ACHIEVING LOW END-TO-END LATENCY WITH A

HANDOFF-BASED DETERMINISTIC ROUTING PROTOCOL

(HDRP) IN DELAY-TOLERANT NETWORKING

Anika Aziz and Shigeki Yamada

National Institute of Informatics, The Graduate University for Advanced Studies

2-1-2 Hitotsubashi, Chiyoda-ku, Tokyo 101-8430, Japan

Keywords: DTN, Bundle, Handoff, HDRP, Latency.

Abstract: DTN is able to adapt any mobility environment where any mobile routers and terminals are combined

owing to the DTN’s flexible hop-by-hop routing schemes. The existing DTN protocols like Epidemic,

Prophet and Spray-and-Wait protocols rely on the message distribution mechanism where each DTN node

produces one or more message copies. They can naturally adapt to the mobile situation where the

destination node moves from an old connection endpoint to a new connection endpoint because any

message copy may luckily be able to reach the new connection endpoint where the mobile node is newly

connected. These protocols suffer from long latencies because message copies are not immediately

forwarded until any suitable condition for forwarding is met. To solve these problems, we propose a

Handoff–based Deterministic Routing Protocol (HDRP) that makes the best use of general handoff

mechanisms intended for the IP network. This handoff mechanism includes the registration of locations by

mobile nodes and backward propagation and caching of these locations over the experienced route. Our

simulation results indicate that HDRP outperforms other existing protocols especially in terms of end-to-end

latency.

1 INTRODUCTION

The architecture and protocols devised to be used in

Delay and Disruption Tolerant Networking (DTN)

are well suited for mobile and extreme environments

lacking continuous connectivity (Ott, 2005). The

DTN architecture is featured by dynamic hop-by-

hop routing and the custody transfer mechanism.

The Custody Transfer concept refers to the

acknowledged delivery of a message from one DTN

hop to the next and the corresponding passing of

reliable delivery of the responsibility. A DTN node

which has taken custody of a Bundle will buffer it

until a suitable next hop is found (Fall, 2003). This

also means that routing should dynamically be

changed, depending on the ongoing situations. So,

the re-routing function is equipped with the DTN

architecture as hop-by-hop routing.

The existing DTN protocols like Epidemic,

Prophet and Spray-and-Wait protocols (Vahdat and

Becker, 2000), (Lindgren and Schelen, 2003),

(Spyropoulos and Raghavendra, 2005) handle

mobile situations, based on the message distribution

mechanism where each DTN node produces one or

more message copies, wait for a suitable condition

for forwarding like meeting a node with higher

delivery predictability in Prophet, then distributes

them possibly on a hop-by-hop basis toward the

destination node, and makes any lucky one of the

copies reach the destination node. Therefore, the

existing DTN protocols can naturally adapt to the

mobile situation where the destination node moves

from an old connection endpoint to a new

connection endpoint because any message copy may

luckily be able to reach the new connection endpoint

where the mobile node is newly connected. However

the existing DTN Protocols suffer from low delivery

ratio because their routing decisions are based on the

local knowledge given by the next hop node. The

existing DTN protocols also suffer from long

latencies because message copies are not

immediately forwarded until any suitable condition

for forwarding is met. These problems suggest that

any global knowledge on end-to-end path from the

source node to the destination node should be more

Aziz A. and Yamada S. (2010).

ACHIEVING LOW END-TO-END LATENCY WITH A HANDOFF-BASED DETERMINISTIC ROUTING PROTOCOL (HDRP) IN DELAY-TOLERANT

NETWORKING.

In Proceedings of the International Conference on Wireless Information Networks and Systems, pages 13-22

DOI: 10.5220/0002987800130022

 SciTePress

exploited to enable immediate forwarding that

eliminates any opportunistic waiting.

We assumed a practical environment with fixed

routers and mobile or fixed terminals. Because

when we project the future use of network, we find

that more and more computer and network resources

will be ubiquitously located in fixed locations just

like the Wireless LAN environment. We propose a

Handoff–based Deterministic Routing Protocol

(HDRP) that makes the best use of general handoff

mechanisms intended for the IP network. Here, the

handoff refers to the dynamic event in which

communications are maintained with the network by

transferring the connection to a neighbouring

network access point. The proposed handoff-based

mechanism includes the registration of locations by

mobile nodes and backward propagation and

caching of these locations. When a mobile node

moves to a new location, it registers its location (the

name of the router it belongs to) with the DTN

router and this location information is propagated to

and cached in every DTN router over the

experienced route to update the Proxy List (PL) at

each router. As every DTN router maintains the

connectivity information with adjacent DTN routers

in the PL, the DTN router can select the best

possible next hop for bundles destined to the mobile

node in a deterministic way. Our simulation results

indicate that HDRP outperforms other existing

protocols like Epidemic, PROPHET and Spray-and-

Wait especially in terms of end-to-end latency.

2 MOTIVATION

The mobility environment supported by existing

protocols in DTN is by having forwarding decision

on the basis of local knowledge given by the next

hop node and is done opportunistically depending

on some condition to be fulfilled. These lead to

degraded performances in terms of delivery ratio and

end-to-end latency. The forwarding process can be

improved by making use of the location information

of the mobile node and back propagating and

caching this information on the experienced route of

the mobile node. As every DTN router maintains the

connectivity information with adjacent DTN routers

in the PL, the DTN router can select the best

possible next hop for Bundles destined to the mobile

node in a deterministic way. The novelty of the work

lies in gathering the routing information through the

Hand off process which provides the location

information of the MH to the previous router as part

of the process and hence helps to route the data more

deterministically and quickly to the MH. Moreover

the Back Propagation and caching of this location

information at each of the routers in the experienced

route of the MH provides option to choose the best

route to reach the destination. This feature adds

more dynamic and improved performance to the

HDRP.

3 THE PROPOSED SCHEME

3.1 The System Model

Our system model assumes an environment of

interconnected fixed DTN routers. We have

considered the same network environment as the

WLAN environment which is very practical if we

project the future use of network.

Figure 1: Handoff Bundles from one node to another after

MH changes location.

There are two types of End nodes, Fixed Host

(FH) and Mobile Host (MH) which are

communicating with each other through these

routers. The FHs are connected with DTN routers

and the MHs are moving around following a map

based movement model (Keränen and Kärkkäinen,

March 2009). An MH can communicate directly

with another MH if they come within each others’

range.

If an MH move to a new location it registers its

location to the new router and this location

information is propagated back to the old router. The

old router then hand off the data destined for the MH

to the new router. Our main focus was to propose a

routing protocol which is based on this handoff

technique and at the same time to utilize the hop-by-

hop routing and custody transfer mechanism of the

DTN routers.

The DTN nodes communicate using the Bundle

Protocol for DTN and the protocol data unit is

known as Bundle which is the aggregated messages.

Basically two types of Bundles are used -the data

type and the Status Report (SR) type, latter of which

WINSYS 2010 - International Conference on Wireless Information Networks and Systems

is an administrative type of record for sending

acknowledgement to a custody transfer request etc

(Scott and Burleigh, November, 2007).

3.2 The Routing Protocol

Our proposed routing protocol named Handoff-

based Deterministic Routing Protocol (HDRP) has

some key conceptual features and technical features.

This section explains each of these features in detail

along with an example of a particular protocol

sequence.

Every router has a Proxy List (PL) where it

keeps record of all other routers in the network and

the next hop to choose to reach each of the routers.

When an MH moves to a new location it registers its

location with the new router after receiving a beacon

from that router. The registration message, REG

contains [MH, Previous Master (PM)] addresses that

is, the address of the MH and the old router. After

registration is done the new router becomes the

Current Master (CM) of this MH and forwards a

Handoff Message containing (MH, CM) to the

Previous Master.

In the mean time, when the old router senses

(senses periodically whether the MH is within its

range) that the MH has moved away it starts

buffering the bundle destined for that MH. Upon

contacted by the new router (through the handoff

message), the old router handoff the buffered

bundles to the new router and finally the bundles are

forwarded to the MH. The old router also updates

the PL with the (MH, CM) information so that it can

forward the subsequent bundles destined for that

particular MH using this route update. The process

of handing over the buffered data from the old router

to the new router is done through the hop-by hop

routing method of DTN and the bundles are kept in

the buffer of the old router until a new route is

established to the destination with the help of the

custody transfer mechanism.

Depending on the situation whether the direction

of communication is from FH to MH or from MH to

FH and whether the Bundle/SR has been lost during

sending/ receiving process, there can be different

protocol sequences for the handoff.

Figure 2 shows one of those protocol sequences

between different DTN nodes in our model where

MH fails to receive a Bundle due to its movement.

In this diagram, a FH is sending Bundles to a

MH through Router1 (old router). The MH changes

its location and moved to Router2 (new router). The

transfer of the data and SR bundles with specific

functions are shown in the figure. To accomplish the

Figure 2: Protocol sequences showing a handoff situation

and route update by Back propagation.

handoff process successfully, we extend the Bundle

specified in the IRTF standardization in order to

include the auxiliary addresses and its associated

fields in the SR. The Handoff latency has been so far

defined in different ways in different works that deal

with the handoff problem (The ONE), (Manzoni et

al.), (Yavatkar and Bhagawat, 1994). We have

defined the Handoff latency as the time from “when

the MH receives the beacon from the new router” to

“the time when the MH receives the first Bundle

through the newly established route”. Here we have

assumed the best possible case for the arrival of the

beacon that is we have assumed that as soon as the

MH entered into the range of a router it receives a

beacon from that router.

The above figure shows the simplest case when

the old and new routers are only one hop away from

each other. Our protocol also works efficiently

even

if the MH has moved far away that is even if there

are one or more routers in between the old and new

routers. In our system model, we have assumed that

epidemic protocol is used for initial Bundle delivery

to the router that will initiate the handoff. This is the

situation before any MH in the network starts doing

registration or any handoff has taken place. A very

large sized buffer at the routers is assumed to cope

with the situation of buffer overflow for the custody

transfer.

As every DTN router in the HDRP maintains the

connectivity information (through PL) with adjacent

DTN routers, the DTN router can select the best

possible next hop for Bundles destined to the MH in

a deterministic way. The Forwarding mechanism

also plays a vital role in achieving the deterministic

routing: A router always look for a direct connection

while forwarding a bundle. If it is not found then the

router consults the PL and lastly it goes for the

ACHIEVING LOW END-TO-END LATENCY WITH A HANDOFF-BASED DETERMINISTIC ROUTING

PROTOCOL (HDRP) IN DELAY-TOLERANT NETWORKING

flooding technique. A Flood List (FL) is maintained

for each of the Bundles to be flooded through all the

connections attached to a HDRP router. Bundles are

sent according to the following priority: (1) Data

from Buffer, (2) Data from Flood List (FL), (3)

Handoff message, and (4) SR (Status Report). As

shown, the data type always gets the priority over

other types of Bundle.

3.3 The Bundle Protocol Extension

The features that we need to implement in our

routing protocol required certain fields in the

standard Bundle block format which is not specified

in the present Bundle Protocol Specification (Scott

and Burleigh, 2007). So, we propose some extension

to the present Bundle Block format. To accomplish

the Handoff process, the MH needs to do registration

with the newly found router after receiving beacon

from it:

 During registration the MH will inform the

Current Master (CM) about its Previous Master

(PM) and for this a field should carry the EID

of the Previous Master.

 If When the CM will forward a Handoff

message to the PM it needs to inform about the

EID of the new MH that has just completed

registration with it and used to reside with the

old one.

We assume that this type of EID information can be

carried as an auxiliary EID field in the payload

block.

Figure 3: Extension to the Bundle block to support

handoff mechanism in DTN.

As shown in Figure 3, A Bundle normally have

the Primary Block and Payload Block, the extension

Block is optional. The extension to the Bundle block

is carried out in following steps:

 The ‘Bundle payload variable’ field normally

carries Data but the field can also carry

Administrative records like special Status

Report.

 In this case, a flag in the Primary block

indicates if it is carried in the Bundle payload

field (Scott and Burleigh, 2007).

 The ‘Record type code’, ‘Administrative record

flag’ and ‘record content’ field will indicate

that the following information is carried to

accomplish a handoff process.

 Finally the status flag and the reason code of

the ‘Record content’ specifies about the

auxiliary address and the auxiliary EID type is

given with the value and meaning at the end of

the Status Report.

The extension in the Bundle block format that we

have proposed will not have any influence on the

operation of the current Bundle protocol.

In Back propagation, the route update

information of a particular MH is propagated back in

its experienced route. The concept is implemented in

the routing protocol. We do not need to make any

change in the Bundle block format to support this

mechanism. The route update propagation and

caching at each of the routers in the experienced

route involve the Handoff message and REG which

is supported by the Bundle extension that we have

proposed earlier.

Our protocol is also suitable to work in an

environment where mobile routers are used. After

receiving the Handoff Message, the Previous Router

(PM) of the MH sends Bundles destined for that MH

to its Current master (CM). If the CM changes its

position by this time due to mobility, the Bundles

can still reach the destination because if the PM fails

to reach the CM by direct connection or PL it will

ultimately go for the flooding technique as the last

resort to reach the CM of the MH. As a result, even

if the CM is a mobile router it will eventually get the

Bundles to be delivered to the MH.

On the other hand, if it happens that the PM

changes its position while the MH is going through

the registration process to its CM, the scenario will

be handled in a similar way as the case when the PM

is multi hop away from the CM.

4 PERFORMANCE EVALUATION

AND ANALYSIS

4.1 Simulation Network Model

Our network model consists of Fixed routers

connected in a certain topology, Fixed end nodes

connected to some of these routers and different type

WINSYS 2010 - International Conference on Wireless Information Networks and Systems

of mobile nodes moving around this fixed

infrastructure network to communicate with other

Table 1: Parameters used in the simulation.

Parameter Description (Values)

Node type

Fixed Routers: scenario 1 for 26

Routers; scenario2 for 65 Routers.

End nodes: The numbers were varied

from 124 to 1000.

Connections &

movement

model

Most of the Routers are connected

with each other;

Map based movement model (Keränen

and Kärkkäinen, March 2009)

Mobile node

types

Pedestrians, cars, trams

Transmitting

speed of the

Routers & End

nodes

20M,250k Bytes per second

Transmitting

range of the

Routers & End

nodes

300m

Message

interval&

Message size

Message interval of (1,2000), (25,35),

(10,20) and (1,5) ( per second) with

random distribution;

Message size is randomly varied

between 500KB and 1MB

Buffer size Varied from 10Mbytes to 300Mbytes

Mobility

speed(M)

∑(Minimum speed, maximum speed)

in m/s of each type of mobile node

groups × no. of hosts in that

group/total no. of nodes; M1,M2,M3

and M4 are calculated by varying the

range of the speed for each mobile

node types and finally by varying all

together.

Simulation time 43K ~= 12 hours

Message TTL

40mins (for discarding messages)

Alive time/Back

Propagated

(BP) Routing

update expired

time/cache time

We varied the value for 5 sec, 30 sec,

160 sec, 600 sec and 3000 sec.

end nodes. Communication is possible between any

pair of end nodes through one or more routers. The

mobile nodes can communicate directly with each

other if they are within the communication range.

Different parameters used in the simulation are listed

in Table 1. We have used the ONE simulator

(Keränen and Kärkkäinen, 2009), (The ONE) to

build and simulate our network model.

We made some modification and do some

extension in the ONE simulator in order to

implement our protocol. Our HDRP Routing

protocol extends the Active Router module used in

the ONE simulator. Fields and methods have been

created to implement the Handoff mechanism which

was not included in any DTN routing algorithm in

ONE before. Handoff Reports have been generated

by extending the Report module.

4.2 Simulation Results

4.2.1 Performance at Different Traffic

Intensity

In ONE simulator we can set different Message

interval values within a minimum and maximum

range. We varied this interval for (1, 2000), (25, 35),

(10, 20) and (1, 5) per second. For each of these

ranges, messages are generated randomly within the

limits which actually indicate how much densely the

messages are generated within our specified

simulation time. That is why here we refer the

different Message interval as the different traffic

intensity of the network.

The basic HDRP is enhanced by us by

combining the Back Propagation technique and

hence we also have simulation results for HDRP

(BP) which gave better performance. Our devised

protocol has been compared with Epidemic,

PRoPHET and Spray & Wait routing protocol in

DTN. These protocols are renamed as FixedEpi,

FixedPro and FixedSnW respectively as they are

applied to a network which has fixed infrastructure

that is fixed DTN routers.

Figure 4: Latency at different traffic intensity.

Figure 5 depicts that that the HDRP outperforms all

other protocol in terms of the end-to-end average

latency of the network. Whereas each of the

PRoPHET, SnW and Epidemic has latency in the

range of 700 sec the latency for the HDRP is less

than 50 sec. The reason behind HDRP performing so

much better than other protocols are mentioned

below:

• The efficient Forwarding mechanism of

HDRP: In HDRP when a router has a message it

ACHIEVING LOW END-TO-END LATENCY WITH A HANDOFF-BASED DETERMINISTIC ROUTING

PROTOCOL (HDRP) IN DELAY-TOLERANT NETWORKING

looks for whether a connection is available: at

first the router tries whether a direct connection

can be found to the destination. If it is not there

then the router consults its Proxy List (PL) to

see if there is some information about the next

hop to reach the destination for the message. If

this second attempt also fails then the router

tries to send out the message by flooding it to

the available outgoing connections. The router

uses the flooding method as the last resort to

forward the message to its destination. In most

of the cases it can found a direct route or a

suitable next hop from its PL. Using HDRP a

router does not need to wait for a suitable

condition for forwarding to meet as in

PRoPHET a node with higher delivery

predictability has to be found or in a Spray and

Wait protocol the destination itself should be

there if the sparying phase is finished.

• In our system model we consider the fixed

DTN routers interconnected with each other and

the end nodes, that is the FH and the MH are

communicating through this routers. During this

communication in between the fixed routers

there is no waiting time because of the fixed

links. The only waiting time is between the

Source and the router next and the Destination

and the router next. This logical time is also

very minimal. This contributes to the low end-

to-end latency of the network.

• The existing DTN routing protocols deals

with only the mobile nodes and it is required to

wait until the next hop mobile node physically

moves to the wireless range of the previous hop

node and also the forwarding condition needs to

be satisfied before the routing takes place. This

leads to the larger value of overall end-to-end

latency.

HDRP (BP) gives slightly worse performance (avg.

38 sec.) than that of HDRP (avg. 32 sec.) because

of the fact that now more bundles can reach the

destination from the distant routers using the

cached route update information of the Back

Propagation technique.

Figure 5 also depicts how the other protocols will

perform in the same environment. It is found that

PRoPHET performs well when the traffic density is

low but the performance overall deteriorates as the

traffic density increases. Since this protocol works

based on finding a suitable node to forward with

higher delivery predictability than the previous one,

it can be concluded that increasing the traffic density

does not help much in finding that suitable next hop.

On the other hand the Spray and Wait (SnW)

protocol shows overall same performance for all

types of traffic density and the latency is larger than

the PRoPHET. Epidemic presents quite a low profile

than all other protocols.

Figure 6 presents the comparative situations of

the end-to-end latency for all the delivered messages

in the above mentioned protocols. This figure clearly

shows the lower latency range for the HDRP where

about 90% of the messages contribute between 5 to

15 sec latency whereas in case of PRoPHET and

SnW protocols most of the messages have latency

between 256 to 1025 sec range. This reveals that in

HDRP most of the messages are delivered to the

destination very quickly but in other protocols

majority of the messages takes longer time toreach

the destination and hence the end-to-end latency

increases. In this chart the HDRP (1, 5) gives more

end-to-end average latency than the HDRP (1, 500)

owing to the heavy traffic intensity which causes

more delay for the Bundles to reach the destinations.

We have plotted the PRoPHET (1,5) and SnW (1,5)

to show the comparison between the protocols when

the network traffic is very high.

Figure 5: Latency values of different number of messages.

4.2.2 Performance at Different Router

Density

We have simulated our network model for two

different topologies: i) Few Routers (FR):26 routers

ii) Many Routers (MR): 65. The routers are not fully

connected but they are well connected. They are

placed at different positions of the map of our model

so that the mobile nodes plying around the city map

can fall within the range of one or other to

accomplish their communication. It can be

intuitively guessed that increasing the router density

WINSYS 2010 - International Conference on Wireless Information Networks and Systems

will certainly improve the delay performance in our

system. But we wanted to show how much would be

the difference if the number of the routers are more

than double.

Figure 7 depicts that HDRP and HDRP (BP)

have lower latency when Many Routers are present

than the Few Routers. This amount is substantially

lower than other protocols. As the number of router

increases more routers can be used to reach the

destination quickly. We found very low latency

values especially in case of MR. When the router

number increases from 26 to 65, the latency

decreases from 50sec (avg) to 25 sec (avg.) in case

of HDRP and from 60 sec (avg.) to 30 (avg.) sec in

case of HDRP (BP).

Figure 6: Latency values of different number of routers.

Another point worth mentioning here is the

transmitting range of the routers. We have used the

300 m transmitting range. With lower transmitting

range the performance degrades. And with higher

transmitting range we got same performances as

with the 300m range.

4.2.3 Performance for Different Node

Density

We wanted to show what will happen if the number

of end nodes communicating in our working

environment increases keeping the fixed router

numbers at 26. We tried with different end node

numbers from 124 to approximately 1000 nodes. For

the wide range of (120 to 1000 numbers of nodes),

both HDRP and HDRP (BP) gave much lower

latency value than others. Figure 8 shows that the

HDRP is scalable for the different node density.

4.2.4 Effect of Different Mobility Speed

To show how the mobility of the MHs affects our

protocol and others we have chosen different values

of Mobility speed, M by varying the speed of each

type of mobile nodes (pedestrians, cars, trams etc.),

100

200

300

400

500

600

700

800

0 200 400 600 800 1000 1200

Latency(sec)

Numberofnodes

HDRP FixedProphet

FixedEpidemic HDRP(BP)

Figure 7: Latency at different node density.

as explained in Table 1 For example, M1= [(.5, 1.5)

x40+ (2.7, 13.9) x40+ (7, 10) x2+ (7, 10)

x2]/84=4.833. Here the pedestrians speed has the

distribution of (.5, 1.5), no of pedestrians is 40;

speed distribution for the cars are (2.7, 13.9), no of

cars is also 40; trums1 and trums2 both have the

distribution as (7, 10) and the total number of mobile

nodes are 84. Finally, the total speed is divided by

the total number of nodes that is 84 and we get the

M1 value as 4.833.We varied the speed range of the

different type of mobile nodes and calculated the

M2, M3 and M4 respectively.

200

400

600

800

M1

(4.833)

M2

(7.8809)

M3

(18.2142)

M4

(27.261)

Laten cy(sec)

HDRP FixedPROPHET FixedEpidemic

Figure 8: Latency for different mobility speed.

Figure 9 shows that the latency of HDRP

decreases to about 50% of its value at M4 than M1.

As the moblity of the nodes increases from 4.833 to

27.261 that is more than 6 times, now more Bundles

can reach their destination faster than before. Thus

the latency of HDRP decreases to 21 sec from 43 sec

which is almost half. As we know that in Epidemic

protocol the message can spread faster in the

network if the speed of the mobile nodes increases

ACHIEVING LOW END-TO-END LATENCY WITH A HANDOFF-BASED DETERMINISTIC ROUTING

PROTOCOL (HDRP) IN DELAY-TOLERANT NETWORKING

and thus can reach the destination within small time.

So the latency for Epidemic decreases to 403 sec to

724 sec as mobility goes from M1 to M4. But

PRoPHET is less effeced by mobility than Epidemic

and ofcourse from HDRP as its operation is guided

by the suitable forwarding condition to be made.

4.2.5 Effect of Route-cache Time Variation

In the HDRP with Back Propagation technique we

varied the Alive time or route- cache time at each of

the routers from 5 sec to 3000 sec value range.

Because of the increased cache time at the routers,

few more Bundles get their way to the destination

deterministically using the cached route information.

The latency increases to 31.27 sec from 22.82 sec

which shows that now Bundles from the far away

routers are now contributing in the latency values

and so there is a increase in the overall latency.

5 RELATED WORK

5.1 Related Work on Handoff

Technologies in TCP/IP Protocol

There have been ample research works going on the

Mobility issues particularly Handover techniques in

Mobile Wireless environment. After wireless

networking technology became popular people tried

to develop mechanism that will deal with both the

wired and wireless part of a network efficiently.

Different methods were devised to overcome the

problems associated with the TCP to handle mobility

in the wireless environment (Manzoni et al., 1995), (

Yavatkar and Bhagawat, 1994), (Balakrishnan et

al.), (Caceres and Iftode, 1994). In spite of many

improvements these methods have the drawback of

end-to-end session management, TCP slow start

mechanism etc. I-TCP, Snoop-TCP, M-TCP and few

other protocols were developed to handle the

handoff situations efficiently through the use of

mediation by the Mobility Support Router (MSR)

(Bakre and Badrinath, 1997). But these methods also

suffer from the problem of large Handoff Latency

due to the connection states transfer between the old

and new MSR. In HDRP the rerouting during the

Handoff is done with the help of the hop-by-hop

reliability mechanism and custody transfer of the

DTN technology. This protocol does not have the

end-to-end session management or connection state

transfer problem during handoff. When handoff

takes place, the MH registers its location to the new

router and this location information is propagated

back to the experienced route and cached there so

that any Bundle destined to that MH can be

deterministically delivered to the destination.

The handoff latency is reduced in HDRP in

comparison to I-TCP in terms of number of message

exchanges:

Between MH and its CM it is similar because in

case of I-TCP we have Beacon/Greet/Grack and in

case of HDRP we have Beacon/REG/ SR

correspondingly. But between the CM and the PM

the number of message exchanges is not same

because I-TCP has Fwd Ptr/Fwd Ack/MHState/ACK

and HDRP has HO message/Data forwarding/SR.

Within the CM and PM routers, in case of I-TCP,

there are number of internal message exchanges

between the components of the router to accomplish

the handoff process but HDRP does not require any

internal message exchanges for the handoff to take

place.

Mobile IP, the mobility extension to the Internet

Protocol devises all the techniques to handle

mobility related and hence handover situations at the

network layer. But it also suffers from many

problems regarding the duration of handover and the

scalability of the registration procedure (Schiller). If

we consider a large number of mobile nodes

changing networks quite frequently, a high load on

the home agents as well as on the networks is

generated by registration and binding update

messages. The message delivery in HDRP does not

involve going through any home agent and update

messages do not need to travel so far. The old router

simply consults the PL and forwards the messages

destined for that particular mobile node. This

process is a very simple one and takes reasonably

less amount of time.

IP micro mobility-protocols like Cellular IP

(Campbell and Gomez-Castellanos, 2000),

(Campbell et al., 2000) or others are developed to

complement mobile IP by offering fast and almost

seamless handover control in limited geographical

areas. But they accompanies additional network

load induced by forwarding packets on multiple

paths. An additional cost of these schemes is that

communication, signaling and information state

exchange are required between the base stations for

these approach to work. On the other hand the

Handoff protocol in HDRP implements handover of

the messages with minimum number of control

message exchanges and no additional cost of

overhead. In case of Cellular IP, the back

propagation of route update packet takes place

between the MH and the crossover gateway of the

cellular network. In case of HDRP, the back

WINSYS 2010 - International Conference on Wireless Information Networks and Systems

propagation takes place along the experienced route

of the MH that is through all the Previous Masters of

the MH. The distance between the MH and the

crossover Gateway is very important in case of

Cellular IP because while considering the Hard

handoff, the notification time from the new base

station to the old base station should be less than the

round trip time from the MH to the crossover

Gateway. This reduces the packet loss. On the other

hand, in HDRP (BP) the route update propagates

until sometime defined by the Alive time of the

route update Bundle at each of the router.

Another technique used in Cellular IP to reduce

the packet loss is the use of soft handoff technique

where the semisoft packet creates new routing cache

mappings between the crossover and the new base

stations, beforehand. In case of HDRP we didn’t use

any kind of route cache mapping creation before the

actual handoff takes place.

Many schemes have been developed considering

cross layer approach that is considering the Link

Layer triggering to the Network layer and how they

jointly reacts to handle the handover problems

(Blondia et al..,2003). In HDRP the handling of

both routing and handoff is done in a single bundle

layer which reduce cross layer interaction and

synchronization overhead and thus makes the

handoff latency smaller. An interaction between the

Bundle layer and the Physical layer is present during

the registration process by receiving the Beacon.

There are methods like Daelalus Implementation

(Seshan et al., 1996) that anticipates a handoff using

the received signal strength and multicast data

destined for the MH to nearby base stations in

advance. Combined with intelligent buffering

techniques at the base station, this provides good

performance without explicit data forwarding. But

this method has the inefficiency in handling the

routing of packets to the base station and the

overhead of buffering packets at several base

stations. During handoff in HDRP, we do not need

to consider any multicasting technique neither do we

need to apply any routing in advance. Hop by hop

routing decision is taken dynamically and buffering

is accomplished through custody transfer mechanism

efficiently.

5.2 Related Work on DTN Routing

Protocols

A number of routing protocols have been targeted

towards the context of intermittently connected

mobile networks with opportunistic connectivity.

Many of these protocols assume that all nodes are

mobile and have developed algorithms to transfer

message between these nodes. Flooding is one of the

popular techniques among these. Epidemic Routing

(Vahdat and Becker, 2000) is the protocol that

extends the concept of flooding in intermittently

connected mobile networks. It shows good

performance in a DTN environment where random

pair-wise exchanges of messages among MHs

ensure eventual message delivery and performs well

in terms of maximizing message delivery rate and

minimizing message latency until other protocols

were devised. PRoPHET (Lindgren and Schelen,

2003), a probabilistic routing protocol for such

networks assumes non-random mobility of nodes to

improve the delivery rate of messages while keeping

buffer usage and communication overhead at a low

level. The Spray and Wait routing protocol

(Spyropoulos and Raghavendra, 2005) manages to

significantly reduce the transmission overhead of

flooding-based schemes and have better

performance with respect to delivery delay

especially when the wireless channel has high

contention. These flooding based routing protocols

do not make use of the global knowledge and hence

suffers large latencies. We wanted to make use of

the knowledge of the location of the mobile node

and propose a handoff based routing protocol which

can route Bundles in a deterministic way. The route

update information during handoff and Back

Propagation and caching of this location information

over the experienced route improves the

performances.

In comparison to Epidemic, PRoPHET and

Spray & Wait protocols HDRP is deterministic in

nature and this is a more logic based routing

protocol. With carefully designed forwarding

mechanism and message prioritizing technique,

under different scenarios, it is possible to achieve

better delivery delay than the other protocols

mentioned above.

6 CONCLUSIONS

The HDRP protocol is a simple but efficient

handoff-oriented protocol that integrates the DTN

features with Custody Transfer and hop-by-hop

routing and the existing Internet-based handoff

schemes like mobile-IP, cellular-IP and I-TCP. This

integration is not a simple result that simply

combines the two different technologies but a

sophisticated and well-considered result because

DTN architecture is based on hop-by-hop routing

and fundamentally different from the end-to-end

ACHIEVING LOW END-TO-END LATENCY WITH A HANDOFF-BASED DETERMINISTIC ROUTING

PROTOCOL (HDRP) IN DELAY-TOLERANT NETWORKING

routing of the Internet architecture. Therefore we

have devised a unique integration that fully utilizes

the DTN features.

HDRP gives better performance than the already

existing DTN protocols in terms of Delivery ratio

and end-to-end latency by making use of the

location information of the MH and applying the

Back Propagation of the route update information

technique efficiently. The protocol shows superior

performance even for high traffic loads and it is

possible to achieve very low end-to-end latency with

the help of this protocol.

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