitive
  traffic
• multiplexed unicast suitable for data
  transmission

4

• Early estimation of newly bound paths capacity
  helps to smoothly transfer the transmission rate
  in handoff
• Two options
• XCAST multi-path transmission with a certain
  level of data redundancy.
• multiplexed unicast multi-path transmission of
  data flows without redundancy.
• Key point per path transmission rate control.

5

• Illustration
• XCAST

MN loses connection with COA1 and only connects
to COA2
Throughput of XCAST/handoff
Overall transmission rate of video streams
MN starts to receive both from COA1 and COA2
again.
MN starts to receive both from COA1 and COA2
Tr1
MN lost connection with COA2
Tr2
MN only receives from COA1
MN starts estimation on path2 to COA2
MN starts estimation on path1
6

• Multiplexed unicast

MN loses connection with COA1 and only connects
to COA2
Overall transmission rate of video streams
Throughput of multiplexed unicast
MN starts to receive both from COA1 and COA2
again.
MN starts to receive both from COA1 and COA2
Tr1
MN lost connection with COA2
Tr2
MN only receives from COA1
MN starts estimation on path2 to COA2
MN starts estimation on path1
7

• From this slide on, we will concentrate on the
  streaming media transmission with XCAST.

8
Application Requirements

• Streaming media
• Enhancing the quality
• Retransmission is not always a proper means of
  error recovery due to the restriction of timely
  delivery
• To enhance quality, not only supporting higher
  smooth bandwidth over time but also providing
  robustness to error are important
• Demultiplexed multicast may suit
• A certain kind of data redundancy is acquired to
  reduce the error rate

9
Features of XCAST handoff Scheme

• XCAST handoff with multiple binding of COA and
  early estimation of path capacity
• Features
• throughput is the maximum of bandwidth in all
  paths currently used by different COAs
• by sending duplicated packets to the mobile node,
  it is much stronger against link errors
• with early estimation of path capacity and
  multiple binding, there is less fluctuation
• by sending out duplicated packets using XCAST, we
  achieve better synchronization in real time
  traffic
• Its good for rate and QoS sensitive traffic.

10
Required Schemes

• Registration of multiple COAs
• COA acquisition
• COA binding update
• Route optimization and binding update
• Demultiplexing and multiplexing of a data stream
  to utilize the multiple paths
• Per-path congestion control scheme
• Grouping COAs (Multicast tunnel construction)
• Multicast mechanism XCAST

11
Registration of Multiple COAs

• COAs acquisition

Wireless cell
Base station
router HA
home network
Wireless Network Gateway
Internet
Wireless cell
MN
CN
router
Base station
Each registration will have a limited
lifetime associated to it.
12
Registration of Multiple COAs

• Further steps
• COA acquisition
• In IPv4, we can use DHCP or Foreign Agent
  Advertisement to acquire COA.
• In IPv6, we acquire the current network prefix
  through network address auto-configuration.
• A Binding Update message is sent to Home Agent to
  inform the new binding of COA.
• Home Agent records the new binding and send back
  a Binding Acknowledgement.

13
Registration of Multiple COAs

• COAs binding updates

Wireless cell
Base station
Packets can not really arrive at MN through this
path. Lower layer protocol will inform the loss
of the connection.
router HA
home network
Wireless Network Gateway
Internet
Wireless cell
CN
router
MN
Base station
14

• Changing of COAs (Cond)

Wireless cell
Base station
router HA
home network
Wireless Network Gateway
Internet
Wireless cell
CN
router
MN
Base station
15
Registration of Multiple COAs

• Annotation to the previous animation
• Binding of COAs should be refreshed by Binding
  Update messages periodically before the Life time
  expires.
• MN can actively send a Binding Update message
  with Life Time set to 0 to relinquish the old
  binding.
• Missing Binding Updates of a certain COA means to
  erase the binding from Binding Cache in HA and CN.

16
Registration of Multiple COAs

• Route Optimization

Wireless cell
Base station
router HA
home network
Wireless Network Gateway
Internet
Wireless cell
MN
Unicast transmission from CN to HA.
CN
router
Base station
Tunnel starts from HA and ends at MN at first.
17
Registration of Multiple COAs

• Reason for route optimization
• The route from CN to MN is not the optimal one
  since it goes from CN to HA, then to MN. It is
  called the triangle route.
• Optimal route is from CN directly to MN which
  does not go through HA.
• Thus, CN needs to have the binding cache to
  optimize its route to the MN directly.

18

• Route Optimization (Contd)

Wireless cell
Binding Update of COA1 to HA and CN.
Base station
router HA
home network
Wireless Network Gateway
Internet
Wireless cell
MN
Tunnel starts from CN and ends at MN after
optimization.
CN
router
Binding Update of COA2 to HA and CN.
Base station
19
Registration of Multiple COAs

• Annotation to previous animation
• Binding update in route optimization
• mobile nodes will have a binding update list
  containing all the nodes need to be informed
  about the new binding. That list includes HA and
  CN.
• By sending Binding Update message to all hosts in
  the binding update lists, current CNs can be
  informed of the new binding directly.
• After CN received the Binding Update message from
  the mobile node, CN can re-tunneling the packets
  toward the new binding address without the help
  from HA.
• HA needs to keep the refreshed binding for the
  new connections from new CNs.

20
Demultiplexing/multiplexing of a Data Stream

• We demultiplex the data stream and construct
  several tunnels between CN and MN
• Each tunnel can be multicast tunnels or unicast
  tunnel.
• Tunnels transmission rate is decided by the
  grouping policy of different COAs and current
  available bandwidth towards each of the COAs.
• The total throughput of data stream is the
  summation of transmission rate of all tunnels.
• Tunnel construction can be dynamic to reflect the
  current set of COA bindings and available
  bandwidth towards each COA.

21
Demultiplexing/multiplexing of a Data Stream

• Demultiplex/multiplex illustration

Tunnel1
w1
COA1
Tunnel2
w2
COA2
Application data
Application data
Tunnel3
w3
COA3
Multiplex
Demultiplex
Tunnel4
w4
COA4
Sender window for each tunnel
Receiver window for each path
In this example, we have four different tunnels
Tunnel1--gt COA1,COA2,COA3 Tunnel2--gt
COA1,COA2 Tunnel3--gt COA3,COA4
Tunnel4--gt COA4
22
Per Path Congestion Control

• Congestion control is still based on each path to
  a specific COA instead of per-tunnel.
• Grouping of COAs into tunnels is based on the
  reported available bandwidth to all COAs.
• Grouping policy can be application-specific and
  may result in dynamic structure and transmission
  rates in tunnels.
• The scheme is sender-initialized since it
  requires all paths information.
• Best suitable multicast scheme XCAST

23
Per Path Congestion Control

• Per-Path Congestion Control Illustration

Sender window for each tunnel
Receiver window for each path
Tunnel1
w1
COA1
Tunnel2
w2
COA2
Application data
Application data
Tunnel3
w3
COA3
Multiplex
Demultiplex
Tunnel4
w4
COA4
In the same example, we also have four different
paths to four different COAs. The transmission
rate of each path is Path1 Tunnel1Tunnel2
Path2 Tunnel1Tunnel2 Path3
Tunnel1Tunnel3 Path4 Tunnel3Tunnel4 Key
point tunneling is the data forwarding mechanism
while congestion control is applied to a path.
24
Per Path Congestion Control

• Advantages
• With per path congestion control, we have more
  accurate and more timely knowledge about
  available bandwidth in each paths.
• When handoff happens, through per path congestion
  control, its easy to estimate the available
  bandwidth earlier.
• When transmission rate fluctuates, sender can
  capture the changing rate in the path faster.
• By acquiring accurate knowledge of all the paths,
  more intelligent usage of bandwidth can be
  applied in the sender. Thus increase the
  throughput.

25
Per Path Congestion Control

• Requirements of per path congestion control
• Differentiating the packets sent through
  different paths
• Sending exact the amount of packets through a
  specific path according to the estimated window
  size
• Changing the number of packets sent through a
  path dynamically without affecting other paths
  congestion status
• Best suitable multicast scheme XCAST.

26
Grouping of COAs

• Grouping of COAs into tunnels is based on
• Currently reported available bandwidth of all
  paths to COAs
• Application-specific requirements
• ie. Different levels of redundancy, redundancy
  ratio for each level.
• Dynamic creating groups of COAs for a tunnel
  based on scheduling of packets according to
  current available bandwidth in the paths.

27
Grouping of COAs

• Single layer video transmission with specified
  ratio of redundancy(Contd)
• Illustration

Path1
Deficit Round Robin according to the window sizes
28
Grouping of COAs

• Single layer video transmission with specified
  ratio of redundancy (Contd)
• Annotation
• Each path will have a credit equal to its window
  size associated.
• For each packet, the scheduler randomly chooses
  different paths that have a positive credit and
  decrease all affected paths credit by one.
• Credit of each path equals the number of packets
  that still allowed to be sent by the congestion
  window.
• The number of paths chosen in each iteration
  equals the redundancy ratio of the video stream.

29

• Single layer video transmission with specified
  ratio of redundancy (Contd)
• Note
• Because of the random choice in the scheduler,
  the number of tunnels is dynamic.
• If the available bandwidth in the paths is so
  unbalanced that we can not have groups of paths
  with equal accumulative bandwidth, the redundancy
  ratio is not guaranteed.
• Ie. If redundancy ratio is 2 and we have three
  paths with bandwidth of 1Mbps, 2Mbps, and 10Mbps,
  the tunnels we can acquire will be a 3Mbps
  multicast tunnel with redundancy ratio 2 and a
  unicast tunnel of 7Mbps.

30
Grouping of COAs

• Multi layer video transmission with different
  levels of redundancy.
• Number of tunnels is decided by the number of
  different available transmission rates.
• Grouping of paths is according to the ordering of
  available bandwidth through each path.
• A tunnel with more paths has higher redundancy
  level.
• Multicast tunnels are used and the multicast
  group for each tunnel is dynamic.

31
Grouping of COAs

• Multi layer video transmission with different
  levels of redundancy. (Contd)
• Illustration

Tunnel1
Assume capacity of the four paths is in this
order COA1ltCOA2ltCOA3ltCOA4. Transmission rate of
each tunnel can be calculated as Tunnel1 COA1
Tunnel2 COA2-COA1 Tunnel3 COA3-COA2
Tunnel4 COA4-COA3.
32
Grouping of COAs

• Multi layer video transmission with different
  levels of redundancy. (Contd)
• Illustration (Contd)
• Data subset for each tunnel
• Different tunnels have different levels of
  redundancy.

path1 sequence 1
2 3
4 .
path2 sequence 1 2
3 4 5 6
7 8 .
path3 sequence 1 2 3
4 5 6 7 8 9
10 11 12 .
path4 sequence 1 2 3 4
5 6 7 8 9 10 11 12
13 14 15 16 .
Tunnel1 packets
Tunnel2 packets
Tunnel3 packets
Tunnel4 packets
33
Grouping of COAs

• Multi layer video transmission with different
  levels of redundancy. (Contd)
• Illustration (Contd)
• Multi-layer transmission

34
Multicast mechanism XCAST

• Requirements in the above schemes
• Dynamic group membership in multicast tunnels
  because of rate fluctuation and handoff.
• Small groups involved in handoff (limitation on
  the number of COAs).
• Dynamic creating of new groups is required in per
  path congestion control and dynamic scheduling in
  the demultiplexer.
• For scalability to the number of mobile nodes,
  large number of multicast group addresses are
  needed.

35
Multicast mechanism XCAST

• The natural difference between XCAST and ISM
• XCAST doesnt need the intermediate routers to
  keep group information, thus can deal with
  dynamic groups with less control overhead.
• All group member changes will be handled by the
  end system.
• No need to update the intermediate routers
  status about group membership information.
• End system have knowledge of all the receivers
  addresses specifically.
• New group can be constructed on-demand and
  instantly.
• Per path congestion control and dynamic group
  creation in demultiplexer are possible.
• XCAST is suitable for small group multicast,
  while ISM deals with large number of group
  members.
• XCAST doesnt have address allocation problem,
  while ISM needs special network address space.
  Thus XCAST is suitable for large number of small
  groups while ISM is suitable for small number of
  large groups.

36
Multicast mechanism XCAST

• Tradeoffs between XCAST and ISM
• Advantages of ISM mobility support
• Fast connectivity recovery
• COA bindings does not need to be sent to the end
  system to acquire data packets.
• It takes shorter time to recover the connectivity
• Less binding updates involved in mobile IP
  registration

37
Multicast mechanism XCAST

• Tradeoffs between XCAST and ISM(Contd)
• Disadvantage of ISM mobility support
• High overhead and delay incurred for dynamic
  group membership changes and dynamic group
  creation.
• Thus, per path congestion control and dynamic
  group creation in demultiplexer are not possible,
  which make the convergence time to the available
  bandwidth much longer.
• Only static number of layers and transmission
  rate of layers are possible, which causes lower
  throughput in multi-layer transmission.
• Without explicit knowledge of all the receivers,
  it can not differentiate necessary probing
  packets to each receivers. So no knowledge of
  exact bandwidth in the paths can be acquired.
• Minimum bandwidth of all the receivers in a
  multicast group is taken as the transmission rate
  for the whole group.

38
Multicast mechanism XCAST

• Tradeoffs between XCAST and ISM(Contd)
• XCAST can acquire more efficient and cautious
  usage of multiple available bandwidth with less
  processing and communication overhead in the
  network, but need end-to-end delay to finish the
  control of handoff.
• ISM can not acquire high throughput and adapt to
  the new link capacity so well as XCAST does and
  will incur more processing and communication
  overhead in the network because of the dynamic
  group maintenance, but can provide shorter
  recovery time for the connectivity.