1. Chapter 1: Introduction Internet Structure & Protocols
IT 424
Networks2
Chapter 1: Introduction
Internet Structure & Protocols
Ack.: Slides are adapted from the slides of the book: “Computer Networking” – J. Kurose, K. Ross

2. Overview What’s the Internet? Internet Hardware
Internet Software (Protocols)
Overview
Internet Performance
Internet History

3. Learning Outcomes 1
Define the structure of the Internet in terms of software and hardware 2
Identify the roles of end systems and the network core 3
Differentiate between circuit switching and packet switching 4
Explain the Internet structure as a network of networks 5
Describe the protocol stack in the Internet and the role of each layer 6
Evaluate the performance of the network in terms of end-to-end delay, packet loss and throughput

4. Overview What’s the Internet? Internet Hardware
Internet Software (Protocols)
Overview
Internet Performance
Internet History

5. What’s The Internet? Service View
mobile network
global ISP
regional ISP
home
network
institutional
Infrastructure that provides services to applications:
Web, VoIP, , games, e-commerce, social nets, …
Provides programming interface to applications
Hooks that allow sending and receiving app programs to “connect” to Internet
Provides service options, analogous to postal service

6. What’s The Internet? Component View Internet: “network of networks”
mobile network
global ISP
regional ISP
home
network
institutional
Internet: “network of networks”
Interconnected ISPs (Internet Service Providers)
Protocols control sending, receiving of messages
E.g., TCP, IP, HTTP, Skype,
Components: hardware + software
Internet standards
RFC: Request For Comments
IETF: Internet Engineering Task Force

7. Overview What’s the Internet? Internet Hardware
Internet Software (Protocols)
Overview
Internet Performance
Internet History

8. Internet Hardware Millions of connected computing devices:
mobile network
global ISP
regional ISP
home
network
institutional
smartphone PC
server
wireless
laptop
Millions of connected computing devices:
hosts = end systems running network applications
Communication links
Fiber, copper, radio, satellite
Transmission rate: bandwidth
wired
links
wireless
Packet switches: forward packets (chunks of data)
Routers and switches
router

9. A Closer Look at Network Structure
Internet Hardware – Network Structure
A Closer Look
at Network Structure
mobile network
global ISP
regional ISP
home
network
institutional
1-Network edge:
Hosts: clients and servers
Servers often in data centers
2- Network core:
Interconnected routers
Network of networks
3-Access networks, physical media:
Wired, wireless communication links

10. 1. The Network Edge “Fun” internet appliances End systems (hosts):
Hardware - 1. The Network Edge
1. The Network Edge
End systems (hosts):
Run application programs
e.g., WWW,
at “edge of network”
IP picture frame
Web-enabled
toaster +
weather forecaster
Slingbox: watch,
control cable TV remotely
Tweet-a-watt:
Monitor energy use
Internet
refrigerator
Internet phones
“Fun” internet appliances

11. Host: Sends Packets of Data
Hardware - 1. The Network Edge
Host: Sends Packets of Data
Host sending function:
Takes application message
Breaks into smaller chunks, known as packets, of length L bits
Transmits packet into access network at transmission rate R
Link transmission rate, aka link capacity, aka link bandwidth
R: link transmission rate
host 1 2
two packets,
L bits each

12. 2. The Network Core Mesh of interconnected routers Packet-switching:
Hardware - 2. The Network Core
2. The Network Core
Mesh of interconnected routers
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

13. Packet Switching Station breaks long message into packets
Hardware - 2. The Network Core
Packet Switching
application
transport
network
data link
physical
Station breaks long message into packets
Packets sent one at a time to the network
Packets from separate messages interleaved with other packets for transmission.
network
data link
physical
application
transport
network
data link
physical

14. Packet-Switching: Store-and-Forward
Hardware - 2. The Network Core
Packet-Switching:
Store-and-Forward
source
R bps
destination 1 2 3
L bits
per packet
Takes time to transmit (push out) L-bit packet into link at R bps
Store and forward: entire packet must arrive at router before it can be transmitted on next link

15. Packet Switching: Queuing Delay, Loss
Hardware - 2. The Network Core
Packet Switching: Queuing Delay, Loss A B C
R = 100 Mb/s
R = 1.5 Mb/s D 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

16. Alternative Core: Circuit Switching
Hardware - 2. The Network Core
Alternative Core: Circuit Switching
End-end resources allocated to, reserved for “call” between source & destination:
In diagram, each link has four circuits.
call gets 2nd circuit in top link and 1st circuit in right link.
Dedicated resources: no sharing
circuit-like (guaranteed) performance
Circuit segment idle if not used by call (no sharing)
Commonly used in traditional telephone networks

17. Circuit Switching: FDM versus TDM
Hardware - 2. The Network Core
Circuit Switching: FDM versus TDM
4 users
Example:
Frequency Division Multiplexing (FDM)
Frequency
Time
Time Division Multiplexing (TDM)
Frequency
Time

18. Packet Switching versus Circuit Switching
Hardware - 2. The Network Core
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 .0004 N
users
1 Mbps link
…..
Q: What happens if > 35 users ?

19. Packet Switching versus Circuit Switching
Hardware - 2. The Network Core
Packet Switching versus Circuit Switching
Packet Switching
Circuit Switching
Advantages
Flexibility, high throughput, cheap, simple connection
Disadvantages
Complex routing, performance?
Advantages
Simple, correct ordering, low delay
Disadvantages
Expensive, wasteful, slow connection setup
VS.

20. Packet Switching versus Circuit Switching
Hardware - 2. The Network Core
Packet Switching versus Circuit Switching
Is packet switching a “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: How to provide circuit-like behavior?
Bandwidth guarantees needed for audio/video apps
Still an unsolved problem
Q: Human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)?

21. 3. Access Networks Q: How to connect end systems to edge router?
Hardware - 3. Access Networks
3. Access Networks
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?

22. to/from headend or central office
Hardware - 3. Access Networks
Access Network:
Home Network
wireless
devices
to/from headend or central office
often combined
in single box
wireless access
point (54 Mbps)
router, firewall, NAT
cable or DSL modem
wired Ethernet (100 Mbps)

23. Enterprise Access Networks (Ethernet)
Hardware - 3. Access Networks
Enterprise Access Networks (Ethernet)
Ethernet
switch
institutional mail,
web servers
institutional router
institutional link to
ISP (Internet)
Typically used in companies, universities, etc
10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates
Today, end systems typically connect into Ethernet switch

24. Wireless Access Networks
Hardware - 3. Access Networks
Wireless Access Networks
Shared wireless access network connects end system to router
- via base station aka “access point”
to Internet
to Internet
Wireless LANs:
within building (100 ft)
802.11b/g (WiFi): 11, 54 Mbps transmission rate
Wide-area wireless access
provided by telco (cellular) operator, 10’s km
between 1 and 10 Mbps
3G, 4G: LTE

25. Internet Structure: Network of Networks
Hardware – Internet Structure
Internet Structure: Network of Networks
End systems connect to Internet via access ISPs (Internet Service Providers)
Residential, company and university ISPs
Access ISPs in turn must be interconnected.
So that any two hosts can send packets to each other
Resulting network of networks is very complex
Evolution was driven by economics and national policies
Let’s take a stepwise approach to describe current Internet structure

26. Internet Structure: Network of Networks
Hardware - Internet Structure
Internet Structure: Network of Networks
access
net …
Question: given millions of access ISPs, how to connect them together?

27. Internet Structure: Network of Networks
Hardware - Internet Structure
Internet Structure: Network of Networks
access
net …
connecting each access ISP to each other directly doesn’t scale: O(N2) connections.
Option: connect each access ISP to every other access ISP?

28. Internet Structure: Network of Networks
Hardware - Internet Structure
Internet Structure: Network of Networks
access
net …
global ISP
Option: connect each access ISP to a global transit ISP? Customer and provider ISPs have economic agreement.

29. Internet Structure: Network of Networks
Hardware - Internet Structure
Internet Structure: Network of Networks
access
net …
ISP B
ISP A
ISP C
But if one global ISP is viable business, there will be competitors …

30. Internet Structure: Network of Networks
Hardware - Internet Structure
Internet Structure: Network of Networks
access
net …
ISP B
ISP A
ISP C
IXP
peering link
Internet exchange point
But if one global ISP is viable business, there will be competitors …. which must be interconnected

31. Internet Structure: Network of Networks
Hardware - Internet Structure
Internet Structure: Network of Networks
access
net …
ISP B
ISP A
ISP C
IXP
regional net
… and regional networks may arise to connect access nets to ISPS

32. Internet Structure: Network of Networks
Hardware - Internet Structure
Internet Structure: Network of Networks
access
net …
ISP B
ISP A
IXP
regional net
Content provider network
… and content provider networks (e.g., Google, Microsoft, Akamai ) may run their own network, to bring services, content close to end users

33. Internet Structure: Network of Networks
Hardware - Internet Structure
Internet Structure: Network of Networks
At center: small # of well-connected large networks
“Tier-1” commercial ISPs (e.g., Level 3, Sprint, AT&T, NTT), national & international coverage
Content provider network (e.g, Google): private network that connects it data centers to Internet, often bypassing tier-1, regional ISPs

34. Tier-1 ISP: e.g., Sprint … to/from backbone peering to/from customers
Hardware - Internet Structure
Tier-1 ISP: e.g., Sprint …
to/from customers
peering
to/from backbone
POP: point-of-presence

35. Overview What’s the Internet? Internet Hardware
Internet Software (Protocols)
Overview
Internet Performance
Internet History

36. Protocol “Layers” Networks are complex, with many “pieces”: hosts
Internet Software
Protocol “Layers”
Networks are complex,
with many “pieces”:
hosts
routers
links of various media
applications
protocols
hardware, software

37. Why Layering? Dealing with complex systems:
Internet Software
Why Layering?
Dealing with complex systems:
Explicit structure allows identification, relationship of complex system’s pieces
layered reference model for discussion
Modularization eases maintenance, updating of system
change of implementation of layer’s service transparent to rest of system
e.g., change in gate procedure doesn’t affect rest of system
Layering considered harmful?

38. ISO/OSI Reference Model
Internet Software
ISO/OSI Reference Model
Presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventions
Session: synchronization, checkpointing, recovery of data exchange
Internet stack “missing” these layers!
these services, if needed, must be implemented in application
needed?
application
presentation
session
transport
network
link
physical

39. Internet Protocol Stack
Internet Software
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 destination source application transport network link
Internet Software
Encapsulation
source
message M
application
transport
network
link
physical
segment Ht Ht M
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. Overview What’s the Internet? Internet Hardware
Internet Software (Protocols)
Overview
Internet Performance
Internet History

42. How Do Loss and Delay Occur?
Network Performance
How Do Loss and Delay Occur?
Packet being transmitted (delay) A
Free (available) buffers: arriving packets
dropped (loss) if no free buffers B
Packets queueing (delay)
Packets queue in router buffers
Packet arrival rate to link (temporarily) exceeds output link capacity
Packets queue, wait for turn

43. Packet Loss buffer (waiting area) packet being transmitted A B
Network Performance - Packet Loss
Packet Loss A B
packet being transmitted
packet arriving to
full buffer is lost
buffer
(waiting area)
Queue (aka buffer) preceding link in buffer has finite capacity
Packet arriving to full queue dropped (aka lost)
Lost packet may be retransmitted by previous node, by source end system, or not at all

44. Four sources of packet delay
Network Performance - Delay
Four sources of packet delay A B
propagation
transmission
nodal
processing
queueing
dnodal = dproc + dqueue + dtrans + dprop
dproc: nodal processing
check bit errors
determine output link
typically < msec
dqueue: queueing delay
time waiting at output link for transmission
depends on congestion level of router

45. Four sources of packet delay
Network Performance - Delay
Four sources of packet delay A B
propagation
transmission
nodal
processing
queueing
dnodal = dproc + dqueue + dtrans + dprop
dtrans: transmission delay:
L: packet length (bits)
R: link bandwidth (bps)
dtrans = L/R
dprop: propagation delay:
d: length of physical link
s: propagation speed in medium (~2x108 m/sec)
dprop = d/s
dtrans and dprop
very different

46. Throughput server sends bits (fluid) into pipe pipe that can carry
Network Performance - Throughput
Throughput
server sends bits
(fluid) into pipe
pipe that can carry
fluid at rate
Rs bits/sec)
Rc bits/sec)
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

47. Throughput bottleneck link Rs bits/sec Rc bits/sec Rs bits/sec
Network Performance - Throughput
Throughput
Rs < Rc What is average end-end throughput?
Rc bits/sec
Rs bits/sec
Rs > Rc What is average end-end throughput?
Rs bits/sec
Rc bits/sec
Link on end-end path that constrains end-end throughput
bottleneck link

48. 10 connections (fairly) share backbone bottleneck link R bits/sec
Network Performance - Throughput
Throughput: Internet Scenario Rs Rc R
Per-connection end-end throughput: min(Rc,Rs,R/10)
In practice: Rc or Rs is often bottleneck
10 connections (fairly) share backbone bottleneck link R bits/sec

49. Overview What’s the Internet? Internet Hardware
Internet Software (Protocols)
Overview
Internet Performance
Internet History

50. Internet History 1961-1972: Early packet-switching principles
1972: ARPAnet public demo
NCP (Network Control Protocol) first host-host protocol
first program
ARPAnet has 15 nodes
1961: Kleinrock - queueing theory shows effectiveness of packet-switching
1964: Baran - packet-switching in military nets
1967: ARPAnet conceived by Advanced Research Projects Agency
1969: first ARPAnet node operational

51. Internet History 1972-1980: Internetworking, new and proprietary nets
1970: ALOHAnet satellite network in Hawaii
1974: Cerf and Kahn - architecture for interconnecting networks
1976: Ethernet at Xerox PARC
late70’s: proprietary architectures: DECnet, SNA, XNA
late 70’s: switching fixed length packets (ATM precursor)
1979: ARPAnet has 200 nodes
Cerf and Kahn’s internetworking principles:
minimalism, autonomy - no internal changes required to interconnect networks
best effort service model
stateless routers
decentralized control
define today’s Internet architecture

52. Internet History 1980-1990: new protocols, a proliferation of networks
New national networks: Csnet, BITnet, NSFnet, Minitel
100,000 hosts connected to confederation of networks
1983: deployment of TCP/IP
1982: smtp protocol defined
1983: DNS defined for name-to-IP- address translation
1985: ftp protocol defined
1988: TCP congestion control

53. Internet History 1990, 2000’s: commercialization, the Web, new apps
late 1990’s – 2000’s: more killer apps: instant messaging, P2P file sharing network security to forefront est. 50 million host, 100 million+ users backbone links running at Gbps
early 1990’s: ARPAnet decommissioned
1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)
early 1990s: Web
hypertext [Bush 1945, Nelson 1960’s]
HTML, HTTP: Berners-Lee
1994: Mosaic, later Netscape
late 1990’s: commercialization of the Web

54. Internet History 2005-present ~750 million hosts
Smartphones and tablets
Aggressive deployment of broadband access
Increasing ubiquity of high-speed wireless access
Emergence of online social networks:
Facebook: soon one billion users
Service providers (Google, Microsoft) create their own networks
Bypass Internet, providing “instantaneous” access to search, emai, etc.
E-commerce, universities, enterprises running their services in “cloud” (eg, Amazon EC2)

55. Conclusion
Conclusion
The Internet consists of network edge, network core and access
Packet switching is more suitable for the transmission of bursty data in the Internet
Layering architecture is very useful to isolate layers. Updating and changing one layer will not affect the others.
The performance of the network is measured by packet loss, throughput and delay
Delay is caused by four components: processing delay, transmission delay, propagation delay and queuing delay.
Processing, transmission, and propagation delay can be calculated. Queuing delay can’t be predicted

56. References
References
Computer Networking: A Top-Down Approach Featuring the Internet by James Kurose and Keith Ross, Addison Wesley, (chapter 1 )
Internet Protocol (RFC791)
A Brief History of the Internet, S. Segaller, TV Books, New York, 1998