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Communication Systems15th lecture

Chair of Communication SystemsDepartment of Applied Sciences

University of Freiburg2008

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Communication SystemsLast lecture – UMTS, WCDMA, Wireless LAN

Last lecture devoted to telephony networks and UMTS encoding – WCDMA on the air interface

WCDMA uses Code Division Multiplexing instead of Time Division Multiplexing and Frequency Division Multiplexing

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

Standardization of Wireless LAN technology started in1997 the IEEE approved 802.11

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 SystemsLast lecture – Wireless LAN standards

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

Most modern devices are equipped with g standard adapters by now

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 SystemsThis lecture – Wireless LAN and wireless technologies

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

not all requirements could be met with GSM, UMTS or WLAN

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

UMTS covers greater areas, but costs are rather high and bandwidth is medium compared to WLAN technology

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 SystemsThis lecture – Wireless LAN and wireless technologies

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

suboptimal regarding power consumption

layer 2 security

every-where access

user-authentication

bandwidth compared to classical Ethernet infrastructure Therefore we have additional concepts tackling some of the

issues mentioned above Bluetooth for low-power, short-range, low-bandwidth communication

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Communication SystemsThis lecture – More on wireless technologies

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 SystemsThis lecture – Network fusion

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 SystemsWiMAX - Worldwide Interoperability for Microwave Access

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: 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 SystemsWiMAX- characteristics

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 SystemsWiMAX- characteristics

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 SystemsWiMAX - standards

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Communication SystemsWiMAX – architecture and application

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Communication SystemsWiMAX – architecture and application

WiMAX system consists of two parts WiMAX Base station (tower): can cover up to 10 km radius WiMAX Subscriber station (receiver): sits in your laptop or computer

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 Point to Point for backhaul Point to Multi-Point Base station for Subscriber station

Typical areas of application of WiMAX Residential and SOHO High Speed Internet Access Small and Medium Business WiFi Hot Spot backhaul

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Communication SystemsWiMAX – wireless services

Line-of-sight 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

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 SystemsWiMAX – reference model

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Communication SystemsWiMAX – reference model

Service-Specific Convergence Sublayer (CS): 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.

MAC Common Part Sublayer (MAC CPS): 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 SystemsComparison of WiMAX and Wi-Fi

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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

Communication SystemsBluetooth technology - introduction

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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

Communication SystemsBluetooth - 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

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

Communication SystemsBluetooth - characteristics

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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

Communication SystemsBluetooth network topology - Piconet

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Interconnected piconets, one master per piconet A few devices shared between piconets No central network structure: “Ad-hoc” network

Communication SystemsBluetooth network topology -Scatternet

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Communication SystemsBluetooth 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

Communication SystemsBluetooth 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

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

Communication SystemsBluetooth protocol stack

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Communication SystemsBluetooth profiles and dependencies

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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Bluetooth profiles were written to make sure that the application level works the same way across different manufacturers' products

Bluetooth applications: 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

Communication SystemsBluetooth - applications

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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

...

Communication SystemsBluetooth – applications, devices

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Often Bluetooth is the best way to link devices like mobile phones to a laptop

mobile linux # hcitool scanScanning ... 00:0E:07:47:93:1B T610mobile linux # hcitool cc 00:0E:07:47:93:1Bmobile linux # hcitool dc 00:0E:07:47:93:1B Scan for Bluetooth devices within the range of the BT adaptor

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

Communication SystemsBluetooth in Linux OS – an example for the rfcomm layer

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hciconfig - show the Bluetooth device and its propertiesmobile 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:0mobile linux # hcitool devDevices: hci0 00:04:76:C8:4A:E8mobile linux # l2ping 00:0E:07:47:93:1BPing: 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 63.05ms0 bytes from 00:0E:07:47:93:1B id 201 time 48.13ms0 bytes from 00:0E:07:47:93:1B id 202 time 45.13ms3 sent, 3 received, 0% loss 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

Communication SystemsBluetooth in Linux OS – an example for the rfcomm layer

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In next step the emulated serial link could be startedmobile linux # rfcomm connect 1 00:0E:07:47:93:1B 1Connected /dev/rfcomm1 to 00:0E:07:47:93:1B on channel 1Press CTRL-C for hangupmobile linux # pppd call gprs-o2wapPress CTRL-C to close the connection at any stage!defining PDP context...rATZOKAT&FOKATV1E0S0=0&D2&C1OK 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, ...)

Communication SystemsBluetooth in Linux OS

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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 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 band is reserved for WLAN only range is more restricted than with 802.11b bandwidth is increased up to 54Mbit

Communication SystemsBluetooth compared to WLAN

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Communication SystemsBluetooth vs WLAN - comparison

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Communication SystemsBluetooth v. Wi-Fi – comparison (cont.)

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 Systemsnetwork technologies and network fusion

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 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

But by now both worlds learn of each other and closing the gaps in between ...

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Communication Systemsnetwork fusion

For a rather long time telephone and data networks were different entities – remember the network taxonomy packet orientated vs. circuit switched packet orientation is rather efficient in bandwidth using but

cannot give any guarantees on packet delivery 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 Systemsreal time communication

Traditional telephony networks are circuit switching networks rather centrally operated

setup of connection in-band or out of band before communication starts

no routing delays in transmit

reserved bandwidth for every connection

rather homogeneous transport media More and more real time services are handled over the Internet, but

hop-by-hop routing without clear hierarchy, principles, protocols discussed in the beginning of this lecture

different media and bandwidth

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Communication Systemsreal time communication

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!!)

many new “telephone companies” evolve to offer services, the old providers have to think on new strategies

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 Systemsdelay in communication

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) No setup delay in datagram networks, but routing decision for

every packet in every router

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Communication Systemsdelay in communication

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) 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 Systemsdelay in communication

Ping between two hosts connected via 100Mbits ethernet Linux-OS, between 550MHz PII/Cel and P4/2,4GHz, 100Mbits

interface cards

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Communication Systemsdelay in communication

Processing delay is time for Evaluating header information

Check for bit errors

Decision on outgoing route Should be in order of microseconds in high speed routers and

servers Protocols implemented in hardware

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)

Packets have to wait (a certain time) until sent out

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Communication Systemsdelay in packet switched networks

Propagation of signal in physical medium may add to delay too Normally in order of nanoseconds in LAN and milliseconds in WAN

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 Systemsdelay in packet switched networks

Propagation and transmission delays are different Propagation is the travel time of one signal (single bit)

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 Systemsdelay in packet switched networks

The delay of packets in the output queue dqueue is most important Depends on the traffic intensity

Even when average traffic rate is lower than bandwidth long queues may build up with very bursty traffic

First packet is sent out directly all following can suffer increasing delay

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 Systemsdelay in packet switched networks

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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Voice over IP and Quality of Service: Major challenges: delay and delay variation (jitter)

Delay jitter is the variability of source-to-destination delays of packets within the same packet stream

Voice applications are usually interactive

Delay requirement for a telephone system: max. 150ms-250ms We identified some of the sources of delay in a voice over IP

system: OS delay: 10-100 milliseconds (digitization of analogous data,

compression and inter software data handling) ... Special multimedia protocol is introduced next lecture ...

Communication Systemsrequirements towards network

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Communication SystemsInformation – Job Offer :)

The professorship of communication systems offers some hiwi positions for the upcoming semester!

up to 3, 4 hiwis (depending on the number of participants) for the new “communication systems” lecture next semester (consecutive to “Systeme II”)

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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Bluetooth and WLAN http://dienst.isti.cnr.it/Dienst/Repository/2.0/Body/ercim.cnr.isti/2004-TR-

27/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/802.15.1-

2005.pdf http://bluetooth.com/NR/rdonlyres/7F6DEA50-05CC-4A8D-B87B-

F5AA02AD78EF/0/Protocol_Architecture.pdf

Communication SystemsEnd/Literature for this topic

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WiMAX 802.16: http://standards.ieee.org/getieee802/download/802.16-2004.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/

Finneran.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)

Communication SystemsEnd/Literature for this topic