In the following exercise, we are going to study the CoAP protocol (Constraint Application Protocol ) used in Wireless Sensor Network (WSN), to simplify implementation in Sensor Nodes which have very limited resources in term of memory, computing power and energy. The standard is generic and does not make any assumption on Layer 2, but in our case we will suppose that layer 1 and 2 are IEEE 802.15.4. At layer 3, the 6LoWPAN protocol compresses the 40 bytes of the IPv6 header into 20 bytes. Another characteristic of WSN, is the high error rate on the radio link which leads to frame losses.
Good book for the class: OPEN SYSTEMS NETWORKING: TCP/IP AND OSI, David M. Piscitello A. Lyman Chapin, Addison-Wesley Professional Computingk, 1993
Finally we have a look on the Connection Oriented mode and the Datagram, se the main differences in term of Quality of Service. When also visit the famous hour glass model for IP or how the OSI RM can be reviewed by IETF.
Network Layer We look in more detail and at layer 3, why it is good to cut the information in little pieces called packets. We study French geography and why packets offer a better multiplexing and good performances.
We study the framing, how we divided a continuous flow of information into limited size PDUs and the meaning of all HDLC fields.
Data Link Layer The exercises shown that Send and Wait protocol does not offer good performances when propagation delay is long compared to transmission time. In that case it is better to send several unacknowledged frames instead of waiting for acknowledgments before sending another frame. We study HDLC protocol which can be view as the ancestor of … Read moreRES1 Data Link Layer (9/12)
Data Link Layer Now we have all the element to build our first protocol called Send and Wait. We will try to formalize its description to make it look like a real standard. We use Finite State Machine to describe its behavior.
Data Link Layer (2) Then we go really into the communication world. We see how we can detect a transmission error using CRC and that a frame with a wrong CRC will be discarded.
Data Link Layer We will wend more time on the Data Link layer, since here we can illustrate the protocol behaviors and detail all the elements. First we start empirically to build a stupid protocol used be a cook to send an omelet recipe to a student. We will see that the basic hypothesis (negatively … Read moreRES1 Omelet protocol (6/12)
Physical layer Even if we don’t focus too much on the physical layer, we see the property we expect from the physical layer (such as clock synchronization) and some way to code binary information.