Computer Networks (CIS-2151) Home Page

This is the home page for Peter Chapin's Computer Networks course notes for the Spring 2023 semester. Here you will find electronic versions of class handouts, homework assignments, lecture slides, and links to other references of interest. If you are a student taking Computer Networks consider bookmarking this page.

The Zoom meeting URL gives you access to the live lectures.
The homework submission area and grade book are on Canvas but all other course resources are here.
The course syllabus gives an overview of the course and its content, lists course resources, and describes the grading policy and related issues.
Vermont State University's Policy 502 puts restrictions on the ways in which university owned networks can be used. See, in particular, Part IV in the document linked above. These policies are intended to promote a more secure environment by documenting activities that are considered inappropriate and subject to sanction. Unfortunately, certain activities need to be done in some of our CIS classes, such as this one, that violate Policy 502. The administration is aware of this and has granted the CIS department a limited exemption to Policy 502 as applied to computers directly connected (with a wire) to two subnetworks controlled by the department, one on the Williston campus, and one on the Randolph campus.
I've prepared some general information on submitting assignments.
My home page contains other resources of potential interest.

Lecture Topics

The lectures for this course are on Zoom. The labs for the course will be face-to-face.

2023-01-17. Course introduction and overview. Preparations for Lab #1.
2023-01-19. Number systems. More preparations for Lab #1.
2023-01-24. Introduction to the layered architectures and IPv4 addresses.
2023-01-26. Discussed Lab #2, and the IPv4 header format. Demonstrated how to use tshark to capture and dissect packets. Discussed time-to-live (TTL).
2023-01-31. Introduced IPv6.
2023-02-02. Discussed Lab #3. Continued discussion IPv6.
2023-02-07. Discussed IPv4 address classes, CIDR, and ICMP.
2023-02-09. Discussed Lab #4, traceroute, and ARP.
2023-02-14. Discussed IPv4 fragmentation, MTUs, and path MTU discovery.
2023-02-16. Demonstrated the IPv6 tunnel between Lemuria and Twilight.
2023-02-21. No class (Vacation).
2023-02-23. No class (Vacation).
2023-02-28. Started discussion of TCP: background, and opening and closing connections.
2023-03-02. Continued discussion of TCP: receiver window.
2023-03-07. Discussed the TCP congestion window, slow start, and retransmission timeouts.
2023-03-09. Discussed Lab #7. Introduced UDP.
2023-03-14. Finished discussing UDP and DNS. Discussed Lab #8 on the DNS protocol.
2023-03-16. Discussed TLS, character sets, and introduced SMTP and email protocols.
2023-03-21. Additional discussion of character sets, particularly Unicode. Discussed the Simple Mail Transport Protocol (SMTP) with a demonstration.
2023-03-23. Discussed Lab #9. Discussed the format of mail messages and MIME.
2023-03-28. Started discussion of link layer issues (Ethernet and IEEE 802.11).
2023-03-30. Briefly discussed other network protocols to create a more complete context around the TCP/IP protocol stack.
2023-04-04. No class (Vacation).
2023-04-06. No class (Vacation).
2023-04-11. Discussed error correction and detection.
2023-04-13. Started discussing analog communications: modulation schemes.
2023-04-18. Discussed noise and the Shannon-Hartley Theorem.

Slides

Lemuria's Network Topology.
Number Systems.
Slides for Chapter 2 in the text (an introduction).
IP Protocol (version 4)
IP Protocol (version 6)
IP Details (version 6)
TCP Details, Part 1
TCP Details, Part 2
UDP Details
DNS. The Domain Name System (see RFC-1035)
TLS
Character Sets
SMTP
Mail Message Format
MIME
Slides for Chapter 12 in the text (on Ethernet).
Other Network Protocols
Slides for Chapter 6 in the text (on error detection/correction).
Data Communications.

Lab Assignments

The lab set is summarized in the lab summary document, along with links to specific lab handouts and supporting code samples.

Samples

This packet capture shows the effect of doing tracert on a Windows system to Google. This capture was done on Comcast's network and IPv6 was used by default. Notice that in this case tracert used ICMP echo requests to probe the network at ever increase hop distances. This is different from what traceroute on Linux does (which is to use UDP datagrams as probes).
This zip archive contains Windows executables for both a daytime client and a daytime server, with versions for both IPv4 and IPv6.
Here are some examples of MIME encoded email messages: Sample1.eml, Sample2.eml, Sample3.eml, Sample4.eml. MIME is a kind of protocol that exists above SMTP. It describes the way in which email messages are formatted.
This packet capture shows the IEEE 802.11 wireless frames on my home network. This capture was done using Wireshark on a Mac.

Resources/Articles

Linux

PuTTY is a free SSH client program for Windows. It is relatively simple, yet provides a rich collection of features. I have a document that describes how to set up and use PuTTY to access Lemuria. If you are a Mac user, you might find these notes about SSH on the Mac useful.
I wrote an overview of Unix that provides some conceptual background and describes some basic commands. It is an old document, and rather too long, but you may still find it useful. There are many other descriptions of basic Linux commands online. There are also cheat sheets.
For transferring files to and from Lemuria, you might find WinSCP useful. Use the "SFTP" transfer method (file transfer over SSH) and don't forget to specify the non-standard port 2221 and host of lemuria.cis.vtc.edu.
Although outside the scope of this course, this reference on different tunnel types that can be set up on a Linux system is interesting.

Tools

My tshark quick-start page has some information about getting started with tshark

Other

An Introduction to Computer Networks is a free textbook about networking by Peter L. Dordal. You might find it a useful supplement to the text for this class.
The ASCII character set is commonly used, although many modern systems use the much larger (and more complex) Unicode character set.
A list of IPv4 network masks.
IP address classes are, to some extent, now obsolete thanks to classless inter-domain routing (CIDR). However, you should still be aware of them. Take note of the private address ranges in the different classes.
The RFC Editor page is where you can find a complete collection of all RFC ("Request For Comments") documents. These documents are the output of the Internet Engineering Task Force (IETF) that manages the various networking standards used on the Internet. IPv4 is described in RFC-791. Here are some additional notes about the IP protocol and header fields:
- There is a nice page on Wikipedia describing the Type of Service field in the original RFC and how its meaning has evolved over time.
- Here is more information about the Time to Live field.
- Details on how the IPv4 header checksum is calculated.
The Internet Control Message Protocol is defined by RFC-792. It is used by routers and hosts to exchange control information.
Here are some details about IP fragmentation. Wikipedia's description of maximum transmission units (MTUs) is a good overview of the topic. Path MTU discovery is a method for finding the minimum MTU on a path from the source to a destination. It is used to avoid IP fragmentation. Its use is required with IPv6 since IPv6 packets can't be fragmented by routers. Here is another article that describes MTUs and path MTU discovery.
The Domain Name System (DNS) is described by a variety of RFCs. RFC-1035 describes the protocol.
ASCII, ISO-646, ISO-8859, C0 and C1, ISO-2022
Unicode Consortium, Unicode Technical Site
UTF-32, UTF-16, UTF-8, BOM
RFC-1149. A Standard for the Transmission of IP Datagrams on Avian Carriers.
Wikipedia's article on Ethernet frame format.
Some notes on how to get Wireshark to see the IEEE 802.11 frames (they are normally translated into "fake" Ethernet frames by the network driver).
A nice video on YouTube that demonstrates Hamming error correcting codes.
The Wikipedia article on the radio spectrum gives an overview of the various ranges or radio frequencies and what they are called.
The Wikipedia article on the electromagnetic spectrum puts the radio spectrum in a larger context and shows where optical frequencies fit into the picture.
Here is a page that shows a simple form of Shannon's formula relating digital bandwidth to analog bandwidth and signal-to-noise ratio. Wikipedia also has a good page on the Shannon-Hartley Theorem.