ICN Research Group                                          Paulo Mendes
Internet-Draft                                                    Airbus
Intended Status: Experimental                                 Rute Sofia
Expires: September 1, 2019                  COPELABS,University Lusofona
                                                    Vassilis Tsaoussidis
                                                  Sotiris Diamantopoulos
                                              Christos-Alexandros Sarros
                                         Democritus University of Thrace
                                                          Carlos Borrego
                                                             Joan Borrel
                                      Autonomous University of Barcelona
                                                       February 28, 2019

    Information-centric Routing for Opportunistic Wireless Networks


   This draft describes the Data reAchaBility BasEd Routing (DABBER)
   protocol, which has been developed to extend the reached of Named
   Data Networking based routing approaches to opportunistic wireless
   networks. By "opportunistic wireless networks" it is meant multi-hop
   wireless networks where finding an end-to-end path between any pair
   of nodes at any moment in time may be a challenge. The goal is to
   assist in better defining opportunities for the transmission of
   Interest packets towards the most suitable data source, based on
   metrics that provide information about: i) the availability of
   different data sources; ii) the availability and centrality of
   neighbor nodes; iii) the time lapse between forwarding Interest
   packets and receiving the corresponding data packets. The document
   presents an architectural overview of DABBER followed by
   specification options related to the dissemination of name-prefix
   information to support the computation of next hops, and the ranking
   of forwarding options based on the best set of neighbors to ensure a
   short time-to-completion.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

Mendes, et al.         Expires September 1, 2019                [Page 1]

Internet-Draft                   dabber                February 28, 2019

   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."

   This Internet-Draft will expire on February 28, 2019.

Copyright and License Notice

   Copyright (c) 2018 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.

Table of Contents

   1. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1. Contextual Aspects  . . . . . . . . . . . . . . . . . . . .  5
     1.2. Applicability . . . . . . . . . . . . . . . . . . . . . . .  6
     1.3. NFD Adjustment to Opportunistic Networks  . . . . . . . . .  7
     1.4. Conventions . . . . . . . . . . . . . . . . . . . . . . . .  9
   2. DABBER Architecture . . . . . . . . . . . . . . . . . . . . . .  9
     2.1. Assumptions and Requirements  . . . . . . . . . . . . . . . 10
     2.2. Naming  . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     2.3. LSA Dissemination . . . . . . . . . . . . . . . . . . . . . 12
     2.4. Multiple path Computation . . . . . . . . . . . . . . . . . 14
       2.4.1. Name Prefix Validity Computation  . . . . . . . . . . . 14
       2.4.2. Update of DABBER internal information . . . . . . . . . 16
       2.4.2. Update of RIB of the local NFD  . . . . . . . . . . . . 17
     2.5. Packet Forwarding . . . . . . . . . . . . . . . . . . . . . 17
     2.6. Loop Prevention . . . . . . . . . . . . . . . . . . . . . . 18
   3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . . 18
     3.1. Overall Operation Example . . . . . . . . . . . . . . . . . 19
     3.2. Peer Discovery and Face Setup . . . . . . . . . . . . . . . 20
     3.3. Peer Communication Modes  . . . . . . . . . . . . . . . . . 21
     3.4. Multi-homing Wireless Communication . . . . . . . . . . . . 22
     3.5. LSA Exchange  . . . . . . . . . . . . . . . . . . . . . . . 23
     3.6. Loop Avoidance  . . . . . . . . . . . . . . . . . . . . . . 24
     3.7. Failure and Recovery  . . . . . . . . . . . . . . . . . . . 25
     3.8. Interface towards a Contextual Agent  . . . . . . . . . . . 25

Mendes, et al.         Expires September 1, 2019                [Page 2]

Internet-Draft                   dabber                February 28, 2019

     3.9. Adjustment to data source mobility  . . . . . . . . . . . . 25
   4. Interoperability  . . . . . . . . . . . . . . . . . . . . . . . 27
     4.1. Interoperability with NDN operation over DTNs . . . . . . . 27
     4.2. Interoperability with NDN operation in wired networks . . . 27
       4.2.1. Interoperability with NLSR  . . . . . . . . . . . . . . 27
       4.2.2. Interoperability with broadcast based forwarding  . . . 28
   5. Security Considerations . . . . . . . . . . . . . . . . . . . . 28
   6. Implementation and Deployment Experience  . . . . . . . . . . . 29
     6.1  Improvement of Network Service Discovery  . . . . . . . . . 29
       6.1.1. Peer Registration Service . . . . . . . . . . . . . . . 30
       6.1.2. Peer Announcement Service . . . . . . . . . . . . . . . 30
       6.1.3. Leader Service  . . . . . . . . . . . . . . . . . . . . 31
       6.1.4. Disconnect Detector Service . . . . . . . . . . . . . . 31
   7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 32
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 32
     8.1  Normative References  . . . . . . . . . . . . . . . . . . . 32
     8.2  Informative References  . . . . . . . . . . . . . . . . . . 32
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 34

Mendes, et al.         Expires September 1, 2019                [Page 3]

Internet-Draft                   dabber                February 28, 2019

1. Introduction

   In a networking scenario where an increasing number of wireless
   systems, such as end-user nodes and mobile edge nodes, are being
   deployed, there are two networking paradigms that are highly
   correlated to the efficiency of pervasive data sharing: Information-
   Centric Networking (ICN), and opportunistic wireless networking. The
   latter concerns the capability of exploiting any potential wireless
   communication opportunity to exchange data in a multi-hop wireless
   networks, where it is difficult to find an end-to-end path between
   any pair of nodes at any moment in time.

   Combining opportunistic networking with ICN principles is relevant to
   efficiently extend the applicability of information-centric
   networking to novel scenarios, such as affordable pervasive access;
   low cost extension of access networks; edge computing; vehicular

   This document describes the Data reAchaBility BasEd Routing (DABBER)
   routing protocol for information-centric wireless opportunistic
   networks [24]. These networking architectures are operationally
   located on the Internet fringes (Customer Premises). In such areas,
   networking experiences intermittent connectivity and variable
   availability of nodes due to their movement and/or due to other
   constrains, e.g., limited battery, storage, and processing.

   DABBER has been therefore designed to be compatible with the routing
   deployed within ICN access networks. Its main purpose is to assist in
   extending the reach of multi-hop transmission to opportunistic
   environments, in a seamless and fully interoperable way.

   It is our understanding that routing in such wireless environments
   needs to be done based on strategies that take into consideration, at
   a network level, the context of wireless nodes, and not just the
   history of contacts among wireless nodes. The goal is to assist in
   better defining opportunities for the transmission of Interest
   packets over time and space. Such opportunities can be better
   addressed if routing metrics take into consideration, as common in
   opportunistic environments, measures of centrality, as well as
   measures of node and data availability.

   Being NDN[1][2] a well established ICN framework, the first step
   proposed by this draft is to consider the current de facto NDN
   routing, Named-data Link State Routing protocol (NLSR)[19][20], in a
   way that allows the benefits of link-state approaches, while
   delimiting its downsize in the context of the wireless medium.

   Although DABBER specification allows an easier integration with NDN

Mendes, et al.         Expires September 1, 2019                [Page 4]

Internet-Draft                   dabber                February 28, 2019

   access networks based on NSLR (e.g. the messaging systems based on
   the synchronization of LSA is the same), its operation is completely
   independent of NSLR. This means that DABBER can be used in any
   isolated wireless opportunistic network, or by any wireless node that
   frequently attaches to fix NDN networks (e.g. by using a Wi-Fi link),
   which do not have NLSR as their routing protocol.

   DABBER is intended as complementing existing forwarding protocols for
   opportunistic networks (e.g., Prophet [12], Scorp [13], dLife
   [14][18], BubbleRap [15]).

1.1. Contextual Aspects

   Prior art in forwarding solutions for opportunistic networks showed
   that data transmission in such wireless environments needs to be done
   based on strategies that take into consideration, at a network level,
   the context of wireless nodes, and not just the history of contacts
   among wireless nodes.

   This section provides an example on how to obtain contextual
   information that defines the availability and centrality of a
   wireless node, based on a specific operational example that is being
   developed in the context of the H2020 UMOBILE project [17].

   Contextual information is obtained in a self-learning approach, by
   software-based agents running in wireless nodes, and not based on
   network wide orchestration. Contextual agents are in charge of
   computing node and link related costs concerning availability and
   centrality metrics. Contextual agents interact with DABBER via well-
   defined interfaces. This to say that the contextual self-learning
   process is not an integrating part of the routing plane, as it would
   add additional complexity to the simplified routing plane of NDN.

   The contextual agent (named Contextual Manager, CM [7]) installed in
   each wireless node can therefore be seen as an end-user background
   service that seamlessly captures wireless data to characterize the
   affinity network (roaming patterns and peers' context over time and
   space) and the usage habits and data interests (internal node
   information) of a node. Data is captured directly via the regular MAC
   Layer (e.g., Wi-Fi, Bluetooth, LTE) as well as via native
   applications for which the user configures interests or other type of
   personal preferences. For instance, an application can request a one-
   time configuration of categories of data interests (e.g., music,

   Based on the defined interface (cf. section 3.6), DABBER is able of
   querying the local Contextual Manager about the characteristics of
   neighbor nodes, based on three types of information: i) Node

Mendes, et al.         Expires September 1, 2019                [Page 5]

Internet-Draft                   dabber                February 28, 2019

   availability (metric A); ii) Node centrality (metric C); iii)  Node
   similarity (metric S).

   Node Availability (A) gives an estimate of the node availability
   based on the usage of internal resources over time and space, such as
   the time spent per application category (e.g. per day), as well as
   the usage of physical resources (battery status; CPU status, etc).

   Node Centrality (C) provides awareness about the node's affinity
   network neighborhood context. For instance, the more visited networks
   a node has over a period of time, the more central a node is
   (increases the possibility for data transmission); The higher the
   number of connections a node has over a period of time, the more
   central a node is; The higher the node degree of node over a period
   of time, the higher is its centrality; The lower the distances
   traversed by the node are, the higher is its centrality.

   Node similarity (S) provides awareness about a node's similarity
   towards neighbor nodes, based on the assumption that the more similar
   nodes are, the higher the probability of more robust data exchange
   between those nodes. This metric relies on a cosine similarity to
   provide a link cost between peer nodes. In the case of DABBER,
   similarity is computed based on the number of encounters between peer
   nodes and the average duration of such encounters.

   The detailed specification of the contextual manager is out of scope
   of this document. Nevertheless, code for such an agent is being
   provided openly in the context of the H2020 UMOBILE project [7]. What
   is relevant to have in mind, from a routing perspective, is that this
   contextual plane provides weights (A, C and S) to assist the routing
   protocol in ranking next hops, which is an aspect highly relevant in
   the context of multiple path routing. We believe that contextual
   awareness can assist NDN routing schemes in better dealing with
   topological variability, by anticipating changes derived from prior

1.2. Applicability

   DABBER is being developed to allow the deployment of wireless NDN
   networks where nodes and links can be intermittently available, such
   as in the case of emergency situations [25]. From an end-to-end
   perspective we can consider two scenarios: the NDN wireless network
   is at the fringes of the NDN core; the NDN wireless network can
   interconnect different NDN fixed networks.

   While the latter may support applicability scenarios typical of
   Delay-Tolerant Networks  (DTN)[21][22] for instance tunneling traffic
   over an area lacking network deployment, the former allows the

Mendes, et al.         Expires September 1, 2019                [Page 6]

Internet-Draft                   dabber                February 28, 2019

   extension of the applicability of information-centric networking to
   novel scenarios such as affordable pervasive data access, low cost
   extension of access networks, edge computing, and vehicular networks:

   Affordable pervasive data access:
      This scenario encompasses the implementation of NDN in personal
      mobile nodes (e.g. smartphones) allowing users to share data and
      messaging services by exploiting existing intermittent wireless
      connections (e.g. Wi-Fi, Wi-Fi direct) in environment without/or
      limited Internet access.

   Low cost extension of access networks:
      This scenario refers to the usage of wireless nodes (mobile or
      fix) to extend the reach of an NDN networks while reducing CAPEX

   Edge/Fog computing:
      This scenario is related to the efforts being done to bring cloud
      computing closer to the end-users. This scenario encompasses a
      large set of heterogeneous (wireless and sometimes autonomous)
      decentralized nodes able of communicating, directly or via an
      infrastructure, in order to perform storage and processing tasks
      without the intervention of third parties. This scenario deals
      with nodes that might not be continuously connected to a network,
      such as laptops, smartphones, tablets and sensors, as well as
      nodes that may be intermittently available due to scarce
      resources, such as wireless access routers and even Mobile Edge
      Computing (MEC) servers.

   V2X networks:
      This scenario deals with the intermittent connectivity between
      vehicles as well as between vehicles and the infrastructure.

1.3. NFD Adjustment to Opportunistic Networks

   The main functionality of the Named-Data Networking Forwarding Daemon
   (NFD) [7] is to forward Interest and Data packets. This section
   provides a set of design considerations that need to be considered to
   allow the operation of NFD in opportunistic wireless networks. Such
   considerations have been implemented in a new branch of NDN, called
   NDN-OPP [3], which code of available on GitHub

   NDN-OPP introduces a few modifications in the way NFD performs its
   forwarding, by leveraging the concept of Faces in order to adapt the
   operation of the NFD to the intermittent property of wireless
   connections. This is done by the implementation of a new type of
   face, called Opportunistic Face - OPPFace.

Mendes, et al.         Expires September 1, 2019                [Page 7]

Internet-Draft                   dabber                February 28, 2019

   Each OPPFace is based on a system of packet queues to hide
   intermittent connectivity from NFD: instead of dispatching packets
   from the FIB, the OPPFace is able of delaying packet transmission
   until the wireless face is actually connected. OPPFaces are kept in
   the Face Table of the forwarder and their state reflects the wireless
   connectivity status: they can be in an Up or Down state, depending
   upon the wireless reachability towards neighbor nodes. Since packet
   queuing is concealed inside OPPFaces, no other part of the NFD or any
   existing forwarding strategy needs to be changed.

   OPPFaces can be implemented by using any direct wireless/cellular
   communication mode (e.g., Ad-Hoc Wi-Fi, Wi-Fi Direct, D2D LTE, DTN).

   The current operational version of NDN-OPP (V1.0) makes usage of
   group communications provided by Wi-Fi Direct. In this case there is
   a one-to-one correspondence between an OPPFace and a neighbor node.
   In this peer-to-peer scenario, OPPFaces can be used in two
   transmission modes: connection-oriented, in which packets are sent to
   a neighbor node via a reliable TCP connection over the group owner;
   connection-less, in which packets are sent directly to a neighbor
   node during the Wi-Fi direct service discovery phase. In the latter
   case data transmission is limited to the size of the TXT record (900
   bytes for Android 5.1 and above).

   In the peer-to-peer scenario of Wi-Fi direct, DABBER operates as
   follows: routing information is shared among all members of a Wi-Fi
   direct group, while Interest Packets are forwarded to specific
   neighbors. With Dabber it is the carrier of an Interest packet that
   decides which of the neighbors will get a copy of the Interest
   packet. Hence, with the current implementation of NDN-OPP, DABBER
   places a copy of the Interest packet in the OPPFaces of selected
   neighbors. In what concerns the dissemination of routing information,
   it is ensured by: i) node mobility, meaning that nodes carry such
   information between Wi-Fi direct groups; ii) information is passed
   between neighbor groups via nodes that belong to more than one group.

   In a scenario where NDN-OPP would have OPPFaces implemented based on
   a broadcast link layer, such as ad-hoc Wi-Fi, only one OPPFace would
   be created in each node. Such OPPFace would be used to exchange
   packets with any neighbor node, making use of the overhearing
   property of the wireless medium. Since with DABBER, it is the carrier
   that decides which of the neighbors are entitle to get a certain
   Interest packet, DABBER would need to encode in the Interest packet
   information about the ID of the neighbors that should process the
   overheard Interest packet.

   This means that the operation of DABBER is the same independently of
   the nature of the link layer protocol, the only different being the

Mendes, et al.         Expires September 1, 2019                [Page 8]

Internet-Draft                   dabber                February 28, 2019

   number of transmissions that needs to be done at the link layer to
   forward Interest packets and to disseminate routing information.

   Besides the OPPFaces towards neighbor wireless nodes, NDN-OPP makes
   use of the Wi-Fi Face, already defined in NFD, and will integrate the
   DTN Face developed in the UMOBILE project[23]. This means that DABBER
   is able of exploiting any available wireless Face (OPPFace, Wi-Fi
   Face, DTN Face). Future versions of NDN-OPP will allow DAGGER to
   exploit interfaces to other wireless access networks, such as LTE.

   A detailed specification of NDN-OPP and OPPFaces can be found in [3].
   In the remainder document we will refer to OPPFaces, Wi-Fi Faces and
   DTN Faces simply as Faces.

1.4. Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119. In this
   document, these words will appear with that interpretation   only
   when in ALL CAPS. Lower case uses of these words are not to be
   interpreted as carrying significance described in RFC 2119.

2. DABBER Architecture

   This section presents an overview of the overall DABBER protocol
   architecture. The three major considerations to architect DABBER are:

      i) In opportunistic networks it is not possible to know the
      complete network topology. Hence, there is no need to disseminate
      Adjacency information.

      ii) In opportunistic networks it is not efficient to flood the
      network, as shown by all prior solutions based on controlled
      packet replication forwarding ([12][13][14][18][15]) instead of
      broadcast as used in Epidemic routing.

      iii) Selecting the best set of neighbors to replicate packets to,
      may not be efficient if based only on connectivity based
      information (e.g. inter-contact times, contact duration).

   DABBER relies on the same message formats, message exchange process,
   and same data structures (RIB and FIB), made available by NDN, and
   used by NLSR. As shown in figure 1, both protocols are able of
   populating the FIB with a list of next hops towards each name prefix.
   This is done based on the information collected from neighbor nodes
   and stored in the RIB.

Mendes, et al.         Expires September 1, 2019                [Page 9]

Internet-Draft                   dabber                February 28, 2019

                Node A                Node B
             +----------+          +------------+
        N -  |1        2| - N----- |1          2|
             |          |          |            |
             |3        4| - N      |3          4|
             +----------+   |      +------------+
                            |         Node C
                            |       +------------+
                             ------ |1          2|
                                    |            |
                                    |3          4|

                        RIB                                  FIB
           +----------------------------+      +-----------------------+
           |Prefix Name | Face   | Cost |      | Prefix Name |  Faces  |
           +----------------------------+      +-----------------------+
           |     N      |  2     |  3   |      | N           |  2,1,4  |
           |     N      |  4     |  10  |      |             |         |
           |     N      |  1     |  5   |      +---------------------- +

   Figure 1: RIB and FIB Management, node A.

   However, NLSR needs to build a full network topology, based on
   Adjacency Link State Advertisements (LSA), to compute shortest paths
   towards each node in the network (based on a simple extension of the
   Dijkstra's algorithm). After this, NLSR computes shortest paths
   towards each data source by associating each router with name
   prefixes, based on the information exchanged via Prefix LSAs. Such
   name prefixes are ordered in the FIB based on the distance of the
   path towards the data source (shortest first).

   While NLSR relies on the dissemination of Adjacency and Prefixes
   LSAs, DABBER only requires the dissemination of Prefix LSAs and does
   not require the computation of shortest paths: DABBER replaces the
   path cost used by NSLR with a data reachability cost, as described in
   section 2.4, reducing the impact that topological changes would have
   on the stability of routing information.

   The computation of data reachability costs towards different data
   sources, based on the local dissemination of name prefixes, aims to
   avoid flooding the wireless network with Interest packets that would
   otherwise be broadcast to all potential data sources.

2.1. Assumptions and Requirements

Mendes, et al.         Expires September 1, 2019               [Page 10]

Internet-Draft                   dabber                February 28, 2019

   DABBER relies on the following assumptions:

      o Mobile nodes are able of exploiting wireless connectivity. For
      instance having NDN-OPP installed.

      o Mobile nodes can be a source and destination of data, being able
      of operating as a router: there is not a clear distinction, in
      terms of routing process, between sources, destinations, and

   In terms of requirements:

      o LSAs must be exchanged based on Interest / Data messages, as in

      o A synchronization mechanism should be used to exchange LSAs
      among neighbor node, as in NSLR.

      o LSAs should be used to distribute only name prefix reachability,
      since building a network topology based on adjacency information
      is not feasible in an opportunistic network.

      o Multiple next-hops for each name prefix must be computed based
      on local information that encodes data reachability.

      o Link failure recovery must be local and hence, the recovery
      process should be based on the operation of OPPFaces (UP/Down link

      o IP addresses or any other form of addressing a node in the
      network must not be considered, as in NLSR.

      o Selective information diffusion must be considered, in order to
      avoid network flooding.

      o Data sources must set the validity of name prefixes - validity v
      - as an integer that represents the expiration date of the data.

2.2. Naming

   DABBER makes use of NDN hierarchical naming scheme to identify each
   wireless node. This strategy is similar to the one used by NLSR. The
   difference is in the name semantics: being a routing protocol for
   wired networks, NLSR uses names that reflect network structures and
   operational practices, making it easy to identify routers belonging
   to the same network, and operator realms. In NLSR each router is
   named according to the network it resides in, the specific site it

Mendes, et al.         Expires September 1, 2019               [Page 11]

Internet-Draft                   dabber                February 28, 2019

   belongs to, as well as an assigned router name, i.e.,
   /<network>/<site>/<router>. For example, /ATT/AtlantaPoP1/router3.
   This semantics provide additional topological information to the
   routing process.

   With DABBER, we assume that DABBER is installed in mobile devices
   (e.g. smartphones), which have a contract with a mobile operator. In
   a networking environment, a hierarchical naming scheme still makes
   sense to identify to which network operator does the mobile node
   belongs to and to the home site, in case the mobile operator has more
   than one operational site. This naming scheme still makes sense even
   if DABBER is only used to exchange traffic over 802.11, wifi direct
   or 802.11 adhoc links, and never over a cellular interface.

   Since DABBER is used to exchange data directly between mobile nodes
   in an opportunistic networking scenario, it makes use of a
   hierarchical naming scheme that reflects the way mobile roaming
   works: When a mobile node is used outside its home, it attempts to
   communicate with a visited mobile network. The visited network
   recognizes that the node does not belong to any of its networks, and
   checks if there is a roaming agreement between the home network and
   one of the networks of the visited operator. If so the call is routed
   towards an international transit network.

   Based on the operation of a mobile network, the following semantics
   is used to name DABBER nodes:/<network>/<operator>/<home>/<node>,
   where <network> represents the international transit network allowing
   roaming services for the mobile operator; <operator> refers to the
   operator providing the mobile service; <home> is the network site of
   the mobile operator where the node is registered; <node> is the
   mobile equipment.

   The hierarchical name is used to implement a trust model to allow
   nodes to verify the signature of routing messages, as described in
   section 5.

   The information included in the hierarchical name may be used to
   select next hops belonging to the same operator network, or nodes
   that have the same home network. It is assumed that an opportunistic
   wireless network is build based on wireless direct connectivity
   between nodes that may belong to different operators and home
   networks, but that may have roaming patterns that allows them to have
   frequent wireless contacts.

2.3. LSA Dissemination

   DABBER runs on top of NDN, making use of Interest/Data packets to

Mendes, et al.         Expires September 1, 2019               [Page 12]

Internet-Draft                   dabber                February 28, 2019

   exchange LSAs. This means that while IP-based routing protocols push
   updates to other routers, DABBER nodes need to pull the updates.
   DABBER can use any underlay communication channels (e.g., TCP/UDP
   tunnels, Link layer TXT records) to exchange LSA information.

   DABBER benefits from NDN built-in data authenticity: since a routing
   update is carried in an NDN data packet and every NDN data packet
   carries a signature, a DABBER node can verify the signature of each
   LSA message to ensure that it was generated by the claimed origin
   node and was not tampered during dissemination.

   Similarly to what happens with NLSR, DABBER disseminates LSAs via a
   data synchronization mechanism (e.g. ChronoSync [9], PartialSync
   [10]) of the local LSDB.

   The main differences towards NLSR are:

      o Contrary to NLSR, DABBER does not disseminate Adjacency LSAs to
      reflect the status of the links towards neighbor nodes.

      o As NSLR, DABBER advertises Prefix LSAs every time a new name
      prefix is added or deleted to the LSDB. However in the case of
      DABBER, name prefixes are advertised with a cost/metric related to
      the validity of the associated data.

   This peer synchronization approach is receiver-driven, meaning that a
   node will request LSAs only when it has CPU cycles. Thus it is less
   likely a node will be overwhelmed by a flurry of updates. In order to
   remove obsolete LSAs, every node periodically refreshes each of its
   own LSAs by generating a newer version. Every LSA has a lifetime
   associated with it and will be removed from the LSDB when the
   lifetime expires. The LSA format is shown in Figure 2.

        Prefix LSA
     |  LSA  | Number of |Prefix 1|Cost| ... |Prefix N|Cost| Signature |
     |  Name | Prefixes  |        |    |     |        |    |           |

   Figure 2: Prefix LSA format.

   Each LSA used by DABBER has the name
   <network>/<operator>/<home>/<node>/DABBER/LSA/Prefix/<version>. The
   LSA <version> is increased by 1 whenever a node creates a new version
   of the LSA.

   A detailed description of the LSA exchange process is provided in
   section 3.3.

Mendes, et al.         Expires September 1, 2019               [Page 13]

Internet-Draft                   dabber                February 28, 2019

2.4. Multiple path Computation

   As mentioned, DABBER considers that there is a set of potential next-
   hops via which a name prefix N can be reached with a certain cost k.
   This cost k represents the probability of reaching a data object
   identified by N via a Face F, and is related to the time validity of
   the name prefix (v). The rationale for this approach is that the
   selection of faces that have a lower cost k (higher validity v) will
   improve data reachability. The validity of a name prefix is set by
   the data source as an integer that represents the expiration date of
   the data.

   Since different nodes can announce the same name prefix, a certain
   name prefix may be associated with different values of k (as v shall
   differ) over different faces, depending upon the nodes announcing
   such name prefix: this lead to the identification of multiple next
   hops, each one with a different cost.

   The computation of multiple next hops is performed every time DABBER
   has a new Name Prefix LSA (or a new version of an existing Name
   Prefix LSA) in its LSDB (c.f. section 2.3). The sequence of
   operations, as described in the following sub-sections are: Computes
   a new value for the validity of a new Name Prefix in the LSDB;
   Updates DABBER internal routing table; Updates the LSDB with the data
   reachability information (validity) of the current node towards the
   new Name Prefix; Updates the RIB based on the DABBER internal routing
   table, following a Downwards Path Criterion (FIB is updated by NFD
   based on the RIB content). Periodically DABBER will update the
   validity values of all Name Prefixes in its internal routing table,
   performing the consequent updates of the local LSDB and RIB, and

2.4.1. Name Prefix Validity Computation

   When DABBER is notified that a new Prefix LSA was entered in the LSDB
   or an existing Prefix LSA has a new version, it computes a new
   validity for each name prefix in such Prefix LSA.

   DABBER starts by computing a new validity v for a prefix N depending
   upon the validity announced by the neighbor, and the relevancy of the
   "relation" between the two neighbor nodes (e.g., node A and node B).
   The cost of the Name Prefix, passed to NFD, will then be computed as
   an inversely proportional value to its validity.

   The relevancy of the "relation" between two neighbor nodes can be,
   e.g., a measure of similarity [7], where similarity is seen as a link
   measure, i.e., it provides a correlation cost between a node and its
   neighbors. Or such relation can be weighted based, as is common in

Mendes, et al.         Expires September 1, 2019               [Page 14]

Internet-Draft                   dabber                February 28, 2019

   opportunistic environments, on metrics derived from average contact
   duration thus allowing a node to adjust the Name Prefix validity
   based on the probability of meeting the respective neighbor again. In
   the current implementation of DABBER, the "relation" between two
   neighbor nodes is computed based on the three metrics (A, C, and S)
   provided by the local contextual manager, plus a metric computed by
   DABBER itself: the time reachability.

   The variable considered by DABBER for the computation of the validity
   (and cost) of a Name prefix passed by a neighbor Na are:

      o Validity (V) - Represents the expiration date of the data
      associated with the Name Prefix. Currently it is the UNIX
      Timestamp (10 digit integer).

      o Similarity metric (S) towards the neighbor Na, as passed by the
      contextual manager (S >= 0), aiming to select neighbors with whom
      the current node has a good communication link.

      o Availability metric (A) towards the neighbor Na, as passed by
      the contextual manager ( 0 < A < 1), aiming to select neighbors
      able to process Interest packets with high probability.

      o Centrality metric (C) towards the neighbor Na, as passed by the
      contextual manager ( C >= 0), aiming to select neighbors with high
      probability of successfully forwarding Interest packets.

      o Time reachability (T) which corresponds to the RTT between
      sending an Interest packet towards the source of such Name Prefix
      and receiving a data packet. (0 < T < 1). Currently the value of T
      is computed as (current time when data packet of received - time
      when Interest packet was sent) / Validity of Name Prefix. Time
      reachability allows DABBER to select next hops that lead to closer

         Neighbor table
     |   Face     | Status | Metric C | Metric A | Metric S |
     |     1      |    UP  |    6     |   0.3    |    12    |
     |     2      |  DOWN  |    4     |   0.8    |    8     |
     |     3      |    UP  |    1     |   0.8    |    9     |

   Figure 3: Neighbor table.

   The values C, A and S provided by the contextual manager are stored

Mendes, et al.         Expires September 1, 2019               [Page 15]

Internet-Draft                   dabber                February 28, 2019

   in a Neighbor Table as shown in figure 3. Since an OPPFace is created
   by NDN-OPP (c.f. section 1.3), the table is indexed by the number of
   faces. The higher the values of C, A and S, the most preferential a
   neighbor is.

   T is measured by observing the flow of Interest and Data packets.
   Thus, the lowest the T, the most preferential a Face is. Although
   different nodes may have a different implementation of a face ranking
   logic, the relevancy of T in comparison to C and A should be higher,
   since T reflects the measured delay to reach a data source, while C
   and A are indicators of the neighbors potential as relays.

   Based on the above mentioned metrics the Validity of a new Name
   Prefix (V) is updated based on two operations:
      o V' = f (V, S') = trunc (V * S'), where:

         S' = (S - Smin) / (Smax - Smin); Smin = 0 and Smax = max (Smax,

      o V'' = f (V', C', A, T) = 0.3* trunc (V' * (C'+A)) + 0.7 * trunc
      (V' * T), where:

          C' = (C - Cmin) / (Cmax - Cmin); Where Cmin = 0 and Cmax = max
         (Cmax, C)

2.4.2. Update of DABBER internal information

   After the computation of the validity of the Name Prefix taking into
   account the relation of the current node with the neighbor announcing
   it (c.f. section 2.4.1), DABBER updates its internal routing table
   and its LSDB. The information on the routing table will be used to
   updated the RIB of the local NFD and the information of the LSDB will
   be announced to all the neighbor by Chronosync.

   To update the Internal routing table, DABBER adds an entry Na for the
   Name Prefix with a validity V''. The routing table is then ordered by
   name prefix in decreased order of validity.

   To update its local LSDB updated with validity of current node
   towards the Name Prefix, DABBER can use two methods:
      o Maximal method: Name Prefix entry on current node LSA updated
      with max (V'', current value on LSA).

      o Average method: Name Prefix entry on current node LSA updated
      with max ( average (cost of Name Prefix entries on local routing

Mendes, et al.         Expires September 1, 2019               [Page 16]

Internet-Draft                   dabber                February 28, 2019

      table), current value on LSA).

2.4.2. Update of RIB of the local NFD

   After computing the new value of the validity V'' of a name prefix,
   as described in section 2.4.1, DABBER updates the RIB entry of that
   name prefix with the face over which the Name Prefix LSA was received
   and the new cost of such Name prefix. The cost (k) of the Name Prefix
   is computed based on its validity as k = trunc (100/V'').

   DABBER assigns selection logics to name prefix, such as NDN assigns
   forwarding strategies to name prefixes.

   There may be different available logics to choose from:

      o Increase diversity - The new Face is included in the RIB entry,
      if the computed cost k helps to increase diversity of the name
      prefix. For instance the new cost k is higher than the average
      costs already stored for that name prefix, affected by a
      configured diversity constant. This is include all neighbors with
      cost = trunc (100/V''), such that 1/V'' - Avr (Costs in RIB for N)
      > X (predefined value).

      o Downward Path Criterion - It is a non-equal cost multi-path
      logic that is guaranteed to be loop-free. Based on the Downward
      Path Criterion, the X faces (the maximum number X of desirable
      faces can be defined by configuration) to be considered for a name
      prefix include the one with the lowest cost k plus X-1 faces that
      have a cost k lower than the cost that the current node has itself
      to the name prefix. This is include X neighbors with cost =
      trunc(100/V''), such that cost is the lowest value of 1/V'' or
      cost < 1/ V.

      o Downward Path Criterion extension - Also considers any face over
      which the name prefix can be reached with a cost k equal to the
      cost that the current node has itself to the name prefix. To avoid
      packet from looping back, there is the need to add a tiebreaker,
      which assures that traffic only crosses one direction of equal-
      cost links. This is, include X neighbors with cost = trunc
      (100/V''), such that cost is the lowest value of 1/V'' or cost
      <=1/ V.

2.5. Packet Forwarding

   Packets are forwarded based on the information that is stored in the
   FIB, which is updated by the NFD when there is an update of the RIB
   (multicast forwarding strategy used).

Mendes, et al.         Expires September 1, 2019               [Page 17]

Internet-Draft                   dabber                February 28, 2019

   In order to support the operation of NDN in intermittently connected
   networks, a new type of Face was added to NFD, Opportunistic Faces
   (OPPFaces), which allows forwarded packets to be queued, being
   dispatched as soon as a wireless channel is established. The new
   concept of Opportunistic Faces aims to provide support for
   intermittent communications without requiring any other changes to
   NFD itself. This makes co-existence of the opportunistic networks
   side-by-side with traditional communication schemes possible.

   The implementation of the OPPFaces depends upon the specific link
   layer protocols based on two basic policies: In the presence of a
   peer-to-peer link layer protocol, such as Wi-Fi Direct or D2D LTE,
   one OPPFace should be created for each wireless neighbor; In the
   present of broadcast link layer protocols, such as Ad-Hoc Wi-Fi, a
   unique OPPFace should be created.

   The state of an Opportunistic Face reflects the fact that the
   corresponding neighbor device is currently reachable in the Wi-Fi
   Direct range. Based on this information, the Opportunistic Face
   decides whether to simply queue the packet or attempt a transmission
   over the associated Opportunistic Channel.

   Based on the feedback provided by the wireless channel, the Face can
   decide whether to remove the packet from the queue once it has been
   passed on to its intended peer. Furthermore, the Opportunistic Face
   integrates a mechanism to automatically flush the queue whenever the
   Face is brought up upon detection of the corresponding peer being
   available in the same Wi-Fi Direct Group.

2.6. Loop Prevention

   Given the multi-path nature of DABBER, the incoming Face might appear
   among the potential next-hops for a given name prefix. For this
   reason, DABBER applies the Incoming Face Exclusion principle [11] in
   order to prevent forwarding Interest packets back though the Face
   them came from, thus removing two-hop loops.

   Furthermore, in order to detect longer forwarding loops (more than
   two hops), DABBER relies on the nonce-based detection scheme
   available in NDN in order to drop a looping packet as soon as it is
   received the second time.

   In addition, DABBER considers a loop removal mechanism, which takes
   care of disabling the Face responsible for the looping once it is
   detected, as described in section 3.4.

3. Protocol Overview

Mendes, et al.         Expires September 1, 2019               [Page 18]

Internet-Draft                   dabber                February 28, 2019

3.1. Overall Operation Example

   We consider the scenario in Figure 4 to assist in the protocol
   operation overview: namely to understand to role of DABBER to allow
   extension of NDN operation towards wireless dynamic networks. In
   Figure 4, nodes A, B, and C reside in an opportunistic network and
   run DABBER, while nodes E and F are wireless edge routers running
   another NDN routing/forwarding protocol, such as NLSR. G is a
   wireless node running DABBER.

        |    +---+           |
        |    | B | .         |
        |    +---+  .2+---+  |   +---+    +---+     +---+
        |+---+        | C |3 ... | E |....| F  |....| G |
        || A |.......1+---+  |   +---+    +---+     +---+
        |+---+               |

   Figure 4: End-to-end operational example.

   In our example, Node A starts producing some content derived, for
   instance, from the use of an application (such as a data sharing
   application). The produced content is stored in its local Content
   Store with the name /NDN/video/Lisbon/nighview.mpg. Node B stores in
   its Content Store a data object with name
   /NDN/video/Lisbon/river.mpg, which node B received from a neighbor
   (meaning that B have already synchronize its LSDB with such a

   Due to the update of the Content Store, the name prefix
   /NDN/video/Lisbon/ is stored in the LSDB of node A and B with a
   validity of 864000 and 518400 in the case of node A and B
   respectively. In the case of node A, the cost k of the name prefix
   equals the validity v of the data object, e.g., v=864000 seconds (10
   days) stipulated by the application. In the case of node B the
   validity is the result of the computation process described in
   section 2.4.

   From a routing perspective, storing a name prefix in the local LSDB
   allows the node to share the respective Prefix LSA on all its Faces,
   excepting on the Face over which the LSA was previously received, as
   explained in section 3.3. This LSA exchange is done when the OPPFaces
   are up, as described in section 3.2. Node C, which got a new Prefix
   LSA from nodes A and B, will:

      o Update its LSDB with the Prefix LSAs received from node A and
      node B.

Mendes, et al.         Expires September 1, 2019               [Page 19]

Internet-Draft                   dabber                February 28, 2019

      o Update its internal routing table with two new entries for the
      name prefix /NDN/video/Lisbon/, associated with the face towards A
      (face1) and with the face towards B (face2), after computing the
      values of V' and V'' for the received validity values:

         o The validity of the name prefix is updated based on the
         metric configured for node C: average inter-contact time.

         o Let's assume that A and C encounter each other frequently,
         while B and C do not meet frequently. This means that node C
         stores 2 new entries for prefix /NDN/video/Lisbon/ in its
         internal routing table related to face2 with a validity for A
         higher than the one for B.

      o Update its LSDB with the validity of the current node towards
      the Name Prefix following the maximal or average methods (c.f.
      section 2.4.2).

      o Update the RIB with one new entry for the name prefix
      /NDN/video/Lisbon/ with two faces (face 1 and face 2) with a cost
      inversely proportional to the validity of the Name Prefix.

   Based on the status of the FIB (updated based on the status of the
   RIB) all interest packets that node C gets for the name prefix
   /NDN/video/Lisbon/ will be forwards to the number of faces associated
   to the used forwarded strategy, but respecting the ranking of faces
   done by DABBER.

   When node C gets in the range of router E (wireless edge router) it
   will exchange disseminate routing information, based on some
   interoperability issues need to be considered, as described in
   section 4.

3.2. Peer Discovery and Face Setup

   In an opportunistic network DABBER needs to manage the dynamic
   connectivity among neighbor nodes. For this proposes the DABBER
   protocol relies on a background process, the Connectivity Manager.

   The current version of DABBER comes with a Connectivity Manager for
   Wi-Fi Direct. However, such connectivity manager can be easily
   extended to integrate other type of wireless or cellular support. The
   description provided in this sub-section is adjusted to the case of
   Wi-Fi Direct.

   When booted, the Connectivity Manager starts reacting to changes in
   the peers available within scanning range of the current node. It
   oversees managing the connection to a Wi-Fi Direct Group and

Mendes, et al.         Expires September 1, 2019               [Page 20]

Internet-Draft                   dabber                February 28, 2019

   automatically joins a Group if it is not part of one.

   Upon the reception of notifications regarding changes in the peers
   detected in the neighborhood, the Connectivity Manager updates its
   internal peer list. If it is not currently connected to a Wi-Fi
   Direct Group, it performs a selection heuristic to determine which
   node to connect to. The motivation behind this selection process is
   to attempt to minimize the number of Wi-Fi Direct Groups in a certain
   area given that nodes can only transmit packets within the Group they
   are currently connected to.

   The heuristic simply favors whichever Group Owner is already detected
   among the available peers. In the case there is exactly one Group
   Owner, the current node attempts to join its Group. If more than one
   or no Group Owners are available, the heuristic selects the non-
   client node with the highest UUID. If the selected node is not the
   current node, a connection is attempted. This heuristic guarantees
   that the current node will never attempt to connect to a client, thus
   breaking an existing Group. Also, all nodes located in an area, and
   that have the same view of available peers, will all select the same
   node as the Group Owner to which connection should be attempted.

   For each node detected in a Wi-Fi Direct Group, a new instance of an
   OPPFace is created. The status of an OPPFace tells us if the
   connectivity link towards a specific node is up or down. Based on
   this information, the OPPFace decides whether to simply queue packets
   (when OPPFace is down) or flush the queue (when OPPFace is up).

   In order to achieve this, whenever the node joins a Wi-Fi Direct
   Group, it gets registered in the Group so that other nodes can send
   packets to it. After this setup, all service changes detected within
   the Group (connectivity up or down) are reflected into the Neighbor
   Table (c.f. Figure 3). Upon disconnection from the Group, the node is
   unregistered and the node returns to a state of waiting for a Group
   to be joined.

3.3. Peer Communication Modes

   This section describes the two communication methods implemented to
   allow for direct communication between wireless neighbors over Wi-Fi
   Direct: connection-oriented and connectionless.

   The connection-oriented solution allows peers to exchange packets by
   means of a reliable TCP connection established over the Wi-Fi direct
   group owner. This type of communication system is used mostly for
   large packets that may require reliable communication. The
   connection-oriented solution requires the formation of a Wi-Fi direct
   group by the connectivity manager. Once a device joins to the group,

Mendes, et al.         Expires September 1, 2019               [Page 21]

Internet-Draft                   dabber                February 28, 2019

   it will receive a list containing information related to each
   connected device. Since we are working with opportunistic networks,
   it is common that some devices could join or leave the group
   frequently. In order to deal with it, the group owner is also
   responsible to keep the list of connected devices updated.

   The connection-less communication method allows peers to exchange
   packets directly without the establishment of any Wi-Fi direct group,
   by exploiting the TXT records available during the Wi-Fi Direct
   service discovery phase. This type of communication is used to
   exchange small packets that require fast transmission (e.g. emergency
   apps, Chronosync status messages). The connection-less solution
   allows peers to exchange a short number of bytes without the
   establishment of a TCP socket. To use this methodology, each device
   has to listen to all announced UUID related with it. Every time that
   a device needs to send a packet, it serializes the packet and starts
   announcing it, during the service discovery exchange, over TXT Record
   with the UUID of the destination. Android versions above 5.1 allow
   the transfer of up to 900 bytes.

   In order to implement a reliable connection-less solution, the
   Connectivity Manager maintains a TXT Record for each intended
   recipient of packets, which contains data packets and an
   acknowledgement list. Since the sequence and order in which devices
   probe and respond to one another is not controlled, a device might
   perform the acknowledgement of a given packet received from a remote
   peer, but might receive the packet again in the next TXT Record in
   the event the remote peer does not successfully probes the current
   device to get the pending acknowledgements.

   The decision of using a connection-oriented or connection-less
   communication is based on the following reasoning:
      o Hypothesis 1: Packets are exchanged between two wireless peers
      over a reliable TCP socket is such socket already exists;

      o Hypothesis 2: If a TCP connection does not exist, decision is
      take based on packet size. The connection-less mechanism is used
      for fast dispatching of small packets (limited to the size if the
      TXT record, which depends upon the Android version; Bigger packets
      will require the establishment of a reliable TCP connection over
      the Wi-Fi direct group owner.

3.4. Multi-homing Wireless Communication

   Although DABBER is being specified for the operation of NDN
   opportunistic wireless networks, wireless devices can exploit the
   present of Wi-Fi infrastructure connections made available by a
   nearby Wi-Fi Access Point.

Mendes, et al.         Expires September 1, 2019               [Page 22]

Internet-Draft                   dabber                February 28, 2019

   For this propose, beside using the new OPPFaces , DABBER also makes
   use of the Wi-Fi Face previously implemented in NFD. The Wi-Fi face
   may provide higher communication resilience and lower delays, as well
   as the possibility for wireless devices to exchange data with
   standard NDN devices deployed in a faraway location.

   Currently DABBER allows packets to be forwarded to a subset of
   available faces (OPPFaces, and Wi-Fi Faces). A more static
   alternative can be to avoid replicating Interest packets among
   wireless peers devices when a Wi-Fi network is available.

   It is expected that NDN-aware Access Points will be able to provide
   wireless devices with the IP address of the local NDN router within
   wireless beacons. In the current version this information is made
   available during the configuration phase. By default, the system is
   configured to connect to the NDN router deployed in COPELABS, but
   another NDN router may be selected.

3.5. LSA Exchange

   DABBER performs the dissemination of LSAs based on a process able of
   synchronizing the content of LSDBs. In this sense, all LSAs are kept
   in the LSDB as a name set, and DABBER uses a hash of the LSA name set
   as a compact expression of the set. Neighbor nodes use the hashes of
   their LSA name sets to detect inconsistencies in their sets. For this
   reason, neighbor nodes exchange hashes of the LSDB as soon as
   OPPFaces are UP.

   Current version of DABBER makes use of ChronoSync as synchronization
   mechanism. Chronosync allows DABBER to define a collection of named
   data in a local repo as a slice. LSA information are synchronized
   among neighbor nodes, since Chronosync keeps the repo slice
   containing the LSA information in sync with identically defined
   slices in neighboring repositories.

   If a new LSA name is detected in a repo, ChronoSync notifies DABBER
   to retrieve the corresponding LSA in order to update the local LSDB.
   DABBER can also request new LSAs from Chronosync when resources (e.g.
   CPU cycles) are available.

   Figure 5 shows how an LSA is disseminated between two neighbor nodes
   A and B, when the OPPFace is UP. To synchronize the slice
   representing the LSDB information in the repo, ChronoSync, on each
   node, periodically sends Sync Interests with the hash of its LSA name
   set / slice (step 1). When Node A has a new Prefix LSA in its LSDB,
   DABBER writes it in the Chronosync slice (step 2). At this moment,
   the hash value of the LSA slide of node A becomes different from that

Mendes, et al.         Expires September 1, 2019               [Page 23]

Internet-Draft                   dabber                February 28, 2019

   of node B. As a consequence, the Chronosync in node A replies to the
   Sync Interest of node B with a Sync Reply with the new hash value of
   its local LSA slice (step 3). The Chronosync in node B identifies the
   LSA that needs to be synchronized and notifies DABBER about the
   missing LSA, and updates its LSA name set (step 4). Since DABBER on
   node B has been notified of the missing LSA, DABBER sends an LSA
   Interest message to retrieve the missing LSA (step 5). DABBER on node
   A sends the missing data in a LSA Data message (step 6).  When DABBER
   on node B receives the LSA data, it inserts the LSA into its LSDB.
   Chronosync on nodes A and B compute a new hash for updated the set
   and send a new Sync Interest with the new hash (step 7).

         Node A                            Node B
     +----------------------------+     +----------------------------+
     |            +-------------+ |     |+-------------+             |
     |    DABBER  |  Chronosync | |     ||  Chronosync |   DABBER    |
     |            +-------------+ |     |+-------------+             |
     +----------------------------+     +----------------------------+
            |            |  Sync Interest (1) |              |
            |            |------------------->|              |
            |            |<-------------------|              |
            | New LSA (2)|                    |              |
            |----------> |                    |              |
            |            |    Sync Reply (3)  |              |
            |            |------------------->|              |
            |            |                    |  Notify (4)  |
            |            |                    |------------->|
            |            |   LSA Interest (5) |              |
            |            |   LSA Data (6)     |              |
            |            |                    |              |
            |            |  Sync Interest (7) |              |
            |            |------------------->|              |
            |            |<-------------------|              |

   Figure 5: LSA exchange process.

   When more than one LSA needs to be synchronized, the issued LSA
   Interest packet will contain information about as many LSAs as
   allowed by the Link maximum transmission unit. In the same sense one
   LSA Data packet may include also be used to transport information
   about more than one LSA.

3.6. Loop Avoidance

   In addition to the loop avoidance mechanism of NDN, DABBER considers
   a loop removal mechanism, which takes care of disabling the Face

Mendes, et al.         Expires September 1, 2019               [Page 24]

Internet-Draft                   dabber                February 28, 2019

   responsible for the looping once it is detected.

3.7. Failure and Recovery

   As described in section 3.2, DABBER relies on a connectivity manager
   that is able to react to changes in the peers available within the
   wireless scanning range of the current node.

   Upon detection of a Wi-Fi Direct Group, the connectivity manager
   automatically joins that Group, if it is not part of one.

   Upon the reception of notifications regarding changes in the peers
   detected in the neighborhood, the Connectivity Manager updates its
   internal peer list.

3.8. Interface towards a Contextual Agent

   The interface between DABBER and CM provides the former with periodic
   information concerning a node's centrality (C) and a node's
   availability (A), as well as with a similarity weight (S) between
   peers (link relevancy).

   This interface integrates premises to perform specific requests to
   get the computed values C and A for a list of peers provided by
   DABBER. The peers are identified by hashed MACs.

   The interface integrates also a premise to provide a similarity
   weight (S) between two peers passed by DABBER to the CM. For
   instance, if DABBER requests similarity between node A (sender) and
   node B (potential successor), then the CM computes similarity for
   both nodes based on a specific period of time. Such analysis can
   assist in a better selection of peers for data transmission, for

3.9. Adjustment to data source mobility

   As NDN uses a publish/subscribe communication model, where request
   resolution and data transfer are decoupled, it is especially relevant
   to solve the problem of data source mobility. Supporting data source
   mobility requires, first of all, finding the new location of the
   source each time data sources move, and, second, updating the name
   resolution system according to the new location, in order to maintain
   the consistency of NDN forwarding.

   This sub-section described a new feature of DABBER which follows a
   new reactive approach to face the challenges of the data source
   mobility and consistent forwarding in Mobile ICNs. To this end,
   DABBER is using the efficient dissemination method for Opportunistic

Mendes, et al.         Expires September 1, 2019               [Page 25]

Internet-Draft                   dabber                February 28, 2019

   Networks [26] to efficiently discover data sources by replicating
   Interest messages in an efficient way that avoids network flooding.

   With this new feature the prospective forwarders for a given Interest
   message (which are denoted as discoverers) are limited in number and
   carefully selected in terms of three criteria:

      o Centrality: how well connected a node is in the network. The
      more central a node is, the bigger the chances are to find a data

      o Reliability: the likeliness a node does not drop messages. The
      more reliable a node is, the least probable is that the Interest
      message will be discarded.

      o Similarity: how alike the contacted candidate node is in terms
      of shared acquaintances. The less similar, the more likely is that
      it will find different nodes in the future.

   A combination of these three criteria defines a reward function
   (discoverer suitability) of an Optimal Stopping (OS) problem. If a
   node finds a new node with a certain value for the discoverer
   suitability it is difficult to know whether this value is a good one
   when compared with what a node could find in future contacts. This
   decision is not trivial: if a node chooses early-contacted discoverer
   candidates, good results are not guaranteed because selected
   discoverers could have a low discoverer suitability metric. On the
   other end of the spectrum, selecting late-contacted discoverer
   candidates does not guarantee either good discoverer nodes since it
   is likely that good candidates with high discovery suitability values
   would be skipped.

   DABBER is so extended with the ability to perform an OS-based
   strategy that allows nodes to select the most suitable node among all
   of the contacted ones to forward the Interest message. This strategy
   relies on the existence of an optimal set of stopping values such
   that the nth discoverer node for a certain Interest message is the
   first contacted node which is the best of all the previously explored
   nodes, if the node has contacted the first stopping value. If this
   node is not found, then it will be the first node which is the second
   best of all the previous nodes, if the node has contacted the second
   stopping value, and so on. Otherwise, if these nodes are not found,
   then, the nth discoverer node will be the last nth node before
   reaching the last contacted node. This makes the dissemination of the
   Interest messages in Mobile NDNs efficient, even, and pervasive all
   over the network, increasing the delivery ratio while decreasing the
   network overhead.

Mendes, et al.         Expires September 1, 2019               [Page 26]

Internet-Draft                   dabber                February 28, 2019

4. Interoperability

   As mentioned in section 1.2 DABBER is being developed to allow the
   deployment of wireless NDN networks where nodes and links can be
   intermittently available. In this section we analyze the
   interoperability of DABBER in two scenarios: the NDN wireless network
   is at the fringes of a wired NDN core; the NDN wireless network can
   interconnect topologically separated NDN networks or hosts, via a

4.1. Interoperability with NDN operation over DTNs

   In this sub-section, we review the deployment of DABBER over existing
   DTNs. We only consider deployment scenarios where NDN is deployed as
   an overlay over a DTN. In this case, the existing DTN infrastructure
   and implementation are leveraged to extend NDN operation in
   challenged networks. We consider scenarios such as data mulling,
   services to remote locations, and interconnecting different NDN hosts
   (fixed or mobile)[23].

   In such challenged network topologies, OPPFaces may not be able to
   cope well with long delays or disruption due to frequent
   disconnections and node mobility, severely hampering network
   operations. A DTN face integrated into NDN-OPP provides the latter
   with a robust communications platform supporting communications in
   these conditions, by providing the option to propagate Interests to,
   and return Data from, remote NDN hosts or networks. These are assumed
   to typically reside in access points and wireless edge routers, or
   mobile devices and have a corresponding DTN face implementation.

   DABBER will employ the DTN face, either in a hop-by-hop or a multi-
   hop fashion, when it senses, through the connectivity manager, that
   the OPPFaces do not provide a high probability of successful data
   delivery (e.g. Time-to-completion is too high). As DTN faces operate
   as regular faces, multiple path computation is performed using the
   procedure described in section 2.4.

4.2. Interoperability with NDN operation in wired networks

   In this sub-section we analyze the interoperability of DABBER with
   two potential configurations of an NDN access network based on: a
   routing protocol able of disseminating name prefix information, such
   as NLSR; a broadcast based forwarding approach.

4.2.1. Interoperability with NLSR

   The LSA dissemination mechanism described in section 3.3 is used to
   ensure interoperability with NLSR. Such mechanism ensures the

Mendes, et al.         Expires September 1, 2019               [Page 27]

Internet-Draft                   dabber                February 28, 2019

   interoperability between a DABBER node and a NLSR edge router, since
   the specification used by DABBER follows the same message structure
   and sequence of the mechanism used by NLSR [19][20].

   However, when DABBER is executing the LSA dissemination procedure
   over a Wi-Fi face (towards a NLSR edge router), the following updates
   to the procedure described in section 3.3 need to be done in order to
   account for the changes between DABBER and NLSR as stated in section
      o DABBER will ignore all notifications that Chronosync will send
      related to Adjacency LSAs.

4.2.2. Interoperability with broadcast based forwarding

   Broadcast-based forwarding is a common mechanism in the design of
   some networks, such as switched Ethernet and mobile ad-hoc networks.
   In NDN networks this means that NFD broadcasts Interest packets that
   do not match an entry in the FIB, inserting then into the FIB the
   forwarding path learned through observation of Data return paths. The
   main challenge in broadcast based forwarding schemes is the prefix
   granularity problem: determine the name prefix of an inserted FIB
   entry from the Data name. Several solutions exist [16], including the
   announcements of name prefixes, as done by DABBER.

   In any case DABBER interoperability with such NDN networks relies on
   the following considerations:

      o When in contact with a wireless edge router, DABBER always
      forward Interest packet towards the Wi-Fi Face, even when the
      Interest packet does not match an entry in the FIB. o Interest
      packets received from a wireless edge router will not be
      broadcast. Interest packets will be forwarded if they match an
      entry in the FIB, or dropped otherwise.

5. Security Considerations

   As happens with NLSR, DABBER routing messages are carried in NDN data
   packets containing a signature. Hence, a DABBER node can verify the
   signature of each routing message to ensure that it was generated by
   the claimed origin node and was not tampered with during
   dissemination. For this propose, DABBER makes use of a hierarchical
   trust model for routing, as used by NLSR within a single domain, to
   verify the keys used to sign the routing messages.

   Following the name structure described in section 2.2, DABBER models
   the trust management as a five-level hierarch, as in NLSR, although
   reflecting a different administrative structure: <network> represents
   the authority responsible by the international transit network

Mendes, et al.         Expires September 1, 2019               [Page 28]

Internet-Draft                   dabber                February 28, 2019

   allowing roaming services; <operator> represents the operator
   providing the mobile service; <home> represents the network site of
   the mobile operator where the node is registered; <node> represents
   the mobile equipment. Each node can create a DABBER process that
   produces LSAs.

   With this hierarchical trust model, one can establish a chain of keys
   to authenticate LSAs. Specifically, a LSA must be signed by a valid
   DABBER process, which runs on the same node where the LSA was
   originated. To become a valid DABBER process, the process key must be
   signed by the corresponding node key, which in turn should be signed
   by the registered home network of the network operator. Each home
   network key must be signed by the operator key, which must be
   certified by the network authority using the network key, which is
   called trust anchor in NDN.

   Since keys must be retrieved in order to verify routing updates,
   DABBER allows each node to retrieve keys from its neighbors. This
   means that a DABBER node will use the NDN Interest/Data exchange
   process to gathers keys from all its direct neighbors. Upon the
   reception of an Interest of the type /<network>/broadcast/KEYS each
   neighbor looks up the requested keys in their local key storage and
   return the key if it is found. In case a neighbor does not have the
   requested key, the neighbor can further query its neighbors for such
   key. The used key retrieval process makes use of a broadcast
   forwarding strategy, stopping at nodes who either own or cache the
   requested keys.

6. Implementation and Deployment Experience

   DABBER is implemented as the routing scheme for the NDN framework for
   Opportunistic Networks (NDN-OPP) [3]. NDN-OPP is an extension of the
   NDN Android implementation, aiming to support NDN communication in
   wireless networks by exploiting direct communication between wireless
   nodes, as well as intermittent Wi-Fi connectivity to the Internet
   (NDN global test-bed).

   NDN-OPP has been demonstrated in ACM ICN 2017 in Berlin [4], as well
   as in the NDNComm in Memphis [5]. NDN-OPP code is available in
   GitHub: https://github.com/COPELABS-SITI/ndn-opp

6.1  Improvement of Network Service Discovery

   This section provides information about a set of improvements that
   were included in the operation of Wi-Fi Direct during the development
   of DABBER. Such improvements are related to the operation of the
   Network Service Discovery mechanism.

Mendes, et al.         Expires September 1, 2019               [Page 29]

Internet-Draft                   dabber                February 28, 2019

   NSD gives access to services that other devices provide on a local
   network. NSD implements the DNS-based Service Discovery (DNS-SD)
   mechanism, which allows services to be requested by specifying their
   type and the name of a device instance that provides the desired
   service. DNS-SD is supported both on Android and on other mobile

   NSD was also implemented on NDN-OPP, were it is responsible for
   detecting other devices that are using NDN-OPP via a Wi-Fi Direct

   After a set of tests, the DNS-SD library revealed some flaws: it was
   noticed that in some old versions of Android, sometimes devices could
   not get registered. This means that such devices could not be
   discovered. Moreover, registration and discovering processes revealed
   to be too slow. For that reason, NSD service should be running all
   the time, not only to detect new devices but also device
   disconnections. Once NDN-OPP deals with opportunistic communications,
   it should be capable of performing such processes quickly.

   Hence, in order to solve these issues, we developed a NSD similar
   implementation, based on the following guidelines: since a device
   joins a Wi-Fi Direct network, that device already knows the group
   owner's IP address. Then, we use this information to build a solution
   based on sockets, which has higher performance. Our solution
   implementation has four main components. All of them are explained in
   the next sub-sections.

6.1.1. Peer Registration Service

   The registration service allows devices in a Wi-Fi group to discover
   NDN-OPP peers by sharing information via the group owner. When a Wi-
   Fi Direct connection is performed successfully, the device that
   performed this connection only knows the group owner's IP address. In
   order to be discovered, this device must advertise that it already
   joined the network. In order to do that, the device should make its
   IP address and UUID available in the group. These data is
   encapsulated in an NsdInfo object that is serialized and then sent
   over a socket to the group owner: the register service remains
   sending this object in configured time intervals.

   If the Wi-Fi Direct connection goes down, the mechanism that sends
   these objects stops. Then, eventually the Disconnect Detector Service
   classifies this device as a disconnected device.

6.1.2. Peer Announcement Service

Mendes, et al.         Expires September 1, 2019               [Page 30]

Internet-Draft                   dabber                February 28, 2019

   This component is responsible to guarantee communications among all
   connected peers. In order to do that, the Discovery Service uses a
   socket system: when a device tries to register itself, it starts by
   sending, to the group owner, a NSD packet containing its personal
   information. The Announcement Service, which runs on the group owner,
   receives this packet through a socket and will notify all registered

6.1.3. Leader Service

   This service is instantiated only by the group owner. The group owner
   is responsible to keep the list of connected devices consistent and
   updated. In order to do that, when a device joins a network and
   registers itself, the group owner will be notified. The Leader
   Service will receive the UUID and IP address of the registered device
   and then, if that device is not already in the list, the Leader
   Service will add it, and also notify all connected devices in order
   to keep them updated.

   The periodical registration requests are sent by the Register Service
   in order to inform the Leader Service that this device is still
   alive. Also a copy of these requests is sent to Disconnect Detector
   Service that decides when a device is considered disconnected.

   When a device is considered disconnected, the Disconnect Detector
   Service notifies the Leader Service saying that this device is
   considered disconnected. At that moment, the Leader Service removes
   that device from the list of connected devices, and notifies all
   connected devices.

6.1.4. Disconnect Detector Service

   Since the group owner does not know when a device leaves the network,
   we developed an additional component to deal with it. The Disconnect
   Detector Service is responsible to define when a device is considered
   disconnected from the network.

   The Disconnect Detector Service runs periodically, incrementing a
   counter per each device. When this counter achieves a pre-configured
   number, that device is considered disconnected; The Disconnect
   Detector Service notifies the Leader Service that such device is
   disconnected. This notification is performed through onPeerLost

   The reset of this counter is performed every time the Leader Service
   receives a register request from that device.

Mendes, et al.         Expires September 1, 2019               [Page 31]

Internet-Draft                   dabber                February 28, 2019

7. Acknowledgments

   The research leading to these results received funding from the
   European Union (EU) Horizon 2020 research and innovation programmer
   under grant agreement No 645124(Action full title: Universal, mobile-
   centric and opportunistic communications architecture, Action
   Acronym: UMOBILE).

   We thank all contributors, as well as the valuable comments offered
   by Lixia Zhang (UCLA) and Lan Wang (University of Memphis) to improve
   this draft.

8.  References

8.1  Normative References

   [1] Lixia Zhang, Deborah Estrin, Jeffrey Burke, Van Jacobson, James
        D. Thornton, Diana K. Smetters, Beichuan Zhang, Gene Tsudik, KC
        Claffy, Dmitri Krioukov, Dan Massey, Christos Papadopoulos,
        Tarek Abdelzaher, Lan Wang, Patrick Crowley, Edmund Yeh "Named
        Data Networking", NDN Technical Report NDN-001, October 2010.

   [2] A. Afanasyev, J. Shi, B. Zhang, L. Zhang, I. Moiseenko, Y. Yu, W.
        Shang, Y. Li, S. Mastorakis, Y. Huang, J. P. Abraham, E.
        Newberry, S. DiBenedetto, C. Fan, C. Papadopoulos, D. Pesavento,
        G. Grassi, G. Pau, H. Zhang, T. Song, H. Yuan, H. B. Abraham, P.
        Crowley, S. O. Amin, V. Lehman, M. Chowdhury, and L. Wang, "NFD
        Developer's Guide", NDN, Technical Report NDN-0021, February

   [3] Miguel Tavares, Paulo Mendes, "NDN-Opp: Named-Data Networking in
        Opportunistic Networks", Technical Report COPE-SITI-TR-18-01,
        January 2018.

8.2  Informative References

   [4] Seweryn Dynerowicz, Paulo Mendes, "Named-Data Networking in
        Opportunistic Networks", in ACM ICN, Berlin, Germany, September

   [5] Seweryn Dynerowicz, Omar Aponte, Paulo Mendes, "NDN Operation in
        Opportunistic Wireless Networks", in NDNcomm, Memphis, USA,
        March 2017

   [6] Christos-Alexandros Sarros, Sotiris Diamantopoulos, Sergi Rene,
        Ioannis Psaras, Adisorn Lertsinsrubtavee, Carlos Molina-Jimenez,
        Paulo Mendes, Rute Sofia, Arjuna Sathiaseelan, George Pavlou,

Mendes, et al.         Expires September 1, 2019               [Page 32]

Internet-Draft                   dabber                February 28, 2019

        Jon Crowcroft, Vassilis Tsaoussidis, "Connecting the Edges: A
        Universal, Mobile centric and Opportunistic Communications
        Architecture", IEEE Communication Magazine, February 2018

   [7] Rute C. Sofia, Igor Santos, Jose Soares, Sotiris Diamantopoulos,
        Christos-Alexandro Sarros, Dimitris Vardalis, Vassilis
        Tsaoussidis, Angela; d'Angelo, "UMOBILE D4.5 - Report on Data
        Collection and Inference Models" Technical Report, September

   [8] NDN Project, "NFD Developer's Guide", Technical Report NDN-0021,
        October 2016.

   [9] Zhenkai Zhu and Alexander Afanasyev, "Let's ChronoSync:
        Decentralized Dataset State Synchronization in Named Data
        Networking", in Proc. IEEE ICNP, Goettingen, Germany, Oct 2013

   [10] Minsheng Zhang, Vince Lehman, and Lan Wang, "PartialSync:
        Efficient Synchronization of a Partial Namespace in NDN", NDN
        Technical Report NDN-0039, June 2016.

   [11] Klaus Schneider, Beichuan Zhang, "How to Establish Loop-Free
        Multipath Routes in Named Data Networking", NDN Technical Report
        NDN-0044, April 2017.

   [12] A. Lindgren, A. Doria, E. Davies, S. Grasic, "Probabilistic
        Routing Protocol for Intermittently Connected Networks, IETF RFC
        6693, Aug 2012.

   [13] Waldir Moreira, Paulo Mendes, Susana Sargento, "Social-aware
        Opportunistic Routing Protocol based on User's Interactions and
        Interests", in Proc. of AdhocNets, Barcelona, Spain, October

   [14] Waldir Moreira, Paulo Mendes, Susana Sargento, "Opportunistic
        Routing based on daily routines", in Proc. of IEEE WoWMoM
        workshop on autonomic and opportunistic communications, San
        Francisco, USA, June, 2012

   [15] P. Hui, J. Crowcroft, and E. Yoneki, "Bubble rap: social-based
        forwarding in delay tolerant networks," Mobile Computing, IEEE
        Transactions on, vol. 10, pp. 1576-1589, November, 2011.

   [16] Junxiao Shi, Eric Newberry, Beichuan Zhang, "On Broadcast-based
        Self-Learning in Named Data Networking", in Proc. Of IFIP
        Networking, Stockholm, Sweden, June 2017

   [17] The H2020 UMOBILE project. Grant number 645124, 2015-2018.

Mendes, et al.         Expires September 1, 2019               [Page 33]

Internet-Draft                   dabber                February 28, 2019

        Available via http://www.umobile-project.eu/

   [18] Waldir Moreira, Paulo Mendes and Eduardo Cerqueira,
        "Opportunistic Routing based on Users Daily Life Routine", IETF
        Internet Draft (draft-moreira-dlife-04), May 2014

   [19] Vince Lehman, A K M Mahmudul Hoque, Yingdi Yu, Lan Wang,
        Beichuan Zhang, Lixia Zhang "A Secure Link State Routing
        Protocol for NDN", NDN Technical Report NDN-0037, January 2016.

   [20] Vince Lehman, Muktadir Chowdhury, Nicholas Gordon, Ashlesh
        Gawande, "NLSR Developer's Guide", November 2017.

   [21] V. Cerf, S. Burleigh, A. Hooke, L. Torgerson, R. Durst, K.
        Scott, K. Fall, H. Weiss, "Delay-Tolerant Networking
        Architecture", IETF RFC 4838, April 2007

   [22] K. Scott, S. Burleigh, "Bundle Protocol Specification", IETF RFC
        5050, November 2007

   [23] C.A. Sarros, A. Lertsinsrubtavee, C. Molina-Jimenez, K.
        Prasopoulos, S. Diamantopoulos, D. Vardalis, A. Sathiaseelan,
        "ICN-based Edge Service Deployment in Challenged Networks"
        (demo), in Proceedings of the 4th ACM Conference on Information-
        Centric Networking, Berlin, Germany, September 26-28, 2017

   [24] Paulo Mendes, Rute Sofia, Vassilis Tsaoussidis, Sotiris
        Diamantopoulos, Christos-Alexandros Sarros, "Information-centric
        Routing for Opportunistic Wireless Networks", in ACM ICN,
        Boston, USA, September 2018.

   [25] Miguel Tavares, Omar Aponte, Paulo Mendes, "Named-data Emergency
        Network Services", in ACM MOBISYS, Munich, Germany, June 2018.

   [26] Borrego, Carlos, Joan Borrell, and Sergi Robles. "Efficient
        broadcast in opportunistic networks using optimal stopping
        theory." Ad Hoc Networks 88 (2019): 5-17

Authors' Addresses

   Paulo Mendes
   Airbus Defence and Space GmbH
   Willy-Messerschmitt Strasse 1
   82024 Taufkirchen
   Email: paulo.mendes@airbus.com

Mendes, et al.         Expires September 1, 2019               [Page 34]

Internet-Draft                   dabber                February 28, 2019

   URI: http://www.paulomilheiromendes.com

   Rute Sofia
   COPELABS, University Lusofona
   Campo grande 376
   1749-024 Lisboa
   Email: rute.sofia@ulusofona.pt
   URI: http://www.rutesofia.com

   Vassilis Tsaoussidis
   Democritus University of Thrace
   University Campus
   69100 Komotini
   Email: vtsaousi@ee.duth.gr

   Sotiris Diamantopoulos
   Democritus University of Thrace
   University Campus
   69100 Komotini
   Email: diamantopoulos.sotiris@gmail.com

   Christos-Alexandros Sarros
   Democritus University of Thrace
   University Campus
   69100 Komotini

   Carlos Borrego
   Department of Information and Communications Engineering
   Autonomous University of Barcelona
   08193 Bellaterra

   Joan Borrell
   Department of Information and Communications Engineering
   Autonomous University of Barcelona
   08193 Bellaterra

Mendes, et al.         Expires September 1, 2019               [Page 35]