What is the Speed of the Internet?

Internet Computing Laboratory @ KUT

Youn-Hee Han

Computer Network2

Media Types for Internet

Internet data flows across: Copper wire Fiber Wireless (radio)

Physics tells us that these all represent electromagnetic propagation

Einstein Says… The speed of light, hence the speed of electromagnetic

propagation is a constant C = 300 x 106 m/s = 3.0 x 108 m/s

Hence the speed of the Internet is: 300 x 106 m/s = 3.0 x 108 m/s well… not exactly

Computer Network3

Propagation Speed

“C” is the speed of propagation in “free space”It is well known that…

Copper: 2.3 x 108 m/s Fiber: 2.0 x 108 m/s Radio: 3.0 x 108 m/s

“Speed” of the Internet is… between 2.0 x 108 and 3.0 x 108 m/s

Let’s assume Internet propagation speed S… S = 2.0 x 108 m/s

Computer Network4

How Long Will It Take To Download?

Let’s download the following image file from a location

Assume the distance D is 5288 km If it were just one bit!

D / S = 5288 * 1000 / 2.0 x 108 = 26.4 x 10-3 sec

Size: 62,728 bytes D / S = 62,728 x 8 x 26.4 x 10-3

= 13,248 s = 3.7 hours!

Is this correct?

62,728 bytes

Computer Network5

How Long Will It Take To Download?

One bit at a time!

Computer Network6

How Long Will It Take To Download?

Keeping the Pipe Full!

Computer Network7

Four sources of packet delay

Processing Delay (=Dproc ) Time to examine the packet’s header and determine where to direct the packet

Queuing Delay (= Dqueue) Time to exist in queue In Input queue, it depends on the number of earlier-arriving packets that are queued In Output queue, it depends on the number of waiting for transmission across the link

Transmission Delay (= Dtrans ) Time to push all of the packet’s bits into the link (= Packet Length / Transmission Rate) E.g., Packet Length: 1,500 Bits, Transmission Rate : 100 Mbps, Transmission Delay = ?

Propagation Delay (=Dprop) Time to propagate from the beginning of the link to the end of the link (= Distance / Propagation

Speed) E.g., Distance: 1Km, Propagation Speed: 3*10^8 m/sec, Propagation Delay = ?

Queuing (Input queue) Processing

Queuing (Output queue)

Transmission Propagation

Computer Network8

1. nodal processing: check bit errors determine output link

2. queueing time waiting at output

link for transmission depends on

congestion level of router

Four sources of packet delay

A

B

propagation

transmission

nodalprocessing queueing

Computer Network9

3. Transmission delay:R=link bandwidth (bps) =Transmission Rate L=packet length (bits)time to send bits into link = L/R

4. Propagation delay:d = length of physical links = propagation speed in medium (~2x108 m/sec)propagation delay = d/s

Note: s and R are very different quantities!

Four sources of packet delay

A

B

propagation

transmission

nodalprocessing queueing

Computer Network10

Total Delay

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

proptransqueueprocnodal ddddd

Computer Network11

Delay and Loss in Packet-Switched Network

Queuing Delay and Packet Loss Queuing delay depends on

Packet arrival rates, Link transmission rate, Traffic pattern (periodic or in bursts), etc.

Traffic Intensity (=TI) in input queue To estimate the extent of the queuing delay L: the average packet length (bits) a: the average packet arrival rate at the queue (packets/sec) R: Processing rate (in bits/sec)

If TI > 1, Packet Loss (Drop) happens at the queue

R

aLTI

Design your system so that TI is no greater than 1Golden Rule

1

Avera

ge q

ueu

ing

dela

y Traffic Intensity

Computer Network12

Packet Size Issue Revisited`

Huge-packet Switching Network Small-packet Switching Network

0

5

10

15

Time (in seconds)

01234

49995000500150025003

Time (in msec.)

Link Transmission Rate – 1.5 MbpsLarge-packet Length - 7,500,000 bitsSmall-packet Length – 1,500 bits (Total Number of Packets – 5,000 packets)

Queuing & Processing & Propagation Delays are zero

Assumption Packetizing

One hop delivery delay- 5 seconds = 7,500,000 bits / 1.5 Mbps

Total delivery delay- ?

One hop delivery delay- 1 msec. = 1,500 bits / 1.5 Mbps

Total delivery delay- ?

Router

Router

Source Host Destination Host Router

Router

Source Host Destination Host

pipelining: each link works in parallel