Multicast& Traffic Shaping Issues
Yasushi NAGASAKA
Hiroshima Institute of Technology

1. DataCollection Message Flows
2. Multicast Messages
3. Traffic Shaping
4. Summary

Two scenarios of message flows ‘classic’ scenario
 DFM sends DFM_Decision to all ROSs. And theysends ROS event fragments to one SFI.
 PUSH message flow ‘request-reply’ scenario

 DFM sends DFM_SFIAssign to one SFI. And theSFI sends SFI_DataRequest to all ROSs to get
ROS event fragments.
 PULL message flow
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Multicast & Traffic Shaping Issues - Yasushi Nagasaka

2‘Classic’ Scenario

SFI10.Jul.2002

Multicast & Traffic Shaping Issues - Yasushi Nagasaka

3‘Request-Reply’ Scenario
SFI10.Jul.2002

Multicast & Traffic Shaping Issues - Yasushi Nagasaka

4MulticastMulticast is very important method when we try to send thesame data to many hosts.

In DataCollection dataflow, the multicast is applied tofor ‘classic’ scenario
DFM_Decision DFM_Clearfor ‘request-reply’ scenario
SFI_DataRequest
 DFM_ClearThe problem isthe multicast messages are non-reliable,
 i.e., the multicast has a possibility of packet losses

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because these messages are sent with datagram.
Multicast & Traffic Shaping Issues - Yasushi Nagasaka

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Reliable multicast messages (1)Unicast messagesThe sender sends the message to each receiver individually.
This scheme improves the probability of delivery,
 increases the overhead, and guarantees delivery, in case of TCP, but even more overhead.

Replicated messages


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Every message is sent twice or more in subsequent multicasts.
This scheme
 causes extra bandwidth on the network, and just adds reliability, but doesn’t guarantee delivery.

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Reliable multicast messages (2)Negative AcknowledgementsEvery multicast message is sent with a unique sequence counter. The
receiver sends back the acknowledgement which tells an undelivered
message exists.
In this scheme, the problems are the recovery protocol which is not simple, and negative acknowledgement explosion.

QoS controlled messages in the sending hosts.


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The messages controlled by QoS are sent in defined time intervals.
This situation results to avoid the packet loss, because one of thereasons of packet loss is that the messages are sent in very short timeintervals.
This scheme may improve reliability.

Multicast & Traffic Shaping Issues - Yasushi Nagasaka

7What is QoS?
 QoS Control Technology

 the technology to control data traffic on a pernode basis.

 Bandwidth Allocation, Error Rate, Transfer Latency, …
 Classification

 The output packets are classified and put into the classified
queues according to rules, for example, the destination
addresses, the port numbers, and so on.

 Queue Management and Scheduling A timing to send the data are controlled at the point of output
queue by scheduler.
PCQueuesPacketClassifier

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Multicast & Traffic Shaping Issues - Yasushi Nagasaka

Estimator

Scheduler

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Using Multicast in DataCollection
Multicast potentially not 100 % reliable And making multicast reliable adds overheadImpact on lost multicast messages for DataCollection

DFM_Decision message lost (PUSH)
SFI_DataRequest message lost (PULL)

SFI realizes via missing fragment, SFI can re-ask.
SFI realizes via missing fragment, SFI can re-ask.

DFM_Clear message lostROB buffer potentially overflows
 DFM could add to DFM_Clear message the oldest LVL1_ID still inthe system
 ROB would clear accordingly

100 % reliable multicast probably not required

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Multicast & Traffic Shaping Issues - Yasushi Nagasaka

9Traffic ShapingThe event builder dataflow is funnel shaped.
All senders send each fragment to one receiver at the same time.

This situation causes congestion and potential packet loss.

In order to avoid these problems, traffic shaping is relevant for both‘classic’ and ‘request-reply’, scenarios.

Traffic shapingTraffic randomization at the level of the ROSs (PUSH)


Traffic shaping at the SFI (PULL)The SFI controls traffic shaping by sending the SFI_DataRequest to individual
groups of ROSs.

Bandwidth allocation with QoS in the ROS hosts10.Jul.2002

The ROSs decide the event fragment to send at specific algorithm.

QoS in the ROS can restrict the allocated bandwidth to each SFI
This avoids congestion in the network.

Multicast & Traffic Shaping Issues - Yasushi Nagasaka

10Summary of Traffic Shaping
 Traffic shaping depends on the traffic scenario,

PUSH or PULL.

 In case of PUSH, traffic shaping may lead to

additional requirements to the ROS; special algorithms to control the sending offragments to the SFI
 or, apply the QoS in the ROS hosts

 QoS works on an IP stack only, TCP or UDP

 In case of PULL, SFI can control the traffic.
 may increase message rate to be handled by SFI.
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Multicast & Traffic Shaping Issues - Yasushi Nagasaka

11Summary Multicast
 An infrequent loss of multicast messages will

not cause problems for TDAQ, if ROBs canclear old events as defined by DFM.

 Traffic Shaping
 Traffic shaping is handled either at the SFI orin the ROSs.
 QoS can be beneficial if applied in the ROSs.

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