April Tuesday, 8
Lab #1
Grading is in progress
Homework #1
Hardcopy due Thursday, January 17 (beginning of class) Helpful link for P7: http://hyperphysics.phy-astr.gsu.edu/Hbase/math/disfcn.html#c2
Lab #2
First session starts today at 2:00
Quiz #1
Thursday in class
Apply to MECOP
Deadline is April 10
Anybody interested in an REU in AI?
See me after class or send me an email
Change in Paulson's office hours
M: 12:00 2:00 pm W: 10:00 - 11:50 am, 1:00 - 2:50 pm R: 2:00 - 3:50 pm F: 10:00 - 11:50 am other times by appointment Might change (again)
Today's topics
Physical media Structure of the Internet Network layering models Networks attacks
Security
Homework/problems
Physical Media
Why is it needed?
to propagate bits between sender/receiver pairs
What is it?
a physical link that lies between sender & receiver
Two types of media:
guided media: signals propagate in solid media unguided media: signals propagate freely, e.g., wireless radio
Guided Media: twisted-pair copper wire
two insulated copper wires
Category 3: 10 Mbps Ethernet Category 5: 100Mbps Ethernet
still used for high-speed LAN; e.g., ADSL rate depends on thickness and distance make up 99% of wired connections may pick up interference ("noise")
RJ-45 twisted pair
connector: both ends same; used with hubs, switches crossover: one end each; direct connection
Pins 1, 2: transmit Pins 3, 6: receive Pins 4, 5, 7, 8: not used for network data
Guided Media: coaxial cable
two concentric copper conductors baseband:
single channel on cable legacy Ethernet
broadband:
multiple channels on cable hybrid fiber-coax cable (HFC)
Cable TV rate depends on thickness and distance less interference than twisted pair
Baseband and broadband
Baseband uses a small part of wave spectrum and sends only one signal at a time Broadband uses a larger part of the wave spectrum and uses frequency division multiplexing to send multiple signals at the same time
Frequency division multiplexing (FDM)
Achieves multiplexing by using different carrier frequencies Frequencies must be separated to avoid interference Receiver can "tune" to specific frequency and extract modulation for that one channel Useful only in media that can carry multiple signals with different frequencies
high-bandwidth required
Guided Media: fiber optic cable
glass fiber carrying light pulses, each pulse represents one bit high-speed operation:
high-speed point-to-point transmission (e.g., 10's100's Gbps)
low error rate:
immune to electromagnetic noise and other interference
Wave length division
Frequency division multiplexing can be applied to optical transmission
known as wave-length division multiplexing (WDM) When many wavelengths are used, the term becomes Dense Wave Division Multiplexing (DWDM)
Informally, color division multiplexing Receiver separates frequencies using a prism
red, orange, etc
Unguided media: wireless radio
signal carried in electromagnetic spectrum
in the air
no physical "wire" effects of propagation environment :
reflection obstruction by objects interference
Radio link types
terrestrial microwave
e.g. up to 45 Mbps channels
LAN (e.g., Wifi)
11Mbps, 54 Mbps
wide-area (e.g., cellular)
e.g. 3G: hundreds of Kbps
satellite
Kbps to 45Mbps channel (or multiple smaller channels) 270 msec end-end delay geostationary vs. low altitude
The internet
Many (possibly incompatible) network technologies No single technology is appropriate for every situation Internetworking uses routers to enable communication among networks of dissimilar technologies Result is virtual network* whose details are invisible
*Acts like a network
What's the Internet: "physical" view
millions of connected computing devices: called hosts or end systems
e.g., Laptops, workstations running network apps route r se r rve local I S P workstation m obile
communication links
e.g., fiber, copper, radio, satellite
re gional I S P
routers & switches:
forward packets (chunks of data) com pany ne twork
What's the Internet: "logical" view
network protocols
control sending/receiving of msgs e.g., TCP, IP, HTTP, FTP, PPP
route r se r rve local I S P
workstation m obile
Internet: "network of networks"
loosely hierarchical public Internet versus private intranet
re gional I S P
Internet standards
IETF: Internet Engineering Task Force for protocols/standards
RFC: Request for comments
IEEE: for links, e.g., Ethernet
com pany ne twork
What's the Internet: a "service" view
communication infrastructure enables distributed applications:
Web, email, games, ecommerce, file sharing
communication services provided to applications:
Connectionless (unreliable) connection-oriented (reliable)
Internet structure: network of networks
"Hierarchy": tier 1, tier 2, and tier 3 at center: "tier-1" ISPs
e.g., MCI, Sprint, AT&T, Cable and Wireless, national/international coverage
Tie provide also r-1 rs inte rconne at public ct ne twork acce points ss (NAPs)
Tie provide r-1 rs inte rconne ct (pe r) private e ly
Tie 1 I S r P
NAP
Tie 1 I S r P
Tie 1 I S r P
Internet structure: network of networks
"Tier-2" ISPs: smaller (often regional) ISPs
Connect to one or more tier-1 ISPs, possibly other tier2 ISPs
Tie I S also r-2 Ps pe r private with e ly e othe ach r, inte rconne at ct NAP
Tie I S r-2 P Tie I S is custom r r-2 P e of tie provide r-1 r
Tie I S r-2 P
Tie 1 I S r P
NAP
Tie 1 I S r P
Tie I S r-2 P
Tie 1 I S r P
Tie I S r-2 P
Tie IS r-2 P
Internet structure: network of networks
"Tier-3" ISPs and local ISPs
"access" networks (closest to end systems)
local IS P Local and tie 3 rI S arecustom rs Ps e of highe tie IS r r Ps conne cting the to m re of I nte t st rne Tie 3 r IS P Tie I S r-2 P local IS P local IS P Tie I S r-2 P local IS P
Tie 1 I S r P
NAP
Tie 1 I S r P
local IS P Tie I S r-2 P local IS P
Tie 1 I S r P
Tie I S r-2 P local IS P
Tie IS r-2 P local IS P
Internet structure: network of networks
a packet passes through many networks
local IS P
Tie 3 r IS P Tie I S r-2 P
local IS P
local IS P Tie I S r-2 P
local IS P
Tie 1 I S r P
NAP
Tie 1 I S r P
local IS P Tie I S r-2 P local IS P
Tie 1 I S r P
Tie I S r-2 P local IS P
Tie IS r-2 P local IS P
Protocol "Layers"
Networks are complex! many "pieces": hosts routers links of various media applications protocols hardware, software
Question:
Is there any hope of organizing structure of network? Or at least organizing our discussion of networks?
Layering of airline functionality
ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing
departure airport
ticket (complain) baggage (claim gates (unload) runway (land) airplane routing airplane routing airplane routing
arrival airport
ticket baggage gate takeoff/landing airplane routing
intermediate air-traffic control centers
Layers: each layer implements a service via its own internal-layer actions relying on services provided by layer below
Internet protocol stack
application: supporting network applications
FTP, SMTP, HTTP
application transport ne twork link physical
transport: process-process data transfer
UDP
TCP, network: routing of datagrams from source to destination
IP, routing protocols
link: data transfer between neighboring network elements
PPP, Ethernet
physical: bits "on the wire"
ISO/OSI reference model
presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machinespecific conventions session: synchronization, checkpointing, recovery of data exchange Internet stack "missing" these layers! these services, if needed, must be implemented in application application pre ntation se se ssion transport ne twork link physical
Why layering?
Dealing with complex systems:
explicit structure allows identification, relationship of complex system's pieces layered reference model for discussion modularization eases maintenance, updating of system change of implementation of layer's service transparent to rest of system e.g., change in gate procedure doesn't affect rest of system
Layered software: stacks
Software implemented from layered design has layered organization Software modules can be viewed as "stacks" (not the stack data structure) on both computers
Stacks
Constraints
1. The software for each layer depends only on the services of the software provided by neighboring layers (well-defined interfaces) 2. The software at layer n at the destination receives exactly the same protocol message sent by layer n at the sender (consistency) These constraints mean that protocols within a protocol stack can be
tested independently modified/replaced independently
source
message se e gm nt Ht datagram Hn Ht fram Hl Hn Ht e
M M M M
application transport ne twork link physical
Encapsulation
link physical switch
de stination
M Ht Hn Ht Hl Hn Ht M M M
Hn Ht Hl Hn Ht
M M
application transport ne twork link physical
ne twork link physical
Hn Ht
M
router
Problems
More about packet loss and delay Calculations
How do loss and delay occur?
packe be transm d (de t ing itte lay)
A B
packe que ing (de ts ue lay) packe ge droppe (loss) ts t d if no fre buffe e rs
Packet loss
queue (buffer) preceding link in buffer has finite capacity packet arriving at a full queue is dropped (lost) lost packet may be retransmitted by previous node, by source, or not at all
A B
buffe r (waiting are a) packe be transm d t ing itte
packe arriving to t full buffe is lost r
Nodal delay
d nodal = d proc + d queue + d trans + d prop
dproc = processing delay
typically a few s or less
dqueue = queuing delay
depends on congestion
dtrans = transmission delay
= L/R, significant for low-speed links
dprop = propagation delay
a few s to hundreds of ms
Queueing delay (revisited)
Packet arrival rate = a packets/sec Packet length = L bits
queue
Link bandwidth = R bits/sec
Every second: aL bits arrive to queue Every second: R bits leave the router Question: what happens if aL > R ? Answer: queue will fill up, and packets will get dropped!!
aL/R is called traffic intensity
Queueing delay (revisited)
Packet arrival rate = a packets/sec Packet length = L bits
queue
Link bandwidth = R bits/sec
aL/R ~ 0: average queueing delay is small aL/R 1: delays become large aL/R > 1: more "work" than can be serviced, average delay infinite!
Homework Problem #6 (P13)
N packets arrive simultaneously Packet length = L bits Link bandwidth = R bits/sec
Question: what is the average queuing delay for the N packets? Answer: 1st packet delay =0; 2nd packet delay=L/R; 3rd packet delay = 2L/R; etc So, average delay = (L/R + 2L/R + ... + (N-1)L/R)/N = L(N-1)/(2R) sec.
"Real" Internet delays and routes
What do "real" Internet delay & loss look like? Traceroute 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 determines interval between transmission and reply.
3 probe s 3 probe s 3 probe s
"Real" Internet delays and routes
trace route gaia.cs.um du to www.e com : ass.e ure .fr
Thre de m asure e from e lay e m nts gaia.cs.um du to cs-gw.cs.um du ass.e ass.e
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 trans-oce anic 8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms link 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 * * * * m ans no re e sponse(probelost, route not re r plying) 18 * * * 19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms
Chapter 1: Summary
Covered a "ton" of material! Internet overview what's a protocol? network edge, core, access network packet-switching versus circuit-switching Internet structure performance: loss, delay, throughput layering, service models security history
You now have: context, overview, "feel" of networking more depth, detail to follow!
Chapter 1: review problems
Problem 1
L=100Byte s
trans. rateR = ? Host B
8
Host A
Question:
At what rate (bandwidth) R would the propagation delay equal the transmission delay?
distance= 2 km spe d = 2x10 m , e /s
Answer:
Propagation delay = 2x103 (m)/2x108 (m/s) = 10-5 sec Transmission delay = 100x8 (bits)/R Prop. Delay = trans. Delay => R=105x100x8 = 80 Mbps
Chapter 1: review problems
Problem 2: Voice over IP
L=48 Byte s a=64Kbps
trans. rateR = 1Mbps Host B de prop = 2m c lay se
Host A
Host A
converts analog to digital at a=64Kbps groups bits into L=48Byte packets sends packet to Host B as soon it gathers a packet
Host B
As soon as it receives the whole packet, it converts it to analog
Question:
How much time elapses from when the 1st bit is created until that bit is decoded?
Chapter 1: review problems
Problem 2: Voice over IP
L=48 Byte s a=64Kbps
trans. rateR = 1Mbps Host B de lay_prop = 2m c se
Host A
Answer:
Time to process 1st pkt: 48x8 (bits)/64x1000 (b/s) = 6 msec Time to push 1st pkt to link: 48x8 (bits)/1x106 (b/s) = 0.384 msec Time to propagate: 2 msec Total delay = 6 + 0.384 + 2 = 8.384 msec
Quiz #1
Thursday, April 10, in class Covers
Chapter 1 (except 1.6 "Networks Under Attack") Lectures 1 3 Homework #1 Labs #1
15 questions, 30 minutes
Short-answer, calculation, multiple-choice There are no "trick questions"
Calculator and one 4x6 notecard (both sides) permitted
No sharing
Questions?
Read K&R Chapter 2, Sections 1 6 Sign up for Lab #2 Homework #1 due Thursday (boc) Quiz #1 Thursday in class