1. CMPE 252A : Computer Networks
Chen Qian
Computer Engineering
UCSC Baskin Engineering
Lecture 1
Slides source: Kurose and Ross, Simon Lam, Katia Obraczka
Introduction

2. Welcome to CE 252A! Class information: When: Tu Th 01:30PM-03:05PM.
Where: Engineering
Class Web page:
It is your responsibility to read EVERY sentence on the class website. You also need to check the website at least twice every week to access timely updates to the class

3. About the Instructor Chen Qian. Office: E2 231.
qian "at" ucsc.edu
Office hours: Tuesday, 11am-12pm
Research lab: E2 211

4. Pre-Requisites CMPE 150 or undergrad level networking course.
Graduate level computer programming skills (for project).

5. Teaching Assistants Xin Li xli178 at ucsc.edu Huazhe Wang
hwang137 at ucsc.edu

6. Highly recommend to buy it! It is good based on my experience.
Books
Lecture:
Computer Networking: A Top Down Approach,
by Kurose and Ross
5th, 6th and 7th ed are all good
You are recommended to read the book BEFORE some classes. However the exam questions are ALL related to the material in the slides.
Highly recommend to buy it! It is good based on my experience.

7. Grading Reading reports 10% Survey study 25% Midterm 25%
Course project 40%

8. Student Responsibilities: Academic Integrity
All submitted work must be individual.
OK to have discussions on ideas but turn in your own work.
Survey is individual!
Project can be done in a group of at most three students. But each student must submit her/his own report about her/his own contribution.
Ask instructor and TAs if there are any questions.
For more info, go to:

9. Student Responsibilities: Academic Integrity
Academic integrity violations will not be tolerated.
Cheating quizzes.

10. Student Responsibilities
Attendance.
Lectures.
Keep up with material covered in lecture
Readings (chapters in the book).
Sample questions.
Keep up with reading assignments and project.
Turn in the assignments on time!

11. Resources Instructor. TAs. Class Web page.
Lecture notes will be posted before class.
Office hours

12. Student Feedback Feedback is always welcome!
Chance to do it at the end of the quarter.
But you can also do it during the quarter…

13. Lectures The more interactivity, the better! Ask questions!
Or answer my questions.
Lecture notes:
Will be posted on-line before class.
But…

14. Project You may choose one of the following. 1. Recommended Project
Will be announced later
2. Self-defined Project
Any topic related to networking
Submit your proposal by 10/17
Need approval from me to continue

15. Reading reports
Introduction

16. Survey paper
Introduction

17. Midterm Exam November 9th.
Close book, can bring one-side 8.5"x11" note
Introduction

18. Assignment Submission
Submit hardcopy of your reading reports and survey paper
the project report and code

19. Assignment late submission policy
20% deduction for each day late.

20. Administrative Info Communication: E-mail preferred.
Send to both instructor AND TAs.

21. Course Outline Basic Knowledge of computer networking
Application layer
Transport layer
Network layer
Link layer
Advanced topics
Software defined networks
Cloud and data center networks
Wireless and mobile networks
Internet of things
Network security

22. My background
PhD in Computer Science (2013), University of Texas at Austin
Advisor: Simon Lam – researcher of the chapter for “The Link Layer” pp 511 22

23. BTW…. Simon Lam’s PhD advisor was Leonard Kleinrock, Professor at UCLA
researcher of the chapter for “Chapter 1”
Introduction

24. My Research Network algorithms, protocols, and systems
Routing, switching, management, etc.
Current focus: Internet of Things, Software Defined Networking, and Network Security
Introduction

25. Networks: overview 1.1 Terms of a network 1.2 network edge
end systems, access networks, links
1.3 network core
packet switching, circuit switching, network structure
1.4 protocol layers
Introduction 25

26. What are the components of a computer (communication) network?
Links, nodes, and
Terminals/hosts/end systems/servers
What’s the difference between “nodes” and “hosts”?

27. Nodes and hosts
Source: K. Salah Module 3.4

28. Nodes and Terminals
Terminals = Hosts, End-User Devices

29. What are the performance metrics we care about?
Latency
Bandwidth/throughput
Bandwidth: the max throughput a communication link can provide
Scalability
When size is large, will there be a problem?
Memory, cpu, latency, etc.
Reliability
When some nodes/hosts fail
Security
Financial cost
Introduction

30. Any network design is a trade-off
What are the trade-offs of the following designs:
Encryption/decryption
Redundancy
Peer-to-peer networks
Introduction

31. What’s the Internet: “Nuts and Bolts” View
Internet: “network of networks”
hierarchical
Institutional network
Mobile network
Global ISP
Home network
Regional ISP

32. What’s the Internet: “Service” View
Communication Infrastructure
enables distributed applications:
Web, VoIP, , games, e-commerce, file sharing
Communication services provided to apps:
reliable data delivery from source to destination
“best effort” (unreliable) data delivery
Institutional network
Mobile network
Global ISP
Home network
Regional ISP

33. A closer look at network structure:
network edge:
hosts: clients and servers
servers often in data centers
mobile network
global ISP
regional ISP
home
network
institutional
access networks, physical media: wired, wireless communication links
network core:
interconnected routers
network of networks

34. The network core
packet-switching: hosts break application-layer messages into packets
forward packets from one router to the next, across links on path from source to destination
each packet transmitted at full link capacity

35. Packet Switching: queueing delay, loss
R = 100 Mb/s D
R = 1.5 Mb/s B E
queue of packets
waiting for output link
queuing and loss:
If arrival rate (in bits) to link exceeds transmission rate of link for a period of time:
packets will queue, wait to be transmitted on link
packets can be dropped (lost) if memory (buffer) fills up

36. Alternative core: circuit switching
end-end resources allocated to, reserved for “call” between source & dest:
dedicated resources: no sharing
circuit-like (guaranteed) performance
circuit segment idle if not used by call (no sharing)
Commonly used in traditional telephone networks

37. Packet switching versus circuit switching
packet switching allows more users to use network!
example:
1 Mb/s link
each user:
100 kb/s when “active”
active 10% of time
circuit-switching:
10 users
packet switching:
with 35 users, probability > 10 active at same time is less than *
….. N
users
1 Mbps link
Q: how did we get value ?
Q: what happens if > 35 users ?

38. Packet switching versus circuit switching
is packet switching a “slam dunk winner?”
great for bursty data
resource sharing
simpler, no call setup
excessive congestion possible: packet delay and loss
protocols needed for reliable data transfer, congestion control
Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)?

39. Internet protocol stack
application: supporting network applications
FTP, SMTP, HTTP
transport: process-process data transfer
TCP, UDP
network: routing of datagrams from source to destination
IP, routing protocols
link: data transfer between neighboring network elements
Ethernet, (WiFi), PPP
physical: bits “on the wire”
application
transport
network
link
physical

40. Encapsulation source destination application transport network link
message M
application
transport
network
link
physical
segment Ht M Ht
datagram Ht Hn M Hn
frame Ht Hn Hl M
link
physical
switch
destination
network
link
physical Ht Hn M Ht Hn Hl M M
application
transport
network
link
physical Ht Hn M Ht M Ht Hn M
router Ht Hn Hl M

41. Next class
Please read Chapter 2 of the textbook BEFORE Class 41