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Chapter 6: Wireless and Mobile Networks
Objectives
Introduction Wireless links,
characteristics CDMA
IEEE 802.11 wireless LANs (“wi-fi”)
Cellular Internet Access architecture standards (e.g., GSM)
Principles: addressing
and routing to mobile users
Mobile IP Handling mobility in
cellular networks Mobility and higher-
layer protocols
2
1. Wireless Internet:Introduction
3
What Is Wireless Networking?What Is Wireless Networking?
The use of infra-red (IR) or radio frequency (RF) signals to share information and resources between devices
A hot computer industry buzzword: Lots of advertising by companies and media Wireless Broadband, 3G wireless, 4G, WAP,
iMode, Bluetooth, WiFi Mobile Internet, Pervasive Computing,
Nomadic Computing, M-commerce Ubiquitous; Global; Revolutionary
4
Two Popular 2.4 GHz Two Popular 2.4 GHz Standards:Standards:
IEEE 802.11 Fast (11b) High Power Long range Single-purpose Ethernet replacement Easily Available
• Apple Airport, iBook, G4• Cisco Aironet 350
Bluetooth Slow Low Power Short range Flexible Cable
replacement
5
Pros and Cons of 802.11:Pros and Cons of 802.11: Pro:
High bandwidth (up to 11 Mbps) Two modes of operation: infrastructure vs. ad hoc
Con: Incompatibility between old and new cards Signal blocked by reinforced concrete or tinted
glass No standard for hand-off between base stations Some channel numbers overlap spectrum High power consumption in laptops
6
BluetoothBluetooth
Think USB, not Ethernet Cable replacement technology Created by Ericsson PAN - Personal Area Network
1-2 Mbps connections 1600 hops per second FHSS Includes synchronous, asynchronous, voice connections
Small, low-power, short-range, cheap, versatile radios
Used as Internet connection, phone, or headset Master/slave configuration and scheduling
7
Future of Wireless Future of Wireless
Higher data rates Better security Wider selection of products Lower prices Zero configuration networking More end-user focus Better software Less visible More popular
8
2. Background:Networking Terminology
9
Internet Protocol Stack Application: supporting network
applications and end-user services FTP, SMTP, HTTP, DNS, NTP
Transport: end to end data transfer TCP, UDP
Network: routing of datagrams from source to destination IPv4, IPv6, BGP, RIP, routing protocols
Data Link: hop by hop frames, channel access, flow/error control PPP, Ethernet, IEEE 802.11b
Physical: raw transmission of bits
Application
Transport
Network
Data Link
Physical
001101011...
10
Wireless Internet Technologies Mobile devices (e.g., notebooks,
laptops, PDAs, cell phones, wearable computers)
Wireless network access Bluetooth (1 Mbps, up to 3 meters) IEEE 802.11b (11 Mbps, up to 100 meters) IEEE 802.11a (55 Mbps, up to 20 meters)
Operating modes: Infrastructure mode (access point) Ad hoc mode
Wireless Web, WiFi “hot spots”
11
Elements of a wireless network
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network: route among themselves
12
Wireless Link CharacteristicsDifferences from wired link ….
decreased signal strength: radio signal attenuates as it propagates through matter (path loss)
interference from other sources: standardized wireless network frequencies (e.g., 2.4 GHz) shared by other devices (e.g., phone); devices (motors) interfere as well
multipath propagation: radio signal reflects off objects ground, arriving ad destination at slightly different times
…. make communication across (even a point to point) wireless link much more “difficult”
13
Code Division Multiple Access (CDMA) used in several wireless broadcast channels
(cellular, satellite, etc) standards unique “code” assigned to each user; i.e., code
set partitioning all users share same frequency, but each user
has own “chipping” sequence (i.e., code) to encode data
encoded signal = (original data) X (chipping sequence)
decoding: inner-product of encoded signal and chipping sequence
allows multiple users to “coexist” and transmit simultaneously with minimal interference (if codes are “orthogonal”)
14
CDMA: two-sender interference
15
Chapter 6: Wireless and Mobile Networks
Introduction Wireless links,
characteristics CDMA
IEEE 802.11 wireless LANs (“wi-fi”)
Cellular Internet Access architecture standards (e.g., GSM)
Principles: addressing and routing to mobile users
Mobile IP Handling mobility in
cellular networks Mobility and higher-
layer protocols
16
IEEE 802.11 Wireless LAN
802.11b 2.4-5 GHz unlicensed
radio spectrum up to 11 Mbps direct sequence
spread spectrum (DSSS) in physical layer
• all hosts use same chipping code
widely deployed, using base stations
802.11a 5-6 GHz range up to 54 Mbps
802.11g 2.4-5 GHz range up to 54 Mbps
All use CSMA/CA for multiple access
All have base-station and ad-hoc network versions
17
Where does 802.11 live in the OSI?Telnet, FTP, Email, Web, etc.
IP, ICMP, IPX
TCP, UDP
Logical Link Control - 802.2 (Interface to upper layer protocols)
MAC
802.3, 802.5, 802.11
Phy. Layer Convergence Protocol
LAN:10BaseT,10Base2,10BaseFLWLAN: FHSS, DSSS, IR
Application
Presentation
Session
Transport
Network
Data Link
Physical
Wireless lives at Layers 1 & 2 only!
18
802.11: Channels, association 802.11b: 2.4GHz-2.485GHz spectrum divided
into 11 channels at different frequencies AP admin chooses frequency for AP interference possible: channel can be same as
that chosen by neighboring AP! host: must associate with an AP
scans channels, listening for beacon frames containing AP’s name (SSID) and MAC address
selects AP to associate with may perform authentication will typically run DHCP to get IP address in
AP’s subnet
19
Avoiding collisions
idea: allow sender to “reserve” channel rather than random access of data frames: avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to BS using CSMA RTSs may still collide with each other (but they’re
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets!
20
framecontrol
durationaddress
1address
2address
4address
3payload CRC
2 2 6 6 6 2 6 0 - 2312 4
seqcontrol
802.11 frame: addressing
Address 2: MAC addressof wireless host or AP transmitting this frame
Address 1: MAC addressof wireless host or AP to receive this frame
Address 3: MAC addressof router interface to which AP is attached
Address 4: used only in ad hoc mode
21
hub or switch
AP 2
AP 1
H1 BBS 2
BBS 1
802.11: mobility within same subnet
router H1 remains in same
IP subnet: IP address can remain same
switch: which AP is associated with H1? self-learning: switch
will see frame from H1 and “remember” which switch port can be used to reach H1
22
Mradius ofcoverage
S
SS
P
P
P
P
M
S
Master device
Slave device
Parked device (inactive)P
802.15: personal area network
less than 10 m diameter replacement for cables
(mouse, keyboard, headphones)
ad hoc: no infrastructure master/slaves:
slaves request permission to send (to master)
master grants requests
802.15: evolved from Bluetooth specification 2.4-2.5 GHz radio band up to 721 kbps
23
Chapter 6: Wireless and Mobile Networks Introduction Wireless links,
characteristics CDMA
IEEE 802.11 wireless LANs (“wi-fi”)
Cellular Internet Access architecture standards (e.g., GSM)
Principles: addressing and routing to mobile users
Mobile IP Handling mobility in
cellular networks Mobility and higher-
layer protocols
24
Mobile Switching
Center
Public telephonenetwork, andInternet
Mobile Switching
Center
Components of cellular network architecture
connects cells to wide area net manages call setup handles mobility
MSC
covers geographical region base station (BS) analogous to 802.11 AP mobile users attach to network through BS air-interface: physical and link layer protocol between mobile and BS
cell
wired network
25
Cellular networks: the first hopTwo techniques for sharing
mobile-to-BS radio spectrum
combined FDMA/TDMA: divide spectrum in frequency channels, divide each channel into time slots
CDMA: code division multiple access
frequencybands
time slots
26
Cellular standards: brief survey2.5 G systems: voice and data channels for those who can’t wait for 3G service: 2G extensions general packet radio service (GPRS)
evolved from global system for mobile communication (GSM) Uses FDM/TDM for the air interface data sent on multiple channels
enhanced data rates for global evolution (EDGE) also evolved from GSM, using enhanced modulation Date rates up to 384Kbps
CDMA-2000 (phase 1) data rates up to 144Kbps evolved from IS-95, which uses CDMA
3G systems: ( CDMA phase II) voice/data Universal Mobile Telecommunications Service (UMTS)
GSM next step, but using CDMA CDMA-2000
27
Chapter 6: Wireless and Mobile Networks Introduction Wireless links,
characteristics CDMA
IEEE 802.11 wireless LANs (“wi-fi”)
Cellular Internet Access architecture standards (e.g., GSM)
Principles: addressing and routing to mobile users
Mobile IP Handling mobility in
cellular networks Mobility and higher-
layer protocols
28
What is mobility?
spectrum of mobility, from the network perspective:
no mobility high mobility
mobile wireless user, using same access point
mobile user, passing through multiple access point while maintaining ongoing connections (like cell phone)
mobile user, connecting/ disconnecting from network using DHCP.
29
Mobility: approaches
Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. routing tables indicate where each mobile
located no changes to end-systems
Let end-systems handle it: indirect routing: communication from
correspondent to mobile goes through home agent, then forwarded to remote
direct routing: correspondent gets foreign address of mobile, sends directly to mobile
30
Mobility: approaches
Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it: indirect routing: communication from
correspondent to mobile goes through home agent, then forwarded to remote
direct routing: correspondent gets foreign address of mobile, sends directly to mobile
not scalable
to millions of mobiles
31
Indirect Routing: moving between networks suppose mobile user moves to another
network registers with new foreign agent new foreign agent registers with home agent home agent update care-of-address for mobile packets continue to be forwarded to mobile
(but with new care-of-address) mobility, changing foreign networks
transparent: on going connections can be maintained!
32
Chapter 6: Wireless and Mobile Networks Introduction Wireless links,
characteristics CDMA
IEEE 802.11 wireless LANs (“wi-fi”)
Cellular Internet Access architecture standards (e.g., GSM)
Principles: addressing and routing to mobile users
Mobile IP Handling mobility in
cellular networks Mobility and higher-
layer protocols
33
Mobile IP
RFC 3220 has many features we’ve seen:
home agents, foreign agents, foreign-agent registration, care-of-addresses, encapsulation (packet-within-a-packet)
three components to standard: indirect routing of datagrams agent discovery registration with home agent
34
Mobile IP: agent discovery agent advertisement: foreign/home agents
advertise service by broadcasting ICMP messages (typefield = 9)
RBHFMGV bits reserved
type = 16
type = 9 code = 0 = 9
checksum = 9
router address
standard ICMP fields
mobility agent advertisement
extension
length sequence #
registration lifetime
0 or more care-of-addresses
0 8 16 24
R bit: registration required
H,F bits: home and/or foreign agent
35
Mobile IP: registration example
visited network: 79.129.13/ 24 home agent
HA: 128.119.40.7 f oreign agent
COA: 79.129.13.2 COA: 79.129.13.2
….
I CMP agent adv. Mobile agent MA: 128.119.40.186
registration req.
COA: 79.129.13.2 HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 9999 identification:714 ….
registration req.
COA: 79.129.13.2 HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 9999 identification: 714 encapsulation format ….
registration reply
HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 4999 Identification: 714 encapsulation format ….
registration reply
HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 4999 Identification: 714 ….
time
36
Handling mobility in cellular networks
home network: network of cellular provider you subscribe to (e.g., Sprint PCS, Verizon) home location register (HLR): database in
home network containing permanent cell phone #, profile information (services, preferences, billing), information about current location (could be in another network)
visited network: network in which mobile currently resides visitor location register (VLR): database with
entry for each user currently in network could be home network
37
Mobility: GSM versus Mobile IP
GSM element Comment on GSM element Mobile IP element
Home system Network to which the mobile user’s permanent phone number belongs
Home network
Gateway Mobile Switching Center, or “home MSC”. Home Location Register (HLR)
Home MSC: point of contact to obtain routable address of mobile user. HLR: database in home system containing permanent phone number, profile information, current location of mobile user, subscription information
Home agent
Visited System Network other than home system where mobile user is currently residing
Visited network
Visited Mobile services Switching Center.Visitor Location Record (VLR)
Visited MSC: responsible for setting up calls to/from mobile nodes in cells associated with MSC. VLR: temporary database entry in visited system, containing subscription information for each visiting mobile user
Foreign agent
Mobile Station Roaming Number (MSRN), or “roaming number”
Routable address for telephone call segment between home MSC and visited MSC, visible to neither the mobile nor the correspondent.
Care-of-address
38
Wireless, mobility: impact on higher layer protocols
logically, impact should be minimal … best effort service model remains unchanged TCP and UDP can (and do) run over wireless,
mobile … but performance-wise:
packet loss/delay due to bit-errors (discarded packets, delays for link-layer retransmissions), and handoff
TCP interprets loss as congestion, will decrease congestion window un-necessarily
delay impairments for real-time traffic limited bandwidth of wireless links
39
Chapter 6 Summary
Wireless wireless links:
capacity, distance channel impairments CDMA
IEEE 802.11 (“wi-fi”) CSMA/CA reflects
wireless channel characteristics
cellular access architecture standards (e.g., GSM,
CDMA-2000, UMTS)
Mobility principles: addressing,
routing to mobile users home, visited networks direct, indirect routing care-of-addresses
case studies mobile IP mobility in GSM