ECE Department: University of Massachusetts, Amherst

ECE 354Spring 2009

Lab 3: Transmitting and ReceivingEthernet Packets

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Big Picture Introduction

Transmit and Receive Ethernet packets between two DE2 boards

Implement the 5-layer Internet model Primarily written in C code Use a preexisting SOPC system from the

DE2_NET project

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Skills to learn

Understanding previously written code Using a peripheral device: DM9000A chip Connect to a device that you did not design:

DM9000A Ethernet chip Internet protocol stack

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Additional Hardware

Two DE2 boards Ethernet cable

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Overview of Lab

Each group should specify the information in Layers 2 through 5 (Link, Network, Transport, and Application)

The payload should be 16 bits selected by 16 switches on the DE2 board and should be displayed on the LEDs of the other DE2 board

Only packets with the correct source MAC, IP, and port addresses should be allowed to update the LEDs

Each group should modify the DM9000A.H file so that the last byte of the MAC address matches their group number

Test protocol compliance by working with another group and using their MAC address as your destination MAC address and your own MAC as the source.

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Overview of DE2_NET project

Sends a malformed broadcast Ethernet packet Important files: hello_led.c, DM9000A.c, and DM9000A.h Three functions to control DM9000A chip

• DM9000_init();• TransmitPacket(TXT, length);• ReceivePacket(RXT, &length);

Copy the DE2_NET and fixpaths from the DE2 CD Switch the workspace and select the directory that you

saved DE2_NET in If running two boards on the same computer, make two

folders with each holding a copy of the DE2_NET project

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The Internet protocol stack

Consists of 5 layers: Application, Transport, Network, Link, and Physical layer

A majority of you have learned about these layers in Computer Networking course

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Layers you will use

Create an Application Layer (5) message by using the sixteen switches on the DE2 board

Encapsulate the message into segment at the Transport Layer (4)

Encapsulate the segment in a datagram at the Network Layer (3)

Encapsulate the datagram in a frame at the Link Layer (2)

The frame will be sent over the Physical Layer (1)

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User Datagram Protocol (UDP) – Layer 4 (Transport Layer)

The Application Data will be encapsulated within a UDP segment

The Segment Header includes the Source Port, Destination Port, Length of Segment, and Checksum (2 bytes each, total of 8 bytes)

The Source and Destination Port numbers can be determined by the user, but the Length and Checksum will have to be calculated

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The Network Layer (3) - IPv4

The Segment from the Transport Layer will be encapsulated within an IPv4 Datagram

Dominant network layer protocol on the internet Data-oriented protocol to be used on a packet

switched network, such as Ethernet Note about Checksums:

• Begin by first setting the checksum field of the header to zero.

• Checksums involve the one’s compliment addition operation. In C take the one’s compliment of a number A by: unsigned int complimentA = ~A

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IPv4 packet structure

Packet consists of two sections:

The parts of each section that you will use in the is lab are:

Version: IP packet version (4) Header length (between 5 and

15) Total Length (size of datagram)

header and data

Identification: uniquely identifying fragments

Header checksum Source and Destination address Data

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Link Layer (2) – Ethernet Frame

The Datagram from the Network Layer is encapsulated within an Ethernet Frame

The Destination and Source MAC addresses should be set to uniquely identify each DE2 board

Extra credit will be awarded if you perform CRC Checksum, otherwise set it to a value of zero

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The Physical Layer (1)

Refers to the network hardware or physical cabling

Provides the means of transmitting raw bits You can also use a loopback (included with kit) to send

packets back your own board

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What to demonstrate

Display data payload on the red binary LEDs Display the number of packets transmitted on

the seven segment display Only packets with the correct source MAC

address, IP address, and port address should be displayed

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Where does this project lead?

The next Lab (number 4) will put Lab 2 and Lab 3 together

Implement a reliable system

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References

The two documents located at DE2_System\Datasheets\Ethernet

DE2_NET project

Information about the Internet protocol stack can be found here:• http://en.wikipedia.org/wiki/Main_Page• http://www.google.com/

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