UbiCom Book Slides
Chapter 11
Ubiquitous Communication
Stefan Poslad
http://www.eecs.qmul.ac.uk/people/stefan/ubicom
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environments and interaction
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Chapter 11: Overview
Chapter 11 focuses on:
• Internal system properties: distributed
• External interaction with ICT environment
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5 Main Properties for UbiCom Systems
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UbiCom System Model Focussing on
Interaction in Virtual Computing
Environments
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Related Chapter Links
•
•
•
•
•
Distributed Computing (Chapter 3)
Mobile Services (Chapter 4)
Intelligent Interaction (Chapter 9)
Mobile Distributed Systems (Chapter 4)
Management of Distributed Systems (Chapter 12)
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Chapter11: Overview
The slides for this chapter are also expanded and split into
several parts
• Part A: Introduction
• Part B: Audio Networks
• Part C: Data networks: Fixed
• Part D: Data networks: Wireless
• Part E: Video & Multi-Content Access Networks
• Part F: Ubiquitous Networks: PLC, PAN, BAN, Mobile
• Part G: Network Access Control
• Part H: Service-Oriented Networks 1
• Part I: Service-Oriented Networks 2
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Chapter11: Overview
The slides for this chapter are also expanded and split into
several parts
• Part A: Introduction 
• Part B: Audio Networks
• Part C: Data networks: Fixed
• Part D: Data networks: Wireless
• Part E: Video & Multi-Content Access Networks
• Part F: Ubiquitous Networks: PLC, PAN, BAN, Mobile
• Part G: Network Access Control
• Part H: Service-Oriented Networks 1
• Part I: Service-Oriented Networks 2
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Ex: Communication Networks
• Time order the following networks:
– Internet (data), radio (audio), television, telephone
• Which became established first for mass-use: when &
why?
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Introduction
• Ubiquitous applications need to access relevant remote
external information and tasks, anywhere and anytime.
• Different applications require different combinations of
network functions and services, e.g., data streaming,
minimal jitter, specific media access control etc.
• Different networks support different sets of communication
functions in different ways.
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Introduction
Key design issues:
• Should comms functions be largely transparent to services
(network-oriented) versus should comms be exposed via
some interfaces & configured / controlled by services
(service-oriented).
• Should networked services be accessible from anywhere
versus selectively accessing networked services, e.g.,
some services may be limited to a locality?
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Introduction
• Many general and introductory texts and descriptions about
networking are specialised towards specific types of
networks, e.g.,
– ???
–
• An interpretation of UbiCom:
– Ubiquitous Communication
– Any content on any network, anytime, anywhere
• Hence, complete range of different media networks is
treated holistically here
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Network Communication Functions
Communication involves the following key functions:
• Encoding and Modulation
• Signal Distribution
• Channel sharing and efficiency:
– Medium Access Control (MAC)
– Logical Link Control (LLC
• Error checking and correction:
• Data Transfer Control
– buffered vs. unbuffered.
– Asynchronous vs. synchronous
•
•
•
•
Data Routing
Message security
Metadata:
Transcoding.
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Network Communication Functions
• Explain all these in detail in next slides
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Digital Communication
• Historically, audio / video content transmitted in analogue
form although these transmissions
• Gradually being replaced by digital signal modulation of
analog.
• Signals as digital standards become established
• N.B. Strictly speaking, all physical transmissions of signals
are analogue, however, the modulation of signals may
convey digital information.
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Benefits of Digital Communication
• Benefits for using digital transmissions?
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Chapter11: Overview
The slides for this chapter are also expanded and split into
several parts
• Part A: Introduction
• Part B: Audio Networks 
• Part C: Data networks: Fixed
• Part D: Data networks: Wireless
• Part E: Video & Multi-Content Access Networks
• Part F: Ubiquitous Networks: PLC, PAN, BAN, Mobile
• Part G: Network Access Control
• Part H: Service-Oriented Networks 1
• Part I: Service-Oriented Networks 2
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Types of Audio Networks
•
•
•
•
•
•
•
PSTN Voice Networks
Intelligent Networks (IN)
IP Multimedia Subsystems (IMS)
ADLS Broadband
Telecoms WWAN
Telecoms WLAN: DECT
Audio Broadcast (Radio Entertainment) Networks
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Audio Networks
• 1st type of pervasive communications network
Two basic types:
• Audio unicast networks (PSTN)
• Audio broadcast (radio) networks
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Public Switched Telephone Network
(PSTN)
• PSTN orig. designed to support voice communication (not
data, video)
• Analogue -> digital transmissions
• Still use separate networks for voice & data although
convergence of voice, data and audio-video progressing
• Phones (fixed & mobile) act as PSTN access devices
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Public Switched Telephone Network
(PSTN)
Home users
• Single-line local loop to external local switching station
Work users
• Phones connect to a private circuit switched network or
Private Branch Exchange (PBX) to access external
networks.
• etc.
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PSTN
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PSTN
• Core network orig. circuit switched not packet-switched
networks
• Designed to 1st set up dedicated circuit of links between
switching offices
–
• Circuit switching used in Telecoms networks used hierarchy
~5 levels
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PSTN
• PSTNs were designed to be very resilient.
• Circuit switching can enable a higher QoS per call but at
the expense of non-optimal use of the channel,
–
• Interleaved multiple data streams  throughput
– E.g.,
• Later digital telecoms networks
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Intelligent Networks (IN)
• Earliest digital telecommunication networks designed to
support specific services, supported using specialised
logic contained in specialised switching network elements.
• New features / services have to be added and implemented
directly in core switch systems -> very long development
times for new services
• -> Intelligent Networks (IN) network service model,
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Intelligent Networks (IN)
• Supports independent component-based services in
general purpose computer nodes rather in special
switching nodes.
• Enables service providers to drive new services rather than
network providers
– able to use these to form flexible overlay networks
– such as toll free calls, e.g., “0800” numbers.
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IP Multimedia Subsystems (IMS)
• Active development in new IN services has declined in
recent years
• Focus on development of telecom services & APIs rather
than on developing new telecom network protocols.
• Although, there seems to be a clear move to IP based
networks, in shorter term, hybrid IN and Internet service
architectures for mobile users are being proposed such as
IP Multimedia Subsystems (IMS).
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IMS
• A key challenge is application-layer control (signalling)
protocol for controlling voice/video session, multimedia
conference, messaging and Presence over IP.
• Control can be performed using the IETF SIP (Session
Initiation Protocol) replacing ITU’s earlier H.323 protocol.
• Basic entities in a typical SIP system involve?
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IMS
• SIP can use 3 different types of MCU:
– full mesh,
– mixer
– multicast.
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Asynchronous Digital Subscriber Line
(ADSL) Broadband
• ADSL  transmission capability over existing physical
– e.g., copper-wire PSTN type, access networks.
• Audio telephony use ~ 3 kHz bandwidth but typical line
transmits usable signals up to approximately 1MHz.
• High-frequency signals however face more transmission
challenges such as ..
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Telecoms: ADSL
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Telecoms WWAN
• Wireless Wide-Area Networks (WWAN)support anywhere
access for mobile or cell phone users,
• WWAN differ w.r.t:
– Geographic region
– on the Generation (G) of the wireless network such as 1G analogue
and 2G digital.
• These differ primarily on the way they are designed to
share access to the wireless network amongst different
users.
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Telecoms WWAN
• WWAN differ primarily on the way they are designed to
share access to wireless network amongst different users.
• Global System for Mobile Communications (GSM)
• Code Division Multiple Access (CDMA)
–
• Networks can interoperate via gateways …
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Telecoms WWAN
• WWAN transmitters or base stations have a limited range
–
• When a user moves between cells, What happens?
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WLAN: DECT (Digital Enhanced
Cordless Telecommunications)
• Deployed > 100 countries worldwide
–
• Access control :
• Frequencies:
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Audio Broadcast (Radio
Entertainment) Networks
• Several benefits in using audio broadcasting or radio?
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DAB
• For digital radio, the Eureka 147 Digital Audio Broadcast
(DAB) standard is most commonly used and is coordinated
by the World DMB Forum.
• DAB uses the MPEG-1 Audio Layer 2 audio (MP2) codec
for audio broadcasting while personal players use the MP3
codec.
• Original objectives of DAB were to ?
• DAB+ standard with a better and more efficient
transmission codec has been proposed.
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Chapter11: Overview
The slides for this chapter are also expanded and split into
several parts
• Part A: Introduction
• Part B: Audio Networks
• Part C: Data networks: Fixed 
• Part D: Data networks: Wireless
• Part E: Video & Multi-Content Access Networks
• Part F: Ubiquitous Networks: PLC, PAN, BAN, Mobile
• Part G: Network Access Control
• Part H: Service-Oriented Networks 1
• Part I: Service-Oriented Networks 2
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Internet
•
•
•
•
•
•
Early Internet (1960s) was based upon several innovations.
Shift from batch to time-shared computers.
Shift from P2P topology
Shift from analogue to digital communication
Support for high capacity and resilient network paths
Large data was split into fixed size data packets
Shift from circuit switched to packet-switched data model
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Network Protocols
• Types of data and control packets are defined in a network
communication protocol
• Data packet size:
–
• Data segmentation.
• .
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Network Protocols
• Types of packet to data packets called control packets,
•
• Each data packet is labelled with the address
• Enables packets from multiple messages to be multiplexed
to use the same part of the network.
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Data Packet Protocols
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Addressing
• Before communication can occur between network
elements, e.g., computers, they need to be allocated
network addresses.
• Explain ….
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Address Space Size
• IPv4 supports 32 bit (about 4.3 billion) addresses.
• IPv6 supports 128 bit addresses
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Routing and Internetworking
• Multiple paths may be available
•
• Data may be too large to be transmitted
• Normally performed at the network level without
applications being aware of this.
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Packet-switched Routing
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Routing and Internetworking
• Routers examine the addresses of data packets to decide
– ????
• Routers communicate with each other using specialised routing
protocols
–
??
• Dynamic routing ?
• Use of multiple routes ?
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Chapter11: Overview
The slides for this chapter are also expanded and split into
several parts
• Part A: Introduction
• Part B: Audio Networks
• Part C: Data networks: Fixed
• Part D: Data networks: Wireless 
• Part E: Video & Multi-Content Access Networks
• Part F: Ubiquitous Networks: PLC, PAN, BAN, Mobile
• Part G: Network Access Control
• Part H: Service-Oriented Networks 1
• Part I: Service-Oriented Networks 2
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Wireless Data Networks
•
•
•
•
•
•
•
Wireless LANs (WLANs) / WiFi
WiMAX
BlueTooth
ZigBee
InfraRed (IR)
Ultra Wide Band (UWB)
Satellite and Microwave
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Wireless Data Networks
Benefits for using wireless networks:
• Anywhere
• Mobility:
• Less disruptive
• Adaptivity
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Wireless Data Networks
• Wide variety of wireless networks exist.
• Networks vary according to ?:
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Wireless Data Networks: examples
• Most global, wide area and local area wireless networks
are infrastructure dependent and use fixed transmitters,
–
• Ad Hoc Wireless Network the transmitters and routers are
dynamic
– .
• Mobile wireless networks can vary by the range they cover.
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Wireless Data Networks
• Range depends upon ?
–
• Generally, the higher the frequency ……
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Wireless Data Networks
• Spatial Efficiency (SE )
• Power efficiency metric:
• Spatial and power efficiency
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Wireless Data Networks: bandwidth
allocation
• Proliferation of new wireless services
• -> concern over how to (re)allocate scarce radio frequency
(
• New to techniques allow  flexible & efficient spectrum
use?
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Wireless Data Networks: Software
Radio
• Software Radio moves the radio functionality from
hardware into software
• Software radio alters trad. radio design in 3 main ways.
How?
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Wireless LANs (WLANs)
•
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WiMAX
• WiMAX, the Worldwide Interoperability for Microwave
Access, from the WiMAX Forum , is proposed as wireless
wide-area broadband access technology, based upon the
IEEE 802.16 standard
• Etc.
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Bluetooth
• Bluetooth standard for short-range wireless communication
over about 1-100M
• Bluetooth applications include both local communication
and increasingly local control.
• Unlike IR, Bluetooth does not require a line of sight
between the transmitter and receiver.
• Current Bluetooth devices and applications include: ?
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Bluetooth versus WLAN
• ???
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ZigBee
• ZigBee is a specification for a suite of communication
protocols from the ZigBee alliance formed in 2002
• Uses small, low-power digital radios based on the IEEE
802.15.4 standard for Wireless Personal Area Networks
(WPAN)
• etc
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ZigBee versus Bluetooth
• ???.
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Infrared (IR)
• Infrared (IR): a short-range low bandwidth data
communication
– …..
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Ultra-Wideband (UWB)
• Transmits information at data rates exceeding 100 M bits /
s, spread over a large bandwidth (>500 MHz), in the 3.1–
10.6 GHz frequency range at a low power range, over short
distances.
• Provide an efficient use of scarce radio bandwidth while
enabling both high data rate wireless connectivity
• Uses:
– Short-range: BANs, PANs and within buildings
– Longer-range, low data rate applications: radar, collision obstacle
avoidance, precision altimetry & imaging systems
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Satellite and Microwave Comms
• Geostationary satellites use simpler antennae design and
configuration & small No. of satellites can be interlinked to
provide global coverage.
• Satellite design issues?
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Internetworking WLANs
• Benefits to internet wireless networks: ?
•
• WLAN can access Internet for mobile computer,
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Internetworking WLANs
• Mobile phone use faster? Cheaper? WLAN at hot spots
– requires OS support pipelines across heterogeneous networks.
• Generic Access Network (GAN), also known as Unlicensed
Mobile Access (UMA), is a telecommunication system
allowing seamless roaming and handover between local
area networks and wide area networks using dual-mode
mobile phones.
• Femtocells, small cellular access points which provide
enhanced coverage & converged voice, data and video
services such as IPTV
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Chapter11: Overview
The slides for this chapter are also expanded and split into
several parts
• Part A: Introduction
• Part B: Audio Networks
• Part C: Data networks: Fixed
• Part D: Data networks: Wireless
• Part E: Video & Multi-Content Access Networks 
• Part F: Ubiquitous Networks: PLC, PAN, BAN, Mobile
• Part G: Network Access Control
• Part H: Service-Oriented Networks 1
• Part I: Service-Oriented Networks 2
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Universal Content Networks / Network
Convergence
• Services  delivered over common network
• Audio and Video (AV) broadcast Content Based Networks
(CBN) have different drivers compared to Telecoms and
network networks.
• Telecoms networks are developed to support duplex or
two-way, one-to-one communication, global interoperability
• Internet developed (initially) to support asynchronous
communication.
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Audio and Video (AV) broadcast
Content Based Networks (CBN)
• Digital AV CBN designed to transmits streamed audio &
video
– ….
• Broadcast networks are designed more for:
– ……
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Audio and Video (AV) broadcast
Content Based Networks (CBN)
• AV CBN oriented to for a regional rather than global
customer base.
• Video content is richer and it is more likely to be tailored to
a specific region in terms of language and culture.
• Receivers have limited control over live broadcasts
• Video synchronisation with audio (& metadata) is complex
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Internet and Common Codecs
• Internet focussed most on alphanumeric data transmission
• support for managing reliable and unreliable data streams,
mainly for paired senders and receiver.
• support for scalable AV content streamed broadcasts over
Internet still maturing
• Adoption of compatible standards for the triple-play (audio,
video and alphanumeric data) will facilitate their integration.
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PSDN: IP and UDP
• UDP ( User Datagram Protocol) used to support mutlicast
– .
• Unreliable transport protocols, e.g., UDP can be used to
transmit media streams.
• Depending on the protocol and the extent of the loss,
receivers may be able to recover the data using
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Streaming Media over IP networks
• Protocols designed to stream media over IP networks.
• RTP and RTCP built on top of unreliable UDP
• RTSP built on top of reliable TCP
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Combined Voice and Data networks:
ADSL
• In residential & SME buildings, single external comms line
is used to access multiple services, e.g., voice, text, video,
• ADSL is replacing use of older ISDN, dial-up modems
• There are different types of access device or modem, e.g.,
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Voice over IP (VoIP)
• Use of IP network, to In transmitting voice as data packets
& interleave text data and voice over same network
• Requirements \/
–
• Delays can be caused by ?
–
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Combined Audio-Video and Data
Content Distribution Networks
• Traditionally, the three different types of conventional
networks for broadcasting audio-video entertainment
content are:
– VHF TV
– Satellite TV
– Cable TV.
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Integrating Analogue Video and Text:
Teletext
• Analogue television broadcast signal can be augmented
with text data by embedding this data in the Vertical
Blanking Interval or VBI part of the television signal.
• In EU: called Teletext data transmission; closed-captioning
in USA
• ….
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Digital Video Broadcasting (DVB)
•
•
•
•
•
DVB replacing analogue video broadcasting
Multiple standards for digital video broadcasting
.
DVB system is the most widely used
DVB is modelled like TCP/IP at an abstract level
•
• All data is transmitted as MPEG-2 transport streams.
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Multimedia Broadcast networks
• Triple-play networks, e.g., Web documents VoIP, video
streaming.
• Quad-play networks: triple-play + mobile phone
• Need to multiplex heterogeneous packets from multiple
applications which have different sensitivities to time delays
and jitter. Several ways to this in IPv4 networks?
•
• IPv6 has more inbuilt support for this.
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Multiplexing heterogeneous packets
from multiple applications (IPv4)
• MPLS
•
• Differentiated Services (Diffserv)
•
• Resource Reservation Protocol (RSVP)
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On-demand, Interactive and
Distributed Content
In contrast, Video-On-demand (VoD) Benefits?
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Chapter11: Overview
The slides for this chapter are also expanded and split into
several parts
• Part A: Introduction
• Part B: Audio Networks
• Part C: Data networks: Fixed
• Part D: Data networks: Wireless
• Part E: Video & Multi-Content Access Networks
• Part F: Ubiquitous Networks: PLC, PAN, BAN & Mobile
• Part G: Network Access Control
• Part H: Service-Oriented Networks 1
• Part I: Service-Oriented Networks 2
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Pervasive Networks: Types
Already covered some examples of pervasive networks
• Mobile Telecoms Networks such as GSM, UTMS
• Wireless data networks: WiFi, Bluetooth, Zigbee etc
In addition will cover
• Power Line Communication (PLC)
• Personal Area Networks (PAN)
• Body Area Networks (BAN)
• Mobile Users Networks
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Pervasive Telecoms Networks
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Pervasive Wireless Networks
Challenges
•
•
•
•
•
Signal Transmission
Overlapping Networks
Power Consumption & Transmission Efficiency
Soft Boundaries & Access Control
Interference
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Power Line Communication (PLC)
• An alternative to ubiquitously access data and A-V content.
• Wherever there is an electricity PL connection, same
network that conducts electricity to deliver energy
• PL can be used modulate electricity as a signal and can be
used as a channel to communicate data/AV content.
• PLC describes a range of systems for using electricity
distribution wires for simultaneous distribution of data.
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Wireless Personal Area Networks
(WPAN)
• Specified by the IEEE P802.15 working group
• PAN is normally confined to a person or object typically <10
M in all directions and envelops two or more objects or
persons whether stationary or in motion.
• Could WLAN standard be used for PANs?
–
• Bluetooth, Zigbee and IR can be used to implement a PAN.
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Wireless Personal Area Networks
(WPAN)
Typical WPAN applications include ??
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Body Area Network or BAN
• Consists of a set of mobile and compact
intercommunicating sensors that are either wearable or
implanted into the human body.
• A typical BAN application can monitor vital body
parameters and movements
– E.g., monitor EEG, ECG, and EMG signals
• Data Management?
– Either to store them in some device on the body for later upload and
analysis
– To periodically transmit data in real-time via some external network
interface
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BAN
• Can Bluetooth or ZigBee be used for BAN?
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BAN
• Electronic devices can be connected as part of near field
BANs to exchange digital information by capacitively
coupling picoamp currents through the body (Zimmerman).
• Low-frequency carrier, less than one megahertz, was used.
Why?
–
• Zimmerman demonstrated a near-field BAN system to
support business processes
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Inter-BAN Application
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Mobile Users Networks
• Not all network access by mobile users, applications and
devices need be via wireless networks and vice versa
• Wireless access devices can be static and mobile users
can move in between wired or wireless hotspots such as in
Internet cafes.
• Mobility vs. portability network support.
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Mobile User Networks: Design Issues
• Design issues include?
• We can also classify mobile network support in terms of ?
–
• Advantage of mobile user support at the network level of
the network protocol stack means that mobility, at least to
some extent, is transparent to applications.
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Concepts: Mobile vs. Wireless
Services
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Mobile Addresses
• Network location or address for a mobile user needs to be
determined in order for a user to receive data.
• It is easier to send (somewhere) as the user just has to
locate the nearest access network base station.
• There are two basic approaches to mobile user addressing:
– ????.
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Message Routing for Mobile Users
Different types of routing for mobile users can be
classified along 2 dimensions:
• Fixed versus variable routes
• Single versus multi-path routes
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Message Routing for Mobile Users:
single path route
• Example of single path route is Mobile IP consisting of
Mobile Node, Home agent and foreign agent
• Mobile IP performs three main functions:
– Discovery:.
– Registration
– Tunnelling
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Message Routing for Mobile Users:
single path route
Mobile IP performs three main functions:
• Discovery
•
• Registration
• Tunnelling:
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Multi-Path Routing in Mobile Ad hoc
Networks (MANETs)
• In contrast to fixed computer networks, ad hoc networks:
– use connections established for duration of 1 session
– require no base station or fixed router.
• Ad hoc networks that support mobile nodes are called
Mobile Ad hoc Networks (MANETs)
• Rather than used dedicated router nodes, each node is
willing to forward data for other nodes, and so the
determination of which nodes forward data is made
dynamically based on the network connectivity, hence the
name ad hoc
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MANETs
• Instead, devices discover others within range to form a
network for those computers.
• Devices may search for target nodes that are out of range
by flooding the network with broadcasts that are forwarded
by each node.
• Connections can be made over multiple nodes (multi-hop
ad hoc network).
• Routing protocols then provide stable connections even if
nodes are moving around.
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MANETs
MANETs Applications:
• in situations where a useful network infrastructure is not
already in place
– E.g., in natural disaster
• in armed conflict situations
• Wireless multiplayer gaming
– E.g., Sony's PlayStation and the Nintendo Dsi and Wii game
consoles
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MANET
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Chapter11: Overview
The slides for this chapter are also expanded and split into
several parts
• Part A: Introduction
• Part B: Audio Networks
• Part C: Data networks: Fixed
• Part D: Data networks: Wireless
• Part E: Video & Multi-Content Access Networks
• Part F: Ubiquitous Networks: PLC, PAN, BAN & Mobile
• Part G: Network Access Control 
• Part H: Service-Oriented Networks 1
• Part I: Service-Oriented Networks 2
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Network Design Issues
• Network Access Control
• Controlling Network Access: Firewalls, NATs and VPNs
• Group Communication: Transmissions for Multiple
Receivers
• Internetworking Heterogeneous Networks
• Separating Management and Control from Usage
• Ubiquitous versus Localised Access
• Global Use: Low-cost Access Networks for Rural Use
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Network Access Control: Mobile
Phone
• Different networks use a range of access control
techniques to:
– handle network resource allocation problems
– allow multiple users to access network media with limited capacity.
• TDMA:
• CDMA:
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Network Access Control: WLAN
• WLANs often based on sharing freq. between several active
users.
• Many simultaneous users may cause packet collisions ->
waste channel bandwidth
• Difficulty to detect some (hidden) nodes -> design to avoid
packet collisions.
• WLANs typically use a MACA type transmission protocol.
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Network Access Control: LAN
• A further option is to use CSMA/CD
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Network Access Control: LAN
• Token-based systems control access to local networks
using special control messages, tokens, which continuously
circulate throughout a system,
– e.g., structured as a token ring topology.
• …
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Controlling Network Access:
Firewalls, NATs and VPNs
• Many ICT resources connected to the Internet are
protected to control access to specific resources by
specific users or to a closed user group.
• If access is not restricted what happens?
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Controlling Network Access:
Firewalls, NATs and VPNs
How to protect access to local networks?
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Controlling Network Access: Firewalls
Routes versus Firewalls
• A router / special purpose computer that ….
–
• Firewalls designed according to which level of network they
work:
–
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Controlling Network Access: Firewalls
Packet-level firewalls
• …
•
Application level firewalls
•
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Controlling Network Access: NAT
• Network Address Translation (NAT)
• Firewalls
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Controlling Network Access: NAT
• .
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Controlling Network Access: VPN
• Useful to restrict the use of resources on remote networks
to specific users that are accessed over a public Internet.
• Common technique to achieve this is a VPN
• .
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Controlling Network Access: VPN
• Users normally authenticate themselves at VPN client or
access device to gain access to remote resources via VPN:
• Several types of VPN / Service
– ????
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Controlling Network Access: VPN
Persistence of messaging
• Proxy host
• Bastion host
Network Interfaces Available
• ???
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Multicasts: Transmissions for Multiple
Receivers
• Sending the same message from a single source to a
defined group of multiple receivers, multicast
communication or group communication is useful. Why?
–
• Hardware vs. software support
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Multicasts: Transmissions for Multiple
Receivers
• To avoid the overhead in managing large groups, groups
can be split into hierarchies
–
• Messages can be tagged with sequenced identifiers to
indicate ordering.
• Acknowledgements can be used to support more reliable
group communications.
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Multicasts: Transmissions for Multiple
Receivers
• Group membership may or may not be visible to the
members depending upon the design.
– ???
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Low-cost Access Networks for Rural
Use: VSAT
Very Small Aperture Terminal (VSAT):
• .
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Ubiquitous versus Localised Access
• Networks can be designed for local context-aware access:
• Used to tailor services for local needs.
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Ubiquitous versus Localised Access
• Services can be restricted to local access because?
–
• Local services can also be designed to have access control
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Ubiquitous Access: WANs
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Global Use: Low-cost Access
Networks for Rural Use
• In theory, wireless networks could be ubiquitous but in
practice they aren’t in many regions.
• Currently, the total worldwide Internet usage penetration
was only about 18% but only about 4% in Africa (2007).
• but 29% of the global population use GSM type mobile
phone technology (2007), more if other types of mobile
phone are also included.
• People in some rural areas may not be able to pay much
• Hence low-cost networks and access terminals are
needed.
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Low-cost Access Networks for Rural
Use
• In rural areas, several low cost network access methods
have been developed?
–
–
–
–
CorDECT
PrintCast
VSAT
Mesh Network
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Low-cost Access Networks for Rural
Use: VSAT
Very Small Aperture Terminal (VSAT):
• ??.
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Low-cost Access Networks for Rural
Use: CorDECT
CorDECT system
• Based on the DECT standard which initially was designed
for use with cordless telephones.
• Uses MC-TDMA to performs both time and frequency
division in order to accommodate multiple channels.
• Typically operates over distances of up to 10 KM with data
rates supporting data rates of 35 and 70kbps. T
• Conventional listen before you talk type MAC is
problematic when used in low bandwidth transmission over
several km
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Low-cost Access Networks for Rural
Use: PrintCast
• PrintCast system: leverage broadcast TV as a service access network.
• …….
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Chapter11: Overview
The slides for this chapter are also expanded and split into
several parts
• Part A: Introduction
• Part B: Audio Networks
• Part C: Data networks: Fixed
• Part D: Data networks: Wireless
• Part E: Video & Multi-Content Access Networks
• Part F: Ubiquitous Networks: PLC, PAN, BAN & Mobile
• Part G: Network Access Control
• Part H: Service-Oriented Networks 1 
• Part I: Service-Oriented Networks 2
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Service-oriented Networks
•
•
•
•
Internetworking
Network-Dependent vs. Independent Services
Separating Management and Control from Usage
Service Orientation in Edge Network
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Internetworking Heterogeneous
Networks
• Ideally, universal access means
– any type of data
– may be accessed simultaneously
– anywhere over any kind of network
• Historically, many separate types of communication
network exist that are not interlinked.
• Networks are heterogeneous in terms of the physical media
that electromagnetic signals propagate through.
– e.g., signals may propagate through wired copper or optical fibre
networks or through wireless or Over-The-Air, (OTA) networks.
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Internetworking Heterogeneous
Networks
• Different types of physical or links of the network have
different signal capacities and have different signal
attenuation and hence different requirements for signal
amplification and repeaters.
• Each type of physical media network,
– e.g., Ethernet, Point to Point Protocol (PPP) defines its own
protocols to partition, structure data into packets for transmission.
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Inter-Network Architecture
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Separating Management and Control
from Usage
• Are different options for designing application use versus
control and management of networks
• Architectural model can separate concerns about:
– media access,
– control of the communication
– management of the communication.
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Separating Management and Control
from Usage
• Management
– … FCAPS functions.
• Control
• .
• Application centric model
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Separating Management and Control
from Usage
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Separating Management and Control
from Usage
• in-band signalling:
•
• out-of-band signalling
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Separating Management and Control
from Usage
• In some systems, each major application uses its own
dedicated network,
• Hence management is application (network) specific.
• As multimedia content applications are becoming
integrated into single networks, …..
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Network Dependent Services
•
Traditionally, different application services were coupled to
specific networks because different applications need
different levels of support for:
–
–
–
–
–
–
Data transmission functions, such as latency,
sequencing,
performance and reliability,
channel sharing,
data control
security.
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Network Independent Services
•
Simpler to design networks to support 1 specific set of
application requirements rather than to support multiple
applications. Why?
• Disadvantages?
–
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Service-Oriented Networks
Focus was on network oriented models
• To use a service, users must subscribe to a particular
network and service configuration on the network,
– e.g., voice calls via a telecoms network and audio-video content via
an audio-video wireless broadcast network.
Focus has now shifted to service- oriented models
• Focus is on core networks that support multiple services
• Services are coupled less to specific networks
• Services can be available across heterogeneous networks
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Paradigm Shift from Network-Oriented to
Service Orientated Architectures
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A Simple Network Topology
• Simplest network topology is to have only one network
– E.g., analogue VHF radio network from transmitter to receiver
• Next simplest network topology is to partition network into 2
parts:
– Access network or edge network
– Core network
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Service-Orientation: in Edge Network
Important design decision is whether or not to put the
complexity or intelligence for service specific
communication:
• into the core network,
– e.g., PSTN
• Or in the edge network
• Or in both
– e.g., IP networks.
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Service-Orientation: in Edge Network
• Motivation for end-to-end or edge-based complexity?
• A main argument is that “functions placed at low levels of
system may be redundant or of little value when compared
with cost of providing them at that low level.”
•
This implies that networks that are simple and neutral as
possible should be used
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Service-Orientation: in Edge Network
• Widespread adoption of IP in the core network has given
the Internet a nearly universal interoperability
– allows all end users to access Internet applications and content on
a non discriminatory basis.
• IP provide a network neutrality vision for comms & content
delivery worlds in which every end user can obtain access
to every available application and piece of information is
quite compelling.
• However, it has led to some content providers resisting
more open access to the edge network as they will lose
market share.
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Chapter11: Overview
The slides for this chapter are also expanded and split into
several parts
• Part A: Introduction
• Part B: Audio Networks
• Part C: Data networks: Fixed
• Part D: Data networks: Wireless
• Part E: Video & Multi-Content Access Networks
• Part F: Ubiquitous Networks: PLC, PAN, BAN & Mobile
• Part G: Network Access Control
• Part H: Service-Oriented Networks 1
• Part I: Service-Oriented Networks 2 
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Service-Oriented Networks 2
This part gives an overview of network paradigms that
support some more flexible messaging
• Content-based Networks (CN)
• Programmable Networks
• Overlay Networks
• Mesh Networks
• Cooperative Networks
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Content-based Networks (CN)
• CN is a network in which the flow of messages through the
network is driven by the content of the messages, rather
than by linking specific senders to specific receivers.
• With this communication pattern, receivers subscribe to the
types of content that are of interest to them without regard
to any specific source (unless that is one of the selection
criteria).
• Senders simply publish information without addressing it to
any specific destination.
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Programmable Networks
• Typically, service providers do not have access to the
router, in order to optimise network use for different
applications.
– e.g., router control environments algorithms & router states,
• This makes the deployment of new network services, which
could be far more flexible than proprietary control systems,
impossible due to the closed nature of network nodes.
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Programmable Networks
• Programmable networks allow some of the network
elements to be reprogrammed dynamically
– .
• Disadvantages?
– .
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Programmable Networks
• 2 two main initiatives to establish programmable networks:
– DARAPA’s Active Networks (AN) program
– Open Signalling (Opensig) community.
• Difference in focus between these two?
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Overlay Network
• An overlay network is a virtual network built on top of a
physical network that provides a (virtual) infrastructure to
one or more applications.
• It handles the forwarding and handling of application data
in ways that can differ from or in competition with the basic
underlying physical network such as the Internet or PSTN.
• It can be operated in an organised and coherent way by
third parties, which may include collections of end-users.
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Overlay Network
Motivation for Overlay networks
• ????
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Overlay Network
• Another issue is that different applications may need
different levels of reliability, performance and latency and
security and access control.
–
• Application specific overlay networks can be incrementally
deployed on end-hosts running an overlay protocol,
–
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Mesh Networks
• In a full mesh network topology, every network node is
connected using point-to-point connections to every other
one. Cons?
– connecting every node to every other node is costly to wire and
costly power wise to transmit to each other.
• Hence, in practice, mesh networks are usually partial mesh
networks, in which each node is not connected to every
other node.
• Partial mesh networks tend to combine ring and star based
network topologies.
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Full Mesh
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Partial Mesh
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Wireless Mesh Networks (WMNs)
• Are partial mesh, ad hoc, networks that can significantly
improve the performance, at a lower cost and at a lower
power output compared to other types of WLAN
–
•
WMN is lower power because it uses a set of lower power
multi-hop transmissions rather than needing a single more
powerful transmission to base-station.
• WNM may be a suitable solution in rural areas where
conventional base-station wireless type network support or
DSL support maybe patchy.
• However, each WMN receiver is now more complex and
more costly as it must also act as a relay.
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Wireless Mesh Networks (WMNs)
• Instead of using a sophisticated and costly, centralised
base stations, each wireless receiver in a WMN can act as
a relay point or node for other receivers within range
• -> WMN acts as a kind of cooperative network for its users.
• WMNs can be used to ??
– .
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Wireless Mesh Networks (WMNs)
• In WMNs, each node operates not only as a host but also
as a router (mesh–clients), forwarding packets on behalf of
other nodes that may not be within direct wireless
transmission range of their destinations
• In addition, dedicated mesh routers which contain
additional routing capabilities and bridging and gateway
function to other networks.
• WMN can also dynamically self-organise and self-configure
mesh connectivity to support ad hoc multi-hop networking.
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Wireless Mesh Network (WMN)
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Cooperative Networks
• Some network access devices cannot access multiple
networks in order to communicate, they just have access to
1 network connection
• Some other network access devices have inbuilt support to
heterogeneous network access,
– e.g
•
Each of these networks must be used in isolation they do
not interoperate.
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Cooperative Networks
• Multiple types of the same type of physical and network
layer may exist
– because multiple independent users and providers may offer overlapping
wireless networks within the same vicinity but yet again these do not
interoperate.
• These overlap and the coincidence of multiple overlapping
networks will increase as more networks get installed but
yet again these networks do no interoperate.
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Cooperative Networks
• Cooperative communication is designed to enable singleantenna mobile access devices to reap some of the
benefits of being Multiple Input Multiple Outputs (MIMO)
systems
• A specific problem that cooperative communication can
solve at the physical media layer concerns signal fading
– because thermal noise, shadowing due to fixed obstacles and due
to signal attenuation can vary significantly over the course of a
given transmission.
• Transmitting independent copies of the signal that will face
independent fading generates diversity and can effectively
combat the deleterious effects of fading through combining
these multiple signals.
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Chapter11: Overview
The slides for this chapter are also expanded and split into
several parts
• Part A: Introduction 
• Part B: Audio Networks 
• Part C: Data networks: Fixed 
• Part D: Data networks: Wireless 
• Part E: Video & Multi-Content Access Networks 
• Part F: Ubiquitous Networks PLC, PAN, BAN & Mobile 
• Part G: Network Access Control 
• Part H: Service-Oriented Networks 1 
• Part I: Service-Oriented Networks 2 
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Summary & Revision
For each chapter
• See book web-site for chapter summaries, references,
resources etc.
• Identify new terms & concepts
• Apply new terms and concepts: define, use in old and
new situations & problems
• Debate problems, challenges and solutions
• See Chapter exercises on web-site
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Exercises: Define New Concepts
• Client-server, etc
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Exercise: Applying New Concepts
• What is the difference between client-server and P2P model?
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