WCN UNIT II ppts - Weebly · 2018. 10. 13. · . Connectionless Service • A connectionless...
27
UNIT II INTRODUCTION TO WIRELESS INTRODUCTION TO WIRELESS NETWORKING www.jntuworld.com www.jntuworld.com www.jwjobs.net
Transcript of WCN UNIT II ppts - Weebly · 2018. 10. 13. · . Connectionless Service • A connectionless...
UNIT II
INTRODUCTION TO WIRELESS INTRODUCTION TO WIRELESS NETWORKING
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
The cellular telephone system isresponsible for providing coveragethroughout a particular area known ascoverage region or market
Wireless Network
coverage region or marketThe interconnection of many such marketsdefines a wireless network capable ofproviding service to mobile usersthroughout country or continent
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Common air interface
Handshake communication
protocol
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
wired1. Transfer of information takes
place over landline trunked lines (trunks) made of OF cables, copper cables, microwave links and satellite links.
2. Network configurations are virtually static. Distance is a constraint for the subscribers
wireless1. Transfer of information takes
place with the help of signals which travel in air as ElectroMagnetic waves.
2. Network configurations are highly dynamic. The network configuration gets rearranged every time a subscriber moves into a different coverage constraint for the subscribers
3. Subscriber’s change of residence needs reprogramming at the local CO of subscriber.
4. The available bandwidth can be increased by installing high capacity cables.
into a different coverage region .
3. Wireless networks must reconfigure themselves for users within small intervals of time to provide roaming and handoff facility.
4. W/L networks are constrained by the little RF cellular B/W provided for each user.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Local Exchange
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
PSTN-Public switched telephone N/W1. LATA-Local access and transport area.Geographical grouping of towns is taken care by
LATA.2. LEC- Local exchange carrier.
IntraLATA telephone service.IntraLATA telephone service.
3. CO-Central Office-Provides PSTN connection to CPE.
4. CPE-Customer Premises Equipment-PBX or Residence telephone.
LATA LATALECSurrounding
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
PSTN5. PBX-Private Branch Exchange-Office
connections are dealt by PBX.--Intra PBX – No LEC involved. --Connection of PBX to CO is maintained by LEC.6. IXC-Inter Exchange Carriers are used to 6. IXC-Inter Exchange Carriers are used to
connect different LEC’s throughout the country or continent.
LEC LECIXCLong Distance
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Limitations of Wireless NetworksNetworks
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Limitations:1. Extreme complex communication system.2. Radio channel is extremely hostile and
random in nature.3. Growth in wireless systems leads to increase
in BS’s which increases the switching burden in BS’s which increases the switching burden of MSC
4. Extra overhead is required for MSC as the geographical location of MU changes constantly.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Wireless Links: High Bit Error Rate
• Decreasing signal strength–Disperses as it travels greater distance–Attenuates as it passes through matter
10
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Wireless Links: High Bit Error Rate
• Interference from other sources– Radio sources in same frequency band– E.g., 2.4 GHz wireless phone interferes with 802.11b
wireless LAN– Electromagnetic noise (e.g., microwave oven)– Electromagnetic noise (e.g., microwave oven)
11
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Wireless Links: High Bit Error Rate
• Multi-path propagation– Electromagnetic waves reflect off objects– Taking many paths of different lengths–Causing blurring of signal at the receiver–Causing blurring of signal at the receiver
12
receivertransmitter
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Dealing With Bit Errors
• Wireless vs. wired links– Wired: most loss is due to congestion– Wireless: higher, time-varying bit-error ate
• Dealing with high bit-error ratesDealing with high bit-error rates– Sender could increase transmission power
• Requires more energy (bad for battery-powered hosts)• Creates more interference with other senders
– Stronger error detection and recovery• More powerful error detection codes• Link-layer retransmission of corrupted frames
13
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Wireless Links: Broadcast Limitations• Wired broadcast links
– E.g., Ethernet bridging, in wired LANs– All nodes receive transmissions from all other nodes
• Wireless broadcast: hidden terminal problem
14
AB
C •A and B hear each other•B and C hear each other•But, A and C do not
So, A and C are unawareof their interference at B.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Wireless Links: Broadcast Limitations
• Wired broadcast links– E.g., Ethernet bridging, in wired LANs– All nodes receive transmissions from all other
nodes
• Wireless broadcast: fading over distance
15
A B C
A’s signalstrength
space
C’s signalstrength
•A and B hear each other•B and C hear each other•But, A and C do not
So, A and C are unawareof their interference at B.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Merging Wireless Networks and PSTN1. Signaling and Voice traffic were sent on the
same trunked lines i.e., a single physical connection was used to handle both of them.
2. In mid 1980’s when W/L evolved , the PSTN was transformed into two parallel networks-was transformed into two parallel networks-one for voice and other for setup, which is known as Common Channel Signaling(CCS).
3. Access to signaling N/W is provided by IXC’s.4. North America- Signaling-SS7.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Development of Wireless Networks
First generation wireless Networks:1. Based on analog technology. All cellular systems used FM, and
cordless telephones used a single BS to communicate with single portable terminal.
2. Did not have CCS.
Eg: AMPS. Forward Voice channel Voice circuitsEg: AMPS.
Mobile User Base Station MSC
Reverse Voice channelForward Voice channel
Forward setup channel
Reverse Setup channel
Voice circuits
9600bps Data Link
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
• The system control for each market resides in MSC, which maintains all mobile related information and controls each mobile handoff.
• Autonomous Registration-The MU notifies a serving MSC of its presence and location.
• IS-41 relies on the concept of Autonomous Registration.• MSC also performs network management functions such as
call handling and processing, billing, fraud detection within call handling and processing, billing, fraud detection within the market.
• MSC is interconnected with the PSTN via trunks and a tandem switch.
• MSC’s are connected to other MSC’s via dedicated signaling channels for exchange of location, validation and call signaling information.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
First Generation Wireless N/W’s1. Provide analog speech and inefficient, low-rate
data transmission between the MU and BS.2. Until early 1990’s the user had to register manually
each time he/she entered any market.3. Evolution of IS-41 standard allowed different 3. Evolution of IS-41 standard allowed different
cellular systems to automatically accommodate users who roam into new coverage region.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Second Generation(2G)• Employ digital modulation and advance call
processing capabilities.Eg:GSM,lS-95, IS-136 standards of US,PersonalAccess Comm. Systems(PACS), Digital European Cordless Telephone(DECT-Europe).
• MSC’s burden is downsized by the deployment of • MSC’s burden is downsized by the deployment of BSC’s(Base Station Controller), which is inserted b/w several BS’s and MSC.
• Use digital voice coding and digital modulation. CCS is introduced.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
• Unlike First generation which is only developed for voice, the 2G has been specifically designed to provide paging, and other data services such as facsimile and high data rate network access.
• The handoff process involved is Mobile assisted i.e., MAHO(Mobile Assisted Handoff).
Second Generation(2G)
MAHO(Mobile Assisted Handoff).• The mobile units also perform several other
functions such as received power reporting, adjacent BS scanning, data encoding and encryption, which is not seen in First generation.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Third generation(3G)• Mainly developed to provide single set of
standards that can meet wide range of wireless applications and provide universal access throughout the world.
• A universal personal communicator will provide access to a variety of voice, data and provide access to a variety of voice, data and video communication services.Eg: B-ISDN, 3G PCS,3G PCN,UMTS(Europe)
• Packet Radio communication is used providing high speed and reliable information transfer.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Traffic Routing in Wireless Networks
The voice call should always be continuous in nature, whereas the control and signaling information can be bursty and can share the network with other bursty users.
Routing services determine the priority and the type of service to be given to all the users.type of service to be given to all the users.
Two Types:1. Connection-oriented (Virtual Circuit Routing)2. Connectionless(Datagram Services)
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Connection Oriented ServiceConsider the case when you make a telephone call. • Pick up your telephone• Dial the destination number which is unique• Say what you want to convey• Hang up your phone
A similar mode of operation is followed in the case of connection oriented services
• Establish a connection between the sender and the receiver
• Make use of the connection by sending and receiving information
• When done, terminate the existing connection
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Connectionless Service• A connectionless services, as it’s name suggests, is just
a service with no pre established connection. • It is more like a postal system wherein you send and
receive mails with the help of destination address and several offices that route your mails to the correct destination.destination.
• The packets send need not arrive in the same order in which they are sent. This is basically because all packets might not take the same route since there is no preset connection in such services. The routers route the packets according to their built in algorithms and the receiver might need to re order the packet.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
