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 Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. 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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 Shi, et al. Expires April 15, 2016 [Page 2] Internet-Draft amcud October 2015 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. Shi, et al. Expires April 15, 2016 [Page 3] Internet-Draft amcud October 2015 +----------+ |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. Shi, et al. Expires April 15, 2016 [Page 4] Internet-Draft amcud October 2015 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]. Shi, et al. Expires April 15, 2016 [Page 5] Internet-Draft amcud October 2015 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 Shi, et al. Expires April 15, 2016 [Page 6]