The document summarizes a framework for evaluating opportunistic routing protocols using the OMNeT++ simulator. It describes opportunistic routing protocols like ExOR and MORE, and the standard OLSR protocol. It outlines the common functionalities of the simulation framework, including neighbor discovery, packet buffering, and transmission reliability control. Simulation results show that opportunistic routing achieves higher throughput than OLSR, especially in lossy channels, and its performance improves with higher node density and channel rates but degrades with too many potential forwarders due to increased collisions.

1. IFIP/ACM LANC 2012
7th Latin American Networking Conference
Performance Evaluation of Opportunistic
Routing Protocols: A Framework-based
Approach using OMNeT++
Zhongliang Zhao, Björn Mosler, Torsten Braun
Universität Bern, Switzerland
braun@iam.unibe.ch, cds.unibe.ch

2. Torsten Braun: Performance Evaluation of Opportunistic Routing Protocols
Overview
> Opportunistic Routing Protocols
— Extreme Opportunistic Routing (ExOR)
— MAC-independent Opportunistic Routing and Encoding (MORE)
> Optimized Link State Routing (OLSR)
> Simulation Framework for Opportunistic Routing Protocols
— Common Functionalities of Simulation Framework
> Evaluation
— Simulation Setup
— Throughput Dependent on Channel Rate
— Impact of Node Density
— Impact of Number of Disjoint Routes
— Encountered Collisions
— Throughput for Different Transmission Rates
— Batch Transmission Delay for Different Channel Quality
> Conclusions
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3. Torsten Braun: Performance Evaluation of Opportunistic Routing Protocols
Opportunistic Routing Protocols
> make of use broadcast nature of wireless communications
> target transient nature of wireless channel and node mobility
> Basic operation
— Sender/forwarder does not select a next node,
but a list of candidate forwarders.
— Only one node will forward the packet
based on current channel conditions and node availability.
> Examples
— ExOR
— MORE
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4. Torsten Braun: Performance Evaluation of Opportunistic Routing Protocols
ExOR
> ExOR operates on batches of packets
> Source node includes in each packet a list of candidate forwarders
prioritized by closeness (according to a cost metric, e.g., expected
number of transmissions) to the destination.
> Receiving nodes buffer correctly received packets and await end of
batch.
> Highest priority forwarder broadcasts buffered packets,
including its copy of the ―batch map‖ in each packet.
Batch map contains the sender's best guess of the highest priority
node to have received each packet.
> Remaining forwarders transmit in order, but only send packets that
were not acknowledged in the batch maps of higher priority nodes.
> Forwarders continue to cycle through the priority list until 90 % of the
packets have been received.
> Remaining packets are transferred with traditional routing.
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5. Torsten Braun: Performance Evaluation of Opportunistic Routing Protocols
MAC-independent Opportunistic Routing
and Encoding (MORE)
> MORE integrates opportunistic routing and intra-flow network coding.
> Random mixing packets before forwarding ensures that routers hearing
the same transmission do not forward the same packets.
> Source
— When ready to send, source keeps creating coded packets using a
random linear combination of K native packets in the current batch.
— Source proceeds with next batch when acknowledged by destination..
— Data packets are always coded and carry a list of forwarders / code
vector.
> Forwarder
— If a node is in the forwarder list, the arrival of an innovative packet
triggers broadcasting the packet by creating a new random linear
combination
> Destination
— Once destination receives K innovative packets, it decodes the whole
batch and sends an ACK back to the source.
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6. Torsten Braun: Performance Evaluation of Opportunistic Routing Protocols
Optimized Link State Routing (OLSR)
> Broadcast of link state information
> Forwarding of broadcast messages by nodes in set
of Multi-Point Relays (MPR)
> Each node computes its MPRs. This allows to reach
each hop in 2-hop-neighborhood (learning of 2-hop-
neighborhood by Hello messages). Algorithm:
— N1/2: set of 1/2-hop-neighbors
— Selection of nodes in N1 that are the only neighbors
in N1 of a node in N2.
— Assignment of a degree for each node in N1:
number of nodes not yet covered in N2
— Selection of nodes in N1 with highest degree until all
nodes in N2 are covered.
> Hello messages indicate asymmetry of links.
> MPRs distribute Link State messages. MPR indicates
nodes that selected itself as MPR (MPR selectors)
> Proactive / periodic exchange of MPR selectors in
Topology Control messages
> Establishment of routing entries for each node in the
network using Dijkstra‗s Shortest Path algorithm
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7. Torsten Braun: Performance Evaluation of Opportunistic Routing Protocols
OMNeT++ based Simulation Framework
for Opportunistic Routing Protocols
> Class hierarchy built on assumption that all opportunistic routing
protocols share certain functionalities
> Common procedures (virtual functions)
— Opportunistic Candidate Selection
– Sending node periodically polls neighbor nodes within its radio range.
– Adoption of certain attributes, e.g., geographic region or movement
values
— Forwarder Selection
– defines rules how the actual forwarding node is picked from candidate
set.
— Forwarder Role Change Notification
– enables winning forwarder to announce its new role and responsibility
to neighboring nodes and to make them aware of the selection winner.
— Collision Avoidance
– is about how the nodes coordinate with each other to avoid collisions.
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8. Torsten Braun: Performance Evaluation of Opportunistic Routing Protocols
Common Functionalities of
Simulation Framework
> Neighbour Discovery & Management
— important for forwarder selection
— adopted from INETMANET
> Packet Buffer Management
— Related data structures and corresponding operation for nodes store
and manipulate received packets
> Transmission Reliability Control
— INETMANET includes several channel propagation models
— INETMANET link layer implementation is adapted to control packet
transmission.
> Node Interface Management
— Nodes inside the network may be equipped with more than one
antenna/interfaces to increase network throughput.
— Management for multiple interfaces necessary to support
multi-channel communication.
> ETX/EAX Calculation and Distribution
— Candidate selection is usually based on determining a forwarder
priority list based on ETX/EAX values.
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9. Torsten Braun: Performance Evaluation of Opportunistic Routing Protocols
Simulation Setup
> Additional parameters
— 32 packets per batch, 1024 bytes packet size
— 20 simulation runs
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10. Torsten Braun: Performance Evaluation of Opportunistic Routing Protocols
Throughput Dependent on Channel Rate
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11. Torsten Braun: Performance Evaluation of Opportunistic Routing Protocols
Impact of Node Density
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12. Torsten Braun: Performance Evaluation of Opportunistic Routing Protocols
Impact of Number of Disjoint Routes
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13. Torsten Braun: Performance Evaluation of Opportunistic Routing Protocols
Encountered Collisions
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14. Torsten Braun: Performance Evaluation of Opportunistic Routing Protocols
Throughput of ExOR and OLSR for
Different Channel Qualities
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15. Torsten Braun: Performance Evaluation of Opportunistic Routing Protocols
Batch Transmission Delay of ExOR and
OLSR for Different Channel Qualities
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16. Torsten Braun: Performance Evaluation of Opportunistic Routing Protocols
Conclusions
> Framework implemented in OMNeT++ simulator
— facilitates the implementation of opportunistic routing protocols.
— decouples opportunistic routing into four general steps and
abstracts them as virtual functions.
— provides some other functions shared by most opportunistic routing
protocols
— has been used for evaluations of MORE and ExOR and
comparison with OLSR
> Obtained Results
— Earlier related work reported that opportunistic routing makes
sense under low traffic scenarios (inter-packet gap > 1 s).
This does not hold for ExOR and MORE, since batch transmission
sends packets continuously without any delay.
— Opportunistic routing may achieve significant performance gain in a
lossy wireless environment and it will reach an improvement for
high channel transmission rate scenarios.
— Number of potential forwarders has strong influence on
performance. A large number of potential forwarders may
introduce collisions that will eliminate the benefits it introduces.
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17. Torsten Braun: Performance Evaluation of Opportunistic Routing Protocols
Thanks for Your Attention !
> braun@iam.unibe.ch
> http://cds.unibe.ch
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