ECEN4533 Data Communications Lecture #4 14 January 2013 Dr. George Scheets

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Read 2.3, 2.5


Problems 1.6, 2.6, 2.8


Quiz #1, Lecture 12, 4
February


Open book & notes


Calculators are allowed


No Smart Phones


ECEN4533 Data Communications

Lecture #4 14 January 2013

Dr. George Scheets


Read 3.1


Ignore Probability Equations until Review


Scan Design Problem #1


Problems 2.7, 3.1, 3.2


Quiz #
1



Lecture 12, 4
February (Live)


<

11 February (
Async

Distance Learning)


Extra Credit (up to 20 points)


Find errors in text or solutions.

ECEN4533 Data Communications

Lecture #5 16 January 2013

Dr. George Scheets


Read 3.2


Problems 3.9, 3.10


Quiz #1



Lecture 12, 4 February (Live)


<

11 February (
Async

Distance Learning)


Design #1 due 1 February (Live)


8 February (
Async

DL)


Late =
-
1 per working day


No Class next Monday

ECEN4533 Data Communications

Lecture #6 18 January 2013

Dr. George Scheets


PSTN

Call Sequencing


User Dials Number


Routing Protocol Determines path thru network


Affected Core Switches notified


Time Slots reserved to support call

Time Slot = 1 byte every 1/8000
th

second for 64 Kbps


Switches continuously move bytes arriving on input time
slot(s) to appropriate output line and time slot(s)


User “sees” dedicated nailed up bandwidth


Source TCP opens logical connection with Sink


Packets transferred, logical connection closed


Switch resources released when user hangs up

ISDN connection

using PSTN

Long Distance & Local Carriers


dedicate

64 Kbps to our use (Circuit Switching).

node c

PST

Network

PC

node a

PC

Carrier PSTN Network

1

3

PSTN Switch

PC

PC

Switches move bytes from input to output.

Bytes get moved at
line speeds.

Trunk capacity is dedicated.

Moving Traffic with Packets


Layer 7 Application


Word Perfect


2,920B file to move


Layer 6 Presentation


Windows API



Layer 5 Session


TCP



Layer 4 Transport


TCP


Maximum TCP Segment Size assumed to be 1460B

(Parameter in Windows Registry)


Chops file into 2 x 1460B packets, adds 20B TCP Header to each


Layer 3 Network


IP


Adds 20B IP Header to each packet


Layer 2 Data Link


Undefined


Adds 10B Layer 2 Header to each frame


Layer 1 Physical


Undefined

Wired Phone

CO

CO

Analog

Voice


Digital Bit Stream

(1's & 0's) @ 64 Kbps


Generally analog from phone to CO


One twisted Pair


At Central Office


Filtered (BW about 3.5 KHz)


Analog Voltage is Sampled 8,000 times/second


Rounded off to 1 of 256 possible voltages


Converted to a fixed length 8 bit code word

Analog

Voice

Ex) Internet

Local connection


dedicates

64 Kbps to our use.
ISP provides


connectivity on a random, as needed, basis.

Location a

Location b

ISP Network

PC

PC

Internet Service Provider Backbone

1

3

Router

Routers move packets from input to output.

Packets get full trunk line speed.

Trunk capacity shared randomly, as needed.

PC

PC

45 Mbps

Internet Call Sequencing


Assuming an "Always On" 64 Kbps connection...


Similar to DSL or Cable Modem (but slower)


... Logical connections opened between end devices


TCP (Layer 5). Routers do not monitor!!


Router I/O decisions based on Layer 3 IP address


Best match found in Look
-
Up Table


Router Tables updated independently of traffic


‘Hello’ packets exchanged every 10 seconds with adjacent
routers


More detailed routing information (who is connected to
whom)
exchanged intermittently


Router determines best output port, generally for blocks of
hierarchical IP addresses

Moving Traffic with Packets


Layer 7 Application


Word Perfect


2,920B file to move


Layer 6 Presentation


Windows API



Layer 5 Session


TCP



Layer 4 Transport


TCP


Maximum TCP Segment Size assumed to be 1460B

(Parameter in Windows Registry)


Chops file into 2 x 1460B packets, adds 20B TCP Header to each


Layer 3 Network


IP


Adds 20B IP Header to each packet


Layer 2 Data Link


Undefined


Adds 10B Layer 2 Header to
each frame


Layer 1 Physical


Undefined

Ex) ATM

Local Carriers


dedicate

64 Kbps to our use.
IXC provides random


connectivity on an as
-
needed basis.

Location a

locationc

Carrier ATM Network

PC

PC

ATM Backbone

ATM Switch

Switches move cells from input to output.

Cells get full trunk line speed.

Trunk capacity shared randomly, as needed.

ATM Call Sequencing


End device requests logical connection


Routing Protocol determines path thru network


Affected Core Switches notified


Look
-
Up table updated to show proper output port
where specific input cells should be placed


Switch resources (bandwidth, buffer space) reserved as
appropriate


User appears to see dedicated nailed up bandwidth


Path is known as a Virtual Circuit


TCP opens logical connection with far site


Packets transferred, TCP logical connection closed


Switch resources released when user finished

Moving Traffic with ATM Cells


Layer 7 Application


Word Perfect


2,920B file to move


Layer 6 Presentation


Windows API



Layer 5 Session


TCP



Layer 4 Transport


TCP


Maximum Segment Size assumed to be large, say 64 KB


2,920B file not segmented. Adds 20B TCP Header


Layer 3 Network


IP


Adds 20B IP Header


Layer 2 Data Link


ATM


Adds 8B padding & 8B SAR Trailer.


Chops into 2976/48 = 62 cells (53 byte cell size). Adds 5B ATM
header to each cell.


Layer 1 Physical


Undefined

Internet Packet Format

Traffic

?? 20 20 0
-
1460 ??

IP

TCP

Layer 2

Header

Layer 2

Trailer?

Probably originated or passed through an Ethernet.

Internet Protocal v4

TOS

TTL

Source Address

Destination Address

4 Bytes

802.3

LAN

LAN

OSU Campus Network (> 2001)

Routers

OneNet

Ethernet

Switch

802.3

LAN

802.3

LAN

LAN

LAN

OSU 2009 Internet Connectivity

Example
Tracert

Handy site for figuring out who owns IP addresses:


www.arin.net


(has links to databases covering other regions)

Tracer
ou
t
e

to WWW.CISCO.COM


4 Internal OSU
-
Stillwater routers


3
OneNet

routers (all in Tulsa?)


5 Cogent Communications routers


te4
-
3.ccr01.
tul
01.atlas.cogentco.com


te2
-
2.mpd01.
dfw
01.atlas.cogentco.com


1
Akamai

Technologies (Hosting Service)


(3:30 pm, 12Sept11,
rtt

= 8
msec
, 12 routers)

Tracer
ou
t
e to WWW.TULSA.COM


4 Internal OSU
-
Stillwater routers


3
OneNet

routers (Tulsa?)


4 Cogent Communications routers



te4
-
4.1052.ccr01.
tul
01.atlas.cogentco.com



te0
-
2
-
0
-
7.ccr22.
dfw
01.atlas.cogentco.com


1 Global Crossing router


GigabitEthernet2
-
3.ar2.
HOU1
.gblx.net


4 Routers in Houston


te2
-
5.dsr01.
hstntx
2.networklayer.com


The Planet server (hosting service)


(3:55 pm, 12Sept11,
rtt

= 14
msec
, 16 routers)

# Routers not necessarily f(distance)

Launched 14 September 2011, 2 miles from OSU campus


1 Scheets' home router


5 SBC (now AT&T) & AT&T routers


dist2
-
vlan50.
okcyok
.sbcglobal.net


ggr6.
dlstx
.ip.att.net


3 Cogent Communications routers


te3
-
2.ccr01.
tul
01.atlas.cogentco.com


3
ONENET

routers


Probably in Tulsa, maybe Oklahoma City


3 Oklahoma State routers


(11:19 am, 14Sept11,
rtt

= 71
msec
, 15 routers)

Fall 2007 Weird Route Seen by Student

Tulsa to OSU Stillwater


Tracert launched from Tulsa, hit

Atlanta

Washington, D.C.

Illinois

Kansas City

Tulsa

Oklahoma City

OSU Stillwater


Internet Protocal v6

4 Bytes

Flow Label

Destination Address

Source Address

Hop Limit

RedNeckNet ISP

Salina

Joplin

Stillwater

Lubbock

Dallas

Little Rock

RedNeckNet VoIP

Full Mesh

N(N
-
1)/2 Connections

RedNeckNet VoIP

Bus

5 Connections

RedNeckNet VoIP

Star

5 Connections

Grading


Real World:


1 team gets full credit


Everyone else gets a zero


Partial credit


Awarded on Quizzes & Tests


NOT AWARDED ON DESIGN PROJECTS!


Real world designs don't get partial credit


Either Work or They Don't



Double check your work!!!

Use a spreadsheet

StatMux

frequency

1

3

1

2

Different channels use
all

of

the frequency
some

of the time,

at random, as needed
.

CDM

frequency

Different channels use
all


of the bandwidth
all
of the time.


Channels use different

codes.


Other channels cause

noise
-
like interference.

CDMA: 3D View

code #1

code #2

code #3

frequency

time