1. CS 3214 Computer Systems
Lecture 21
Godmar Back

2. Announcements Project 5 due Nov 16 Ex 7 due Nov 18 Project 6 due Dec 8
CS 3214 Fall 2011

3. Some of these slides are substantially derived from slides provided by Jim Kurose & Keith Ross. Copyright on this material is held by Kurose & Ross. Used with permission. The textbook is Computer Networking: A Top Down Approach Featuring the Internet Jim Kurose, Keith Ross, Addison-Wesley, July 2004
Part 1
Networking
CS 3214 Fall 2011

4. The Internet: “nuts and bolts” view
local ISP
company
network
regional ISP
router
workstation
server
mobile
millions of connected computing devices: hosts = end systems
running network apps
communication links
fiber, copper, radio, satellite
transmission rate = bandwidth
routers: forward packets
CS 3214 Fall 2011

5. The Internet: “nuts and bolts” view
protocols control sending, receiving of msgs
e.g., TCP, IP, HTTP, FTP, PPP
Internet: “network of networks”
loosely hierarchical
public Internet versus private intranets
Internet vs internet
Internet standards
RFC: Request for comments
IETF: Internet Engineering Task Force
router
workstation
server
mobile
local ISP
regional ISP
company
network
CS 3214 Fall 2011

6. Network Virginia
Source: Sean Gillespie
CS 3214 Fall 2011

7. “Real” Internet delays and routes
traceroute: from host in Silicon Valley (keeda.stanford.edu) to host in Frankfurt, Germany (
> traceroute
traceroute to ( ), 30 hops max, 38 byte packets
1 Gates-rtr.Stanford.EDU ( ) ms ms ms
2 bbr2-rtr.Stanford.EDU ( ) ms ms ms
3 border2-rtr.Stanford.EDU ( ) ms ms ms
4 g1.ba21.b sfo01.atlas.cogentco.com ( ) ms ms ms
5 g1-1.core02.sfo01.atlas.cogentco.com ( ) ms ms ms
6 p14-0.core01.dca01.atlas.cogentco.com ( ) ms ms ms
7 p2-0.core01.iad01.atlas.cogentco.com ( ) ms ms ms
8 lambdanet.iad01.atlas.cogentco.com ( ) ms ms ms
9 LON-2-pos210.uk.lambdanet.net ( ) ms ms ms
10 DUS-2-pos700-0.de.lambdanet.net ( ) ms ms ms
11 DUS de.lambdanet.net ( ) ms ms ms
12 titanic.luka.de ( ) ms ms ms
CS 3214 Fall 2011

8. The Internet: a service view
communication infrastructure enables distributed applications:
Web, , games, e-commerce, file sharing
communication services provided to apps:
Connectionless unreliable
Connection-oriented reliable
CS 3214 Fall 2011

9. A closer look at network structure:
network edge: applications and hosts
network core:
routers
network of networks
access networks, physical media: communication links
CS 3214 Fall 2011

10. The network edge: end systems (hosts): client/server model
run application programs
e.g. Web,
at “edge of network”
client/server model
client host requests, receives service from always-on server
e.g. Web browser/server; client/server
peer-peer model:
minimal (or no) use of dedicated servers
e.g. Gnutella, KaZaA
CS 3214 Fall 2011

11. Connection-oriented service
Goal: data transfer between end systems
handshaking: setup (prepare for) data transfer ahead of time
Hello, hello back human protocol
set up “state” in two communicating hosts
TCP - Transmission Control Protocol
Internet’s connection-oriented service
TCP service [RFC 793]
reliable, in-order byte-stream data transfer
loss: acknowledgements and retransmissions
flow control:
sender won’t overwhelm receiver
congestion control:
senders “slow down sending rate” when network congested
CS 3214 Fall 2011

12. Connectionless service
Goal: data transfer between end systems
same as before!
UDP - User Datagram Protocol [RFC 768]:
connectionless
unreliable data transfer
no flow control
no congestion control
TCP-friendliness
App’s using TCP:
HTTP (Web), ssh (remote login), SMTP ( ), Bittorrent (file-sharing), XMPP (instant messenging)
App’s using UDP:
streaming media, teleconferencing, DNS, Internet telephony
CS 3214 Fall 2011

13. The Network Core
the fundamental question: how is data transferred through net?
circuit switching: dedicated circuit per call: telephone net
packet-switching: data sent thru net in discrete “chunks”
How are the network’s resources shared?
CS 3214 Fall 2011

14. What’s a protocol? a human protocol and a computer network protocol:Hi
TCP connection
req Hi
TCP connection
response
Got the
time?
Get
2:00
<file>
time
CS 3214 Fall 2011

15. Services vs Protocols (horizontal component)
Layer k may interact with peer layer k only via protocols
CS 3214 Fall 2011

16. Encapsulation source destination application transport network link
message
segment
datagram
frame
source
application
transport
network
link
physical Ht Hn Hl M
destination
router
switch
Encapsulation
CS 3214 Fall 2011

17. TCP/IP Reference Model
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18. TCP/IP Reference Model
See:
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19. TCP/IP Hourglass View UDP Ethernet IP Wireless ATM TCP NFS DNS FTP
HTTP
Application
Transport
Internet
Host-To-Network
CS 3214 Fall 2011

20. Typical Implementation
User App
Socket
Network Device
IP Layer
TCP Layer
user
Kernel: “top-half”
Kernel: “sw interrupt”
Kernel: “hw interrupt”
may cross
multiple
boundaries!
CS 3214 Fall 2011