IT 347: Chapter 1
Instructor: Christopher Cole
Some slides taken from Kurose & Ross book
Top-down?
 Networking layers
 Application layer = “high growth area”
 The Web, P2P, media streaming, etc.
application
presentation
session
transport
network
link
physical
Internet protocol stack
 application: supporting network applications – send
messages
 FTP, SMTP, HTTP
application
 transport: process-process data transfer – send
segments
 TCP, UDP
transport
 network: routing of datagrams from source to
destination
 IP, routing protocols
 link: data transfer between neighboring network
elements – send frames
 PPP, Ethernet
 physical: bits “on the wire”
 Ethernet over twisted pair, coax, fiber, etc.
1-3
Introduction
network
link
physical
source
message
segment
M
Ht
M
datagram Hn Ht
M
frame Hl Hn Ht
M
Encapsulation
application
transport
network
link
physical
link
physical
switch
destination
M
Ht
M
Hn Ht
Hl Hn Ht
M
1-4
M
application
transport
network
link
physical
Introduction
Hn Ht
Hl Hn Ht
M
M
network
link
physical
Hn Ht
M
router
 Hosts or End Systems
 Computer, laptop, phone, gaming consoles, web cams, TVs
(security systems, toasters, etc.)
 Connected together with
 Communication links (twisted pair, coax, fiber)
 Packet switches (routers or link-layer switches)
 Information is sent (and split up into) packets (header added
to each package)
 Transmission rate (each link is different)
 ISPs connect you to the internet
 Protocols control what happens
 TCP and IP are important to internet
 Internet standards by Internet Engineering Task Force (IETF)
 They put out Requests for Comments (RFCs)
 Define HTTP, SMTP, etc.
 Project 1 has the protocol of creating a client-server program.
What’s a protocol?
a human protocol and a computer network protocol:
Hi
TCP connection
request
Hi
TCP connection
response
Got the
time?
Get http://www.awl.com/kurose-ross
2:00
<file>
time
Q: Other human protocols?
1-7
Introduction
The network edge:
 end systems (hosts):
Mobile network
Global ISP
 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:


1-8
minimal (or no) use of
dedicated servers
e.g. Skype, BitTorrent
Introduction
Home network
Regional ISP
Institutional network
How do you connect?
 Dial-up
 Cable
 shared
 DSL
 Downstream 50 kHz to 1 Mhz
 Upstream 4 kHz to 50 kHz
 Phone 0 to 4 kHz
 Fiber to Home
 FIOS (also shared?)
 Other
 WiMAX, 3G access
 http://www.wigle.net (wireless networks)
Physical Media
 Often, the cost is not the physical link, but the labor of
installation
 Twisted Pair Copper
 1 Gbps (faster now?)
 Coaxial Cable
 Fiber Optics
 Incredibly long distances (overseas)
 Internet Backbone
 Satellite (hundreds of Mbps)
 Radio
Packet Switching
 Packets (long messages split up)
 Source & Destination address
 Go through each switch
 Output queue
 Packet loss
 Circuit switching/packet switching
 How does a packet get through? Forwarding table
ISPs and Internet Backbones
 Relatively small number of Tier 1 ISPs all linked together
(Sprint, Verizon, MCI, AT&T, Level3, Qwest)
 How do you know if you are Tier 1?
 These are Internet Backbone networks
 Tier 2 are customers of Tier 1 and providers to rest
 Sometimes peer with each other
Internet structure: network of networks
 a packet passes through many networks!
local
ISP
Tier 3
ISP
Tier-2 ISP
local
ISP
local
ISP
local
ISP
Tier-2 ISP
Tier 1 ISP
Tier 1 ISP
1-13
local
IntroductionISP
Tier-2 ISP
local
ISP
Tier 1 ISP
Tier-2 ISP
local
ISP
Tier-2 ISP
local
ISP
Okay, any Questions?
Delays
 Processing Delay: time it takes for router to read header of packet






(microseconds)
Queuing Delay: time to wait in line to get pushed to the wire (0 time if there is
nobody in the queue)
Transmission Delay: Time to push the packet out onto the wire. Depends on the
speed of the link and length of packet. Packet Length = L bits, link speed =
R Mbps. Transmission delay = L/R
Propagation Delay: depends on the distance between the two routers. d is
distance between routers, and s is propagation speed of link (typically 2x10^8
meters/sec to 3). Measure d/s.
dnodal = dproc + dqueue + dtrans + dprop
traffic intensity: L/R is in important number again. If a is the average queuing
delay, La/R should never be > 1 (otherwise packets will just stack up)
Other delays: modulation/encoding delay for modems, etc.
Throughput
 throughput: rate (bits/time unit) at which bits transferred
between sender/receiver
 instantaneous: rate at given point in time
 average: rate over longer period of time
link
capacity
that
can carry
server,
with
server
sends
bits pipe
Rs bits/sec
fluid
at rate
file of
F bits
(fluid)
into
pipe
Rs bits/sec)
to send to client
1-16
Introduction
link that
capacity
pipe
can carry
Rfluid
c bits/sec
at rate
Rc bits/sec)
Throughput (more)
 Rs < Rc What is average end-end throughput?
Rs bits/sec
Rc bits/sec
 Rs > Rc What is average end-end throughput?
Rs bits/sec
Rc bits/sec
bottleneck link
link on end-end path that constrains end-end throughput
1-17
Introduction
Network Security
 The internet was not made with security in mind
 SMTP protocol
 Denial of Service attacks
 Anybody can sniff packets
 IP spoofing
 Man in the middle attacks