CS-435 Network Technology & Programming …hy435/material/CS435-lecture10.pdfCS-435 Network...

Network Technology & Programming LaboratoryCS-435spring semester 2016

Stefanos Papadakis & Manolis SpanakisUniversity of Crete

Computer Science Department

<CS-435> Network Technology and Programming Laboratory

CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016

CS-435

• Lecture preview

• Wireless Networking

• IEEE 802.11



Exciting developments….

• Personal computer systems market growing rapidly today

• Laptop, Net-books, PDAs, Tablets, Smart-phones

• Wireless telecommunications grow rapidly too

• Cellular communication systems

• (2G/3G/ 4G…is coming)

• Need not to be used only for voice/video but also data transmissions

• Wireless LANs (WLANs)

• public places, universities, airports, hotels, city areas, coffee houses, etc.

• Short range wireless systems usage grows

• Bluetooth, UWB, WUSB, Zigbee, WiMAX

New services and applications demand wireless internetworking

systems (i,e, AmI services, smart spaces, gamming, etc)



Convergence of wireless

telecommunications

Telecommunications

Computer information

Consumer Entertainment

BEFORE

TODAY

Telecommunications



FUTURE

Telecommunications





Evolution …

• Wireless systems yesterday• 2G Cellular: ~30-70 Kbps.• WLANs: ~10 Mbps.

• Wireless systems today • 3G Cellular: ~300-3600 Kbps.

• WLANs: ~70 Mbps.

• Next Generation• 4G• Mesh Networks• LTE

• Desired features :• Always on

• Accessible: Anytime, anywhere

• Voice and multimedia

• Intuitive and simple

• Secure, trusted and reliable

• Technology Enhancements : • Hardware:

• Better batteries.

• Better circuits/processors

• Link: • Antennas

• Modulation

• Coding

• Adaptivity

• Bandwidth

• Network: • Dynamic resource allocation.

• Mobility support



Wireless Market Segments

Fixed Mobile

Broadband Multiservice

2G+

Cellular

3G

Cellular

Residential/

Premise/ Campus

LMDSMMDS Data

Services

GPRS

Mobile IP

Packet

Data/Voice

UMTS

BLUE

TOOTH

IEEE

802.11

Wireless Internetworking

Overview



Frequency Bands

• Industrial, Scientific, and Medical (ISM) bands

• Unlicensed, 22 MHz channel bandwidth



Standardization of Wireless

Networks (IEEE 802 LAN MAN standards committee)

Application

Presentation

Session

Transport

Network

Data Link

Physical

ISO

OSI

7-layer

modelLogical Link Control

Medium Access (MAC)

Physical (PHY)

IEEE 802.11x

standards



IEEE 802.11 Overview

• Adopted in 1997.

Defines:

• MAC sub-layer

• MAC management

protocols and services

• Physical (PHY) layers

• IR

• FHSS

• DSSS

Goals

To deliver services in

wireless networks

To achieve high throughput

To achieve secure

communications

To achieve highly reliable

data delivery

To achieve continuous

network connection.



IEEE 802.11 Overview

• Components• Mobile station (MS)

• BSS - Basic Service Set

• IBSS : Infrastructure BSS :

QBSS

• ESS - Extended Service Set

• A set of infrastructure BSSs.

• Connection of APs

• Tracking of mobility

• DS – Distribution System

• AP communicates with

another

•Services• Station services

• authentication • de-authentication• privacy• delivery of data

• Distribution Services• Association• Disassociation• Re-association• Distribution• Integration



Ex.



network

infrastructure

: Wireless hosts

• laptop, Tablet, SmartPhon, etc

• End clients running applications

• may be mobile or fixed

(immobile)

• wireless does not always

mean mobility

The Elements of a wireless

network



network

infrastructure

: Base Stations• connected to wired network

• Relay-responsible for sending

packets between wired network

and wireless host(s) in its

“coverage area”

• e.g: cell towers 802.11 access

points

• handoff: mobile

changes base

station providing

connection into

wired network


network




network

network

infrastructure

: Wireless Link• Typically used to connect end

stations to base station

• Can also be used as

backbone link

• multiple access protocol

coordinates link access

• various data rates,

transmission distances



The Infrastructure-less Wireless paradigm:

Wireless Ad Hoc Networking

• Peer-to-peer communications.

• No base stations required

• nodes communicate only to other

nodes in proximity

• Self organizing network

• No backbone infrastructure required

• Dynamic network topology

• Routing can(or must) be multi-hop,

distributed and performed by the

networking nodes

• Heavily constrained

• Battery resources

• Radio Resources

• Computational capabilities

• Storage abilities



The Infrastructure-less Wireless paradigm:

Wireless Ad Hoc Networking

Design issues: • Capacity generally unknown

• Transmission, access, and routing strategies are generally ad-hoc.

• Cross-layer design critical and

challenging

• Energy constraints impose design tradeoffs for communication and networking

• Emerging application domain,

• Flexible network infrastructure

• Still unknown



A special Case: Sensor

Networks.• Application specific networks

• Monitoring

• Safety

• Event Detection

• Lots of tiny inexpensive devices

(not always)

• Key Differences:

• Gateways / Processing nodes

• Connection to some

infrastructure

• Bottlenecks



Some well known link layer

standards

384 Kbps

56 Kbps

54 Mbps

5-11 MbpsHSDPA

1 Mbps802.15

802.11b

802.11{a,g}

IS-95 CDMA, GSM

UMTS/WCDMA, CDMA2000

802.11 p-to-p links

2G

3G

Indoor

10 – 30m

Outdoor

50 – 200m

Mid range

outdoor

200m – 4Km

Long range

outdoor

5Km – 20Km

Rate

3G+

270 Mbps 802.11n



Wireless Link Characteristics

Differences from wired links…• the signal strength: radio signal attenuates as it

propagates in space (path loss)

• interference: from other sources: standard wireless

network frequencies • e.g., 2.4 GHz: shared by other devices (e.g., phone); devices

(motors) interfere as well

• e.g., 5 GHz: Radars

• multipath propagation: radio signal bounces off from

different objects and surfaces (i.e, the ground, buildings,

etc), arriving at the destination at slightly different times

• ….make communication across (even for point to

point) wireless links more challenging



A B

C

Hidden terminal problem

• B, A hear each other

• B, C hear each other

• A, C can not hear each other

means A, C unaware of their

interference at B

A B C

A’s signalstrength

space

C’s signalstrength

Due to Signal fading:

• B, A hear each other

• B, C hear each other

• A, C can not hear each other

interfering at B

Multiple wireless senders and receivers create additional problems (not just

the multiple access ones):

Wireless Link Characteristics



Wireless network

characteristics

A B C D

Exposed terminal problem

- B hears the transmission

on C ➔ D

- Assumes channel is busy

- Defers from accessing the channel to avoid collisions

- A could well accept any transmission from B…

Multiple wireless senders and receivers create additional problems (not just

the multiple access ones):



IEEE 802.11 family The IEEE 802.11 is a standard introduced by IEEE in June 1997 used for wireless Ethernet networks.

Below is a listing of each of the wireless IEEE standards currently available. Home users should only be

concerned about 802.11a, 802.11b, or 802.11g for their home wireless network.

Standard Description

IEEE 802.11 The initial release of the standard capable of transmissions of 1 to 2 Mbps and operates in the

2.4 GHz band.

IEEE 802.11a Capable of transmissions of up to 54 Mbps and operates in the 5 GHz band.

IEEE 802.11b Introduced in 1999, 802.11b is capable of transmissions of up to 11 Mbps and operates in the

2.4 GHz band.

IEEE 802.11c Defines wireless bridge operations

IEEE 802.11d Defines standards for companies developing wireless products in different countries.

IEEE 802.11e Defines enhancements to the 802.11 MAC for QoS.

IEEE 802.11f Defines Inter Access Point Protocol (IAPP)

IEEE 802.11g Capable of transmissions of up to 20 Mbps and operates in the 2.4, 3.6 and 5 GHz bands.

IEEE 802.11i Improved encryption (WPA).

IEEE 802.11j 802.11 extension used in Japan.

IEEE 802.11n Operates using the 2.4GHz and 5GHz bandwidths. It utilizes multiple-input, multiple-output (MIMO)

antennas to improve data transfer speeds.



IEEE 802.11 Wireless :

LAN the 3 household names

802.11b• 2.4GHz unlicensed radio spectrum

• up to 11 Mbps

• direct sequence spread spectrum (DSSS) in

physical layer

• all hosts use same chipping code

• widely deployed, using base stations

802.11a • 5-6GHz range

• up to 54 Mbps

802.11g • 2.4GHz range

• up to 54 Mbps

All protocols use: CSMA/CA for multiple

access

All protocols can operate in:

Infrastructure or ad-hoc mode



IEEE 802.11 Wireless:

is there more?• IEEE 802.11 - THE WLAN STANDARD was original 1 Mbit/s and 2 Mbit/s, 2.4 GHz RF and infrared [IR]

standard (1997), all the others listed below are Amendments to this standard, except for Recommended

Practices 802.11F and 802.11T.

• IEEE 802.11a - 54 Mbit/s, 5 GHz standard (1999, shipping products in 2001)

• IEEE 802.11b - Enhancements to 802.11 to support 5.5 and 11 Mbit/s (1999)

• IEEE 802.11c - Bridge operation procedures; included in the IEEE 802.1D standard (2001)

• IEEE 802.11d - International (country-to-country) roaming extensions (2001)

• IEEE 802.11e - Enhancements: QoS, including packet bursting (2005)

• IEEE 802.11F - Inter-Access Point Protocol (2003) Withdrawn February 2006

• IEEE 802.11g - 54 Mbit/s, 2.4 GHz standard (backwards compatible with b) (2003)

• IEEE 802.11h - Spectrum Managed 802.11a (5 GHz) for European compatibility (2004)

• IEEE 802.11i - Enhanced security (2004)

• IEEE 802.11j - Extensions for Japan (2004)




is there more?• IEEE 802.11-2007 - A new release of the standard that includes amendments a, b, d, e, g, h, i & j. (July

2007)

• IEEE 802.11k - Radio resource measurement enhancements (2008)

• IEEE 802.11l - (reserved and will not be used)

• IEEE 802.11m - Maintenance of the standard. Recent edits became 802.11-2007. (ongoing)

• IEEE 802.11n - Higher throughput improvements using MIMO (multiple input, multiple output antennas)

(November 2009)

• IEEE 802.11o - (reserved and will not be used)

• IEEE 802.11p - WAVE - Wireless Access for the Vehicular Environment (such as ambulances and

passenger cars) (working - 2009?)

• IEEE 802.11q - (reserved and will not be used, can be confused with 802.1Q VLAN tagging)

• IEEE 802.11r - Fast roaming Working "Task Group r" - (2008)

• IEEE 802.11s - Mesh Networking, Extended Service Set (ESS) (working - Jul 2010?)

• IEEE 802.11T - Wireless Performance Prediction (WPP) - test methods and metrics Recommendation

(2008)




is there more?

• IEEE 802.11u - Interworking with non-802 networks (for example, cellular) (proposal evaluation - Mar

2010?)

• IEEE 802.11v - Wireless network management (early proposal stages - Sept 2010?)

• IEEE 802.11w - Protected Management Frames (early proposal stages - 2009?)

• IEEE 802.11x - (reserved and will not be used, can be confused with 802.1x Network Access Control)

• IEEE 802.11y - 3650-3700 MHz Operation in the U.S. (2008)

• IEEE 802.11z - Extensions to Direct Link Setup (DLS) (Aug 2007 - Dec 2011)

• IEEE 802.11aa - Robust streaming of Audio Video Transport Streams (Mar 2008 - May 2011)

• IEEE 802.11ac - Very High Throughput <6GHz (Sep 2008 - Dec 2014)

• IEEE 802.11ad - Extremely High Throughput 60GHz (Dec 2008 - Dec 2014)



802.11

Channels: 802.11b: 2.4GHz-2.485GHz• Spectrum divided into 11 channels at different frequencies

• AP admin chooses frequency (channel) for AP

• interference possible: frequency can be neighboring to the

one chosen by neighboring AP…!!!

• Association: Host must associate with an AP• Scans channels,

• Listening for beacon frames containing AP’s SSID

(Service Set Id) & MAC address

• Selects AP to associate with

• Perform authentication (if necessary)

• Run DHCP to get IP address in AP’s subnet (if required)



IEEE 802.11 MAC Protocol: CSMA/CA

Why CA and not CD (like Ethernet)?

Collision detection mechanisms are a good idea for

a wired LAN but they cannot be used in Wireless

LANs because: 1) A collision detection mechanism would require the

implementation of a Full Duplex radio capable of transmitting

and receiving simultaneously

2) On a wireless environment we cannot assume that all stations

“hear/see” each other (proprietary assumption for CD

schemes)

3) When a station wishes to transmits and senses the wireless

medium does not necessarily means that the medium is

actually idle.



IEEE 802.11 MAC Protocol: CSMA/CA

802.11 sender• If channel sensed idle for DIFS then

• transmit entire frame (no CD)

• If sensed channel busy then • start random back-off:

• timer counts down while sensing channel

• As long as channel idle then: transmit when timer expires

• Otherwise increase random back-off interval …up to?

• When all else fails after a maximum number of failed

retries send packet anyways.

802.11 receiver• If frame received OK

• Wait for SIFS (why??)

• return ACK after ACK needed also due to hidden

terminal problem

sender receiver

DIFS

data

SIFS

ACK



Avoiding collisions (the ‘CA’ part in CSMA/CA)

• Allow sender to “reserve” channel rather than

random access of data frames

• avoid collisions of long data frames

1. Sender first transmits a small request-to-send (RTS) packets

to BS using CSMA• RTSs may still collide with each other

(but they’re short ➔ chances are slim for RTS collisions)

2. BS broadcasts clear-to-send CTS in response to RTS

3. CTS heard by all nodes

4. Sender transmits data frame• Other stations defer transmissions



RTS-CTS exchange

APA B

time

DATA (A)

reservation collision

B defers



frame

controlduration

address

1

address

2

address

4

address

3payload CRC

2 2 6 6 6 2 6 0 - 2312 4

seq

control

802.11 frame: addressing

Address 2: MAC address

of wireless host or AP transmitting this frame

Address 1: MAC addressof wireless host or APto receive this frame Address 3: MAC address

of initial transmitter or final recipient

Address 4: used only in ad hoc mode



Internet

AP

host1 R1

AP MAC host1 MAC R1 MAC

address 1 address 2 address 3

802.11 frame

R1 MAC AP MAC

dest. address source address

802.3 frame

802.11 frame: addressing



frame

controlduration

address

1

address

2

address

4

address

3payload CRC

2 2 6 6 6 2 6 0 - 2312 4

seq

control

TypeFrom

APSubtype

To

AP

More

fragWEP

More

data

Power

mgtRetry Rsvd

Protocol

version

2 2 4 1 1 1 1 1 11 1

duration of reserved transmission time (RTS/CTS)

frame seq #

frame type(RTS, CTS, ACK, data)

802.11 frame: more

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