Routing protocols for delay tolerant networks can be categorized as either flooding or forwarding strategies. Flooding strategies replicate messages to multiple nodes to increase delivery probability but use more resources, while forwarding strategies select a single path using network knowledge to minimize resource usage but have lower delivery probability. The survey compares these routing protocol categories and their advantages for different applications in delay tolerant networks, which must deal with intermittent connectivity and large delays.

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