Effective Buffer and Storage Management in DTN Nodes Stylianos Dimitriou, and Vassilis Tsaoussidis Dept. of Electrical and Computer Engineering Democritus University of Thrace Xanthi, Greece E-DTN ’09 – St. Petersburg, Russia

Why storage management (1/2)  Contact opportunities in DTN networks can be either deterministic or stochastic.  The time space between two data transmissions may be long and usually varies during the connection.  Persistent storage is used in DTN nodes to accommodate data in cases of intermittent connectivity. E-DTN ’09 – St. Petersburg, Russia2/11

Why storage management (2/2)  Due to node mobility and, occasionally, service disruption, the communication between two nodes, may change from high-delay to earth-like.  In earth-like communications, the need for persistent storage is trivial.  A DTN node should be able to adjust its storage management based on communication characteristics.  With efficient storage and buffer management, we can achieve better resource exploitation and service differentiation. E-DTN ’09 – St. Petersburg, Russia3/11

Solution  We propose a mechanism that decreases the delay in cases of frequently communicating nodes via better storage management.  The proposed mechanism maintains data that will be transmitted soon in the buffer, and moves the rest of the data in persistent storage.  Aims to decrease the delay inflicted by unnecessarily moving packets from buffer to storage and back. E-DTN ’09 – St. Petersburg, Russia4/11

Node mobility  In DTN networks, usually delays are long.  Queuing and processing delay is only a small part of the total delay, and thus negligible.  The aim is to achieve better bandwidth usage.  Due to node mobility, two nodes may engage in constant low-delay transmissions.  In this case, the delay required to move packets from buffer to storage and back becomes a significant part of the total delay. E-DTN ’09 – St. Petersburg, Russia5/11

Proposed model E-DTN ’09 – St. Petersburg, Russia6/11

Allowed packet transfers  1. LDT buffer  Persistent Storage:  New HD packets / no communicating opportunity.  Old LD packets / full LDT buffer.  2. Persistent Storage  HDT buffer:  Old HD packets / communicating opportunity occurs.  Old LD packets / communicating opportunity occurs.  3. LDT buffer  HDT buffer:  New HD packets / communicating opportunity occurs. E-DTN ’09 – St. Petersburg, Russia7/11

Distinguishing LD and HD traffic  We calculate the average storage delay of all flows.  Flows with bigger average storage delay than the average, are classified as HD.  E-DTN ’09 – St. Petersburg, Russia8/11

Conclusions  DTN networks involve node mobility which may vary significantly the propagation delay throughout a connection.  Nodes may involve in low-delay communication which resembles wired communications.  Managing buffer and storage is necessary to maintain high transmission rates in these cases.  The proposed scheme aims to resolve the lack of flexibility of Bundle Protocol to adjust to node mobility. E-DTN ’09 – St. Petersburg, Russia9/11

Future work  Determine the optimal sizes for LDT and HDT.  Review the WFQ scheme.  Review the algorithm that updates the average delay.  Evaluate the mechanism, both analytically and experimentally. E-DTN ’09 – St. Petersburg, Russia10/11

Questions?  Thank you E-DTN ’09 – St. Petersburg, Russia11/11