Error Correction.ppt

Engineering Internet QoS 1
QoS in Mobile Wireless
Networks

Outline
o Applications
o Mobile Wireless Networks
 Wireless Lan, Bluetooth, Cellular Networks
o Mobile services over IP, Cellular IP
o Mobility and QoS
o Research Directions

Mobile Applications
o Traditional Voice calls to stay
o New services: Internet data applications
 WWW, file transfer, e-mail
o Multimedia applications
 Video conferencing, multicasting
 3G IP-enabled handsets already supporting
voice and multimedia calls

Wireless LAN
Reprinted with Permission from “Engineering Internet QoS - Jha & Hassan, Artech House Publishing, Norwood, MA, USA. www.artechhouse.com

IEEE 802.11b
o Most popular LAN standard
o Free, unlicensed instrumentation, scientific and
Medical (ISM) band
o Support for 11 Mbps (Legacy Ethernet 10 Mbps)
o No infrastructure needed
o Quick deployment as adhoc networks
o HIPERLAN (ETSI) – 23.5 Mbps
 Expensive
 Slow deployment

Bluetooth
o Low cost
o 10 to 100 meter range
o Free ISM band
o Nominal data rate of 1 Mbps
o Several applications
 Office environment, Home environment,
Personal Area network, Public environment,
Adhoc networking

Cellular Networks

Cellular Network Standards
o GSM
 Circuit switched, 9.6 Kbps
o General Packet Radio System (GPRS)
 9.6 – 28.8 Kbps and higher rates
o Third Generation
 IP based communication between mobile handset
and network
 144 Kbps inside vehicle, 384 Kbps for pedestrians
and 2 Mbps inside building (fixed wireless access)

Mobile IP

Cellular IP

Impact of Mobility on QoS
o Several limits and constraints in mobile
environment that poses additional
challenges for QoS support
o Three major areas
 Effect of wireless links
 Effect of movement
 Limitation on portable devices

Effect on wireless links
o Much higher bit error rate (BER)
 QoS mechanisms must deal with high packet
loss
o Quality Variation on links
 Weather condition, interference with other
users, barriers such as buildings, distance
from Base stations
 Some predictable (can be modeled
statistically) but most unpredictable

Error Correction
o Forward Error Correction (FEC)
 More bits to correct, higher overhead
 Know link quality in advance
o Adaptive FEC
 Appropriate selection of FEC dynamically
 complex logic in System

Effect on Movement
o User free to move
 Route changes during a session
o Resource reservation for QoS
 Complex when route changes frequent and not
predictable
o Handoff problem
 When user moves out of coverage of a BS or AP
 Easy in circuit switch network
• no Relocation of processing, data and other contexts

Limitations on portable devices
o PDAs, Mobile phones, handsets have
limited processing power, memory and
interface
o Power restrictions
 Intermittent availability
o Network QoS no good if device can’t cope
 QoS management techniques must consider
end system capabilities

Intserv and mobility
o RSVP reserves QoS along the path
 Path changes dynamically in mobile networks
o MRSVP
 Reserve resources in advance where the mobile host
will visit in future
 Uses MSPEC to specify this
• Easy when mobility pattern regular, GPS in car etc may be of
help
• What if pattern unpredictable?
 Proxy agents to reserve on behalf of mobile hosts in
future locations

Passive Reservations
o Future location reserved resources may be
wasted
o Let “best effort” use it until needed
o MRSVP not a standard yet.
 Reference [11] has good coverage

Diffserv and mobility
o SLA needed between ISPs and users
 Fixed network SLA negotiation process manual (Web
form etc. )
o Mobile user may be in a foreign netwok
 SLA need to be negotiated dynamically
 Needs signaling for this purpose
o Resource problems similar to Intserv
 Needs must be available in new network/locaiton

Context Aware handoff
o Context
 QoS parameters (PHB for diffserv), packet filtering
rules, security and other features
 Known to base stations
o Best effort: rerouting only
o Multimedia: Re-routing + context transfer
 To be done in real-time
 During handoff for smooth context transfer
 IETF standard in progress

Application Adaptivity
o Hideable fluctuations
 Increased latency, reduced signal quality
 Traditional mechanisms
• FEC, jitter buffering
o Non-hideable fluctuations
 Loss of power in mobile terminals, resource shortage
in new location, moving from high-speed to low-
speed cells – typical in 3G
 Application adaptivity: e.g., Switch from color to b/w

Resrouce Reservation research
o MRSVP (discussed earlier), several
modifications to RSVP suggested
o Mahadevan & Sivalingam
 Partition network into hierarchy
• Internet at top, base stations at bottom
• Interdomain mobility uses Mobile IP, local mobility
handled by routing table changes
• New QoS parameters such as loss profiles,
probability of seamless connection, rate redution

Resource Management and handoff
o Predictive resource estimation
o Dynamically reserve resource in cells likely
to be visited
o Admission control to account for potential
handoff from neighbours
o Special packet scheduling techniques

Transport Layer issues
o Traditional TCP
 Missing ACK interpreted as sign of congestion
 Trigger slow start algorithm
o Mobile/Wireless network
 Packet loss on wireless link
 Handoff of mobile terminals
o Several proposals
 I-TCP, M-TCP, Freeze-TCP

TCP Optimizations
o Divide connection into two parts
 Fixed (traditional TCP)
 Wireless segment (optimize)
o TCP connections terminated at access point that
acts as a proxy for mobile hosts
 I-TCP, Snoop TCP, M-TCP (various optimisations)
o Freeze TCP: Modification of TCP on mobile host
only
 Other end and intermediate routers not affected

Error Correction.ppt

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