Bluetooth Quality of Service

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Bluetooth Quality of Service

• A Comnet lab project by
• Omry Yeshurun 037606175
• Dotan Perry 037609708
• Supervisor Alex Sprintson

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Overview Quality of Service
Quality of Service (QoS) is a term relating to
the ability to differentiate between the service
given to certain entities (applications, devices,
flows etc.) For instance real-time applications,
that require a limit on delay time, would receive
higher priority over WWW browsing traffic that is
less sensitive to delay.
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Bluetooth Model Structure
Focus of Project
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Goals

• Implement QoS support into BlueZ stack (L2CAP
  layer).
• Improve support for Real-time application running
  over Bluetooth.
• Demonstrate improved performance in different
  scenarios.

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Project Focus

• QoS is a very broad issue, including many
  aspects, such as transmit and receive priorities,
  drop precedence etc..
• We will focus only on transmit and receive
  priorities.
• BlueZ has many unresolved QoS issues awaiting
  solution, in all layers.
• We will focus on the L2CAP layer, specifically on
  the transmitting and receiving queues to HCI
  layer.

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Current Situation

• L2CAP packets are too big for HCI, and so they
  are segmented into several HCI packets. The HCI
  packets are enqueued and dequeued into the
  transmitting and receiving queues sequentially.
• When a high priority packet arrives, it has to
  wait for previous packets to be transmitted.
• Conclusion There is no provision for QoS support
  in L2CAP.

Refer to www.dei.unipd.it/bigbig/quos/
Bluetooth_QoS_ING_A_part_I.pdf
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Current Situation Packet Structure
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The Single Buffer Solution

• When a high-priority packet arrives, it is
  inserted into the transmit queue even if it is
  transmitting a low-priority packet.
• Upon receiving the first segment of the
  high-priority packet, re-assembly will restart
  and after the high-priority packet is
  reassembled, the low-priority packet reassemble
  will resume.

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Single Buffer - Example
Reassemble of low-priority packet completed
Reassemble of high-priority packet completed
f/x First segment out of x segments c
Continuation segment
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Single Buffer Packet Structure
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The Flush Problem

• Consider a case where two packets are in the
  transmit queue. When the link fails and a flush
  of the transmit buffer occurs, both packets are
  lost !
• Alternative use two logical links.

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The Double Buffer Solution

• All packets are divided according to priority
  between two transmit and receive queues.
• All transmission and reception of packets from
  different priorities would be independent, thus
  creating a separate logical link for each
  priority.

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Double Buffer - Implementation
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Double Buffer - Implementation

• Replace the existing single transmit receive
  queues in L2CAP with two priority queues each.
• Upon connection establishment and configuration,
  auto-negotiate QoS compatibility on both sides
  and enable QoS is possible, using reserved flags
  in the auto-negotiation protocol.
• Using Reserved fields in L2CAP packet, allow
  for implementation of two classes of service.

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Double Buffer Packet Structure
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Double Buffer Implementation Details

• Packet modification (as shown before).
• Addition of a transmit and receive queue for the
  high-priority logical link.
• Setting an auto-negotiation routine to determine
  QoS support in target device.
• Establish a packet differentiation criteria.

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Schedule
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References

• http//www.dei.unipd.it/bigbig/quos/Bluetooth_QoS
  _ING_A_part_I.pdf
• http//www.ets-japan.com/new/Flow_Specification__
  Flush_Timeout_v0-7d.pdf
• http//www.ets-japan.com/new/L2CAP_Flow_and_Error_
  Control_v0-7.pdf