Disruption Tolerant Network Coding scenarios often rises from mobile wireless networks where due to limited transmission power, fast node mobility,sparse node density, and frequent equipment failures, there is often no contemporaneous path from the source to destination nodes. Before going to the depth of DTN, it is recommended to review traditional non-coding routing schemes for broadcast and unicast applications in DTNs, and the basic operations of Random Linear Coding (RLC).

1. Network Coding in Disruption
Tolerant Network
Presented by- Faheema Monica (S20141501)
University of Science and Technology, Beijing

2. Contents
Fundamentals of
Disruption
Tolerant Network
• Introduction to DTN
• Working principles
• Bundle protocol
• DTN vs Classical networking
• Potential applications of DTN
• DTN’s applicability to NASA
Applications of
Network Coding
in DTN
• Random Linear Coding
• Coding benefits for Broadcast communication
• Coding benefits for Unicast applications
• Network Coding Improves Delay vs. Transmission Number Trade-
off
• Conclusion

3. DTN (Disruption Tolerant Network)
 A networking architecture provides communication
in unstable and stressed environments where the
network would face disruptions, high bit error.
 DTN provides:
 reliable data transfer without complete cotemporaneous end
to end path to destination,
 retransmission from closet relay node rather than sender,
 custody transfer and return receipt operations,
 DTN can reduce delay and increase throughput.

4.  Store-Carry-Forward
DTN routing adopts a so
called store-carry-forward
paradigm. Under this
paradigm, each node in the
network stores a packet that
has been forwarded to it by
another node, carries the
packet while moves around,
and forward it to other relay
nodes or to the destination
node when they come within
transmission range.
Working principles of DTN

5. Bundle Protocol
A different approach to TCP/IP: BP ;RFC 5050

6. DTN vs. Classical(Wireless) Networking
DTN
Classical
networking

7. DTN vs. Classical
Networking
Classical
networking
DTN

8. DTN vs. Classical
Networking
DTN
Classical
networking

9. DTN vs. Classical
Networking
DTN
Classical
networking

10. Potential applications of DTN:
1. Space Agencies:
2. Military and Intelligence:
3. Commercial:
4. Public Service and Safety:
5. Personal Use:
6. Environmental Monitoring:

11.  Space operations require
coordination of data
transfers across the space
link with the scheduled
ground contacts. This is done
manually by DTN.
 DTN enables the decoupling
of these two activities by
allowing onboard data to be
held in persistent storage
until a contact is available, at
which time it is
automatically sent to the
Command and Data
Handling (C&DH) for
downlink.
DTN’s applicability to NASA and International Space
Mission

12. Random Linear Network coding is a technique, which can be used to improve a
network's throughput, efficiency and scalability, . Instead of simply relaying the
packets of information they receive, the nodes of a network take several packets
and combine them together for transmission. This can be used to attain the
maximum possible information flow in a network.
In broadcast transmission schemes allows close to optimal throughput using a
decentralized algorithm. Nodes transmit random linear combinations of the
packets they receive, with coefficients chosen from a Galois field. If the field size is
enough large, the probability that the receiver(s) will obtain linearly independent
combinations (and therefore obtain innovative information) approaches 1. It
should however be noted that, although random network coding has excellent
throughput performance, if a receiver obtains an insufficient (or lost) number of
packets, it is extremely unlikely that they can recover any of the original packets.
This can be addressed by sending additional random linear combinations until the
receiver obtains the appropriate number of packets.
RANDOM LINEAR NETWORK CODING

13. Let see the Example of the butterfly network coding:
The butterfly network is often used to illustrate how
random linear network coding can outperform routing. Two
source nodes have information A and B that must be
transmitted to the two destination nodes (at the bottom),
which each want to know both A and B. Each edge can carry
only a single value (we can think of an edge transmitting a
bit in each time slot).
If only routing were allowed, then the central link would be
only able to carry A or B, but not both. Suppose we send A
through the center; then the left destination would receive
A twice and not know B at all. Sending B poses a similar
problem for the right destination. We say that routing is
insufficient because no routing scheme can transmit both A
and B simultaneously to both destinations. Using a simple
code, as shown (random linear network coding), A and B
can be transmitted to both destinations simultaneously by
sending the sum of the symbols through the center – in
other words, we encode A and B using the formula "A+B".
The left destination receives A and A + B, and can calculate
B by subtracting the two values. Similarly, the right
destination will receive B and A + B, and will also be able to
determine both A and B.

14. Theorem 1:
 We assume that all packets are of the same length with P bits
payload. When RLC is used in packet data networks, the payload
of each packet can be viewed as a vector over a finite field, Fq of
size q, more specifically, where the addition and multiplication
operations are over Fq .
 The coefficient α=(α1,...αk) is called the encoding vector, and the
resulting linear combination, x is an encoded message. We say
that two or more encoded messages are linearly independent if
their encoding vectors are linearly independent. Each original
packet, mi, can be viewed as a special combination with
coefficients αi = 1, and αj = 0, ∀j ≠i.

15. Control Signaling
Before presenting the benefits of RLC in DTN, let have a look to the different
existing control signaling:
Control Signaling
 Because of the ad hoc nature and dynamically changing topology of DTNs, nodes
perform beaconing in order to discover their neighbors (via broadcasting
periodic beacon packets), and/or exchange with neighbors information about
packets/coded packets they carried. Such control signaling is useful for nodes
to decide whether to transmit and what information to transmit. The following
different levels of control signaling have been considered:
 No Signaling: Under this most basic case no information about the
neighborhood is available. Nodes decide to transmit packets without knowing
whether there is a neighboring node or not.
 Normal Signaling: Under normal signaling, each node periodically transmits
beacon messages in order to discover neighboring node, nodes within its
transmission range. With normal signaling, a node typically only transmits
information when it detects at least one neighbor.
 Full Signaling: Under full signaling, each node not only performs periodic
beaconing to discover its neighbors, but also exchanges with its neighbors
information about what packets or coded packets are stored locally, the
sequence numbers of packets or the encoding vectors of coded packets. Based
on such information, a network node typically only transmits to its neighbors if
it has useful information for them.

16. Coding Benefits for Energy Efficiency:
Consider a network of N nodes, where each node has generated a packet to be broadcast to all the
other nodes. Assume nodes move according to the uniform at random mobility model, i.e., at each
time slot each node independently jumps to a new location in the terrain selected uniformly at
random. At each time slot, each node decides to turn off or on its radio respectively, with
probability p and 1-p. Assume there is no control signaling (no information about neighboring
nodes and the information they carry). In each time slot, each node that is turned on randomly
chooses a packet to transmit (under a non-coding scheme), or transmits a random linear
combination of its coded packets to its neighbors (under an RLC scheme). There are on average (1-
p) N transmissions in the network at each time slot.
Theorem 2: Broadcasting to all receivers can be achieved using on average the:
time slots, without using network coding;
time slots, using network coding with a large enough
field size, q.
Which one is better?
Of course Tnc is better with a small time slot than Tw.
Coding Benefits for Broadcast Network
Communication

17. Simulation results have
confirmed that the block
delivery delay under the RLC
scheme is very close to the
minimum block delivery delay,
as shown in FIG5-A, which
plots the empirical cumulative
distribution function (CDF) of
minimum block delivery delay,
and the block delivery delay
achieved by the RLC and the
non-coding scheme over 100
different simulation runs each
with a different random seed.
Coding Benefits for Unicast Network Communication
Figure 10.5: DTN with N=101 nodes,
homogeneous exponential inter-meeting
time with rate"=0.0049, bandwidth
constraint of b=1 packet per contact, and
unlimited buffer space.

18. The RLC scheme improves the delay versus number of transmission trade-offs
Simulation studies reported compared the block delivery delay versus
transmission number trade-off achieved by the non-coding scheme with
binary spray-and-wait applied to each of the K packets, the token- based RLC
scheme and the E-NCP scheme. Figure 10.7 plots the average block delivery
delay versus number of transmissions, for a block of K=10 packets, under
different token limits, for the cases both without buffer constraints (a) and
with buffer constraint of B = 2 (b). We observe that, with a similar number of
transmissions, the RLC schemes achieve smaller block delivery delay than
non-coding schemes, and the token-based RLC scheme outperforms the E-
NCP scheme, especially for small numbers of transmissions. The results for a
limited relay buffer case further establish the benefits of the RLC schemes in
reducing block delivery delay without increasing transmission overheads：
Network Coding Improves Delay vs. Transmission
Number Trade-off

19. Figure 10.7: Block delivery delay vs transmission number trade-off under the same
network setting as Fig. 10.5except for the bandwidth and buffer constraints.

20. Figure 10.9: Block delivery delay vs transmission number trade-off with full
signaling and normal signaling, the network setting is the same as that of fig 10.5
RLC and no coding scheme under different control signaling:

21.  In this presentation, at first we have introduced the DTN concept,
presented the opportunities offered by DTN, and shown how
DTN-based communication may represent an opportunity for
satellite networking.
 And then in later part, our main focus was to show the
performance evaluation of RLC based routing schemes both for
broadcast and unicast network communications, unicast network
communications and broadcast network communication having
been the object of a larger amount of research. We highlighted
both theoretic results and simulation studies findings. For both
communication models, the RLC based scheme provides better
trade-off between energy consumption and delivery performance.
Conclusion