HAW Hamburg

Berliner Tor 7 Hamburg D-20099 Germany +4940428758067 Cenk.Guendogan@haw-hamburg.de

HAW Hamburg

Berliner Tor 7 Hamburg D-20099 Germany t.schmidt@haw-hamburg.de http://inet.haw-hamburg.de/members/schmidt

link-lab & FU Berlin

Hoenower Str. 35 Berlin D-10318 Germany mw@link-lab.net http://www.inf.fu-berlin.de/~waehl

ICN Research Group Constrained IoT devices often operate more efficiently in a loosely coupled environment without maintaining end-to-end connectivity between nodes. Information Centric Networking naturally supports this demand by replicated data distribution and hop wise forwarding. This document outlines a deployment option for NDN in low-power and lossy networks (LLNs) that follows a publish-subscribe pattern. The proposed protocol scheme simplifies name-based routing significantly and facilitates even large off-duty cycles for constrained nodes.

In the emerging Internet of Things (IoT), it is expected that large quantities of very constrained sensors and actuators collect, communicate, and process massive amounts of machine data. Early experiments with constrained nodes show promising results for different deployments of ICN communication . Characteristics of constrained nodes: Battery-powered with sleep cycles Failing nodes Low power lossy networks Challenges of NDN deployment Complexity of name-based routing State management at nodes Clear separation between control and data plane Adaptation to constrained wireless transmission Mobility management

Multiple scenarios have been discussed in and that evaluate the applicability of ICN in IoT. We consider two characteristic constrained IoT scenarios with the enumerated challenges: for home, building, and factory automation, stationary monitoring, ... Reliability, resilience of operation Radio coordination, coverage Energy constraints, device lifetime Interference with rivaling appliances for urban or rural mobility and sensing, industrial Internet in widespread environments, disaster recovery and rescue ... Exploit connectivity when available Large off-duty cycles of nodes Partitioned networks Limited dependability Environmental impact and disturbance IoT scenarios usually impose routing requirements to support mobile nodes, handle failing links and to be resilient against attacks. A secure and autonomous bootstrapping is essential, especially for large-scale IoT deployments.

ICN decouples content consumers from data producers (decoupling in space). A more sophisticated decoupling can be provided with the publish-subscribe messaging pattern that further adds a decoupling in time and synchronization. Constrained devices in LLNs can leverage this loose coupling to increase sleep cycles and delegate the authority over as much information as possible to more powerful devices that act as content proxies. In , once content is published to the content proxy (CP) by a producer (P), consumers (C) can retrieve this content from (CP) without interacting with the producer. This indirection when retrieving information allows (P) to align sleep cycles accordingly to the period of generating new sensor readings, instead of handling content requests from any consumers (C).

TODO: The problem of PUSH

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 . The use of the term, "silently ignore" is not defined in RFC 2119. However, the term is used in this document and can be similarly construed. This document uses the terminology of , , and for ICN entities. The following terms are used in the document and defined as follows: Many-to-One communication pattern, where multiple devices send sensor readings to one gateway. Stable node for replicating content. A Gateway that enables content transfer to and from a remote cloud storage, possibly by performing some kind of protocol translation. Prefix Advertisement Message. Name Advertisement Message.

The publish-subscribe system is centered around prefix-specific content proxies (CPs) that are deployed in IoT edge networks. Such proxy function can be hosted on the Cloud- or Internet Gateway, or may reside on a stable, less constrained node within the IoT infrastructure. It is assumed that a CP is present for each prefix covering publishable content. Implementing a pub-sub NDN involves several steps that are bound to the tight requirements of resource-constrained devices. These steps include: Building the prefix-specific routing topology tailored to constrained networks Mapping Publish to NDN semantics Mapping Subscribe to NDN semantics

A (sensor) node that wants to publish a data item needs to rely on path information towards the Content Proxy. Following the approach of PANINI , default routes will be established as follows. Each CP in the local IoT sub-network advertises the prefix(es) it represents to the routing system. It does so by broadcasting Prefix Advertisement Messages (PAMs) on the link layer (see for the corresponding protocol details). Nodes that newly receive PAM advertisements will add or refresh a prefix-specific default route in their FIB. Intermediate nodes in a multi-hop environment also re-broadcast PAMs, so that the entire sub-network is flooded and default route entries build a shortest path tree (SPT) towards the CP as shown in (alternatively, a DODAG w.r.t. a gateway for redundant CPs).

Information flowing from constrained sensor nodes towards a gateway is the prevalent communication pattern in the IoT (converge cast). The publish-subscribe system hence establishes a default routing (see sample FIB in ) and uses the tree topology with default routes towards the CP as a first step of content aggregation. Content replication towards other CPs, an Internet gateway, or into a cloud can follow subsequently. Prefix Face Lifetime /P/ Fx Ft ... ... ... It is noteworthy that the role of the new PAM message remains orthogonal to the existing Interest or Data semantics. A PAM never carries data nor requests, but persists on the control plane of name-based routing. User applications stay unaffected, and continue to rely on the NDN-specific request-response paradigm. Each node in the tree calculates a rank based on the rank of its parent and a routing metric. Hence, the rank is an indication for the position within the tree and is strictly monotonically increasing in the downwards direction from root to leaf. For simplicity, this document uses the hop-count routing metric to calculate the rank. Future work can focus on more elaborate routing metrics, e.g., to reduce packet retransmissions or improve load balancing for publish operations. The Routing Information Base (RIB) contains the following information: Variable length prefix to configure a prefix-specific default route 16-bit unsigned integer indicating a node's rank 8-bit unsigned integer to store SPT related flags The appropriate face towards the parent node is stored. Entries in the NAM Cache are <name,downstream_face> tuples. The NC is consolidated when propagating name advertisements.

In classical publish-subscribe systems, a Publish is typically implemented as a push mechanism on the data plane. However, this contradicts the request-response paradigm employed by NDN. To adapt the Publish operation to NDN semantics, it is split into two phases and the required push mechanism is performed on the control plane with a link-local scope. The two phases consist of: Announcing names of Named Data Objects (NDO) on the control plane Requesting NDOs on the data plane In the first phase, the name of the NDO to publish is advertised to the prefix-specific upstream neighbor by encoding it with TLV format in a unicast link-local Name Advertisement Message (NAM) adopted from PANINI . Once an upstream neighbor receives an unsolicited NAM, the name is extracted and along with the incoming face stored in the NAM Cache (NC) as a <name,downstream_face> tuple. This link-local content signaling does not establish any data paths in the PIT, nor does it modify the FIB or the Content Store (CS). In the second phase and as a result of an unsolicited NAM, the content is requested from the downstream neighbor accordingly to the standard NDN scheme with an Interest message for the name recorded in the NC on the recorded face. When a downstream neighbor replies with the content (Data message), this neighbor removes the corresponding NC entry and the NDO to publish is successfully replicated one hop closer towards the content proxy. NC entries are thus short-lived for hop-wise replication only. Both phases are iteratively repeated hop-wise until the content proxy is reached. Being the root of this prefix-specific spanning tree, the content proxy has no further prefix-specific upstream neighbor and the replication terminates. It is noteworthy, that both phases can be interleaved, so that NAMs are signaled to the upstream neighbor, while the content is requested from the downstream neighbor. (a) depicts the hop-wise replication of a published content on the gradient towards the (CP). In this example, the name /HAW/temp_t is advertised by the producer (P) to its parent node (A). (A) extracts the name from the NAM and stores it along with the incoming face in its NC. (A) then propagates the NAM further to its parent (CP) and simultaneously requests the content from (P) as depicted in (b). Likewise in (c), (CP) reacts to the incoming NAM by requesting the content from (A). NC states from (A) and (P) are removed as soon as they respond to the request.

(CP) | | ,----(CP)<-, | | / | | NAM | / | | | / / | | / | | | / | | | / / | | (A)<-, | | ,-(A)<-, | | `>(A)---' Data | | \ | NAM | | | \ | Data | | \ | | \ | | | | \ | | | \ | | (P) | | Interest `--->(P) | | (P) | | /HAW/temp_t | | /HAW/temp_t | | /HAW/temp_t | +-------------+ +------------------------+ +-------------------+ (a) Adv. Name (b) Replicate Content (c) Finish publish ]]>

In the proposed publish-subscribe system, the Subscribe operation is equivalent to an Interest-based request of previously learned content names. A device can learn about new content in various ways: Name Advertisements of the CP via dedicated prefix path (TODO) or broadcast. By polling a dedicated data structure at the CP that records publishings and updates. Such a data structure may contain indicators about the periodicity of sensor readings to align periodic polling schemes to sensor reading intervals. By encoding topics into a hierarchical naming scheme of the form routing prefix / topic / unique_part. Inerest timeouts for these names serve as subscription periods and must be refreshed or retriggered for every publishing to adhere to the flow control approach of NDN / CCNx. TODO

The hop-wise replication described in transparently supports publish operations in partitioned networks. When a publish operation fails to replicate content and no backup parent is in the vicinity ( (b)), the node marks its sub-DAG as floating by propagating PAMs with the floating bit set and the NC entry is preserved. Once a sub-DAG becomes connected to another parent, the publishing is resumed ( (c)).

A node receiving a PAM from its parent with the floating bit set may rejoin the tree using another parent in the neighborhood that is connected to the content proxy. Rejoining the tree may result in a worse rank.

TODO

TODO

TODO: add ABNF TODO: add mappings of PAM and NAM to the NDN and CCNx dialects

8-bit unsigned integer. Indicates a PAM. 1-bit floating flag. Indicates that a sub-tree is not connected to the content proxy, when set. 7-bit unused field. It MUST be initialized to zero by the sender and MUST be ignored by the receiver. 16-bit unsigned integer. Indicates a node's position in the SPT. 16-bit unsigned integer. Indicates the length of the following prefix in bytes. Variable length prefix used to configure a default route within the SPT.

8-bit unsigned integer. Indicates a NAM. 8-bit unused field. It MUST be initialized to zero by the sender and MUST be ignored by the receiver. 16-bit unsigned integer. Indicates the accumulated length of all options.

8-bit unsigned integer. Indicates the name option (0x00). 16-bit unsigned integer. Indicates the length of the name, excluding the type and length field. Variable length name.

TODO

INRIA FU Berlin INRIA HAW Hamburg FU Berlin HAW Hamburg HAW Hamburg HAW Hamburg FU Berlin

This work was stimulated by fruitful discussions ... We would like to thank all active members for constructive thoughts and feedback. In particular, the authors would like to thank (in alphabetical order) Emmanuel Baccelli, Michael Frey, Oliver Hahm, Peter Kietzmann, Dirk Kutscher, Martine Lenders, Joerg Ott, Hauke Petersen, and Felix Shzu-Juraschek. This work was partly funded by the German Federal Ministry of Education and Research, project I3.