Transcript Internet: A Fast Revision

“Vision for Trustworthy Computing”,
Bill Gates, 15 Jan 2002
“…now, when we face a choice between
adding features and resolving security
issues, we need to choose security.”
1
Internet Technologies
An example of how the system works*
Assume:
FTP is our application example.
Ethernet is the underlying technology at
the data link layer.
*
Two slides of revision for some of you.
2
Application(say FTP)
TCP
IP
Ethernet Driver
Physical Layer
Ethernet
3
SS
User
Data
TCP
Header
IP
TCP
Header Header
Ethernet
Header
IP
TCP
Header Header
App.
User
Header
Data
App.
User
Header
Data
App.
User
Header
Data
App.
User
Header
Data
46 to 1500 bytes for Ethernet
SS SS
SS
SS
SS
SS
SS
SS
SS
Ethernet
Trailer
4
Original Internet Principles

End-to-End Design: Based on the assumption that
end-points can trust one another.
 To move the functionality
 away from the network,
and,
 towards the edges of the system.
 Reduces the complexity of the network.
 Reduces the cost of future upgrades
 New applications can be added without modifying
the network.
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Original Internet Principles
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Packet Switched Communication facility
Different Networks connected through
Routers (used essentially for routing only).
Internet communication to continue despite
loss of networks or routers.
Cater to distributed management of
resources.
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Original Internet Principles (continued)

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Addresses that are simple, hierarchical and
that can be overloaded for both naming a
node and for routing to it.
Higher level functionality at the edges and
dumb network
A single data delivery service (IP) to cater to
both connectionless, unreliable datagram
service (UDP) as well as to a reliable stream
service (TCP).
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New Environment

Untrustworthy end-points
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More demanding applications
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Denial of service attacks
Spam e-mails
Requirement for high throughput
Requirement for guaranteed delivery (e.g. audio
or streaming video)
ISPs view wide BW and/or guaranteed data
transport services as a competitive
differentiator.
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New Environment
Islands of wide BW and/or guaranteed
service along with content servers,
designed for technologists.
Responses to the new environment:

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Modify the end-nodes
Add functions to the core of the network
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Firewalls
NATs
Traffic Filters
9
The Internet
Internet Characteristics
&
Architecture
as it exists today
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Table1:Internet Traffic Characteristics
Flow Type
% of
Flows
% of
Bytes
Ave. No.
of Units
Ave. No.
of Bytes
Web S to C
20.0
34.0
16.5
8270
Web C to S
23.3
3.3
12.5
710
MBONE
0.01
20.0
10,088
6,344,202
DNS
32.0
3.2
__
__
Others
25.7
35.4
__
__
C: client;DNS: Domain Name System;S: Server;MBONE:Multicast Backbone
Source: Antonio Rodriquez-Moral, “LIBRA.” Bell Labs Technical Journal, 2(2): 42-67, Spring
1997.
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Table2: Routing Persistence
Time
% of Total
Comments
Seconds
NA
Used in load balancing
Minutes
NA
In tightly coupled routers
10s of minutes
9
Changes usually through different
cities or Autonomous Systems
Hours
4
Usually intra network changes
6+hours
19
Usually intra network changes
Days
68
(a)
(b)
50% of these routes persist for
< 7 days
Other 50% persist for > 7 days
Source: Vern Paxson, “End-to-End Routing Behaviour in the Internet”, IEEE/ACM
Transactions on communications, 5(5), October 1997.
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Table3: Internet Traffic Characteristics

Round Trip Delay (RTT)
Most RTTs are within 70-160 ms
ITU-T G.114: limit RTT to 300 ms or less
However…Surveys show some people tolerate
large RTTs of 800 ms
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Packet Loss
Very bursty
Affects contiguous packets
Order of Packet Arrival
Studies underway, but…Paxson study shows out-of
sequence arrival not unusual
Source: Ulyees Black, “Advanced Internet Technologies”, pages 70-71, 1999.
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Packet Loss
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Data transmission: masked by TCP
Audio/Video: ears and eyes catch it
Audio System: G.T23.1 masks a loss of
up to 10% if the loss is random and
independent. It uses the previous
packet to simulate the lost packet.
But the packet loss in Internet is bursty.
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Packet Loss


Forward Error Correction system: uses
the technology used in mobile wireless
system --by sending many copies of the
coded voice. If even one copy arrives
safely, the operation is effective.
Since UDP is used for audio/video, the
out-of-sequence arrival is also a
problem.
15
Internet: Example of a small part
HA
HB
Ethernet
HX
R1
45 Mbps
T1 Line
* SLIP (Serial Line IP) is now
rarely used.
R2
155 Mbps
For point-to-point (relay-type)
connections through
T1/SONET lines, PPP (Point to
Point Protocol) is used.
SONET
Internet
SONET
R3
T1 Line
R4
H1
H2
HN
Ethernet
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T Lines
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Frame: carries 24 channels of 8 bits + 1 bit
for sync.=193 bits
T1: 8000 frames per second
1.544 Mbps => DS1
T2: 4 DS1’s
6.312 Mbps => DS2
T3: 7 DS2’s
44.376  45 Mbps => DS3
T4: 6 DS3’s
274.176 Mbps
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T Lines
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ANSI – Synchronous Optical Network SONET
ITU-T – Synchronous Digital Hierarchy SDH
SONET rates:
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OC1
51.84 Mbps
OC3 155.520 Mbps
OC12 622.080 Mbps
OC-24 1.244 Gbps
OC-48 2.488 Gbps
OC-192 9.953 Gbps
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DNS
RIP
FTP
TELNET
OSPF
SMTP
BGP
UDP
TCP
ICMP
IP
ARP
RARP
ETHERNET
PPP
Physical Layer
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
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Ethernet Type
 ARP
080616
 RARP
803516
 IP
080016
IP Protocol
 OSPF 89
 UDP
17
 TCP
6
 ICMP
1
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UDP Ports
 RIP
520
 DNS
53
TCP Ports
 BGP
179
 DNS
53
 SMTP
25
 TELNET 23
 FTP
21
 HTTP
80
 Lotus Notes 1352
 HTTP PROXY 8080
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