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ECEN4533 Data Communications
Lecture #9
28 January 2013
Dr. George Scheets




Read: 4.4
Problems: 4.1, Web 6.1
Design #1 due 1 February (Live)
 8 February (Async DL)
 Late = -1 per working day
Quiz #1
 Lecture 12, 4 February (Live)
 < 11 February (Async Distance Learning)
ECEN4533 Data Communications
Lecture #10
30 January 2013
Dr. George Scheets




Read: 5.1 - 5.4
Problems: 5.1 - 5.3
Design #1 due 1 February (Live)
 8 February (Async DL)
 Late = -1 per working day
Quiz #1
 Lecture 12, 4 February (Live)
 < 11 February (Async Distance Learning)
ECEN4533 Data Communications
Lecture #11
1 February 2013
Dr. George Scheets




Read: 5.7 - 5.8
Problems: None
Design #1 due 1 February (Live)
 8 February (Async DL)
 Late = -1 per working day
Quiz #1 (open book & notes)
 Lecture 12, 4 February (Live)
 < 11 February (Async Distance Learning)
POTS at the CO Switch

Band Pass Filter suppresses energy
outside voice bandwidth (300 - 3,400 Hz)
Twisted
Pair Cable
64 Kbps
A/D Converter
Band Pass
Filter
(.3 - 3.4KHz)
Code
8 bits/sample
Sampler
Fs = 8 KHz
Quantize
256 levels
Nyquist's Sampling Theorem

Want to have a shot at perfectly
reconstructing a sampled signal?
 Sample

at a rate > twice the maximum frequency.
Example: Phone system
 Maximum

frequency around 3.5 KHz, fs = 8 Ksps
Example: Compact Disk
 Maximum
frequency around 20 KHz, fs = 44.1 Ksps
Video undersampling
30 video stills/second
27 wheel revs/second
0.9 wheel revs/still
time t=0
time = 1/30
Spoke would appear
to be moving backwards.
time = 2/30
PC Dial-Up Modems & POTS
PC Bit Stream has a significant amount
of energy below 0.5 KHz
 Modems shift the energy into the pass
band of the filter

PC
Twisted
Pair Cable
64 Kbps
A/D Converter
Band Pass
Filter
(.3 - 3.4 KHz)
Code
8 bits/sample
Sampler
Fs = 8 KHz
Quantize
256 levels
Sources of POTS delay
Source CO
Local Loop
PCM
Coder
POTS
TDM Trunk TSI
...
Trunk resources are dedicated
to each voice call via TDM.
PCM
Coder
POTS
Local Loop
TDM Trunk TSI
Destination CO
Intermediate
Digital
Voice
Switches
Example) Coding a
Microphone Output
m(t) volts (air pressure)
time (sec)
Energy from about 300 - 3,400 Hz.
A/D Convertor
m(t) volts (air pressure)
1/8000 second
time (sec)
Step #1)
Sample the waveform at rate > 2*Max Frequency.
Telephone voice is sampled at 8,000 samples/second.
A/D Convertor. 1 bit/sample.
Example) N = 2. Assign 0 or 1 to voltage.
3.62 v, output a 1
t1
time (sec)
0 < Voltage < +5v, Assign Logic 1
-5v < Voltage < 0, Assign Logic 0
Bit Stream Out = 1111110000111...
A/D Convertor. 1 bit/sample.
Example) N = 2. Assign 0 or 1 to voltage.
0 < Voltage < +5v, Assign Logic 1
-5v < Voltage < 0, Assign Logic 0
Far side gets... 1111110000111 (13 samples)
Need to output 13 voltages.
What does a 1 represent? A 0?
Receive a 1? Output +2.5 v (mid-range)
Receive a 0? Output -2.5 v (mid-range)
Hold the voltage until next sample
A/D Convertor. 1 bit/sample.
Input to the transmitter.
Output at the receiver.
+2.5 v
-2.5 v
Considerable Round-Off error exists.
A/D Convertor. 2 bits/sample
Example) N = 4. Assign 00, 01, 10 or 11.
3.62 v, Assign 11
+2.5 v
time (sec)
t1
-2.5 v
2.5 < Voltage < 5 , Assign 11
0 < Voltage < 2.5, Assign 10
-2.5 < Voltage < 0, Assign 00
-5 < Voltage < -2.5, Assign 01
Bit Stream Out =
11111011111100
000000101011...
A/D Convertor. 2 bits/sample.
Input to the transmitter.
Output at the receiver.
+3.75 v
+1.25 v
-1.25 v
Receive 11? Output 3.75v
Receive 10? Output 1.25v
Receive 00? Output -1.25v
Receive 01? Output -3.75v
Reduced Round-Off error exists.
-3.75 v
Circuit Switched Voice (POTS)
 Telephone
System uses Pulse Code Modulation
 Equal
length code word assigned to all voltages
 N = 256 voltage levels
 Log2256 = 8 bits per code word
 A/D
Converter
 samples
voice 8,000 times/second
 rounds off voice to one of 256 voltage levels
 transmits 8 bits to far side
 D/A
Converter
 receives
8 bit code word
 outputs one of 256 voltage levels for 1/8000th sec.
1/8th Second of Voice
1/8th Second of Voice
1/8th Second of Voice
Sampling & Quantizing Examples
 fs
= 16 KHz
 4096
quantiles
 256 quantiles (approximate phone quality)
 32 quantiles
 4 quantiles (generally 2 levels used!)
 4096
 fs
quantiles
= 16 KHz
 fs = 8 KHz (some interference)
 fs = 2 KHz
 fs = 1 KHz
SONET Hierarchy

Basic Building Block:
 51.84
Mbps STS-1 Frame
 8,000 frames/second
 810 bytes/frame, 36 bytes for OA&M

Optical Carrier-N?
N

byte interleaved STS-1 signals (TDM)
OC-1
51.84 Mbps
OC-3
155.52 Mbps
OC-12 622.08 Mbps
OC-48 2.48832 Gbps
OC-192 9.95328 Gbps
OC-768 39.81312 Gbps
T Carrier & SONET
Technology used in Leased Lines
 Mid-1960’s (T Carrier) &
Late-1980’s (SONET) technology
 Covers OSI Layers 1 & 2 (not packet-aware!)
 Guaranteed Bandwidth using
Circuit Switching & TDM

 End-to-End
path mapped in advance
 Provides fixed number of bytes, 8000 times
second, for customer use
 As they arrive, switches repetitively move input
bytes to appropriate output & TDM slot
Leased Line Networks

Last Mile Connectivity
 Fractional
T-1 (4 Wire Twisted Pair)
N*64 Kbps, N = 1 - 23
 T-1 (4 Wire Twisted Pair)
1.536 Mbps (24*64 Kbps)
 Fractional T-3 (Coax)
N T-1's, N = 1 - 27
 T-3 (Coax)
28 T-1's + Overhead (45 Mbps)

Last Mile or Long Haul Connectivity
 OC-
N, N = 1, 3, 12, 48, & 192 (SONET)
N*51.84 Mbps (Fiber)
ISO OSI Seven Layer Model
Leased Line (Circuit Switched, TDM)
Organized around Frames:1/8000th second entity







Layer 7
Layer 6
Layer 5
Layer 4
Layer 3
Layer 2
Layer 1
Application
Presentation
Session
Transport
Network
Data Link
Physical
SONET, T-Carrier (PPP)
SONET, T-Carrier
Carrier Switches are byte-aware, NOT packet-aware.
Leased Line Packet Format
7
Point-to-Point
Protocol
20
20
IP
TCP
6-1460
Data + Padding
Leased Line Backbone
Cross-Connect
Leased Line ‘Cloud’
Trunk capacity shared via TDM & Circuit Switching
Carrier Leased Line Network
LAN
Cross-Connect
LAN
Nailed up end-to-end connectivity (a Circuit).
Bit pipe. No packet processing between Routers.
Circuit Switched connections waste
bandwidth for bursty traffic.
traffic
1.536 Mbps Line Speed
146 Kbps Average
time
Idle Time >> Active Time
Load = 9.456%
Carrier Leased Line Network
ATM
Frame Relay
Router
TDM Switch
Route once (circuit setup).
Path through Network nailed down.
Switches forward based on Time Slots per 1/8000th sec.
Long Haul U.S. Traffic
Primarily carried on fiber
 Running SONET or OTN
 Generally OC-48, 192, & 768; some 100 Gbps
 Wavelength Division Multiplexing common

 Each
OC-N drives a laser
 lasers tuned to different frequencies
 injected onto same fiber strand

SONET BW parceled out to users
 Circuit
 TDM
Switching
WDM: 32 OC-768’s (1.274 Tbps)
#1 STS-768 Laser
Detector #1 STS-768
#1
@ f1
#2 STS-768 Laser
Detector #2 STS-768
#2
@ f2
Fiber in the
ground
#32 STS-768 Laser
@ f32
Optical
Combiner
Optical
Splitter
Detector #32 STS-768
#32
Systems are also available that can map an arbitrary input
(doesn’t have to be SONET or OTN based) onto an optical wave.
Leased Lines
 Covers
OSI Layers 1 & 2
 64 Kbps - 10 Gbps Line Speed
 TDM, Circuit Switched
 Based on 1960 & 1990 technology
Switches are byte aware
 Common:
Corporate Connectivity
 Very Common: ISP Connectivity
Page Info
Nov 2007
IEEE 802.3 Ethernet




Covers OSI Layers 1 & 2
10 Mbps Line Speed
Packet Switch, StatMux
Based on late 1970’s technology
 Computing

Power & Memory was Expensive
Initially Shared System
Polite Conversation (CSMA/CD)
 One
Node talks at a time
 Need to talk? Wait til line quiet
 Nobody deliberately butts in

Switched Ethernet now more common
ISO OSI Seven Layer Model
Ethernet (Packet Switched, StatMux)
Layer 7
 Layer 6
 Layer 5
 Layer 4
 Layer 3
 Layer 2
 Layer 1

Application
Presentation
Session
Transport
Network
Data Link
Physical
802.3
802.3
802.3 Ethernet Frame Format
Bytes: 7
1
6
MAC
Destination
Address
6
2
MAC
Source
Address
20
20
6-1460
4
IP
TCP
Data + Padding
CRC
Duplex: We're not talking apartments

Simplex
Only one node can talk (one way traffic)
 Commercial

Radio Station
Half Duplex
Only one node can talk at a time
 Walkie-Talkie

Full Duplex
Both nodes can talk at same time
 Telephone
802.3 Flow Chart (NIC)
No
Packet to
Send?
Drop Packet.
Notify Higher Layer
Yes
Set Collision Couter
=0
Traffic on
Network?
No
Back-Off
Yes
16th Collision?
Yes
Bump Collision
Counter by +1
No
Send Packet
Yes
Collision?
No
Jam
802.3 Back-Off Algorithm

choose random number
1st Collision
0, 1
2nd Collision
0, 1, 2, 3
3rd Collision
0, 1, ..., 6, 7
4th Collision
0, 1, ..., 14, 15
10th Collision 0, 1, ..., 1022, 1023

15th Collision 0, 1, ..., 1022, 1023
16th Collision Punt
Wait (Random Number*.0000512) seconds
10Base5 & 10Base2 (Obsolete)
Coax Cable
PC
PC
Printer
Logical & Physical Bus
All nodes monitor traffic
Nodes share 10 Mbps
10Base5 "Vampire Tap"
10Base2 "T" connection
Images from Wikipedia
10BaseT & Shared Hub
PC
PC
Hub
PC
PC
Logical Bus & Physical Star
Shared hub (OSI Level 1) copies input bits to all outputs.
All nodes monitor traffic.
10BaseT & Shared Hub
PC
Twisted Pair
Cabling
PC
Hub
PC
PC
Logical Bus & Physical Star
Each PC gets 2.5 Mbps on average.
10BaseT & Switched Hub
PC
PC
Switched
Hub
PC
PC
Logical Bus & Physical Star
Switched Hub (OSI Level 1 & 2) copies packet to proper output.
Only the destination monitors traffic.
10BaseT & Switched Hub
PC
PC
Switched
Hub
PC
PC
Logical Bus & Physical Star
This system can move up to 20 Mbps
10BaseT & Switched Hub
PC
PC
Switched
Hub
PC
PC
Logical Bus & Physical Star
Each node shares 10 Mbps
with the Switched Hub.
10BaseT & Switched Hub
PC
reception is
screwed up
PC
PC
Switched
Hub
PC
Using Half Duplex 10BaseT,
a collision occurs if PC & Switched Hub
simultaneously transmit.
Full Duplex System
PC
PC
Switched
Hub
PC
PC
All 10 Gbps, most 1 Gbps, & many 100 Mbps systems are
Full Duplex.
NIC’s are designed to simultaneously transmit & receive.
Line no longer shared. No Collisions. No need for CSMA/CD.
Campus Network 1993
Ethernet Switched Hubs
On Power Up know nothing
 When a packet arrives at an input port...

 Look-Up
Table consulted
 Source MAC address not in table?
 Table
Updated: MAC address & Port matched
 Destination
 Packet
broadcast to all outputs (a.k.a. flooding)
 Desination
 Packet
MAC address not in table?
MAC address in table?
shipped to proper output
Ethernet Switched Hubs

Look-up Table updated as packets arrive
 Ethernet

MAC Address : Port #
Flooding does not scale well on WAN
 OK
on LAN with a probably a few hundred
addresses
 Too much unnecessary traffic on WAN with
millions of addresses

Ethernet is making way into MAN & WAN
 Requires
modified protocols
Ethernet Flavors
802.3 10 Mbps
 802.3u 100 Mbps (Fast Ethernet)
 802.3z 1 Gbps Ethernet
 802.3ae 10 Gbps Ethernet
 802.3ba 40 & 100 Gbps Ethernet

Shared Ethernet
PC
Hub
PC
PC
Hub
PC
PC
PC
Hub
PC
Hub
PC
All nodes share the system's 10 Mbps.
Multiple paths = feedback loop = mess.
PC
Switched Ethernet
PC
PC
Switched
Hub
PC
Switched
Hub
PC
PC
PC
PC
Switched
Hub
Switched
Hub
PC
PC
Each node shares 10 Mbps with its switch.
Network can move > 10 Mbps at any instant.
Multiple paths usually not used.
Ethernet & Switched Hub
Server
Server
PC
PC
Server
Switched
Hub
PC
Different speeds are used
for different connections.
PC
PC
To the
rest of the
world.
10/100 Mbps
1 Gbps
10 Gbps
Two Types of Addresses


Local (Layer 2 MAC)
End-to-End (Layer 3 IPv4)
Link Transmitter
Link Receiver
MAC
Destination
Address
MAC
Source
Address
Information Sink (Destination) Exception: NAT
Information Source
IP
TCP
Data + Padding
CRC
Whose Address goes where?




Generally, PC's don't directly connect to Router
 Usually connected to Switched Hub
Using IPCONFIG /ALL ...
Ethernet MAC address (hard-wired)
 00 50 04 C1 73 50 (6 Bytes, Base 16)

Last byte is 0101 0000
Alpha-Numeric IP Address (usually fixed)
 es303f-2.ceat.okstate.edu
 host name - network name
Domain Name Server
 Converts alpha-numeric IP address to numeric
Whose Address goes where?

Numeric IP Address (assigned on Power Up)
 Dynamic
Host Configuration Protocol (DHCP)
 139.78.79.157 (4 Bytes, Base 10) on 31 Jan 2004

Default Gateway (assigned on Power Up)
 Dynamic
Host Configuration Protocol (DHCP)
 139.78.79.254 Router IP Address
 Where to send packets when destination not part
of your network
 ceat.okstate.edu

Generally, Router sets the network boundary
Packet to Print?
Must know destination IP Address



At my computer's IP Layer...
Adds 20B IP Header to each packet
Source IP address = My computer
(Terminating) Destination IP address = Printer
Is Information Sink IP address on my network?
Yes? Tell Layer 2 to use
Information Sink's MAC address
No? Tell Layer 2 to use Router's MAC Address
Shared 802.3 Ethernet
R
PC
PC
Hub
Pr
Hub
PC
PC
PC
Hub
Hub
PC
10 Nodes Share 10 Mbps
Printer part of "ceat.okstate.edu".
PC
PC
Whose address goes where?
Printer MAC
MAC
Destination
Address
PC MAC
MAC
Source
Address
Information Sink (Printer IP)
Information Source (PC IP)
IP
TCP
Data + Padding
CRC
Hub ignores packet contents, copies bits to all outputs.
Shared 802.3 Ethernet
R
PC
PC
Hub
Pr
Hub
PC
PC
PC
Hub
Hub
PC
All nodes will see
packets from PC to Printer.
PC
PC
Switched Ethernet
R
PC
PC
Switched
Hub
Pr
Switched
Hub
PC
PC
PC
PC
Switched
Hub
Switched
Hub
PC
PC
Packet formatting same as before.
Only the Printer will see packets from the PC.
Switched Ethernet
PC
R
PC
Pr
Switched
Hub
PC
PC
PC
PC
Switched
Hub
Switched
Hub
PC
PC
Packets need to cross a network boundary.
Whose address goes where?
Connection from PC to Router
Router MAC
MAC
Destination
Address
PC MAC
MAC
Source
Address
Information Sink (Printer IP)
Information Source (PC IP)
IP
TCP
Data + Padding
CRC
IP addresses don't match MAC addresses.
Whose address goes where?
Printer MAC
MAC
Destination
Address
Router MAC
MAC
Source
Address
Information Sink (Printer IP)
Information Source (PC IP)
IP
TCP
Data + Padding
CRC
Connection from Router to Printer
Whose address goes where?
MAC addresses change when router crossed.
Stay same through an Ethernet Switch.
MAC
Destination
Address
MAC
Source
Address
IP addresses remain unchanged end-to-end.
IP
TCP
Data + Padding
CRC
Frame Relay
Early ‘90’s technology
 Covers OSI Layer 2
 N*64 Kbps or N*1.54 Mbps connections
 Virtual Circuits
Route once on circuit set up.
 Packet Switch, StatMux Backbones
 Accessed by Routers with proper
interface
 Being replaced by the Internet

Frame Relay Backbone
FR Switch
Frame Relay ‘Cloud’
Trunk capacity shared via StatMux & Packet Switching
Frame Relay Backbone
Corp.
LAN
FR Switch
Corporate Routers or
FRAD's usually attached to FR backbones.
Corp.
LAN
ISO OSI Seven Layer Model
Frame Relay Switch (Layer 1 & 2)
Layer 7
 Layer 6
 Layer 5
 Layer 4
 Layer 3
 Layer 2


Layer 1
Application
Presentation
Session
Transport
Network
Data Link
Physical
Word Perfect
Windows API
TCP, Windows
TCP, Windows
IP, Windows
Frame Relay,
T Carrier or SONET
T Carrier or SONET
Frame Relay Packet Format
(Assuming Ethernet LAN)
3
20
20
0-1460
3
FR
Header
IP
TCP
Data
FR
Trailer
Header includes 10 bit DLCI
Locally Unique Address (Valid between I/O ports)
Trailer includes 2 byte Frame Check Sequence
Only checks for errors in FR header
TCP error checking should catch any payload error
Frame Relay Connectivity
Server
LAN
#2
LAN #1
VC #2
PC
VC #1
FR Switch
Suppose we need to
connect to three LAN's.
LAN
#3
Server
Frame Relay VC Set Up





Client requests connectivity from Carrier
Carrier arranges for Leased Line to nearest Point of
Presence
Technician runs Routing Algorithm on a Work Station
 Paths through network generated
 Appropriate Switches Notified
DLCI's Assigned
I/O mappings updated in Switch Look-Up Tables
Source Router ships all FR traffic down same leased line
 FR switches use DLCI to properly output
Note LAN #2 & #3 can communicate with each
other thru edge router of LAN #1
Frame Relay Backbone
Server
LAN
LAN
PC
FR Switch
Look Up tables map
Input DLCI and Port to
Output DLCI and Port. Reverse path DLCI's not shown.
LAN
Server
Moving Packets
PC1 > Ethernet (Switched) Hub > Router1 > FR1 >
FR2 > Router2 > Ethernet (Switched) Hub > Server

PC1 injects Ethernet Packet
 Destination
IP Address of Server (info sink)
 Router Ethernet MAC Address

Router1
 Examines,
processes, strips off Ethernet Header
 Examines Destination IP Address & Routing Table
 Sees best path is over FR network

Router1 injects FR Packet
 DLCI
375 carrying Layer 3-7 info
Frame Relay Backbone
Server
2 LAN
1
LAN
2
PC
1
FR Switch
Look Up tables map
Input DLCI and Port to
Output DLCI and Port.
LAN
Server
Moving Packets
PC1 > Ethernet (Switched) Hub > Router1 > FR1 >
FR2 > Router2 > Ethernet (Switched) Hub > Server

FR Switch 1
 Examines
FR Look Up Table
 DLCI 375 on input from Router1 maps to
DLCI 177 on output to FR Switch 2

FR Switch 1 injects FR packet
 DLCI
177 carrying Layer 3-7 info
Frame Relay Backbone
Server
2 LAN
1
LAN
2
PC
1
FR Switch
Look Up tables map
Input DLCI and Port to
Output DLCI and Port.
LAN
Server
Moving Packets
PC1 > Ethernet (Switched) Hub > Router1 > FR1 >
FR2 > Router2 > Ethernet (Switched) Hub > Server

FR Switch 2
 Examines
FR Look Up Table
 DLCI 177 on input from Switch1 maps to
DLCI 177 on output to Router2

FR Switch 2 injects FR packet
 DLCI
177 carrying Layer 3-7 info
Frame Relay Backbone
Server
2 LAN
1
LAN
2
PC
1
FR Switch
Look Up tables map
Input DLCI and Port to
Output DLCI and Port.
LAN
Server
Moving Packets
PC1 > Ethernet (Switched) Hub > Router1 > FR1 >
FR2 > Router2 > Ethernet (Switched) Hub > Server

Router 2
 Strips
off FR Header
 Examines Destination IP Address
& Routing Table
 Sees best path is over Internal LAN

Router 2 injects Ethernet Packet
 Server
Ethernet MAC
(Assuming Server is on same subnet as Router)
ATM







Mid ‘90’s technology
Covers OSI Layer 2, Line Speeds < OC-48
Virtual Circuits
Route once on circuit set up.
Five classes of service
Cell Switch (53 bytes), StatMux or TDM
Failed at desktop
OK on Carrier WAN
& Corporate Backbone
Fading from the scene
Being replaced by Internet
ISO OSI Seven Layer Model
ATM Switch
Layer 7
 Layer 6
 Layer 5
 Layer 4
 Layer 3
 Layer 2


Layer 1
Application
Presentation
Session
Transport
Network
Data Link
Physical
Word Perfect
Windows API
TCP, Windows
TCP, Windows
IP, Windows
ATM, SONET
or T Carrier
T Carrier,
or SONET
ATM Cell #1 Format AAL5
5
20
20
8
ATM
Header
IP
TCP
Data
Header includes 24 or 28 bit VPI & VCI
Follow on cells carry remainder of the packet.
Carrier ATM Network
LAN
ATM Switch
What appears to be nailed up end-to-end
connectivity (a Virtual Circuit). Switch
I/O mappings similar to Frame Relay.
LAN
StatMux
ATM Version
Different channels use all of
the frequency some of the time,
at random, as needed.
frequency
1
empty cell
2
1
3
empty cell
1
Can
also
use
TDM.
OSU Campus Network ('95 - '01)
OneNet
802.3
LAN
802.3
LAN
802.3
LAN
LAN
ATM Switch
ATM-Ethernet
Switch
LAN
LAN
ATM Network
Frame Relay
Routers
ATM Switch
All kinds of boxes are
typically hanging off carrier ATM Switches.
ATM PVC Set Up




Client requests connectivity from Carrier
Carrier arranges for Leased Line to nearest Point of
Presence
Technician runs Routing Algorithm on a Work Station
 Paths through network generated
 Appropriate Switches Notified
VPI's and VCI's Assigned
I/O mappings updated in Switch Look-Up Tables
Switch Resources reserved, depending on CoS requested
Corporate ATM switch (or Router with a plug-in ATM
compatible card) ships all traffic down same leased line
 ATM switches use VPI & VCI to properly output
ATM Connection Admission
Control
Procedure for setting up VC’s
 End user requests call set-up
Provides destination, CoS, parameters
 Switches determine if resources are
available
Sufficient Buffer Space?
Sufficient unreserved trunk bandwidth?
 Call is rejected if insufficient resources

ATM Connection Admission Control

CBR VC’s



VBR VC’s



Reserve Average Trunk BW
Reserve Buffers to cover bursts
ABR VC’s



Reserve Peak Trunk BW
Reserve Minimal Buffer Space
Reserve Minimum Trunk BW
Reserve Buffers to cover bursts
UBR VC’s


Reserve Nothing
Allow VC establishment if spare BW & Buffers
above some minimum
The Internet
VAST collection of interconnected
networks
 Mid ‘70’s technology
 Key Building Block:
Routers running IP (Layer 3)
 Packet Switch, StatMux
 Designed for data

Internet Service Provider Backbone
Router
Packet Switched Statmux Network.
Full duplex trunks.
Washington D.C. Area - 2000
ISO OSI Seven Layer Model
IP Router







Layer 7
Layer 6
Layer 5
Layer 4
Layer 3
Layer 2
Application
Word Perfect
Presentation
Windows API
Session
TCP, Windows
Transport
TCP, Windows
Network
IP, Windows
Data Link
Ethernet, FR, ATM
SONET, OTN, T-Carrier, PPP, WiFi
Layer 1 Physical
Ethernet, SONET,
OTN, T-Carrier, DSL, Cable Modem, WiFi
Internet Service Provider Network
LAN
LAN
Router
LAN
Corporate Routers & Other ISP Routers attached.
ISP trunks could be...
Leased Lines
ISP
Router
ISP
Router
Cross-Connect
Nailed up end-to-end connectivity (a Circuit).
Bit pipe. No packet processing between Routers.
Light Path (Wave) Connectivity
(OC-48, OC-192, or OC-768)
ISP
Router
ISP
Router
Optical Switch
Nailed up end-to-end connectivity (a Circuit).
Light Path. No packet processing between Routers.
Internet Packet Format
??
Layer 2
Header
20
IP
20
TCP
0-1460
Traffic
??
Layer 2
Trailer?
Probably originated on an Ethernet.
Internet

Router Line Speeds generally
 T1
to OC-768 on the WAN, some 100 Gbps
(Mostly Leased Line or Light Waves)
 10/100/1,000/10,000 Mbps (Ethernet) on the LAN
 Some Ethernet making it into MAN
Hierarchical Alpha-Numeric Names
[email protected]
 Datagrams

 Independent
I/O decisions on every packet
 Not guaranteed to follow same path