PTE1564

Jaringan Komputer
Kelas Teknik Komputer

0812 7770 9019

abdillah.mahyuddin@uin-suska.ac.id
abdill01.wordpress.com
Bab 1: Outline
1.1 what is the Internet?
1.2 network edge
1.3 network core
1.4 delay, loss, throughput in networks
1.5 protocol layers, service models
1.6 networks under attack: security
1.7 history

Introduction 1-2
The network core
 mesh of interconnected
routers

Introduction 1-3
Network communication methods
 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

 Circuit-switching
 end-end resources allocated to, reserved for "call"
between source & dest.

 Analogy
 Car vs Train
Introduction 1-4
Packet-switching: store-and-forward

L bits
per packet

3 2 1
source destination
R bps R bps

 takes L/R seconds to transmit one-hop numerical

(push out) L-bit packet into example:
link at R bps
 L = 7.5 Mbits
 store and forward: entire
packet must arrive at router  R = 1.5 Mbps
before it can be transmitted  one-hop transmission
on next link delay = 5 sec
 end-end delay = 2L/R (assuming
zero propagation delay) more on delay shortly …
Introduction 1-5
Packet Switching: queueing delay, loss

R = 100 Mb/s C
A
D
R = 1.5 Mb/s
B
queue of packets E
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

Introduction 1-6
 Two key network-core functions
routing: determines source- forwarding: move packets
destination route taken by from router’s input to
packets appropriate router output
 routing algorithms

routing algorithm

local forwarding table

header value output link
0100 3 1
0101 2
0111 2 3 2
1001 1
11
01

dest address in arriving

packet’s header
Introduction 1-7
Alternative core: circuit switching
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
Introduction 1-8
Packet switching versus circuit switching
is packet switching a "slam dunk winner?"
 within same capacity, allows more users to use network
 great for bursty data
 resource sharing
 simpler, no call setup
 excessive congestion possible: packet delay and loss
 protocols are 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)?
Introduction 1-9
Internet structure: network of networks
Question: given millions of access ISPs, how to connect them
together?
access
… access
net
access
net …
net
access
access net
net
access
access net
net
…

…
access access
net net

access
net
access
net

access
net
access
… net
access
net
access
net
…
access
net

Introduction 1-29
Internet structure: network of networks
Option: connect each access ISP to every other access ISP?

access
… access
net
access
net …
net
access
access
net
… … net

access
access net
net

Low Scalability
…

…
…
access access
…

net net

access
net
access
net

access
net
access
…

… net
access
net
access
net
…
access
net

Introduction 1-30
Internet structure: network of networks
Option: connect each access ISP to a global transit ISP?
Customer ISPs and provider ISPs have economic agreement.

access
… access
net
access
net …
net
access
access net
net
access
access net
net
…

…
global
access
net ISP access
net

access
net
access
net

access
net
access
… net
access
net
access
net
…
access
net

Introduction 1-31
Internet structure: network of networks
But if one global ISP is viable business, there will be competitors
….

access
… access
net
access
net …
net
access
access net
net
access
access net
net
ISP A
…

…
access access
net ISP B net

access
ISP C
net
access
net

access
net
access
… net
access
net
access
net
…
access
net

Introduction 1-32
Internet structure: network of networks
But if one global ISP is viable business, there will be competitors
…. which must be interconnected
Internet exchange point
…
access
access
access
net net …
net
access
access net
net

access
IXP access
net
net
ISP A
…

…
access IXP access
net ISP B net

access
ISP C
net
access
net

access
net
peering link
access
… net
access
net
access
net
…
access
net

Introduction 1-33
Internet structure: network of networks
… and regional networks may arise to connect access nets to
ISPS

access
… access
net
access
net …
net
access
access net
net

access
IXP access
net
net
ISP A
…

…
access IXP access
net ISP B net

access
ISP C
net
access
net

access
net regional net
access
… net
access
net
access
net
…
access
net

Introduction 1-34
Internet structure: network of networks
… and content provider networks (e.g., Google, Microsoft) may run
their own network, to bring services, content close to end users.

access
… access
net
access
net …
net
access
access net
net

access
IXP access
net
net
ISP A
…

…
Content provider network
access IXP access
net ISP B net

access
ISP B
net
access
net

access
net regional net
access
… net
access
net
access
net
…
access
net

Introduction 1-35
 Internet structure: network of networks

Tier 1 ISP Tier 1 ISP Google

IX IX IX
P P P
Regional ISP Regional ISP

access access access access access access access access

ISP ISP ISP ISP ISP ISP ISP ISP

 at center: small # of well-connected large networks

 "tier-1" commercial ISPs (e.g., Level 3, Sprint, AT&T, NTT), national &
international coverage
 content provider network (e.g, Google): private network that connects it
data centers to Internet, often bypassing tier-1, regional ISPs Introduction 1-17
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

Introduction 1-18
How do loss and delay occur?
packets queue in router buffers
 packet arrival rate to link (temporarily) exceeds output link
capacity
 packets queue, wait for turn

packet being transmitted (delay)

B
packets queueing (delay)
free (available) buffers: arriving packets
dropped (loss) if no free buffers
Introduction 1-19
Four sources of packet delay
A

B
nodal
processing queueing
dnodal = dproc + dqueue

dproc: nodal processing delay dqueue: queueing delay

 check bit errors  time waiting at output link for transmission
 determine output link  depends on congestion level of router
 typically < msec
Introduction 1-20
Four sources of packet delay
transmission
A propagation

B
nodal
processing queueing
dnodal = dproc + dqueue + dtrans + dprop

dtrans: transmission delay: dprop: propagation delay:

 L: packet length (bits)  d: length of physical link
 R: link bandwidth (bps)  s: propagation speed in medium (~2x108 m/s)
 dtrans = L/R  dprop = d/s
dtrans and dprop:
Introduction 1-21
very different
Caravan analogy
100 km 100 km
ten-car toll toll
caravan booth booth

 car ← bit;  time to "push" entire

 caravan ← packet caravan through toll
 cars "propagate" at booth onto highway
 100 km/hr = 12*10 = 120 sec
 toll booth takes 12 sec to  time for last car to
service car ← bit transmission propagate from 1st to
time 2nd toll booth:
 Q: How long until caravan is 100km/(100km/hr) =
lined up before 2nd toll booth? 1 hr
 A: 62 minutes
Introduction 1-22
"Real" Internet delays and routes
whatdo "real" Internet delay & loss look like?
traceroute/tracert program provides:
 delay measurement
 from source to router along end-end Internet path towards
destination.
 for all i:
 sends three packets that will reach router i on path
towards destination
 router i will return packets to sender
 sender times interval between transmission and reply.

3 probes 3 probes
3 probes
Introduction 1-23
"Real" Internet delays, routes
traceroute: gaia.cs.umass.edu to www.eurecom.fr
3 delay measurements from
1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms gaia.cs.umass.edu to cs-
2
3
gw.cs.umass.edu
border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms
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 trans-oceanic
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 link
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 * * * * means no response (probe lost, router not
19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms
replying)
Introduction 1-24
Packet loss
 queue (aka buffer) preceding link in buffer has finite
capacity
 packet arriving to full queue dropped (aka lost)
 lost packet may be retransmitted by previous node, by
source end system, or not at all

buffer
A packet being transmitted
(waiting area)

B
packet arriving to
full buffer is lost
Introduction 1-25
Throughput
throughput: rate (bits/time unit) at which bits
transferred between sender/receiver
 instantaneous: rate at given point in time
 average: rate over longer period of time

server,
server withbits
sends linkpipe
capacity
that can carry linkpipe
capacity
that can carry
file of into
(fluid) F bits
pipe fluid at rate
Rs bits/sec fluid at rate
R bits/sec
to send to client c
Rs bits/sec) Rc bits/sec)

Introduction 1-26
Throughput (more)
Rs < Rc What is average end-end throughput?

Rs bits/sec Rc bits/sec

Rs > Rc What is average end-end throughput?

Rs bits/sec Rc bits/sec

bottleneck
link
link on end-end path that constrains end-end throughput
Introduction 1-27
Chapter 1: Next Week
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

Introduction 1-28