Innehåll, föreläsning 1 (idag)
Innehåll, föreläsning 2 (fredag)
• introduktion till datornät
• trådlösa lokala nät
– trådlös kommunikation
– kommunikationsnät
– atm-nät
– switchade nät
– protokoll
– tcp/ip
– ad hoc-nät
– WLAN (IEEE 802.11)
• arkitektur, MAC-lager/DCF, säkerhet
– WPAN (Bluetooth)
• Glomosim-labben
Innehåll, föreläsning 3
(måndag)
TDDC22
Mobila trådlösa nätverk, föreläsning 1
• gsm-nät
• satelliter
av Juha Takkinen
Avdelningen för databas- och informationsteknik (ADIT), IDA/LiU
2007-01-18
Ljusbilder baserade på boken Wireless communications and
networks, © William Stallings, 2002, Prentice Hall
Wireless Communication Background [1]
Wireless Communication Background [2]
• Wireless telegraph - 1896 (Marconi)
• Cellular Communication
– encoding alphanumeric characters in analog signal
–
–
–
–
– 1901 - sent telegraphic signals across the Atlantic
Ocean
• Satellite communication - first 1960
• Wireless networks: WAN, MAN, LAN, MANET,
HAN, PAN
• Radio, television
• Mobile telephony
by 2004 - 1 billion users!
since 1996 exceed new fixed subscribers
new services, e.g. mobile Internet
different standards (AMPS, GSM, PCS …) =>
need for unification IMT 2000
• Broadband wireless communication
– WLAN to Home Networks
– high data rate from 2 Mbps to over 100 Mbps
Convenient and often less expensive than fixed
networks
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Introduction to wireless communication systems
4
Introduction to wireless communication systems
1
Communication Networks
Wireless Communication Background [3]
• WAN - Wide Area Networks
• MAN - Metropolitan Area Networks
• LAN - Local Area Networks
• Wireless communication problems
– lack of industry-wide standards and thus
interoperability
– technical limitations, e.g transmission problems
– political limitations, e.g. frequency spectrum
– devices limitations
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Introduction to wireless communication systems
Introduction to wireless communication systems
Wide Area Networks
Metropolitan Area Networks
Local Area Networks
• WAN - Wide Area Networks
• LAN - Local Area Networks
– large geographic areas
– may rely on circuits provided by a common carrier, e.g
telephone network
– traditional data rates up to 64 Kbps for regular subscribers
and 1.544Mbps for business subscribers
– smaller geographic area in comparison with previous
networks, e.g. a building
– usually owned by an organization
– internal data much higher than for previous networks
– traditional data rates up from 1 to 20 Mbps
– high-speed WAN - possible data rates over 100 Mbps
– high-speed LAN data rate from 100 Mbps to 10 Gbps
• MAN - Metropolitan Area Networks
– traditional techniques in WAN not appropriate for
organizations
– need for private and public networks with high capacity
– smaller geographical area than WAN
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Introduction to wireless communication systems
Introduction to wireless communication systems
Switched Networks
•Stations
•Switching nodes
•Communication Network
Frågor
ÎStations-to-nodes
ÎNodes-to-nodes
ÎNot fully connected
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Introduction to wireless communication systems
2
Switching Techniques
Circuit Switching [1]
• Dominant technology for voice/data communication today
(e.g. PSTN-public switched telephone network)
• Communication phases
– Circuit establishment -> end-to-end circuit between stations
– Information transfer -> data exchanged between end
stations
– Circuit disconnect -> circuit release
• Circuit Switching
Îdedicated communication path between two stations
• Packet Switching
Îdata transmitted in blocks and may be send on separate
paths
Switching node 1
Switching node M
Network
A
B
Switching node N
10
•
–
–
–
Introduction to wireless communication systems
Introduction to wireless communication systems
Circuit Switching [2]
Packet Switching
•
–
–
–
Some benefits
network transparent to user
delay at each node negligible
fixed data rate
11
Data to be sent divided in packets
typical packet size - 1000 bytes
control information added to original data as headers
each node receiving a packet will forwards it to the next
node until it reaches the destination
• Efficiency problem
– unused channel capacity, e.g. idle time
– introduced delay due to call establishment
Application Data
Heade
r
Data
Heade
r
Data
Heade
r
Data
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Introduction to wireless communication systems
Introduction to wireless communication systems
Packet Switching vs. Circuit Switching
Packet Switching - Datagram Approach
• Datagram
• Advantages
– each packet treated independently
– each node choose the next node based on neighbors
information
– packets not need to follow same route
– exit or destination nodes reconstruct the data by ordering
received packets
– exit or destination nodes determine lost packets and may
employ recovery techniques
Î call setup avoided
– greater line efficiency
– data-rate conversion
– call block for heavy traffic may be avoided on the cost of
delay
– can use priorities
• Disadvantages
–
–
–
–
each node forwarding operation introduce delay
overall packet delay may experience extensive variations
overhead data have to be included in packets
nodes need to have more processing capabilities
Î flexible
Î reliable
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Introduction to wireless communication systems
15
Introduction to wireless communication systems
3
Datagram Approach- example
Packet Switching - Virtual Circuit Approach
• Virtual Circuit
– preplanned route before sending packets
– the route is used by all packets from source to destination
information
– similar with a circuit for a logical connection
Î original packets order at the receiver
Î packets arrive correctly
Î minimal delay at nodes
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Introduction to wireless communication systems
Introduction to wireless communication systems
Virtual Circuit Approach- example
Asynchronous Transfer Mode (ATM) [1]
• Similar with packet switching
• Transfer data chunks in fixed size packets called cells
• Minimal error and flow control capabilities
• Multiple logical connections called virtual channel connections
(VCC) multiplexed over a single physical interface
• VCC analogue with a virtual circuit in packet-switching
• VCC used for:
– user-user: data and signaling between users
– user-network: control signaling
– network-network: traffic management and routing
• a group of VCC -> a virtual path connection (VPC)
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Introduction to wireless communication systems
Introduction to wireless communication systems
Asynchronous Transfer Mode (ATM) [2]
Asynchronous Transfer Mode (ATM) [3]
• Virtual channel connection characteristics
• ATM Service Categories
– Quality of Service (QoS): use parameters such as cell loss and cell
delay
– Real-time Services: constant bit rate (CBR) and real-time variable
bit rate (rt-VBR)
– Switched and semipermanent VCC: switched and dedicated
connections
– Cell sequence integrity
– Non-real-time Services: non-real-time variable bit rate (nrt-VBR),
available bit rate (ABR) and unspecified bit rate (UBR)
• ATM Application Examples
– Traffic parameters negotiation (e.g. average data rate, peak
duration) and usage monitoring (e.g. congestion management)
–
–
–
–
–
• Virtual path connection characteristics
– Same first four characteristics as for VCC
– Virtual channel identifier restriction within VCC: several virtual
channel may be reserved for network management
videoconferencing (CBR)
100 %
distance learning (CBR)
banking transaction (nrt-VBR)
remote terminal (UBR)
LAN interconnection (ABR)
VBR
CBR
Tid
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Introduction to wireless communication systems
ABR, UBR
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Introduction to wireless communication systems
4
Protocols
Protocol: A set of rules used for two or more peers to
communicate
• Needed for the successful data transfer!
– e.g. sender must connect to network and indicate the
destination
– e.g. sender want to know if receivers can receive data
– e.g. data format translation needed
Frågor
• Protocol features:
– Syntax: data format
– Semantics: control data for data management and error
handling
– Timing: speed matching and sequencing
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Introduction to wireless communication systems
TCP/IP Protocols Reference Model [2]
TCP/IP Protocols Reference Model [1]
• Physical Layer
•
•
–
–
–
–
–
– between transmission device and transmission medium
– handle hardware details (e.g. data rate)
Started from ARPANET (1970)
Based on layers of services concept:
Application
Transport
Internet
Network
Network access
Physical
• Network Access Layer:
– between an end system and the network
– functions dependent of network type such as LAN (e.g.
Ethernet) or packet switching (e.g X25)
– handle packet movement across the network
• Internet Layer
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– provide routing functions for data relay over
interconnected networks
– use Internet Protocol (IP)
– implemented in end systems and routers (i.e. entities that
connect networks and relay data between them)
Introduction to wireless communication systems
TCP/IP Protocols Reference Model [3]
TCP/IP - How Does It Works? [1]
• Communication example
• Transport Layer
– send data between applications running on computers
– implemented usually by using Transmission Control
Protocol (TCP) or User Datagram Protocol (UDP)
– use secondary address named port for identifying the
sending and receiving process
– TCP: connection-oriented, two-way connection, reliable
(e.g. use checksum), fragmentation, order received data
– UDP: datagram-oriented (e.g. send one chunk of data),
connectionless, unreliable
• Application Layer
– manage details of applications
– build upon TCP or UDP
– example: Telnet, FTP, SMTP (e.g. mail), HTTP
Introduction to wireless communication systems
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Introduction to wireless communication systems
End System A
End System
B
Application
Application
Transport
Transport
Router N
Internet
Internet
Internet
Internet
Network access
Network
access
Network
access
Network access
Physical
Physical
Physical
Physical
Networ
k
Networ
k
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Introduction to wireless communication systems
5
OSI Reference Model [1]
TCP/IP - How Does It Works? [2]
• Developed by International Organization for
Standardization (ISO)
• Model for computer architecture
• Seven Layers
• Data processing flow
example
End System
Data
TCP Segment
User data
Application
TCP
header
User data
Transport
IP Datagram
IP header
TCP
header
User data
Internet
Network header
IP header
TCP
header
User data
Network access
–
–
–
–
–
–
–
Physical
Network frame
Application
Presentation
Session
Transport
Network
Data Link
Physical
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Introduction to wireless communication systems
Introduction to wireless communication systems
OSI Reference Model [2]
TCP/IP and OSI Reference Models
• OSI does not replaced TCP
• TCP-based protocols were already mature when
OSI was developed
• OSI is more complex than TCP
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Introduction to wireless communication systems
Introduction to wireless communication systems
Summary
Frågor
•
•
•
•
•
•
•
•
Wireless Communication
Wireless Networks
Switched Networks
Circuit Switching
Packet Switching
Protocols
TCP/IP Reference Model
OSI Reference Model
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Introduction to wireless communication systems
6
Additional References
Communication Frequency Spectrum
• Electromagnetic spectrum and applications (Tanenbaum 2003)
• Tanenbaum A. (2003), Computer Networks. Fourth
Edition. Prentice Hall.
•Toh, C-K (2002), Ad-Hoc Mobile Wireless Networks.
Prentice Hall.
• William Stallings, (2004), Data and computer
communication. Seventh Edition. Prentice Hall.
• Geier J. (2002), Wireless LANs. SAMS Publishing.
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Introduction to wireless communication systems
Wireless Networks Background
• Aspects of Wireless Networks
– mobility and convenient deployment
– scarce frequency spectrum
– wireless implications such as transmission problems (e.g.
interference, path loss, fading), security, battery,
installation, health
• Wireless networks
– Cellular: GSM, PCS, IMT 2000
– Satellite: IRIDIUM, Globalstar
– WLAN: IEEE 802.11, HiperLAN
– Ad-Hoc, PAN, HAN
7