Data Communication & Computer Networks
CS 1652
Jack Lange
University of Pittsburgh
The slides are adapted from the publisher’s material
All material copyright 1996-2009
J.F Kurose and K.W. Ross, All Rights Reserved
1-1
Course Objectives
 Understand modern data communication
systems and computer networks
Understand the key concepts
 How they are designed & implemented
 How they are operated
 How they are likely to evolve in the future

 Course Approach
Top-down : from what’s familiar to nuts and bolts
 The Internet as the main focus
 Hands-on experience on networked systems

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Administrativia
 Instructor: Jack Lange
 Email: jacklange@cs.pitt.edu
 Office: Sennott Square #5407
 Office Hours: Weds. 2-4PM
Teaching Assistant: TBD
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Communication
 Course homepage



http://www.cs.pitt.edu/~jacklange/teaching/cs1652-f13/
Announcements, clarifications, corrections
Additional resources for projects
 Google Group



http://groups.google.com/group/pitt-cs1652-f13
pitt-cs1652-f13@googlegroups.com
Private discussion group
• Open venue for class discussions and questions

Based on email (Pitt addresses)
• Email me if you want to use a different one
TextBooks
 Computer Networking: A Top-Down Approach
James Kurose and Keith Ross
 Fifth/Sixth Edition, Addison Wesley, 2010

 TCP/IP Illustrated, Volume I: The Protocols
Richard Stevens
 Addison Wesley, 1994

Class meeting times
 Lecture
 Tues/Thurs: 4:00-5:15PM
 Sennott Square, Rm. 6110
 Lab Sessions
 Sennott Square, Rm. 5506
 Periodically replace lectures
 Hands on exercises
 Answer project question
 Hopefully guest lectures
1-6
Networking Lab
 Sennott Square, Rm. 5506
 16 Linux machines (Fedore Core 13)
 Login: Hopefully will be your Pitt login
 Available for projects
• Can use other machines, but…
• Must work on lab equipment
 Dual NICS
 1 internal network interface to be used for projects
 1 external network interface for external access
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Homework
 Reading assignments
 Expected to read before each class
 Homework
 4 problem sets spaced over semester
 Projects
 Web server (20%)
 TCP (50%)
 Routing (30%)
 Check Syllabus!
Grading
 Grading
 Midterm (20%)
 Final (20%)
 4 Homework (10%)

3 Projects (50%)
 Late policy
 Submit by midnight of the due date
 10% penalty for every day late
Projects
 Work in groups of 2

C/C++ is required
 Lot of work, but will be worth it

Build a TCP stack and a Web server that runs on it

IP routing
 Highly Recommended: OS or having some
familiarity with Unix systems programming,
preferably in C or C++

Minet is in C++

BUILDING software is 50% of the grade of this class
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Today’s topic
 Computer Networks Overview

What’s the Internet?
• Nuts and bolts vs. service view

What’s a protocol?
• A set of rules between communicating entities

Network edge/core
• Hosts, access networks, physical media
• Packet switching/circuit switching, Internet structure
 Goal


Get “feel” and terminology
More depth, detail later in course
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What is the internet?
 Flows, packets, and bits
 Optical light, electricity, and radio waves
 Servers, clients, and peers
 Hosts, switches, and routers
What’s the Internet: Hardware view
 millions of connected
PC
server
computing devices:
hosts = end systems
wireless
laptop
cellular
smartphone 

access
points 
wired
links
communication links
fiber, copper, radio,
satellite
transmission rate =
bandwidth
Mobile network
Global ISP
Home network
Regional ISP
Institutional network
 routers: forward
router
packets (chunks of
data)
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What’s a protocol?
human protocols:
 “what’s the time?”
 “I have a question”
 introductions
… specific msgs sent
… specific actions
taken when msgs
received, or other
events
network protocols:
 machines rather than
humans
 all communication activity in
Internet governed by
protocols
protocols define format, order
of msgs sent and received
among network entities, and
actions taken on msg
transmission, receipt
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What’s a protocol?
a human protocol and a computer network protocol:
TCP connection
request
Hi
Hi
TCP connection
response
Got the
time?
2:00
Get http://www.awl.com/kurose-ross
time
<file>
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Where are we?
 What’s the Internet?

Nuts and bolts vs. service view
 What’s the protocol?
 Network edge/core
Hosts, access networks, physical media
 Packet switching/circuit switching, Internet
structure

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A closer look at network structure:
 network edge:
applications and hosts
 access networks,
physical media: wired,
wireless communication
links
 network core:



interconnected routers
network of networks
Edge routers “uplink” to
core routers
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The network edge: Traditionally where the action is
 end systems (hosts):

run application programs

e.g. Web, email

at “edge of network”
peer-peer
 client/server model


client host requests, receives service
from always-on server
e.g. Web browser/server; email
client/server
client/server
 peer-peer model:


minimal (or no) use of dedicated
servers
e.g. Skype, BitTorrent
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Internet structure: network of networks
 roughly hierarchical
 at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T,
NTT, Quest, Level3, Global Crossing, Tata, Savvis,
TeliaSonera), national/international coverage
 treat each other as equals
Tier-1
providers
interconnect
(peer)
privately
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
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Internet structure: network of networks
 “Tier-2” ISPs: smaller (often regional) ISPs

Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs
Tier-2 ISP pays
tier-1 ISP for
connectivity to
rest of Internet
 tier-2 ISP is
customer of
tier-1 provider
Tier-2 ISP
Tier-2 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISP
Tier 1 ISP
Tier-2 ISPs
also peer
privately with
each other.
Tier-2 ISP
Tier-2 ISP
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Internet structure: network of networks
 “Tier-3” ISPs and local ISPs

last hop (“access”) network (closest to end systems)
local
ISP
Local and tier3 ISPs are
customers of
higher tier
ISPs
connecting
them to rest of
Internet
Tier 3
ISP
Tier-2 ISP
local
ISP
local
ISP
local
ISP
Tier-2 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISP
local
local
ISP
ISP
Tier 1 ISP
Tier-2 ISP
local
ISP
Tier-2 ISP
local
ISP
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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
Tier-2 ISP
local
local
ISP
ISP
Tier 1 ISP
Tier-2 ISP
local
ISP
Tier-2 ISP
local
ISP
1-17
Tier-1 ISP: e.g., Sprint
POP: point-of-presence
to/from backbone
peering
…
….
…
…
…
to/from customers
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What’s the Internet: Software-ish view
 protocols control sending,
Mobile network
receiving of msgs


e.g., TCP, IP, HTTP, Skype,
Ethernet
Provides meaning
 Internet standards


Global ISP
RFC: Request for comments
IETF: Internet Engineering Task
Force
Home network
Regional ISP
Institutional network
 Internet: “network of networks”


loosely hierarchical
public Internet versus private
intranet
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What’s the Internet: Service view
 communication infrastructure
enables distributed
applications:
 Web, VoIP, email, games,
e-commerce, file sharing
 communication services
provided to apps:
 reliable data delivery from
source to destination

“best effort” (unreliable)
data delivery
1-16
Access networks and physical media
Q: How to connect end
systems to edge
router?
 residential access nets
 institutional access
networks (school,
company)
 mobile access networks
Keep in mind:
 bandwidth (bits per
second) of access
network?
 shared or dedicated?
1-22
Ethernet Internet access
100 Mbps
Institutional
router
100 Mbps
To Institution’s
ISP
Ethernet
switch
1 Gbps
100 Mbps
server
 Typically used in companies, universities, etc
 10 Mbps, 100Mbps, 1Gbps, 10Gbps Ethernet
 Today, end systems typically connect into Ethernet
switch
1-32
Wireless access networks
 shared wireless access network
connects end system to router

via base station aka “access point”
 wireless LANs:

802.11b/g (WiFi): 11 or 54 Mbps

802.11n: ~450Mbps
router
base
station
 wider-area wireless access



provided by telco operator
~1Mbps over cellular system
(EVDO, HSDPA, 3G)
next up: WiMAX (10’s Mbps) over
wide area
mobile
hosts
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Digital Subscriber Line (DSL)
Existing phone line:
0-4KHz phone; 4-50KHz
upstream data; 50KHz-1MHz
downstream data
home
phone
Internet
DSLAM
telephone
network
splitter
DSL
modem
home
PC




central
office
Also uses existing telephone infrastruture
up to 1 Mbps upstream
up to 8 Mbps downstream
dedicated physical line to telephone central office
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Residential access: cable modems
Diagram: http://www.cabledatacomnews.com/cmic/diagram.html
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Cable Network Architecture: Overview
Typically 500 to 5,000 homes
cable headend
cable distribution
network (simplified)
home
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Cable Network Architecture: Overview
server(s)
cable headend
cable distribution
network
home
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Cable Network Architecture: Overview
cable headend
cable distribution
network (simplified)
home
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Cable Network Architecture: Overview
FDM (next class):
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Channels
cable headend
cable distribution
network
home
1-30
Fiber to the Home (FTTH)
ONT
optical
fibers
Internet
OLT
ONT
optical
fiber
central office
optical
splitter
ONT
 Optical links from central office to the home
 Two competing optical technologies:

Passive Optical Network (PON) – e.g. Verizon FIOS

Active Optical Network (AON) – Switched Ethernet
 Much higher Internet rates; fiber also carries
television and phone services
1-31
Home networks
Typical home network components:
 DSL or cable modem
 router/firewall/NAT
 Ethernet
 wireless access
point
to/from
cable
headend
cable
modem
router/
firewall
Ethernet
wireless
laptops
wireless
access
point
1-34
Physical media
 Bit: propagates between
transmitter/rcvr pairs
 physical link: what lies
between transmitter &
receiver
 guided media:

signals propagate in solid
media: copper, fiber, coax
Twisted Pair (TP)
 two insulated copper
wires


Category 3: traditional
phone wires, 10 Mbps
Ethernet
Category 5:
100Mbps Ethernet
 unguided media:

signals propagate freely,
e.g., radio
1-35
Physical media: coax, fiber
Coaxial cable:
 two concentric copper
conductors
 bidirectional
 baseband:

single channel on cable
• Digital signal

legacy Ethernet
Fiber optic cable:
 glass fiber carrying light pulses,
each pulse a bit
 high-speed operation:

high-speed point-to-point
transmission (e.g., 10’s-100’s Gps)
 low error rate: repeaters spaced
far apart ; immune to
electromagnetic noise
 broadband:

multiple channels on cable
• Analog Signal

HFC
1-36
Physical media: radio
 signal carried in
electromagnetic spectrum
 no physical “wire”
 bidirectional
 propagation environment
effects:
Radio link types:
 terrestrial microwave

e.g. up to 45 Mbps channels
 LAN (e.g., Wifi)

11Mbps, 54 Mbps
 wide-area (e.g., cellular)
3G cellular: ~ 1 Mbps

reflection

obstruction by objects
 satellite

interference


Kbps to 45Mbps channel (or multiple
smaller channels)

270 msec end-end delay

geosynchronous versus low altitude
1-37
Summary
 The Internet can be defined as


A set of hosts running distributed applications
communicating via routers
Infrastructure providing popular services
 Protocols define the message formats, orders,
actions on transmission and reception
 Access networks: at the network edge



Residential (dial-up, DSL, Cable, FTTH)
Institutional (Ethernet)
Wireless (Wi-fi, WiMAX)
1-38
Cable modems
 Does not use telephone infrastructure

Instead uses cable TV infrastructure
 HFC: hybrid fiber coax

asymmetric: up to 30Mbps downstream, 2
Mbps upstream
 network of cable and fiber attaches homes to
ISP router
 homes share access to router
 unlike DSL, which has dedicated access
1-25