Alternative custodians for congestion control in dtns

Author: Matthew Seligman, Kevin fall, Padma mundur

Publication: sigcomm

Annual: 2006

Technorati labels: routing, delay tolerant networks, congestion control

Storage routing (SR) is a set of algorithms invoked by a dtn custodian when congestion becomes evident and when it abates.

 

Main Idea:

With the onset of congestion, the algorightms provide a selection of messages to migrate and a set of alternative Dian (s) to which the selected messages are to be migrated. the custodian then invokes the conventional dtn custody transfer mechanic to transfer the selected messages to alternative storage locations using the push operation. when a custodian has sufficient storage resources to take custody for messages, it invokes a retrieval algorithm to migrate, or pull, messages for which it may have had custody earlier toward their destination (s ).

Three steps:

• Message selection.
• Node Selection
• Retrieval Selection

 

Message selection:

Three selection factor types considered are temporal, size, and priority.

Table 1. Push Policy Description and usage

The dtn architecture suggestes the idea that when a custodian becomes congested it may cease accepting custody for subsequent messages (a form of flow congrol ). but it't suitable in networks where sources produce data continously.

In some sense, this approach cocould be characterized as a form of congestion management implemented using distributed storage load balancing.

Message shoshould be deleted as a last resort, only when there is no available storage at any neighboring node.

Node selection:

The simplest way to select alternative custodians is to select targets in the topological (hop count) sense.

Aggregate migration cost (minimus value is 0 and maximum is 1 ):

Storage cost:

Transmission Cost:

To find targes, a form of Expanding Ring Search (ERS) may be employed from a current custodian C.

Message retrieval:

The descriof which messages to migrate at this point mirror the push described earlier, cannot in this case the descriis made by the specified er rather than the sender.

Simulation:

The MSG selection policy is pushtail and the node selection uses the procedure described above. The MSG retrieval algorithm selects a message from all sufficiently small messages available in NC (1 ).

Assumptions:

• No separate flow control
• Node must take custody when forwarding messages
• Custodian nodes drop as a last resort
• Nodes are using Ric with respect to storage
• Each link has the same bandwidth in both directions ctions
• Each link is either up or down.

Simulator: a custom simulation enviroment was developed based on the generic YAC-SIM discrete event simulation engine and augmented with custom simulation software supporting intermittent links, custody transfer, and the other dtn mechanisms.

Simulation results:

Three Sr variations are compared: No Sr, Sr with k = 1 and SR with K = 2