Introduction to Data Networking

1
Introduction to Data Networking
2
Introduction to this class

• Me Stephan Bohacek
• bohacek_at_udel.edu, 302-831-4274, skype
  Stephan.Bohacek
• http//www.eecis.udel.edu/bohacek
• Syllabus (online)

3
Syllabus (also online)

• Textbook Kurose and Rose. Computer Networking,
  2007 (the 4th edition). This book is required
• Prerequisites Introduction to probability, C/C
  programming
• Grading homework1/3, projects1/3, final1/3.
  Homework and projects turned in late will be
  marked off 2.5 per day (including weekends).
  Grades of online discussion are based on the
  number and qualtiy of postings. These postings
  may be in the form of questions and answers. A
  good question will count toward your discussion
  grade.
• There will be programming assignments. This can
  be done on Linux or on Windows with Visual
  Studio. Evans 132 has linux machines and remote
  access is possible. Also, with your EECIS user
  name and password, MS visual studio can be
  downloaded for free from here

4
Syllabus (also online)
5
Today networking basics

• Movie on the history of the Internet
• Core components of the Internet the protocol
  stack
• Multiplexing, circuit switching, and packet
  switching
• Loss and delays
• The structure of the Internet
• This lecture covers much of chapter 1 in the
  textbook.

6
Today networking basics

• Movie on the history of the Internet
• Core components of the Internet the protocol
  stack
• Multiplexing, circuit switching, and packet
  switching
• Loss and delays
• The structure of the Internet
• This lecture covers much of chapter 1 in the
  textbook.

7
Today networking basics

• Movie on the history of the Internet
• Core components of the Internet the protocol
  stack
• Multiplexing, circuit switching, and packet
  switching
• Loss and delays
• The structure of the Internet
• This lecture covers much of chapter 1 in the
  textbook.

8
Core components

• End-hosts
• Applications
• ?
• Packets
• ?
• Routers and gateways and groups of routers (ISPs)
• Links
• ?
• Protocols

9
Core components

• End-hosts
• Applications
• Web
• Email
• File transfer
• File sharing
• Packets
• TCP
• UDP
• Routers and gateways and groups of routers (ISPs)
• Links
• Fiber
• Coaxial
• Twisted pair
• Wireless
• Protocols

10
Application Layer where the applications live

• Email
• Rules/protocols for how an end-host gets mail
  from the mail server
• Web
• Rules/protocols for how the end-hosts gets a web
  page from the web servers
• Question
• How is a networking application different from a
  non-networking application (e.g., MS Word). That
  is, why do we say that an application is a bunch
  of rules? MS-Word is not a bunch of rules?
• Answer The networking applications must
  communicate, and rules are required to define the
  communication.
• Roles that end-hosts play
• Client, server, and peer
• The client asks the server for a service.
• E.g., The client asks the server to send a mail
  for it.
• The client asks the server for a web page
• The client asks the server to translate a web
  address to an IP address.
• Peer A host can act as both a client and a
  server. But usually in one transaction, the host
  takes only one role

• End-hosts
• Applications
• Web
• Email
• File transfer
• File sharing
• Packets
• TCP
• UDP
• Routers and gateways and groups of routers (ISPs)
• Links
• Fiber
• Coaxial
• Twisted pair
• Wireless
• Protocols

11
Layers 1-4

• End-hosts
• Applications
• Web
• Email
• File transfer
• File sharing
• Packets
• TCP
• UDP
• Routers and gateways and groups of routers (ISPs)
• Links
• Fiber
• Coaxial
• Twisted pair
• Wireless
• Protocols

Which are the end-host?
client
server
Routers
12
Layers 1-4

• Why is this a good approach?
• Small problems are easier
• to understand/solve.
• 2.Different solutions can be
• mixed and matched

Goal move messages from server to the
client Approach break the problem into little
pieces. Each piece is a layer in the protocol
stack

• End-hosts
• Applications
• Web
• Email
• File transfer
• File sharing
• Packets
• TCP
• UDP
• Routers and gateways and groups of routers (ISPs)
• Links
• Fiber
• Coaxial
• Twisted pair
• Wireless
• Protocols

client
server
13
Layers 1-4

• End-hosts
• Applications
• Web
• Email
• File transfer
• File sharing
• Packets
• TCP
• UDP
• Routers and gateways and groups of routers (ISPs)
• Links
• Fiber
• Coaxial
• Twisted pair
• Wireless
• Protocols

• Top down approach of breaking problems into small
  pieces
• Transport layer
• Reliability The server must make sure that the
  client gets the data
• Congestion control (or lack there of)
• Congestion Control The server should send data
  as fast as possible, but not too fast
• TCP provides these features (services), while UDP
  does not
• Network layer (could be called the routing layer,
  but it isnt)
• The packets must find their way through the
  network.
• Each packet has the IP address of the destination
• By examining the IP address, routers decide where
  to send the packet next
• Link Layer or MAC layer
• Links connect the routers/gateways and end-hosts
• This layer provides logical and control for
  communicating across links.
• Services that this layer might provide include
• congestion control, media access, error
  detection/correction

14
Layers 1-4

• End-hosts
• Applications
• Web
• Email
• File transfer
• File sharing
• Packets
• TCP
• UDP
• Routers and gateways and groups of routers (ISPs)
• Links
• Fiber
• Coaxial
• Twisted pair
• Wireless
• Protocols

• Top down approach of breaking problems into small
  pieces
• ..
• Link Layer or MAC layer
• Links connect the routers/gateways and end-hosts
• This layer provides logical and control for
  communicating across links.
• Services that this layer might provide include
• congestion control, media access, error
  detection/correction

• Media access. The air is a shared medium. If
  two nodes transmit at the same time, there will
  be a collision. Thus, a scheme must be developed
  to determine which node transmits when.
• Error detection/correction. If interference does
  occur, then errors might occur. If an error is
  detected, then
• the error could be corrected with forward error
  correction, or
• the receiving link could request a retransmission

15
Layers 1-4

• End-hosts
• Applications
• Web
• Email
• File transfer
• File sharing
• Packets
• TCP
• UDP
• Routers and gateways and groups of routers (ISPs)
• Links
• Fiber
• Coaxial
• Twisted pair
• Wireless
• Protocols

• Top down approach of breaking problems into small
  pieces
• Transport layer
• Reliability The server must make sure that the
  client gets the data
• Congestion control (or lack there of)
• Congestion Control The server should send data
  as fast as possible, but not too fast
• TCP provides these features (services), while UDP
  does not
• Network layer (could be called the routing layer,
  but it isnt)
• The packets must find their way through the
  network.
• Each packet has the IP address of the destination
• By examining the IP address, routers decide where
  to send the packet next
• Link Layer or MAC layer
• Links connect the routers/gateways and end-hosts
• This layer provides logical and control for
  communicating across links.
• Services that this layer might provide include
• congestion control, media access, error
  detection/correction
• Physical layer
• Logical bits are encoded as physical quantities,
  e.g., as voltage levels, as shifts in phase,
• This course does not cover the physical layer

16
Protocols

• End-hosts
• Applications
• Web
• Email
• File transfer
• File sharing
• Packets
• TCP
• UDP
• Routers and gateways and groups of routers (ISPs)
• Links
• Fiber
• Coaxial
• Twisted pair
• Wireless
• Protocols

protocols define format, order of msgs sent and
received among network entities, and actions
taken on msg transmission, receipt
Hi
TCP connection request
Hi
Got the time?
200
17
Internet protocol stack

• application supporting network applications
• FTP, SMTP, HTTP
• transport process-process data transfer
• TCP, UDP
• network routing of datagrams from source to
  destination
• IP, routing protocols
• link data transfer between neighboring network
  elements
• PPP, Ethernet
• physical bits on the wire

18
ISO/OSI reference model

• presentation allow applications to interpret
  meaning of data, e.g., encryption, compression,
  machine-specific conventions
• session synchronization, checkpointing, recovery
  of data exchange
• Internet stack missing these layers!
• these services, if needed, must be implemented in
  application
• needed?

19
Today networking basics

• Movie on the history of the Internet
• Core components of the Internet the protocol
  stack
• Multiplexing, circuit switching, and packet
  switching
• Loss and delays
• The structure of the Internet
• This lecture covers much of chapter 1 in the
  textbook.

20
Circuit switching versus Packet switching

• Packet switching brought the networking
  revolution
• Circuit switching
• Virtual circuit networking
• A half-way point between packet switched and
  circuit switched networking

21
Circuit switching

• Circuit switching
• Old style phone system
• Each connection gets its own wire or bandwidth
• Note calls must be set-up.
• E.g.,
• Me operator, get my the president.
• Operator one moment please.
• Then she plugs a cable into a socket so now I
  have a physical wired between me and the
  president.
• Instead of each connection getting a whole wire,
  connections can share a wire via multiplexing
• The first automatic circuit switching was
  developed by Almon Strowger an undertaker.
  There were two undertakers in a small town and
  the switch board operator was the wife of the
  other undertaker. So Strowger invented an
  automatic circuit switch to rid both husband and
  wife of employment.

22
Frequency division multiplexing
On each hop, the connection gets its own bandwidth
toll office
End office
phone
TV is frequency division multiplexing
23
Time division multiplexing
64kbits
1
2
3
bytes
Overhead is 1 bit per 824 bits 8000bps
1/8000 sec per byte
7 bits of data and one bit for control (data or
not), so it really 56kbps of data
Note all the control overhead if the bit is 1,
then payload is control. Lots of control is
needed to setup a circuit. How is it possible to
get channels at each hop? Also, if there is not
data, then nothing is sent. This wastes data. But
the circuit is yours, guaranteed!
24
Packet switching - Statistical multiplexing

• Data is in packets, not streams.
• Must be digital
• Each packet has an address
• A switch/router reads the whole packet, then
  reads the address and forwards the packet store
  and forward

25
Packet switching - Statistical multiplexing

• Data is in packets, not streams.
• Must be digital
• Each packet has an address
• A switch/router reads the whole packet, then
  reads the address and forwards the packet store
  and forward

If destination is 1, then next hop is C
If destination is 1, then next hop is B
B
If destination is 1, then next hop is
A
C
D
client
Server address 1
F
E
26
Packet switching - Statistical multiplexing

• Data is in packets, not streams.
• Must be digital
• Each packet has an address
• A switch/router reads the whole packet, then
  reads the address and forwards the packet store
  and forward
• No reservations are needed. First come first
  serve.
• Major benefit
• If you need more bandwidth, then you can get it,
  it you dont need it, then maybe someone else can
  use it.
• Major drawback
• What happens if two packets arrive at a switch
  and both need to go to the same output interface.
  Picture. One packet is either dropped, or is
  placed in a buffer. Either way, something bad has
  happened, the packet is gone, or is delayed. This
  would never happen on a circuit switched network.
  ? queuing delay and packet loss ?

27
Packet vs. Circuit Switching

• If usage is random (e.g., web surfing)
  statistical multiplexing is better.
• Suppose that
• A 5Mbps link
• Each user needs 50kbps
• And each user is active 20 of the time. (note
  that this condition does not matter for circuit
  switching. Why?)

How many users can be accommodated under packet
switching and how many can be accommodated under
packet switching?
Circuit switching case
The total number of users that can be
accommodated with circuit switching is 5e6/50e3
100 users
28
Packet Switching Case

• Now if there are 200 users, what is the
  probability that there are 150 or more active
  users?
• In this case, there would be a problem, since the
  network cannot support more than 100 active
  users.

Simpler questions What is the probability of 150
particular users being active and 50 other being
inactive?
29
Packet Switching Case

• What is the probability of more than 100 users
  being active?

The probability of 101 users being active plus,
102 users being active, plus, ., 200 users being
active, which is
30
Packet Switching vs. Circuit Switching

• A couple of things

• This means that
• when you walk into the switching center, the
  probability of finding overload is 10-8.
• Or, if you random access the link, the
  probability of finding it in overload.
• Once you find it in overload, or not, the
  probability that is will be in overload in the
  next second is more complicated and requires
  queuing theory. This analysis might reveal worst
  performance.

• In this example, we assumed 20 user utilization
  (they were active 20 of the time)
• Is this large or small?
• If it the user utilization is smaller, then the
  difference between packet switching and circuit
  switching is even larger. But it is smaller, then
  there is less of a difference.
• What is your user utilization?
• For web surfing
• For cell phone usage
• For music streaming

31
Packet Switching vs. Circuit Switching

• If loss and delay are permissible and usage is
  random, then packet switching is better than
  circuit switching.
• If usage is very regular (e.g. TV!), circuit
  switching is best.
• If losses and delay are not permissible, then
  circuit switching is best (e.g., remote
  controlled surgery).
• With packet switching, congestion control is
  required. Also, there is more overhead for each
  packet.
• For circuit switching, once the circuit is setup,
  it can be very efficient. But circuits must be
  set-up.
• So, for short file transfer, packet switching is
  good but for long file transfers, circuit
  switching might be better.

There is a subtle difference between packet
switching and statistical multiplexing.
Statistical multiplexing means to use the
resource as needed. This leads to the performance
improvements mentioned but also the complications
(delay and loss). The phone network uses circuit
switching, but the circuits are statistically
multiplexed between users. In packet switching,
links are statistically multiplexed.
32
Packet Switching Statistical Multiplexing
100 Mb/s Ethernet
C
A
statistical multiplexing
1.5 Mb/s
B
queue of packets waiting for output link

• Sequence of A B packets does not have fixed
  pattern, bandwidth shared on demand ? statistical
  multiplexing.
• TDM each host gets same slot in revolving TDM
  frame.

33
Packet-switching store-and-forward
L
R
R
R

• Example
• L 7.5 Mbits
• R 1.5 Mbps
• transmission delay 15 sec

• takes L/R seconds to transmit (push out) packet
  of L bits on to link at R bps
• store and forward entire packet must arrive at
  router before it can be transmitted on next link
• delay 3L/R (assuming zero propagation delay)

more on delay shortly
34
Today networking basics

• Movie on the history of the Internet
• Core components of the Internet the protocol
  stack
• Multiplexing, circuit switching, and packet
  switching
• Loss and delays
• The structure of the Internet
• This lecture covers much of chapter 1 in the
  textbook.

35
Losses and delay in packet switched networks

• Losses
• Transmission losses
• In fiber links, bit-error is 10-12 or better
  (i.e., less).
• What is the probability of packet error when
  there are 1400 bytes in a packet?
• In wireless links, the bit-error rate can be very
  high
• Congestion losses.
• If too many packets arrive at the same time, then
  the buffers will fill up and packets are lost.
• Increasing the link speeds or reducing the number
  of users can reduce the probability of loss.
• Increasing the size of the buffer reduces losses,
  but also increases delay.
• Delay
• Queuing delay
• Transmission delay
• Propagation delay
• Processing delay

36
Queuing delay

• Queuing delay occurs for the same reason as
  congestion losses.
• The more the network is utilized, the high the
  queueing delay (and losses)
• Utilization ? actual use / maximum possible
  use

• Suppose that
• the link bit-rate is Z,
• there are X users
• Each users uses data rate Y, with probability P,
  and use no bandwidth with probability 1-p.

? XP/Z
37
Queuing delay

• Is it possible to have a network run at full
  utilization?

No! The average delay would be infinite!
From queuing theory Delay ?/(1- ?)
?
38
Delay in packet switched networks

• Delay
• Queuing delay
• Transmission delay
• Propagation delay
• Processing delay

How long does it take to transmit a packet? How
long does it take to get all the bits from node
on to the wire/air/fiber?

• Suppose
• Link bit rate is 10 Mbps
• Packet size is 1400 bytes
• How long to transmit the packet?

39
Delay in packet switched networks

• Delay
• Queuing delay
• Transmission delay
• Propagation delay
• Processing delay

How long does it take for a bit to travel along a
wire/fiber/through the air?

• Suppose
• Speed of light in a vacuum 3e8 m/s while in a
  fiber it is 2e8m/s
• How long does it take to transmit a bit from NY
  to LA 3962km
• 20ms propagation delay
• How about from NY to Jakarta, Indonesia
  16,179km
• 80ms
• How about to a Geostationary satellite?
• 250-300 (up and back)
• Medium orbit satellites (e.g., GPS)
• 120ms
• Low-earth orbit satellites (low earth? What about
  middle-earth?)
• Iridium at 10ms
• Note, Iridium paid 5 billion for the network and
  sold for 25million (1/2-on sale 99.5 off,
  everything must go)
• Teledesic. 10ms

40
Fun with Propagation Delay
How long is a bit? Suppose that a links transmits
at 10mbps. How long is a bit?
How long does it take to a bit? 1/10106
10-7 How far does the electric signal go in 107
sec? 10-7 2e8 20 meters.
How long many bits fit in a fiber at 10Mbps from
NY to Jakarta? 16,179km103/20 0.1 MB
How long many bits fit in a fiber at 10 Gbps from
NY to Jakarta? 16,179km103/20 100 MB
Satellite transmissions are subject to
transmission loss (e.g., rain can cause
interference), The satellite sending station
could wait for and ACK from the other side and
resend the data if no ACK appeared (a link layer
solution) But this would cause out-of-order
delivery So the satellite could hold the packets
until the lost one is retransmitted. How large
would the buffer need to be if the bit rate was
3Gbps? Answer .53e9/8187MB (assuming no
processor delay)
41
Delay in packet switched networks

• Routers take a bit of time to process packets.
• moving packets inside the router
• Finding which is the next hop
• Applying security or QoS

• Delay
• Queuing delay
• Transmission delay
• Propagation delay
• Processing delay

42
How to measure delay?

• Ping ping 216.109.124.73
• Ping gives help
• (linux) Ping I 10 216.109.124.73 file.txt
• Then read it in excel and plot delay
• Traceroute (linux), tracert (windows)
• Traceroute 216.109.124.73 gives the routers and
  an estimate of the delay to each router.

43
Today networking basics

• Movie on the history of the Internet
• Core components of the Internet the protocol
  stack
• Multiplexing, circuit switching, and packet
  switching
• Loss and delays
• The structure of the Internet
• This lecture covers much of chapter 1 in the
  textbook.

44
Internet structure network of networks

• roughly hierarchical
• at center tier-1 ISPs (e.g., Verizon, Sprint,
  ATT, Cable and Wireless), national/international
  coverage
• treat each other as equals

Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
45
Tier-1 ISP e.g., Sprint
46
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 1 ISP
Tier 1 ISP
Tier 1 ISP
47
Internet structure network of networks

• Tier-3 ISPs and local ISPs
• last hop (access) network (closest to end
  systems)

Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
48
Internet structure network of networks

• a packet passes through many networks!

Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
49
ISPs and the structure of the Internet

• Video of a Network Access Point (NAP) in Los
  Angeles

50
MEET ME ROOM
Said to be the most interconnected space in the
world and the most expensive real estate in North
America, the Meet Me Room (a telco industry
term) is the heart of One Wilshire. Here the
primary fiber optic cables are routed, split, and
shared. Because of the presence of so many telcos
in this room and the ability to freely
interconnect between them, rackspace here becomes
extremely valuable. For comparison, the average
price for office space in downtown Los Angeles is
1.75 per square foot per month. At the Meet Me
Room, 250 per square foot would be a bargain.
51
CABLE RISERS
Some 1,800 known conduits contain the fiber optic
cables that flow through the buildings
stairwells and vertical utility corridors, called
risers. Cable connects the commercial telco
tenants on floors 5 through 29 to the 4th floor
Meet Me Room, and to a new, wireless Meet Me
Room constructed on the 30th floor.
52
SURFACE CABLE MAP
Whenever a permit is pulled by a city contractor
for any underground repairs outside One Wilshire,
the various telco companies with cable in the
area come out and paint the cable routes on the
asphalt, creating a visible graphic of the
complexity of what lies just under the surface.
53
HVAC
Computers generate a lot of heat, and maintaining
a stable, cool temperature and a low humidity is
essential in telco hotels, so tenants sometimes
demand to install their own cooling systems to
safeguard their equipment. At One Wilshire, these
units are installed primarily on the third floor
roof. A new closed loop cooling system has been
installed on the 30th floor roof.
54
CABLE MINING
As tenants needs change, cables can go unused.
Cable mining is performed to thin out the
obsolete cables and future congestion is
alleviated through the installation of dedicated
new ducts.
55
ELECTRICITY
Power is supplied by DWP, but in the event of a
blackout, the buildings five generators will
kick in. It takes the generators three seconds to
start up and stabilize. During this brief period,
the entire building runs on batteries. There are
11,000 gallons of diesel stored on site, enough
to run the generators for 24 hours before being
refueled.
56
MICROWAVE
On the roof, microwave antennas link up One
Wilshire to transmission towers located around
the city. Though fibers higher capacity has
given it dominance over microwave at One
Wilshire, microwaves relatively low cost over
long distances continues to make it economical
for some applications. The roofs clear line of
sight to the south, west, and to other
high-rises, along with the ability to interface
with the fiber inside, continues to make One
Wilshire an attractive location for
microwave-based transmission.
57
READING A ROOF
Much can be learned about a buildings function
by examining its roof. The existence of telco
hotels in the region around One Wilshire is
indicated by the presence of new and extensive
cooling units on the roofs of adjacent buildings,
many of which were nearly vacant until the telco
companies moved in.
58
POINT OF ENTRY
The main fiber optic cables connecting One
Wilshire to the world enter the building from
under the street through closets in the walls of
the buildings parking garage. Given the
importance of the building to the global
communications network, access to the parking
garage is controlled, and the building is said to
be monitored continuously by federal security
officials.
59
MEET ME ROOM
Said to be the most interconnected space in the
world and the most expensive real estate in North
America, the Meet Me Room (a telco industry
term) is the heart of One Wilshire. Here the
primary fiber optic cables are routed, split, and
shared. Because of the presence of so many telcos
in this room and the ability to freely
interconnect between them, rackspace here becomes
extremely valuable. For comparison, the average
price for office space in downtown Los Angeles is
1.75 per square foot per month. At the Meet Me
Room, 250 per square foot would be a bargain.
60
CABLE RISERS
Some 1,800 known conduits contain the fiber optic
cables that flow through the buildings
stairwells and vertical utility corridors, called
risers. Cable connects the commercial telco
tenants on floors 5 through 29 to the 4th floor
Meet Me Room, and to a new, wireless Meet Me
Room constructed on the 30th floor.
61
SURFACE CABLE MAP
Whenever a permit is pulled by a city contractor
for any underground repairs outside One Wilshire,
the various telco companies with cable in the
area come out and paint the cable routes on the
asphalt, creating a visible graphic of the
complexity of what lies just under the surface.
62
HVAC
Computers generate a lot of heat, and maintaining
a stable, cool temperature and a low humidity is
essential in telco hotels, so tenants sometimes
demand to install their own cooling systems to
safeguard their equipment. At One Wilshire, these
units are installed primarily on the third floor
roof. A new closed loop cooling system has been
installed on the 30th floor roof.
63
CABLE MINING
As tenants needs change, cables can go unused.
Cable mining is performed to thin out the
obsolete cables and future congestion is
alleviated through the installation of dedicated
new ducts.
64
ELECTRICITY
Power is supplied by DWP, but in the event of a
blackout, the buildings five generators will
kick in. It takes the generators three seconds to
start up and stabilize. During this brief period,
the entire building runs on batteries. There are
11,000 gallons of diesel stored on site, enough
to run the generators for 24 hours before being
refueled.
65
MICROWAVE
On the roof, microwave antennas link up One
Wilshire to transmission towers located around
the city. Though fibers higher capacity has
given it dominance over microwave at One
Wilshire, microwaves relatively low cost over
long distances continues to make it economical
for some applications. The roofs clear line of
sight to the south, west, and to other
high-rises, along with the ability to interface
with the fiber inside, continues to make One
Wilshire an attractive location for
microwave-based transmission.
66
READING A ROOF
Much can be learned about a buildings function
by examining its roof. The existence of telco
hotels in the region around One Wilshire is
indicated by the presence of new and extensive
cooling units on the roofs of adjacent buildings,
many of which were nearly vacant until the telco
companies moved in.
67
POINT OF ENTRY
The main fiber optic cables connecting One
Wilshire to the world enter the building from
under the street through closets in the walls of
the buildings parking garage. Given the
importance of the building to the global
communications network, access to the parking
garage is controlled, and the building is said to
be monitored continuously by federal security
officials.
68
Homework

• Page 61. Questions (3, 7), 8, (9), (10), 11, 13,
  14, 19, (20), 21, (22), (23)
• Page 63. Problems 2, (3), 6, 7, 8, (10), (11),
  (12)
• Use trace route to determine the average number
  of hops between 10 destinations of your choice.
• Use ping to determine the propagation delay.
  Specifically, send very small packets (these will
  be 24 bytes).Then send ICMP packets with larger
  payload. Compare the difference in the RTT and
  determine the transmission time.
• Do links have time-varying delay? To answer this
  questions run trace route at different times of
  the day (e.g., the middle of the night, morning,
  afternoon, etc) and compare the delay times.