Delay-Tolerant Networking Research Group Wenfeng Shi
Internet Draft Qi Xu
Intended status: Experimental Bohao Feng
Expires: October 5, 2016 Huachun Zhou
Beijing Jiaotong University
April 4, 2016
A Mechanism Coping with Unexpected Disruption in Space Delay
Tolerant Networks
draft-shi-dtn-amcud-01.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
C`ontributions 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.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
at any time. It is inappropriate to use Internet-Drafts as
reference material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
This Internet-Draft will expire on October 5, 2016.
Shi, et al. Expires October 5, 2016 [Page 1]
Internet-Draft amcud April 2016
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with
respect to this document. Code Components extracted from this
document must include Simplified BSD License text as described in
Section 4.e of the Trust Legal Provisions and are provided without
warranty as described in the Simplified BSD License.
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...................................... 5
5. IANA Considerations ......................................... 5
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 October 5, 2016 [Page 2]
Internet-Draft amcud April 2016
interference frequently and this may lead to unpredictable
disruption for a period of time. Then, the subsequent bundles cannot
be transmitted successfully by the initial contact information, and
retransmission is 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 to deal with such situations.
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 the contact window.
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,
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 temporary disrupted and recalculates the route for
subsequent bundles. Besides, a disruption advertisement for the
unavailable contact is sent to upstream nodes. When receiving the
advertisement, related nodes create disrupting contacts to prevent
the use of disrupted links indicated by the advertisement. However,
the advertisement may be useless when it arrives at some nodes whose
related contacts do not become available until the expiration of the
advertisement. Hence, a disruption advertisement group is defined to
assure the effectiveness of the contact disruption advertisement.
The group contains nodes indicated in corresponding contacts whose
"from time" are earlier than the disrupting contact's "to time".
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 "recovery" and can be used for the following
bundles and a contact recovery advertisement is sent to nodes
Shi, et al. Expires October 5, 2016 [Page 3]
Internet-Draft amcud April 2016
belonging to the advertisement group. Otherwise, the node sends a
probe message again T seconds later. In this way, the node probes
the disrupted link periodically until the contact is recovered or
expired.
+----------+
|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 the contact between Satellite1 and Satellite2
is available from 1s to 300s, the contact between Stallite1 and
Satellite3 from 100s to 300s, the contact between Satellite3 and
Satellite4 from 100s to 300s, the contact between Satellite2 and
Satellite4 from 1s to 300s, the contact between Satellite2 and
Satellite3 from 1s to 300s, the contact between Satellite4 and
Satellite 5 from 400s to 500s. 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 "temporary disrupted" and recalculates
routes for the subsequent bundles. Thus, those bundles will be sent
to Satellite3 and then to Satellite4 and Satellite5. In addition,
the disruption advertisement group is computed by Satellite2
containing Satellite1, Satellite3 and Satellite4. When Satellite1
Shi, et al. Expires October 5, 2016 [Page 4]
Internet-Draft amcud April 2016
receives the advertisement, it will mark the contact from Satellite2
to Satellite4 as "disrupted" and use Satellite3 as the relay.
At the same time, Satellite2 will send the probe message to
Satellite4 periodically and check if the link is recovered. If
Satellite2 receives a response, it will mark the contact as
"recovery" and send contact recovery advertisement to satellites
included in the advertisement group. If Satellite2 does not receive
a response after sending the probing messages, it will resend the
probing message again after T seconds until the disrupted contact is
expired.
4. Security Considerations
To be done.
5. IANA Considerations
To be done.
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 October 5, 2016 [Page 5]
Internet-Draft amcud April 2016
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 October 5, 2016 [Page 6]