Routing Protocols for Delay Tolerant Network:

A Survey and Comparison

Authors:R. S. Mangrulkar

& Dr. Mohammad Atique

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.

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

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.

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

destinationo High probability of message delivery to succeedo No global or local knowledge about network

Flooding Strategy1. 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 messagesvery less resources are required

large delay and less probability of message delivery

Flooding Strategy2. 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

Flooding Strategy3. 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

Flooding Strategy4. 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

Flooding Strategy5. 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 prioritieso current cost to destinationo current cost from sourceo the expiry time and generation time …

Flooding Strategy6. 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.

Flooding Strategy7. 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)

Flooding Strategy8. 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

Flooding Strategy9. 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

Flooding Strategy10. 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.

Flooding Strategy11. 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

Flooding Strategy12. 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

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

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 consumptiono Faster since the best path routing is used

Forwarding Strategy1. 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

Forwarding Strategy2. 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

Forwarding Strategy3. 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

Forwarding Strategy4. Bubble Rap Forwarding Strategy• Focus on issues of o Community – divide the nodes in specific communities or

groupso 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

Forwarding Strategy5. 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 messagesConsume fewer resource in the limited network

Forwarding Strategy6. CREAST• An opportunistic forwarding protocol based on

conditional residual* time

• 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

*Residual = remaining after most of sth has gone

Forwarding Strategy7. 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 rateLower end-to-end delay compared shortest path routing

protocols

Forwarding Strategy8. 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

Forwarding Strategy9. 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

Forwarding Strategy10. 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

Forwarding Strategy11. 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.

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

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