Presenter: Anika Aziz National Institute of Informatics (NII), The Graduate University for Advanced...
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Transcript of Presenter: Anika Aziz National Institute of Informatics (NII), The Graduate University for Advanced...
Presenter:Anika AzizNational Institute of Informatics (NII),The Graduate University for Advanced Studies, Tokyo, Japan
In a Delay Tolerant Network (DTN), a custodian node which is storage constrained, can mitigate the congestion by reserving buffer space and applying queuing algorithm as a function of priority classes that is Class Of Services(COS).
These COS can be mapped to a shared Priority Queuing (PQ) approach or to the separate PQs with different thresholds of the buffer.
The DTN architecture, the Bundle protocol
Custody transfer in DTN Congestion in DTN The Storage Routing (SR) Proposed algorithms Analysis & comparison of the algorithms
Conclusion Q & A
An acknowledged transfer of data to persistent, reliable storage
A msg B
ack (store the msg)
(delete the msg) custody transfer complete
(assumes custodytransfer complete)
- To use hop-by-hop reliability to improve end-to-end reliability- To free retransmission buffers at a sender as soon as possible - When faced with persistent demand…….congestion occurs
Rate based or window based congestion control techniques-nearly ineffective
A region under the administrative control of a single entity can apply some form of admission control as a proactive means
If its insufficient or unavailable, reactive means ( involving direct flow control) must be used
Different solutions…cease accepting bundles with custody transfer & move bundles somewhere else
int
-Message selection-Node selection push-Retrieval selection pull alternate custody transfer
source custody transfer int dest
-No custody refusal - Messages are dropped under the worst case situation
Networks containing traffic sources which continuously generate application data (e.g. sensor networks) can not be flow controlled instead Storage routing
Apply some standard queue management or scheduling algorithm
Priority classes that is Classes Of Service (COS), “bulk”,” normal” and “expediated” priorities,
Applications specify the COS & data lifetime (TTL) for each message they send, based upon its desire to affect the delivery urgency for messages
Push Lowest Priority mechanism as the push policy
Expanding Ring Search (ERS) method
Enqueue ׀m׀at n
Priority0 ? ?
Find alternative custodian x such that ax(t)>׀m׀
Is x Found?(ERS)
Drop׀m׀
Push ׀m׀ to x
Fn(t) is
increased
Y
N
Y
N
Compare with others in the queue
Is it the lowest one?
Y
N
Push the lowest one in the queue
If all are of equal priority, push the message with the
highest TTL
Does ׀m׀ has the highest TTL?
Y
N
Is still|m| > Fn(t)?
N
Y
Message ׀m׀ arrives at node n
Fn(t)<׀m׀
?
YN
Figure 4. The SR algorithm: COS mapped to the shared PQ
?Fn(t) <׀m׀
Priority0 ?
Priority1 ?
N
Y
Y Y
N
N
Priority 2ABM2
ABM1Compute avg queue length of Fn(t)
avg<minth0 ?
is selected for push ׀m׀policy
Y
avg>max0 ?
Drop
Y
Look into residual TTLvalue
N
High residual TTL?
Y
N
Active Buffer Management (ABM0) technique
Enqueue ׀m׀At node n
Message ׀m׀ arrives at node n
N
Figure 5. SR algorithm: COS mapped to PQ and thresholds of Active Buffer Management
Both the algorithm ensures to push the lowest priority message
Messages are dropped in the worst case situation
the 2nd approach works more dynamically and precisely
No Priority Inversion & Head-Of-Line blocking
The value of Custody Transfer and DTN congestion remains to be fully understood… until the DTN architecture is widely deployed and carries significant traffic loads
Similar story as TCP protocol specification included no management of congestion… more than 10 years after the 1st experiments with Internet technology were performed.