This document discusses different types of networks: 1. The Internet is the common network used for activities like reading news and social media. 2. The Deep Web is a subset not indexed by search engines so it requires directly visiting sites instead of searching. It exists because the Internet is too large to fully index. 3. The Dark Web requires special software to access and is often associated with illegal activities like drug sales, though it also has legitimate uses. It sits on additional private networks like Tor and I2P.

1. Network Core Part
Computer Networks – CSE331
Lecture 2

2.  The Internet: This is the easy one. It’s the common Internet everyone uses to
read news, visit Facebook, and shop. Just consider this the “regular” Internet.
 The Deep Web: The deep web is a subset of the Internet that is not indexed
by the major search engines. This means that you have to visit those places
directly instead of being able to search for them. So there aren’t directions to
get there, but they’re waiting if you have an address. The Deep Web is largely
there simply because the Internet is too large for search engines to cover
completely. So the Deep Web is the long tail of what’s left out (your email,
dropbox, fb account etc).
 The Dark Web: The Dark Web (also called Darknet) is a subset of the Deep
Web that is not only not indexed, but that also requires something special to
be able to access it, e.g., specific proxying software or authentication to gain
access. The Dark Web often sits on top of additional sub-networks, such as Tor,
I2P, and Freenet, and is often associated with criminal activity of various
degrees, including buying and selling drugs, etc. While the Dark Web is
definitely used for those things more than the standard Internet or the Deep
Web, there are many legitimate uses for the Dark Web as well.

3.  Why search engine can not index deep web
But I hope you will prefer the light

4. central office
ISP
telephone
network
DSLAM
voice, data transmitted
at different frequencies over
dedicated line to central office
 use existing telephone line to central office DSLAM
 data over DSL phone line goes to Internet
 voice over DSL phone line goes to telephone net
 < 2.5 Mbps upstream transmission rate (typically < 1 Mbps)
 < 24 Mbps downstream transmission rate (typically < 10 Mbps)
DSL
modem
splitter
DSL access
multiplexer

5. cable
modem
splitter
…
cable headend
Channels
V
I
D
E
O
V
I
D
E
O
V
I
D
E
O
V
I
D
E
O
V
I
D
E
O
V
I
D
E
O
D
A
T
A
D
A
T
A
C
O
N
T
R
O
L
1 2 3 4 5 6 7 8 9
frequency division multiplexing: different channels transmitted
in different frequency bands

6. data, TV transmitted at different
frequencies over shared cable
distribution network
cable
modem
splitter
…
cable headend
CMTS
ISP
cable modem
termination system
 HFC: hybrid fiber coax
 asymmetric: up to 30Mbps downstream transmission rate, 2 Mbps upstream
transmission rate
 network of cable, fiber attaches homes to ISP router
 homes share access network to cable headend
 unlike DSL, which has dedicated access to central office

7.  typically used in companies, universities, etc
 10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates
 today, end systems typically connect into Ethernet switch
Ethernet
switch
institutional mail,
web servers
institutional router
institutional link to
ISP (Internet)

8.  shared wireless access network connects end system to router
 via base station aka “access point”
wireless LANs:
 within building (100 ft)
 802.11b/g (WiFi): 11, 54 Mbps
transmission rate
wide-area wireless access
 provided by cellular
operator, 10’s km
 between 1 and 10 Mbps
 3G, 4G: LTE
to Internet to Internet

9. host sending function:
 takes application message
 breaks into smaller chunks, known
as packets, of length L bits
 transmits packet into access
network at transmission rate R
 link transmission rate, aka link
capacity, aka link bandwidth
R: link transmission rate
host
12
two packets,
L bits each
packet
transmission
delay
time needed to
transmit L-bit
packet into link
L (bits)
R (bits/sec)
= =

10.  mesh of interconnected routers
 packet-switching: hosts break
application-layer messages into
packets
 forward packets from one
router to the next, across links
on path from source to
destination
 each packet transmitted at full
link capacity

11.  takes L/R seconds to transmit
(push out) L-bit packet into link
at R bps
 store and forward: entire packet
must arrive at router before it
can be transmitted on next link
 end-end delay = 2L/R (assuming zero
propagation delay)
one-hop numerical example:
 L = 7.5 Mbits
 R = 1.5 Mbps
 one-hop transmission
delay = 5 sec
more on delay shortly …
source
R bps
destination
123
L bits
per packet
R bps
Time to reach 3 packets to destination? 4L/R

12. A
B
CR = 100 Mb/s
R = 1.5 Mb/s
D
Equeue of packets
waiting for output link
queuing and loss:
 If arrival rate (in bits) to link exceeds transmission rate of link for a period of
time:
 packets will queue, wait to be transmitted on link
 packets can be dropped (lost) if memory (buffer) fills up

13. forwarding: move packets
from router’s input to
appropriate router output
routing: determines source-destination
route taken by packets
 routing algorithms
routing algorithm
local forwarding table
header value output link
0100
0101
0111
1001
3
2
2
1
1
23
dest address in arriving
packet’s header

14.  LB-3 Computer Science Department, UET, Lahore,
Punjab, Pakistan
 LB-3 Computer Science Department, UET, Lahore,
Punjab
 LB-3 Computer Science Department, UET, Lahore
 LB-3 Computer Science Department, UET
 LB-3 Computer Science Department
 LB-3

15. forwarding: move packets
from router’s input to
appropriate router output
routing: determines source-destination
route taken by packets
 routing algorithms
routing algorithm
local forwarding table
header value output link
0100
0101
0111
1001
3
2
2
1
1
23
dest address in arriving
packet’s header

16. end-end resources allocated to,
reserved for “call” between
source & dest:
 In diagram, each link has four circuits.
 call gets 2nd circuit in top link and
1st circuit in right link.
 dedicated resources: no sharing
 circuit-like (guaranteed)
performance
 circuit segment idle if not used by call
(no sharing)
 Commonly used in traditional
telephone networks

17. FDM
frequency
time
TDM
frequency
time
4 users
Example:

18.  A have to send 64000 bits to B over circuit switch over TDMA
 Link speed 1Mbps
 Link has 20 slots
 Setup time 0.2s
 Sol:
 Per circuit speed 1Mbps/20 = 50Kbps
 64000/50000 = 1.28s
 1.28+0.2 = 1.3s
 Did not has other delays like propogation

19. example:
 1 Mb/s link
 each user:
• 100 kb/s when “active”
• active 10% of time
 circuit-switching:
 10 users => 1Mbps/100kbps
 packet switching:
 with 35 users, probability >
10 active at same time is
less than .0004
packet switching allows more users to use network!
N
users
1 Mbps link
http://www.danielsoper.com/statcalc/calculator.aspx?id=71

20. is packet switching a “winner?”
 great for bursty data
 resource sharing
 simpler, no call setup
 excessive congestion possible: packet delay and loss
 protocols needed for reliable data transfer, congestion
control
 Q: How to provide circuit-like behavior?
 bandwidth guarantees needed for audio/video apps
 still an unsolved problem (chapter 7)
Q: human analogies of reserved resources (circuit switching) versus on-demand
allocation (packet-switching)?

21.  History (Reading Assignment)
 Ross book
 1.3, 1.6