Download EECI Course M07 -2mm TU-Berlin, February 22-25, 2016

EECI Course M07
TU-Berlin, February 22-25, 2016
Modeling, analysis and design of
wireless sensor and actuator networks
MAC layer: IEEE 802.15.4, Markov chain modeling,
Performance analysis
Alessandro D’Innocenzo - University of L’Aquila
Carlo Fischione - KTH Royal Institute of Technology
February 22, 2016
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
1 / 44
Previous lecture
Application
Presentation
Session
Transport
Routing
MAC
Phy
How information is modulated and transmitted over the wireless channel?
What is the successful probability to receive bits?
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
2 / 44
This lecture
Application
Presentation
Session
Transport
Routing
MAC
Phy
When a node gets the right to transmit messages?
What is the mechanism to get such a right?
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
3 / 44
This lecture’s learning goals
What is the Medium Access Control (MAC)?
What are the options to design MACs?
What is the MAC of IEEE 802.15.4?
How to select the IEEE 802.15.4 MAC parameters to satisfy the closed loop control
requirements?
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
4 / 44
Outline
Definition and classification of MACs
I
TDMA, FDMA, CSMA, ALOHA
I
Hidden and exposed terminals
The IEEE 802.15.4 protocol
Performance analysis of IEEE 802.15.4
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
5 / 44
Medium Access Control - MAC
MAC: mechanism for controlling when sending a message (packet) and when
listening for a message
MAC is one of the major components for energy expenditure in WSNs
I
I
Receiving packets is about as expensive as transmitting
Idle listening for packets is also expensive
Typical power consumption of a node
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
6 / 44
Problems for MACs
1. Collisions: wasted effort when two messages collide
2. Overhearing: wasted effort in receiving a message destined for another node
3. Idle listening: sitting idly and trying to receive a message when nobody is sending
4. Protocol overhead
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
7 / 44
The hidden terminal problem
Terminal, another word for node
Hidden terminal problem:
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
8 / 44
The hidden terminal problem
A
B
C
D
Terminal, another word for node
Hidden terminal problem:
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
8 / 44
The hidden terminal problem
A
B
Transmit range:
(depends on the channel, transmit power,...)
distance past which the SNR is in outage
C
D
Terminal, another word for node
Hidden terminal problem:
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
8 / 44
The hidden terminal problem
A
B
Transmit range:
(depends on the channel, transmit power,...)
distance past which the SNR is in outage
C
D
Terminal, another word for node
Hidden terminal problem:
I
Node A wants to send a message to B
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
8 / 44
The hidden terminal problem
A
B
Transmit range:
(depends on the channel, transmit power,...)
distance past which the SNR is in outage
C
D
Terminal, another word for node
Hidden terminal problem:
I
I
Node A wants to send a message to B
Node C wants to send a message to D
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
8 / 44
The hidden terminal problem
A
B
Transmit range:
(depends on the channel, transmit power,...)
distance past which the SNR is in outage
C
D
Terminal, another word for node
Hidden terminal problem:
I
I
I
Node A wants to send a message to B
Node C wants to send a message to D
Node A does not hear transmitter C sending messages that can be received by
B and D
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
8 / 44
The exposed terminal problem
A
B
C
D
Exposed terminal problem:
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
9 / 44
The exposed terminal problem
Transmit range of B
Transmit range of C
A
B
C
D
Exposed terminal problem:
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
9 / 44
The exposed terminal problem
Transmit range of B
Carrier sense range of B
Transmit range of C
A
B
C
D
Carrier sense range:
Carrier sense range of C
(depends on the channel, transmit power,...)
distance within a transmitter can be heard/sensed at a receiver
Exposed terminal problem:
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
9 / 44
The exposed terminal problem
Transmit range of B
Carrier sense range of B
Transmit range of C
A
B
C
D
Carrier sense range:
Carrier sense range of C
(depends on the channel, transmit power,...)
distance within a transmitter can be heard/sensed at a receiver
Exposed terminal problem:
I
B wants to send messages to A
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
9 / 44
The exposed terminal problem
Transmit range of B
Carrier sense range of B
Transmit range of C
A
B
C
D
Carrier sense range:
Carrier sense range of C
(depends on the channel, transmit power,...)
distance within a transmitter can be heard/sensed at a receiver
Exposed terminal problem:
I
I
B wants to send messages to A
C wants to send messages to D
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
9 / 44
The exposed terminal problem
Transmit range of B
Carrier sense range of B
Transmit range of C
A
B
C
D
Carrier sense range:
Carrier sense range of C
(depends on the channel, transmit power,...)
distance within a transmitter can be heard/sensed at a receiver
Exposed terminal problem:
I
I
I
B wants to send messages to A
C wants to send messages to D
Transmitter B hears transmitter C which is not causing collisions at the
receiver A. A is not in the transmit range of C
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
9 / 44
The exposed terminal problem
Transmit range of B
Carrier sense range of B
Transmit range of C
A
B
C
D
Carrier sense range:
Carrier sense range of C
(depends on the channel, transmit power,...)
distance within a transmitter can be heard/sensed at a receiver
Exposed terminal problem:
I
I
I
I
B wants to send messages to A
C wants to send messages to D
Transmitter B hears transmitter C which is not causing collisions at the
receiver A. A is not in the transmit range of C
Transmitter C hears B, but D is not in the transmit range of B
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
9 / 44
Important MACs for WSNs
TDMA - Time Division Multiple Access
I
I
Time is divided into time slots
Every node is assigned to transmit at a time slot
FDMA - Frequency Division Multiple Access
I
As TDMA, but is the carrier frequency to be divided into slots
CSMA - Carrier Sense Multiple Access
I
I
A node listens (channel assessment) if the channel if free or busy from other
transmissions
If free, transmit the message; if busy, back-off the transmission
ALOHA
I
If a node has a message, it draws a random variable and transmits according
to the outcome
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
10 / 44
TDMA
A central node decides the TDMA schedules
I
I
I
Simple and no packet collisions
Burdens the central node coordinator
Not feasible for large networks
TDMA is useful when network is divided into smaller clusters
I
In each cluster, MAC can be controlled at local head
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
11 / 44
Slotted ALOHA
n number of nodes attempting to transmit
Time slots vs Node ID
The slotted ALHOA works on top of TDMA
Nodes are synchronized
p probability that a node can transmit a message (because of free channel
assessment)
Probability of successful message transmission
n.p(1 − p)n−1
Probability that a slot is taken
Carlo Fischione (KTH)
p(1 − p)n−1
EECI Course M07 TU-Berlin
February 22, 2016
12 / 44
Schedule and contention-based MACs
Schedule-based MACs (TDMA, FDMA)
I
I
I
I
A schedule regulates which node may use which slot at which time
Schedule can be fixed or computed on demand
Collisions, overhearing, idle listening no issues
Time synchronization needed
Contention-based MACs (CSMA, ALHOA)
I
I
I
Based on random access
Risk of packet collisions
Mechanisms to handle/reduce probability/impact of collisions required
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
13 / 44
More in general
Wireless
Medium
Access
Centralized
Schedulebased
Fixed
assignment
Carlo Fischione (KTH)
Distributed
Contentionbased
Demand
Schedulebased
Fixed
assignment
EECI Course M07 TU-Berlin
Contentionbased
Demand
February 22, 2016
14 / 44
Outline
Definition and classification of MACs
The IEEE 802.15.4 protocol
I
I
I
Introduction
Physical layer
MAC layer
Performance analysis of IEEE 802.15.4
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
15 / 44
IEEE 802.15.4 protocol architecture
Now we study the MAC of the standard IEEE 802.15.4
IEEE 802.15.4 is the de-facto reference standard for low data rate and low power
WSNs
Characteristics:
I
I
I
I
Low data rate for ad hoc self-organizing network of inexpensive fixed, portable
and moving devices
High network flexibility
Very low power consumption
Low cost
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
16 / 44
IEEE 802.15.4 networks
IEEE 802.15.4 network composed of
I
I
Full-function device (FFD)
Reduced-function device (RFD)
A network includes at least one FFD
The FFD can operate in three modes:
I
I
I
A personal area network (PAN)
coordinator
A coordinator
A device
An FFD can talk to RFDs or FFDs
RFD can only talk to an FFD
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
17 / 44
IEEE 802.15.4 network topologies
Star topology
Peer-to-peer topology
PAN Coordinator
PAN Coordinator
Full Function Device
Reduced Function Device
Communication Flow
3 types of topologies
I
I
I
Star topology
Peer-to-peer topology
Cluster-tree
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
18 / 44
Cluster-tree topology
First PAN Coordinator
PAN Coordinator
Device
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
19 / 44
IEEE 802.15.4 physical layer
Frequency bands:
I
I
I
2.4 - 2.4835GHz GHz, global, 16 channels, 250Kbps
902.0 - 928.0MHz, America, 10 channels, 40Kbps
868 - 868.6MHz, Europe, 1 channel, 20Kbps
Features of the PHY layer
I
I
I
I
I
I
Activation and deactivation of the radio transceiver
Transmitting and receiving packets across the wireless channel
Energy detection (ED, from RSS)
Link quality indication (LQI)
Clear channel assessment (CCA)
Dynamic channel selection by a scanning a list of channels in search of
beacon, ED, LQI, and channel switching
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
20 / 44
IEEE 802.15.4 physical layer
PHY
(MHz)
Frequency band
(MHz)
Spreading parameters
Data parameters
Chip rate
(kchip/s)
Modulation
868-868.6
300
BPSK
20
20
902-928
600
BPSK
40
40
Binary
868/915
(optional)
868-868.6
400
ASK
250
12.5
20-bit PSSS
902-928
1600
ASK
250
50
5-bit PSSS
868/915
(optional)
868-868.6
400
O-QPSK
100
25
16ary Orthogonal
902-928
1000
O-QPSK
250
62.5
16ary Orthogonal
2400-2483.5
2000
O-QPSK
250
62.5
16ary Orthogonal
868/915
2450
Bit rate
(kb/s)
Symbol rate
(ksymbol/s)
Symbols
Binary
Frequency bands and propagation parameters for IEEE 802.15.4 physical layer
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
21 / 44
Physical layer data unit
SFD indicates the end of the SHR and the start of the packet data
PHR: PHY header
PHY payload < 128 byte
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
22 / 44
IEEE 802.15.4 MAC
The MAC provides two services:
I
I
Data service
Management service
MAC features: beacon management, channel access, GTS management, frame
validation, acknowledged frame delivery, association and disassociation
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
23 / 44
Superframes
Superframe structure:
I Format defined by the PAN coordinator
I Bounded by network beacons
I Divided into 16 equally sized slots
Beacons
I Synchronize the attached nodes, identify the PAN and describe the structure
of superframes
I Sent in the first slot of each superframe
I Turned off if a coordinator does not use the superframe structure
Superframe portions: active and an inactive
I Inactive portion: a node does not interact with its PAN and may enter a
low-power mode
I Active portion: contention access period (CAP) and contention free period
(CFP)
I Any device wishing to communicate during the CAP competes with other
devices using a slotted CSMA/CA mechanism
I The CFP contains guaranteed time slots (GTSs)
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
24 / 44
IEEE 802.15.4 CSMA/CA
A Carrier Sense Multiple Access/ Collision Avoidance (CSMA/CA) algorithm is
implemented at the MAC layer
If a superframe structure is used in the PAN, then slotted CSMA-CA is used in the
CAP period
If beacons are not used in the PAN or a beacon cannot be located in a
beacon-enabled network, unslotted CSMA-CA is used
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
25 / 44
CSMA/CA
Each device has 3 variables: NB, CW and BE
NB: number of times the CSMA/CA algorithm was required to backoff while
attempting the current transmission
I
It is initialized to 0 before every new transmission
BE: backoff exponent
I
How many backoff periods a device shall wait before attempting to assess the
channel
CW: contention window length (used for slotted CSMA/CA)
I
I
Is the number of backoff periods that need to be clear of activity before the
transmission can start
It is initialized to 2 before each transmission attempt and reset to 2 each time
the channel is assessed to be busy
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
26 / 44
CSMA/CA
CSMA-CA
(1)
N
Slotted?
Y
NB=0,
BE=macMinBE
NB=0, CW=2
Battery life extension?
Flow diagram to transmit
a packet with CSMA/CA
in the modalities slotted
(left, also called beacon
modality) and unslotted
(right, also called
beaconless modality)
Y
BE=lesser of
(2,macMinBE)
N
BE=macMinBE
Locate backoff
period boundary
(2)
Delay for random(2BE 1) unit backoff periods
(2)
Delay for random(2BE 1) unit backoff periods
(3)
Perform CCA on
backoff period boundary
(3)
Perform CCA
Channel Idle?
Y
Channel Idle?
(5)
(4)
N
CW=2,NB=NB+1,
BE=min(BE+1,
macMaxBE)
CW=CW+1
NB> macMaxCSMABackoffs?
CW=0?
Y
Failure
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
Y
(5)
N
N
Y
Success
(4)
N
N
NB=NB+1,
BE=min(BE+1,
macMaxBE)
NB> macMaxCSMABackoffs?
Y
Failure
Success
February 22, 2016
27 / 44
Guarantee Time Slot, GTS
The GTSs always appear at the end of the active superframe starting at a slot
boundary immediately following the CAP
The PAN coordinator may allocate up to 7 GTSs
A GTS can occupy more than one slot period
SO < 15. If SO=15, the superframe will not be active anymore after the beacon
BO < 15. If BO=15, the superframe is ignored
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
28 / 44
GTS
A GTS allows a device to operate within a portion of the superframe that is
dedicated exclusively to it
A device attempts to allocate and use a GTS only if it is tracking the beacons
GTS allocation:
I
I
I
I
Undertaken by the PAN coordinator only
A GTS is used only for communications between the PAN coordinator and a
device
The GTS direction is specified as either transmit or receive
A single GTS can extend over one or more superframe slots
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
29 / 44
Uplink MAC: beacon and non-beacon-enabled
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
30 / 44
Downlink MAC: beacon and non-beacon-enabled
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
31 / 44
Outline
Definition and classification of MACs
The IEEE 802.15.4 protocol
Performance analysis of IEEE 802.15.4
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
32 / 44
IEEE 802.15.4 Performance Analysis
But what is the performance of the IEEE 802.15.4 protocol as function of the
protocol parameters?
Performance indicators are important: We could set the protocol parameters that
give the right performance so to ensure close loop stability
Performance indicators:
I
Reliability or probability of successfully receiving a message
I
Delay to successfully receiving a message
I
Energy consumption to transmit messages
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
33 / 44
IEEE 802.15.4 Performance Analysis
We consider a star network, and model the IEEE 802.15.4 protocol behaviour by a
Markov chain
The performance analysis of IEEE 802.15.4 is complex
For pedagogical purposes, we restrict ourselves to the unlostted CSMA/CA
The goal of the analysis is to derive expressions for the probability that a packet is
successfully received, the delay in the packet delivery, and the average energy
consumption
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
34 / 44
Unslotted CSMA/CA
Delay for random(2BE 1) unit backoff periods
Perform CCA
Channel Idle?
Y
N
NB=NB+1,
BE=min(BE+1,
macMaxBE)
NB> macMaxCSMABackoffs?
Y
Failure
Success
Every nodes implements the CSMA/CA described in this diagram
CSMA/CA protocol parameters
I
I
I
I
BE
NB
macMaxBE, which we call BEmax
macMaxCSMABackoffs
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
35 / 44
IEEE 802.15.4 Performance Analysis
The analysis is developed in two steps
1. we study the behavior of a single node by using a Markov model to obtain the
stationary probability that a node attempts its carrier channel assessment
(CCA), φ
2. we couple the per user Markov chains to obtain an additional set of equations
that give the stationary probability of free channel assessment, α
The solution of the set of equations in 2. provides us φ and α
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
36 / 44
-2,0
-2,X
. . .
-1,L-1
. . .
Per-node Markov Chain Model for unslotted CSMA/CA
1
-1,0
1/W0
0,0
1
0,1
1
0,2
. . .
0,W 0-2
1
1,2
. . .
1,W 1-2
1
0,W0-1
1
1,W1-1
1/W1
1/W1
1/W 1
1,0
1
1,1
Pf
Ps
. . .
. . .
. . .
. . .
. . .
m,2
. . .
m,W m-2
. . .
1/W m
m,0
1
m,1
1
1
m,Wm-1
X is the time before a node generates a message to transmit
L is the duration of the message transmission measured in slots
Wi is the delay window, (BEmax − BEmin ) ≤ i ≤ NB. W0 = 2BEmin . Wi is
doubled each stage until Wi = Wmax = 2BEmax
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
37 / 44
Per-node Markov Chain Model for unslotted CSMA/CA
c(t) is the stochastic process representing the delay to successfully transmit a
message at time t
s(t) is the stochastic process representing the number of times the channel is
sensed busy before a message transmission (s(t) ∈ {0, · · · , NB})
s(t) = −1 denotes the transmission stage of a message
s(t) = −2 denotes the “unsaturated traffic” (a node does not continuously
generates messages, but only from time to time)
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
38 / 44
Per-node Markov Chain Model for unslotted CSMA/CA
{s(t), c(t)} is a two-dimensional Markov with the following transition probabilities:
P{i, k|i, k + 1} = 1,
1−α
P{0, k|i, 0} =
,
W0
α
P{i, k|i − 1, 0} =
,
Wi
1
P{0, k|N B, 0} =
.
W0
k≥0
(1)
i < NB
(2)
i ≤ NB, k ≤ Wi − 1
(3)
(4)
Eq. (1) is the condition to decrement the counter over an horizontal delay line of
the Markov chain
Eq. (2) states that it is only possible to enter the first delay line from a stage that is
not the last one (i < NB) after sensing the channel idle and hence transmitting a
message
Eq. (3) gives the probability that there is a failure on channel assessment and the
node selects a state in the next delay level
Eq. (4) gives the probability of starting a new transmission attempt when leaving
the last delay line, following a successful or failed message transmission attempt
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
39 / 44
Per-node Markov Chain Model for unslotted CSMA/CA
Denote the Markov chain steady-state probabilities by
bi,k = P{(s(t), c(t)) = (i, k)} ,
for i ∈ {−1, NB} and k ∈ {0, max(L − 1, Wi − 1)}.
Proposition 1 The probability that a node attempts a clear channel assessment is
φ=
NB
X
i=0
bi,0 = b0,0
1 − αNB+1
.
1−α
(5)
Proposition 2 Let N be the number of nodes. The probability that a node finds a
channel busy during CCA satisfies
α = (L + 1)[1 − (1 − φ)N −1 ](1 − α) .
(6)
The solution to the system of equations (5) and (6) gives φ and α
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
40 / 44
Performance Indicators for unslotted CSMA/CA
Proposition 3 The Reliability is
R
=
NB
X
(1 − φ)N −1 (1 − α)αi = (1 − φ)N −1 (1 − αNB+1 ) .
(7)
i=0
Proposition 4 Let rs be the slot duration. The Delay is
!
" NB
#
i
X X
Wk + 1 αi (1 − α)
D=
+ L rs ,
2
1 − αNB+1
i=0
(8)
k=0
Proposition 5 Let Pl , Pt and Ps be the average energy consumption in idle-listen,
transmit and sleep states respectively. The Energy Consumption is
!
L−1
X−1
NB W
NB
i −1
X
X
X
X
X
E =Pl
bi,k +
bi,0 + Pt
b−1,i + Ps
b−2,i
(9)
i=0 k=1
Carlo Fischione (KTH)
i=0
EECI Course M07 TU-Berlin
i=0
i=0
February 22, 2016
41 / 44
Performance analysis of unslotted CSMA/CA
The proofs of the previous propositions are given in
I
I
P. Park, C. Fischione, K. H. Johansson, “Modeling and Stability Analysis of
Hybrid Multiple Access in IEEE 802.15.4 Protocol”, ACM Trans. Sens. Net.,
2013.
P. Park, P. Di Marco, C. Fischione, K. H. Johansson, “Modeling and
Optimization of the IEEE 802.15.4 Protocol for Reliable and Timely
Communications”, IEEE Trans. on Par. and Dist. Sys., 2013.
Knowledge of the performance indicators of IEEE 802.15.4 allows to select the
protocol parameters as function of the closed loop control requirements
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
42 / 44
Conclusions
Application
Presentation
Session
Transport
Routing
MAC
Phy
We have seen a MAC classification,
I
TDMA, ALOHA, CSMA
Seen in detail the most popular protocol for WSNs, IEEE 802.15.4
Identifying interdependencies between MAC protocol and other layers/applications
is difficult
I
I
I
Which is the best MAC for which application?
How to optimally select the best MAC for given control requirements?
How to optimally select the MAC parameters for given control requirements?
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
43 / 44
Next lecture
Now that we know how nodes get the right to access the wireless medium, we
would like to see how a message is routed over possible paths
Routing protocols
I
I
How a node decides to route a message?
What are the mechanisms to get such a decision?
Carlo Fischione (KTH)
EECI Course M07 TU-Berlin
February 22, 2016
44 / 44