Internet DRAFT - draft-shi-dtnrg-amcud
draft-shi-dtnrg-amcud
Delay-Tolerant Networking Research Group Wenfeng Shi
Internet Draft Qi Xu
Intended status: Experimental Bohao Feng
Expires: April 15, 2016 Huachun Zhou
Beijing Jiaotong University
October 14, 2015
A Mechanism Coping with Unexpected Disruption in Space Delay
Tolerant Networks
draft-shi-dtnrg-amcud-00.txt
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Abstract
This document proposes a coping mechanism used to deal with the
unpredictable disruption problem in Space Delay Tolerant Networks
(DTN) [RFC4838]. Since Licklider Transmission Protocol (LTP)
[RFC5326] provides retransmission-based reliability for bundles,
several times of retransmissions can be seen as a failure occurred
over links. The proposed mechanism is used to direct the following
packets to other nodes and probes the availability of the links
which has disrupted unexpectedly.
Table of Contents
1. Introduction ................................................ 2
2. Conventions used in this document............................ 3
3. The coping mechanism......................................... 3
4. Security Considerations...................................... 4
5. IANA Considerations ......................................... 4
6. References .................................................. 5
1. Introduction
Since the moving trajectory of nodes is scheduled in the space
network, it's possible to have a prior knowledge of contact
information between any nodes. Consequently, routing algorithms such
as Contact Graph Routing (CGR) [CGR] can calculate a delivery path
from the source to destination hop by hop based on the connectivity
relationship, propagation delay, data rate, etc.
However, due to the complexity of the space network, the satellite
and its associated links suffer from the electromagnetic
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interference frequently and this may lead to unpredictable
disruption for a period of time. Then, the subsequent bundles sent
by the source using the initially contact information cannot be
transmitted successfully and retransmission is also occurred. As a
result, not only the timeliness of bundles cannot be guaranteed but
also limited resources of the node and link are consumed and wasted.
Thus, it is important to make a mechanism to handle the unexpected
disruption problem.
This draft proposes a coping mechanism. It works with Licklider
Transmission Protocol (LTP) [RFC5326] and routing algorithms such as
Contact Graph Routing (CGR) and it is used to not only direct the
following bundles to other nodes when the disruption is occurred but
also probe the availability of the disrupted links during its
claimed valid time.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3. The coping mechanism
Since LTP provides retransmission-based reliability for bundles,
which are the minimal data units in Bundle Protocol (BP) [RFC5050],
several times of retransmissions can be seen as a failure occurred
over links. Suppose CGR is used as the routing algorithm. Once the
retransmission is detected for more than two times, the contact used
in CGR is regarded as temporary corruption. Then, the node marks
this contact as "probing" and recalculates the route for subsequent
bundles.
When T seconds elapse, a probing message is sent by the node to the
destination shown in the disputed contact to check if the
connectivity has been recovered. The time T can be either a fixed
value or a dynamic one estimated by the node based on some
algorithms. If the corresponding response message is received, the
contact is remarked as "normal" and can be used for the following
bundles. Otherwise, the node sends a probe message again T seconds
later. In this way, the node probes the disrupted link periodically.
If the contact still can't be recovered after n times of probing,
this contact is marked as "disrupted" and the node advertises this
result to its immediate neighbors.
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+----------+
|Satellite2|
+----------+
/ | \
/ | \
/ | \
/ | \
+----------+ | +----------+ +----------+
|Satellite1| | |Satellite4|------|Satellite5|
+----------+ | +----------+ +----------+
\ | /
\ | /
\ | /
\ | /
+----------+
|Satellite3|
+----------+
Fig. 1 Example of unexpected contact disruption.
An example is given to explain the contact disruption handling
mechanism. Assume that either Satellite2 or Satellite3 can be used
by Satellite1 as relays to send bundles to Satellite5. At initial,
Satellite2 is selected to be used. Suppose at one time, the link
from Satellite2 to Satellite4 is disrupted. When Satellite2 detects
the retransmission of bundles two times, it marks the contact to
Satellite4 as "probe" and recalculates routes for the subsequent
bundles. Thus, those bundles will be sent to Satellite3 and then to
Satellite4 and Satellite5.
At the same time, Satellite2 will send the probe message to
Satellite4 periodically and check if the link is recovered. If
Satellite2 does not receive a response after sending n probing
messages, it will mark the contact as "disrupted" and advertises the
result to Satellite1 and Satellite3. When Satellite1 receives the
advertisement, it will mark the contact from Satellite2 to
Satellite4 as "disrupted" and use Satellite3 as the relay.
4. Security Considerations
To be done.
5. IANA Considerations
To be done.
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6. References
[RFC4838] Burleigh S, Hooke A, Torgerson L, et al. RFC4838-Delay-
Tolerant Networking Architecture[J]. 2007.
[RFC5326] Ramadas M, Burleigh S, Farrell S. RFC 5326, Licklider
Transmission Protocol Specification[J]. IRTF DTN Research
Group, 2008.
[RFC5050] Burleigh, S. Bundle protocol specification. No. RFC 5050.
2007.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[I-D. burleigh-dtnrg-cgr] Burleigh S. Contact Graph Routing: draft-
burleigh-dtnrg-cgr-01, July 2010[J].
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Authors' Addresses
Wenfeng Shi
Beijing Jiaotong University
Beijing, 100044, P.R. China
Email: 14111038@bjtu.edu.cn
Qi Xu
Beijing Jiaotong University
Beijing, 100044, P.R. China
Email: 15111046@bjtu.edu.cn
Bohao Feng
Beijing Jiaotong University
Beijing, 100044, P.R. China
Email: 11111021@bjtu.edu.cn
Huachun Zhou
Beijing Jiaotong University
Beijing, 100044, P.R. China
Email: hchzhou@bjtu.edu.cn
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