Its a CCN base work related to delays and thruput

1. Computer
Networking: A
Top Down
Approach
6th edition
Jim Kurose, Keith Ross
Addison-Wesley
March 2012
Computer Communications
& Networks
CSNC-2413
• Introduction
Lec: 3,4

2. Chapter 1: roadmap
1.1 what is the Internet?
1.2 network edge
 end systems, access networks, links
1.3 network core
 packet switching, circuit switching, network structure
1.4 delay, loss, throughput in networks
1.5 protocol layers, service models
1.6 networks under attack: security
1.7 history
2

3.  Mesh of interconnected routers
 Fundamental ques:
“how is data transferred thru
network”
 Circuit switching
̶ resources along the path reserved
for Tx duration
̶ e.g, telephone network
̶ guaranteed service
 Packet switching
̶ N/W resources used on demand
̶ e.g, Internet
̶ best effort service
The network core
3

4. Circuit switching
 Each link shown has four circuits
 call gets 2nd circuit in top link
and 1st circuit in right link
 dedicated resources, no sharing
 circuit-like performance
(guaranteed)
 circuit segment idle, if not used
by call (no sharing)
4
 Network establishes an end-to-end connection between hosts
 Resources reserved for the “call” (buffer space, B/W)

5. Multiplexing in Circuit switching
5
 A circuit in a link is implemented using FDM (Freq Div Mux) or TDM
(Time Div Mux)
FDM
 freq spectrum divided
into freq bands
 each connection
allocated a freq band
TDM
 time divided into frames,
with fixed number of
slots
 each connection
allocated a time slot in
every frame

6. 6
Time Division Mux (TDM)

7. 7
TDM : DeMux

8. TDM circuit: data Tx rate
8
 How to determine data Tx rates
of TDM circuit/channel…
 What is TDM circuit/channel…
Given…
Frame rate = 8000 frames/sec
Slot size = 8 bits
Data Rate = Frame Rate x Slot Size
Sol…
Data rate of one circuit = 8000 x 8 = 64 kbps
Data rate of TDM line = 8000 x 8 x 4 = 256 kbps

9. TDM circuit: file Tx time
9
 How much time it takes to send a 640 kbits file from Host A to Host B
over a circuit switched network. All links in network use TDM with 24
slots and have a line rate of 1.536 Mbps. Also, it takes 500 ms to
establish the circuit before transmission can take place.
Given…
TDM line rate = 1.536 Mbps Frame size = 24 slots
Circuit establishment delay = 500 ms File size = 640 kbits
Sol…
Data rate of one TDM circuit = 1.536 Mpbs / 24 = 64 kbps
Tx time of file = 640 Kbits / 64 kbps = 10 sec
Total File sending time = 500 ms + 10 sec = 10.5 sec
(actual file sending time would also involve propagation delay…)

10. Bandwidth division into “pieces”
Dedicated allocation
Resource reservation
 Packet-switching:
 hosts break application-layer
messages into smaller chunks, packets
 forward packets from one router to the
next, across a set of links
 sources use network resources on
demand
 each packet Tx at full link capacity
The network core
10

11. Packet switching
Host sending function…
 application message broken
into packets of length L bits
 pkts Tx into access network at
transmission rate, R
 R is link Tx rate,
aka link bandwidth
R: link transmission rate
host
1
2
two packets,
L bits each
packet
transmission
delay
time needed to
transmit L-bit
packet into link
L (bits)
R (bits/sec)
= =
11
 Total Tx delay for 2 pks = 2L/R

12. Packet-switching: Store-and-forward
 Store and Forward: entire pkt
must arrive at router before it
can be Tx on next link
 end-end delay (1 pkt) = 2L/R
 end-end delay (3 pkts) = 4L/R
one-hop numerical example:
 L = 7.5 Mbits
 R = 1.5 Mbps
 one-hop transmission
delay = 5 sec
12
(assuming zero propagation delay)

13. Packet-switching: queueing delay, loss
13
Queuing delay & Loss:
 aggregate resource demand can exceed the amount available
 if arrival rate at input link, exceeds Tx rate of output link…
 pkts will be queued (delayed), waiting for Tx
 pkts can be dropped (lost), if buffer fills up

14.  Statistical Multiplexing: on-demand resource allocation;
pkts of A & B do not have fixed sequence at output link
 TDM: pre-allocated time slots; each host gets same slot in TDM frame
A
B
C
10 Mb/s
Ethernet
1.5 Mb/s
D E
statistical multiplexing
queue of packets
waiting for output
link
Packet-switching: Statistical Mux
14

15. 15
Statistical Mux vs TDM

16. ……...
 N users over 1 Mbps link
 each Tx at 100 kbps when “active”;
active 10% of time
 Circuit-switching supports10 users
 Packet-switching allows more users
because of Tx being intermittent
Packet switching may allow more users to use network…
N users
1 Mbps link
Packet-switching Vs Circuit-switching
Packet switching may allow a user access to greater B/W…
 In circuit-switching, a user can only utilize his part of B/W
 1/10 of B/W for 10 users
 In packet-switching, with less number of users active at any given time,
a user may avail more B/W
16

17. How do loss & delay occur?
Packets incur delays in routers….
 If packet arrival rate to link (temporarily) exceeds output link
capacity
 packets are queued; wait for turn to Tx (delayed)
A
B
packet being transmitted
packets queued (delayed)
free (available) buffers
17

18. Packet loss
 each output link has a buffer (queue) of finite capacity
 packet arriving to full queue is dropped (lost)
 lost packet may be retransmitted by previous node, by source
end system, or not at all
A
B
packet being transmitted
packet arriving to
full buffer is lost
buffer
(waiting area)
18

19. Four sources of packet delay
dproc: nodal processing
 check bit errors
 determine output link
 typically < msec
dqueue: queueing delay
 time waiting at output link
for Tx
 depends on congestion
level of router
dnodal = dproc + dqueue + dtrans + dprop
19

20. dtrans: transmission delay
 L: packet length (bits)
 R: link bandwidth (bps)
 dtrans = L/R
dprop: propagation delay
 d: length of physical link
 s: propagation speed in medium
(~2x108 m/sec)
 dprop = d/s
dtrans & dprop
very different
Four sources of packet delay
20
dnodal = dproc + dqueue + dtrans + dprop

21. “Real” Internet delays and
routes
 What do “real” Internet delay & loss look like?
 Traceroute program: provides delay measurement from
source to each router, along end-end Internet path, towards
destination
 For all i:
 send three packets that will reach router i on path towards
destination
 router i will return packets to sender
 sender times the interval between transmission and reply
3 probes 3 probes
3 probes
21

22. 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
8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms
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 * * *
18 * * *
19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms
traceroute: gaia.cs.umass.edu to www.eurecom.fr
Three delay measurements from
gaia.cs.umass.edu to cs-gw.cs.umass.edu
means no response (probe lost, router not replying)
trans-oceanic
link
22
“Real” Internet delays and
routes

23. Throughput
 Throughput : rate (bits/sec) at which bits transferred
between sender/receiver
 instantaneous: rate at given point in time
 average: rate over longer period of time
server with
file of F bits
to send to client
link capacity
Rs bits/sec
link capacity
Rc bits/sec
server sends bits
(fluid) into pipe
pipe that can carry
fluid at rate
Rs bits/sec)
pipe that can carry
fluid at rate
Rc bits/sec)
23

24.  Rs < Rc What is average end-end throughput?
 Rs > Rc What is average end-end throughput?
link on end-end path that constrains end-end throughput
bottleneck link
Rs bits/sec Rc bits/sec
Rs bits/sec Rc bits/sec
24
Throughput

25. Network Architecture
 Network communications - a complex task
 To deal with this complexity… SIMPLIFY
 comm task broken up into modules
 modules arranged in a layered vertical stack
 each layer/module performs a subset of the comm function
 Forms a Network Architecture
• multiple layers
• each layer has one/more Protocols
• protocols perform specific comm tasks
• provide/obtain services to/from higher/lower layer
25

26. Example of a
layered network
system
Network Architecture
Network Architecture
A structured set of protocols to implement the
communication functions
application
transport
network
link
physical
26

27. Why Layered Architecture
 Network Architecture is a layered architecture
 provides modularity
• changes in one layer do not require changes in other
layers
 modularization eases system maintenance, updation
 facilitates process of network evolution
• changes in underlying technologies
• increase in application demands
 layering considered harmful…??
27

28. Internet protocol stack
 Application: support network applications
 FTP, SMTP, HTTP, DNS
 Transport: process-process data transfer,
flow control, error control, congestion
control
 TCP, UDP
 Network: global addressing, routing of
datagrams from source to destination
 IP
 Link: data transfer between neighboring
network elements
 Ethernet, 802.11 (WiFi), PPP
 Physical: bits “on the wire”
application
transport
network
link
physical
28

29. Reference Models
 Some of the protocols and networks in TCP/IP model
29

30. ISO/OSI reference model
 Presentation: allow applications to
interpret meaning of data, e.g.,
encryption, compression, machine-
specific conventions
 Session: synchronization, check-
pointing, recovery of data exchange
 Internet stack “missing” these
layers!
 these services, if needed, must be
implemented in application
 needed?
application
presentation
session
transport
network
link
physical
30

31. Encapsulation
31
 Path data takes down/up the
protocol stack at sender, switch,
router & receiver
 Principle of encapsulation

32. Summary
1.1 what is the Internet?
1.2 network edge
 end systems, access networks, links
1.3 network core
 packet switching, circuit switching, network structure
1.4 delay, loss, throughput in networks
1.5 protocol layers, service models
1.6 networks under attack: security
1.7 history
32