Notes

What is SPIN? Explain SPIN in detail.
Sensor Protocol for Information via Negotiation or SPIN is a data-centric negotiation-based family of information dissemination protocols for WSNs, designed to address the deficiency of flooding (In flooding, a node sends a packet received, to all its neighbors other than the neighbor which sent the packet to it) and gossiping (a node receiving a packet, instead of broadcasting, the node sends it to only one of its randomly selected neighbor, and the neighbor in turn sends the packet to one of its randomly selected neighbor).
The simplicity of flooding and gossiping is appealing, as both protocols use simple forwarding rules and do not require topology maintenance. The performance of these algorithms in terms of packet delay and resource utilization, however, quickly deteriorates with the size of the network and the traffic load. The main objective of SPIN and its related family members is to address the shortcomings of conventional information dissemination protocols and overcome their performance deficiencies. The basic tenets of this family of protocols are data negotiation and resource adaptation

flooding gossiping

SPIN exploits data naming, whereby nodes associate metadata with data they produce and use these descriptive data to perform negotiations before transmitting the actual data. A receiver that expresses interest in the data content can send a request to obtain the data advertised. The use of meta data descriptors eliminates the possibility of overlap, as nodes can limit their requests to name only the data that they are interested in obtaining.
Each node in the network can probe its associated resource manager to keep track of its resource consumption before transmitting or processing data. When the current level of energy becomes low, the node may reduce or completely eliminate certain activities, such as forwarding third party metadata and data packets. The resource adaptation feature of SPIN allows nodes to extend their longevity and consequently, the lifetime of the network. This is call as Resource adaptation
To carry out negotiation and data transmission, nodes running SPIN use three types of messages.
• The first message type, ADV, is used to advertise new data among nodes.
• The second message type, REQ, is used to request an advertised data of interest.
• The third message type, DATA, contains the actual data collected by a sensor, along with a metadata header.
This way of communication is known as the three-way handshake protocol.

SPIN basic protocol operations

The simplest version of SPIN, referred to as SPIN-PP, is designed for a point to-point communications network. The three-step handshake protocol is used by SPIN-PP.
An extension of this basic protocol, SPIN-EC, additionally incorporates a threshold based resource-awareness mechanism to complete data negotiation. When its energy level approaches the low threshold, a node running SPIN-EC reduces its participation in the protocol operations.
Both SPIN-PP and SPIN-EC are designed for point-to-point communication. A third member of the SPIN family, SPIN-BC, is designed for broadcast networks. In these networks, nodes share a single channel for communications. In this class of networks, when a node sends out a data packet on the broadcast channel, the packet transmitted is received by all the other nodes within a certain range of the sending node. The SPIN-BC protocol takes advantage of the broadcasting capability of the channel and requires that a node which has received an ADV message does not respond immediately with an REQ message. Instead, the node waits for a certain amount of time, during which it monitors the communications channel. If the node hears an REQ message issued by another node which is interested in receiving the data, it cancels its own request, thereby eliminating any redundant requests for the same message. Furthermore, upon receiving an REQ message, the advertising node sends the data message only once, even when it receives multiple requests for the same message.
SPIN-RL, extends the capabilities of SPINBC to enhance its reliability and overcome message transmission errors caused by a lossy channel. Enhanced reliability is achieved by periodic broadcasting of ADV and REQ messages. Each node in SPIN-BC keeps track of the advertisements it hears and the nodes where these advertisements originate. If a node requesting specific data of interest does not receive the data requested within a certain period of time, it sends the request again. Furthermore, improved reliability can be provided by readvertising metadata periodically.
Explain the different modes layers of MAC protocol
The main objective of most MAC-layer protocols is to reduce energy waste caused by collisions, idle listening, overhearing, and excessive overhead. These protocols can be categorized into two main groups: schedule- and contention-based MAC-layer protocols. Schedule-based protocols are a class of deterministic MAClayer protocols in which access to the channel is based on a schedule. Channel access is limited to one sensor node at a time. This is achieved based on preallocation of resources to individual sensor nodes. Contention-based MAC-layer protocols avoid preallocation of resources to individual sensors. Instead, a single radio channel is shared by all nodes and allocated ondemand. Simultaneous attempts to access the communications medium, however, results in collision. The main objective of contention-based MAC layer protocols is to minimize, rather than completely avoid, the occurrence of collisions. To reduce energy consumption, these protocols differ in the mechanisms used to reduce the likelihood of a collision while minimizing overhearing and control traffic overhead.
So we can see the first and main differences between the two models is that one focus on giving a schedule time to de medium to each node, even if it doesn’t need it, avoiding for entirely the collision, but wasting resources, on the other hand the Contention-based protocol gives access to the medium on demand but is still open to collision.
Schedule-based MAC
• A schedule exists, regulating which participant may use which resource at which time (TDMA component)
• Typical resource: frequency band in a given physical space (with a given code, CDMA)
• Schedule can be fixed or computed on demand. Usually: mixed – difference fixed/on demand is one of time scales
• Usually, collisions, overhearing, idle listening no issues
• Needed: time synchronization
Contention-based protocols
• Risk of colliding packets is deliberately taken
• Hope: coordination overhead can be saved, resulting in overall improved efficiency
• Mechanisms to handle/reduce probability/impact of collisions required
• Usually, randomization used somehow
References
http://sensors-and-networks.blogspot.com/2011/10/spin-sensor-protocol-for-information.html
WIRELESS SENSOR NETWORKS, KAZEM SOHRABY DANIEL MINOLI TAIEB ZNATI, 2007, Published simultaneously in Canada.
http://www.uta.edu/utari/acs/ee5369/Karl%20slides/sensys-ch5-mac.pdf