Transcript Chapter4b

Chapter 4
Wireless LAN Technologies
and Products
2001/11/02
Prof. Huei-Wen Ferng
1
General Description
Overview of Technologies
2001/11/02
Prof. Huei-Wen Ferng
2
Technology Trends



Physical layers of WLAN are based on
SS (FHSS and DSSS) and IR
technologies
Frequency bands: ISM band
Date rate:
• Current products/standards: 1~54 Mbps
• Future: 100 Mbps and above
2001/11/02
Prof. Huei-Wen Ferng
3
Wireless LAN Wish List

High speed
• At least as fast as today’s Ethernet

Low cost
• Not much more than today’s Ethernet

Coverage
• Throughout the building or campus







No use of the battery of the mobile computer, or at least
minimal impact
No interference with other equipments
Easy installation, use, and management
Easy repair and upgrading
PCMCIA form factor
No external antenna
Co-operability of different wireless LAN systems
2001/11/02
Prof. Huei-Wen Ferng
4
Effect of Multi-path Fading


Multi-path: a number of different
paths of signals arrives at the
receiver
Signals of different propagation
delays can degrade performance
2001/11/02
Prof. Huei-Wen Ferng
5
2001/11/02
Prof. Huei-Wen Ferng
6
2001/11/02
Prof. Huei-Wen Ferng
7
Network Architecture
2001/11/02
Prof. Huei-Wen Ferng
8
Network Architecture (Cont’d)

Infrastructure
• Connectivity is accomplished by access
point (AP) between a station and other
station or network

Ad-hoc network
• This network is set up temporarily to
meet some immediate need
• It has no centralized server, like AP
2001/11/02
Prof. Huei-Wen Ferng
9
MAC Protocols

Three MAC protocols for wireless
LANs
• Listen Before You Talk MAC protocol
• Integrated wireless LAN MAC protocol
• Polling MAC protocol
2001/11/02
Prof. Huei-Wen Ferng
10
Listen Before You Talk MAC
protocol


LBT is basically a non-persistent CSMA
protocol
It differs from CSMA in two ways
• An RTS packet is transmitted before data is
transmitted to the receiver, then the receiver
transmits a CTS packet to be heard by all
nodes to grant data transfer from the sending
node
• After RTS/CTS packets, the sending node
transmit the data

LBT or RTS/CTS scheme avoids the hidden
node problem
2001/11/02
Prof. Huei-Wen Ferng
11
Integrated CSMA/TDMA MAC
Protocol


A hybrid of reservation and random access
The frame is segmented into
• Two reservation intervals for isochronous
Traffic
• One interval for random access traffic

Movable boundary by a control function
• Infrastructure: by AP
• Ah-hoc: the function is distributed among the
nodes
2001/11/02
Prof. Huei-Wen Ferng
12
2001/11/02
Prof. Huei-Wen Ferng
13
Contents of Headers

Header AH:
• Length of TA, TB, TC
• BSID: Unique ID of the AP
• NET_ID: Network ID
• NEXT_FREQ/NEXT_CODE/NEXT_CHNL
• <Si, Wi>: AP transmit Si packets to
user Wi
2001/11/02
Prof. Huei-Wen Ferng
14
Contents of Headers (Cont’d)

Header BH:
• The length of TB, TC
• <Si, Vi, Wi>: User Vi transmits Si
packets to user Wi

Header CH:
• The length of TC
• K: current estimate of users attempting
transmission in random access section
2001/11/02
Prof. Huei-Wen Ferng
15
Polling MAC Protocol

Incorporate the fairness issue
• E.g., stock trading application

Mechanism
• A node has a packet to send, it first
sends a request to the control point
• The control point polls the users in turn
by referencing the request queue
• Data needs ACK and goes through an AP,
therefore, no ad-hoc networking
2001/11/02
Prof. Huei-Wen Ferng
16
2001/11/02
Prof. Huei-Wen Ferng
17
Power Management


In order to achieve low power budgets,
the WLAN adaptor must sleep as much as
possible
Three States are defined for WLAN
adapter:
• Transmit state

Transmitter is turned on
• Awake state

Receiver is powered on and ready to receive
• Doze state

2001/11/02
Transceiver dozing
Prof. Huei-Wen Ferng
18
Power Management (Cont’d)



The power savings scheme is with the help
of AP
The AP buffers traffic for dozing nodes
The AP informs nodes of traffic in
broadcast packets called Traffic Delivery
Information Messages (TDIM)
• The frame header include: which stations have
data to receive, how much data to receive, and
when it will be delivered
2001/11/02
Prof. Huei-Wen Ferng
19
Power Management (Cont’d)

The node will wake up when
• they are transmitting
• they have data to receive in the specify time
• during the frame header to check the TDIM


The node periodically check the frame
header
Palm-top computer do not wake up every
frame. They remain sleep as long as they
wish
2001/11/02
Prof. Huei-Wen Ferng
20
Interconnection with Backbone
Networks

Connecting with the same network
• Done below the network layer using
MAC layer bridges

Mobility between different networks
• Done at the network layer via new
protocols such as Mobile IP
2001/11/02
Prof. Huei-Wen Ferng
21
Mobility within the Same Network


Mobile nodes are roaming in the
same area that are covered by
different APs in the same network
Each AP contains three components
• A WLAN interface card (AP<->Node)
• A wired LAN interface card (AP<>Network)
• A MAC layer bridge to filter the traffic
between the wireless subnet and the
backbone
2001/11/02
Prof. Huei-Wen Ferng
22
2001/11/02
Prof. Huei-Wen Ferng
23
Bridges


Bridging is used to filter traffic from
different wired segments of a large
LAN
Differences among repeater, bridge,
and router?
2001/11/02
Prof. Huei-Wen Ferng
24
Mechanism of Bridges



When a bridge is first installed, it
acts as a repeater
Then as a traffic goes through it, it
learns which nodes are on which LAN
segment and forms a table
Next time it receives a packet, it
forwards it only on the LAN segment
destined; otherwise, it broadcasts on
all LAN segments
2001/11/02
Prof. Huei-Wen Ferng
25
Timers






The entries in the table are not kept
forever
Bridges have a timer for each node
The age-out timers in wired LANs are on
the order of hours
The age-out timers in wireless LANs are
on the order of minutes
What happen if the age-out timer is too
short?
What happen if the age-out timer is too
long?
2001/11/02
Prof. Huei-Wen Ferng
26
Additional Functions of Bridges



Buffering between different speed
LANs
Changing frame formats between
incompatible LANs
Adding and deleting fields within the
frame, e.g., 802.3 has a data length
field but 820.4 doesn’t
2001/11/02
Prof. Huei-Wen Ferng
27
MAC Layer Bridging Protocols

Spanning tree bridges
• Need a distributed database of where all the nodes are
and the best way to reach any node
• The network topology takes shape using multiple
bridges
• The way to form the topology


Using a distributed algorithm for selecting a root bridge
and a tree that reaches every other bridge
Source routing bridges
• Rely on the source node, which keeps a table of where
other nodes are
• It includes the route the packet is to take in the header
• Places greater burden on the nodes
2001/11/02
Prof. Huei-Wen Ferng
28
Mobility among Different Networks
(Mobile IP)

The goals of mobile IP are:
•
•
•
•
Mobility is handled at the network layer
Transport and higher layers are unaffected
Applications do not need to change
The infrastructure of non-mobile routers are
unaffected
• Non-mobile hosts are unaffected
• Continuous operation occurs across multiple
networks
• Security is as good as with existing networks
2001/11/02
Prof. Huei-Wen Ferng
29
Mobile IP


Briefly Speaking, to take a mobile IP
address for mobility with minor
changes
At present, IP address is associated
with a fixed network location like a
phone number
2001/11/02
Prof. Huei-Wen Ferng
30
Mobile IP (Cont’d)

Terms Definition used in Mobile IP
operations:
• Mobile host (MH): a movable host
• Home address (HA): a permanent IP
address used to identify an MH anytime
• Home network (HN): the logical network
where an MH’s HA resides
• Care of address (COA): a temporary
address used to locate an MH at some
particular instant
2001/11/02
Prof. Huei-Wen Ferng
31
Mobile IP (Cont’d)



Agents: in the routers to implement the
new software offering mobile capabilities
Home Agent (->HLR): An agent that
redirects packet from a home network to
the COA of an MH
Foreign Agent (->VLR): a specialized
forwarding agent that
• Offers a COA
• Maintains and performs mapping between the
COA and HA of an MH
2001/11/02
Prof. Huei-Wen Ferng
32
Mobile IP (Cont’d)
Boston
San Francisco
Washington
Triangle routing
2001/11/02
Prof. Huei-Wen Ferng
33
Mobile IP (Cont’d)

Triangle routing
• Not too bad if only one or two packets

For many packets, FA in Boston
sends a message to the fixed node in
Washington and asks it to use the
mobile node’s COA instead its HA,
the packets then go directly from
Washington to Boston
2001/11/02
Prof. Huei-Wen Ferng
34
The operation of Mobile IP
2001/11/02
Prof. Huei-Wen Ferng
35
The Operation of Mobile IP (Cont’d)

How does a MH find an FA?
• Through the advertisements

FAs send out service advertisements that
announce their willingness to provide COA
to visiting MHs
• MH can send out a solicitation packet
asking if a FA is in the vicinity
2001/11/02
Prof. Huei-Wen Ferng
36
Packet Types of Mobile IP







Advertisement packet
Solicitation packet
Registration
MH to FA registration packet
FA to HA registration packet
HA to FA registration ACK packet
FA to MH registration ACK packet
2001/11/02
Prof. Huei-Wen Ferng
37
2001/11/02
Prof. Huei-Wen Ferng
38
The PCS Model for Mobility



In cellular and PCS networks, each
person has a unique number similar
to Mobile IP address
This number is stored in Home
Location Register (HLR)
When user is visiting foreign location,
he/she is automatically registered
with a Visitor Location Register (VLR)
2001/11/02
Prof. Huei-Wen Ferng
39
PCS Call Flow
Destination HLR
(4)
(3)
Calling
UPT user
(2)
Originating
network
Called
UPT user
(1)
Source HLR
2001/11/02
Terminating
network
Authentication: (1),(2)
Service profile, routing: (3),(4)
Prof. Huei-Wen Ferng
40
Wireless LAN Standards

IEEE 802.11
• IEEE 802.11
• IEEE 802.11a
• IEEE 802.11b

High-performance radio LAN
(HiperLAN)
• HiperLAN type 1
• HiperLAN type 2
2001/11/02
Prof. Huei-Wen Ferng
41
IEEE 820.11
2001/11/02
Prof. Huei-Wen Ferng
42
HiperLAN

HiperLAN Type 1 (H/1)
• A connectionless packet-based broadband WLAN standard at 5 GHz in 1996

HiperLAN Type 2 (H/2)
• A connection-oriented high-performance
technology at 5 GHz in 2000
2001/11/02
Prof. Huei-Wen Ferng
43
Resources

ETSI/BRAN website
• http://www.etsi.org/bran
2001/11/02
Prof. Huei-Wen Ferng
44
2001/11/02
Prof. Huei-Wen Ferng
45
References




R. A. Dayem, Mobile Data and Wireless
LAN Technologies
William Stallings, “IEEE 802.11: Moving
Closer to Practical Wireless LANs”, IEEE IT
Pro, 2001
B. H. Walke et al., “IP over Wireless Mobile
ATM-Guaranteed Wireless QoS by
HiperLAN/2”, Proc. Of IEEE, 2001
Perkins, “Mobile Networking Through
Mobile IP”, IEEE Internet Computing, 1998
2001/11/02
Prof. Huei-Wen Ferng
46