1. Computer Networks
Orientation

2. Chapter 1: Orientation 1.0 Why Networking 1.1 What is the Internet?
1.2 Network Structure
Network edge
Network core
Network access and physical media
1.3 Internet structure and ISPs
1.4 Delay & loss in packet-switched networks
1.5 Protocol layers, service models
1.6 History

3. Why Networking ! Distributed Software Resource Sharing Communication
Application (will be discussed): WEB, , 3-tier appl., …
Database
Directory
Resource Sharing
File, Software, Data, … (Network File System, File Transfer, …)
CPU, Memory, Peripherals, …
Communication
, Chat, TV, Radio, Video Conference, Telephone, .
Virtual Terminal (Remote Login)

4. Application Software Platform Services Graphics Data Interchange
Data Management
User Interface
Software Engineering
Communication Services
Application Agent
Application Program Interface (API)
Platform (OS + Hardware)
Application process
Application process
Application Program Interface (API)
Platform (OS + Hardware)
Inter-process Communication

5. Distributed Applications or Network Application: Client/Server
Application Software (Client Part)
Application Software (Server Part)
Client (user) Agent
Server Agent
Application Program Interface (API)
Application Program Interface (API)
System
Networking Software & Hardware
Networking Software & Hardware
Platform (OS + Hardware)
Platform (OS + Hardware)
Client Agents Examples:
Internet Explorer, Opera
MS’s Outlook + SMTP, Netscape’s Messenger + SMTP, Eudora + SMTP
… next slide
Communication
Network

6. Client/Server Applications
Application Process
(Client Side)
Application Process
(Server Side)
Application process
Application Program Interface (API)
Application Program Interface (API)
Networking Software & Hardware
Networking Software & Hardware
Platform (OS + Hardware)
Platform (OS + Hardware)
Server Agents Examples:
Internet Information Sever,
Appachi
SQL query engines
Networking (Communication) Software Examples: TCP, UDP; IP…
Communication
Network

7. Communicating Entities
Do the computers communicate?
Do the users communicate?
Do the processes communicate?
Web client process
Web server process
user
Communication
Network
Mail client process
Mail client process
user
user
Mail server process

8. Layered Application Model
Presentation
User Interface
Business (Application Logic)
Data (Database Access)
Client Part
Application Software
Server Parts

9. Client Part
Presentation: The client agent remains focused on presenting information to or receiving input from the user.
User Interface: User’s access to the application logic via client agent. It can be dynamic and configured by user. It is build on the top of the user interface control.
Dynamic User Interface:
Customizing the look (example:
Customizing the content ( examples: my.yahoo.com , )

10. Server Parts Business Rules (Application Logic) Data (Database Access)
Units of processing or algorithms that represents concept of importance to the organization using database.
Data (Database Access)
Logic to connect to database; access/manipulate data held within databases.

11. Layered Application: 3-Tier Client/Server Model
Runs by Application
Server Agent
Run by Client Agent
Business
(Application Logic)
User Interface
Presentation
user
Application Sever
Runs by Database
Server Agent
Client Workstation
(rich client)
Communication
Network
Data
(Data Access and Storage)
Run by Client Agent
User Interface
Presentation
user
Data Server
Database
Mobile Client
Workstation
(thin client)

12. “Logical Tiers vs Physical Tiers
Application Model
Logical Tiers
Presentation
User Interface
Business
Data
Physical Tiers
Client workstation
Application server
Data Base
Presentation
Client Workstation
User Interface
Business (Application Logic)
Application Server
Data
(Database Access)
Database

13. Chapter 1 Outline 1.0 Why Networking 1.1 What is the Internet?
1.2 Network Structure
Network edge
Network core
Network access and physical media
1.3 Internet structure and ISPs
1.4 Delay & loss in packet-switched networks
1.5 Protocol layers, service models
1.6 History

14. Local ISP (LAN) LAN Switch Router Telephone Lines Repeater hub Servers
Client
Printer
Server
LAN Switch
Remote Access Server
Modem pools
Telephone
Lines
Router
External Link
Servers
modem
modem
External Link
Router

15. internet: network of networks
Mobile network
Global ISP
router
links
server
Home network
modem
Regional ISP
workstation
Base Station
mobile station
Stelite
Company network

16. Internet millions of connected computing devices: hosts, end-systems
PCs workstations, servers, …
Personal Data Assistances, phones, …
running network apps
communication links
fiber, copper, radio, satellite
transmission rate = bandwidth
routers: forward packets
Networking Hardware and Software
Protocols, Hubs, LAN Switches, Repeaters,

17. Internet protocols control sending, receiving of messages
e.g., TCP, IP, HTTP, FTP, PPP, …
Internet: “network of networks”
loosely hierarchical
public Internet versus private intranet
Internet standards (IAB)
RFC: Request for comments
IETF: Internet Engineering Task Force

18. Popular Internet Applications
The Web
Instant Messaging
Login into a remote computer (Telnet, Virtual Terminal, SSH)
P2P file sharing
File Transfer
Multi-User Networked games
Stored Video/Audio
Real time Video/Audio
Internet Telephone
Secure Shell or SSH is a set of standards and an associated network protocol that allows establishing a secure channel between a local and a remote computer.

19. Internet Services Examples? Goals? Search Engines (Google)
(Yahoo, Hotmail)
Shopping (Amazon)
Auctions (eBay)
Instance Massaging (AOL, Yahoo)
P2P file sharing (Gnutella)
E-learning
Games …
Goals?
Fast service (low latency)
Service all users (scalability)
Always available (fault tolerance)

20. intranet the Internet Intranet: access is denied from outside intranet
router
firewall
intranet
the Internet
Intranet: access is denied from outside
A private corporate network consisting of hosts, routers, and networks that use TCP/IP technology. An intranet may or may not connect to the global Internet.

21. extranet Extranet: an internet of networks each of which is belong to
Company 3
Company 1
Company 2
Extranet: an internet of networks
each of which is belong to
individual company or organization

22. IP addressing: ICANN
Q: How does an ISP get block of addresses and Names?
A: ICANN: (Internet Corporation For Assigned Names and Numbers)
The organization that took over the IANA duties after Postel’s death.
IANA: (Internet Assigned Number Authority) Essentially one individual (Jon Postel). IANA was originally responsible for assigning IP addresses and the constants used in TCP/IP protocols. Replaced by ICANN in 1999.

23. IP addressing: ICANN
ICANN coordinates the assignment of identifiers that must be globally unique for the Internet to function.
allocates addresses
manages DNS
assigns domain names, resolves disputes
assigns default port numbers
sets protocol parameter

24. DNS Root Servers (a) NSI Herndon, VA (c) PSInet Herndon, VA
(b) USC-ISI Marina del Rey, CA
(l) ICANN Marina del Rey, CA
(e) NASA Mt View, CA
(f) Internet Software C. Palo Alto, CA
(i) NORDUnet Stockholm, Sweden
(k) RIPE London, UK
(m) WIDE Tokyo, Japan
(a) NSI Herndon, VA
(c) PSInet Herndon, VA
(d) U Maryland College Park, MD
(g) DISA Vienna, VA
(h) ARL Aberdeen, MD
(j) NSI (TBD) Herndon, VA

25. What’s the Internet: a service view
Mobile network
communication infrastructure enables distributed applications:
Web, , games, e-commerce, database., file (MP3) sharing
communication services provided to apps:
connectionless
connection-oriented
Global ISP
Home network
Regional ISP
Company network

26. Chapter 1: Outline 1.0 Why Networking 1.1 What is the Internet?
1.2 Network Structure
Network edge
Network core
Network access and physical media
1.3 Internet structure and ISPs
1.4 Delay & loss in packet-switched networks
1.5 Protocol layers, service models
1.6 History

27. Network Structure network edge: 1- applications network core:
Mobile network
Global ISP
network edge:
1- applications
2- hosts (end-systems)
network core:
1- routers
2- links between routers
access networks, physical media:
1- communication links
2- modems
Home network
Regional ISP
Company network

28. The network edge:✓ end systems (hosts): client/server model
Mobile network
end systems (hosts):
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. Skyp, Bit Torent ✓
Global ISP ✓ ✓ ✓
Home network ✓ ✓
Regional ISP ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
Company network

29. Applications Client-Server Client Side Software Server Side Software
Peer Side ✓ ✓ ✓ ✓
Client Side
Software
Client-Server
Client Side Software
Server Side Software ✓ ✓
2. Peer-to-Peer ! (chapter 2) ✓ ✓ ✓ ✓ ✓ ✓
Server Side
Software ✓ ✓
Peer Side

30. Server Types Web server File Server (example: Network File System)
Database Server
Application Server
Groupware Server
Software Server
Object Server
Proxy Server
DNS Server

31. Network edge: connection-oriented service
Goal: data transfer between end systems
handshaking: setup (prepare for) data transfer ahead of time
set up “state” in two communicating hosts

32. Network edge: connectionless service
Goal: data transfer between end systems
No handshaking: No setup (no preparation for) data transfer ahead of time.
Data transfer without any notice.

33. Chapter 1 Outline 1.0 Why Networking 1.1 What is the Internet?
1.2 Network Structure
Network edge
Network core
Network access and physical media
1.3 Internet structure and ISPs
1.4 Delay & loss in packet-switched networks
1.5 Protocol layers, service models
1.6 History

34. The Network Core: ✓ mesh of interconnected routers
Mobile network ✓
Global ISP
mesh of interconnected routers
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” ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
Home network ✓ ✓ ✓ ✓ ✓ ✓ ✓
Regional ISP ✓ ✓ ✓ ✓ ✓ ✓ ✓
Company network

35. Network Core: Circuit Switching
Mobile network
Global ISP
End-end resources reserved for “call”
link bandwidth, switch capacity
dedicated resources: no sharing
circuit-like (guaranteed) performance
call setup required
Home network
Regional ISP
Company network

36. Network Core: Circuit Switching
network resources (e.g., bandwidth) divided into “pieces”
pieces allocated to calls
resource piece idle if not used by owning call (no sharing)
dividing link bandwidth into “pieces”
frequency division
time division

37. Packet Switching: Statistical Multiplexing
10 Mbs
Ethernet C
statistical multiplexing A
1.5 Mbs
empty
buffer B
queue of packets
waiting for output
link D E
Sequence of A & B packets does not have fixed pattern  statistical multiplexing.
In TDM each host gets same slot in revolving TDM frame.

38. Packet switching versus circuit switching
Packet switching allows more users to use network!
User: 1
1 Mbps link
User: N
Switch
Each user:
sends 100 kbps when “active”
is active p =10% of time

39. How many Users? Circuit-Switch connect up to 10 simultaneous users.
11th and beyond be blocked!
binomial distribution
The probability that k users be active together:
Packet-Switch connect all users.
Example: if N=35 users,
for active users ≤ 10 probability >
for active users > 10 probability <
No Blocking for 11th and after. There is queue instead.

40. Packet Switching Users
Switch supports 35 simultaneous users (connections)
Up to 10 users be active: no queue, packet switching has almost the same delay performance as circuit switching.
More than 10 users be active: output queue begin to grow and the connections experience queuing delay.
Because the probability of having 11 or more simultaneous active users is ,almost the same delay performance as circuit switching.
Packet switching allows more than 3 times the number of users.

41. Packet switching versus circuit switching
Great for bursty trafic
resource sharing
simpler
no call setup
Excessive congestion:
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 applications.

42. Traffic Profiles Constant-bit-rate traffic Variable-bit-rate traffic
Bursty traffic

43. Packet-switching: store-and-forwardL R R R
Takes L/R seconds to transmit (push out) packet of L bits on to link or R bps
Entire packet must arrive at router before it can be transmitted on next link: store and forward
delay = 3L/R
Example:
L = 7.5 Mbits; message size
R = 1.5 Mbps; link bandwidth
message transmission time = L/R = 5 sec
delay = 3L/R = 15 sec

44. Packet Switching: Message SegmentingL
Now break up the message into 5000 packets
Each packet 1,500 bits
1 msec to transmit packet on one link
pipelining: each link works in parallel
Delay reduced from 15 sec to sec

45. Packet-switched networks: forwarding
Goal: move packets through routers from source to destination
we’ll study several path selection (i.e. routing)algorithms (chapter 4)
datagram network:
destination address in packet determines next hop
routes may change during session
virtual circuit network:
each packet carries tag (virtual circuit ID), tag determines next hop
fixed path determined at call setup time, remains fixed thru call
routers maintain per-call state

46. Network Taxonomy Telecommunication networks Circuit-switched networks
Packet-switched
networks
FDM
TDM
Networks
with VCs
Datagram
Networks
Internet is a Datagram network and provides both
connection-oriented (TCP) and connectionless services
(UDP) to applications.

47. Chapter 1 Outline 1.0 Why Networking 1.1 What is the Internet?
1.2 Network Structure
Network edge
Network core
Network access and physical media
1.3 Internet structure and ISPs
1.4 Delay & loss in packet-switched networks
1.5 Protocol layers, service models
1.6 History

48. Access networks and physical media
Q: How to connection 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? ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
Regional ISP ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
Company network

49. Residential access: point to point access
Dialup via modem
up to 56Kbps direct access to router (often less)
Can’t surf and phone at same time: can’t be “always on”
modem
ADSL: asymmetric digital subscriber line
up to 1 Mbps upstream (today typically < 256 kbps)
up to 8 Mbps downstream (today typically < 1 Mbps)
FDM: 50 kHz - 1 MHz for downstream
4 kHz - 50 kHz for upstream
0 kHz - 4 kHz for ordinary telephone

50. Company access: local area networks
company/univ local area network (LAN) connects end system to edge router
Ethernet:
shared or dedicated link connects end system and router
10 Mbs, 100Mbps, Gigabit Ethernet
deployment: institutions, home LANs happening now
LANs: chapter 5
modem

51. Wireless access networks
shared wireless access network connects end system to router
via base station aka “access point”
wireless LANs:
802.11b (WiFi): 11 Mbps
wider-area wireless access
provided by telco operator
3G ~ 384 kbps
Will it happen??
WAP/GPRS in Europe
router
base
station
mobile
stations (hosts)

52. Home networks Typical home network components: ADSL or cable modem
router/firewall/NAT
Ethernet
wireless access point
(Network Address Translation) A technology that allows hosts with private addresses to communicate with an outside network such as the global Internet.
router/Firewall/NAT
wireless
laptops
to/from
Internet
cable modem
Ethernet (switched)
wireless access point

53. Physical (Transmission) Media-Link
Physical Media (link) : what lies between transmitter & receiver.

54. Twisted Pair Twisted Pair (TP) Unshielded/Shielded UTP/STP
Category 3: traditional phone wires, 10 Mbps Ethernet
Category 5 TP: 100Mbps Ethernet …

55. Physical Media: coax, fiber
Coaxial cable:
two concentric copper conductors
bidirectional
baseband:
single channel on cable
legacy Ethernet
broadband:
multiple channel on cable
HFC
Fiber optic cable:
glass fiber carrying light pulses, each pulse a bit
high-speed operation:
high-speed point-to-point transmission (e.g., 5 Gps)
low error rate: repeaters spaced far apart ; immune to electromagnetic noise

56. Cables
LAN Twisted-Pair Cables
Fiber Optic and Patch Cords

57. Physical media: radio Radio link types: terrestrial microwave
e.g. up to 45 Mbps channels
LAN (WLAN)
2Mbps, 11Mbps
wide-area
3G: hundreds of kbps
WiMAX
satellite
up to 50Mbps channel (or multiple smaller channels)
270 msec end-end delay
geosynchronous versus LEOS
signal carried in electromagnetic spectrum
no physical “wire”
bidirectional
propagation environment effects:
reflection
obstruction by objects
interference

58. IEEE Standards View of Wireless Network Technologies
WWAN
<15 km
(proposed)
MAN
<5 km
70 Mbit/s
802.16a/e
WiMAX
Standard for
Fixed broadband
Wireless.
WLAN
<100 m
11-54 Mbit/s
802.11a/b, e, g, h
Wi-Fi®
Includes a/b/g.
PAN
<10 m
~1 Mbit/s
(Bluetooth)
(UWB) *
(ZigBee)**

59. LAN, MAN, WAN
Source:

60. WIMAX: Worldwide Interoperability for Microwave Access
Goal of WIMAX:
Provide high-speed Internet access to home and business subscribers, without wires.
Frequency range:
10-66 GHz and sub 11 GHz
Supports:
Legacy voice systems
Voice over IP
TCP/IP
Applications with different QoS requirements.

61. Chapter 1 Outline 1.0 Why Networking 1.1 What is the Internet?
1.2 Network Structure
Network edge
Network core
Network access and physical media
1.3 Internet structure and ISPs
1.4 Delay & loss in packet-switched networks
1.5 Protocol layers, service models
1.6 History

62. Tier Definition-Tier 1
Tier 1 providers make settlement-free interconnection arrangements with other Tier 1 providers, in which the two networks agree to carry each other's traffic (so-called "peering" with one another) at no cost.
No Tier 1 carriers have to pay for IP transit to any other Tier 1, and in general all other ISPs directly or indirectly pay the Tier 1s for access to their networks.
Tier 1 providers own the physical medium over which information is carried, as well as the network equipment which manages that information.

63. Tier 1 IPv4 ISPs
The following are believed to be the only Tier 1 ISPs worldwide:
AOL Transit Data Network (ATDN)-AS 1668
AT&T-AS 7018
Global Crossing (GX)-AS 3549
Level 3-AS 3356
Verizon Business (UUnet)-AS 701
Nippon Telegraph and Telephone Corp. (NTT)-AS 2914
Qwest-AS 209
SAVVIS (Cable & Wireless America)-AS 3561
Sprint Nextel Corporation-AS 1239
In the Internet, an autonomous system (AS) is a collection of IP networks and routers under the control of one entity (or sometimes more) that presents a common routing policy to the Internet. See RFC 1930 for additional detail on this updated definition.

64. Tier-1 ISPs Interconnection
Links Data Rates: 622Mbps, Gbps
POPs
▪▪▪
Private “peering” agreements between two backbone companies often bypass NAP 1
POPs
▪▪▪
POPs
▪▪▪ 9 2
NAP
NAP
POP: Point Of Presence ( a group of routers) 4
NAP: Network Access Point 3
POPs
▪▪▪
▪▪▪
POPs
Tier-2 ISPs

65. AT&T Global Network

66. Sprint US backbone network
DS3 (45 Mbps)
OC3 (155 Mbps)
OC12 (622 Mbps)
OC48 (2.4 Gbps)
Seattle
Atlanta
Chicago
Roachdale
Stockton
San Jose
Anaheim
Fort Worth
Orlando
Kansas City
Cheyenne
New York
Pennsauken
Relay
Wash. DC
Tacoma …
to/from customers
peering
to/from backbone ….
POP: point-of-presence

67. UUNET US backbone network

68. Tier Definition-Tier 2, 3
There is no formal interconnection hierarchy, lower-tier companies are divided into two categories:
Tier 2 - A network who peers with other networks, but still pays for transit to reach some portion of the Internet.
Tier 3 - A network who solely purchases transit from other networks to reach the Internet.
Many of Tier 2 and 3 companies are very large Internet providers, but since they purchase IP transit from other networks they are not considered Tier 1.

69. Tier-2 ISPs / Access ISPs
▪▪▪
To Tier-1 ISP
POPs
▪▪▪▪
Tier-2
ISP
Tier-2
ISP
Access
ISP
Servers
modem
Remote Clients
Access
ISP C o m 3
RAS +
Modem Pool
modem
Clients

70. Internet structure: network of networks
roughly hierarchical
at center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity, Sprint, AT&T), national/international coverage
treat each other as equals
NAP
Tier-1 providers also interconnect at public network access points (NAPs)
Tier 1 ISP
Tier-1 providers interconnect (peer) privately
Tier 1 ISP
Tier 1 ISP

71. 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 ISPs also peer privately with each other, interconnect at NAP
Tier-2 ISP
Tier-2 ISP
Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet
tier-2 ISP is customer of
tier-1 provider
Tier 1 ISP
NAP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISP
Tier-2 ISP
Tier-2 ISP

72. Internet structure: network of networks
“Tier-3” ISPs and local ISPs
last hop (“access”) network (closest to end systems)
local
ISP
local
ISP
Tier 3
ISP
local
ISP
local
ISP
Local and tier- 3 ISPs are customers of
higher tier ISPs
connecting them to rest of Internet
Tier-2 ISP
Tier-2 ISP
Internet
Connection
Providers (ICPs)
For local ISPs
Tier 1 ISP
NAP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISP
local
ISP
Tier-2 ISP
Tier-2 ISP
local
ISP
local
ISP
local
ISP

73. End to End Communication
a packet passes through many networks!
Access
ISP
Tier 3
ISP
Access
ISP
Access
ISP
Access
ISP
Tier-2 ISP
Tier 1 ISP
NAP
Tier 1 ISP
Tier 1 ISP
Access
ISP
Access
ISP
Access
ISP
Access
ISP

74. Chapter 1 Outline 1.0 Why Networking 1.1 What is the Internet?
1.2 Network Structure
Network edge
Network core
Network access and physical media
1.3 Internet structure and ISPs
1.4 Delay & loss in packet-switched networks
1.5 Protocol layers, service models
1.6 History

75. How do loss and delay occur?
packets queue in router buffers
packet arrival rate to link exceeds output link capacity
packets queue, wait for turn
packet being transmitted (delay) A
free (available) buffers: arriving packets
dropped (loss) if no free buffers
packets queue (delay) B

76. Four sources of packet delay
1. nodal processing:
check bit errors
determine output link
2. queueing
time waiting at output link for transmission
depends on congestion level of router
transmission A
propagation B
nodal
processing
queue

77. Delay in packet-switched networks
3. Transmission delay:
R=link bandwidth (bps)
F =number of bits in packet (bits)
time to send bits into link = F/R
4. Propagation delay:
d = length of physical link
s = propagation speed in medium (~2x108 m/sec)
propagation delay = d/s
Note: s and R are very
different quantities!
transmission A
propagation B
nodal
processing
queue
bit length: s/R [m]
packet length: Fs/R [m]

78. Caravan analogy car=bit caravan = packet
toll booth 10 3
toll booth 2 1
ten-car caravan
120 km
car=bit
caravan = packet
cars speed (km/hr) = propagation speed (m/sec)
service rate at toll booth (car/sec) = bandwidth (bit/sec)

79. Caravan Analogy. toll booth 120 km cars speed = 120 km/hr = 2km/min3 10 1
4km
cars speed = 120 km/hr = 2km/min
toll booth takes 12 sec to service a car ( car/sec)
Q: How long until caravan is lined up before 2nd toll booth?
Time to “push” entire caravan through toll booth onto highway = 12*10 = 120sec = 2min
Time for last car to propagate from 1st to 2nd toll both: 120km/(120km/hr)= 1 hr
A: 62 minutes

80. Caravan Analogy.. toll booth 120 km toll booth10
toll booth 9
20km 8 7 3 2
20km 1
cars speed = 1200 km/hr = 20km/min
toll booth takes 1min to service a car ( 1 car/min)
Q: Will cars arrive to 2nd booth before all cars serviced at 1st booth?
After (1+6) min, 1st car at 2nd booth and 3 cars still at 1st booth.
1st bit of packet can arrive at 2nd router before packet is fully transmitted at 1st router!

81. Bit Length bit length = s/R Packet length = Fs/R
s = propagation speed of energy in the link (medium) [m/sec]
R = link bandwidth [bps]
F = number of bits in packet [bits]
Example : s= 200m/µs;
R=10Mbps [Tbit =0.1 µs];
F= 500 Byte = 4000 bit
20m
link
source
destination
Propagation direction
4000
3999 1 2 3 4
20×4000 m

82. Links: Delay and Bandwidth
Latency for propagating data along the link
Corresponds to the “length” of the link
Typically measured in seconds
Bandwidth (Capacity)
Amount of data sent (or received) per unit time
Corresponds to the “capacity” of the link
Typically measured in bits per second
delay x bandwidth
(bit)
Bandwidth
(Bps)
Delay
(sec)

83. Transmission and Propagation Delays
R bits per second (bps)
T seconds
F bits T
Transmission time = F/R
time
Propagation delay =T = Link Length/speed
1/speed = 3.3 nanosec/m in free space
4 nanosec/m in copper
5 nanosec/m in fiber

84. Transmission and Propagation Examples
T >> F/R T
F = 1 Kbyte
R = 1 Gbps
100 Km, fiber =>T = 500 μsec
F/R = 8 μsec
time
F/R
T << F/R T
F = 1 Kbyte
R = 100 Mbps
1 Km, fiber => T = 5 μsec
F/R = 80 μsec
F/R
time

85. Queuing Delay The queue has Q bits when packet arrives.
Packet has to wait for the queue to drain before being transmitted.
Capacity = R bps
Propagation delay = T sec
F bits
Q bits
Queueing Delay = Q/R T
F/R
time

86. Queuing delay. R=link bandwidth (bps) F=packet length (bits)
Rin
Rout a I
Average queuing delay 1
R=link bandwidth (bps)
F=packet length (bits)
a=average packet arrival rate
I=traffic intensity = Fa/Rout
I ~ 0: average queuing delay small
I —> 1: delays become large
I > 1: more “work” arriving than can be serviced, average delay infinite!

87. Total delay dprocess = nodal processing delay dqueue = queuing delay
typically a few msecs or less
dqueue = queuing delay
depends on congestion
dtrans = transmission delay
= F/R, significant for low-speed links
dprop = propagation delay
d/s, a few microsecs to hundreds of msecs

88. Switching: Store and Forward
A packet is stored (queued) before being forwarded (sent)
10 Mbps
5 Mbps
100 Mbps
10 Mbps
Sender
Receiver
F/10Mbps
F/5Mbps T
F/100Mbps
time
F/10Mbps
Throughput = F/T bps

89. Store and Forward: Two Packets Example
10 Mbps
5 Mbps
100 Mbps
10 Mbps
Receiver
Sender T
time
Throughput = 2F/T bps

90. Network Throughput
10 Mbps
5 Mbps
100 Mbps
10 Mbps
Receiver
Sender
Equivalent
R= 2F/T
Receiver
Sender
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

91. “Real” Internet delays and routes
What do “real” Internet delay & loss look like?
Traceroute program: provides delay measurement from source to router along end-end Internet path towards destination. For all i:
sends three packets that will reach router i on path towards destination
router i will return packets to sender
sender times interval between transmission and reply.
3 probes
3 probes
3 probes

92. “Real” Internet delays and routes
traceroute: gaia.cs.umass.edu to
Three delay measements from
gaia.cs.umass.edu to cs-gw.cs.umass.edu
1 cs-gw ( ) 1 ms 1 ms 2 ms
2 border1-rt-fa5-1-0.gw.umass.edu ( ) 1 ms 1 ms 2 ms
3 cht-vbns.gw.umass.edu ( ) 6 ms 5 ms 5 ms
4 jn1-at wor.vbns.net ( ) 16 ms 11 ms 13 ms
5 jn1-so wae.vbns.net ( ) 21 ms 18 ms 18 ms
6 abilene-vbns.abilene.ucaid.edu ( ) 22 ms 18 ms 22 ms
7 nycm-wash.abilene.ucaid.edu ( ) 22 ms 22 ms 22 ms
( ) 104 ms 109 ms 106 ms
9 de2-1.de1.de.geant.net ( ) 109 ms 102 ms 104 ms
10 de.fr1.fr.geant.net ( ) 113 ms 121 ms 114 ms
11 renater-gw.fr1.fr.geant.net ( ) 112 ms 114 ms 112 ms
12 nio-n2.cssi.renater.fr ( ) 111 ms 114 ms 116 ms
13 nice.cssi.renater.fr ( ) 123 ms 125 ms 124 ms
14 r3t2-nice.cssi.renater.fr ( ) 126 ms 126 ms 124 ms
15 eurecom-valbonne.r3t2.ft.net ( ) 135 ms 128 ms 133 ms
( ) 126 ms 128 ms 126 ms
17 * * *
18 * * *
19 fantasia.eurecom.fr ( ) 132 ms 128 ms 136 ms
trans-oceanic
link
* means no reponse (probe lost, router not replying)

93. Packet Loss
Queue ( buffer) preceding a link in buffer has finite capacity
When packet arrives and find a full queue, packet is dropped (lost)
Fraction of lost packets increases as the traffic intensity increases
Performance at a node is often measured not only in terms of delay, but also in terms of the probability of packet loss.
Lost packet may be retransmitted by previous node, by source end system, or not retransmitted at all

94. Chapter 1 Outline 1.0 Why Networking 1.1 What is the Internet?
1.2 Network Structure
Network edge
Network core
Network access and physical media
1.3 Internet structure and ISPs
1.4 Delay & loss in packet-switched networks
1.5 Protocol layers, service models
1.6 History

95. Network Models The network model is defined in 3-D space.
App. Software (User) Plane:
Data Communication.
Control Plane:
Connection setup and connection Maintenance,
Resources access control and access level control.
Management Plane:
Measurement and management of network performance.
We study this part only!
App. Software
(User)
Plane
Management
Control
Network Model.

96. Complex Systems and Layering
Breaks up a complex system into smaller manageable sub-systems,
can compose simple service to provide complex ones
Abstraction of implementation details,
separation of implementation and specification,
can change implementation as long as service interface is maintained,
Can reuse functionality,
upper layers can share lower layer functionality.

97. Breaking a Complex System
Networking software and hardware is a complex system.
Complex system is organized into layers.
Organization is hierarchical:
Lower layer entity provide service(s) to upper layer entity.
Peer entities communicate based on a protocol.
Process
Process
Services
communications
Services
Entity5
Entity5
Services
Services
Entity4
Entity4
Services
Services
Entity3
Entity3
Services
Services
Entity2
Entity2
Services
Services
Entity1
Entity1
Computer 1
Computer 2

98. Layers n & n+1 Service Interface
Some Terminologies
Service access point (SAP) (port number, e.g. 80 for http)
interface between an upper layer and a lower layer
Protocol data unit (PDU)
packets exchanged between peer entities
Service data units (SDU)
packets handed to a layer by an upper layer
PDUn = SDUn + header or trailer
Layern+1 Entity
PDUn+1
Layern+1 Entity
SAPn
SAPn
Layers n & n+1 Service Interface
SDUn
SDUn
Layern Entity
PDUn
Layern Entity

99. Layering: A Modular Approach
Sub-divide the problem
Each layer relies on services from layer below
Each layer exports services to layer above
Interface between layers defines interaction
Hides implementation details
Layers can change without disturbing other layers
Application
Application-to-application channels
Host-to-host connectivity
Link hardware

100. Protocols A protocol is:
a set of rules and formats
that govern the communication between communicating peers,
a set of valid meaning full messages
that exchanged between communicating peers.
A protocol is necessary for any function that requires cooperation between peers

101. Protocol Messages and Actions
Syntax of a message
what fields does it contain?
in what format?
Semantics of a message
what does a message mean?
for example, not-OK message means receiver got a corrupted file
Actions to take on receipt of a message
for example, on receiving not-OK message, retransmit the entire file

102. Protocol Architecture
protocol = agreed upon conventions (for communication)
architecture = method or style of building
So “protocol architecture” is the common “design style” for:
set of related network protocols.

103. ISO OSI reference model
A set of protocols is open if
protocol details are publicly available
changes are managed by an organization whose membership and transactions are open to the public
A system that implements open protocols is called an open system
International Organization for Standards (ISO) prescribes a standard to connect open systems
open system interconnect (OSI)
Has greatly influenced thinking on protocol stacks

104. ISO OSI Reference model Service architecture Protocol architecture
formally defines what is meant by a layer, a service etc.
Service architecture
describes the services provided by each layer and the service access point
Protocol architecture
set of protocols that implement the service architecture
compliant service architectures may still use non-compliant protocol architectures

105. Intermediate systems (Routers)
OSI Seven Layers
layer-to-layer communication (services)
Peer-layer communication (protocol)
Physical link
Application
Application
Presentation
Presentation
Session
Session
Transport
Transport
Network
Network
Network
Network
Data Link
Data Link
Data Link
Data Link
Physical
Physical
Physical
Physical
End system 1 (host)
Intermediate systems (Routers)
End system 2 (host)

106. Five Layers Application Programs Services
Process-to-Process Channels (end to end actions)
Host-to-Host Connectivity (hop by hop actions)
Link Management
(hop to hop delivery)
(hides physical network from upper layers)
Hardware
(physical interface)

107. Internet Layers Application Application Presentation Session Transport
ftp, http, …
ASCII/Binary IP
TCP
Ethernet
Application
Application
Presentation
Transport
Session
Transport
Network
Network
Link
Link
Physical
The 7-layer OSI Model
The 4-layer Internet model

108. OSI model vs TCP/IP model
application
presentation
Session
transport
network
Link
physical
application
transport
network
interface
application
transport
network
link
physical
TCP/IP (Internet) Protocol

109. Protocol Functions -1 Data manipulation (touching / moving)
Move to/from net
Error detection
Buffering for retransmission
Encryption
Moving to/from app address space
Presentation formatting

110. Protocol Functions - 2 Control transfer Flow / congestion control
Detecting network transmission problems: loss, duplication, re-ordering
Acknowledgement
Multiplexing
Time stamping
Framing

111. Summary of layers

112. Proprietary Protocols
AppleTalk [Apple Computer Inc.]
DECnet [Digital Equipment Corporation]
IPX/SPX (netware) [Novell Communications]
Server Message Block (SMB) and Common Internet File System (CIFS) [Microsoft]
Systems Network Architecture (SNA) [IBM] …

113. Why seven layers? Need a top and a bottom ( 2 layers )
Need to hide physical link, so need datalink ( 1 layer )
Need both end-to-end and hop-by-hop actions; so need at least the network and transport layers ( 2 layers )
Session and presentation layers are not so important, and are often ignored
So, we need at least 5, and 7 seems to be excessive
Note that we can place functions in different layers

114. Physical Layer Moves bits between physically connected end-systems
Standard prescribes
coding scheme to represent a bit
shapes and sizes of connectors
bit-level synchronization

115. DataLink Layer Communication over a single link,
Introduces the notion of a frame
set of bits that belong together,
Idle markers tell us that a link is not carrying a frame,
Begin and end markers delimit a frame,
Uses unique local addresses,
Very dependent on underlying physical link properties,
Usually bundle both physical and datalink layer on host adaptor card
example: Ethernet.

116. Network Layer
Carrying data from source to destination in a hop by hop manner.
Hides way of behaving and feature that a datalink layer has.
Provides unique network-wide addresses
At intermediate systems
participates in routing protocol to create routing tables
responsible for forwarding packets
scheduling the transmission order of packets
choosing which packets to drop

117. Transport Layer end-to-end communication,
Transport layer creates the abstraction of an error-controlled, flow-controlled and multiplexed end-to-end link,
Some transport layers provide fewer services,
e.g. simple error detection, no flow control, and no retransmission,
lightweight transport layer,

118. Session Layer Not common
Provides full-duplex service, expedited data delivery, and session synchronization
Token management.
Duplex
if transport layer is simplex, concatenates two transport endpoints together
Expedited data delivery
allows some messages to skip ahead in end-system queues, by using a separate low-delay transport layer endpoint
Synchronization
allows users to place marks in data stream and to roll back to a prespecified mark

119. Presentation Layer
Unlike other layers which deal with headers presentation layer touches the application data
Hides data representation differences between applications
e.g. endian-ness
characters (ASCII, unicode, EBCDIC.)
Can also encrypt data
Usually ad hoc
Postal network
translator translates contents before giving it to chief clerk
Internet
no standard presentation layer
only defines network byte order for 2- and 4-byte integers

120. Application Layer Provide services to the application process,
Hides the networking for the application process,
Very dependent on the application process properties,
Usually bundle with the application process.

121. Protocol Scalability- 1
Computer networks will grow in 4 respects: 
size (number of devices connected and number of routers),
speed (bandwidth of the physical layer),
type of service (integrated data/multimedia/computing/… networks),
growth of wireless and mobile connections.
For a network protocol to be scalable, it must work over a wide range of growth in these 4 areas. 

122. Protocol Scalability- 2
For size it must supports:
Orders of magnitude growth in the address space,
Additional demands upon the routing protocols used to deliver packets to a destination. 
For speed:
Orders of magnitude increases in bandwidth (hence data rate) dramatically change the relative importance of transmission time and latency (which is essentially fixed) in the calculations used in flow/congestion control algorithms. 

123. Protocol Scalability- 3
For type of service:
New services challenge the “best effort” delivery philosophy of the original network design.
Quality Of Service parameters is changing when new services and applications introduced.
For wireless and mobile:
Access, Handovers and Air-Capacities are the issues behind the growth of wireless nodes.

124. Layers and Addresses application transport network link physical
Application Layer
domain name
e.g.
Transport Layer
the identity of the application in the destination host
Port number: 2 bytes
e.g. 80
Network Layer
the network identity of the destination host
IP address: 4 bytes for IPv4
e.g
Link Layer
the identity of network interface card
MAC address (physical address): 6 bytes
e.g E-6A-93
application
transport
network
link
physical

125. Layering and Data-1 Each layer takes data from above
adds header information to create new data unit
passes new data unit to layer below
Source process
Destination process M
application
transport
network
link
physical
application
transport
network
link
physical M
message
segment M Ht M Ht Hn Hl Tl Ht
datagram Hn M M Ht Hn Hl Tl
frame
PDUs: frame, datagram (packet), segment, message

126. Layering and Data-2 Different devices switch different things
Physical layer: electrical signals (repeaters and hubs)
Link layer: frames (bridges and switches)
Network layer: packets (routers)
Application gateway
Transport gateway
Frame header
Packet header
TCP header
User Data+
App. header
Router
Bridge, switch
Repeater, hub

127. NETWORK Layering and Protocol Appl. Soft. Appl. Soft. application
App. Layer Protocols
(ftp, http, SMTP, …)
Transport Layer
Protocol (TCP, UDP)
Network Layer
Protocols (IP, OSPF, RSVP)
Link Layer
Protocols (Ethernet, FDDI, …)
application
transport
network
link
physical
Physical Layer
Physical Communication Channel

128. Protocol layering and data
App. Process decides to send
a message to its counterpart
Message
App. Process
App. Layer adds its header,
sends the message to transport layer Ha
Message
application
Transport layer breaks down
the message into several parts,
add its header to each part
And makes segments.
It sends one-by-one segments
to network layer
transport Ht Ht Ht Ht
network

129. Encapsulation1 source destination application transport network link
message M
application
transport
network
link
physical
segment Ht M Ht
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

130. Encapsulation2 source destination application transport network link
message M
application
transport
network
link
physical
segment Ht M
datagram Ht Hn M
frame Ht Hn Hl M
link
physical
switch
destination
network
link
physical
application
transport
network
link
physical
router

131. Protocol Layer Data [throughput] Units
Appl. Soft.
Appl. Soft.
[tps], [HTTPops/s]
,[NFS IOPS]
application
transport
network
link
physical
application
transport
network
link
physical
message
[mes/sec]
Segment
[seg/sec]
Datagram
[Packet/sec]
Frame
[frame/sec]
Baud = changes in signal/sec
1st layer PDU
(physical frame)
[bps]
[Baud], [Hz]
Physical Communication Channel

132. Network Bandwidth, Throughput and Goodput
Application Layer
Transport Layer
Network Layer
Link Layer
Physical layer
Bandwidth Throughput Goodput
Tps, HTTPops/s,…
Segmant/s
Packet/s
Frame/s
Bit/s
Bandwidth: The rate at which the data units can be transmitted.
Throughput: The rate at which the data units are delivered to the receiver computer.
It is a function of load.
Its upper-band is Bandwidth.
Goodput: The rate at which the data units are delivered to the receiver application.
Its upper-band is the Throughput.

133. Throughput, Goodput vs Load
System
Capacity
Load

134. Example: Network Layer Goodput
Efficiency:

135. Protocols/Services application transport network link physical
Application Program
Services
application
transport
network
link
physical
End-to-End
protocols
Transport Services
Hop-to-Hop
protocols

136. What Transport Service does an App Need?
Data loss
some apps (e.g., audio) can tolerate some loss
other apps (e.g., file transfer, telnet) require 100% reliable data transfer
Throughput
some apps (e.g., multimedia) require minimum amount of bandwidth to be “effective”
other apps (“elastic apps”) make use of whatever bandwidth they get
Timing
some apps (e.g., Internet telephony, interactive games) require low delay to be “effective”

137. Requirements of Selected Network Applications
Data loss
Throughput
Time Sensitive
file transfer
no loss
elastic no
web documents
elastic (few kbps)
real-time
audio/video
loss-tolerant
audio: few kbps-1Mbps
video:10kbps-5Mbps
yes, 100s of msec
stored audio/video
same as above
interactive games
few kbps-10kbps
instant messaging
yes and no

138. From Application Viewpoint
API
App. Software
transport
network
link
physical
application
Controlled
by OS
by App. Soft.
Application Program Interface (API)
Communication Software & Hardware
Platform (OS + Hardware)
Application Software

139. Layering: Physical Communication
data
application
transport
network
link
physical
Host A
Router R
modem
network
link
physical
application
transport
network
link
physical
Host B
modem
data
application
transport
network
link
physical
application
transport
network
link
physical

140. Layering: Logical Communication-1
application
transport
network
link
physical
modem
Each layer:
distributed
“entities” implement layer functions at each node
entities perform actions, exchange messages with peers

141. Layering: Logical Communication
application
transport
network
link
physical
modem
data
ack
E.g.: transport
take data from app
add addressing, reliability check info to form “datagram”
send datagram to peer
wait for peer to ack receipt
analogy: post office

142. TCP/IP protocol stack mime ftp http smtp telnet snmp tftp rtp dns …
ftp: file transfer protocol
http; hypertext transfer protocol
Smtp: simple mail transfer protocol
Mime: multipurose Internet mail extensions
telnet=virtual terminal
icmp: Internet control message protocol
ospf: open shortest path first protocol
rsvp: resource reservation protocol
igmp: Internet group management protocol
simple network
management pr.
trival file
transfer pr.
real time pr.
mime
ftp
http
smtp
telnet
domain name
service
snmp
tftp
rtp
dns …
Transmission Control Pr. (TCP)
User Datagram Pr. (UDP)
arp: address resolution protocol
rarp: reverse address resolution protocol
rsvp
igmp
Internet Protocol (IP)
icmp
ospf
arp
rarp
Ethernet, Wireless, token ring, FDDI, ATM, Frame relay, SNA, X25

143. IP HourGlass middle age: a narrowing mind, a widening waist IP TCP UDP
Applications
Token
radio, copper, fiber
802.11
PPP
Eth. IP
TCP
UDP
Applications
Token
radio, copper, fiber
802.11
PPP
Eth.
diffserv
intserv
mcast
mobile
NAT
IPSEC
IP “hourglass”
Middle-age IP “hourglass” ?
middle age: a narrowing mind, a widening waist

144. IP HourGlass Modern: a expanding mind, a slim waist IP TCP UDP
overlay
services
Token
radio, copper, fiber
802.11
PPP
Eth.
client
server
apps
application overlays IP
TCP
UDP
Applications
Token
radio, copper, fiber
802.11
PPP
Eth.
IP “hourglass”
Modern IP “hourglass” ?
Modern: a expanding mind, a slim waist

145. Chapter 1 Outline 1.0 Why Networking 1.1 What is the Internet?
1.2 Network Structure
Network edge
Network core
Network access and physical media
1.3 Internet structure and ISPs
1.4 Delay & loss in packet-switched networks
1.5 Protocol layers, service models
1.6 History

146. Common View of the Telphone Network
brain (smart)
lock (you can’t get in)
brick (dumb)

147. Common View of the IP Network

151. Internet Host Count
Internet Systems Consortium, Inc. (ISC) is a nonprofit corporation
dedicated to supporting the infrastructure of the universal connected self-organizing Internet and
has autonomy to participates by developing and maintaining core production quality software, protocols, and operations.

152. Internet Standard: RFCs
Introduction Year
RFC Numbers
ftp://ftp.rfc-editor.org/in-notes/rfc-editor/tutorial.latest.pdf

153. 1961-1972: Early packet-switching principles
Internet History
: Early packet-switching principles
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
1972:
ARPAnet demonstrated publicly
NCP (Network Control Protocol) first host-host protocol
first program
ARPAnet has 15 nodes

154. 1972-1980: Internetworking, new and proprietary nets
Internet History
: Internetworking, new and proprietary nets
1970: ALOHAnet satellite network in Hawaii
1973: Metcalfe’s PhD thesis proposes Ethernet
1974: Cerf and Kahn - architecture for interconnecting networks
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

155. 1980-1990: new protocols, a proliferation of networks
Internet History
: new protocols, a proliferation 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
new national networks: Csnet, BITnet, NSFnet, Minitel
100,000 hosts connected to confederation of networks

156. 1990, 2000’s: commercialization, the Web, new apps
Internet History
1990, 2000’s: commercialization, the Web, new apps
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
Late 1990’s – 2000’s:
more killer apps: instant messaging, peer2peer file sharing (e.g., Naptser)
network security to forefront
est. 50 million host, 100 million+ users
backbone links running at Gbps

157. References & Links Complimentary Hyperlinks References and Hyperlinks
This part provides hyperlinks to interesting (and hopefully useful) computer-networking resources. Most of these resources provide complimentary information to the material in chapter 1. If you're asked to write a paper pertaining to a specialized topic in computer networking, these resources should serve as a good starting point for your research.
References and Hyperlinks

158. Complimentary Hyperlinks 1
IEEE History Center
Oral Histories that have been collected to commemorate the 50th Anniversary of the IEEE Communications Society. A number of interesting interviews with pioneers in the field.
International Engineering Consortium: Web ProForum Tutorials
More than 150 tutorials on communications and networking topics, with a focus on cutting edge technology. The tutorials vary in terms of their technical depth, but many are outstanding, and all are extremely well-written and very readable. This is the first place we look when looking for an on-line survey or tutorial.

159. Complimentary Hyperlinks 2
Broadband: Bringing home the bits
Extensive report on the importance and future of residential broadband access from the Computer Science And Telecommunications Board, National Research Council, January 2002
Webopedia
Online dictionary for computer and Internet technology
Internet Economics
Comprehensive index for resources relating to Internet economics, including regulation and pricing.

160. Complimentary Hyperlinks 3
traceroute.org
As discussed in Section 1.6, Traceroute provides routes and packet delays between pairs of hosts in the Internet. This site gives you direct access to hundreds of source hosts from which you can trace routes to arbitrary destination hosts. Choose a country, a source host in that country, and any destination host -- then see how the packets weave their way through the Internet.
Internet Engineering Task Force (IETF)
The IETF is an open international community concerned with the development and operation of the Internet and its architecture. The IETF was formally established by the Internet Architecture Board (IAB), in The IETF meets three times a year; much of its ongoing work is conducted via mailing lists by working groups. Typically, based upon previous IETF proceedings, working groups will convene at meetings to discuss the work of the IETF working groups. The IETF is administered by the Internet Society, whose Web site contains lots of high-quality, Internet-related material.

161. Complimentary Hyperlinks 4
Henning Schulzrinne's Internet Technical Resources
Henning Schulzrinne has an extensive - although not always current - index of online resources for the Internet.
The Association for Computing Machinery (ACM)
A major international professional society that has technical conferences, magazines, and journals in the networking area. The ACM Special Interest Group in Data Communications (SIGCOMM), is the group within this body whose efforts are most closely related to networking

162. Complimentary Hyperlinks 5
The Institute of Electrical and Electronics Engineers (IEEE)
The other major international professional society that has technical conferences, magazines, and journals in the networking area. The IEEE Communications Society, and the IEEE Computer Society, are the groups within this body whose efforts are most closely related to networking.
The Project
As discussed in Section 1.2, the project is a scientific experiment that uses Internet-connected computers to search for extraterrestrial intelligence. You can download the SETI program directly from this site.
Nerds A Brief History of the Internet
This is the Web site for the highly entertaining and informative PBS video on the history of the Internet. The PBS video, Triumph of the Nerds, about the history of personal computers, is also recommended.

163. Complimentary Hyperlinks 6
Leonard Kleinrock's Personal History of the Internet
Professor Leonard Kleinrock made numerous important contributions to Internet technology and to the field of computer networking. This page provides his own interesting and highly entertaining description of the early history of the Internet.
The DSL Forum
DSL Forum is a consortium of nearly 250 leading industry players covering telecommunications, equipment, computing, networking and service provider companies. The site is rich in information about developments in digital subscriber loop and broadband access to the home.
Cable-modems.org
This site has many tutorials on cable modems, hybrid fiber-coax, and related topics. Also includes reviews of cable modem products.

164. Complimentary Hyperlinks 7
A note on Internet Request for Comments (RFCs): Copies of Internet RFCs are maintained at multiple sites. The RFC URLs below all point into the RFC archive at the Information Sciences Institute (ISI), maintained the the RFC Editor of the Internet Society (the body that oversees the RFCs). Other RFC sites include (located in France), and (located in Japan). 
Internet RFCs can be updated or obsoleted by later RFCs. We encourage you to check the sites listed above for the most up-to-date information. The RFC search facility at ISI, will allow you to search for an RFC and show updates to that RFC. 

165. References and Hyperlinks 1
"Frequently Asked Questions,"
[Abramson 1970] N. Abramson, "The Aloha System--Another Alternative for Computer Communications," Proceedings of Fall Joint Computer Conference, AFIPS Conference, p. 37, 1970. 
[ADSL 1998] ADSL Forum, "ADSL Tutorial,"
[Almanac 1998] Computer Industry Almanac,

166. References and Hyperlinks 2
[AT&T Apps 1998] AT&T, "Killer Apps,"
[AT&T Bandwidth 1999] AT&T, "Bandwidth: The Need for Speed,"
[AT&T Optics 1999] AT&T, "What are fiber optics?,"
[Baran 1964] P. Baran, "On Distributed Communication Networks," IEEE Transactions on Communication Systems, Mar Rand Corporation Technical report with the same title (Memorandum RM-3420-PR, 1964).

167. References and Hyperlinks 3
[Berners-Lee 1989] T. Berners-Lee, CERN, "Information Management: A Proposal," Mar. 1989, May
[Bertsekas 1991] D. Bertsekas and R. Gallagher, Data Networks, 2nd Ed. , Prentice Hall, Englewood Cliffs, NJ, 1991. 
[Bush 1945] V. Bush, "As We May Think," The Atlantic Monthly, July
[Cable 1998] Cable Data News, "Overview of Cable Modem Technology and Services,"

168. References and Hyperlinks 4
[Cerf 1974] V. Cerf and R. Kahn, "A Protocol for Packet Network Interconnection," IEEE Transactions on Communications Technology, Vol. COM-22, No. 5, pp  
[Cisco LAN 1998] Cisco Systems Inc., "Designing Switched LAN Internetworks,"
[Clark 1988] D. Clark, " The Design Philosophy of the DARPA Internet Protocols, Proceedings of ACM SIGCOMM'88, (Stanford, CA), Aug. 1988, Vol. 18, No. 4,
[Cusumano 1998] M.A. Cusumano and D.B. Toffle, Competing on Internet Time: Lessons from Netscape and its Battle with Microsoft, Free Press, 1998 

169. References and Hyperlinks 5
[Daigle 1991] J. N. Daigle, Queuing Theory for Telecommunications, Addison-Wesley, Reading, MA, 1991. 
[DEC 1990] Digital Equipment Corporation, "In Memoriam: J. C. R. Licklider ," SRC Research Report 61, Aug
[Dertouzos 1999] M. Dertouzos, "The Future of Computing," Scientific American, August 1999, pp  
[Fraser 1983] A. G. Fraser, "Towards a Universal Data Transport System," IEEE Journal on Selected Areas in Communications, Vol. SAC-1, No 5, pp  

170. References and Hyperlinks 6
[Fraser 1993] A. G. Fraser (1993). "Early Experiments with Asynchronous Time Division Networks," IEEE Network Magazine, Vol. 7, No. 1, pp  
[Goodman 1997] D. Goodman (Chair), The Evolution of Untethered Communications, National Academy Press, Washington DC, Dec
[Green 1992] P. Green, Fiber Optics Networks, Prentice Hall, 1992 
[Greenberg 1997] I. Greenberg, "The Future of the Living Room."

171. References and Hyperlinks 7
[Haynal 1999] R. Haynal, "Internet Backbones,"
[Huston 1999a] G. Huston, "Interconnection, Peering, and Settlements - Part I," The Internet Protocol Journal, Vol. 2, No. 1, (June 1999).
[Huston 1999b] G. Huston, "Interconnecting, Peering, and Settlements - Part II," The Internet Protocol Journal, Vol. 2, No. 2 (June 1999).
[Iren 1999] S. Iren, P. Amer, P. Conrad, "The Transport Layer: Tutorial and Survey," ACM Computing Surveys, Vol 31, No 4, (Dec 1999).
[Jacobson 1988] V. Jacobson, "Congestion Avoidance and Control," Proceedings of ACM SIGCOMM '88, pp. (Stanford, CA, Aug. 1988), , ftp://ftp.ee.lbl.gov/papers/congavoid.ps.Z 

172. References and Hyperlinks 8
[Kegel 1999] Dan Kegel's ISDN Page,
[Kleinrock 1961] L. Kleinrock, "Information Flow in Large Communication Networks," RLE Quarterly Progress Report, July 1961. 
[Kleinrock 1964] L. Kleinrock, 1964 Communication Nets: Stochastic Message Flow and Delay, McGraw-Hill, NY, NY, 1964. 
[Kleinrock 1975] L. Kleinrock, Queuing Systems, Vol. 1, John Wiley, New York, 1975. 
[Kleinrock 1976] L. Kleinrock, Queuing Systems, Vol. 2, John Wiley, New York, 1976. 
[Kleinrock 1998] L. Kleinrock, "The Birth of the Internet,"
[Leiner 1998] B. Leiner, V. Cerf, D. Clark, R. Kahn, L. Kleinrock, D. Lynch, J. Postel, L. Roberts, and S. Woolf, "A Brief History of the Internet,"
[List 1999] "The List: The Definitive ISP Buyer's Guide,"

173. References and Hyperlinks 9
[Lucky 1997] R. Lucky, "New Communication Services - What Do People Want?", Proceedings of the IEEE, Oct. 1997, pp  
[Metcalfe 1976] R. M. Metcalfe and D. R. Boggs. "Ethernet: Distributed Packet Switching for Local Computer Networks," Communications of the Association for Computing Machinery, Vol. 19, No. 7, (July 1976), pp
[Mills 1998] S. Mills, "TV set-tops set to take off," CNET News.com, Oct
[NAS 1995] National Academy of Sciences, The Unpredictable Certainty: Information Infrastructure Through 2000, National Academy of Sciences Press,

174. References and Hyperlinks 10
[Network 1996] Network Wizards, "Internet Domain Survey", July 1996,
[Network 1999] Network Wizards, "Internet Domain Survey," Jan. 1999,
[Pacific Bell 1998] Pacific Bell, "ISDN Users Guide,"
[Perkins 1994] A. Perkins, "Networking with Bob Metcalfe," The Red Herring Magazine, Nov
[Quittner 1998] J. Quittner, M. Slatalla, Speeding the Net: The Inside Story of Netscape and How it Challenged Microsoft, Atlantic Monthly Press, 1998. 

175. References and Hyperlinks 11
[Ramaswami 1998] R. Ramaswami, K. Sivarajan, Optical Networks: A Practical Perspective, Morgan Kaufman Publishers, 1998 
[RFC 001] S. Crocker, "Host Software," RFC 001 (the very first RFC!). 
[RFC 793] J. Postel, "Transmission Control Protocol," RFC 793, Sept
[RFC 801] J. Postel, "NCP/TCP Transition Plan," RFC 801 Nov
[RFC 1034] P. V. Mockapetris, "Domain Names--Concepts and Facilities," RFC 1034, Nov
[Roberts 1967] L. Roberts, T. Merril, "Toward a Cooperative Network of Time-Shared Computers," AFIPS Fall Conference, Oct  
[Ross 1995] K. W. Ross, Multiservice Loss Models for Broadband Telecommunication Networks, Springer, Berlin, 1995. 
[Segaller 1998] S. Segaller, Nerds 2.0.1, A Brief History of the Internet, TV Books, New York, 1998. 

176. References and Hyperlinks 12
[Thinplanet 2000] Thinplanet homepage,
[Turner 1986] J. Turner, "New Directions in Communications (or Which Way to the Information Age?)," Proceedings of the Zürich Seminar on Digital Communication, (Zurich, Switzerland, Mar. 1986), pp ,. 
[W3C 1995] The World Wide Web Consortium, "A Little History of the World Wide Web,"
[Wakeman 1992] Ian Wakeman, Jon Crowcroft, Zheng Wang, and Dejan Sirovica, "Layering Considered Harmful," IEEE Network, Jan. 1992, p  

177. References and Hyperlinks 13
[Waung 1998] W. Waung, "Wireless Mobile Data Networking The CDPD Approach," Wireless Data Forum,
[Wireless 1998] Wireless Data Forum, "CDPD System Specification Release 1.1,"
[Wood 1999] L. Wood, "Lloyds Satellites Constellations,"
[Ziff-Davis 1998] Ziff-Davis Publishing, "Ted Nelson: Hypertext pioneer," by Addison Wesley Longman A division of Pearson Education.