Lec2 Taxonomy

7/28/2019 Lec2 Taxonomy

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Taxonomy 1-1

Lec 2: Internet Connectivity:

Packet SwitchingECE5650


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Taxonomy 1-2

Backbone ISPISP ISP

Recap: Internet Physical Structure

Residential access Modem DSL Cable modem Wireless

Campus access Ethernet FDDI Wireless

The Internet is a network ofnetworks Each individually administrated

network is called an AutonomousSystem (AS)

We can roughly divide the networksinto access networks and transitnetworks


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Taxonomy 1-3

Recap: Layered protocol stack

application: supporting networkapplications FTP, SMTP, HTTP

transport: process-process data

transfer TCP, UDP

network: host-host data transfer IP

link: data transfer betweenneighboring network elements PPP, Ethernet

physical:bits on the wire

application

transport

network

link

physical


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Taxonomy 1-4

Recap: Histroy

60s: packet switching theory, ARPNET ARPANET was an attempt to investigate the feasibility

of packet switching ARPANET was built on top of telephone networks

70s: internetworking, Ethernet

80s: applications: email, ftp, telnet, etc 90s: web killer appl and commercialization

totally distributed, autonomous systems roughlyhierarchical where ISPs interconnect at PoP and NAP

Today: As important as utility services backbone speed: about 10 Gbps number of hosts: about 400 millions


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Taxonomy 1-5

Outline

Network Taxonomy Broadcast vs Switched Networks

Circuit Switched vs packet switched

Switched Network Performance Delay, Lose, Throughtput

Security


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Taxonomy 1-6

The Network Core

mesh of interconnectedrouters

thefundamentalquestion: how is datatransferred through net?

circuit switching:dedicated circuit percall: telephone net

packet-switching: datasent thru net indiscrete chunks


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Taxonomy 1-7

Network Core: Circuit Switching

End-end resourcesreserved for call

link bandwidth and

switch capacity pre-determined

dedicated resourceswith no sharing of

bandwidth guaranteed

performance

call setup required


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Taxonomy 1-8

Network Core: Circuit Switching

network resources(e.g., bandwidth)divided into pieces

pieces allocated to calls

resource piece idleifnot used by owning call(no sharing)

dividing link bandwidthinto pieces

frequency division

time division


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Taxonomy 1-9

Circuit Switching: FDM and TDM

Frequency Domain Mux (FDM)

bandwidth/

frequency

of the link

time

Time Domain Mux (TDM)Transmission rate of single circuit = frame rate in frames/sec * #bits in a slot

bandwidth/

frequency

of the link

time

4 users/slots

Example:

Slot4 slots/frame

Note: Circuit is analogous to connection


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Taxonomy 1-10

circuitestablishment

DATAdatatransmission

circuittermination

propagation delayfrom A to Node 1

propagation delayfrom B To A

processing delay at Node 1

Circuit Switching in MultiHop Route


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Taxonomy 1-11

Network Core: Packet Switching

each end-end data streamdivided intopackets

user A, B packets sharenetwork resources

each packet uses full linkbandwidth

resources used as needed

resource contention: flow-control needed as

aggregate resourcedemand can exceed

amount available congestion control

needed as packetsqueued and wait for

link use store and forward:

packets move one hopat a time

Bandwidth division into piecesDedicated allocation

Resource reservation


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Taxonomy 1-12

Packet Switching: Statistical Multiplexing

Sequence of A & B packets does not have fixed pattern,on demand sharing of resources (statisticalmultiplexing).

A

B

C10 Mb/sEthernet

1.5 Mb/s

D E

statistical multiplexing

queue of packetswaiting for outputlink

Header Data Trailer


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Taxonomy 1-13

Host A

Host BHost E

Host D

Host C

Node 1 Node 2

Node 3

Node 4

Node 5

Node 6 Node 7

Packet Switching


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Taxonomy 1-14

Packet 1

Packet 2

Packet 3

Packet 1

Packet 2

Packet 3

Packet 1

Packet 2

Packet 3

processingandqueueingdelay ofPacket 1 atrouter 2

propagationdelay fromHost A torouter 1

transmissiontime of Packet 1at Host A

Timing Diagram of Packet Switching


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Taxonomy 1-15

Packet switching vs Circuit Switching: AnExample

Problem: 1 Mbps link and each user needs 100kbps when active and is active 10% of time.

circuit-switching FDM: Max #users = (1,000,000 b/s)/(100,000 b/s) = 10

packet switching: Min #users = 10

Max is > 10 due to the probability that users are

inactive 90% of time

Packet switching allows more users to use network!

N users1 Mbps link


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Taxonomy 1-16

Packet Switching vs Circuit Switching

Great for bursty data

resource sharing

simpler, no call setup Excessive congestion: 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

Is packet switching a slam dunk winner?


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Taxonomy 1-17

Packet-switched Networks: Forwarding

Goal:move packets through routers from source to dest

(1) Packet-switched datagram network:

destination address in packet determines next hop Entire packet must arrive at router before it can be transmitted

on next link

routes may change during session

analogy: driving, asking directions

(2) Packet-switched virtual circuit network: each packet carries tag (VC ID), tag determines next hop

fixed path determined at call setup time, remains fixed thru call

routers maintainper-call state

L


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Taxonomy 1-18

Host A

Host BHost E

Host D

Host C

Node 1 Node 2

Node 3

Node 4

Node 5

Node 6 Node 7

Virtual-Circuit Switching

Three phases VC establishment

Data transfer

VC disconnect


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Taxonomy 1-19

Virtual-Circuit Packet Switching

Example: Asynchornous Transfer Mode (ATM)networks; Multiple Label Packet Switching (MPLS) inIP networks

Hybrid of circuit switching and datagram switching

each packet carries a shorttag (virtual-circuit (VC) #);tag determines next hop

fixed path determined atVirtual Circuit setup time,

remains fixed thru flow routers maintain per-flow

state what state do routers

maintain for datagram switching?

IncomingInterface

IncomingVC#

OutgoingInterface

OutgoingVC#

1 12 2 22

1 16 3 1

2 12 3 22


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Taxonomy 1-20

Packet 1

Packet 2

Packet 3

Packet 1

Packet 2

Packet 3

Packet 1

Packet 2

Packet 3

Host 1 Host 2Node 1 Node 2

propagation delay

between Host 1

and Node 1VC

establishment

VC

termination

data

transfer

Timing Diagram of Virtual-Circuit Switching


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Taxonomy 1-21

Datagram Switching vs. Virtual CircuitSwitching

What are the benefits of datagramswitching over virtual circuit switching?

What are the benefits of virtual circuit

switching over datagram switching?


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Taxonomy 1-22

Network Taxonomy

Broadcast networks Nodes share a common channel; information transmitted

by a node is received by all other nodes in the network

Examples: TV, radio

Switched networks Information is transmitted to a small sub-set (usually

only one) of the nodes

commnetworks

switched

networks

broadcast

networks


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Taxonomy 1-23

Switched Network

Switchednetworks

Circuit-switchednetworks

FDM TDM

Packet-switchednetworks

Networkswith VCs

DatagramNetworks

(Internet)(X.25,Frame relay, ATM)

Course Subject


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Taxonomy 1-24

Outline

Network Taxonomy Broadcast vs Switched Networks Circuit Switched vs packet switched

Switched Network Performance Delay: Loss

Throughput

Security


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Taxonomy 1-25

Delay Calculation in Circuit Switched Networks

Transmission delay:

R = reserved bandwidth(bps)

L = packet length (bits)

time to send a packet

into link = L/R

Propagation delay:

d = length of physical link s = propagation speed in

medium (~2x105 km/sec)

propagation delay = d/s

Propagation delay: delay for the firstbit to go from a source to a destination

Transmission delay: time to pump

data onto link at reservedrate

DATA

d/s

L/R

Time


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Taxonomy 1-26

An Example

Propagation delay suppose the distance between A and B is 4000 km, then

one-way propagation delay is:

Transmission delay suppose we reserve a one slot GSM channel

a GSM frame can transmit about 115 kbps

A GSM frame is divided into 8 slots

each reserved one slot GSM has a bandwidth of about 14 Kbps(=115/8)

then the transmission delay of a packet of 1 Kbits is

msskm

km 20/000,200

4000

mskbps

kbits 7014

1


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Taxonomy 1-27

An Example (cont.) Suppose the setup message is very small, and the total setup

processing delay is 200 ms Then the delay to transfer a packet of 1 Kbits from A to B

(from the beginning until host receives last bit of the file) is:

ms31070202020020

DATA

20 + 200

20

20

70

Host A Host B

time


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Taxonomy 1-28

Another example

How long does it take to send a file of 640,000bits (1 byte=8bits) from host A to host B over acircuit-switched network? All links are 1.536 Mbps (Mega Bits Per Second)

Each link uses TDM with 24 slots/sec 500 msec to establish end-to-end circuit (setup time

including propagation delay)

Single circuit speed = 1.536 Mbps / 24 = 64kbps

File transmission time = 500 msec + file size/speed

= 0.5 sec + 640,000 bits / 64 kbps

= 10.5 sec


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Taxonomy 1-29

How do loss and delay occur inpacket switching?

packets queuein router buffers packet arrival rate to link exceeds output link capacity

packets queue, wait for turn

A

B

packet being transmitted (delay)

packets queueing (delay)

free (available) buffers: arriving packets

dropped (loss) if no free buffers


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Taxonomy 1-30

Four sources of packet delay

1. Processing delay atrouter: check bit errors

determine output link

A

B

propagation

transmission

nodalprocessing queueing

2. Queueing delay atrouter time waiting at output

link for transmission

depends on congestionlevel of router


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Taxonomy 1-31

Delay in packet-switched networks

3. Transmission delay oflink:

R=link bandwidth (bps)

L=packet length (bits)

time to send bits intolink = L/R

4. Propagation delay ofmedium:

d = length of physical link

s = propagation speed in

medium (~2x108 m/sec) propagation delay = d/s

A

B

propagation

transmission

nodal

processing queueing

Note: s and R are verydifferent quantities!


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Taxonomy 1-32

Total Delay in Datagram Networks

Packet 1

Packet 2

Packet 3

Packet 1

Packet 2

Packet 3

Packet 1

Packet 2

Packet 3

nodalprocessingand queueing

delay ofPacket 1 atNode 2

propagationdelay betweenHost 1 andNode 2

transmission

time of Packet 1at Host 1

Host 1 Host 2Node 1 Node 2


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Taxonomy 1-33

Total End-End Delay

N = #links between source and destination = #routers + 1

dproc = processing delay at router (task 1)

typically a few microsecs or less

dqueue = queuing delay at router (task 2)

depends on congestion (neglect if light traffic)

dtrans = transmission delay for router to put data on medium (task 3)

= L/R, significant for low-speed links

dprop = propagation delay at medium (task 4) a few microsecs to hundreds of msecs

)()( proptransqueueprocnodalend-end ddddNdNd

N

q

qpropd

qtransd

qqueued

qprocdendend

d1

homogeneous l inks

heterogeneous l inks


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Taxonomy 1-38

Real Internet delays and routes

What do real Internet delay & loss look like?

Traceroute program (in Unix) or Tracert (MS-DOS): provides delay measurement from source torouter along end-end Internet path towardsdestination. For all i: sends three packets that will reach router ion path

towards destination

router iwill return packets to sender

sender times interval between transmission and reply.3 probes

3 probes

3 probes


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Taxonomy 1-39


traceroute: jis.mit.edu to wayne state

1 W92-RTR-1-W92SRV21.MIT.EDU (18.7.21.1) 0.435 ms 0.367 ms 0.249 ms

2 EXTERNAL-RTR-1-BACKBONE.MIT.EDU (18.168.0.18) 0.815 ms 0.704 ms 0.539 ms

3 EXTERNAL-RTR-2-BACKBONE.MIT.EDU (18.168.0.27) 20.266 ms 0.667 ms 0.561 ms

4 nox230gw1-Vl-526-NoX-MIT.nox.org (192.5.89.89) 0.659 ms 5.859 ms 0.587 ms5 nox230gw1-PEER-NoX-NOX-192-5-89-10.nox.org (192.5.89.10) 5.844 ms 5.829 ms 5.796 ms

6 chinng-nycmng.abilene.ucaid.edu (198.32.8.82) 35.703 ms 33.674 ms 32.154 ms

7 mren-chin-ge.abilene.ucaid.edu (198.32.11.98) 29.647 ms 33.975 ms 36.040 ms

8 ge-1-3-0x189.aa1.mich.net (192.122.182.17) 31.860 ms 31.891 ms 31.874 ms

9 v27.wsu3.mich.net (198.108.23.133) 33.405 ms 33.480 ms 33.508 ms

10 141.217.154.98 (141.217.154.98) 34.833 ms 33.710 ms 33.698 ms

11 * * *12 * * *

3 delay measures


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Taxonomy 1-40


Tracing route to www.yahoo.akadns.net [216.109.118.67]

over a maximum of 30 hops:

1 1 ms 1 ms 1 ms 192.168.0.1

2 11 ms 9 ms 8 ms 64.230.197.241

3 7 ms 7 ms 7 ms 64.230.235.85

4 7 ms 7 ms 7 ms 64.230.235.97

5 12 ms 12 ms 12 ms rtp627197rts [64.230.220.254]6 13 ms 13 ms 12 ms 64.230.242.205

7 12 ms 12 ms 12 ms bx3-toronto12-pos5-0.in.bellnexxia.net [206.108.107.234]

8 13 ms 13 ms 13 ms if-7-0.core1.TTT-Scarborough.teleglobe.net [209.58.25.69]

9 31 ms 32 ms 31 ms if-3-3.mcore3.NJY-Newark.teleglobe.net [216.6.57.33]

10 36 ms 36 ms 36 ms if-13-0.core1.AEQ-Ashburn.teleglobe.net [216.6.57.42]

11 37 ms 36 ms 36 ms ix-14-2.core1.AEQ-Ashburn.teleglobe.net [63.243.149.110]

12 36 ms 36 ms 36 ms vlan200-msr1.dcn.yahoo.com [216.115.96.161]13 35 ms 36 ms 36 ms ge3-1.bas2-m.dcn.yahoo.com [216.109.120.146]

14 36 ms 36 ms 37 ms p4.www.dcn.yahoo.com [216.109.118.67]

Trace complete.

It took 13 routers to get from my house to www.yahoo.com

3 delay (end-end)measurements for each ofthe 3 msgs

Note: an * in one of the routers result means no response (probe lost, router did notreply for at least one of the 3 msgs)

tracert www.yahoo.com


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Taxonomy 1-41


Ping program: checks if a host is live or not andprovides RTT delay measurement from source todestination along end-end Internet path. sends n requests of size 32 bytes and calculates avg RTT

sender times interval between transmission and reply. ping -n

nprobes


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Taxonomy 1-42


Pinging www.yahoo.akadns.net [68.142.226.34] with 32 bytes of data:

Reply from 68.142.226.34: bytes=32 time=38ms TTL=51




Ping statistics for 68.142.226.34:

Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),

Approximate round trip times in milli-seconds:Minimum = 38ms, Maximum = 39ms, Average = 38ms

RTTs

ping www.yahoo.com


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Taxonomy 1-43

Outline


Switched Network Performance Performance Metrics:

Delay: Loss

Throughput

Security


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Taxonomy 1-44

Packet loss

queue (aka buffer) preceding link in buffer hasfinite capacity

packet arriving to full queue dropped (aka lost)

lost packet may be retransmitted by previousnode, by source end system, or not at all

A

B

packet being transmitted

packet arriving tofull bufferis lost

buffer(waiting area)


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Taxonomy 1-45

Throughput

throughput:rate (bits/time unit) at whichbits transferred between sender/receiver instantaneous:rate at given point in time

average:rate over long(er) period of time

server, withfile of F bits

to send to client

link capacityRsbits/sec

link capacityRcbits/sec

pipe that can carryfluid at rateRsbits/sec)

pipe that can carryfluid at rateRcbits/sec)

server sends bits(fluid) into pipe


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Taxonomy 1-46

Throughput (more)

Rs< Rc What is average end-end throughput?

Rsbits/sec Rcbits/sec

Rs> Rc What is average end-end throughput?

Rsbits/sec Rc

bits/sec

link on end-end path that constrains end-end throughput

bottleneck link


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Taxonomy 1-47

Throughput: Internet scenario

10 connections (fairly) sharebackbone bottleneck link Rbits/sec

RsRs

Rs

Rc

Rc

Rc

R

per-connectionend-end

throughput:min(Rc,Rs,R/10)

in practice: Rc orR

sis often

bottleneck


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Taxonomy 1-48

Outline


Switched Network Performance Performance Metrics:

Delay: Loss

Throughput

Security


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Taxonomy 1-49

Network Security

attacks on Internet infrastructure: infecting/attacking hosts: spyware, virus, worms, Trojan

Horse, unauthorized access, and malware in geneal Malware: sw designed to infiltrate or damage a computer system

w/o the owners informed consent [Wikipedia]; based onintention of its creator, rather than any features

In law, malware is defined as a computer contaminant

denial of service: deny access to resources (servers, link BW) Vulnerability attack; BW flooding; Connection flooding

Internet not originally designed with security in mind

original vision:a group of mutually trusting users attachedto a transparent network

Internet protocol designers playing catch-up

Security considerations in all layers!


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Taxonomy 1-50

What can bad guys do: malware?

Spyware: infection by downloading

web page with spyware

records keystrokes, websites visited, upload infoto collection site

Virus infection by receiving

object (e.g., e-mail

attachment), activelyexecuting

self-replicating:propagate itself toother hosts, users

Worm: infection by passively

receiving object that getsitself executed

self- replicating: propagatesto other hosts, users

Sapphire Worm in 2003: aggregate scans/sec

in first 5 minutes of outbreak (CAIDA, UWisc data)

Double in every 8.5 sec

90% infected in 10 min


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Taxonomy 1-51

Denial of service attacks

attackers make resources (server, bandwidth)unavailable to legitimate traffic by overwhelmingresource with bogus traffic

1. select target

2. break into hostsaround the network(collectively, known asbotnet)

3. send packets towardtarget fromcompromised hosts

target


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Taxonomy 1-52

Sniff, modify, delete your packets

Packet sniffing: broadcast media (shared Ethernet, wireless)

promiscuous network interface reads/records allpackets (e.g., including passwords!) passing by

A

B

C

src:B dest:A payload

Ethereal (Wireshark) software used for end-of-chapter labs is a (free) packet-sniffer


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Taxonomy 1-53

Masquerade as you

IP spoofing:send packet with false source address

A

B

C

src:B dest:A payload

M squ d s u


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Taxonomy 1-54

Masquerade as youMan-in-the-middle attack

IP spoofing:send packet with false source address record-and-playback: sniff sensitive info (e.g.,

password), and use later

password holder isthat user from system point of

view

A

B

C

src:B dest:A user: B; password: foo


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Taxonomy 1-55

Masquerade as you

IP spoofing:send packet with false source address record-and-playback: sniff sensitive info (e.g.,

password), and use later

password holder isthat user from system point of

view

A

B

later ..C

src:B dest:A user: B; password: foo


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Summary

Network Taxonomy Broadcast

Circuit Switch

Packet switch Virtual circuit switch

Switched Network Performance Delay, packet loss, throughput

Security

Date post:	03-Apr-2018
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