6: Wireless and Mobile Networks 6-1
89-850 Communication Networks: Wireless and Mobile Communication Networks
Prof. Amir HerzbergBIU, Dept. of CS
From ch.6 of Kurose and Ross, 3rd edition; and [KMK], ch. 8.
Computer Networking: A Top Down Approach Featuring the Internet, 3rd edition. Jim Kurose, Keith RossAddison-Wesley, July 2004. All material copyright 1996-2004
J.F Kurose and K.W. Ross, All Rights Reserved
6: Wireless and Mobile Networks 6-2
Background: Wireless and Mobile Networks
# wireless (mobile) phone subscribers now exceeds # wired phone subscribers!
Computer nets: laptops, palmtops, PDAs, Internet-enabled phone promise anytime untethered Internet access
Internet telephony: a reality, an earthquake Two important (but different) challenges
Wireless link: no CD (e.g. hidden-terminal), reliability, security
Mobility of computers and users; provisioning Plus: limited computing power and energy
6: Wireless and Mobile Networks 6-3
Wireless and Mobile Communication Networks: Outline6.1 Introduction
Wireless 6.2 Wireless links,
characteristics 6.3 IEEE 802.11
wireless LANs (“wi-fi”)
Sensor and personal-area networks
Mobility 6.5 Principles:
addressing and routing to mobile users
6.6 Mobile IP 6.7 Cellular networks 6.8 Mobility and
higher-layer protocols
6.9 Summary
6: Wireless and Mobile Networks 6-4
Elements of a wireless network
network infrastructure
wireless hosts laptop, PDA, IP phone run applications may be stationary
(non-mobile) or mobile wireless does not
always mean mobility
6: Wireless and Mobile Networks 6-5
Elements of a wireless network
network infrastructure
base station typically connected to
wired network relay - responsible for
sending packets between wired network and wireless host(s) in its “area” e.g., cell towers,
802.11 access points
6: Wireless and Mobile Networks 6-9
Wireless network characteristicsLower Signal/Noise ratio (cf. wired networks)Limited, shared spectrum: orthogonal signals
(FDMA/CDMA/TDMA) or `collisions as noise`
AB
C
Hidden terminal problem B, A hear each other B, C hear each other A, C can not hear each
other
A B C
A’s signalstrength
space
C’s signalstrength
Signal fading: B, A hear each other B, C hear each other A, C can not hear each other
interfering at B
6: Wireless and Mobile Networks 6-10
Wireless Link CharacteristicsDifferences from wired link ….
Energy and computing-power limitations Decreased signal strength
• Obstacles and hidden-terminal problem• Collision detection hard or impossible
More noise• Interference from other sources• Multipath propagation different delays
interferences between paths or (multipath) fading
Lower signal/noise Higher bit error rate
…. more “difficult”
6: Wireless and Mobile Networks 6-11
Hi/Low BER States Model Wireless links often have two BER states
High, Low E.g., due to (multipath) fading
Model by two-state Markov model:
Good Badg
(1 g)
b
(1 b)
Simplify: all packets Ok in `Good`, fail in `Bad`
6: Wireless and Mobile Networks 6-13
Wireless and Mobile Communication Networks: Outline6.1 Introduction
Wireless 6.2 Wireless links,
characteristics 6.3 IEEE 802.11
wireless LANs (“wi-fi”)
Ad-hoc, sensor and personal-area networks
Mobility 6.5 Principles:
addressing and routing to mobile users
6.6 Mobile IP 6.7 Cellular networks 6.8 Mobility and
higher-layer protocols
6.9 Summary
6: Wireless and Mobile Networks 6-14
IEEE 802.11 Wireless LANs802.11WirelessLANs
5-6 GHz2.4-5 GHz
(unlicensed)
Up to 11Mbps
802.11blo-cost, good propagation;
but slow, interferences
Up to 54 Mbps
802.11a 802.11g
All use CSMA/CA for multiple access All have base-station and ad-hoc network
versions
6: Wireless and Mobile Networks 6-16
802.11 LAN: Infrastructure and Ad-Hoc modes Infrastructure mode: wireless
host communicates with base station base station = access point
(AP) Basic Service Set (BSS) (aka
“cell”) contains:• wireless hosts (mobiles)• access point (AP): base
station Extended Service Set (ESS)
• One or more BSS • Connect by LANswitch or DS• DS=Distribution System
Ad hoc mode: hosts only• =Independent BSS (IBSS)
BSS 1
BSS 2
Internet
LAN switch
AP
AP
DS
router
6: Wireless and Mobile Networks 6-18
802.11 Media Access Coordination (MAC)
Point Coordination Function (PCF) Only in Infrastructure mode Access point coordinates transmissions Allows: bounded delay , QoS
Distributed Coordination Function (DCF) Ad-hoc or Infrastructure mode All are peers Like Ethernet, uses CSMA: random access, carrier sense Unlike Ethernet: Ack, no Collision Detection Optional: use RTS/CTS (Request/Clear To Send) No bound on delay (starvation possible) Our focus
6: Wireless and Mobile Networks 6-19
IEEE 802.11 DCF Like Ethernet, uses CSMA:
random access carrier sense: don’t collide with ongoing transmission
Unlike Ethernet: Ack, no Collision Detection no collision detection – transmit all frames to completion ACK: to detect loss without collision detection
Why no collision detection? difficult to receive (sense collisions) when transmitting due
to weak received signals (fading) can’t sense all collisions in any case: hidden terminal, fading And… loss may be due to (higher) error rate of wireless
Goal: avoid collisions: CSMA/CA (Collision Avoidance)
6: Wireless and Mobile Networks 6-20
802.11 DCF MAC Protocol: CSMA/CA[simplified]
802.11 sender1 if sense channel idle then
- transmit entire frame (no Colli. Detect)
2 if sense channel busy then - start random backoff timer- timer counts down while channel idle- transmit when timer expires
802.11 receiverif frame received OK then return ACK else ignore (no NACK!)SIFS: Short Inter-Frame Space – max time
to begin Ack [e.g., 16μsec in 802.11a]
sender receiver
data
ACK
SIFS(e.g.16s)
6: Wireless and Mobile Networks 6-21
802.11 DCF MAC Protocol: CSMA/CA
802.11 sender (when trying to send)
1 if sense channel idle for DIFS then - transmit entire frame (no CD)[DIFS>SIFS+2Tprop for priority to ACK]
2 if sense channel busy then - count down the backoff timer- – but only while channel idle- transmit when timer expires
- If ACK, reduce backoff range by 1- if no ACK, double backoff range, select
time randomly from range, repeat 2
802.11 receiverif frame received OK - return ACK (within SIFS)
sender receiver
DIFS
data
ACK
SIFS(e.g.16s)
DIFS
6: Wireless and Mobile Networks 6-22
Ack
Data
Next MPDU
Src
Dest
Other
Contention Window
Defer Access Backoff after Defer
DIFS
SIFS
DIFS
Src found channel idle for DIFS send data Other sender found channel busy
Wait for DIFS idle time, then exponential backoff delay [slot=Tprop]
802.11 DCF MAC OperationData Frames and their ACK
6: Wireless and Mobile Networks 6-23
Two Additional Mechanisms in 802.11
PCF (Point Coordination Function) Polling to coordinate senders, e.g. to ensure
QoS SIFS < PIFS < DIFS (priorities!)
DCF with RTS/CTS mechanism Can’t detect collision while sending… Collision for long packet is wasteful RTS (Request to Send): request to reserve
channel to send long packet w/o collisions CTS (Clear to Send): approve RTS Optional mechanism
6: Wireless and Mobile Networks 6-24
RTS/CTS [optional in 802.11 MAC] Sender sends small request-to-send (RTS)
RTSs may collide with each other (but are short) Include indication of length of packet transmission
AP broadcasts clear-to-send CTS in response to RTS CTS heard by all nodes
sender transmits data frame other stations defer transmissions for time
specified in CTS Q: if you hear RTS only (no CTS), should you wait?
Avoid data frame collisions completely using small reservation packets!
6: Wireless and Mobile Networks 6-25
Collision Avoidance: RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
6: Wireless and Mobile Networks 6-26
Q: Defer on RTS, CTS or both? Idea 1: RTS contains length, defer till
end
RTS
A B C D
CTSCTS
RTS
data
ACK ACK
6: Wireless and Mobile Networks 6-27
Q: Defer on RTS, CTS or both? Idea 1: RTS contains length, defer till
end Problem: maybe not granted?
Idea 2: defer only on CTSRTS
A B C D
CTSCTS
RTS
data
ACK ACK
RTS
6: Wireless and Mobile Networks 6-28
Q: Defer on RTS, CTS or both? Idea 1: RTS contains length, defer till
end Problem: maybe not granted?
Idea 2: defer only on CTS What if unheard?
RTS
A B C D
CTSCTS
RTS
data
ACK ACK
6: Wireless and Mobile Networks 6-29
Q: Defer on RTS, CTS or both? Idea 1: RTS contains length, defer till
end Problem: maybe not granted?
Idea 2: defer only on CTS What if unheard?
Solution: Defer by CTS
• By length in CTS Defer by RTS…
But only 2 DIFS ! Ok if A hears either
recipient or sender
RTS
A B C D
CTSCTS
RTS
data
ACK ACK
6: Wireless and Mobile Networks 6-30
802.11 DCF MAC Example
ACKData
RTS CTS Data ACK
RTS CTS Data ACK
RTS
RTS
RTS CTS Data ACK
time
time
time
time
time
time
time
time
backoff period
1
2
3
4
1
2
3
4
....
node defers; backoff counter frozen
6: Wireless and Mobile Networks 6-31
Internetrouter
AP
H1 R1
AP MAC addr H1 MAC addr R1 MAC addr
address 1 address 2 address 3
802.11 frame
R1 MAC addr AP MAC addr
dest. address source address
802.3 frame
802.11 addressing & `switching`
AP identified in 802.11frame (Unlike regular switch!!)
AP
6: Wireless and Mobile Networks 6-34
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
Works fine for hub Switch: which AP is
associated with H1? self-learning switch
will see frame from H1 and “remember” port to reach H1
Solution: when H1 joins, AP2 sends switch a packet from H1
6: Wireless and Mobile Networks 6-35
MAC Management, Beacons and Traffic Indication Map (TIM) 802.11 has several MAC management frames
(Re/De)Association req/response, Authentication… Beacon (sent periodically by AP)
Timestamp, Beacon Interval, Capabilities, SSID, Rates, Parameters, Traffic Indication Map (TIM)
Allows host to select AP (or host can send probe) TIM: list of (associated but sleeping) hosts with
packets queued at the access point. Even sleeping hosts (sometimes) listen to Beacon
• To check incoming messages in TIM, get broadcasts• Sleeping to save energy when idle
6: Wireless and Mobile Networks 6-36
Ad Hoc Networking
Ad hoc networks no base stations transmit to other nodes within
link coverage nodes organize themselves into a
network: route among themselves Supported in 802.11 but still
many open issues, research WANET: Wireless Ad-Hoc NETwork MANET: Mobile Ad-Hoc Net (they
move, too!)
6: Wireless and Mobile Networks 6-37
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 Evolved from Bluetooth
6: Wireless and Mobile Networks 6-38
Sensor Networks A special interesting type of Ad-Hoc network… Idea: distribute low-cost `sensors` to perform
measurements, even do actions Applications:
Weather forecasts, natural disaster warnings Detection of physical damages (leakage, fire,…) Military applications: intelligence, smart mines
Properties… Wireless Random location Low cost, energy
6: Wireless and Mobile Networks 6-39
Which Transmission Range? When using AP/Bases, nodes must
reach it Large transmission range
But in sensor networks, WANET? Smaller transmission range Saves energy, allows spectrum reuse
(cellular?) But: requires routing, forwarding by nodes
6: Wireless and Mobile Networks 6-40
Connectivity, Topology, Routing…
Assume nodes distributed uniformly in area [?] One dimensional (line), two (surface), three (space)
Let n be number of nodes Let r(n) be transmission range of node Questions:
Probability that all/most nodes are connected Probability that (almost) entire area is `covered` by
nodes [connected to `base`/`edge`] Number (and cost) of nodes
Routing, scheduling, broadcast protocols for nodes• Using minimal resources (energy, storage)• Minimize collisions
6: Wireless and Mobile Networks 6-41
Sensor Network Tasks/Protocols Routing, forwarding, broadcast Neighbor/topology discovery, organization
E.g. setup spanning tree for efficient broadcast Optimization tasks
• Optimize communication• Load balancing (also to save energy)
Location measurement Clock synchronization
Use to save energy (listen only once per interval) Distributed computation
E.g. to detect image Handling mobility (MANET)
6: Wireless and Mobile Networks 6-48
Wireless and Mobile Communication Networks: Outline6.1 Introduction
Wireless 6.2 Wireless links,
characteristics 6.3 IEEE 802.11
wireless LANs (“wi-fi”)
Mobility 6.5 Principles:
addressing and routing to mobile users
6.6 Mobile IP 6.7 Cellular networks 6.8 Mobility and
higher-layer protocols
6.9 Summary
6: Wireless and Mobile Networks 6-49
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.
Covered in [KR], not in [KMK]
6: Wireless and Mobile Networks 6-50
Mobility: Vocabularyhome network: permanent “home” of mobile(e.g., 128.119.40/24)
Permanent address: address in home network, can always be used to reach mobilee.g., 128.119.40.186
home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote
wide area network
correspondent
6: Wireless and Mobile Networks 6-51
Mobility: more vocabulary
Care-of-address: address in visited network.(e.g., 79.129.13.2)
wide area network
visited network: network in which mobile currently resides (e.g., 79.129.13/24)
Permanent address: remains constant (e.g., 128.119.40.186)
Foreign agent: entity in visited network that performs mobility functions on behalf of mobile.
correspondent: wants to communicate with mobile
6: Wireless and Mobile Networks 6-52
How do you contact a mobile friend:
I wonder where Alice moved to?
Consider friend frequently changing addresses, how do you find her? search all phone books?
call her parents? expect her to let you
know where he/she is?
6: Wireless and Mobile Networks 6-53
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 `breaks` routing (aggregation), allows MITM
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
6: Wireless and Mobile Networks 6-54
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 care-of-address of mobile, sends directly to mobile
not scalable
to millions of mobiles
Breaksroute
aggregation
AllowsMITM
attacks
6: Wireless and Mobile Networks 6-55
Mobility: registration
End result: Foreign agent knows about mobile Home agent knows location of mobile
wide area network
home network
visited network
1
mobile contacts foreign agent on entering visited network
2
foreign agent contacts home agent home: “this mobile is resident in my network”
6: Wireless and Mobile Networks 6-56
Mobility via Indirect Routing
wide area network
homenetwork
visitednetwork
3
2
41
correspondent addresses packets using home address of mobile
home agent intercepts packets, forwards to foreign agent
foreign agent receives packets, forwards to mobile
mobile replies directly to correspondent
6: Wireless and Mobile Networks 6-57
Indirect Routing: comments Mobile uses two addresses:
permanent address: used by correspondent (hence mobile location is transparent to correspondent)
care-of-address: used by home agent to forward datagrams to mobile
foreign agent functions often done by mobile itself triangle routing: correspondent-home-network-
mobile inefficient when correspondent, mobile are in same network
6: Wireless and Mobile Networks 6-58
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: ongoing connections can be maintained!
6: Wireless and Mobile Networks 6-59
Mobility via Direct Routing
wide area network
homenetwork
visitednetwork
4
2
41correspondent requests, receives foreign address of mobile
correspondent forwards to foreign agent
foreign agent receives packets, forwards to mobile
mobile replies directly to correspondent
3
6: Wireless and Mobile Networks 6-60
Mobility via Direct Routing: comments
overcome triangle routing problem non-transparent to correspondent:
correspondent must get care-of-address from home agent what if mobile changes visited network?
6: Wireless and Mobile Networks 6-61
wide area network
1
foreign net visited at session start
anchorforeignagent
2
4
new foreignagent
35
correspondentagent
correspondent
new foreignnetwork
Accommodating mobility with direct routing
anchor foreign agent: FA in first visited network data always routed first to anchor FA when mobile moves: new FA arranges to have
data forwarded from old FA (chaining)
6: Wireless and Mobile Networks 6-62
Response (mobilecorresponding)
Triangle routing: mobile corresponding Using mobile host’s `home’ IP address Foreign network may block for `IP spoofing`
(egress filtering) Indirect via foreign: mobileFA corresp.
Requires FA (Foreign agent) to `spoof` Indirect via home: mobile
homecorresp. Overhead… but works
Direct: mobile corresponding Use temporary IP address (and mobile IP)
6: Wireless and Mobile Networks 6-63
Wireless and Mobile Communication Networks: Outline6.1 Introduction
Wireless 6.2 Wireless links,
characteristics 6.3 IEEE 802.11
wireless LANs (“wi-fi”)
Mobility 6.5 Principles:
addressing and routing to mobile users
6.6 Mobile IP 6.7 Cellular networks 6.8 Mobility and
higher-layer protocols
6.9 Summary
6: Wireless and Mobile Networks 6-64
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
6: Wireless and Mobile Networks 6-65
Mobile IP: indirect routing
Permanent address: 128.119.40.186
Care-of address: 79.129.13.2
dest: 128.119.40.186
packet sent by correspondent
dest: 79.129.13.2 dest: 128.119.40.186
packet sent by home agent to foreign agent: a packet within a packet
dest: 128.119.40.186
foreign-agent-to-mobile packet
6: Wireless and Mobile Networks 6-66
Mobile IP: agent discovery agent advertisement: foreign/home agents
advertise service by broadcasting ICMP messages (typefield = 9)
R bit: registration required
H,F bits: home and/or foreign agent
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 available Care-Of-Addresses (COA)
0 8 16 24
6: Wireless and Mobile Networks 6-67
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
6: Wireless and Mobile Networks 6-68
Wireless and Mobile Communication Networks: Outline6.1 Introduction
Wireless 6.2 Wireless links,
characteristics 6.3 IEEE 802.11
wireless LANs (“wi-fi”)
Mobility 6.5 Principles:
addressing and routing to mobile users
6.6 Mobile IP 6.7 Cellular networks 6.8 Mobility and
higher-layer protocols
6.9 Summary
6: Wireless and Mobile Networks 6-69
Mobile Switching
Center
Public telephonenetwork, andInternet
Mobile Switching
Center
Components of cellular network architecture
connects cells to wide area net manages call setup (more later!) handles mobility (more later!)
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
6: Wireless and Mobile Networks 6-70
Multiple operators (providers)
correspondent
MSC
MSC
MSC MSC
MSC
wired public telephonenetwork
different cellular networks,operated by different providers
recall:
6: Wireless and Mobile Networks 6-71
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
6: Wireless and Mobile Networks 6-72
Public switched telephonenetwork
mobileuser
homeMobile
Switching Center
HLR home network
visitednetwork
correspondent
Mobile Switching
Center
VLR
GSM: indirect routing to mobile
1 call routed to home network
2
home MSC consults HLR,gets roaming number ofmobile in visited network
3
home MSC sets up 2nd leg of callto MSC in visited network
4
MSC in visited network completescall through base station to mobile
6: Wireless and Mobile Networks 6-73
Mobile Switching
Center
VLR
old BSSnew BSS
old routing
newrouting
GSM: handoff with common MSC
Handoff goal: route call via new base station (without interruption)
reasons for handoff: stronger signal to/from new
BSS (continuing connectivity, less battery drain)
load balance: free up channel in current BSS
GSM doesn’t mandate why to perform handoff (policy), only how (mechanism)
handoff initiated by old BSS
6: Wireless and Mobile Networks 6-74
Mobile Switching
Center
VLR
old BSS
1
3
24
5 6
78
GSM: handoff with common MSC
new BSS
1. old BSS informs MSC of impending handoff, provides list of 1+ new BSSs
2. MSC sets up path (allocates resources) to new BSS
3. new BSS allocates radio channel for use by mobile
4. new BSS signals MSC, old BSS: ready
5. old BSS tells mobile: perform handoff to new BSS
6. mobile, new BSS signal to activate new channel
7. mobile signals via new BSS to MSC: handoff complete. MSC reroutes call
8 MSC-old-BSS resources released
6: Wireless and Mobile Networks 6-75
home network
Home MSC
PSTN
correspondent
MSC
anchor MSC
MSCMSC
GSM: handoff between MSCs
anchor MSC: first MSC visited during cal call remains routed
through anchor MSC
new MSCs add on to end of MSC chain as mobile moves to new MSC
Or: optional path minimization step to shorten multi-MSC chain
6: Wireless and Mobile Networks 6-76
home network
Home MSC
PSTN
correspondent
MSC
anchor MSC
MSCMSC
(b) after handoff
GSM: handoff between MSCs
anchor MSC: first MSC visited during cal call remains routed
through anchor MSC
new MSCs add on to end of MSC chain as mobile moves to new MSC
IS-41 allows optional path minimization step to shorten multi-MSC chain
6: Wireless and Mobile Networks 6-78
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 noise, collisions, handoff
TCP interprets loss as congestion, will decrease congestion window un-necessarily
delay impairments for real-time traffic limited bandwidth of wireless links
6: Wireless and Mobile Networks 6-79
Summary
Wireless wireless links:
capacity, distance channel impairments CDMA
IEEE 802.11 (“wi-fi”) CSMA/CA reflects
wireless channel characteristics
cellular access
Mobility principles: addressing,
routing to mobile users home, visited networks direct, indirect routing care-of-addresses
case studies mobile IP mobility in GSM
impact on higher-layer protocols