Introduction to the communication technologies

The Open System Interconnection (OSI) model

The OSI model (cont)

Layer Description Ex.

Application Interaction with the software application FTP

Presentation Data format conversion XDR

Session Connection management SIP

Transport Transfer of data and reliability TCP, UDP

Network Addressing between a source and a destination via one network ore more

IP

Data Link Access medium management, error detection and correction

IEEE 802.3

Physical Specifications to access the medium Signal processing

Network Classification

• Categorization by range➢ WAN➢ MAN➢ LAN➢ PAN➢ BAN

• Categorization by network topology• ...

Network Classification (cont)

The WSI Reference Model for the Wireless World

The new vision of the Wireless World

• The multi sphere model➢ Human is the center of the

services

• Proposed by the Wireless Strategic Initiative➢ Initial partners: Alcatel,

Ericsson, Nokia, Siemens➢ In 2001, it became the

Wireless World Research Forum

The MultiSphere Model

• 6 spheres➢ PAN➢ The Immediate

Environment➢ Instant Partners➢ Radio Accesses➢ Interconnectivity➢ CyberWorld

(Community Area Network)

Building Blocks of the Wireless World

1. Augmented Reality/Cyberworld

2. Semantic Aware Services

3. Peer Discovery

4. End-to-End security and Privacy

5. Co-operative Networks and Terminal

6. Heterogeneous Ad-hoc networking

7. Radio Interfaces

8. Smart Antennas and Base Stations

9. Software Defined Radio

The Communication Element (CE)

Four blocks:

The IEEE 802 Project

Introduction to the IEEE model

• IEEE is the world’s largest professional association dedicated to advancing technological innovation in electricity electronic

• 802 Project➢ Project began in February 1980➢ Standards for LANs and MANs (network with variable-size

packets)➢ Define the Physical and Link Layer of the OSI model developed

by the ISO (International Organization for Standardization)➢ The Link Layer is divided in 2 sub-layers

The Logical Link Control (LLC): IEEE 802.2 The Media Access Control (MAC): IEEE 802.3 (Ethernet), IEEE 802.4

(Token Bus), IEEE 802.5 (Token Ring)

Introduction to the IEEE model (cont)

Applciation Layer

Presentation Layer

Session Layer

Transport Layer

Network Layer

Data Link Layer

Pjysical Layer

ISO

Logical Link Control

Media Access Control

Physical Signal

Transmission Medium

Upper Layers

The OSI model and LAN protocols

The MAC Address

• 48 bits Address

• Composed by 2 parts:➢ 0rganizationally Unique Identifier

(OUI): 3 most significant bytes (see RFC1700 for a list)

➢ Network Interface Controller (NIC) Specific: 3 less significant bytes

• Ex. 12-34-56-78-9A-BC➢ Canonical Format

01001000 00101100 01101010 00011110 01011001 00111101

➢ Non-Canonical Format 00010010 00110100 01010110

01111000 10011010 10111100

The MAC Address (cont)

The Ethernet Case

A little bit of history

• IEEE 802.3 Standards for wired Ethernet networks➢ Beginning 70s, the University of Hawaii propose the Aloha

Protocol Communication between different islands Collision of frames 2400bps

➢ In 1973, Xerox PARC propose a new standard Coaxial cable 3Mbps

➢ In 1976, DIX (DEC, Intel and Xerox) allow Ethernet to become an open standard

10Mbps

➢ 1985, the IEEE 802.3 standard is officially published Allow the implementation of several nodes (CSMA/CD)

The CSMA/CD protocol

• Carrier Sense Multiple Access with Collision Detection

The CSMA/CD protocol (cont)

• The principle is “when a host detects a collision, all the others computers in the LAN should detect it”

• The Slot time (TS) is defined like the twice of the time needed by a signal to travel the length of the maximum theoretical distance between two nodes

• In Ethernet the TS = 51,2μs, which represents 512bits at 10Mbps

• Considering that the speed of electricity in a copper cable is 200,000,000 m/s, what is the maximum theoretical length of a network using this technology?

• Length of frames must be equal or higher than the TS➢ Add a padding if needed

➢ Except for jammings (length = 32bits)

Propagation speed

Medium Propagation Speed

------ -----------------

Thick Coax .77c (231,000 km/sec)

Thin Coax .65c (195,000 km/sec)

Twisted Pair .59c (177,000 km/sec)

Fiber .66c (198,000 km/sec)

AUI Cable .65c (195,000 km/sec)

c refers to the speed of light in a vacuum (300,000 kilometers per second)

Ethernet Cable Types, Lengths and Data Rate

Cable Name Cable Type Maximum Length Data Rate

10Base5 Coax 500m per segment

10Mbps

10Base2 Coax 185m per segment

10Mbps

10BaseT UTP 100m per segment

10Mbps

10BaseF Fiber 4km 10Mbps

100BaseT UTP 100m per segment

100Mbps

100BaseTX 2 pair Cat 5 UTP

100m (hub and network node)

100Mbps

The BEB algorithm

The BEB Algorithm

• BEB: Binary Exponential Backoff

• After a collision, hosts wait d TS before continue sending frames➢ d = rand(0, 2i – 1) 1≤ i < 10➢ d = rand(0, 210 – 1) 10 ≤ I < 16

• After 16 retransmissions, the process is aborted and the upper layer is informed about this failure

The BEB Algorithm

The 802.3D protocol

• CSMA/CD cannot guarantee a bounded access delay to frames transmitted➢ Not adapted for real-time applications

• The CSMA/CDR protocol is the CSMA/CD version for real-time applications➢ This protocol reverts to a toking passing

algorithm when a collision is detected

Ethernet frame format

Frame Format

• Preamble➢ 7 bytes

with value 10101010

• Start Frame Delimiter➢ 1 byte =

10101011

Some possible values of the Type Ethernet field

Example of an Ethernet Frame

Address Resolution MAC - IP

The ARP protocol

• ARP (Address Resolution Protocol) allow to know the MAC address of host from its IP address

The ARP packet

• Hardware Type➢ Ethernet = 1

• Protocol Type➢ IP = 0x0800

• Hardware Address Length➢ Ethernet = 6

• Protocol Address Length➢ IPv4 = 4

• Operation➢ Request = 1➢ Reply = 2

• Sender Hardware Address

• Sender IP Address• Target Hardware

Address➢ Request =

000000000000

• Target IP Address

Example of ARP frames

• Example 1

ADDR HEX

0000 FF FF FF FF FF FF 00 00 C0 48 8C 11 08 06 00 01

0010 08 00 06 04 00 01 00 00 C0 48 8C 11 80 01 00 02

0020 00 00 00 00 00 00 80 01 00 01 00 00 00 00 00 00

0030 00 00 00 00 00 00 00 00 00 00 00 00

• Example 2

ADDR HEX

0000 00 00 C0 48 8C 11 00 00 C0 E5 8C 11 08 06 00 01

0010 08 00 06 04 00 02 00 00 C0 E5 8C 11 80 01 00 01

0020 00 00 C0 48 8C 11 80 01 00 02 00 00 00 00 00 00

0030 00 00 00 00 00 00 00 00 00 00 00 00

ARP messages and the Case of Multicast

• ARP Probe• Gratuitous ARP• The Case of Multicast: Conversion of a

Class D IP address

Introduction to the Wireless Networks

Categorization of Wireless networks according to the range

TAGGING

WPAN

WLAN

WMAN

WRAN

RFID

Wireless Personal Area Network (<10m)

Wireless Local Area Network (<150m)

Wireless Metropolitan Area Network (<5km)

Wireless Regional Area Network (<100km)

IEEE standards for wireless networks

• WPAN➢ IEEE 802.15

IEEE 802.15.1 – Bluetooth IEEE 802.15.3 – UWB (Ultra Wide Band) IEEE 802.15.4 – ZigBee

• WLAN➢ IEEE 802.11 (Wi-Fi)

IEEE 802.11b, a, g IEEE 802.11n IEEE 802.11s

• WMAN➢ IEEE 802.16

IEEE 802.16-2004 IEEE 802.16e/IEEE 802.20 (Wi-Mobile)

• WRAN➢ IEEE 802.22: Unused spaces in TV frequency spectrum 54-862MHz (Wi-RAN)

Wireless Networks: Data Rate vs Range

Wireless Networks: The Frequency bands

http://www.art-telecom.fr/

Wireless Metropolitan Area Network

Example of a WMAN: WiMAX

Example of a WMAN: WiMAX

• Network architecture➢ Point to Point➢ Point to MultiPoint

• Frequency band➢ 2GHz et 11GHz

• Channel bandwidth➢ 1.25 MHz, 5 MHz, 10 MHz or 20 MHz

• Up to 70Mbps• New alternative for last Mile Networks

Example of a WMAN: WiMAX

Wireless Local Area Network

Example of a WLAN: IEEE 802.11

• Network architecture➢ Point to Point➢ Point to MultiPoint

• Frequency band➢ 2.4GHz or 5GHz

• Channel bandwidth➢ 22 MHz

• Rate: 11Mbps - 54Mbps

TM

Example of a WLAN: IEEE 802.11

Example of a WLAN: HomeRF

• Frequency band➢ 2.4 GHz

• Maximum Rate➢ HomeRF1 1.6Mbps➢ HomeRF2 10 Mbit/s

• Range➢ Between 50m and 100m

Example of a WLAN: HiperLAN

• Released in 1991• Frequency band

➢ 5Ghz

• Maximum Rate➢ 20 - 54Mbps

• Range➢ + 30 m

Wireless Personal Area Network

Example of WPAN: Bluetooth

• Frequency band➢ 2.4GHz

• Maximum rate➢ 1Mbps

• Range➢ 10m

• Standards➢ IEEE802.15.1 (Bluetooth)➢ IEEE802.15.3 (Bluetooth

2)

Example of WPAN: Wireless USB

• Frequency band➢ 3.1GHz – 10.6GHz

• Maximum rate➢ 53Mbps - 480Mbps

• Range➢ 3m – 10m

• Specification➢ Wireless USB

Specification Rev 1.1 (September 2010)

Example of WPAN: Wireless Z-Wave

• Frequency band➢ 908.42MHz (USA)

• Maximum Rate➢ 40Kbps

• Range➢ 30m

Example of WPAN: ZigBee

• Frequency band➢ 2.4GHz

• Maximum rate➢ 250Kbps

• Range➢ 10m

• Standard➢ IEEE802.15.4

Wireless Body Area Network

Example of WBAN: NFC

• Near Field Communication (NFC)

• Very low range➢ Only a few centimeters

• Rate➢ ~424Kbps

• Frequency Range➢ Similar to RFID (Radio Frequency

Identification): HF 13.56MHz

• Applications➢ Access control

• NFC Forum: http://www.nfc-forum.org/home

The IEEE802.11 standard

Introduction

• The IEEE802.11 standard describes the characteristics of a Wireless LAN

• The term Wi-Fi is a contraction for Wireless Fidelity. Wireless Fidelity is the name that the Wi-Fi Alliance gave to the first specification➢ Wi-Fi Alliance was founded in 1999 by 3com, Aironet,

Intersil, Lucent Technologies, Nokia and Symbol Technologies

• The yin-yang logo indicates the certification of a product for interoperability

Introduction

• More specifically, IEEE802.11 defines the two lowest layer of the OSI model➢ The Physical Layer (sometimes called the PHY

Layer). The PHY Layer proposes 3 modulations techniques. This layer defines the technologies to transfer raw bits over a physical medium

➢ The Data Link Layer, which is composed by 2 sub-layers

Logical Link Control (LLC) Media Access Control (MAC)

Introduction

• The LLC sub-layer provides the multiplexing and flow control mechanisms that make possible the coexistence of several network protocols on the same physical interface➢ Same as IEEE802.3

• The MAC sub-layer provides the addressing and channel access control mechanisms that make possible share the same link between different terminals

WLAN devices and operating modes

• WLAN devices➢ Wireless Adapters➢ Access Points (AP)➢ Wireless routers➢ Wireless network bridges➢ Wireless repeaters

• 802.11 defines two operating modes➢ Infrastructure mode➢ Ad-hoc mode

Operating modes

Infrastructure mode

• Wireless Stations (STAs) connect to the Access Point (AP) via a wireless link

• Basic Service Set (BSS): set of STAs connected to the same AP

• Each BSS is identified by a BSSID.

• In the infrastructure mode case, this BSSID correspond to the AP's MAC address

• It is possible to connect two BSSs by mean of a Distribution System (DS)➢ Extended SS (ESS)

Infrastructure mode

Infrastructure mode

• An ESS is identified by an ESSID (also called SSID)➢ 32B length (coded in ASCII)➢ ESSID can be considered like the first level of

security

• STAs can transparently change between APs in an ESS (ex. choice the AP with the highest signal quality)➢ Roaming

Infrastructure mode

• To join a cell, STAs sends a probe request on each channel➢ The probe request message indicates the ESSID to join and others

characteristics like the supported data rate

• Upon reception of a probe request, the AP checks whether the ESSID matches its ESSID and if so, the AP sends a probe response containing synchronization information, supported data rate, etc.

• In absence of the requested ESS, the STAs can listen the medium to find a BSS➢ APs can be configured to frequently send a beacon frame to

diffuse the characteristics of the network

Ad-hoc networks

• In ad-hoc mode, nodes connect to one another to form a peer-to-peer network➢ There is not Access points

• Self-organizing network without the need of fixed network infrastructure

• Multi-hop communication➢ Nodes MAY behave like routers and forward packets on

behalf of other nodes

• Decentralized, mobility-adaptive operation

• The set of nodes forms an Independent BSS (IBSS)

Ad-hoc networks

• In ad hoc networks, the coverage area depends on the range of each station in a IBSS

From infrastructure mode to ad-hoc networks

• As we move away from the BS, we move ourselves to pure ad-hoc operations

• Ad hoc networks can be used in several areas

IEEE802.11: The Physical Layer

Radio spectrum

• Radio frequency bands are usually regulated by the government➢ Free spectrum➢ Licensed spectrum➢ Reserved for Astronomy observations

Radio spectrum

• Organizations that regulate the radio spectrum are➢ ETSI (European Telecommunications

Standards Institute) in Europe➢ FCC (Federal Communications Commission)

in USA➢ MKK (Kensa-kentei Kyokai) in Japan➢ l‘ART (Autorité de Régulation des

Télécommunications (ART)) in France

The ISM band

• In 1985, the FCC designated 3 frequency band for the Industry, Scientific and Medical purposes. These parts of radio spectrum can be used without license

• The ISM bands (adopted later in several countries) are 902-928MHz, 2.400-2.4835GHz and 5.725-5.850GHz

• In Europe, the frequency band between 890MHz and 915MHz is reserved for mobile communication (GSM). Only the bands at 2.4GHz and 5GHz can be used without license

PHY Layer

• IEEE802.11 defines 3 Physical Layer➢ DSSS Physical Layer➢ FHSS Physical Layer➢ Infrared (IR) Physical Layer

Direct Sequence Spread Spectrum

• The ISM band at 2.4GHz is divided in 14 channels (13 channels In France and 11 channels in US), each one with a 22MHz bandwidth

• There are only 3 non overlapping channels

Channel 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Frequency band

2.412

2.417

2.422

2.427

2.432

2.437

2.442

2.447

2.452

2.457

2.462

2.467

2.472

2.484

Direct Sequence Spread Spectrum

• DSSS may deliver frames at 1, 2, 5.5 and 11Mbps. The original 802.11 standard specified only 1 and 2 Mbps data rates

• The only coding/modulation used is Baker code (pseudo-random noise, PN). PN = 10110111000

• The chip sequence allow to detect errors during the transmission and introduce error correction techniques

Frequency Hopping Spread Spectrum

• FHSS consists in rapidly changing the transmission frequency in a predetermined pseudo random pattern➢ Initially proposed for military activities

• FHSS uses Gaussian Frequency Shift Keying (GSFK)

• 75 channels with a 1MHz bandwidth

• Transmitter and receiver must be synchronized

• 78 hopping sequences grouped in 3 sets of 26 sequence each. Sequence from same set encounter minimum collision (suitable for collocated systems)

• To lower the amount of collision to acceptable levels, the actual number of collocated systems should be around 15

Frequency Hopping Spread Spectrum

• FHSS Consist in rapidly changing the transmission frequency in a predetermined pseudo random pattern➢ Initially proposed for military activities

• FHSS uses Gaussian Frequency Shift Keying (GSFK)

• 75 channels with a 1MHz bandwidth

• Transmitter and receiver must be synchronized

• 78 hopping sequences grouped in 3 sets of 26 sequence each. Sequence from same set encounter minimum collision (suitable for collocated systems)

• To lower the amount of collision to acceptable levels, the actual number of collocated systems should be around 15

DSSS vs FHSS

IR PHY

• 802.11 specifies also one alternative to the radio communication: the use of an infrared light

• IR PHY was proposed for short- and medium-range communication

• Systems may operate in line-of-sight mode or in diffuse mode (scatter mode)

• Unlike RF (radio frequency), IR cannot pass through walls

• IR support 1Mbps (using 16-PPM scheme) and 2Mbps (using 4-PPM scheme)

IR PHY

The MAC sub-layer

The Data Link Layer

• 2 sub-layer➢ Logical Link Control➢ Media Access Control

• The MACL sub-layer defines two methods to ensure all STAs get access to the medium➢ Distributed Coordination Function (DCF)

All STAs must implement DCF➢ Point Coordination Function (PCF)

Optional

CSMA/CA

• DCF is a method to access the media without synchronization or priority management

• DCF relies on the CSMA/CA alorithm

• CSMA/CA stands for Carrier Sense Multiple Access / Collision Avoidance

• While in wired networks, one station can know when one another is using the medium, this is not possible in Wireless networks➢ CSMA/CA is the equivalent of CSMA/CD for wired networks

• CSMA/CA is a contention-based protocol making certain that all stations first sense the medium before transmitting➢ Avoid collisions➢ Avoid retransmissions

DCF

• DCF uses PCS (Physical Carrier Sensing) and VCS (Virtual Carrier Sensing) to avoid collisions➢ The PCS implementation is based on the Clear

Channel Assessment (CCA) function When the station senses an energy above a specific

threshold the medium is busy➢ VCS uses two different mechanisms to reserve the

medium By mean of the RTS/CTS frames: the overhead may be

important By mean of a timer (NAV)

Inter-Frame spacing

• The time elapsed between two frames is known like Inter-Frame Spacing (IFS)

• There are 4 types of IFS➢ Short IFS (SIFS). Depend on the kind of PHY

FHSS = 28microsec DSSS = 10microsec

➢ Distributed IFS (DIFS) = SIFS + 1TS➢ Point Coordination IFS (PIFS) = SIFS + 2TS➢ Extended IFS (EIFS)

The hidden/exposed node problem

• MS-D ignores the communication between MS-B and MS-C. MS-D sends data to MS-C

• MS-A listen the communication between MS-C and MS-B. MS-A cannot communicate with MS-D

BEB Algorithm

Timers and Constants

• Congestion Window➢ Advised min = 15➢ Advised max = 1023

➢ CWi = min(CWmax, CWmin*2i­1)

• Back-off➢ T = random(0,CW)*TS

Timeslot• FHSS = 50μs• DHSS = 20μs• OFDM = 9μs• ...

DCF

Error Control

• In wireless networks, checking for data corruption is important due to the unreliability nature of the medium

• The MAC sub-layer usually implement the Cyclic Redundancy Check (CRC) to detect errors in the MAC frames ➢ Polynomial of order 32➢ x32+x26+x23+x22+x16+x12+x10+x8+x7+

x5+x4+x2+x+1

802.11 Frame format

• 802.11 frames have the following format

➢ Preamble 80-bit sequence of alternating zeros and one Start Frame Delimiter (SFD) which consist of a 16-bits binary

pattern (0000 1100 1011 1101)

➢ PLCP (Physical Layer Convergence Protocol) header PLCP_PDU Length Word. Number of bytes in the packet PLCP Signaling Field. Rate information Header Error Check Field. 16-bit CRC

➢ MAC Data MAC frame

MAC frame format

General format of a MAC frame

The Frame Control Field contains the following information

Frame Control

• Protocol version➢ 2 bits = 00

• Type and subtype with a length of 2 and 4 bits respectively➢ Management type (00). Association/disassociation messages➢ Control messages (01). Access control to the media➢ Data messages (10). Contains data sent by the upper layer

• ToDS = 1 when the frame is addressed to a Distribution System (the AP).

• FromDS = 1 when the frame comes from a DS➢ What is the value for ToSD ans FromDS in an ad-hoc network?

• More fragments➢ One Fragment belonging to the same frame follows current frame

Frame Control

• Retry = 1 indicates that this frame is a retransmission

• Power Management = 1 indicates that the station enters in power save mode

• More Data. Used by the AP to indicate to a STA that some frames are buffered

• WEP. Set to 1 when the frame body is encrypted with the WEP algorithm

MAC frame format

• Duration/ID.➢ In Power-Save Poll messages this field indicate the ID of the

STA➢ In all other messages, this is the duration value used for the

NAV calculation

• Address 1. The recipient address

• Address 2. Transmitter address

• Address 3. if FromDS=1, then this is the original Source Address. If ToDS = 1, then this is the Destination Address

• Address 4. Wireless Distribution System frame distributed from one AP to another AP

MAC Frame Format

• Sequence Control is used to re-assembly several fragments corresponding to a same frame➢ Sequence number (12 bits) contains the ID of

the fragmented frame➢ Fragment number (4 bits). Number of each

frame sent of a fragmented frame

• CRC

RTS and CTS frames

Type and subtypes (summary)