Post on 29-Dec-2015
transcript
CS 3214Computer Systems
Godmar Back
Lecture 23
Announcements
• Project 5 due Dec 8• Exercise 10 handed out• Exercise 11 coming before Thanksgiving
CS 3214 Fall 2010
NETWORKINGPart 1
CS 3214 Fall 2010
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
CS 3214 Fall 2010
The Internet: “nuts and bolts” view
• millions of connected computing devices: hosts = end systems
• running network apps
• communication links– fiber, copper, radio,
satellite– transmission rate = bandwidth
• routers: forward packets
local ISP
companynetwork
regional ISP
router workstation
servermobile
CS 3214 Fall 2010
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
local ISP
companynetwork
regional ISP
router workstation
servermobile
CS 3214 Fall 2010
Network Virginia
Source: Sean Gillespie
CS 3214 Fall 2010
“Real” Internet delays and routes
> traceroute www.titanic-magazin.detraceroute to www.titanic-magazin.de (62.75.228.90), 30 hops max, 38 byte packets 1 Gates-rtr.Stanford.EDU (171.64.72.1) 0.523 ms 0.339 ms 0.304 ms 2 bbr2-rtr.Stanford.EDU (171.64.1.161) 0.401 ms 0.346 ms 0.334 ms 3 border2-rtr.Stanford.EDU (171.64.1.148) 4.288 ms 1.070 ms 1.458 ms 4 g1.ba21.b003123-1.sfo01.atlas.cogentco.com (66.250.7.137) 5.231 ms 7.975 ms 9.097 ms 5 g1-1.core02.sfo01.atlas.cogentco.com (66.28.6.13) 11.364 ms 16.192 ms 16.961 ms 6 p14-0.core01.dca01.atlas.cogentco.com (66.28.4.210) 85.497 ms 84.084 ms 80.291 ms 7 p2-0.core01.iad01.atlas.cogentco.com (154.54.2.202) 89.268 ms 88.548 ms 90.046 ms 8 lambdanet.iad01.atlas.cogentco.com (154.54.11.162) 156.812 ms 200.935 ms 157.819 ms 9 LON-2-pos210.uk.lambdanet.net (81.209.156.29) 159.647 ms 159.709 ms 166.504 ms10 DUS-2-pos700-0.de.lambdanet.net (82.197.136.18) 176.365 ms 163.668 ms 165.177 ms11 DUS1-5029.de.lambdanet.net (217.71.104.30) 171.229 ms 173.782 ms 171.486 ms12 titanic.luka.de (62.75.228.90) 172.654 ms 183.307 ms 173.239 ms
traceroute: from host in Silicon Valley (keeda.stanford.edu) to host in Frankfurt, Germany (www.titanic-magazin.de)
CS 3214 Fall 2010
The Internet: a service view• communication
infrastructure enables distributed applications:– Web, email, games, e-
commerce, file sharing
• communication services provided to apps:– Connectionless unreliable– Connection-oriented reliable
CS 3214 Fall 2010
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 2010
The network edge:• end systems (hosts):
– run application programs– e.g. Web, email– at “edge of network”
• client/server model– client host requests, receives
service from always-on server– e.g. Web browser/server; email
client/server
• peer-peer model:– minimal (or no) use of
dedicated servers– e.g. Gnutella, KaZaA
CS 3214 Fall 2010
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 2010
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 (email),Bittorrent (file-sharing), XMPP (instant messenging)
App’s using UDP:• streaming media,
teleconferencing, DNS, Internet telephony
CS 3214 Fall 2010
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 2010
What’s a protocol?a human protocol and a computer network protocol:
Hi
Hi
Got thetime?
2:00
TCP connection req
TCP connectionresponseGet http://www.awl.com/kurose-ross
<file>time
CS 3214 Fall 2010
Services vs Protocols
(horizontal component)• Layer k may interact with peer layer k only via
protocols
CS 3214 Fall 2010
messagesegment
datagram
frame
sourceapplicatio
ntransportnetwork
linkphysical
HtHnHl M
HtHn M
Ht M
M
destination
application
transportnetwork
linkphysical
HtHnHl M
HtHn M
Ht M
M
networklink
physical
linkphysical
HtHnHl M
HtHn M
HtHnHl M
HtHn M
HtHnHl M HtHnHl M
router
switch
Encapsulation
CS 3214 Fall 2010
TCP/IP Reference Model
CS 3214 Fall 2010
TCP/IP Reference Model
See: http://www.isc.org/store/logoware-clothing/isc-9-layer-osi-model-cotton-t-shirt
CS 3214 Fall 2010
TCP/IP Hourglass View
UDP
Ethernet
IP
WirelessATM
TCP
NFSDNS FTPHTTP
Host-To-Network
Internet
Application
Transport
CS 3214 Fall 2010
Typical Implementation
may cross
multiple
boundaries!
User App
Socket
Network Device
IP Layer
TCP Layer
user
Kernel:“top-half”
Kernel:“sw interrupt”
Kernel:“hw interrupt”