A Mechanism Coping with Unexpected Disruption in Space Delay Tolerant Networks
draft-shi-dtn-amcud-00

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-dtn-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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