Transcript Mobile IP Principals, Cont…

Southern Methodist University Fall 2003
EETS 8316/NTU CC745-N
Wireless Networks
Lecture 10: Wireless LAN
Instructor: Jila Seraj
email: [email protected]
http://www.engr.smu.edu/~jseraj/
tel: 214-505-6303
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Session Outline
 Wireless LAN
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Wireless LAN
Wish List
— High speed
— Low cost
— No use/minimal use of the mobile equipment
battery
— Can work in the presence of other WLAN
— Easy to install and use
— Etc
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Wireless LAN Architecture
Ad Hoc
Laptop
Server
Laptop
DS
Access Point
Access Point
Pager
PDA
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Laptop
Laptop
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Wireless LAN Architecture, Cont…
Logical Link Control Layer
MAC Layer: Consist of two
sub layer, physical Layer
and physical convergence layer
Physical convergence layer, shields LLC
from the specifics of the physical
medium. Together with LLC it constitutes
equivalent of Link Layer of OSI
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What Is Hidden Node?
A
B
C
A can hear B
C can hear B
A can not hear C
C can not hear A sending data
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LBT MAC Protocol
LBT= Listen Before You Talk
—Based on CSMA-CA
—First send Ready To Send (RTS) to the
receiving node
—Receiving node send a Continue To Send
(CTS) message, takes care of hidden node.
—Data transmission starts after RTS/CTS.
—Data is acknowledged on the MAC level.
Counteract error caused by RF
environment.
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Integrated CSMA/TDMA MAC Protocol
Supports guaranteed bandwidth traffic and
random access traffic
The bandwidth is divided into a random part
and a reserved part.
Random part is LBT, reserved part
During high traffic all bandwidth can be used
for reserved traffic (like wireless telephony)
H1 Reserved-1 H2 Reserved-2 H3 LBT
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Reservation/Polling MAC Protocol
Works only with AP
Fair and slow. First-in-First-Out
Wireless station send a request.
All requests are queued.
Wireless stations are polled in the same order
that the requests have arrive.
All data reception is acknowledged.
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Power Management
Battery life of mobile computers/PDAs are very
short. Need to save
The additional usage for wireless should be
minimal
Wireless stations have three states
—Sleep
—Awake
—Transmit
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Power Management, Cont…
AP knows the power management of each
node
AP buffers packets to the sleeping nodes
AP send Traffic Delivery Information Message
(TDIM) that contains the list of nodes that will
receive data in that frame, how much data and
when.
The node is awake only when it is sending
data, receiving data or listening to TDIM.
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Access Point Functions
Access point has three components
—Wireless LAN interface to communicate with
nodes in its service area
—Wireline interface card to connect to the
backbone network
—MAC layer bridge to filter traffic between
sub-networks. This function is essential to
use the radio links efficiently
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Bridge Functions
Speed conversion between different devices,
results in buffering.
Frame format adaptation between different
incompatible LANs
Adding or deleting fields in the frame to convert
between different LAN standards
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Routing
Building routing tables can be done as
—Source tree, keeps track where other nodes
are and the best way of reaching them. When
sending a packet the route is also determined.
It must be done in each node and is heavy.
—Spanning tree, is built iteratively, each bridge
advertises it identity and all other bridges it
knows and how many hops it takes to get there.
Then each bridge follows a specific algorithm to
calculate how get to each bridge with least hop.
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Bridge Functions, Routing
Create a routing table for sending packets
Listen to all packets being sent.
Find out which nodes are in which sub-network
by analyzing the source address. Store that
data in a routing table.
If a packet is addressed to a known node, only
repeat the data on that sub-network, otherwise
repeat it on all networks.
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Bridge Functions, Routing, Cont…
 Age the entries after a timer value has expired since
the last communication
 If the timer is too long, we might send data to a node
that might have left the sub-network or is turned off or
even gone to coverage area of another access point.
 If the timer is too short, we remove the user too early
and repeat the packet destined to it in all sub-networks.
 Other functions of a bridge, buffering for speed
conversion, changing frame format between LANs.
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Mobility Management
AP has three components
— WLAN interface
— Backbone LAN interface
— MAC layer bridge function
Backbone Network
Access Point
Access Point
Access Point
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Mobility Management, Cont..
A node can associate when it enters the
coverage area of an AP
A node can disassociate when power down or
leaving the service area
It shall re-associate when it handoffs to another
AP.
AP bridge function keeps track of all nodes
associated with it.
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WLAN Addressing
In wireline LAN, each node has an IP
address that is associated with its physical
location
When a device can move from one location
to another, the association between the
physical location and IP address no longer
holds
The solution is presented in mobile IP
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Mobile IP Principals
Internet is a large network and introducing
a new function, e. g. Mobile IP can not be
disruptive.
Constraints of mobile IP are
—Mobility should be at network layer
—No impact on higher levels
—No impact on the nodes not directly involved
in the mobile IP function
—Uninterrupted operation for mobile devices
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Mobile IP Principals, Cont…
The principle is very simple, use c/o
addressing
For each mobile device, we associate a
Home IP address associated with a Home
Network.
The new LAN is called the Visiting Network
The software that takes care of mobility in
each server (router) is called agent.
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Mobile IP Principals, Cont…
Two types of agents, Home Agent and
Visiting Agent.
Whenever the mobile device connects to a
new network, a c/o address is given to it by
the Visiting Agent.
This c/o address is reported to the Home
Agent.
All packets addressed to the mobile device
are addressed to its Home Address, and
thus sent to its Home Network.
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Mobile IP Principals, Cont…
Upon reception of the packet, the Home
Agent recognized the address belonging to
a mobile device.
Home Agents looks up the c/o address in
its table.
The packet is then wrapped in a new packet
with the c/o address on it, called
encapsulation
C/o address causes the packet to be
forwarded to the Visiting Agent.
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Mobile IP Principals, Cont…
Visiting Agent recognizes the received
address as the c/o address, unwrap the
packet; called de-capsulation; and send it
to its intended receiver.
This activity is called tunneling, referring to
the idea creating a tunnel between the
Home Network and Visiting Network and
sending all data to that mobile device on
that tunnel.
Several tunnels can be created between two
networks
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Mobility Management in WLAN
Mobile IP principles are used to take care of
mobility in the wireless LAN.
Every wireless device has an address in its
Home LAN, and gets a c/o address in the
Visiting LAN.
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IEEE 802.11 WLAN, History
1997 IEEE 802.11 working group developed
standard for inter-working wireless LAN
products for 1 and 2 Mbps data rates in 2.4
GHz ISM (industrial, scientific, and medical)
band (2400-2483 MHz)
Required that mobile station should
communicate with any wired or mobile station
transparently (802.11 should appear like any
other 802 LAN above MAC layer), so 802.11
MAC layer attempts to hide nature of wireless
layer (eg, responsible for data retransmission)
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802.11 WLAN History, Cont..
1999 IEEE 802.11a amendment for 5 GHz
band operation and 802.11b amendment to
support up to 11 Mbps data rate at 24 GHz
MAC sub layer uses CSMA/CA (carrier sense
multiple access with collision avoidance)
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802.11 Architecture
MAC Layer
Physical Layer Convergence
Procedure (PLCP)
Physical Medium Dependent
(PMD) sub layer
MAC provides asynchronous, connectionless service
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Frame type and subtypes
Three type of frames
— Management
— Control
— Asynchronous data
Each type has subtypes
Control
— RTS
— CTS
— ACK
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Frame type and subtypes, Cont..
Management
—Association request/ response
—Re-association request/ response
—Probe request/ response
—privacy request/ response
—Beacon (Time stamp, beacon interval, TDIM
period, TDIM count, channels sync info,
ESS ID, TIM broadcast indicator)
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Frame type and subtypes, Cont..
Management…
—TIM (Traffic Indication Map) indicates traffic
to a dozing node
—dissociation
—Authentication
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Authentication
Three levels of authentication
—Open: AP does not challenge the identity of
the node.
—Password: upon association, the AP
demands a password from the node.
—Public Key: Each node has a public key.
Upon association, the AP sends an
encrypted message using the nodes public
key. The node needs to respond correctly
using it private key.
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802.11 MAC Frame Format
MAC Header
Frame Duration Addr 1 Addr 2 Addr 3 Sequence Address 4 User
Control
Control
Data
Protocol
Version
Type Sub type To From
DS DS
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802.11 MAC Frame Format
Address Fields contains
—Source address
—Destination address
—AP address
—Transmitting station address
DS = Distribution System
User Data, up to 2304 bytes long
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IEEE 802.11 LLC Layer
Provides three type of service for
exchanging data between (mobile) devices
connected to the same LAN
—Acknowledged connectionless
—Un-acknowledged connectionless, useful for
broadcasting or multicasting.
—Connection oriented
Higher layers expect error free
transmission
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IEEE 802.11 LLC Layer, Cont..
Destination Source
SAP
SAP
Control Data
Each SAP (Service Access Point) address is
7 bits. One bit is added to it to indicate
whether it is order or response.
Control has three values
—Information, carry user data
—Supervisory, for error control and flow
control
—Unnumbered, other type of control packet
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IEEE 802.11 LLC <-> MAC Primitives
Four types of primitives are
exchanged between LLC and MAC
Layer
Request: order to perform a function
Confirm: response to Request
Indication: inform an event
Response: inform completion of process
began by Indication
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Reception of packets
AP Buffer traffic to sleeping nodes
Sleeping nodes wake up to listen to TIM
(Traffic Indication Map) in the Beacon
AP send a DTIM (Delivery TIM) followed by the
data for that station.
Beacon contains, time stamp, beacon interval,
DTIM period, DTIM count, sync info, TIM
broadcast indicator
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HIPERLAN
1995 ETSI technical group RES 10 (Radio
Equipment and Systems) developed
HIPERLAN/1 wireless LAN standards using 5
channels in 5.15-5.3 GHz frequency range
—Technical group BRAN (Broadband Radio
Access Network) is standardizing
HIPERLAN/2 for wireless ATM
—ETSI URL for Hiperlan information
http://www.etsi.org/frameset/home.htm?/tec
hnicalactiv/Hiperlan/hiperlan2.htm
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HIPERLAN Characteristics
HIPERLANs with same radio frequencies
might overlap
—Stations have unique node identifiers (NID)
—Stations belonging to same HIPERLAN
share a common HIPERLAN identifier (HID)
—Stations of different HIPERLANs using
same frequencies cause interference and
reduce data transmission capacity of each
HIPERLAN
—Packets with different HIDs are rejected to
avoid confusion of data
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HIPERLAN Protocol Layers
Data link layer = logical link control (LLC) sub
layer + MAC sub layer + channel access
control (CAC) sub layer
network
LLC
data link
MAC
CAC
physical
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HIPERLAN Protocol Layers, Cont..
MAC sub layer:
—Keeps track of HIPERLAN addresses (HID
+ NID) in overlapping HIPERLANs
—Provides lookup service between network
names and HIDs
—Converts IEEE-style MAC addresses to
HIPERLAN addresses
—Provides encryption of data for security
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HIPERLAN Protocol Layers, Cont..
MAC sub layer:
—Provides “multi hop routing” – certain
stations can perform store-and-forwarding of
frames
—Recognizes user priority indication (for timesensitive frames)
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HIPERLAN Protocol Layers, Cont..
CAC sub layer:
—Non-preemptive priority multiple access
(NPMA) gives high priority traffic preference
over low priority
—Stations gain access to channel through
channel access cycles consisting of 4
phases:
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HIPERLAN Protocol Layers, Cont…
CAC is designed to give each station (of same
priority) equal chance to access the channel
—First stations with highest priority data are
chosen. The rest will back off until all higher
priority data is transmitted.
—Stations with the same priority level data,
compete according to a given rule to choose
“survivors”
—Survivors wait a random number of time
slots and then listen to see if the channel is
idle
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HIPERLAN Protocol Layers, Cont…
—If the channel is idle then it starts
transmitting.
—Those who could not transmit wait
until next period
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Reading assignment
Mobile Data and Wireless LAN
technologies, Riffat Dayem, Chapters 4, 6
and 8.
Wirless LAN, Jim Geier, Part I chapter 3,
Part II chapter 4
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3G
http://www.3gpp.org/
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