CENG331 P5

8/3/2019 CENG331 P5

1/38

1-1

CENG 334

Introduction

to theInternetworking

Part Four

8/3/2019 CENG331 P5

2/38

1-2

Overview:

Network Core:Packet Switching

Circuit Switching

Internet structure

Performance:

Loss

Delay

Throughput Protocol layers, service models

Security

8/3/2019 CENG331 P5

3/38

1-3

The Network Core

mesh of interconnectedrouters

the fundamental question:how is data transferredthrough net?

circuit switching:dedicated circuit per call:Ex: Telephone Net

packet-switching: datasent thru net in discretechunks

8/3/2019 CENG331 P5

4/38

1-4

Network Core: Circuit Switching

End to End Resourcesreserved for call

link bandwidth, switch

capacity dedicated resources:

no sharing

circuit-like

(guaranteed)performance

call setup required

8/3/2019 CENG331 P5

5/38

1-5

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

8/3/2019 CENG331 P5

6/38

1-6

Circuit Switching: FDM and TDM

FDM

frequency

time

TDM

frequency

time

4 usersExample:

8/3/2019 CENG331 P5

7/38

1-7

Internet structure: network of networks

roughly hierarchical at center: tier-1 ISPs (e.g., Verizon, Sprint, AT&T,

Cable and Wireless), national/international coverage

treat each other as equals

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-1providersinterconnect

(peer)privately

8/3/2019 CENG331 P5

8/38

1-8

Tier-1 ISP: e.g., Sprint

to/from customers

peering

to/from backbone

.

POP: point-of-presence

8/3/2019 CENG331 P5

9/38

1-9


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

Tier-2 ISPTier-2 ISP

Tier-2 ISP Tier-2 ISP

Tier-2 ISP

Tier-2 ISP paystier-1 ISP forconnectivity torest of Internet

tier-2 ISP iscustomeroftier-1 provider

Tier-2 ISPsalso peerprivately witheach other.

8/3/2019 CENG331 P5

10/38

1-10


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

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP



Tier-2 ISP

local

ISPlocalISP

localISP

local

ISP

localISP Tier 3

ISP

local

ISP

local

ISP

localISP

Local and tier-3 ISPs arecustomersofhigher tierISPs

connectingthem to restof Internet

8/3/2019 CENG331 P5

11/38

1-11


a packet passes through many networks!

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP



Tier-2 ISP

local

ISPlocalISP

localISP

local

ISP

localISP Tier 3

ISP

local

ISP

local

ISP

localISP

8/3/2019 CENG331 P5

12/38

1-12

How do loss and delay occur?

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

8/3/2019 CENG331 P5

13/38

1-13

Four sources of packet delay

1. nodal processing: check bit errors

determine output link

A

B

propagation

transmission

nodalprocessing queueing

2. queueing time waiting at output

link for transmission

depends on congestion

level of router

8/3/2019 CENG331 P5

14/38

1-14

Delay in packet-switched networks

3. Transmission delay: R=link bandwidth (bps)

L=packet length (bits)

time to send bits into

link = L/R

4. Propagation delay: d = length of physical link

s = propagation speed inmedium (~2x108 m/sec)

propagation delay = d/s

A

B

propagation

transmission

nodal

processing queueing

Note: s and R are verydifferent quantities!

8/3/2019 CENG331 P5

15/38

1-15

Caravan analogy

cars propagate at

100 km/hr toll booth takes 12 sec to

service car (transmissiontime)

car~bit; caravan ~ packet Q: How long until caravan

is lined up before 2nd tollbooth?

Time to push entire

caravan through tollbooth onto highway =12*10 = 120 sec

Time for last car to

propagate from 1st to2nd toll both:100km/(100km/hr)= 1 hr

A: 62 minutes

tollbooth

tollbooth

ten-carcaravan

100 km 100 km

8/3/2019 CENG331 P5

16/38

1-16

Caravan analogy (more)

Cars now propagate at1000 km/hr

Toll booth now takes 1min to service a car

Q:Will cars arrive to2nd booth before allcars serviced at 1stbooth?

Yes! After 7 min, 1st car

at 2nd booth and 3 carsstill at 1st booth.

1st bit of packet canarrive at 2nd router

before packet is fullytransmitted at 1st router! See Ethernet applet at AWL

Web site

tollbooth

tollbooth

ten-carcaravan

100 km 100 km

8/3/2019 CENG331 P5

17/38

1-17

Nodal 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

8/3/2019 CENG331 P5

18/38

1-18

Queueing delay (revisited)

R=link bandwidth (bps)

L=packet length (bits)

a=average packet

arrival ratetraffic intensity = La/R

La/R ~ 0: average queueing delay small La/R -> 1: delays become large

La/R > 1: more work arriving than can beserviced, average delay infinite!

8/3/2019 CENG331 P5

19/38

1-19

Real Internet delays and routes

What do real Internet delay & loss look like?

Traceroute program: provides delaymeasurement from source to router along end-endInternet path towards destination. 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

8/3/2019 CENG331 P5

20/38

1-20

Packet loss

Queue (Buffer) preceding link in buffer hasfinite capacity

Packet arriving to full queue dropped (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)

8/3/2019 CENG331 P5

21/38

1-21

Throughput

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

average:rate over longer 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

8/3/2019 CENG331 P5

22/38

1-22

Throughput (more)

Rs< Rc What is average end-end throughput?

Rsbits/sec Rcbits/sec

Rs> Rc What is average end-end throughput?

Rs

bits/sec Rc

bits/sec

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

bottleneck link

8/3/2019 CENG331 P5

23/38

1-23

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 or

Rs is oftenbottleneck

8/3/2019 CENG331 P5

24/38

1-24

Protocol Layers

Networks are complex! many pieces:

hosts

routers

links of various media applications

protocols

hardware, software

Question:Is there any hope oforganizingstructure of

network?

Or at least our discussionof networks?

8/3/2019 CENG331 P5

25/38

1-25

Organization of air travel

a series of steps

ticket (purchase)

baggage (check)

gates (load)

runway takeoff

airplane routing

ticket (complain)

baggage (claim)

gates (unload)

runway landing

airplane routing

airplane routing

8/3/2019 CENG331 P5

26/38

1-26

ticket (purchase)

baggage (check)

gates (load)

runway (takeoff)

airplane routing

departureairport

arrivalairport

intermediate air-trafficcontrol centers

airplane routing airplane routing

ticket (complain)

baggage (claim

gates (unload)

runway (land)

airplane routing

ticket

baggage

gate

takeoff/landing

airplane routing

Layering of airline functionality

Layers: each layer implements a service

via its own internal-layer actions

relying on services provided by layer below

8/3/2019 CENG331 P5

27/38

1-27

Why layering?

Dealing with complex systems: explicit structure allows identification,

relationship of complex systems pieces

layered reference model for discussion

modularization eases maintenance, updating ofsystem

change of implementation of layers servicetransparent to rest of system

e.g., change in gate procedure doesnt affectrest of system

layering considered harmful?

8/3/2019 CENG331 P5

28/38

1-28

Internet protocol stack

application: supporting networkapplications FTP, SMTP, HTTP

transport: process-process data

transfer TCP, UDP

network: routing of datagrams fromsource to destination

IP, routing protocols link: data transfer between

neighboring network elements PPP, Ethernet

physical:bits on the wire

application

transport

network

link

physical

8/3/2019 CENG331 P5

29/38

1-29

ISO/OSI reference model

presentation: allow applications tointerpret meaning of data, e.g.,encryption, compression, machine-specific conventions

session:synchronization,checkpointing, recovery of dataexchange

Internet stack missing these

layers! these services, if needed, must

be implemented in application

application

presentation

sessiontransport

network

link

physical

8/3/2019 CENG331 P5

30/38

1-30

sourceapplicationtransportnetwork

linkphysical

Ht

Hn

M

segment Ht

datagram

destination

applicationtransportnetwork

linkphysical

HtHnHl M

HtHn M

Ht MM

networklink

physical

linkphysical

HtHnHl M

HtHn M

Ht

Hn M

HtHnHl M

router

switch

Encapsulationmessage M

Ht M

Hnframe

8/3/2019 CENG331 P5

31/38

1-31

Network Security

The field of network security is about: how bad guys can attack computer networks

how we can defend networks against attacks

how to design architectures that are immune to

attacks

Internet not originally designed with(much) security in mind

original vision:a group of mutually trustingusers attached to a transparent network

Internet protocol designers playing catch-up

Security considerations in all layers!

8/3/2019 CENG331 P5

32/38

1-32

Bad guys can put malware intohosts via Internet Malware can get in host from a virus, worm, or

trojan horse.

Spyware malware can record keystrokes, web

sites visited, upload info to collection site.

Infected host can be enrolled in a botnet, usedfor spam and DDoS attacks.

Malware is often self-replicating: from aninfected host, seeks entry into other hosts

8/3/2019 CENG331 P5

33/38

1-33

Bad guys can put malware intohosts via Internet Trojan horse

Hidden part of someotherwise usefulsoftware

Today often on a Webpage (Active-X, plugin)

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: aggregate scans/secin first 5 minutes of outbreak (CAIDA, UWisc data)

8/3/2019 CENG331 P5

34/38

1-34

Bad guys can attack servers andnetwork infrastructure

Denial of service (DoS): attackers make resources(server, bandwidth) unavailable to legitimate trafficby overwhelming resource with bogus traffic

1. select target

2. break into hostsaround the network(see botnet)

3. send packets towardtarget fromcompromised hosts

target

8/3/2019 CENG331 P5

35/38

1-35

The bad guys can sniff 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

Wireshark software used for end-of-chapterlabs is a (free) packet-sniffer

8/3/2019 CENG331 P5

36/38

1-36

The bad guys can use false sourceaddresses

IP spoofing:send packet with false source address

A

B

C

src:B dest:A payload

8/3/2019 CENG331 P5

37/38

1-37

The bad guys can record andplayback

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

8/3/2019 CENG331 P5

38/38

1 38

Network Security

more throughout this partSecurity with Cryptographic techniques

obvious uses

Documents

CENG331 P5