MANs and WANs

1
MANs and WANs

• Define PAN, LAN, MAN, WAN
• Outline some key GSM techniques
• FDMA, TDMA, SDMA
• Challenge-based authentication
• Packet Circuit-switching
• Describe 3 ways of extending 802 wireless
• Outline current and future WIMAX capability
• Outline concepts of WIMAX

2
Personal, Local, Metropolitan Wide Area
Networks
PAN 10m Bluetooth
LAN 100m WIFI
MAN 30 miles WIMAX
WAN / GAN GSM/UTMS
3
Global System for Mobile Comms

• Mobile wireless voice, data SMS services
• Relatively limited bandwidth
• Good quality
• Uninterrupted phone calls at speed (e.g. car)
• Security
• Access control, authentication via chip and PIN
• But no end-to-end encryption of user data
• Roaming within Europe

4
GSM Architecture
Switching Network Management
fixed network
Base Station Controller
BSC
Base Station
5
GSM Techniques
Time Division Multiple Access Allocate time slots
to different devices
Frequency Division Multiple Access Allocate
different frequencies to different devices
Space Division Multiple Access Allocate different
frequencies to neighbouring areas
What do these mean?

• TDMA FDMA SDMA
• Linear predictive coding optimised for speech
• Reorder bits to reduce effect of burst errors
• Logical channels traffic control
• Remote system management billing
• Handing mobiles between stations
• based on signal strength

Errors tend to occur in clumps. Error correction
can only fix a few bits per block
Spread neighbouring bits across blocks, apply
error-checking, After checking, fix errors, then
restore the original order
6
Linear Predictive Coding

• Predict next value
• Send difference between prediction actual
• Receiver can make same prediction modify
• Will lag behind rapid changes in signal
• Works well for voice data

255
Sending full data 8 bits per sample Sending
difference from prediction 4 bits per sample
Data to be sent
7
Space Division Multiplexing
possible radio coverage of the cell
idealized shape of the cell
cell

• Frequency allocation no touching colours
• different frequencies in adjoining cells
• cell sizes vary from 100 m up to 35 km
• user density, geography, transmitter power etc.
• cells overlap, shape depends on geography

8
Handover Decisions
Received signal level From old station
Received signal level From new Station
Dont just use strongest avoid constant
switching at boundary
Signal Strength
Handover Margin
MS
MS
MS
Old Base Station
New Base Station
Mobile Station Position
9
Challenge-Response Security
Authorisation Centre
Subscriber Identity Module
Random number
Key
random
Key
random
128 bit
128 bit
128 bit
128 bit
Algorithm 3
Algorithm 3
32 bit response (R1)
32 bit response (R2)
Justify this approach
R1 R2?
Master Switching Centre
10
Packet circuit switching
Circuit switching Defines path at set up By a
physical link
Packet switching Data split into packets Each
packet may use different route
Virtual Circuit Data split into packets Route
defined Packets arrive in order
11
Data services in GSM

• Standardized data transmission 9.6 kbit/s
• Advanced coding allows 14.4 kbit/s
• Too slow for Internet multimedia applications
• HSCSD (High-Speed Circuit Switched Data)
• bundling of time-slots to get higher rates
• (e.g., 57.6 kbit/s using 4 slots, 14.4 each)
• ready to use, constant quality, simple
• channels blocked for voice transmission
• GPRS (General Packet Radio Service)
• packet switching
• use free slots if data packets ready to send
• E.g. 115 kbit/s using 8 slots temporarily

12
3G Services The Future

• Wide range of users
• Pedestrian satellite
• Voice data (Packet circuit)
• 144 kb/s moving, 394 kb/s still, 2 Mb/s indoor
• Various types of traffic
• Constant variable bit-rate
• Real-time non-real-time
• Interact with legacy systems inc. PSTN
• Quality of Service Requests

13
Creating a MAN

• Wi-Fi with directional high-gain antennae
• Not scaleable
• sticking-plaster coverage of last mile
• Fixed Access
• Wi-Fi mesh networking
• Wireless inter-AP links
• Mobile Access, flexible
• Issues
• Currently non-standard (802.11s, expected 2008)
• Providing QoS negotiation (802.11e, 2005)

Quality of Service
14
IEEE 802.11 Mesh Networks

• WIFI clusters linked by wireless
• Often use 802.11a for backbone
• high speed
• separate band from 802.11b/g
• Automatically learn and maintain routes
• Provide redundancy
• Avoid congested routes
• Resilient to node loss
• Wide coverage
• Based on low-power links
• Why not just increase power?

15
WIMAX MAN standard

• Worldwide Interoperability for Microwave Access
• Conformity tests for IEEE 802.16 standards.
• IEEE 802.16 Specifications
• Range - 30-mile (50-km) radius from base station
• Speed - 70 megabits per second
• Line-of-sight not needed between user and base
  station
• Frequency bands - 2 to 11 GHz and 10 to 66 GHz
  (licensed and unlicensed bands)
• Defines the Media Access Control and allows
  multiple physical-layer specifications
• Can work with other IEEE 802 specification
  systems
• Can be bridged to WIFI

16
Technical Problems for WIMAX

• Bandwidth
• How to provide enough?
• How to share?
• High low demand
• Multipath interference
• Multipath Delays
• Longer
• WIFI 1 µSec
• WIMAX 10 µSec
• More variable

17
WIMAX Wireless Services

• Non-line-of-sight, WiFi-like
• A small antenna on your computer links to the
  tower.
• Lower frequency range - 2 GHz to 11 GHz
• Longer wavelength diffracts around obstacles.
• 4-6 mile radius
• Line-of-sight
• A fixed dish antenna points at the tower from a
  roof/pole
• The line-of-sight connection is stronger less
  error-prone
• Higher frequencies, up to 66 GHz.
• Less interference and lots more bandwidth.
• 30 mile radius

18
WIMAX Mobility
Full Mobility
Vehicle Speed Mobility gt3G bandwidth Any IP
service
Portability Simple Mobility
Pedestrian Speed Mobility Latency Tolerant
Applications
Stationary Broadband Access Anywhere
Nomadic Usage
Fixed Access
Residential Broadband Access
19
WIMAX Now (ish)

• Fixed Access
• high-performance radio links capable of data
  rates comparable to wired broadband service,
  using equipment that can be self installed
  indoors by users.
• Portable service (Nomadicity)
• User takes an 802.16 modem to a different
  location, re-authenticates and manually
  re-establishes new IP connections and resumes
  broadband.
• Needs security such as strong mutual
  authentication between the user/client device and
  the network AP.
• A centralized mechanism for user authentication
  is needed as users may move between different APs

20
WIMAX In the Future

• Portability with simple mobility
• Automated management of IP connections with
  session persistence or automatic reestablishment
  following transitions between APs.
• Suitable for latency tolerant applications such
  as TCP.
• Inadequate handover performance for delay and
  packet-loss sensitive real-time applications
  (e.g. VoIP).
• Fully mobile (Like 3G voice/data systems).
• Users may be moving.
• Low latency and low loss handovers as users move.

21
Choosing Technology 1

• An ISP wants to expand its service coverage
• Some new customers need a guaranteed level of
  service for certain applications.
• Customers may want to install their own
  equipment.

• WiMAX
• Cheaper than traditional broadband services
• Easy to deploy solution
• Built-in QoS.
• Based on IEEE standards
• WiMAX-certified products are vendor interoperable.

22
Choosing Technology 2

• A school with existing broadband access wants to
  connect a new building and the main courtyard.
• Students and staff use the wireless
  infrastructure and their notebook computers and
  PDAs to access the Internet and the schools
  network resources.
• The network is used to download documents and
  presentations, access Web-based portals (e.g.
  WebCT), review timetables and send instant
  messages.
• The solution is needed immediately
• The school is willing to work with a single
  vendor.

• Wi-Fi mesh-network topology
• Easy expand an existing 802.11-based network
• Products are available today

23
Summary

• Mobile Phone WAN
• Space division multiplexing hand-over
• Security
• Circuit- and packet-switching
• WIMAX - MAN
• 30 mile wireless (line-of-sight)
• Different access protocol
• Less contention better under high load