Networking essentials

1

CS144

An Introduc/on to Computer Networks

What the Internet is

4 Layer Model

Nick McKeown

Professor of Electrical Engineering

and Computer Science, Stanford University

CS144, Stanford University

2

The 4 Layer Internet Model

Network

Link

Transport

Applica/on


3

Peer layers communicate

Network

Link

Transport

Applica/on

Network

Link

Transport

Applica/on

Network

Link

Network

Link


B A

4

Encapsula/on


Network

Link

Transport

Applica/on

A

Network

Link

5


Network

Link

Transport

Applica/on

Network

Link


B

A few last words…

6 CS144, Stanford University

Where do the different layers run?


Network

Link

Transport

Applica/on

Why is the Network Layer oPen

called “Layer 3”?


Applica/on

Presenta/on

Session

Transport

Network

Link

Physical

The 7‐layer OSI Model

Network

Link

Transport

The 4‐layer Internet model

Applica/on h-p

ASCII

IP

TCP

Ethernet

<The End>


1 1 1

CS144



A very brief history of networking and the Internet


Nick McKeown

Professor of Electrical Engineering and Computer Science, Stanford University

2 2 2

Outline

Brief history of networking

Brief history of the Internet


3 3 3 CS144, Stanford University

1,000 BC

Fire Beacons

Carrier Pigeons

Human Messengers

Horse Relays …

Flags

Heliographs: sun’s

rays & reflector

Telescopes

0 1800 AD Today

Semaphore telegraphs

Chappe (France)

Edelcrantz (Sweden)

Telephone

Internet

4 4 4

The Telegraph


5 5 5

Four steps of inven/on

(2,000 BC) Systems to signal a small set of pre‐defined

messages, e.g. beacons.

(1600s) Systems to transmit arbitrary messages, e.g. by

encoding the alphabet.

(1700s) Numeric codes for common words and phrases.

“Compression”.

(1700s) Codes for control signals. “Protocols”.


6 6 6

Protocol Signals by 1800

1.  Ini/aliza/on

2.  Error control: erase, resend.

3.  Rate control: “faster/slower”.

4.  Flow control: stop/wait, selec/ve‐repeat.


7 7 7

Telephone networks in 1900

1.  (1897) Alexander Graeme Bell made the first

telephone call


8 8 8

Outline

Brief history of Networking

Brief history of the Internet


9 9 9

Parallel beginnings


1960

RAND (Paul Baran)

Packet switching for

survivable networks.

MIT (Kleinrock) First

paper on packet

switching theory.

DARPA (Roberts)

plans for

“ARPANET”.

NPL, UK (Davies)

Packet network.

1965 1966

WAN connects two /me‐

sharing computers

1968

First “IMPs” (BBN).

J.C.R. Licklider describes an

Intergalac/c Network connec/ng

everyone on the globe.

Four nodes

interconnected

(UCLA, SRI, UCSB,

Utah)


1970 1980 1990

1st Web browser

New networks appear:

IBM SNA, ALOHAnet,

Cyclades (France).

“Internehng” and TCP

born (DARPA), led by

Vint Cerf and Bob Kahn.

200 hosts on

ARPAnet

100,000 hosts

on Internet

TCP/IP

deployed

NSFNET, etc.

Cisco and IETF

started

11 11 11

Useful References

1.  The Early History of Data Networks G. J. Holzmann, B. Pehrson, IEEE Press 1994.

2.  The Design Philosophy of the

DARPA Internet Protocols.

D. Clark, ACM Sigcomm 1988

3.  Brief History of the Internet B. M. Leiner, V. Cerf, D. D. Clark et al. hjp://www.internetsociety.org/internet/internet‐51/history‐internet/brief‐history‐internet


12 12 12

<The End>



Principle: Layering

1


File Transfer

2

• Data format

• Packetization

• Reliability, error checking

• Congestion and flow control

• Packet delivery and routing

• Link delivery

• Signal modulation and framing


Layering

• Decompose communication into a set of smaller, well-defined components

• Components build on top of one another: they layer

• Each layer has a well-defined interface and clear responsibilities▶ Routing layer does not worry about application

▶ Application layer does not worry about how signals represented

• Each layer can evolve independently

3


Layering

4

Transport

Link

Network


bits/bytes

frames

packets

segments

OSI Model

5

Physical

Link

Network

Transport

Session

Presentation

Application

1.

2.

3.

4.

5.

6.

7.


Layering Principle

• Decompose communication into layers of abstraction

• Separation of concerns

• Each layer can evolve independently

6

Principle: Encapsulation

Layering

• Separation of concerns and responsibilities

• Allows each service to evolve independently

• Examples:▶ Transport: inter-application communication

▶ Link: inter-host communication on a shared link

Physical

Link

Network

Transport

Session

Presentation

Application

Encapsulation

• How layering manifests in data representation

• Layer N data is payload to layer N-1

• Example:▶ HTTP (web) application payload in

▶ a TCP transport segment in

▶ an IP network packet in

▶ an Ethernet link frame.Physical

Link

Network

Transport

Session

Presentation

Application

LinkNetworkTransportapplication data

Encapsulation Flexibility

• Encapsulation allows you to layer recursively

• Example: Virtual Private Network (VPN):▶ HTTP (web) application payload in



▶ a secured TLS presentation message in



▶ an Ethernet link frame.

Encapsulation

• How layering manifests in data representation

• Encapsulated payloads▶ Help separation of concerns

▶ Help enforce boundaries/layering

▶ Simplify layer implementations

Layer 1

Layer 2

Layer 3

Layer 4

Layer 5

Layer 6

Layer 7

An#Introduc+on#to#Computer#Networks#

Principle:*Packet*Switching*

What#is#packet#switching?#

Packet:#A#self=contained#unit#of#data#that#carries#

informa+on#necessary#for#it#to#reach#its#des+na+on.#

CS144,#Stanford#University#

Two#consequences#

1.  No#per=flow#state#required.#

2.  Efficient#sharing#of#links.#


No#per=flow#state#required#

Packet#switches#don’t#need#state#for#each#flow#–#each#packet#is#self=contained.#

No#per=flow#state#to#be#added/removed.#

No#per=flow#state#to#be#stored.#

No#per=flow#state#to#be#changed#upon#failure.#


Efficient#sharing#of#links#

Data#traffic#is#bursty#

–  If#we#reserved#a#frac+on#of#the#links#for#each#flow,#the#

links#would#be#used#inefficiently.#

–  Packet#switching#allows#flows#to#use#all#available#link#

capacity.#

This#is#called#Sta$s$cal(Mul$plexing.#



Principle: Names and Addresses

1


Name vs. Address

• Name: specifies what something is▶ Office: Philip Levis’ office

▶ Host name: market.scs.stanford.edu

▶ Memory: list_ptr

• Address: specifies where something is▶ Office: 412 Gates Hall, 353 Serra Mall, Stanford, CA 94305-9040 USA

▶ IP: 171.66.3.9

▶ Memory: 0x0040005080

• Telephone numbers: names or addresses?

• This is not a hard classification, just a conceptual model

2


Names

• Structure of names affects what you can reference (easily)

• Flat names▶ Stock tickers (GOOG, MSFT), airport codes (NRT, YYZ)

▶ Services: http, ftp, https

▶ Skype IDs

• Tuple pairs▶ Gender: Female; Name: Jennifer Widom; Position: Department Chair

• Hierarchical names▶ maps.google.com

▶ Nick McKeown, Professor of Electrical Engineering and Computer Science, Stanford University

3


Addresses

• Structure of addresses affects what you can reference (easily)

• Flat addresses▶ Memory (0x040004400)

▶ Port numbers (80, 21, 443)

• Tuple pairs▶ x=32, y=100, z=88

▶ latitude=45.211W, longitude=48.111N

• Hierarchical addresses▶ Memory segments (0x1000 in segment 0)

▶ 412 Gates Hall, 353 Serra Mall, Stanford, CA, 94131 USA

4


Downloading a File

• How does one refer to the file?

• Address: http://csl.stanford.edu/~pal/pubs.html▶ Refers to what host the file is on

▶ Refers to where on the host’s file system the file is

• Name: take a hash of pubs.html: 0x27de2b6939d7fb4b0573dbd6dbe2c740▶ Request the file (using a different protocol than http) with hash

▶ If file changes, hash changes

▶ Says nothing about where the file is

5


Internet Names and Addresses

• Internet addresses: 32-bit IPv4, 128-bit IPv6 addresses

• Internet names: domain name system (DNS), www.stanford.edu

• Many more names and addresses at higher layers▶ Service names (http) and ports (80)

▶ SIP identifiers ([email protected]) and email addresses ([email protected])

• Internet Corporation for Assigned Names and Numbers (ICANN)▶ Internet Assigned Numbers Authority (IANA)

6


Two Examples

• http://csl.stanford.edu/~pal vs. http://171.64.73.43/~pal

• A user moving between networks

7


Principle

• Whether you name or address something has deep implications to how your network and or protocol can be used.

• The structure and design of those names and addresses also have deep implications.

8


The End-to-End Principle

1


Application View of the World

2


Why Doesn’t the Network Help?

• Compress data?

• Reformat/translate/improve requests?

• Serve cached data?

• Add security?

• Migrate connections across the network?

• Or one of any of a huge number of other things?

3


The End-To-End Principle

4

The function in question can completely and correctlybe implemented only with the knowledge and help ofthe application standing at the end points of thecommunication system. Therefore, providing thatquestioned function as a feature of the communicationsystem itself is not possible. (Sometimes an incompleteversion of the function provided by the communicationsystem may be useful as a performance enhancement.)We call this line of reasoning. . . “the end-to-endargument.”

- Saltzer, Reed, and Clark, End-to-end Arguments in System Design, 1984


Example: File Transfer

5


Example: Link Reliability

6


“Strong” End to End

7

The network’s job is to transmit datagrams asefficiently and flexibly as possible. Everythingelse should be done at the fringes. . .

– [RFC 1958]


Net Neutrality

8

“Allowing broadband carriers to control what people see and do online would fundamentally undermine the principles that have made the Internet such a success.”

- Vinton Cerf in testimony before Congress February 7, 2006

"I am totally opposed to mandating that nothing interesting can happen inside the net."

- Bob Kahn, speaking at the Computer History Museum, January 9, 2007


Finite State MachinesProtocol Specification

1


Finite State Machines

2

State 1

State 2

State 3



3

State 1

State 2

event causing state transitionactions taken on state transition

State 3



4

State 1

State 2

event causing state transitionactions taken on state transition

eventaction

State 3


FSM Example: HTTP Request

5


FSM Example: TCP Connection

6 http://upload.wikimedia.org/wikipedia/commons/thumb/a/a2/Tcp_state_diagram_fixed.svg/


The Internet(why you should take this course)

1


Societal Change

• Economics: Black Friday, Cyber Monday, E-Fairness legislation

• Dating: okcupid, match.com

• Knowledge: Google books, eBooks, wikipedia

• Communication: IM, VoIP, video telephony

2


Political Change

• Arab spring: SMS, Twitter, U.S. State Department

• Diplomacy: Wikileaks

• Occupy movement: Twitter, Facebook

• By force: Stuxnet worm

3


Economic Change

• #24: Sergey Brin and Larry Page (tied)

• #26: Jeff Bezos

• #35: Mark Zuckerberg

(data from Forbes top billionaires list, April 16 2012)4


Second Industrial Revolution

http://csl.stanford.edu/~pal/ed

Degrees conferred in 2008 and projected job openings/year 2008-2018

5


Roles in the Revolution

6


This Course

• How computer networks work: principles, design, and implementation

• Use these principles to understand the current Internet

• How to apply these principles to help build the future Internet

• How forces shape the Internet: technological, economic, social, political

7

1

CS144


Conges'on

AIMD with a single flow

Nick McKeown



2

AIMD Addi/ve Increase, Mul/plica/ve Decrease


t

cwnd

halved

Drops

If packet received OK: W←W +1

W

If a packet is dropped: W←W

2

3

Animation

Animation at: http://guido.appenzeller.net/anims/


4

4

Single Flow Dynamics


5

Sending rate for a single flow

ACK

Window Size

Round‐trip /me

(1) R x RTT > Window size, W

ACK

Window Size

Round‐trip /me

(2) R x RTT = Window size, W

ACK

Window Size

ACK ACK

A

B


6

Sending rate for single flow

t

Window size RTT

A B

Router buffer

Link rate = C Link rate > C


7

How big should the buffer be? Buffer size, B = RTT ×C Buffer size, B < RTT ×C


8

Observa/ons for single flow

1. Window expands/contracts according to AIMD.

2. …to probe how many bytes the pipe can hold.

3. The sawtooth is the stable operating point.

4. The sending rate is constant.

5. …if we have sufficient buffers (RTT x C).


9

<end>


1

CS144


Conges'on

AIMD with mul-ple flows

Nick McKeown




A B

Router buffer

Link rate = C Link rate > C

3

t

Window size Buffer occupancy

and RTT

One flow vs mul/ple flows


Buffer occupancy

and RTT

t

(Zoom in)

cwnd

One of the flows

One flow

t

Buffer

Occupancy

Mul'ple flows

R =W(t)

RTT(t)= constant

R =W(t)

RTT∝W(t)

4

A

Simple geometric intuition

Drops

t

cwnd

1

RTT

Packet drop rate, p =1/ A, where A =3

8Wmax

2

Throughput, R =A

Wmax

2

!

"#

$

%&RTT

=3

2

1

RTT p

5

Interpre/ng the rate equa/on


R =3

2

1

RTT p

1. RTT→ 0 ⇒ R→∞ ?

2. p→ 0 ⇒ R→∞ ?

6

Observa/ons for mul/ple flows

1. Window expands/contracts according to AIMD.

2. …to probe how many bytes the pipe can hold.

3. Bottleneck will contain packets from many flows.

4. The sending rate varies with window size.

5. AIMD is very sensitive to loss rate.

6. AIMD penalizes flows with long RTTs.


7

<end>



Congestion Control IIRTT Estimation, self-clocking

1


Three Improvements

• Congestion window

• Timeout estimation

• Self-clocking

2


Timeouts

• Round trip time estimation is critical for timeouts▶ Too short: waste capacity with restransmissions, trigger slow start

▶ Too long: waste capacity with idle time

• Challenge: RTT is highly dynamic

• Challenge: RTT can vary significantly with load

3


Pre-Tahoe Timeouts

• r is RTT estimate, initialize to something reasonable

• m, RTT measurement from most recently acked data packet

• Exponentially weighted moving average: r = αr + (1-α)m

• Timeout = βr, β=2

• What’s the problem?

4


TCP Tahoe Timeouts

5

• r is RTT estimate, initialize to something reasonable

• g is the EWMA gain (e.g., 0.25)

• m is the RTT measurement from most recently acked data packet

• Error in the estimate e = m-r

• r = r + g⋅e

• Measure variance v = v + g(|e| - v)

• Timeout = r + βv (β=4)

• Exponentially increase timeout in case of tremendous congestion


RTT Estimation Improvement

6

Pre-Tahoe Tahoe


Three Improvements

• Congestion window

• Timeout estimation

• Self-clocking

7


• In case of a bottleneck link, sender receives acks properly spaced in time

Self-Clocking

8

sender receiver


Self-Clocking Principle

• Only put data in when data has left▶ Want to prevent congestion -- too much data in network

• Send new data in response to acknowledgments

• Send acknowledgments aggressively -- important signal

9


TCP Tahoe

• 1987-8: Van Jacobson fixes TCP, publishes seminal TCP paper (Tahoe)▶ Congestion window, slow start

▶ Timeout considers variance

▶ Self-clocking

• TCP Tahoe solved TCP’s congestion control problem▶ Spawned a huge area of research in TCP variants

▶ Next lecture will talk about Reno and NewReno

▶ Reading: “Congestion Avoidance and Control,” Van Jacobson and Karels.

10


Congestion Control IIIPerformance improvements: TCP Reno, TCP NewReno

1


TCP Tahoe

• On timeout or triple duplicate ack (implies lost packet)▶ Set threshold to congestion window/2

▶ Set congestion window to 1

▶ Enter slow start state

2


TCP Tahoe Review

3

time

windowsize


TCP Reno

• Same as Tahoe on timeout

• On triple duplicate ack▶ Set threshold to congestion window/2

▶ Set congestion window to congestion window/2 (fast recovery)

▶ Retransmit missing segment (fast retransmit)

▶ Stay in congestion avoidance state

4


TCP Reno

5

time

windowsize


TCP Reno Example

6

Timesender

receiver


TCP NewReno

• Same as Tahoe/Reno on timeout

• During fast recovery▶ Keep track of last unacknowledged packet when entering fast recovery

▶ On every duplicate ack, inflate congestion window by maximum segment size

▶ When last packet acknowledged, return to congestion avoidance state, set cwnd back to value set when entering fast recovery

▶ Start sending out new packets while fast retransmit is in flight

7


TCP NewReno Behavior

8

Time


Congestion Control

• One of the hardest problems in robust networked systems

• Basic approach: additive increase, multiplicative decrease

• Tricks to keep pipe full, improve throughput▶ Fast retransmit (don’t wait for timeout to send lost data)

▶ Congestion window inflation (don’t wait an RTT before sending more data)

9


Congestion Control IVWhy AIMD

1


Congestion Control

• Service Provider: maximize link utilization

• User: I get my fair share

• Want network to converge to a state where everyone gets 1/N

• Avoid congestion collapse

2


Congestion Window Size

3

San Francisco Boston

Optimal congestion window size is the bandwidth-delay product


Chiu Jain Plot

4

Flow A rate (bps)

Flo

w B

rate

(bps)


Chiu Jain Plot

5

Flow A rate (bps)

Flo

w B

rate

(bps)

Fair

A=B


Chiu Jain Plot

6

Flow A rate (bps)

Flo

w B

rate

(bps)

Fair

A=B

Efficient

A+B=C


Chiu Jain Plot

7

Flow A rate (bps)

Flo

w B

rate

(bps)

Fair

A=B

Efficient

A+B=C

overload

underload


Chiu Jain Plot

8

Flow A rate (bps)

Flo

w B

rate

(bps)

Fair

A=B

Efficient

A+B=C

overload

underload


Chiu Jain Plot

9

Flow A rate (bps)

Flo

w B

rate

(bps)

Fair

A=B

Efficient

A+B=C

overload

underload

t1

t2

t3

t4

t5

t6

1

CS144



4 Layer Model

Nick McKeown




2


Network

Link

Transport

Applica/on


3


Network

Link

Transport

Applica/on

Network

Link

Transport

Applica/on

Network

Link

Network

Link


B A

4

Encapsula/on


Network

Link

Transport

Applica/on

A

Network

Link

5


Network

Link

Transport

Applica/on

Network

Link


B

A few last words…




Network

Link

Transport

Applica/on




Applica/on

Presenta/on

Session

Transport

Network

Link

Physical


Network

Link

Transport


Applica/on h-p

ASCII

IP

TCP

Ethernet

<The End>


1

CS144



The IP Service

Nick McKeown




CS144, Stanford University 2

The Internet Protocol (IP)

TCP

IP

Data Hdr

Data Hdr

TCP Segment

IP Datagram Network

Link

Transport

Applica/on

The IP Service Model


Property Behavior

Datagram Individually routed packets.

Hop‐by‐hop rou/ng.

Unreliable Packets might be dropped.

Best effort …but only if necessary.

Connec4onless No per‐flow state.

Packets might be mis‐sequenced.

The IP Service Model (Details)

•  Tries to prevent packets looping forever.

•  Will fragment packets if they are too long.

•  Uses a checksum to reduce chances of delivering

to wrong des/na/on.

•  Allows for new versions of IP –  Currently IPv4 with 32 bit addresses

–  And IPv6 with 128 bit addresses

•  Allows for new op/ons to be added to header.


IPv4 Datagram


Flags

Version

Time to Live

“TTL”

Type of

Service

Checksum

Header

Length Total Packet Length

Packet ID Fragment Offset

Protocol ID

Source IP Address

Des/na/on IP Address

(OPTIONS) (PAD)

Bit 0

Data

Bit 31

The Hourglass Model of IP


IP

TCP UDP …

h`p smtp ssh …

Ethernet WiFi DSL …

Summary

We use IP every /me we send and receive

Internet packets.

It provides a deliberately simple service:

–  Datagram

–  Unreliable

–  Best‐effort

–  Connec/onless


<The End>


1

CS144


Rou$ng

Mul$cast Rou$ng

Nick McKeown




2

Mul/cast

R7

R6 R4 R2 R1

R8

R5

R3

A

X

B C D

E

3

Mul/cast

R7

R6 R4 R2 R1

R8

R5

R3

A

X

B C D

E

4

Mul/cast

Techniques and Principles

- Reverse Path Broadcast (RPB) and Pruning

- One versus mul/ple trees

Prac/ce

-  IGMP – group management

- DVMRP – the first mul/cast rou/ng protocol

- PIM – protocol independent mul/cast


5

Flooding


6

Reverse Path Broadcast (RPB) aka Reverse Path Forwarding (RPF)


R7

R6 R4 R2 R1

R8

R5

R3

A

X

B C D

E

7

RPB + Pruning

1.  Packets delivered loop‐free to every end host.

2.  Routers with no interested hosts send prune

messages towards source.

3.  Resul/ng tree is the minimum cost spanning tree

from source to the set of interested hosts.


8

One tree versus several trees?

R7

R6 R4 R2 R1

R8

R5

R3

A

X

B C D

E

9

Mul/cast

Techniques and Principles

- Reverse Path Broadcast (RPB) and Pruning

- One versus mul/ple trees

Prac/ce

- Mul/cast addresses

-  IGMP – group management

- DVMRP – the first mul/cast rou/ng protocol

- PIM – protocol independent mul/cast


10

Addresses and joining a group

IPv4: Class D addresses are set aside for mul/cast.

IGMP* (Internet group management protocol)

-  Between host and directly aaached router.

-  Hosts ask to receive packets belonging to a par/cular

mul/cast group.

-  Routers periodically poll hosts to ask which groups

they want.

-  If no reply, membership /mes out (sod‐state).

CS144, Stanford University *RFC 3376

11

Mul/cast rou/ng in the Internet

DVMRP

-  Distance Vector Mul/cast Rou/ng Protocol (RFC 1075)

-  First Internet rou/ng protocol

-  Uses RPB + Prune

PIM

-  Protocol Independent Mul/cast

-  Two modes: dense mode, sparse mode

-  Dense mode (RFC 3973): Similar to DVMRP

-  Sparse mode (RFC 4601): Builds rendezvous points

through which packets join small set of spanning trees.

12

Mul/cast in prac/ce

Mul/cast used less than originally expected

- Most communica/on is individualized

(e.g. /me shiding)

-  Early implementa/ons were inefficient

-  Today, used for some IP TV and fast dissemina/on

-  Some applica/on‐layer mul/cast rou/ng used

Some interes/ng ques/ons

-  How to make mul/cast reliable?

-  How to implement flow‐control?

-  How to support different rates for different end users?

-  How to secure a mul/cast conversa/on?

1

CS144


Rou$ng

Spanning Tree Protocol

Nick McKeown



2

Outline

Ethernet “routes” packets too.

We know how addresses are learned, but how are

loops prevented?

Ethernet switches build a spanning tree over which

packets are forwarded.

3

Ethernet Switch

1.  Examine the header of each arriving frame.

2.  If the Ethernet DA is in the forwarding table, forward the

frame to the correct output port(s).

3.  If the Ethernet DA is not in the table, broadcast the

frame to all ports (except the one through which the

frame arrived).

4.  Entries in the table are learned by examining the

Ethernet SA of arriving packets.

4

Learning could lead to loops


5

Preven/ng loops Spanning Tree Protocol

The topology of switches is a graph.

The Spanning Tree Protocol finds a a subgraph that

spans all the ver/ces without loops. -  Spanning: all switches are included.

-  Tree: no loops.

The distributed protocol decides: 1.  Which switch is the Root of the tree, and

2.  Which ports are allowed to forward packets along the tree.

6

Example Spanning Tree

S3

S7 S2

S1

S6 S4

1: Pick a single root.

2: Only forward packets on ports on the shortest hop‐count to root.

S9

S5

S8

7

Resul/ng Spanning Tree

S4 S6

S8

S1

S9

S7 S2 S5

S3

8

How it works 1.  Periodically, all switches broadcast a “Bridge Protocol Data Unit” (BPDU)

(ID of sender, ID of root, distance from sender to root).

2.  Ini/ally, every switch claims to be Root: sets distance field to 0.

3.  Every switch broadcasts un/l it hears a 曨be^er杇 message: -  A root with a smaller ID

-  A root with equal ID, but with shorter distance

-  Ties broken by smaller ID of sender.

4.  If a switch hears a be^er message, retransmit message (add 1 to distance).

Root port: The port on a switch that is closest to the Root.

Designated port: The port neighbors agree to use to reach the Root.

All other ports are blocked from forwarding (but s/ll send/receive BPDUs).

Eventually: -  Only the root originates configura/on messages (others retransmit them). -  Locally, switch only forwards on ports.

9

A brief history

1985: STP proposed; IEEE standard in 1990.

S/ll very widely used

2004: STP replaced by RSTP which converges faster.

S/ll, RSTP uses the network inefficiently.

2012: A new standard for Ethernet switches was

introduced Shortest‐Path Bridging (SPB, or

802.1aq). It is a link‐state protocol like OSPF.



Reading an RFC

1


History (RFC 2555)

• RFC 1: “Host Software”▶ “Mindful that our group was informal, junior and unchartered, I wanted to

emphasize these notes were the beginning of a dialog and not an assertion of control.”

• Standardization of format▶ Structure, intellectual property rights, terminology (RFC 2119)

▶ Security, IANA

• Kinds of RFCs: proposed standard, standards-track, informational, experimental, best current practice (BCP)

2


RFC Process (simplified)

• Start with a draft: draft-levis-roll-trickle-00

• Revisions: draft-levis-roll-trickle-XX

• Accepted by working group: draft-ietf-roll-trickle-00

• Revisions: draft-ietf-roll-trickle-XX

• Accepted by working group chair for publication

• Working group, IETF last call

• IESG review

• Approved as an RFC

3


Terminology

• MUST, REQUIRED, SHALL: absolute requirement.

• SHOULD, RECOMMENDED: “mean that there may exist valid reasons in particular circumstances to ignore a particular item, but the full implications must be understood and carefully weighed before choosing a different course.”

• MAY, OPTIONAL: “mean that an item is truly optional.”

4


Example: RFC5681

5

1

CS144


Physical Links

CSMA/CD and Ethernet

Nick McKeown


2

The Link Layer

Network

Link

Transport

Applica/on

Network

Link

Transport

Applica/on

Network

Link

Network

Link

B A

3

Why is Ethernet oIen

referred to as “Layer 2”?


Applica/on

Presenta/on

Session

Transport

Network

Link

Physical


Network

Link

Transport


Applica/on h0p

ASCII

IP

TCP

Ethernet

4

The origins of Ethernet


5

Sharing a “medium”

-  Ethernet is an example of mul/ple hosts sharing

a common cable (“medium”).

-  To share the medium, we need to decide who

gets to send, and when.

-  There is a general class of “Medium Access

Control Protocols”, or MAC Protocols.

-  We will take a look at some examples.


6

Examples of MAC Protocols

Packet‐Switched Radio Network

Aloha

Carrier Sense Mul/ple Access/Collision Detec/on

Ethernet (IEEE 802.3)

Token Passing

Token Ring (IEEE 802.5)

Sim

ple

Random

Complex

Determ

inisFc


7

Goals of MAC Protocols

Medium Access Control protocols arbitrate access to a

common shared channel among a popula/on of users

1.  High u/liza/on of the shared channel

2.  Fair among end hosts

3.  Simple and low cost to implement

4.  Robust to errors; fault tolerant


8

Aloha Network (1968)


Hawaii

Oahu

Kauai

Maui

Molokai

9

Aloha

Frequency 0 Frequency 1

Original Aloha MAC protocol 1.  If you have data to send, transmit it.

2.  If your transmission “collides” with another, retry later.


10

Aloha Protocol

-  Aloha protocol is very simple

-  (Quite) robust against failure of a host.

-  The protocol is distributed among the hosts.

-  Under low‐load, we can expect the delay to be small.

-  Under high‐load, a lot of /me “wasted” sending packets that collide.

Improving performance: 1. Listen for ac/vity (“carrier sense”) before sending a packet. 2. Detect collisions quickly and stop transmigng. 3. AIer collision, pick random wai/ng /me based on the load.


11

CSMA/CD Protocol

All hosts transmit & receive on one channel

Packets are of variable size.

When a host has a packet to transmit: 1.  Carrier Sense: Check the line is quiet before transmigng.

2.  Collision Detec/on: Detect collision as soon as possible. If a collision is

detected, stop transmigng; wait a random /me, then return to step 1.

binary exponen7al backoff


12

CSMA/CD opera/on


A B C D

13

CSMA/CD Packet size requirement


A B C D

L/c

14

<end>



Wireless Networking

1


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300

325

335

405

415

435

495

505510

525

535

16051615

1705

1800

1900

2000

2065

2107

21702173.52190.52194

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2850

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MOBILE FIXED MARITIMEMOBILE


MARITIMEMOBILE

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30.0

30.56

32.0

33.0

34.0

35.0

36.0

37.037.538.038.25

39.0

40.0

42.0

43.69

46.647.0

49.6

50.0

54.0

72.0

73.0

74.674.875.275.476.0

88.0

108.0

117.975

121.9375123.0875123.5875

128.8125

132.0125

136.0

137.0137.025137.175137.825138.0

144.0146.0148.0149.9150.05

150.8152.855

154.0

156.2475157.0375157.1875157.45161.575161.625161.775162.0125

173.2173.4174.0

216.0

220.0222.0225.0

235.0

300

ISM – 6.78 ± .015 M

HzISM

– 13.560 ± .007 MHz

ISM – 27.12 ± .163 M

Hz

ISM – 40.68 ± .02 M

Hz

ISM – 24.125 ± 0.125 G

Hz30 G

Hz

ISM – 245.0 ± 1G

HzISM

– 122.5 ± .500 GHz

ISM – 61.25 ± .250 G

Hz

300.0

322.0

328.6

335.4

399.9

400.05400.15

401.0

402.0

403.0406.0406.1

410.0

420.0

450.0454.0455.0456.0

460.0462.5375462.7375467.5375467.7375470.0

512.0

608.0614.0

698

746

764

776

794

806

821824849851866869894896901901902

928929930931932935940941944960

1215

1240

1300

1350

139013921395

2000

2020

2025

2110

2155

21602180

2200

22902300230523102320

2345

2360

238523902400

24172450

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2900

3000

140014271429.5

1430143214351525

1530

1535

1544

1545

1549.5

1558.5155916101610.61613.81626.5

16601660.51668.4

1670

1675

1700

1710

1755

1850

MARITIME MOBILE SATELLITE(space to Earth) MOBILE SATELLITE (S-E)

RADIOLOCATIONRADIONAVIGATION

SATELLITE (S-E)


RadiolocationAERONAUTICAL

RADIONAVIGATION

SPA CE RESEARCH ( Passive)EARTH EXPL SAT (Passive)RADIO ASTRONOMY

MOBILEMOBILE ** FIXED-SAT (E-S)FIXED

FIXED

FIXED**

LAND MOBILE (TLM)

MOBILE SAT.(Space to Earth)

MARITIME MOBILE SAT.(Space to Earth)

Mobile(Aero. TLM)

MOBILE SATELLITE (S-E)

MOBILE SATELLITE(Space to Earth)

AERONAUTICAL MOBILE SATELLITE (R)(space to Earth)

3.0

3.1

3.3

3.5

3.6

3.65

3.7

4.2

4.4

4.5

4.8

4.94

4.99

5.0

5.155.25

5.35

5.465.47

5.6

5.65

5.83

5.855.925

6.425

6.525

6.706.875

7.0257.075

7.125

7.197.2357.25

7.30

7.45

7.55

7.75

7.90

8.025

8.175

8.215

8.4

8.45

8.5

9.0

9.2

9.3

9.5

10.0

10.45

10.510.5510.6

10.68

10.7

11.7

12.2

12.7

12.75

13.2513.4

13.7514.0

14.2

14.4

14.4714.514.7145

15.1365

15.35

15.415.43

15.6315.716.6

17.1

17.217.317.717.818.318.618.8

19.319.7

20.120.221.2

21.422.022.2122.5

22.55

23.55

23.6

24.0

24.05

24.2524.45

24.65

24.75

25.05

25.2525.527.0

27.5

29.5

29.9

30.0

ISM – 2450.0 ± 50 M

Hz

30.0

31.0

31.3

31.8

32.032.3

33.033.4

36.0

37.0

37.6

38.0

38.6

39.5

40.0

40.5

41.0

42.5

43.5

45.5

46.9

47.0

47.2

48.2

50.2

50.4

51.4

52.6

54.2555.7856.957.0

58.2

59.0

59.3

64.0

65.0

66.0

71.0

74.0

75.5

76.077.077.578.0

81.0

84.0

86.0

92.0

95.0

100.0

102.0

105.0

116.0

119.98

120.02

126.0

134.0

142.0144.0

149.0

150.0

151.0

164.0

168.0

170.0

174.5

176.5

182.0

185.0

190.0

200.0

202.0

217.0

231.0

235.0

238.0

241.0

248.0

250.0

252.0

265.0

275.0

300.0

ISM – 5.8 ± .075 G

Hz

ISM – 915.0 ± 13 M

Hz

INTER-SATELLITE RADIOLOCATIONSATELLITE (E-S)

AERONAUTICALRADIONAV.

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RADIONAVIGATION

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WAVELENGTH

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ACTIVITIES

FREQUENCY

3 x 107m

3 x 106m

3 x 105m

30,000 m3,000 m

300 m30 m

3 m30 cm

3 cm0.3 cm

0.03 cm3 x 10

5Å3 x 10

4Å3 x 10

3Å3 x 10

2Å3 x 10Å

3Å3 x 10

-1Å3 x 10

-2Å3 x 10

-3Å3 x 10

-4Å3 x 10

-5Å3 x 10

-6Å 3 x 10

-7Å

010 Hz

100 Hz1 kHz

10 kHz100 kHz

1 MHz

10 MHz

100 MHz

1 GHz10 GHz

100 GHz1 THz

1013Hz

1014Hz

1015Hz

1016Hz

1017Hz

1018Hz

1019Hz

1020Hz

1021Hz

1022Hz

1023Hz

1024Hz

1025Hz

THE RADIO SPECTRUMMAGNIFIED ABOVE

3 kHz300 GHz

VERY LOW

FREQUENCY (VLF)

Audible Range AM

Broadcast FM

Broadcast Radar

Sub-Millim

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BROADCASTINGFIXED

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BROADCASTING

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BROADCASTINGFIXED

BROADCASTING


BROADCASTINGFIXED

FIXED

FIXED

FIXEDFIXED

FIXED

LANDMOBILE

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F I X E D

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LAND MOBILE MARITIME MOBILE

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MET. AIDS(Radio-sonde)

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Met-Satellite (E-S)

MET-SAT. (E-S)

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MET-SAT. (E-S)

LAND MOBILELAND MOBILEFIXED

LAND MOBILEFIXED

FIXED

FIXED LAND MOBILE

LAND MOBILEFIXED LAND MOBILE

LAND MOBILE LAND MOBILE

LAND MOBILE

MOBILEFIXED

MOBILEFIXED

BROADCASTMOBILEFIXED

MOBILEFIXED

FIXEDLAND MOBILE

LAND MOBILEFIXEDLAND MOBILE

AERONAUTICAL MOBILE

AERONAUTICAL MOBILEFIXEDLAND MOBILE

LAND MOBILELAND MOBILE FIXED

LAND MOBILE FIXEDMOBILE FIXED

FIXEDFIXED

MOBILEFIXED

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LAND MOBILELAND MOBILE

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METEOROLOGICALAIDS

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B-SATR- LOC.FXMOBFixedMobileRadiolocat ionFIXEDMOBILE**Amateur RADIOLOCATION

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MOBILEFIXEDMOBILE SATELLITE (S-E)

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FIXED

FIXED MARITIME MOBILE FIXED

FIXEDMOBILE**

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AmateurMOBILE FIXED SAT(E-S)

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FIXED SATELLITE (S-E) MOBILE SAT. (S-E)

FX SAT (S-E) MOBILE SATELLITE (S-E)FX SAT (S-E)STD FREQ. & TIME MOBILE SAT (S-E)

EARTH EXPL. SAT.MOBILEF IXEDSPACE RES.

F IXED MOBILEMOBILE**F IXED

EARTH EXPL. SAT.F IXEDMOBILE**R A D . A S TS P A C ER E S .

F IXEDMOBILE

INTER-SATELLITE

F IXED

RADIO ASTRONOMY SPACE RES.(Passive)


Radio-location

AmateurRADIO-LOCATION

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F IXED

INTER-SATELLITERADIONAVIGATION

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F IXEDSATELLITE

(E-S)RADIONAVIGATION

F IXEDSATELLITE

(E-S)F IXED

MOBILE SATELLITE (E-S)FIXED SATELLITE (E-S)

MOBILEF IXEDEarth ExplorationSatellite (S-S)

std freq & time e-e-sat (s-s) MOBILEF IXED

e-e-sat MOBILE

SPACERESEARCH (deep space)

RADIONAVIGATIONINTER- SATSPACE RES.

F IXED MOBILE SPACE RESEARCH(space-to-Earth)

SPACERES.

F IXEDSAT. (S-E)

MOBILE F IXED

FIXED-SATELLITE

MOBILEF IXEDF IXEDSATELLITE

MOBILESAT.

F IXEDS A T

MOBILESAT.

EARTHEXPL

SAT (E-S)

EarthExpl.

Sat (s - e)SPACE

RES. (E-S)

FX-SAT(S-E)

FIXED MOBILE BROAD-CASTING

B C S TSAT.

RADIOASTRONOMY F IXED MOBILE* * FIXED

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MOBILERADIONAV.SATELLITE

F IXEDMOBILEMOB. SAT(E-S)RADIONAV.SAT.

MOBILESAT (E-S).

F IXED MOBILE F XSAT(E-S)

MOBILEF IXED

INTER- SAT EARTH EXPL-SAT (Passive)SPACE RES.

INTER- SAT SPACE RES. EARTH-ES

INTER- SATEARTH-ESSPACE RES.M O B I L EF IXEDEARTH

EXPLORATIONSAT. (Passive)

S P A C E RES.

M O B I L E F IXED INTER- SAT

F IXEDM O B I L E

INTER-SAT

RADIO-LOC.M O B I L EF IXEDEARTH


MOBILEF IXED

INTER-SATELLITEF IXEDMOBILE**

MOBILE* *INTER-

SATELLITE

M O B I L EINTER-

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Amateur Sat.AmateurRADIOLOC.AMATEUR SATAMATEURRADIOLOC.

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EARTHEXPL SAT.

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F IXED MOBILE INTER-SATELLITE

SPACERESEARCH

(Passive)

EARTHEXPL SAT.

(Passive)

AmatuerF IXED M O -BILE

INTER-SAT.

SPACERES.

E A R T H EXPL . SAT

INTER-SATELLITE

INTER-SAT.INTER-SAT.

MOBILEFIXED

FX-SAT (S - E)BCST - SAT.B- SAT.MOB** FX-SAT

SPACE RESEARCH

SPACERES..

This chart is a graphic single-point-in-tim

e portrayal of the Table of F

requency Allocations used by the

FC

C and N

TIA

. As such, it does not com

pletely reflect all aspects, i.e., footnotes and recent changesm

ade to the Table of F

requency Allocations. T

herefore, for complete inform

ation, users should consult theT

able to determine the current status of U

.S. allocations.

3

CS1

44, Stan

ford

University

U.S

. DEPA

RTM

EN

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F C

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INF

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5.685.735.90

5.95

6.2

6.525

6.6856.765

7.0

7.1

7.37.35

8.18.195

8.815

8.9659.040

9.4

9.5

9.99.99510.00310.00510.110.15

11.17511.27511.411.611.65

12.05

12.10

12.23

13.213.2613.3613.4113.5713.613.813.8714.014.2514.35

14.99015.00515.01015.10

15.615.8

16.36

17.4117.4817.55

17.917.9718.0318.06818.16818.7818.919.02

19.6819.8019.99019.99520.00520.010

21.0

21.4521.8521.92422.0

22.85523.023.223.35

24.8924.9925.005

25.0125.0725.2125.3325.5525.6726.126.17526.4826.9526.9627.2327.4127.5428.0

29.729.829.8929.9130.0

UN

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NON-GOVERNMENT EXCLUSIVE

GOVERNMENT/NON-GOVERNMENT SHAREDGOVERNMENT EXCLUSIVE

RA

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MARITIMERADIONAVIGATION(RADIO BEACONS)


3

9

14

19.95

20.05

30

30

59

61

70

90

110

130

160

190

200

275

285

300

3 k

Hz

300 k

Hz

300 k

Hz

3 M

Hz

3 M

Hz

30 M

Hz

30 M

Hz

300 M

Hz

3 G

Hz

300 G

Hz

300 M

Hz

3 G

Hz

30 G

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MARITIM

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AERONAUTICAL

RADIONAVIG

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(RADIO BEACO

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AeronauticalM

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Aeronautical Mobile RADIONAVIGATION


MARITIMEMOBILE

AeronauticalRadionavigation

MOBILE (DISTRESS AND CALLING)

MARITIME MOBILE

MARITIMEMOBILE

(SHIPS ONLY)

MOBILE



BROADCASTING

(AM RADIO

)


MARITIME MOBILE (TELEPHONY) MOBILE (DISTRESS AND CALLING)

MARITIM

EM

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LAND MO

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MO

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FIXED

STANDARD FREQ. AND TIME SIGNAL (2500kHz)

STANDARD FREQ. AND TIME SIGNAL

Space Research

MARITIM

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LAND MO

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MO

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AERONAUTICALMOBILE (OR)


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MO

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FIXED

FIXED

FIXED

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MARITIM

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MOBILE*

MOBILE*

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STANDARD FREQ. AND TIME SIGNAL (5000 KHZ)




MO

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AERONAUTICAL MOBILE (OR)FIXEDMOBILE*

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MARITIME MOBILE



FIXEDMobile


AMATEUR

FIXED

Mobile

MARITIME MOBILE

MARITIM

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FIXEDSTANDARD FREQ. AND TIME SIGNAL (10,000 kHz)STANDARD FREQ. Space Research

AERONAUTICAL MOBILE (R)AMATEUR

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Mobile*


FIXED

FIXED

BROADCASTING

MARITIMEMOBILE



RADIO ASTRONOMY

Mobile*

AMATEUR

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Mobile*FIXED

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STANDARD FREQ. AND TIME SIGNAL (15,000 kHz)STANDARD FREQ. Space Research

FIXED


MARITIMEMOBILE

AERONAUTICAL MOBILE (OR)AERONAUTICAL MOBILE (R)

FIXED

FIXED

BROADCASTING


FIXED

MARITIME MOBILE

MobileFIXED


BROADCASTINGFIXED


MARITIME MOBILE

FIXEDFIXED

FIXED

Mobile*

MOBILE**

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STANDARD FREQ. AND TIME SIGNAL (25,000 kHz)


LAND MOBILEMARITIME MOBILE

LAND MOBILE MOBILE**

RADIO ASTRONOMYBROADCASTING

MARITIME MOBILE LAND MOBILE

FIXED MOBILE**FIXED

MOBILE**

MOBILE

FIXED

FIXED

FIXEDFIXED

FIXED

LAND MOBILE

MOBILE**


MOBILE

LAND MOBILE

MOBILE

MOBILE

FIXED

FIXED

MOBILE

MOBILE

FIXED

FIXED

LANDMOBILE

LANDMOBILE

LANDMOBILE

LAND MOBILERadio Astronomy

RADIO ASTRONOMYLAND MOBILE

FIXEDFIXED

MOBILEMOBILE

MO

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LAND MOBILE

FIXED

LANDMOBILE

FIXED

FIXED

MOBILE

MOBILE

LANDM

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AMATEUR

BROADCASTING

(TV CHANNELS 2-4)

FIXED MOBILE

FIXED MOBILE

FIXED MOBILEFIXED MOBILE


BROADCASTING

(TV CHANNELS 5-6)BRO

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RADIO)

AERONAUTICAL

RADIONAVIG

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AERONAUTICAL MOBILEAERONAUTICAL MOBILE




MOBILEFIXEDAMATEUR

BROADCASTING

(TV CHANNELS 7-13)

MO

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FIXED

MO

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FIXED

MO

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FIXED

MO

BILESATELLITE

MO

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FIXED

MO

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MO

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STD. FREQ. & TIME SIGNAL SAT. (400.1 MHz)MET. SAT.

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Earth Expl.Satellite (E-S)


FIXED MOBILERADIOASTRONOMY


LAND MOBILE

Meteorological

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LAND MOBILEBROADCASTING

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BROADCASTING

(TV CHANNELS 21-36)TV BRO

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RADIO ASTRONOMY

RADIOLOCATION

FIXED

Amateur

AERONAUTICAL

RADIONAVIG

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MOBILE**FIXED


Radiolocation



Radiolocation

Radiolocation

Radiolocation

RADIO-

LOCATIO

NRADIO

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Amateur


(Ground)

RADIO-LOCATION

Radio-location

AERO. RADIO-NAV.(Ground)

FIXED SAT. (S-E)

RADIO-LOCATION

Radio-location

FIXED

FIXEDSATELLITE

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FIXED


MOBILE

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RADIO ASTRONOMY Space Research (Passive)


RADIO-LOCATION

Radio-location

RADIONAVIGATION

Radiolocation


Radiolocation

Radiolocation

RADIOLOCATIONRADIO-

LOCATION



METEOROLOGICALAIDS

Amateur

Amateur

FIXED

FIXEDSATELLITE (E-S) MOBILE


FIXEDSATELLITE (E-S)MOBILE

FIXED

FIXED

FIXED

FIXED

MOBILE

FIXED SPACE RESEARCH (E-S)FIXED

FixedMOBILESATELLITE (S-E)FIXED SATELLITE (S-E)






FIXEDSATELLITE

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SATELLITE(E-S)

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FIXED

FIXED

FIXED

FIXED

FIXED

FIXED

MET.SATELLITE (S-E)

MobileSatellite (S-E)Mobile

Satellite (S-E)

MobileSatellite (E-S)(no airborne)

Mobile Satellite(E-S)(no airborne)

Mobile Satellite (S-E)

MobileSatellite (E-S)


EARTH EXPL.SATELLITE(S-E)

EARTH EXPL.SAT. (S-E)

EARTH EXPL.SATELLITE (S-E)

MET.SATELLITE

(E-S)

FIXED

FIXED

SPACE RESEARCH (S-E)(deep space only)

SPACE RESEARCH (S-E)



Radiolocation

Radiolocation

Radiolocation


MeteorologicalAidsRADIONAVIGATION


RADIO-LOCATION

Radiolocation

Radiolocation Amateur

Amateur AmateurSatellite

RADIOLOCATIONFIXED

FIXED

FIXED

F IXED

FIXEDSATELLITE

(S-E)

FIXEDSATELLITE

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Mobile **



RADIOASTRONOMY

SPACERESEARCH (Passive)


RADIOASTRONOMY



SpaceResearch


Radio-location

RADIO-LOCATION

RADIONAVIGATION




SAT. (E-S)

FixedMobileFIXED

MobileFIXED


Space Research

Space Research


(Passive)



FIXED

F IXED MOBILE


MOBILE




EarthExploration

Satellite(S-S)

MOBILEFIXED

MOBILE

F IXEDEarth




FIXEDSATELLITE

(E-S)

MOBILESATELLITE

(E-S)


Time SignalSatellite (S-E)

Stand. Frequencyand Time SignalSatellite (S-E)

FIXED MOBILE

RADIOASTRONOMY

SPACERESEARCH

(Passive)


RADIONAVIGATION

RADIONAVIGATION INTER-SATELLITE

RADIONAVIGATION


SPACE RE..(Passive)

EARTH EXPL.SAT. (Passive)F IXED MOBILE

F IXED MOBILE

F IXED MOBILE

MobileFixed


BROAD-CASTING

B C S TSAT.

FIXED MOBILE

F XSAT(E-S)MOBILEF IXED

EARTHEXPLORATION

SATELLITEFI XED

SATELLITE (E-S)MOBILE

SATELLITE (E-S)

M O B I L EF IXED

SPACERESEARCH

(Passive)

EARTHEXPLORATION

SATELLITE(Passive)


SPACERESEARCH

(Passive)

INTER-SATELLITE

RADIO-LOCATION

SPACERESEARCH F IXED

MO

BILE

FIXE

D

MO

BILE

SATELLITE(E-S)

MOBILESATELLITE

RADIONAVIGATION


EARTHEXPLORATION

SATELLITE

FIXE

DSATELLITE

(E-S)

MOBILEFIXEDFIXEDSATELLITE (E-S)



AmateurSatelliteAmateur

RADIO-LOCATION

MOBILEFIXEDMOBILE

SATELLITE(S-E)

FIXEDSATELLITE

(S-E)

MOBILEFIXEDBROAD-CASTING

SATELLITE

BROAD-CASTING

SPACERESEARCH

(Passive)

RADIOASTRONOM

Y

EARTHEXPLORATION

SATELLITE(Passive)

MOBILE

F IXED

MOBILEFIXED RADIO-LOCATION

FIXEDSATELLITE

(E-S)

MOBILE

SATELLITE


RADIO-NAVIGATION

Radio-location



F IXEDF IXED

SATELLITE(S-E)

SPACERESEARCH

(Passive)

RADIOASTRONOM

Y

EARTHEXPLORATION

SATELLITE(Passive)

FIXED

MOBILE

MOBILEINTER-

SATELLITE

RADIO-LOCATION

INTER-SATELLITE

Radio-location

MOBILE

MOBILE

SATELLITE

RADIO-NAVIGATION



Amateur Amateur SatelliteRADIO-LOCATION

MOBILEFIXED FIXEDSATELLITE (S-E)

MOBILEFIXEDFIXED

SATELLITE(S-E)

EARTHEXPLORATION

SATELLITE (Passive)SPACE RES.

(Passive)

SPACE RES.(Passive)

RADIOASTRONOMY

FIXEDSATELLITE

(S-E)

FIXED

MOBILEFIXED

MOBILEFIXED

MOBILEFIXED

MOBILEFIXED

MOBILEFIXED


RADIOASTRONOMY

EARTHEXPLORATION

SATELLITE (Passive)


SPACERESEARCH

(Passive)INTER-

SATELLITE

INTER-SATELLITE

INTER-SATELLITE

INTER-SATELLITE

MOBILE

MOBILE

MOBILE

MOBILE

SATELLITE

RADIO-NAVIGATION


FIXEDSATELLITE

(E-S)

FIXED

FIXEDEARTH

EXPLORATION SAT.(Passive)

SPACE RES.(Passive)

SPACERESEARCH

(Passive)

RADIOASTRONOM

Y

EARTHEXPLORATION

SATELLITE(Passive)

MOBILEFIXED

MOBILEFIXED

MOBILEFIXED


FIXEDSATELLITE(S-E)



SPACE RES.(Passive)

Radio-location

Radio-location

RADIO-LOCATION

AMATEURAMATEUR SATELLITE

AmateurAmateur Satellite

EARTH EXPLORATIONSATELLITE (Passive)SPACE RES. (Passive)

MOBILE

MOBILE

SATELLITE

RADIO-NAVIGATION


MOBILE

MOBILE

FIXED

RADIO-ASTRONOMY

FIXEDSATELLITE

(E-S)

FIXED

3.03.025

3.155

3.230

3.4

3.5

4.0

4.063

4.438

4.654.7

4.75

4.85

4.9955.0035.0055.060

5.45

MARITIM

EM

OBILE

AMATEURAMATEUR SATELLITEFIXEDMobile

MARITIME MOBILE

STANDARD FREQUENCY & TIME SIGNAL (20,000 KHZ)Space Research


AMATEUR SATELLITE AMATEUR

MET. SAT. (S-E)MOB. SAT. (S-E) SPACE RES. (S-E) SPACE OPN. (S-E)MET. SAT. (S-E)Mob. Sat. (S-E) SPACE RES. (S-E) SPACE OPN. (S-E)MET. SAT. (S-E)MOB. SAT. (S-E) SPACE RES. (S-E) SPACE OPN. (S-E)MET. SAT. (S-E)Mob. Sat. (S-E) SPACE RES. (S-E) SPACE OPN. (S-E)

MO

BILE

FIXED

FIXED Land Mobile

FIXED MOBILE

LAND MOBILE

LAND MOBILE

MARITIME MOBILE MARITIME MOBILE

MARITIME MOBILE

MARITIME MOBILE

LAND MOBILE

FIXED MOBILEMOBILE SATELLITE (E-S)

RadiolocationRadiolocation

LAND MOBILEAMATEUR

MOBILE SATELLITE (E-S) RADIONAVIGATION SATELLITE


METEOROLOGICAL AIDS (RADIOSONDE)

SPACE RESEARCH (S-S)FIXED MOBILE

LAND MOBILEFIXED

LAND MOBILE

FIXEDFIXED

RADIO ASTRONOMY




Fixed

FIXED

MET. SAT.(s-E)

FIXED

FIXED







RADIO ASTRONOMY


FIXED MOBILE

FIXED

FIXED(LOS) MOBILE

(LOS)SPACE

RESEARCH(s-E)(s-s)

SPACEOPERATION

(s-E)(s-s)EARTH


Amateur


AMATEUR


FIXED SAT. (S-E)

FIXED

MO

BILE


FIXEDMOBILEFIXED

SATELLITE (E-S)

FIXEDSATELLITE

(E-S)MOBILE FIXED

SPACERESEARCH (S-E)

(Deep Space)


EARTHEXPL. SAT.(Passive)

300

325

335

405

415

435

495

505510

525

535

16051615

1705

1800

1900

2000

2065

2107

21702173.52190.52194

2495

2501

25022505

2850

3000

RADIO-

LOCATIO

N

BROADCASTING

FIXED

MO

BILE

AMATEUR

RADIOLOCATION

MOBILE FIXED MARITIMEMOBILE


MARITIMEMOBILE

LANDMOBILEMOBILEFIXED

30.0

30.56

32.0

33.0

34.0

35.0

36.0

37.037.538.038.25

39.0

40.0

42.0

43.69

46.647.0

49.6

50.0

54.0

72.0

73.0

74.674.875.275.476.0

88.0

108.0

117.975

121.9375123.0875123.5875

128.8125

132.0125

136.0

137.0137.025137.175137.825138.0

144.0146.0148.0149.9150.05

150.8152.855

154.0

156.2475157.0375157.1875157.45161.575161.625161.775162.0125

173.2173.4174.0

216.0

220.0222.0225.0

235.0

300

ISM – 6.78 ± .015 M

HzISM

– 13.560 ± .007 MHz

ISM – 27.12 ± .163 M

Hz

ISM – 40.68 ± .02 M

Hz

ISM – 24.125 ± 0.125 G

Hz30 G

Hz

ISM – 245.0 ± 1G

HzISM

– 122.5 ± .500 GHz

ISM – 61.25 ± .250 G

Hz

300.0

322.0

328.6

335.4

399.9

400.05400.15

401.0

402.0

403.0406.0406.1

410.0

420.0

450.0454.0455.0456.0

460.0462.5375462.7375467.5375467.7375470.0

512.0

608.0614.0

698

746

764

776

794

806

821824849851866869894896901901902

928929930931932935940941944960

1215

1240

1300

1350

139013921395

2000

2020

2025

2110

2155

21602180

2200

22902300230523102320

2345

2360

238523902400

24172450

2483.52500265526902700

2900

3000

140014271429.5

1430143214351525

1530

1535

1544

1545

1549.5

1558.5155916101610.61613.81626.5

16601660.51668.4

1670

1675

1700

1710

1755

1850


RADIOLOCATIONRADIONAVIGATION

SATELLITE (S-E)



RADIONAVIGATION



FIXED

FIXED**

LAND MOBILE (TLM)



Mobile(Aero. TLM)




3.0

3.1

3.3

3.5

3.6

3.65

3.7

4.2

4.4

4.5

4.8

4.94

4.99

5.0

5.155.25

5.35

5.465.47

5.6

5.65

5.83

5.855.925

6.425

6.525

6.706.875

7.0257.075

7.125

7.197.2357.25

7.30

7.45

7.55

7.75

7.90

8.025

8.175

8.215

8.4

8.45

8.5

9.0

9.2

9.3

9.5

10.0

10.45

10.510.5510.6

10.68

10.7

11.7

12.2

12.7

12.75

13.2513.4

13.7514.0

14.2

14.4

14.4714.514.7145

15.1365

15.35

15.415.43

15.6315.716.6

17.1

17.217.317.717.818.318.618.8

19.319.7

20.120.221.2

21.422.022.2122.5

22.55

23.55

23.6

24.0

24.05

24.2524.45

24.65

24.75

25.05

25.2525.527.0

27.5

29.5

29.9

30.0

ISM – 2450.0 ± 50 M

Hz

30.0

31.0

31.3

31.8

32.032.3

33.033.4

36.0

37.0

37.6

38.0

38.6

39.5

40.0

40.5

41.0

42.5

43.5

45.5

46.9

47.0

47.2

48.2

50.2

50.4

51.4

52.6

54.2555.7856.957.0

58.2

59.0

59.3

64.0

65.0

66.0

71.0

74.0

75.5

76.077.077.578.0

81.0

84.0

86.0

92.0

95.0

100.0

102.0

105.0

116.0

119.98

120.02

126.0

134.0

142.0144.0

149.0

150.0

151.0

164.0

168.0

170.0

174.5

176.5

182.0

185.0

190.0

200.0

202.0

217.0

231.0

235.0

238.0

241.0

248.0

250.0

252.0

265.0

275.0

300.0

ISM – 5.8 ± .075 G

Hz

ISM – 915.0 ± 13 M

Hz


AERONAUTICALRADIONAV.

PL

EA

SE

NO

TE

: THE

SP

AC

ING

ALLO

TTED

THE

SE

RV

ICE

S IN

THE

SP

EC

-TR

UM

SEGM

ENTS SH

OW

N IS N

OT PR

OPO

RTIO

NAL TO

THE AC

TUAL AM

OU

NT

OF SPEC

TRU

M O

CC

UPIED

.

AERONAUTICALMOBILE

AERONAUTICALMOBILE SATELLITE


AMATEUR

AMATEUR SATELLITE

BROADCASTING


EARTH EXPLORATIONSATELLITE

FIXED

FIXED SATELLITE

INTER-SATELLITE

LAND MOBILE

LAND MOBILESATELLITE

MARITIME MOBILE

MARITIME MOBILESATELLITE


METEOROLOGICALAIDS

METEOROLOGICALSATELLITE

MOBILE

MOBILE SATELLITE

RADIO ASTRONOMY

RADIODETERMINATIONSATELLITE

RADIOLOCATION

RADIOLOCATION SATELLITE

RADIONAVIGATION

RADIONAVIGATIONSATELLITE

SPACE OPERATION

SPACE RESEARCH

STANDARD FREQUENCYAND TIME SIGNAL

STANDARD FREQUENCYAND TIME SIGNAL SATELLITE

RADIO ASTRONOMY

FIXE

D

MA

RITIM

E M

OB

ILE

FIXE

D

MA

RITIM

EM

OB

ILEA

eronauticalM

obile

STANDARD FREQ. AND TIME SIGNAL (60 kHz)FIXED Mobile*

STAND. FREQ. & TIME SIG.


Space Opn. (S-E)

MOBILE.SAT. (S-E)

Fixed

StandardFreq. and


FIXED

STANDARD FREQ. AND TIME SIGNAL (20 kHz)

Amateur

MOBILE

FIXED SAT. (E-S)

SpaceResearch

ALLO

CA

TION

US

AG

E D

ES

IGN

ATIO

N

SE

RV

ICE

EX

AM

PL

ED

ES

CR

IPT

ION

Prim

aryFIX

ED

Capital

Letters

Secondary

Mobile

1st Capital w

ith lower case letters

U.S

. DE

PA

RT

ME

NT

OF

CO

MM

ER

CE

Natio

nal T

ele

co

mm

un

icatio

ns a

nd

Info

rmatio

n A

dm

inis

tratio

nO

ffice of Spectrum

Managem

ent

October 2003

MOBILE BROADCASTING

TRAVELER

S INFO

RM

ATION

STATION

S (G) AT 1610 kH

z

59-64 GHz IS DESIG

NATED FOR

UNLICENSED DEVICES

Fixed



* EXCEPT AER

O M

OBILE (R

)

** EXCEPT AER

O M

OBILE

WAVELENGTH

BANDDESIGNATIONS

ACTIVITIES

FREQUENCY

3 x 107m

3 x 106m

3 x 105m

30,000 m3,000 m

300 m30 m

3 m30 cm

3 cm0.3 cm

0.03 cm3 x 10

5Å3 x 10

4Å3 x 10

3Å3 x 10

2Å3 x 10Å

3Å3 x 10

-1Å3 x 10

-2Å3 x 10

-3Å3 x 10

-4Å3 x 10

-5Å3 x 10

-6Å 3 x 10

-7Å

010 Hz

100 Hz1 kHz

10 kHz100 kHz

1 MHz

10 MHz

100 MHz

1 GHz10 GHz

100 GHz1 THz

1013Hz

1014Hz

1015Hz

1016Hz

1017Hz

1018Hz

1019Hz

1020Hz

1021Hz

1022Hz

1023Hz

1024Hz

1025Hz

THE RADIO SPECTRUMMAGNIFIED ABOVE

3 kHz300 GHz

VERY LOW

FREQUENCY (VLF)

Audible Range AM

Broadcast FM

Broadcast Radar

Sub-Millim

eter Visible

Ultraviolet Gam

ma-ray

Cosmic-ray

Infra-sonicsSonics

Ultra-sonicsM

icrowavesInfrared

PL

SX

CRadarBands

LF M

F HF

VHF UHF

SHF EHF

INFRARED VISIBLE

ULTRAVIOLET

X-RAY G

AMM

A-RAY CO

SMIC-RAY

X-ray

ALLO

CA

TIO

NS

FR

EQ

UE

NC

Y

BROADCASTINGFIXEDMOBILE*

BROADCASTINGFIXED BROADCASTING FIXED Mobile

FIXED BROADCASTING

BROADCASTINGFIXED

FIXED

BROADCASTING


BROADCASTINGFIXED

BROADCASTING


BROADCASTINGFIXED

FIXED

FIXED

FIXEDFIXED

FIXED

LANDMOBILE

FIXED




F I X E D


F I X E D M O B I L E

LAND MOBILE MARITIME MOBILE

FIXED LAND MOBILE

FIXED

LAND MOBILE

RADIONAV-SATELLITE

FIXED MOBILE

FIXED LAND MOBILE

MET. AIDS(Radio-sonde)

SPACE OPN. (S-E)

Earth Expl Sat(E-S)

Met-Satellite (E-S)

MET-SAT. (E-S)


Earth Expl Sat(E-S)

Met-Satellite (E-S)


MET-SAT. (E-S)

LAND MOBILELAND MOBILEFIXED

LAND MOBILEFIXED

FIXED

FIXED LAND MOBILE

LAND MOBILEFIXED LAND MOBILE

LAND MOBILE LAND MOBILE

LAND MOBILE

MOBILEFIXED

MOBILEFIXED


MOBILEFIXED

FIXEDLAND MOBILE

LAND MOBILEFIXEDLAND MOBILE

AERONAUTICAL MOBILE

AERONAUTICAL MOBILEFIXEDLAND MOBILE

LAND MOBILELAND MOBILE FIXED

LAND MOBILE FIXEDMOBILE FIXED

FIXEDFIXED

MOBILEFIXED

FIXEDFIXED

BROADCAST

LAND MOBILELAND MOBILE

FIXEDLAND MOBILE

METEOROLOGICALAIDS





AMATEUR

FIXEDMOBILE



MOBILE **



MOBILE


MOBILE** FIXED

MOBILE


SPACE OP.(E-S)(s-s)



MOBILEFIXED

Mobile

R- LOC.



SPACE RES..(S-E)


MARITIME MOBILE

Mobile

FIXED

FIXED



FIXED

FIXED MARITIME MOBILE FIXED

FIXEDMOBILE**

FIXED MOBILE**

FIXED SAT (S-E)AERO. RADIONAV.


Amateur- sat (s-e)

AmateurMOBILE FIXED SAT(E-S)

F IXEDFIXED SATELLITE (S-E)(E-S)

FIXEDFIXED SAT (E-S)MOBILE

Radio-location

RADIO-LOCATION

FIXED SAT.(E-S)

Mobile**




Space Res.(act.)












F IXEDMOBILE

INTER-SATELLITE

F IXED



Radio-location



F IXED



F IXEDSATELLITE


F IXEDSATELLITE

(E-S)F IXED




e-e-sat MOBILE

SPACERESEARCH (deep space)

RADIONAVIGATIONINTER- SATSPACE RES.

F IXED MOBILE SPACE RESEARCH(space-to-Earth)

SPACERES.

F IXEDSAT. (S-E)

MOBILE F IXED

FIXED-SATELLITE

MOBILEF IXEDF IXEDSATELLITE

MOBILESAT.

F IXEDS A T

MOBILESAT.

EARTHEXPL

SAT (E-S)

EarthExpl.

Sat (s - e)SPACE

RES. (E-S)

FX-SAT(S-E)

FIXED MOBILE BROAD-CASTING

B C S TSAT.

RADIOASTRONOMY F IXED MOBILE* * FIXED

SATELLITE (E-S)



MOBILERADIONAV.SATELLITE

F IXEDMOBILEMOB. SAT(E-S)RADIONAV.SAT.

MOBILESAT (E-S).

F IXED MOBILE F XSAT(E-S)

MOBILEF IXED

INTER- SAT EARTH EXPL-SAT (Passive)SPACE RES.

INTER- SAT SPACE RES. EARTH-ES

INTER- SATEARTH-ESSPACE RES.M O B I L EF IXEDEARTH


S P A C E RES.

M O B I L E F IXED INTER- SAT

F IXEDM O B I L E

INTER-SAT

RADIO-LOC.M O B I L EF IXEDEARTH


MOBILEF IXED

INTER-SATELLITEF IXEDMOBILE**

MOBILE* *INTER-

SATELLITE

M O B I L EINTER-

SATELLITE

RADIOLOC. Amateur

Amateur Sat.AmateurRADIOLOC.AMATEUR SATAMATEURRADIOLOC.

SPACERESEARCH

(Passive)

EARTHEXPL SAT.

(Passive)

F IXED MOBILE INTER-SATELLITE

SPACERESEARCH

(Passive)

EARTHEXPL SAT.

(Passive)

AmatuerF IXED M O -BILE

INTER-SAT.

SPACERES.

E A R T H EXPL . SAT

INTER-SATELLITE


MOBILEFIXED


SPACE RESEARCH

SPACERES..

This chart is a graphic single-point-in-tim

e portrayal of the Table of F

requency Allocations used by the

FC

C and N

TIA

. As such, it does not com

pletely reflect all aspects, i.e., footnotes and recent changesm

ade to the Table of F

requency Allocations. T

herefore, for complete inform

ation, users should consult theT

able to determine the current status of U

.S. allocations.

4


Wireless Is Different

r

• Wireless transmission medium is not a wire

• Radiates over space▶ Signal weakens with distance: r2 or faster

▶ Intermediate links

• Uncontrolled medium▶ Signal strength changes over time

▶ Interference from other transmitters

5


Signal Strength

• Obstructions can further weaken signal

• Wireless signals can reflect▶ Multipath: can receive signal in multiple paths/reflections, with different delays

(analogy: echoes in a canyon)

• There is no perfectly uniform antenna

• The world is continuously changing

6


Changing Over Time

2 4 6 8 10Time in secs

-92-90-88-86-84-82-80

RSSI

0.0

0.2

0.4

0.6

0.8

1.0

PR

RReceived Signal

Strength Indicator

Packet Reception Ratio

7


A Real Network: SWAN

The Stanford Wireless Access Network (SWAN) is an 802.11b/g testbed at Stanford. It is part of a research collaboration with King Abdullah University of Science and Technology (KAUST).

2.5 secondsGates Packard

8

CS1

44, Stan

ford

University


S)

300 M

Hz

3 G

Hz

AERONAUTICALMOBILE

AERONAUTICAL AERONAUTICAL

AERONAUTICALMOBILE

AERONAUTICALMOBILE

AERONAUTICAL

FIXEDAMATEUR

FIXED

FIXED

MOBILE**FIXED


Radiolocation


F IXED

FIXEDSATELLITE

(S-E)

Mobile **



SpaceResearch


Radio-location

RADIO-LOCATION

RADIONAVIGATION




SAT. (E-S)

FixedMobileFIXED

MobileFIXED


Space Research

Space Research


(Passive)



FIXED

F IXED MOBILE


MOBILE




EarthExploration

Satellite(S-S)

MOBILEFIXED

MOBILE

F IXEDEarth




MOB. SAT. (S-E) SPACE Mob. Sat. (S-E) SPACE MOB. SAT. (S-E) SPACE Mob. Sat. (S-E) SPACE

FIXED

FIXED

FIXED

M M

MARITIME MOBI

M


LAND MOBILEAMATEUR

RADIO ASTRONOMY




Fixed

FIXED

MET. SAT.(s-E)

FIXED

FIXED







RADIO ASTRONOMY


FIXED MOBILE

FIXED

FIXED(LOS) MOBILE

(LOS)SPACE

RESEARCH(s-E)(s-s)

SPACEOPERATION

(s-E)(s-s)EARTH


Amateur


AMATEUR


FIXEDMOBILEFIXED

SATELLITE (E-S)

FIXEDSATELLITE

(E-S)MOBILE FIXED

SPACERESEARCH (S-E)

(Deep Space)


ISM – 24.125 ± 0.125 G

Hz30 G

Hz

1300

1350

139013921395

2000

2020

2025

2110

2155

21602180

2200

22902300230523102320

2345

2360

238523902400

24172450

2483.52500265526902700

2900

3000

140014271429.5

1430143214351525

1530

1535

1544

1545

1549.5

1558.5155916101610.61613.81626.5

16601660.51668.4

1670

1675

1700

1710

1755

1850



RADIONAVIGATION



FIXED

FIXED**

LAND MOBILE (TLM)



Mobile(Aero. TLM)




12.2

12.7

12.75

13.2513.4

13.7514.0

14.2

14.4

14.4714.514.7145

15.1365

15.35

15.415.43

15.6315.716.6

17.1

17.217.317.717.818.318.618.8

19.319.7

20.120.221.2

21.422.022.2122.5

22.55

23.55

23.6

24.0

24.05

24.2524.45

24.65

24.75

25.05

25.2525.527.0

27.5

29.5

29.9

30.0

ISM – 2450.0 ± 50 M

Hz

119.98

120.02

126.0

134.0

142.0144.0

149.0

150.0

151.0

164.0

168.0

170.0

174.5

176.5

182.0

185.0

190.0

200.0

202.0

217.0

231.0

235.0

238.0

241.0

248.0

250.0

252.0

265.0

275.0

300.0


StandardFreq. and


FIXEDMOBILE

FIXED SAT. (E-S)

SpaceResearch


AERONAUTICAL

F I X E D


MARITIME MOBI

FIXED

FIXED

LAND

RADIONAV-SATELLITE

FIXED

FIXED

FIXEDLAND MOBILE

METEOROLOGICALAIDS





AMATEUR

FIXEDMOBILE



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MOBILE


SPACE OP.(E-S)(s-s)



MOBILEFIXED

Mobile

R- LOC.



SPACE RES..(S-E)



Radio-location

RADIO-LOCATION

FIXED SAT.(E-S)

Mobile**




Space Res.(act.)












F IXEDMOBILE

INTER-SATELLITE

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Radio-location



F IXED



F IXEDSATELLITE


F IXEDSATELLITE

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e-e-sat MOBILE

INTER-SATELLITE


MOBILEFIXED


Interferen

ce

9


Interference

10


Overview

• Wireless networks are increasingly the last hop for personal communications▶ But generally don’t work as well

• Wireless behaves very differently from wired: many complex behaviors!▶ Signal weakens over distance

▶ Signal affected by environment

▶ Intermediate links

▶ External interference

• Different behavior leads to different protocols and algorithms

11


Wireless Media Access Control

1


Basic MAC Goals

• Arbitrate control of the channel so that:▶ One node should be able to use 100%

▶ Multiple nodes should receive a fair share

▶ High utilization under contention

2


Ethernet CSMA/CD

• On transmission:▶ Set n=0

▶ If channel is idle, transmit

▶ If channel is busy, wait until channel is idle for 96 bit times, transmit

• During transmission:▶ If no collision detected, wait 96 bit times, accept next frame for transmission

▶ If collision detected- Send a jam signal

- Choose a time t = (0, 2n) * 512 bit times

- Increment n

- Check channel again at time t

3


Problem with CSMA/CD in Wireless

• On transmission:▶ Set n=0

▶ If channel is idle, transmit

▶ If channel is busy, wait until channel is idle for 96 bit times, transmit

• During transmission:▶ If no collision detected, wait 96 bit times, accept next frame for transmission

▶ If collision detected- Send a jam signal

- Choose a time t = (0, 2n) * 512 bit times

- Increment n

- Check channel again at time t

4


Not a Shared Medium

A B C

5


Wireless: CSMA/CACarrier sense multiple access/collision avoidance

1


Link Layer Acknowledgments

A B C

2


CSMA/CA

• Pick random backoff

• Sense local channel, transmit after backoff

• If packet not acknowledged, backoff again, retry

• If packet acknowledged, accept next packet for transmission

3


802.11 CSMA/CA

• Pick a random initial wait period t

• Periodically check channel, if idle, decrement t

• When t=0, try to transmit▶ If packet received successfully (acknowledged), accept next packet for transmission

▶ If packet not received successfully, double t

▶ If t >= T, drop packet

B1, TX B2, ACKS

4


Problem 1: Hidden Terminals

A B C

5


Problem 2: Exposed Terminals

A B C D

6


Problem 3: Collision or Low SNR?

7

1

CS144



The IP Service

Nick McKeown





The Internet Protocol (IP)

TCP

IP

Data Hdr

Data Hdr

TCP Segment

IP Datagram Network

Link

Transport

Applica/on

The IP Service Model


Property Behavior

Datagram Individually routed packets.

Hop‐by‐hop rou/ng.

Unreliable Packets might be dropped.

Best effort …but only if necessary.

Connec4onless No per‐flow state.

Packets might be mis‐sequenced.

The IP Service Model (Details)

•  Tries to prevent packets looping forever.

•  Will fragment packets if they are too long.

•  Uses a checksum to reduce chances of delivering

to wrong des/na/on.

•  Allows for new versions of IP –  Currently IPv4 with 32 bit addresses

–  And IPv6 with 128 bit addresses

•  Allows for new op/ons to be added to header.


IPv4 Datagram


Flags

Version

Time to Live

“TTL”

Type of

Service

Checksum

Header

Length Total Packet Length

Packet ID Fragment Offset

Protocol ID

Source IP Address

Des/na/on IP Address

(OPTIONS) (PAD)

Bit 0

Data

Bit 31

The Hourglass Model of IP


IP

TCP UDP …

h`p smtp ssh …

Ethernet WiFi DSL …

Summary

We use IP every /me we send and receive

Internet packets.

It provides a deliberately simple service:

–  Datagram

–  Unreliable

–  Best‐effort

–  Connec/onless


<The End>



Wireless: RTS/CTSRequest-to-send/Clear-to-send

1


RTS/CTS

A B C1.

A B C2.

A B C3.

A B C4.

2


Problems with CSMA/CA

• Problem 1: Hidden terminals

• Problem 2: Exposed terminals

• Problem 3: Collision or low SNR?

3


Problem with RTS/CTS: Overhead

A B C

How long do these packets take?

Bitrate CSMA RTS/CTS Overhead

1 Mbps 0.79 0.76 4.0%

2 Mbps 1.44 1.35 6.6%

5.5 Mbps 3.36 2.89 14.1%

11 Mbps 5.89 4.42 25.1%4


Problem with RTS/CTS: Overhead

A B C

Bitrate CSMA RTS/CTS Overhead

1 Mbps 0.79 0.76 4.0%

2 Mbps 1.44 1.35 6.6%

5.5 Mbps 3.36 2.89 14.1%

11 Mbps 5.89 4.42 25.1%5


802.11 Format and Overhead

1


Example 802.11n

MCS

Data Rate (Mta Rate (Mbps)

MCSIndex

SpatialStreams Modulation Coding

20MHz ChaHz Channel 40 MHz ChaMHz ChannelMCSIndex

SpatialStreams Modulation Coding 800ns GI 400ns GI 800ns GI 400ns GI

0 1 BPSK 1/2 6.5 7.2 13.5 15.0

1 1 QPSK 1/2 13.0 14.4 27.0 30.0

2 1 QPSK 3/4 19.5 21.7 40.5 45.0

3 1 16-QAM 1/2 26 28.9 54.0 60.0

4 1 16-QAM 3/4 39 43.3 81.0 90.0

5 1 64-QAM 2/3 52 57.8 108.0 120.0

6 1 64-QAM 3/4 58.5 65.0 121.5 135.0

7 1 64-QAM 5/6 65 72.2 135.0 150.0

2


802.11 (WiFi)

Basic challenge: support wide range and extensible bitrates

3


802.11 (WiFi)

Physical

Link

Network

Transport

Session

Presentation

Application

Basic challenge: support a wide range of and extensible bitrates

4


802.11b PHY

sync SFD signal service length link frame

128 16 8 8 16

bits

1111... ...0000

CRC

16

Physical

Link

Network

Transport

Session

Presentation

Application

Scrambled by PHY

5


802.11 MAC

Physical

Link

Network

Transport

Session

Presentation

Application

Scrambled by PHY

frame control duration addr 1 addr 2 addr 3 network data

2 2 6 6 6

seq no.

6

FCS

4

addr 4

2

bytes


128 16 8 8 16

bits

1111... ...0000

CRC

16

6


Virtual Carrier Sense

Physical

Link

Network

Transport

Session

Presentation

Application

Scrambled by PHY


2 2 6 6 6

seq no.

6

FCS

4

addr 4

2

bytes


128 16 8 8 16

bits

1111... ...0000

CRC

16

7


Virtualizing a Link


2 2 6 6 6

seq no.

6

FCS

4

addr 4

2

bytes

8


802.11 Overhead


128 16 8 8 16

bits

1111... ...0000

CRC

16

Physical

Link

Network

Transport

Session

Presentation

Application

Scrambled by PHY

1Mbps 600Mbps

9


802.11 Summary

• Basic MAC format to work on top of many physical layers

• Needs backwards compatibility▶ Use time, rather than bytes

• MAC control (virtual carrier sense) specified in terms of duration

• Virtualizes the link▶ Embed additional addresses

• Don’t be fooled by 600Mbps!

10


Network Address Translation

1


Strong End-to-End

• “The network's job is to transmit datagrams as efficiently and flexibly as possible. Everything else should be done at the fringes.”

171.64.15.55 157.166.226.26

Internet

2


Network Address Translator (NAT)RFC1631

171.64.15.55 157.166.226.26

Internet

3


NAT Example

10.1.1.9

NAT(128.34.22.8)

NAT(76.18.117.20)

10.0.0.101

A B

18.181.0.31

S

sshd (22)

4


How a NAT Works

NAT(128.34.22.8)

10.0.0.101

A

18.181.0.31

S

5


Types of NATs

6


NAT Internal Mapping

NAT(128.34.22.8)

10.0.0.101

A18.181.0.31

S

10.0.0.101

4512

18.181.0.31

10.0.0.101

80 4512

18.181.0.31

128.34.22.8

80 6641

128.34.22.8

6641

7


Two Questions

• What packets does a NAT allow to traverse mappings?

• How and when does a NAT assign mappings?

• NAT terminology/classification in RFC3489

8


Full Cone NAT

NAT(128.34.22.8)

10.0.0.101

A18.181.0.31

S

10.0.0.101

4512

18.181.0.31

10.0.0.101

80 4512

18.181.0.31

128.34.22.8

80 6641

128.34.22.8

6641

9


Restricted Cone NAT

NAT(128.34.22.8)

10.0.0.101

A18.181.0.31

S

18.181.0.31

10.0.0.101

80 4512

18.181.0.31

128.34.22.8

80 6641

10.0.0.101

4512

18.181.0.31

128.34.22.8

6641

10


Port Restricted NAT

NAT(128.34.22.8)

10.0.0.101

A18.181.0.31

S

10.0.0.101

4512

18.181.0.31

128.34.22.8

80 6641

18.181.0.31

10.0.0.101

80 4512

18.181.0.31

128.34.22.8

80 6641

11


Symmetric NAT

NAT(128.34.22.8)

10.0.0.101

A

18.181.0.31

S10.0.0.101

4512

18.181.0.31

10.0.0.101

3311 4512

18.181.0.31

128.34.22.8

3311 6641

18.181.0.32

S’18.181.0.32

128.34.22.8

3311 9821

10.0.0.101

4512

12


NAT Behavioral Recommendations

• More complications: static mappings, triggers, more complex behaviors

• TCP recommendations: RFC5382

• UDP recommendations: RFC4787

• Hairpinning: packet from internal address to external address translated properly (internal mapped to external)

13


Hairpinning Example

10.0.0.101

A

10.0.0.99

B

NAT(128.34.22.8)

switch

10.0.0.101

4512

128.34.22.8

6641

14


NAT Implications

15


Applications: Incoming Connections

NAT(128.34.22.8)

10.0.0.101

A18.181.0.31

S

10.0.0.101

4512

18.181.0.31

10.0.0.101

80 4512

18.181.0.31

128.34.22.8

80 6641

128.34.22.8

6641

18.181.0.32

B

sshd

16


Connection Reversal

10.0.0.101

A

192.168.2.5

B

18.181.0.31

R

NAT

17


Relays

10.0.0.101

A

192.168.2.5

B

18.181.0.31

R

NAT NAT

18


Applications: NAT Hole-Punching

NAT(128.34.22.8)

NAT(76.18.117.20)

Server(18.181.0.31)

Client A(10.0.0.101)

Client B(10.1.1.9)

19


Transport: No New Transport!

NAT(128.34.22.8)

10.0.0.101

A18.181.0.31

S

10.0.0.101

4512

18.181.0.31

10.0.0.101

80 4512

18.181.0.31

128.34.22.8

80 6641

128.34.22.8

6641

20


NAT Debate

• Tremendously useful▶ Reuse addresses

▶ Security (not opening connections can be good!)

• Tremendously painful▶ Large complication to application development

▶ Speak Freely (pre-Skype VoIP!)

• Debate interesting but pointless: NATs are here to stay

21


The New Hourglass

IP

ICMP TCP UDP

Link and Below

Session and Above

22


NAT Operation Details

23


NAT Internal Mapping

NAT(128.34.22.8)

10.0.0.101

A18.181.0.31

S

10.0.0.101

4512

18.181.0.31

10.0.0.101

80 4512

18.181.0.31

128.34.22.8

80 6641

128.34.22.8

6641

24


UDP

• RFC4787

25


TCP

• RFC5382

26

1 1 1

CS144



The TCP and UDP Service Models


Nick McKeown


2 2 2

Outline

TCP Service Model

UDP Service Model


3 3 3

Transmission Control Protocol (TCP)

Network

Link

Transport

Applica/on

TCP Data Hdr TCP Segment

Bytes

4 4 4



Network

Link

Transport

Applica/on

Network

Link

Transport

Applica/on

Network

Link

Network

Link

B A

5 5 5

The TCP Service Model


Property Behavior

Stream of bytes Byte delivery service.

Connec0on oriented 3‐way handshake for connec/on setup.

Reliable delivery 1.  Acknowledgments indicate delivery.

2.  Checksums detect corrupted data.

3.  Sequence numbers detect missing data.

4.  Flow‐control prevents overrunning

receiver.

In‐sequence Data delivered to applica/on in sequence

transmiTed.

(Conges0on Control Controls network conges/on.)

6 6 6

TCP “stream of bytes” service

Byte 0 Byte 1 Byte 2 Byte 3


Byte 80

Byte 80

A

B

7 7 7

…emulated using TCP “segments”



Byte 80

Byte 80

A

B

8 8 8

The TCP Segment Format

IP Hdr

IP Data

TCP Hdr TCP Data

Source port

Sequence # (of first byte)

Acknowledgment Sequence # Flags

Checksum

HLEN RSVD

URG

ACK

PSH

RST

SYN

FIN Window Size

Urgent Pointer

(TCP Op/ons)

TCP Data

Bit 0 Bit 31

Des/na/on port

9 9 9

Connec/on oriented:

3‐way handshake

Connec/on Setup

3‐way handshake

Client Server

Syn

Syn + Ack

Ack

Connec/on Close/Teardown

2 x 2‐way handshake

Client Server

Fin

(Data +) Ack

Fin

Ack

10 10 10

TCP: Port Demul/plexing

Web

client

Web

Server

Mail

Server

A B

TCP

IP

Mail

client

11 11 11

Ini/al Sequence Numbers

Connec/on Setup

3‐way handshake

Client Server

Syn +ISNA

Syn + Ack +ISNB

Ack

12 12 12

Sequence Numbers

A

B

ISN (ini/al sequence number)

TCP Data

TCP Data

TCP

HDR

TCP

HDR

Sequence number

= 1st byte Ack sequence

number = next

expected byte

13 13 13

TCP Sliding Window

We will learn about several features of TCP in

later lectures:

– Window‐based flow control

– Conges/on control

– Retransmission and /meouts

14 14 14

Outline

TCP Service Model

UDP Service Model


15 15 15

User Datagram Protocol (UDP)

Property Behavior

Connec0onless

Datagram Service

No connec/on established.

Packets may show up in any order.

Self contained

datagrams

Unreliable delivery 1.  No acknowledgments.

2.  Checksum covers header, not data.

3.  No mechanism to detect missing or mis‐

sequenced data.

4.  No flow control.

16 16 16

The UDP Datagram Format

IP Hdr

IP Data

UDP Hdr UDP Data

Source port

Checksum Length

UDP Data

Bit 0 Bit 31

Des/na/on port

17 17 17

UDP: Port Demul/plexing

Process

1

A B

UDP

IP

Process

2

Process

1

Process

2

18 18 18

Summary

TCP provides in‐order, reliable delivery of a

stream of bytes between applica/on processes.

UDP provides a simpler, datagram delivery

service between applica/on processes.


19 19 19

<The End>


1 1 1

CS144



The Internet Control Message Protocol

(ICMP) Service Model


Nick McKeown



2 2 2

Making the Network Layer Work

1.  The Internet Protocol (IP)

–  The crea/on of IP datagrams.

–  Hop‐by‐hop delivery from end to end.

2.  Rou/ng Tables

–  Algorithms to populate router forwarding tables

3.  Internet Control Message Protocol (ICMP)

–  Communicates network layer informa/on

between end hosts and routers

–  Reports error condi/ons

–  Helps us diagnose problems CS144, Stanford University

3 3 3

ICMP runs above the Network Layer

Network

Link

Transport

Applica/on

ICMP Data Hdr ICMP Message

Informa/on about the

network layer

4 4 4

An example


Network

Link

Transport

Applica/on

Network

Link

Transport

Applica/on

Network

Link

B A

5 5 5

The ICMP Service Model


Property Behavior

Repor&ng Message Self‐contained message repor/ng error.

Unreliable Simple datagram service – no retries.

6 6 6

(Some) ICMP Message Types

ICMP Type ICMP Code Descrip<on

0 0 Echo Reply (used by ping)

3 0 Des/na/on Network Unreachable

3 1 Des/na/on Host Unreachable

3 3 Des/na/on Port Unreachable

8 0 Echo Request (used by ping)

11 0 TTL Expired (used by traceroute)


RFC 792

7 7 7

How “ping” uses ICMP

A B

8 8 8

How “traceroute” uses ICMP

A B

9 9 9

Summary

ICMP provides informa/on about the network

layer to end hosts and routers.

It sits above IP and is therefore strictly a

transport layer mechanism.

The commonly used tools “ping” and

“traceroute” both rely on ICMP.




Network Application Examples

1


Network Applications

• Read and write data over network▶ Web browser, web server

▶ Skype clients

▶ BitTorrent clients

• Dominant model: TCP byte stream▶ One side writes, other reads

2

Internet


Byte Stream Model

3

Internet


World Wide Web (HTTP)

4

Internet

Client Server


Skype

5

Internet

Client Client


Skype with Complications

6

Internet

Client ClientNAT


Skype with Complications

7

Internet

Client Client

Rendezvous

NAT


Skype with More Complications

8

Internet

Client ClientNATNAT


Skype with More Complications

9

Internet

Client ClientNATNAT

Relay


BitTorrent

10

Internet

Client

Tracker

ClientClient Client

Client

Client


Byte Stream Model

• Building block of most applications today▶ Other models exist: datagrams, real-time data streams

• Abstracts away entire Internet -- just a pipe between two processes▶ Does so on top of unreliable, “best effort” Internet

• In the Internet, almost always Transmission Control Protocol (TCP)

• Application level controls communication pattern and payloads▶ World Wide Web (HTTP)

▶ Skype

▶ BitTorrent

11


More Reading

• Skype: “An Analysis of the Skype Peer-to-Peer Internet Telephony Protocol.” Salman A. Baset and Henning G. Schulzrinne

• BitTorrent: Wikipedia, also http://wiki.theory.org/BitTorrentSpecification

12


Life of a Packet

1


Byte Stream Model

2

Internet


Byte Stream Model

• Building block of most applications today▶ Other models exist: datagrams, real-time data streams

• Abstracts away entire Internet -- just a pipe between two processes▶ Does so on top of unreliable, “best effort” Internet

• In the Internet, almost always Transmission Control Protocol (TCP)

• Application level controls communication pattern and payloads▶ World Wide Web (HTTP)

▶ Skype

▶ BitTorrent

3


TCP Byte Stream

4

Internet

Client Server


TCP Byte Stream

5

Internet

Client Server

address: 171.67.76.157port: 23946

address: 74.125.127.103port: 80


Inside the Stream

6

Client Server

Routers

address: 171.67.76.157port: 23946

address: 74.125.127.103port: 80


Inside Each Hop

7

dest linkdefault 1171.33.x.x 523.x.x.x 228.33.5.x 4171.32.x.x 267.x.x.x 6216.x.x.x 1

⑥

⑤

④ ③

②

①

address: 216.239.47.186


Under the Hood

• Request web page from www.cs.brown.edu

• Use wireshark to see TCP byte stream establishment and data exchange

• Use traceroute to see route packets take through Internet

8

1

CS144



4 Layer Model

Nick McKeown




2


Network

Link

Transport

Applica/on


3


Network

Link

Transport

Applica/on

Network

Link

Transport

Applica/on

Network

Link

Network

Link


B A

4

Encapsula/on


Network

Link

Transport

Applica/on

A

Network

Link

5


Network

Link

Transport

Applica/on

Network

Link


B

A few last words…




Network

Link

Transport

Applica/on




Applica/on

Presenta/on

Session

Transport

Network

Link

Physical


Network

Link

Transport


Applica/on h-p

ASCII

IP

TCP

Ethernet

<The End>
