CS-435 Network Technology & Programming …hy435/material/CS435-lecture10.pdfCS-435 Network...
Transcript of 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
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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)
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Convergence of wireless
telecommunications
Telecommunications
Computer information
Consumer Entertainment
BEFORE
TODAY
Telecommunications
Computer information
Consumer Entertainment
FUTURE
Telecommunications
Computer information
Consumer Entertainment
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Frequency Bands
• Industrial, Scientific, and Medical (ISM) bands
• Unlicensed, 22 MHz channel bandwidth
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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.
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Ex.
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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
The Elements of a wireless
network
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
The Elements of a wireless
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
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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):
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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.
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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)
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
IEEE 802.11 Wireless:
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)
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
IEEE 802.11 Wireless:
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)
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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)
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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.
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
RTS-CTS exchange
APA B
time
DATA (A)
reservation collision
B defers
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
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