Transcript Communication Systems 14th lecture - Electures

Communication Systems
15th lecture
Chair of Communication Systems
Department of Applied Sciences
University of Freiburg
2008
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Communication Systems
Last lecture – UMTS, WCDMA, Wireless LAN
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Last lecture devoted to telephony networks and UMTS
encoding – WCDMA on the air interface
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WCDMA uses Code Division Multiplexing instead of Time
Division Multiplexing and Frequency Division Multiplexing
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Per participant a binary channelization code is used thus
multiple signals on just one frequency
Switched over then to other mobile technologies, especially
Wireless LAN
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Standardization of Wireless LAN technology started in1997 the
IEEE approved 802.11
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The standard specifies the MAC and the physical layers for
transmissions in the 2.4, 5.0 GHz band (ISM)
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Communication Systems
Last lecture – Wireless LAN standards
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Later on the first really popular standard IEEE 802.11b was
created, which works at additional signal rates of 5.5 and 11
Mbit/s
By the end of the 1990s, the IEEE approved the
specifications of 802.11a, which uses the 5 GHz band,
allowing brutto signal rates of 6, 9, 12, 18, 24, 36, 48 up to 54
Mbit/s
In 2003, the IEEE approved 802.11g as a further evolution of
the 802.11 standard, providing the same performance as
802.11a, while working in the 2.4 GHz band, compatible with
802.11b devices
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Most modern devices are equipped with g standard adapters by
now
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Wireless technology becomes increasingly popular
In 2007 the 802.11n standard was approved – optimizing
modulation, using more than one channel and antennas for
multi-path signal reception
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Communication Systems
This lecture – Wireless LAN and wireless technologies
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Thus we will find more mobile solutions for data
communication than GSM, UMTS and WLAN
There are several reasons for the evolution of new wireless
standards
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not all requirements could be met with GSM, UMTS or WLAN
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the data rates of GSM are rather small compared to todays
multimedia content and demands of modern networked
applications, delay is an important issue for real time
applications and communication
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UMTS covers greater areas, but costs are rather high and
bandwidth is medium compared to WLAN technology
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on the other side GSM and UMTS offer a well established
framework for user administration, accounting and billing on a
really world wide scale
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Communication Systems
This lecture – Wireless LAN and wireless technologies
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WLANs of the most widely used g and a/h (b/n) standards on
the other side offer rather high bandwidth and short delay,
but often
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suboptimal regarding power consumption
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layer 2 security
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every-where access
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user-authentication
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bandwidth compared to classical Ethernet infrastructure
Therefore we have additional concepts tackling some of the
issues mentioned above
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Bluetooth for low-power, short-range, low-bandwidth
communication
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Communication Systems
This lecture – More on wireless technologies
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Bluetooth is widely established and accepted in small mobile
devices like mobile phones, PDAs, headsets, ... to replace
wiring
UWB – Ultra Wide Band as an upcoming high bandwidth
technology which should be able to share bandwidth with
other users and is authorized to operate in the range of 3.1
upto 16GHz
“Wireless DSL” - different wide area network technologies in
the former band of old analogous mobile phone networks to
cover rural areas and offer high speed Internet access in
sparsely populated areas
WiMaX as a new wireless standard for MANs
WiMaX and Bluetooth are covered in this lecture
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Communication Systems
This lecture – Network fusion
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UWB is a rather new technology and not many products are
available by now, but you will find some articles on it in the
net
In the second part of lecture we will switch over again and
talk on fusion of telephony and IP networks
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Communication Systems
WiMAX - Worldwide Interoperability for Microwave Access
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Broadband Wireless MAN Standard
Defines wireless service that provide a communications path
between a subscriber site and a core network such as the public
telephone network and the Internet.
"a standards-based technology enabling the delivery of last mile
wireless broadband access as an alternative to cable and DSL."
Standards:
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IEEE Std 802.16-2004: addresses fixed and portable systems.
Amendment 802.16e: Adds mobility components to the standard, called
“Mobile WiMAX”
WiMAX Forum coordinates interoperability testing -- “WiMAX Forum
Certified”.
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Communication Systems
WiMAX- characteristics
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Frequency ranges 10-66 GHz and 2-11 GHz for the air/physical
layer interface
Broad bandwidth
 Up to 134 Mbit/s in 28 MHz channels
Accommodate either TDD or FDD
Supports different (higher) layer or transport protocols such as
 ATM
 Ethernet
 IP
MAC is designed for very high bit rates (up to 268 Mbit/s each
way), while delivering ATM compatible Quality of Service
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Communication Systems
WiMAX- characteristics
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Frame structure allows terminals to be dynamically assigned uplink
and downlink burst profiles according to their link conditions
MAC uses variable length PDU and other concepts to increase
efficiency
MAC uses a self-correcting bandwidth request/grant scheme that
eliminates the overhead and delay of acknowledgements, while
simultaneously allowing better QoS handling
High security: supports AES and 3DES
IEEE 802.16e allows full mobility at speeds up to 160 km/h
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Communication Systems
WiMAX - standards
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Communication Systems
WiMAX – architecture and application
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Communication Systems
WiMAX – architecture and application
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WiMAX system consists of two parts
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Several base stations are connected with one another by high-speed
backhaul microwave links, allowing for roaming by a WiMAX
subscriber from one base station to another base station area
WiMAX has two main topologies
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WiMAX Base station (tower): can cover up to 10 km radius
WiMAX Subscriber station (receiver): sits in your laptop or computer
Point to Point for backhaul
Point to Multi-Point Base station for Subscriber station
Typical areas of application of WiMAX
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Residential and SOHO High Speed Internet Access
Small and Medium Business
WiFi Hot Spot backhaul
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Communication Systems
WiMAX – wireless services
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Line-of-sight
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A fixed dish antenna points straight at the WiMAX tower from a rooftop
or pole
11 GHz to 66 GHz frequency range
At higher frequencies - there is less interference and lots more
bandwidth
The connection is stronger and more stable, so it is able to send a lot of
data with fewer errors
Non-line-of-sight
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A small antenna on the end-users computer connects to the WiMAX
tower
2 GHz to 11 GHz frequency range
At lower frequencies – longer wavelength transmissions are not as
easily disrupted by physical obstructions – they are better able to
diffract, or bend, around obstacles
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Communication Systems
WiMAX – reference model
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Communication Systems
WiMAX – reference model
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Service-Specific Convergence Sublayer (CS):
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MAC Common Part Sublayer (MAC CPS):
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provides transformation or mapping of external network data, received
through the CS service access point (SAP), into MAC SDUs received by
the MAC Common Part Sublayer (CPS) through the MAC SAP.
provides the core MAC functionality of system access, bandwidth
allocation, connection establishment, and connection maintenance.
receives data from the various CSs, through the MAC SAP, classified to
particular MAC connections.
Data, PHY control, and statistics are transferred between the MAC CPS
and the PHY via the PHY SAP
A separate security sublayer provides authentication, secure key
exchange, and encryption
Physical Layer (PHY) includes multiple specification, each
appropriate to a particular frequency range and application
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Communication Systems
Comparison of WiMAX and Wi-Fi
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Communication Systems
Bluetooth technology - introduction
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Bluetooth is a radio standard and communications protocol
primarily designed for low power consumption, with a short range
(power class dependent: 1 meter, 10 meters, 100 meters) based
around low-cost transceiver microchips in each device
Intended to replace the cable(s) connecting portable and/or fixed
electronic devices
Designed to operate in noisy frequency environments, the
Bluetooth radio uses a fast acknowledgment and frequency
hopping scheme to make the link robust
Bluetooth radio modules operate in the unlicensed ISM band at
2.4GHz, use frequency hopping and change freq. every 42 times
a millisecond, hop is synchronized by cell master
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Communication Systems
Bluetooth - characteristics
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Compared with other systems in the same frequency band, the
Bluetooth radio hops faster and uses shorter packets
Since March 2002, an IEEE standard, namely IEEE 802.15.1
Many existing devices support 1.2, newer the 2.0 (defined 2004),
2.1 (2007, stronger encryption, faster pairing, ...) standards
Unlicensed 2.4GHz radio band, ISM (industrial, scientific,medical)
band - available worldwide, also used by Microwave ovens, 802.11,
HomeRF…
Gross data rate of 1 Mbit/s, 3 Mbit/s for 2.X standards
Basic 10m range extended to 100m with amplifiers/special devices
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Communication Systems
Bluetooth - characteristics
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TDMA - TDD - Frequency hopping
Mixed voice / data paths
Encryption, low power, low cost
Extremely small
Ubiquitous radio link
Bluetooth technology offers built-in simple networking on layer 2
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thus it attracted the academic world to do research on dynamic networks
basing on scattered, moving, emerging and disappearing mobile devices
A Bluetooth device may operate in master mode or in slave mode
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Communication Systems
Bluetooth network topology - Piconet
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A maximum of 8 devices (7 active slaves plus 1 master) form a
Piconet
A piconet is characterized by the master: frequency hopping scheme,
access code, timing synchronization, bit rate allocated to each slave
Only one master: dynamically selected, roles can be switched
Up to 7 active slaves; up to 255 parked slaves
No central network structure: “Ad-hoc” network
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Communication Systems
Bluetooth network topology -Scatternet
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Interconnected piconets, one master per piconet
A few devices shared between piconets
No central network structure: “Ad-hoc” network
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Communication Systems
Bluetooth protocol stack
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Communication Systems
Bluetooth protocol stack
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Radio layer: defines the requirements for a Bluetooth transceiver
operating in the 2.4 GHz ISM band
Baseband layer: describes the specification of the Bluetooth Link
Controller (LC) which carries out the baseband protocols and other
low-level link routines
Link Manager Protocol (LMP): is used by the Link Managers (on
either side) for link set-up and control
Host Controller Interface (HCI): provides a command interface to the
Baseband Link Controller and Link Manager, and access to
hardware status and control registers
Logical Link Control and Adaptation Protocol (L2CAP): supports
higher level protocol multiplexing, packet segmentation and
reassembly, and the conveying of quality of service information
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Communication Systems
Bluetooth protocol stack
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RFCOMM protocol: provides emulation of serial ports over the
L2CAP protocol. The protocol is based on the ETSI standard TS
07.10
Service Discovery Protocol (SDP): provides a means for applications
to discover which services are provided or available
For experimenting the Linux BT stack (www.bluez.org) might be a
good start
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it is a really good implementation of the standard and supports the
various Bluetooth profiles offered by the different devices
it is OpenSource and provides the necessary programming libraries
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Communication Systems
Bluetooth profiles and dependencies
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A profile can
be described
as a vertical
slice through
the protocol
stack
A profile has
dependencies
on the profiles
in which it is
contained
directly and
indirectly
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Communication Systems
Bluetooth - applications
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Bluetooth profiles were written to make sure that the
application level works the same way across
different manufacturers' products
Bluetooth applications:
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Wireless control of and communication between a cell
phone and a hands free headset or car kit.
Wireless networking between PCs in a confined
space and where little bandwidth is required
Wireless communications with PC input devices such
as mice and keyboards
Wireless communications to PC output devices such
as printers
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Communication Systems
Bluetooth – applications, devices
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Built-in in modern laptops or dongles
Wireless communications with PC
input devices such as mice and
keyboards
Wireless communications to PC
output devices such as printers
Transfer of files between devices via
OBEX
Replacement of traditional wired serial
communications in test equipment,
GPS receivers and medical equipment
Thus often a serial interface is
emulated over the BT link as shown
on the following slides ...
Remote controls where infrared was
traditionally used
...
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Communication Systems
Bluetooth in Linux OS – an example for the rfcomm layer
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Often Bluetooth is the best way to link devices like mobile phones to
a laptop
mobile linux # hcitool scan
Scanning ...
00:0E:07:47:93:1B
T610
mobile linux # hcitool cc 00:0E:07:47:93:1B
mobile linux # hcitool dc 00:0E:07:47:93:1B
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Scan for Bluetooth devices within the range of the BT adaptor
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this is much more fun to do on specific fairs like the Cebit, where you
can compile a list of more then 20 devices within range
if your are lucky some of the devices use broken firmware and security
could be overridden – with special tools you can access the mobile
device, get the phone books, alter entries and so on ...
hcitool is just a helper to connect, authenticate, disconnect, ...
to/from a device
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Communication Systems
Bluetooth in Linux OS – an example for the rfcomm layer
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hciconfig - show the Bluetooth device and its properties
mobile linux # hciconfig
hci0:
Type: PCCARD
BD Address: 00:04:76:C8:4A:E8 ACL MTU: 128:8 SCO MTU: 64:8
UP RUNNING PSCAN ISCAN AUTH ENCRYPT
RX bytes:1046 acl:0 sco:0 events:58 errors:0
TX bytes:850 acl:0 sco:0 commands:35 errors:0
mobile linux # hcitool dev
Devices:
hci0
00:04:76:C8:4A:E8
mobile linux # l2ping 00:0E:07:47:93:1B
Ping: 00:0E:07:47:93:1B from 00:04:76:C8:4A:E8 (data size 20) ...
0 bytes from 00:0E:07:47:93:1B id 200 time 63.05ms
0 bytes from 00:0E:07:47:93:1B id 201 time 48.13ms
0 bytes from 00:0E:07:47:93:1B id 202 time 45.13ms
3 sent, 3 received, 0% loss
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l2ping is a layer 2 ping utility to check connection on a specific
linked device
as you can see, the average trip time is much higher than e.g. in
WLAN
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Communication Systems
Bluetooth in Linux OS
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In next step the emulated serial link could be started
mobile linux # rfcomm connect 1 00:0E:07:47:93:1B 1
Connected /dev/rfcomm1 to 00:0E:07:47:93:1B on channel 1
Press CTRL-C for hangup
mobile linux # pppd call gprs-o2wap
Press CTRL-C to close the connection at any stage!
defining PDP context...
rATZ
OK
AT&F
OK
ATV1E0S0=0&D2&C1
OK
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Which is just used as the lower layer protocol for a PPP connection
part between the computer and device
The mobile phone “translates” the data stream for the WAN GSM
interface, GPRS protocol as explained in earlier lecture
Of course there are more options for BT protocols between the two
devices, like OBEX for file transfer (e.g. stored MP3, ...)
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Communication Systems
Bluetooth compared to WLAN
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Bluetooth is oriented to connecting close devices, serving as a
substitute for cables
Wi-Fi is oriented towards computer-to-computer connections, as an
extension of or substitution for cable LANs.
802.11b and Blutooth both utilize the free 2.4GHz band
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no exclusive use
no guarantees
special protocol implementations needed to cope with noise, fading, ...
Bluetooth uses frequency hopping and changes freq. every 42
times a millisecond, hop is synchronized by cell master
802.11a/h WLAN standards use the free 5Ghz band
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band is reserved for WLAN only
range is more restricted than with 802.11b
bandwidth is increased up to 54Mbit
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Communication Systems
Bluetooth vs WLAN - comparison
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Communication Systems
Bluetooth v. Wi-Fi – comparison (cont.)
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Comparison of the older standards ... but only little bit changes for
the newer ones (BT 2.X, WLAN 802.11n)
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Communication Systems
network technologies and network fusion
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By now we have presented a certain range of communication
networks and their underlying technologies
The “early” (means standards dating from the 1970s and
1980s) digital wired and wireless networks were focused on
the transportation of voice
The developers of the first drafts on Internet protocols had
data communication in mind when defining their standards
The processes of standardization were really different
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Closed “clubs” of telephony providers and equipment
manufacturers backed up by their states and a rather open
process in the definition of Internet protocols and applications
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But by now both worlds learn of each other and closing the
gaps in between ...
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Communication Systems
network fusion
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For a rather long time telephone and data networks were
different entities – remember the network taxonomy
 packet orientated vs. circuit switched
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packet orientation is rather efficient in bandwidth using
but cannot give any guarantees on packet delivery
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bandwidth growth and optional QoS helped to offer
service quality near to circuit switching
Why to provide two completely different infrastructures for
rather the same services?
 voice is just another piece of data (and not the biggest
one compared to other applications and services in use)
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Communication Systems
real time communication
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Traditional telephony networks are circuit switching networks
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rather centrally operated
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setup of connection in-band or out of band before communication
starts
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no routing delays in transmit
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reserved bandwidth for every connection
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rather homogeneous transport media
More and more real time services are handled over the Internet,
but
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hop-by-hop routing without clear hierarchy, principles, protocols
discussed in the beginning of this lecture
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different media and bandwidth
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Communication Systems
real time communication
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Voice-over-IP (VoIP) is a big hype at the moment
 every network equipment vendor has some products in
its portfolio (even companies like Siemens are able to
offer products conforming to standards!!)
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many new “telephone companies” evolve to offer
services, the old providers have to think on new
strategies
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all of them hope for reduction of costs and a source for
roaring profits :-)
so TCP/IP is just used for another application/service
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Communication Systems
delay in communication
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This service has to meet some requirements
Important issue in communication – delay and packet loss
(infinite delay)
Many applications heavily depend on near no delay (e.g. real
time communication, like VoIP, Video and multi-user online
gaming ... :-) )
Routing delay
 High setup delay in virtual circuit networks – no delay if
path is set up (imagine telephone network)
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No setup delay in datagram networks, but routing
decision for every packet in every router
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Communication Systems
delay in communication
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Other types of delay
 Transmission, nodal processing, queuing, propagation
delay
Transmission delay (example given with message
segmentation)
 Is L/R (L size of packet in bit, R rate in bit/s)
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e.g. Packet of 1500Byte (standard MTU – max. transfer
unit in ethernets) on 100MBits LAN travels 0,000015s
(=15µs) to be transferred completely
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Communication Systems
delay in communication
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Ping between two hosts connected via 100Mbits ethernet
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Linux-OS, between 550MHz PII/Cel and P4/2,4GHz, 100Mbits
interface cards
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Communication Systems
delay in communication
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Processing delay is time for
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Evaluating header information
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Check for bit errors
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Decision on outgoing route
Should be in order of microseconds in high speed routers
and servers
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Protocols implemented in hardware
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New protocols like Ipv6, implemented in software first, but then
migrated into the circuits
Queuing delay – in packet switching networks overbooking
of resources may occur (no bandwidth reservation as with
VC)
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Packets have to wait (a certain time) until sent out
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Communication Systems
delay in packet switched networks
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Propagation of signal in physical medium may add to delay
too
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Normally in order of nanoseconds in LAN and milliseconds in
WAN
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We cannot do much on it – but we get some problems:
Imagine 300km WAN optical link of 10GBit/s (e.g. in GEANT)
 300km/300.000km/s=0.001s (1ms)
 10GBit/s*0.001s = 0.01GBit = 10MBit “on wire” (signal sent
out but not received by destination)
 => rising “capacity of wire” with rising speed
Important problem in cluster and parallel computing (!) - you
need extremely fast connections on very short distances
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Communication Systems
delay in packet switched networks
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Propagation and transmission delays are different
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Propagation is the travel time of one signal (single bit)
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Transmission measures time for transferring one packet
(independent on distance, but dependent on bandwidth and packet
size)
Processing delay is sum of delays mentioned above
dnodal = dtrans + dproc + dqueue + dprop
Contribution of every delay to dnodal may vary heavily
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Communication Systems
delay in packet switched networks
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The delay of packets in the output queue dqueue is most important
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Depends on the traffic intensity
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Even when average traffic rate is lower than bandwidth long queues
may build up with very bursty traffic
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First packet is sent out directly all following can suffer increasing
delay
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Standard problem on routers with different up-link bandwidth
If outgoing queue is full packets are dropped
Packet losses increase with traffic intensity
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Communication Systems
delay in packet switched networks
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End system to end system delay is sum of all nodal delays along
the path from source to destination
Helper program to get an idea on path and delay is traceroute
(exercises in practical course at the beginning of lecture, see mtr
too)
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Communication Systems
requirements towards network
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Voice over IP and Quality of Service:
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Major challenges: delay and delay variation (jitter)
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Delay jitter is the variability of source-to-destination delays of
packets within the same packet stream
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Voice applications are usually interactive
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Delay requirement for a telephone system: max. 150ms-250ms
We identified some of the sources of delay in a voice over IP
system:
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OS delay: 10-100 milliseconds (digitization of analogous data,
compression and inter software data handling) ...
Special multimedia protocol is introduced next lecture ...
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Communication Systems
Information – Job Offer :)
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The professorship of communication systems offers some hiwi
positions for the upcoming semester!
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up to 3, 4 hiwis (depending on the number of participants) for the
new “communication systems” lecture next semester (consecutive to
“Systeme II”)
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tasks: Preparation of new lecture content (exchange of some topics
to coordinate with “Systeme II”), preparation of the practical
exercises (prepare the playgrounds, design questions, tasks ...),
preparation and correction the theoretical exercise sheets

start 1st October, till 28th February
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Communication Systems
End/Literature for this topic
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Bluetooth and WLAN
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http://dienst.isti.cnr.it/Dienst/Repository/2.0/Body/ercim.cnr.isti/2004-TR27/pdf?tiposearch=cnr&langver=
http://en.wikipedia.org/wiki/Bluetooth
http://www.palowireless.com/infotooth/tutorial.asp
802.15.1 2005: http://standards.ieee.org/getieee802/download/802.15.12005.pdf
http://bluetooth.com/NR/rdonlyres/7F6DEA50-05CC-4A8D-B87BF5AA02AD78EF/0/Protocol_Architecture.pdf
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Communication Systems
End/Literature for this topic
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WiMAX
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802.16: http://standards.ieee.org/getieee802/download/802.162004.pdf
IEEE 802.16a:
http://www.wimaxforum.org/news/downloads/WiMAXWhitepaper.pdf
Telephoy's complete guide to WiMAX:
http://www.wimaxforum.org/news/press_releases/Telephony_WiMAX.pdf
http://computer.howstuffworks.com/wimax1.htm
http://searchnetworking.techtarget.com/searchNetworking/downloads/Fin
neran.pdf
Can WiMAX address your application:
http://www.wimaxforum.org/news/downloads/Can_WiMAX_Address_Your
_Applications_final.pdf
http://www.wimaxforum.org/technolog
For a generic literature overview – please check the end of last
exercises (comsys-exercise06.pdf) slides (available from the
download section of the lectures homepage)
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