Computer Networks:
Wireless Networks
Ivan Marsic
Rutgers University
Chapter 6 – Wireless Networks
Wireless Networks
Chapter 6
Topic:
Mobile Ad-hoc Networks
(MANETs)
 Ad-hoc Network Definition
 Routing Protocols
 Dynamic Source Routing (DSR)
 Ad Hoc On-Demand DistanceVector (AODV)
Ad-hoc Networks
• Each mobile device (node) can act as a router
• Links form and break based on mobility and
environmental factors
• Connectivity (e.g., high probability of instantaneous
end-to-end paths existing) is assumed
Mobile Ad-hoc Networks
(MANETs)
Transmission
range
B
B
C
E
D
A
F
D
A
C
F
E
(a)
(b)
Physical wireless links
Network topology
Network Layer Notation vs.
Link Layer Transmissions (1)
B
packet
packet
A
C
D
F
E
B
A
C
F
D
E
Network Layer Notation vs.
Link Layer Transmissions (2)
Network layer (t)
B
packet
packet
F
D
A
Network layer
Link layer
C
E
B
Link layer (t1)
D
A
C
F
E
B
D
A
Link layer (t2)
C
E
F
Multihop Throughput
Challenge: more hops, less throughput
Links in route share radio spectrum
Extra hops reduce throughput
Throughput = 1
Throughput = 1/2
Throughput = 1/3
Ad-hoc Networks
S
D
• Goal: Nodes within the network can send data between
themselves.
• Challenges:
–
–
–
–
No centralized coordinator to help routing
No “default route” for nodes within the network
Fast topology changes
Limited bandwidth – can’t have too much overhead
Ad-hoc Networks
S
D
• Nodes that want to route messages must:
– Find out about the topology of the network
– Use that topology to do something with the
message
Control Plane
Data Plane
Routing Protocol Categories
Control Plane
• Proactive:
– Nodes actively maintain and share topology
information, regardless of if there is data to send
– Generally timer- or event-based
• Reactive (On-demand):
– “Lazy” approach: Don’t do more work then you
have to
– Only discover topology/routes when there is data
to send
Routing Protocol Categories
Data Plane
• Local next-hop forwarding:
– Consult forwarding table for a next hop
– Completely local decision
• Source routing:
– Source node places complete path in packet
header
– Intermediate nodes don’t have to consult their
forwarding tables
S
A
B
D
ABD
Reactive Protocols
• Names are useful hints at understanding the
protocol properties:
Dynamic Source Routing (DSR)
MANET
Source Routing
Ad-hoc On-demand Distance Vector (AODV)
Reactive
MANET
Next-hop Forwarding
Distance Vector
Dynamic Source Routing (DSR)
• When node S wants to send a packet to node
D, but does not know a route to D, node S
initiates a route discovery.
• Source node S floods the network with route
request (RREQ) packets (also called query
packets).
• Each node appends its own address in the
packet header when forwarding RREQ.
14
Route Discovery in DSR (1)
D
C
E
Y
G
I
F
B
A
K
H
L
J
Z
Route Discovery in DSR (2)
RREQ[C]
C
D
E
RREQ[C]
Y
G
I
F
B
A
K
Z
H
L
J
Broadcast RREQ[C]
Represents a node that has received RREQ for H from C
Route Discovery in DSR (3)
D
C
Y
E
G
RREQ[C, E]
I
F
B
H
RREQ[C, B]
A
K
L
J
Z
Route Discovery in DSR (4)
D
C
E
Y
G
RREQ[C, E, G]
I
F
B
H
RREQ[C, B, A]
RREQ[C, B, A]
A
K
L
J
Z
Route Discovery in DSR (5)
D
C
E
Y
G
RREP[C, E, G, H]
I
F
B
Z
H
RREQ[C, B, A, K]
A
K
L
J
Unicast RREP[C, E, G, H]
Route Discovery in DSR
RREQ[C]
D
C
E
D
C
G
E
G
RREQ[C]
I
F
B
A
H
F
B
J
L
K
I
A
(b)
D
D
C
E
G
E
G
RREQ[C, E, G]
E
RR
I
F
B
F
B
H
RREQ[C, B, A]
, E,
P[C
H
RREQ[C, B, A, K]
RREQ[C, B, A]
A
J
L
K
(a)
C
H
L
K
(c)
J
A
L
K
(d)
J
]
G, H
I
Route Discovery in AODV (1)
Routing tables
D
C
E
G
I
F
B
A
K
H
L
J
Route Discovery in AODV
RREQ(H)
D
C
E
C
G
Destination: C, Next hop: C
D
E
G
RREQ(H)
I
F
B
A
H
F
Dest: C
NxtHop: C
B
J
L
K
I
A
(b)
Dest: H, NxtHop: E
Dest: C, NxtHop: E
D
C
E
G
Dest: C, NxtHop: C
Dest: H, NxtHop: G
D
E
F
F
I
H
RREQ
RREQ(H)
A
C)
EP(
RR
B
H
RREQ(H)
Dest: C, NxtHop: E
Dest: H, NxtHop: H
G
RREQ(H)
I
B
J
L
K
(a)
C
H
L
K
Dest: C, NxtHop: B
(c)
J
A
L
K
(d)
J
Topic:
IEEE 802.11n (MIMO Wi-Fi)
 Physical (PHY) Layer Enhancements
 MAC Layer Enhancements:
 Frame Aggregation
 Block Acknowledgement
 Reverse Direction (RD) Protocol
 Backward Compatibility
IEEE 802.11n - MIMO
Reflecting surface
Receiver
Transmitter
Reflecting surface
802.11n Channel Bonding and
20/40 MHz Operation
20 MHz operation
Phased Coexistence Operation (PCO)
Traffic in
overlapping cells
in 20 MHz channel
(including control frames)
Traffic in
this cell
in 40 MHz channel
(HT greenfield mode)
mode)
20 MHz operation
Transition 40  20 MHz, see:
Traffic in
this cell
in 20 MHz channel
(HTHT-Mixed mode
or
NonNon-HT mode)
mode)
Transition 20  40 MHz, see:
In both 20 MHz and
40 MHz operation,
all control and
management
frames are
transmitted in
primary channel
40 MHz operation
Phased Coexistence Operation (PCO)
Secondary
20 MHz
channel
Primary
20 MHz
channel
Frequency
Traffic in
this cell
in 20 MHz channel
(HTHT-Mixed mode
or
NonNon-HT mode)
mode)
Traffic in
overlapping cells
in 20 MHz channel
(including control frames)
802.11n PHY-layer Frame Format
IEEE 802.11 Terminology
Key:
PPDU
PPDU = PLCP protocol data unit
PSDU = PLCP service data unit
MPDU = MAC protocol data unit
MSDU = MAC service data unit
PSDU = MPDU
MSDU
PHY
preamble
PHY
header
MAC
header
Data
FCS
PLCP = physical (PHY) layer
convergence procedure
MAC = medium access control
802.11n MAC-layer Frame Format
Packet Aggregation
802.11n Frame Aggregation
Data payload
Backoff
(0 to 2304 bytes)
PHY
PHY
MAC
preamble header header
Busy
FCS
Time
SIFS
DIFS
PHY
PHY
MAC
preamble header header
ACK
Overhead
(a)
Overhead
Aggregated data payload
(up to ~64 Kbytes)
Busy
DIFS
PHY
PHY
MAC
preamble header header
(b)
E{b0}=16 slots
FCS
FCS
Frame Aggregation:
A-MSDU and A-MPDU
Block Acknowledgement Session
Transmitter
Receiver
addBA Request
ACK
Block ACK
setup
addBA Response
ACK
Data MPDU
Data MPDU
Data and
Block ACK
transmission
repeated
multiple
times
Data MPDU
BlockAckReq (BAR)
Block ACK
delBA Request
Block ACK
teardown
ACK
Block Acknowledgement Frame
MAC header
bytes:
2
2
Frame Ctrl
6
6
Duration / ID Receiver Address Transmitter Addr.
2
variable
4
BA Control
Block ACK Information
FCS
(a)
bits:
bits:
1
1
1
9
4
Block ACK
Policy
Multi TID
Compressed
Bitmap
Reserved
TID_INFO
4
12
Fragment
Number (0)
bytes:
Starting Sequence Number
2
128
Block ACK
Starting Sequence Control
Block ACK Bitmap
 Basic Block ACK – 128 byte bitmap
bytes:
(b)
2
Block ACK
Starting Sequence Control
bytes:
2
Per TID Info
8
 Compressed Block ACK
- mandatory 8-byte bitmap
- no support for fragmentation
Block ACK Bitmap
2
8
Block ACK
Starting Sequence Control
Block ACK Bitmap
 Multi-TID Block ACK (repeated for each TID)
Block ACK Frame Subfields
Frame fragments
Multi-TID
0
Compressed
Block ACK
Bitmap
frame variant
0
Basic
Block ACK
0
1
Compressed
Block ACK
1
0
reserved
1
1
(a)
Multi-TID
Block ACK
Acknowledged data frames
0 1
2
3 4
5
0
1
2
3
4
5
.
.
.
61
62
63
(b)
…
13 14 15
Block ACK Example
Reverse Direction (RD) Protocol
Unidirectional vs. Bidirectional RTS/CTS Access Scheme
DIFS Backoff
RTS
Data_fwd
SIFS
Busy
SIFS
Transmitter
SIFS
TXOP duration
CTS
Receiver
Time
DIFS
BACK
(a)
TXOP duration
RD responder
CTS
SIFS
RTS
Data_fwd
SIFS
Busy
SIFS
RD initiator
DIFS Backoff
SIFS
RDG/More PPDU = 1
BACKr
DIFS
BACKf
Data_rvs
(b)
RDG/More PPDU = 1
RDG/More PPDU = 0
802.11n Backwards Compatibility
Modes: CTS-to-Self
CTSCTS-toto-self
802.11n
PHY header
802.11n
MAC header
Data
FCS
SIFS
Legacy 802.11 Legacy 802.11
PHY header MAC header
Data frame (HT format)
SIFS
CTS-to-self frame (Non-HT format)
(a) Legacy compatibility mode
ACK
Blocking out non-HT stations with Network Allocation Vector (NAV)
Legacy 802.11
802.11n
PHY header PHY header
802.11n
MAC header
Data
FCS
(b) Mixed compatibility mode
SIFS
Data frame (HT-mixed format)
ACK
Blocking out non-HT stations with spoofed duration value (L-SIG field)
802.11n
PHY header
802.11n
MAC header
(c) Greenfield mode
Data
FCS
SIFS
Data frame (HT format)
ACK
(no protection)
Dual-CTS protection (CTS-to-self)
802.11n
(HT-Greenfield)
A
B
802.11g
(Legacy non-HT)
SIFS
AP
CTS (HT)
AP
A
B
RTS (HT)
Time
CTS-to-self CTS-to-self
CTS (L)
receives
data (HT)
Data (HT)
sets NAV
CTS (HT)
CTS (L)
Data (L)
sets NAV
receives
data (L)
Example of L-SIG Duration Setting
NAV duration
NAV duration
L-SIG duration
Data
CTS
L-SIG duration
L-SIG duration
L-SIG
CF-End
Legacy
preamble
L-SIG
Legacy
preamble
L-SIG
RTS
Legacy
preamble
L-SIG
Legacy
preamble
NAV duration
BACK
802.11n Phased Coexistence
Operation (PCO)
BSS-1
802.11g
(HT-Mixed)
802.11n
(HT-Greenfield)
C
802.11g
(Legacy)
A
802.11n
802.11g
(HT-Mixed)
AP
Another
AP
B
BSS-2
ion
40 MHz phase
20 MHz phase
an
sit
(truncated)
CF--End
CF
Set--PCO
PCO--Phase
Set
AP and A
exchange traffic
in 802.11n
40 MHz channel
(HT greenfield
mode)
mode)
PIFS
CTS--to
to--self
CTS
CTS--to
to--self
CTS
NAV of sta. A
(40 MHz ch.)
CF--End
CF
Beacon
OR
Set--PCO
PCO--Phase
Set
Busy
(traffic in
BSSBSS-2)
PIFS
Primary
20 MHz
channel
Secondary
20 MHz
channel
Tr
Transition
CF--End
CF
20 MHz
phase
AP releases
the 20 MHz
channels
AP reserves
both 20-MHz
channels for
40 MHz phase
Traffic in BSSBSS-1 in
802.11g
20 MHz channel (Non
(Non-HT or HTHT-Mixed mode)
mode)
Traffic in BSSBSS-2
in 802.11g
20 MHz channel
NAV (A)
Time
(truncated)
NAV of station B (primary channel)
(truncated)
NAV of station C (secondary channel)
Topic:
RFID: Radio-Frequency
Identification
 Query Slot Protocol (ALOHA)
for Tag Interrogation
RFID - Query Slot Protocol
Visit http://www.gs1.org/epcglobal/standards for RFID Protocols Class-1 Generation-2
Reader R
Tag T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
slot 0: QueryRequest(Q=2)
( collision )
RN16(T3,T5,T8)
cnt=2
invt=0
cnt=1
invt=0
cnt=0
invt=0
cnt=3
invt=0
cnt=0
invt=0
cnt=2
invt=0
cnt=3
invt=0
cnt=0
invt=0
cnt=1
invt=0
cnt=2
invt=0
cnt=7
cnt=0
cnt=2
cnt=6
cnt=1
cnt=2
cnt=4
cnt=3
cnt=2
cnt=5
cnt=0
cnt=1
cnt=3
cnt=2
cnt=1
cnt=2
cnt=1
cnt=0
NAK
slot 0: QueryAdjust
QQ1 = 3
cnt=5
(T3)
RN16
EPC(T
ACK(R
N16-T3
)
3)
invt=1
slot 1: QueryRepeat
cnt=4
cnt=6
cnt=1
RN16(T6)
ACK(RN1
6-T6)
EPC(T6)
invt=1
slot 2: QueryRepeat
cnt=3
( collision )
RN16(T3,T5,T8)
cnt=5
cnt=0
cnt=4
cnt=0
Classification of QoS
Techniques in 802.11