Transcript Part I: Introduction

University of British Columbia
CICS 515 (Part 1) Internet Computing
Lecture 1 - Overview
Instructor: Dr. Son T. Vuong
Email: [email protected]
May 8, 2012
The World Connected
Introduction
Information and Organization
 Instructor: Dr. Son Vuong
► Email:
[email protected]
► Office Hours: T, Th: 1:00-2:00pm (CS 329)
 TA:
► Jonatan Schroeder
► Shahed Alam
[email protected]
[email protected]
 Lectures: T, Th: 11am-1 pm in DMP 110
 Lab: Th: 2-4 pm (CS 045/051)
Introduction
1-2
Text and Workload
 Text:
Computer Networking: A Top Down Approach
Featuring the Internet, 6th edition. Jim Kurose, Keith
Ross. Addison-Wesley, April 2012.
 Course Load:
►2
Projects/Asgmts (20%)
► 2 Quizzes
(10%)
► Midterm
(25%)
► Final exam
(45%)
► Bonus for class participation, BlueCT + Peerwise (4%)
i
 Late penalty: 5*2 %, 0< i =< 3 (i = # days late)
 Website: www.icics.ubc.ca/~cics515
 Vista: http://www.vista.ubc.ca/ (id=pwd=CWL)
Introduction
1-3
Revised CISC 515 Outline (Tentative)
1.
2.
3.
4.
5.
6.
7.
8.
(T - 08/5) Overview (Chapter 1)
P1
(Th - 10/5) Application Layer (The Web and HTTP) (Ch 2)
(T - 15/5) WebCache and Transport Layer (Ch 3)
(Th - 17/5) Transport Layer (Ch 3)
(T - 22/5) Transport Layer (TCP) (Ch 3) Quiz1
(Th - 24/5) TCP Congestion (P1) P2
(T-29/5) IP (Ch 4) IPv6 (Ch 4) Midterm
(Th - 31/6) Other Protocols (ICMP, DHCP, DNS), Routing
(RIP, OSPF) (Ch 4)
9. (T - 05/6) Routing (RIP, OSPF, BGP) (Ch 4)
10. (Th- 07/6) Data Link protocols (Ethernet) (Ch 5) (P2)
11. (T- 12/6) Wireless Networks (WiFi) (Ch 6) Quiz2
12. (Th-14/6) Review 13. (F-15/6) Final Exam
Introduction
1-4
Chapter 1: Introduction
Our goal:
Overview:
 get context,
 what’s the Internet
overview, “feel” of
networking
 more depth, detail
later in course
 approach:
► descriptive
► use Internet as
example
 what’s a protocol?
 network edge
 network core
 access net, physical media
 Internet/ISP structure
 performance: loss, delay
 protocol layers, service models
 history
Introduction
1-5
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge
1.3 Network core
1.4 Network access and physical media
1.5 Internet structure and ISPs
1.6 Protocol layers, service models
1.7 Delay & loss in packet-switched networks
1.8 History
Introduction
1-6
What’s the Internet: “nuts and bolts” view
 millions of connected
computing devices: hosts,
end-systems
►
►
PCs workstations, servers
PDAs phones, toasters
router
server
workstation
mobile
local ISP
running network apps

communication links
►
►

regional ISP
fiber, copper, radio,
satellite
transmission rate =
bandwidth
routers: forward packets
(chunks of data)
company
network
Introduction
1-7
“Cool” internet appliances
IP picture frame
http://www.ceiva.com/
Web-enabled toaster+weather forecaster
World’s smallest web server
http://www-ccs.cs.umass.edu/~shri/iPic.html
Introduction
1-8
What’s the Internet: “nuts and bolts” view

protocols control sending,
receiving of msgs
►

e.g., TCP, IP, HTTP, FTP, PPP
Internet: “network of
router
server
workstation
mobile
local ISP
networks”
►
►
loosely hierarchical
public Internet versus
private intranet
 Internet standards
► RFC: Request for comments
► IETF: Internet Engineering
Task Force
regional ISP
company
network
Introduction
1-9
What’s the Internet: a service view
 communication
infrastructure enables
distributed applications:
►
Web, email, games, ecommerce, database.,
voting, file (MP3) sharing
 communication services
provided to apps:
►
►
connectionless
connection-oriented
 cyberspace [Gibson]:
“a consensual hallucination experienced daily by
billions of operators, in every nation, ...."
Introduction
1-10
Uses of Internet
•
•
•
•
Business Applications
Home Applications
Mobile Users
Social Issues
Introduction
1-11
Business Applications of Networks

A network with two clients and one server.
Introduction
1-12
Business Applications of Networks (2)

The client-server model involves requests
and replies.
Introduction
1-13
Home Network Applications
 Access to remote information
 Person-to-person communication
 Interactive entertainment
 Electronic commerce
Introduction
1-14
Home Network Applications (2)

In peer-to-peer system there are no fixed
clients and servers.
Introduction
1-15
Home Network Applications (3)

Some forms of e-commerce.
Introduction
1-16
Mobile Network Users

Combinations of wireless networks and
mobile computing.
Introduction
1-17
Classification of Networks

Classification of interconnected
processors by scale.
Introduction
1-18
Example Networks
 The Internet
 Connection-Oriented Networks:
X.25, Frame Relay, and ATM
 Ethernet
 Wireless LANs: 802:11 (WiFi)
Introduction
1-19
Network Perspective
 Network users: services that their
applications need, e.g., guarantee that each
message it sends will be delivered without
error within a certain amount of time
 Network designers: cost-effective design
e.g., that network resources are efficiently
utilized and fairly allocated to different
users
 Network providers: system that is easy to
administer and manage e.g., that faults can
be easily isolated and it is easy to account
for usage
Introduction
1-20
Connectivity
 Building Blocks
► links: coax cable, optical fiber...
► nodes: general-purpose workstations...
 Direct Links
► point-to-point
► multiple
access
Introduction
1-21
Switched Networks
 A network can be defined recursively as:
► two
or more nodes connected
by a physical link,
► or
by two or more networks
connected by one
or more nodes
 Internetworks
 Internet vs internet
Introduction
1-22
A closer look at network structure:
 network edge:
applications and hosts
 network core:
► routers
► network
of networks
 access networks,
physical media:
communication links
Introduction
1-23
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge
1.3 Network core
1.4 Network access and physical media
1.5 Internet structure and ISPs
1.6 Protocol layers, service models
1.7 Delay & loss in packet-switched networks
1.8 History
Introduction
1-24
The network edge:
 end systems (hosts):
►
►
►
run application programs
e.g. Web, email
at “edge of network”
 client/server model
►
►
client host requests, receives
service from always-on server
e.g. Web browser/server;
email client/server
 peer-peer model:
►
►
minimal (or no) use of
dedicated servers
e.g. Gnutella, KaZaA
Introduction
1-25
Network edge: connection-oriented service
Goal: data transfer
between end systems
 handshaking: setup
(prepare for) data
transfer ahead of time
►
►
Hello, hello back human
protocol
set up “state” in two
communicating hosts
 TCP - Transmission
Control Protocol
►
Internet’s connectionoriented service
TCP service [RFC 793]

reliable, in-order bytestream data transfer
►

flow control:
►

loss: acknowledgements
and retransmissions
sender won’t overwhelm
receiver
congestion control:
►
senders “slow down sending
rate” when network
congested
Introduction
1-26
Network edge: connectionless service
Goal: data transfer
between end systems
►
same as before!
 UDP - User Datagram
Protocol [RFC 768]:
Internet’s
connectionless service
► unreliable data
transfer
► no flow control
► no congestion control
App’s using TCP:
 HTTP (Web), FTP (file
transfer), Telnet
(remote login), SMTP
(email)
App’s using UDP:
 streaming media,
teleconferencing, DNS,
Internet telephony
Introduction
1-27
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge
1.3 Network core
1.4 Network access and physical media
1.5 Internet structure and ISPs
1.6 Protocol layers, service models
1.7 Delay & loss in packet-switched networks
1.8 History
Introduction
1-28
The Network Core
 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”
Introduction
1-29
Switching Strategies
 Circuit switching: dedicated circuit;
send/receive a bit stream
► original
telephone network
 Packet switching: store-and-forward;
send/receive messages (packets)
► Internet
Introduction
1-30
Switching Strategies
(a) Circuit switching
(b) Message switching
(c) Packet
switching
Introduction
1-31
Nodal delay
dnodal  dproc  dqueue  dtrans  dprop
 dproc = processing delay
► typically a few microsecs or less
 dqueue = queuing delay
► depends on congestion
 dtrans = transmission delay
► = L/R, significant for low-speed links
 dprop = propagation delay
► a few microsecs to hundreds of msecs
Introduction
1-32
Packet switching versus circuit switching
Is packet switching a “slam dunk winner?”
 Great for bursty data
► 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 apps
► still an unsolved problem (chapter 6)
Introduction
1-33
Packet-switching: store-and-forward
L
R
 Takes L/R seconds to
R
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
R
Example:
 L = 7.5 Mbits
 R = 1.5 Mbps
 delay = 3x 5 sec = 15 sec
forward
 delay = 3L/R
Introduction
1-34
Packet Switching: Message Segmenting
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 5.002 sec
Introduction
1-35
Packet Switching: Message Segmenting
L
R
R
R
R
Now assume the message/packets go through 2
additional switches (over the path of 4 switches)
 What is the total delay to send the message without
breaking into packets (i.e. non-pipelining) ?
 What is the total delay to send the message as 5000
packets (i.e. pipelining) ?
Introduction
1-36
Q 1.1 Peer Instruction packet switching
Now assume the message/packets go through 2
additional switches (over the path of 4 switches)
What is the total delay to send the message
as 5000 packets (i.e. pipelining) ?
Answer:
(A) 25 s (B) 15 s (C) 5.002 s
(E) None of the above
(D) 5.004 s
Introduction
1-37
Q 1.1 Peer Instruction packet switching
Now assume the message/packets go through 2
additional switches (over the path of 4 switches)
What is the total delay to send the message
as 5000 packets (i.e. pipelining) ?
Answer:
(A) 25 s (B) 15 s (C) 5.002 s
(E) None of the above
(D) 5.004 s
Introduction
1-38
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
► analogy: driving, asking directions
 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
Introduction
1-39
Addressing and Routing
 Address: byte-string that identifies a
node
► usually
unique
 Routing: how to forward messages
towards the destination node based on its
address
 Types of addresses
► unicast: node-specific
► broadcast: all nodes on the network
► multicast: some subset of nodes on the
network
Introduction
1-40
Multiplexing
 Time-Division Multiplexing (TDM)
 Frequency-Division Multiplexing (FDM)
L1
R1
L2
R2
L3
Switch 1
Switch 2
R3
Introduction
1-41
Circuit Switching: FDMA and TDMA
Example:
FDMA
4 users
frequency
time
TDMA
frequency
time
Introduction
1-42
Time Division Multiplexing (T1 Carrier)
The T1 carrier (1.544 Mbps).
(1 bit + 24 slots * 8 bits/slot) * 8000 frames/s
= 193 bits/frame * 8000 frames/s = 1.544 Mbps
Introduction
1-43
Peer Instruction 1.1 – T1 TDM
Question

How long does it take to send a file of 640,000 bits
from host A to host B over a (sub)channel (a circuit) in
a T1 TDM based circuit-switched network?
►
►
►
Overall T1 TDM carrier capacity is 1.536 Mbps
Data transmission uses one of the 24 slots of the T1 carrier
500 msec to establish end-to-end circuit
Work it out!
(A) 510 ms (B) 1500 ms (C) 2.5 s (D) 10.5 s
(E) None of the above
Introduction
1-44
1.1 Peer Instruction – T1 TDM
Answer

How long does it take to send a file of 640,000 bits
from host A to host B over a (sub)channel (a circuit) in
a T1 TDM based circuit-switched network?
►
►
►
Overall TDM channel capacity is 1.536 Mbps (T1: 1.544 Mbps
with 8Kbps framing)
Data transmission uses one of the 24 slots of the TDM channel
500 msec = 0.5s to establish end-to-end circuit
Answer: Each circuit= 1.536Mbps/24 = 64Kbps
Tx(file) = 640Kb/64Kbps = 10s plus Tsetup
(A) 510 ms (B) 1500 ms (C) 2.5 s (D) 10.5 s
(E) None of the above
Introduction
1-45
Peer Instruction 1.1 – T1 TDM
Question

How long does it take to send a file of 640,000 bits
from host A to host B over 5 (sub)channels (circuits) in
a T1 TDM based circuit-switched network?
►
►
►
Overall T1 TDM carrier capacity is 1.536 Mbps
Data transmission uses one of the 24 slots of the T1 carrier
500 msec to establish end-to-end circuit
Work it out!
(A) 510 ms (B) 1500 ms (C) 2.5 s (D) 10.5 s
(E) None of the above
Introduction
1-46
1.1 Peer Instruction – T1 TDM
Answer

How long does it take to send a file of 640,000 bits
from host A to host B over 5 (sub)channel (circuits) in
a T1 TDM based circuit-switched network?
►
►
►
Overall TDM channel capacity is 1.536 Mbps (T1: 1.544 Mbps
with 8Kbps framing)
Data transmission uses one of the 24 slots of the TDM channel
500 msec = 0.5s to establish end-to-end circuit
Answer: Each circuit= 1.536Mbps/24 = 64Kbps
Tx(file) = 640Kb/(5x64Kbps) = 2s plus Tsetup
(A) 510 ms (B) 1500 ms (C) 2.5 s (D) 10.5 s
(E) None of the above
Introduction
1-47
Statistical Multiplexing (ATDM)
 On-demand time-division, rather than fixed (STDM)
 Schedule link on a per-packet basis
 Packets from different sources interleaved on link
 Buffer packets that are contending for the link
 Packet queue may be processed FIFO
 Buffer (queue) overflow is called congestion
ATDM or Concentrator
…
Introduction
1-48
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge
1.3 Network core
1.4 Network access and physical media
1.5 Internet structure and ISPs
1.6 Protocol layers, service models
1.7 Delay & loss in packet-switched networks
1.8 History
Introduction
1-49
Protocols
 Building blocks of a network
architecture
 Each protocol object has two different
interfaces:
► service:
operations on this protocol
► peer-to-peer (protocol): messages
exchanged with peer
 Term “protocol” is overloaded
► specification of peer-to-peer interface
► module that implements this interface
Introduction
1-50
Interfaces (Protocol and Service)
Host 1
High-level
object
Protocol
Host 2
SERVICE
interface
PROTOCOL
Peer-to-peer
interface
High-level
object
Protocol
Introduction
1-51
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
Introduction
1-52
What’s a protocol?
a human protocol and a computer network protocol:
Hi
TCP connection
req
Hi
TCP connection
response
Got the
time?
Get http://www.awl.com/kurose-ross
2:00
<file>
time
Q: Other human protocols?
Introduction
1-53
Internet Architecture
 Defined by Internet Engineering Task Force
(IETF)
 Hourglass Design
 Application vs Application Protocol (FTP, HTTP)
FTP
HTTP
NV
TFTP
UDP
TCP
TCP
IP
NET1
NET2
Application
UDP
IP
…
NETn
Network
Introduction
1-54
ISO Architecture
End host
End host
Application
Application
Presentation
Presentation
Session
Session
Transport
Transport
Network
Network
Network
Network
Data link
Data link
Data link
Data link
Physical
Physical
Physical
Physical
One or more nodes
within the network
Introduction
1-55
Reference Models

The TCP/IP reference model.
Introduction
1-56
Layering
 Use abstractions to hide complexity
 Abstraction naturally lead to layering
 Alternative abstractions at each layer
Application programs
Application programs
Process-to-process
Request/reply Message stream
channel
channel
Host-to-host connectivity
Host-to-host connectivity
Hardware
Hardware
Introduction
1-57
Layering: logical communication
Each layer:
 distributed
 “entities”
implement
layer functions
at each node
 entities
perform
actions,
exchange
messages with
peers
application
transport
network
link
physical
application
transport
network
link
physical
network
link
physical
application
transport
network
link
physical
application
transport
network
link
physical
Introduction
1-58
Layering: logical communication
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
data
application
transport
transport
network
link
physical
application
transport
network
link
physical
ack
data
network
link
physical
application
transport
network
link
physical
data
application
transport
transport
network
link
physical
Introduction
1-59
Layering: physical communication
data
application
transport
network
link
physical
application
transport
network
link
physical
network
link
physical
application
transport
network
link
physical
data
application
transport
network
link
physical
Introduction
1-60
Protocol layering and data
Each layer takes data from above
 adds header information to create new data unit
 passes new data unit to layer below
source
M
Ht M
Hn Ht M
Hl Hn Ht M
application
transport
network
link
physical
destination
application
Ht
transport
Hn Ht
network
Hl Hn Ht
link
physical
M
message
M
segment
M
M
datagram
frame
Introduction
1-61
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge
1.3 Network core
1.4 Network access and physical media
1.5 Internet structure and ISPs
1.6 Protocol layers, service models
1.7 Delay & loss in packet-switched networks
1.8 History
Introduction
1-62
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
B
packets queueing (delay)
free (available) buffers: arriving packets
dropped (loss) if no free buffers
Introduction
1-63
1.2 Peer Instruction - Packet Error Prob
Question
Let p be the bit error probability. Assume
packet of length L bits. What's the packet
error probability in terms of p and L?
(A)
(B)
(C)
(D)
(E)
(1- p) **L
1- p**L
1- p * L
1- (1-p)**L
None of the above
Introduction
1-64
1.2 Peer Instruction - Packet Error Prob
Answer
Let p be the bit error probability. Assume packet of
length L bits. What's the packet error probability in
terms of p and L?
(A) (1- p) **L
(B) 1- p**L
prob (not all bits in error)
(C) 1- p * L
(D) 1- (1-p)**L
(E) None of the above
Answer:
(D)
prob(a bit not in error) = 1-p
prob (L bits not in error) = (1-p)**L
prob(packet error) = prob (not all bits not in error)
= 1- (1-p)**L
Introduction
1-65
What Goes Wrong in the Network?
 Bit-level errors (electrical interference) prob=p
 Packet-level errors (congestion) = 1-(1-p)f
 Link and node failures
 Messages are delayed
 Messages are delivered out-of-order
 Third parties eavesdrop
The key problem is to fill in the gap between what
applications expect and what the underlying
technology provides.
Introduction
1-66
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
queueing
Introduction
1-67
Delay in packet-switched networks
3. Transmission delay:
 R=link bandwidth (bps)
 L=packet length (bits)
 time to send bits into
link = L/R
transmission
A
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!
propagation
B
nodal
processing
queueing
Introduction
1-68
Nodal delay
dnodal  dproc  dqueue  dtrans  dprop
 dproc = processing delay
► typically a few microsecs or less
 dqueue = queuing delay
► depends on congestion
 dtrans = transmission delay
► = L/R, significant for low-speed links
 dprop = propagation delay
► a few microsecs to hundreds of msecs
Introduction
1-69
Queueing delay (revisited)
 R=link bandwidth (bps)
 L=packet length (bits)
 a=average packet
arrival rate
traffic intensity = La/R
 La/R ~ 0: average queueing delay small
 La/R -> 1: delays become large
 La/R > 1: more “work” arriving than can be
serviced, average delay infinite!
Introduction
1-70
Digression- Simple Queuing Model
Queuing system – general properties:
Arrival rate: λ = a msg/s
Service rate: μ = R/L msg/s
Service time: Ts = L/R = ρ / a
s/msg
Traffic intensity = Utilization factor = ρ = λ / μ = aL / R
Little Formula: N = λ T = a T or T = N/a
N = Nw + Ns
and T = Tw + Ts
M/M/1 Queue Model (M/M/1 is Kendall’ notation):
Can derive:
# in system: N = ρ / (1- ρ)
# waiting in queue: Nw = ρ2 / (1- ρ)
=> Time in system: T = N/a = Ts / (1- ρ) (using Little formula)
= Tw + Ts = N Ts + Ts = (N+1) Ts
Waiting time: Tw = T – Ts = Ts / (1- ρ) - Ts = (1/ (1- ρ) - 1 )Ts
= ρ Ts / (1- ρ)
= N Ts
Introduction
1-71
“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
Introduction
1-72
“Real” Internet delays and routes
traceroute: gaia.cs.umass.edu to www.eurecom.fr
Three delay measements from
gaia.cs.umass.edu to cs-gw.cs.umass.edu
1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms
2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms
3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms
4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms
5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms
6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms
7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms trans-oceanic
8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms
link
9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms
10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms
11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms
12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms
13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms
14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms
15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms
16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms
17 * * *
* means no reponse (probe lost, router not replying)
18 * * *
19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms
Introduction
1-73
Packet loss
 queue (aka buffer) preceding link in buffer
has finite capacity
 when packet arrives to full queue, packet is
dropped (aka lost)
 lost packet may be retransmitted by
previous node, by source end system, or
not retransmitted at all
Introduction
1-74
Performance Metrics
 Bandwidth (throughput) (a)
► data transmitted per time unit
► link versus end-to-end
► notation
 KB = 210 bytes
(b)
6
 Mbps = 10 bits per second
1 second
1 second
 Latency (delay)
► time to send message from point A to point B
► one-way versus round-trip time (RTT)
► components
Latency = Propagation + Transmit + Queue
Propagation = Distance / c (c=3, 2.3, 2x10**8 m/s)
Transmit = Size / Bandwidth
Introduction
1-75
Bandwidth versus Latency
 Relative importance
► 1-byte: 1ms vs 100ms dominates 1Mbps vs 100Mbps
► 25MB: 1Mbps vs 100Mbps dominates 1ms vs 100ms
 Infinite bandwidth
► RTT dominates
 Throughput = TransferSize / TransferTime
 TransferTime = RTT + TransferSize / Bandwidth
► 1-GB file to 1-Gbps link as 1-MB packet to 1-Mbps
link
Introduction
1-76
Delay x Bandwidth Product
 Amount of data “in flight” or “in the pipe”
 Example: 100ms x 45Mbps = 560KB
Delay
Bandwidth
Introduction
1-77
ITU
 Main sectors
•
•
•
Radiocommunications
Telecommunications Standardization
Development
 Classes of Members
•
•
•
•
National governments
Sector members
Associate members
Regulatory agencies
Introduction
1-78
IEEE 802 Standards
The 802 working groups. The important ones are marked with *. The
ones marked with  are hibernating. The one marked with
† gave up.
Introduction
1-79
Bad Timing

The apocalypse of the two elephants.
Introduction
1-80
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge
1.3 Network core
1.4 Network access and physical media
1.5 Internet structure and ISPs
1.6 Protocol layers, service models
1.7 Delay & loss in packet-switched networks
1.8 History
Introduction
1-81
Internet History
1961-1972: Early packet-switching principles
 1961: Kleinrock - queueing
theory shows
effectiveness of packetswitching
 1964: Baran - packetswitching 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 hosthost protocol
first e-mail program
ARPAnet has 15 nodes
Introduction
1-82
Internet History
1972-1980: 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
Introduction
1-83
Internet History
1980-1990: new protocols, a proliferation of networks
 1983: deployment of




TCP/IP
1982: SMTP e-mail
protocol defined
1983: DNS defined
for name-to-IPaddress translation
1985: FTP protocol
defined
1988: TCP congestion
control
 new national networks:
Csnet, BITnet,
NSFnet, Minitel
 100,000 hosts
connected to
confederation of
networks
Introduction
1-84
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. 100 million host,
500 million+ users
 backbone links running
at Gbps
Introduction
1-85