1. Routing Protocols for
Delay Tolerant Network:
A Survey and Comparison
Authors:
R. S. Mangrulkar
&
Dr. Mohammad Atique

2. Introduction
• DTN evolves from MANET
• Main principal for routing message in DTN is “Store and
Forward”
o Store: Each node in DTN stores incoming message in the buffer.
o Forward: Deliver it to the other desirable nodes towards
destination whenever contact is initiated.
 “Contact” in DTN is the message exchange between two or
more nodes when they move in transmission range of each
other.

3. Introduction
• MANET uses 2 phase approach to deliver data:
1. Setup the route from source to destination
2. transmit data and maintain route information till
transmission is over

4. Routing Strategies in DTN
• Routing in DTN is mainly categorized into:
1. Flooding strategy: replicates the messages to
enough nodes so that the destination nodes
must receive it.
2. Forwarding Strategy: uses knowledge about the
network to select the best path (shortest one) to
the destination.

5. Flooding Strategy
• Multiple copies of the same message will be
created and delivered to a set of nodes called
relay nodes which store the message until they
can “contact” with the destination node.
• Advantages:
o Good chance of bringing the source in contact with
destination
o High probability of message delivery to succeed
o No global or local knowledge about network

6. Flooding Strategy
1. Single Hop Transmission
• the source and destination come in contact with
each other directly
• possible when the source and destination are one
hop apart or immediate neighbor of each other
 no relayed messages
 very less resources are required
 large delay and less probability of message delivery

7. Flooding Strategy
2. Two-Hop Relay
• Source node along with the nodes coming in
contact with source node and working in a
cooperative manner to successfully deliver the
message to the destination
 increases the message delivery probability
 increases the bandwidth and storage consumption
• same fundamental advantages and limitations as
direct transmission

8. Flooding Strategy
3. Tree Based Flooding
• Distribute copies of messages to other relay
nodes which come in contact with the already
discovered node
• One extra control field added to the message
for the information about the number of copies
a relay node can make and forward

9. Flooding Strategy
4. Epidemic Routing
• Assumes that each node has unlimited storage space and
bandwidth being able to store all the messages
transmitted during "contact" phase
• Summary Vector, a list of messages in the database, is
exchanged between nodes, so that the absent messages
in the vector are synchronized.
 Used in sparse(=small) network and small size message
 The message continues to propagate even it is
successfully delivered to destination

10. Flooding Strategy
5. Prioritized Epidemic Routing
• impose a partial ordering of message called
bundles
• Priority functions are used – transmission or
deletion function
Parameters are used to evaluate the priorities
o current cost to destination
o current cost from source
o the expiry time and generation time …

11. Flooding Strategy
6. Spray and Wait
• In Spray phase, each node will flood (spray)
each message to L no. of relay nodes
• The L is initialized by source node
• If destination is encountered, message
transmission is successfully terminated
• Wait phase started when destination is not
encountered, and relay node can only deliver
message during the contact.

12. Flooding Strategy
7. Spray and Focus
• Modification of Spray and Wait
• In Focus phase, a single copy of message is used
to focus limited relay node to route the
message to destination
• Designed for specific application where mobility
of each node is localized (in small area most of
the time)

13. Flooding Strategy
8. MaxProp strategy
• City environment
• Nodes = city buses (high probability to meet)
• Order of stored messages:
– 1st phase: based on hop count information of each
message from low to high
– 2nd phase: based on cost from high to low
• Buffer is utilized in:
– Front end of buffer is used by 1st phase
– Back end of buffer is used by 2nd phase

14. Flooding Strategy
9. Opportunistic Routing with Window-Aware Replication
• Main goal:
– Reduce resource utilization
– Reduce partial and dropped messages during transmission
• Partial messages arises when a node move out of
transmission range while message transmission is going on
• Number of bytes to be transferred is estimated to help utilize
the bandwidth effectively
• Nodes need to be able to measure its speed and direction –
equipped with GPS-like devices

15. Flooding Strategy
10. Cost Efficient Erasure Code Routing (CEECR)
• Based on erasure based coding
• Divides the original message into subsets
(=blocks) and transmits individually
• Decoding technique is used to obtain the
original message
• Advantage of Erasure Coding: chances to
recover original messages in case of failure in
trans.

16. Flooding Strategy
11. Constant Cost Quality Routing (CCQR)
• Message flooding only within high quality
nodes in DTN.
• The nodal cost is used as a parameter referring
to the total number of messages received by a
given node during the entire routing process
• Solve nodal imbalance problems

17. Flooding Strategy
12. A-SMART:
• An Advance Controlled-Flooding Routing with
Group Structures
• Nodes are called companion nodes forming an
ANYCAST group
– Periodically broadcast its group identities and hop
distance to build routing table
• 1st phase: introduce extra phase to route the
message to the companion nodes
• 2nd phase is same as SMART protocol

18. Flooding Strategy
• MSN : Message
– S: Source Node
– D: Destination Node
– R: Relay Nodes
– EN: Encountered Nodes
– EVC: Evolution nodes satisfying evolution
criteria
– L: Specified nodes in Message
– NC: Nodes Encountered during contact
– EN: Nodes storing encoded message
– QN: Quality Nodes
– TCN: Travel Companion Nodes
– HPN: High Probability Nodes
– DPN: Direction and Byte Predicted Nodes
• MDR : Message Delivery Ratio,
– Lw: Low
– N: Normal
– G: Good
• LT : Latency
– L-Low
– N-Normal
• RP: Routing Protocol
• MV: Message Vector
• MPV: Message Probability Vector
• DPV: Delivery Probability Vector

19. Forwarding Strategy
• Makes use of network topology and local/global
knowledge to find the best route path to deliver
the message to the destination.
• No message replication
• Network parameters are required for estimating
a single path
• Advantages:
o No replication -> less bandwidth and consumption
o Faster since the best path routing is used

20. Forwarding Strategy
1. Location Based Routing Stategy
• Each node in the network is assigned the coordinate – GPS
coordinate.
• Then distance formula, calculating minimum distance
between source and destination, is used to estimate the cost
of delivering message
• Path estimation – coordinates of source, destination and
intermediate node
 eliminates the need for storing routing tables and control
information transfer management
 Obstacles
 Mobility of a node changes the physical coordinate

21. Forwarding Strategy
2. Gradient Routing strategy
• Weights are assigned to the nodes representing
suitability of message delivery
• Relay nodes contact one another to have better
metric for message destination, and then pass
the message to the next node
• Suitable for Sensor Network

22. Forwarding Strategy
3. Label Based Forwarding Strategy
• Firstly, create groups, called “labeled group”
• Then, the groups are chosen to be the next node
or groups to forward the message to destination
Efficiently utilize bandwidth and consumption

23. Forwarding Strategy
4. Bubble Rap Forwarding Strategy
• Focus on issues of
o Community – divide the nodes in specific communities or
groups
o Centrality - always becomes centre of attraction
• Global ranking: used for a node to bubble the
message up to the hierarchical rankings tree until it
reaches a node which is in the same community as
the destination node
• Local ranking: further bubble the message until the
message is reached destination or expires

24. Forwarding Strategy
5. NECTAR
• Based on neighborhood contact history –
Neighborhood Index – to determine the most
appropriated route
• Use heuristic knowledge based on mobility
• relay in controlled manner to limit the traffic in the
network.
 Improve the number of delivered messages
 Consume fewer resource in the limited network

25. Forwarding Strategy
6. CREAST
• An opportunistic forwarding protocol based on
conditional residual* time
*Residual = remaining after most of sth has gone
• Conditional residual time – a parameter estimating
the time remaining for a pair of nodes to meet using
only local knowledge of the past contacts.
 Lower end-to-end delay, since no global knowledge
and no future contact schedule is dependent
 Better delivery ratio compared to flooding protocols

26. Forwarding Strategy
7. Conditional Shortest Path Routing (CSPR)
• Based on human mobility traces
• Use conditional intermeeting time
– As a parameter computing the average intermeeting time
between two nodes relative to a meeting with third node
using local knowledge of the past contacts.
– To estimate best path towards destination in shortest
path routing algorithm
 Achieve high delivery rate
 Lower end-to-end delay compared shortest path
routing protocols

27. Forwarding Strategy
8. QoNSW (Quality of Node with Spray and Wait)
• QoN (Quality of Node) refers to the activity of node,
or the number a node meets other different nodes
within given interval of time
• Node: the more meeting to others, the greater QoN
• Find the best suitable relay node to route message
 Significant improvements on Binary Spray and Wait
and Simple Spray and Wait

28. Forwarding Strategy
9. Single Copy Replication routing protocol (SCR)
• duplicate the message to the node selected as best
relay node
• Time Interval – as a parameter to select the node
• Starts message transmission in Critical Transmission
Rang(CTR)
• Stop transferring out of communication range
 Reduces the overhead by decreasing message
delivery failure due to node's movement out of
transmission range

29. Forwarding Strategy
10. CRHC
• Based on Hierarchical forwarding and cluster control
mechanism
• Reduces messages transmission by allowing
transmission permission to Cluster Head
 higher delivery rate and lower delay
 needs to maintain the information regarding partial
nodes of the network luster Head

30. Forwarding Strategy
11. PROCCS
• based on repetitive contact patterns and their time
sequencing to improve routing
• Greedy path probabilistic approach – to calculate
probability of path and then best path is selected as the
path for routing message
• Contact graph – for particular time issued by PROCCS to
calculate best path
 high message delivery ratio with no message replication as
compared to PROPHET and Epidemic.

31. Forwarding Strategy
• S: Source Node
• D: Destination Node
• R: Relay Nodes
• RP: Routing Protocol
• DN: Distance between Neighboring Nodes
• SM: Suitability to deliver message
• SLN: Nodes with same Label
• SCN: Nodes in Same Community
• PCH: Previous Contact History
• CRT: Conditional Residual Time
• CIT: Conditional Intermeeting Time
• QoN: Quality of Nodes
• TI: Time Interval
• CH: Cluster Head
• CPTS: Contact Pattern and Time Sequencing
• HGP: High Greedy Probability Value Nodes
• MDR: Message Delivery Ratio
• LT: Latency
• G: Good
• N: Normal

32. Conclusion
• Routing protocols in DTN are classified into two broad categories
– Flooding
– Forwarding
• Each protocol has its own advantages and disadvantage
• The DTN based applications suffered from less resources as well as
bandwidth.
• Suitable routing protocol in DTV depends on the application for
which Delay Tolerant Network is configured.
• The large delay results in low latency