Posts Tagged ‘English’

Master of Science — HDLC

Tuesday, September 13th, 2016

I2C Bus

Friday, August 1st, 2014

Read carefully the subject before answering. The document given in here describes the I2C bus.

Question1 (1point) Is this standard issued from an official standardization agency (ISO,ITU,…) or from the scientific/industrial community (IEEE,IETF,…)?

Question2 (1point) How many wires are necessary to transport data? What is the purpose of the clock signal?

Question3 (1point) With a bus running at 100Mbit/s, give the modulation rate of the SCL line?

Question4 (1point) Why only one address is needed on the frame?

Question5 (1point) Can the Ack bit be used to detect transmission errors?

Question6 (1point) Does the standard define a method to allocate slave addresses dynamically?

We plan to build a device composed of an Arduin omicro-controller, a LED screen and a keyboard. The goal is to display on the screen messages written on the keyboard.

Question7 (1point) Which element will be the master?

Question8 (1point) Is the master informed when a character is typed on the keyboard?

Question9 (1point) Can text be sent directly from the keyboard to the screen?

Question10 (2points) Give a time diagram describing how a character will be sent from the keyboard to the screen

Question11 (2points) We suppose the bus speed is 100 Mbit/s. The keyboard has to send 10bytes of data, what will be the real throughput for that transfer?(several answers are possible so explain well what are your hypothesis to compute that throughput)

Question12 (1point) What is the benefit of the repeated Start(Sr)?

Question13 (2points) Explain when Clock stretching is needed

Question14 (1point) Can the master broadcast frames to all slaves?

Question15 (3points) Can the master dynamically discovers newly connected devices to the bus? Propose a protocol to do so.


Sunday, February 26th, 2012

The goal of this exercise is to study 6PE (IPv6 Provider Edge) transition mechanism described in draft-ooms-v6ops-bgp-tunnel-00.txt (now published as RFC 4798, since the draft is very old, the solution proposed here are not exactly what have been standardized). This principle is implemented by many major router manufacturers. This proposal combines one IGP, MPLS and BGP to allow an ISP to carry efficiently IPv6 traffic without modifying core routers. Only edge routers have to be modified to understand IPv6 protocol. In the rest of this exercise we will study progressively the Internet Draft and the different elements of this proposal.


RES1 Connection vs datagram (12/12)

Thursday, October 27th, 2011

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.

RES1 Network Layer (11/12)

Thursday, October 27th, 2011

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.

RES1 HDLC Framing (10/12)

Thursday, October 27th, 2011

We study the framing, how we divided a continuous flow of information into limited size PDUs and the meaning of all HDLC fields.

RES1 Data Link Layer (9/12)

Thursday, October 27th, 2011

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 all other anticipation protocols. There is an error in the slides. Instead of an attentive reader will have noticed that the exact formulae is \sum_{i=0}^{\infty} i.x^i=\frac{x}{(1-x)^2}. But the result is correct.

RES1 Send and Wait (8/12)

Thursday, October 27th, 2011

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.

RES1 CRC (7/12)

Thursday, October 27th, 2011

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.

RES1 Omelet protocol (6/12)

Thursday, October 27th, 2011

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 acknowledge when a problem occurs) is not good.