Connection of Sensor Network with TCP/IP Network, Article - 1

There are many situations where sensor networks need to be connected via TCP/IP network. In other words it might be necessary to integrate many sensor networks into one virtual sensor network using TCP/IP network.
To allow users all over the world to use a WSN deployed in some remote place it is necessary to connect WSN to TCP/IP network. The users may issue a query to get information form WSN or it might be necessary to issue a command or some information to a particular node in WSN. The particular node might be one of several higher capability nodes in the WSN.

So connecting WSN with TCP/IP network is very important but due to sensor node’s limitations it is not possible to install full existing TCP/IP stack into a sensor node. So to connect WSN and TCP/IP network many new methods are proposed.

Different authors propose different methods to connect WSN and TCP/IP networks. In “Integrating Future Large-scale Wireless Sensor Networks with the Internet” application level gateway is used to connect WSN and TCP/IP network. This paper classifies WSN as homogeneous and heterogeneous WSN. It provides solutions to connect both homogeneous and heterogeneous networks to TCP/IP networks. Homogeneous sensor network is one in which all sensor nodes have similar capabilities and heterogeneous sensor network is one in which some node have more capabilities than other nodes and outside user wants to interact with the more capable nodes directly. To connect homogeneous sensor network to TCP/IP networks this paper proposes to use a gateway as shown in the figure below. Gateway Based Approach for connecting Sensor Networks with TCP/IP Networks

The gateway is viewed as front end for the distributed database. The user who wants information form WSN may issue query to the gateway. Query optimization is provided through data centric in network processing. The response is obtained from WSN by the gateway and reply is sent to the user. The gateway acts as the interface between WSN and internet.
The advantage of this approach is both WSN and internet can be completely independent; it’s the headache of gateway to do conversions required. And it is most easy approach as very less amount of changes are required to the existing architecture; a gateway need’s to be added in between internet and WSN. The drawback of this approach is that ever gateway has to be designed according to the WSN. And as we see this has single point of failure, i.e. if gateway goes down WSN becomes inaccessible. To overcome the above said problem we can use two or more gateways also.

To connect heterogeneous WSN to TCP/IP network the paper proposes to use an IP overlay over the WSN. In the heterogeneous network some nodes have more capability or some nodes may be acting as cluster heads. These nodes can be given IP address, and these nodes may be directly accessed by the user using internet. In this type of network an IP overlay network is created over the underlying WSN to connect user directly to higher capable nodes. To create an IP overlay network it is necessary to create a tunneling mechanism to allow the more capable nodes to communicate among themselves using address centric approach. To create tunnels between the more capable nodes the paper proposes to use either Directed Diffusion or ACQUIRE protocols. Directed Diffusion can be used for high IP traffic applications and ACQUIRE can be used for low IP traffic applications. The figure below makes the concept clearer.

Heterogeneous network, the red line shows the tunneling formation using Data Diffusion or ACQUIRE protocol.

The red color line in the figure above shows the tunnel between the higher capable nodes using normal sensor nodes. This tunnel makes IP overlay possible over existing WSN architecture. Once the tunnel is established it will be possible to the users to interact with the higher capable nodes directly using existing WSN architecture itself.

A paper called “A Delay-Tolerant Network Architecture for Challenged Internets” proposes to use a method to integrate the challenged networks. Challenged networks are those which have a very long end-end delay, low bandwidth, high rate of network portioning, high error rates. Sensor network can be considered as a challenged network so this paper is applicable to the sensor network also. This paper uses an application layer above transport layer in TCP/IP stack as well as in WSN stack called the bundle layer. This layer is responsible to store and forward packet. This is shown in the figure below.

Connecting WSN and Internet using DTN gateway

It looks similar to gateway approach described before, but it has several dissimilarities with the application level gateway approach. The DTN gateway is universal to connect any network, it is not application based. It takes into account many aspects of different challenged network but application level gateway fails to do so. One region itself can have two or more DTN gateways, so even within a region if partition takes place DTN gateway based approach works where as the earlier one fails.

The network is divided into different regions. One region itself has many DTN gateways. The DTN gateways communicate with each other. Initially routing is done based on the region address using the bundle layer in the DTN gateways. Once the packet reaches the destined region the address of the host is used to reach the host in the destination. The address format will be (region address, host address) host address can be of any type. So this architecture works for any network. This paper speaks about integration of all challenged networks and TCP/IP network. The figure in the next page shows DTN based architecture.

DTN based Architecture

The advantage of this architecture is that it can be used to connect any type of network, and it supports more than one DTN gateway in only one network patch. The DTN gateway takes care of interface between different networks. So every network can be designed independently. The disadvantage of this architecture is the extra bundle layer that needs to be installed.

This Article will be continued in the next post ...