CS 4700 / CS 5700Network Fundamentals

Lecture 4.5: Review from last week

Revised 1/12/14

2

Intro to the class

Use Piazza for everything Really

Unless it’s something truly personal/private Don’t cheat

I will catch you If you have questions about what is cheating,

ask Regrading policy

2 strikes and you’re out Partners allowed on all projects

3

History of the Internet

What were the newideas that revolutionized/distinguished the Internet from other prior networks? Packet switching (why is this a good thing?) No global control Layering to glue together different network

types What was the original Internet called? What

was its design goal? ARPANET, resilient to catastrophic failure

(nuclear) What do you think is the biggest threat to

Internet success?

4

Architecture

What are the 7 ISO layers? Which ones are used in practice?

What does each layer specify? How do we combine layers in data

transmission? What are examples of violations of strict

layering?

5

Saltzer’s paper

Design principle, not a law Low-level functionality begets assumptions,

and when you assume, you … More generally: Systems will fail with some

nonzero probability. The Internet is a very large computer system, so something is almost always going to fail.

Defining endpoint is critical Some endpoints are at the low level

6

Student comments

10/61 students submitted by deadline 40/61 by 10:30am

“I feel that author's assumption of considering an error rate to be acceptable in the system is not the best approach, specially[sic] when today computer systems are used for critical functions like healthcare and can also lead to human fatalities”

Lack of empirical data/analysis/statistics Not enough solutions, too vague Makes assumptions about goals of

underlying system(s)

7

Clark’s paper

Primary goal: Multiplexed use of existing (disparate) communication networks, separately administered

Secondary goals: Priority order shaped the Internet Make it work now, worry about accounting later

(but make it cheap to build) Keep it simple, but know that it might be less

efficient

8

Student comments

22/61 on time 37/61 at 10:30am

Why is 100 bytes a reasonable packet size? What is fate-sharing, why is it easier to engineer?

Location of service-consumer and failure are the same

Why is it hard to support resource management and accountability? Cost-effectiveness & security?

Why TCP? Why ACK on bytes?

Dedicated network vs. Best-effort

9

Project 1 highlights

Key skills Work with TCP sockets (optionally SSL) Follow application-layer protocol Parse data

Use turnin script from (most) any CCS department server It’s a valid CCS server if you can read

/courses/cs5700s14/bin You can work in teams Use any language you want (doesn’t have to be C) Document your code, read instructions carefully! Get started early. I go to bed early.