Transcript Review, Mobile IP Principals, Cont…

Review, Aloha
Aloha
—Stations starts sending when they have
something to send
—Pure Aloha, no contention resolution, relies
on timed-out acks, max throughput
approximately 18%
—Slotted Aloha, no contention resolution,
relies on timed-out acks, only can start
sending in the beginning of a slot, max
through put approximately 36%
EETS 8316/NTU TC 745, Fall 2003
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Southern Methodist University Fall 2003
EETS 8316/NTU CC745-N
Wireless Networks
Review Session
Instructor: Jila Seraj
email: [email protected]
http://www.engr.smu.edu/~jseraj/
tel: 214-505-6303
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Review, Pure ALOHA Throughput
— In equilibrium, throughput (rate of successfully
transmitted frames) = rate of new transmissions, S
S = GP0
where P0 = probability of successful transmission
(no collision)
— P0 depends on “vulnerable interval” for frame, 2T
- transmission attempt at time 0
frame A
- collision if starts in interval (-T,0)
frame B
frame C
-T
0
EETS 8316/NTU TC 745, Fall 2003
- collision if starts in interval (0,T)
time
T
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Review, Slotted ALOHA
Slotted ALOHA is a modification to increase
efficiency
— Time is divided into time slots = transmission time
of a frame, T
— All stations are synchronized (e.g., by periodic
synchronization pulse)
— Any station with data must wait until next time slot
to transmit
— Any time slot with two or more frames results in a
collision and loss of all frames – retransmitted after
a random time
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Review, Slotted ALOHA
“Vulnerable interval” is reduced by factor of
2 to just T
-T
frame A
- transmission attempt at time 0
frame B
- collision if frame B was ready in
interval (-T,0)
0
EETS 8316/NTU TC 745, Fall 2003
time
T
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Review, CSMA
Carrier Sense Multiple Access =
CSMA
Sense the presence of carrier, sense the
channel is free, send data, wait for Ack, resend if timed-out, if busy back off and try
again. Max throughput 60%
EETS 8316/NTU TC 745, Fall 2003
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Review, CSMA (Cont)
Carrier Sense Multiple Access-Collision
Detection (CSMA-CD)
— Send when carrier is free, listen to detect collision.
— CSMA-CA is the method of choice
Carrier Sense Multiple Access-Collision
Avoidance (CSMA-CA)
— Uses two messages before transmission, RequestTo-Send (RTS) and Clear-To-Send (CTS) .
— Method of choice for wireless LAN
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Review, Mobitex, Major features, Cont...
Major features
—Seamless roaming
—Store and forward of messages
—Dependability above 99.99%
—Interoperability and many connectivity
options
—Capacity to support millions of subscribers
—Security against eavesdropping
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Review, Mobitex, Major features, Cont...
Major features
—Packet switching occurs at lowest level of
system hierarchy - relieves backbone traffic
—Packet multicasting (to multiple recipients) is
handled by network
—Closed User Group (CUG) feature
—Frequency depends of the country, 900
MHZ in US and 450 in most others.
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Review, Mobitex - Architecture
NCC
NCC: network
Control center
Main
exchange
Regional
switch
Local
switch
Regional
switch
Local
switch
Base stations use 1-4
frequencies each 8 kb/s
FEP
EETS 8316/NTU TC 745, Fall 2003
Local switch covers a
service
area, each with 10-30
frequency pairs
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Review, Mobitex - Architecture , Cont...
Network Control Center (NCC), provides
network management functions
Main Exchange and Regional Switch have
basically the same function, but they reside
on different level of network hierarchy.
—Packet switching
—Protocol handling (X.25 and HDLC)
—Subscriber data for nodes below
—Multiple connection to other switches
—Alternate routing
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Review, Mobitex - Architecture , Cont...
Local Switches, similar to regional
switches. Also handles
—Communication with base stations
—Connection to host computers via FEP
(Front-End-Processor)
FEP provides
—Protocol conversion to hosts supporting
X.25, TCP/IP, and SNA
—Convert connectionless protocol to
connection oriented protocol.
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Review, Mobitex - common functions
Requires subscription
—individual
—groups of terminals
—host computer
—groups of host computers
Security
—Password based
—ESN
—CUG (Closed User Group)
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Review, Mobitex - Mobility
Mobiles monitor and evaluate signals from
other base stations
At power-up, mobile tries to register with
the last base station in its memory, if
possible
Base station provides necessary
information, such as acceptable signal
strength, neighbor list,etc periodically.
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Review, CDPD
Cellular digital packet data (CDPD):
connectionless packet-switched data
designed to work with an analog cellular
system (e.g., AMPS)
—Originated by IBM as packet-switching
overlay to analog cellular system, early
1990s developed by CDPD Forum, now
developed by Wireless Data Forum
—Overlay system uses unused bandwidth in
cellular system and existing AMPS functions
and capabilities
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Review, CDPD , Cont...
CDPD is a value added system. Other users
do not need to be aware of its presence in
the network. This has implications:
CDPD transmission must not interfere with
transmission of other services
No dedicated bandwidth, uses only idle
time between users, channel-hop
No dedicated Control channel, all Control is
in-band.
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Review, CDPD , Cont...
CDPD is transparent to voice system
—To avoid collisions with voice calls, CDPD
uses channel hopping when antenna
detects a power ramp-up (indicating
initiation of voice traffic)
—Base station closes current transmission
channel within 40 msec and new idle
channel is chosen to hop to
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Review, CDPD , Cont...
CDPD is transparent to voice system
—New channel may or may not be announced
before old channel closed
• If not announced, mobile terminal must
hunt around set of potential CDPD
channels to find new one
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Review, CDPD - Network Architecture
Internet or other
networks
IS
IS
MD-IS
Intermediate systems = generic
packet switches in backbone
network
IS
Mobile data intermediate
systems = packet switches
with mobility management
capabilities
MD-IS
Mobile data base station =
base station
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Review, CDPD - Network Architecture , Cont...
Mobile end system (MES): may be handheld
PDA or laptop or terminal
—Stationary or mobile, but treated as
potentially mobile
—Network Continually tracks location to
ensure that packets are delivered even if
physical location changes
—May sleep - messages are then queued in
network
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Review, CDPD - Network Architecture , Cont...
Mobile data base station (MDBS): mobile
data link relay
—Supports CDPD MAC and data link
protocols across radio interface
—Handles radio channel allocation,
interoperation of channels between CDPD
and voice calls, tracks busy/idle status of
channels
—Often co-located with AMPS base stations
(shares AMPS antenna)
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Review, CDPD - Network Architecture , Cont...
Mobile data intermediate system (MD-IS)
—Mobility management: location tracking,
registration, authentication, encryption
• Exchange location information by CDPDspecific mobile network location protocol
(MNLP)
• “Mobile home function” (MHF) in home
network maintains current location info
for a mobile end system and forwards
packets
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Review, CDPD - Network Architecture , Cont...
Mobile data intermediate system (MD-IS)
• “Mobile serving function” (MSF) in visited
network maintains info for visiting mobile
end systems in its area (through
registration process)
—Accounting and billing (based on usage)
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Review, CDPD , Cont...
CDPD network layer
—Internet protocol (IP and mobile IP) and
connectionless network protocol (CLNP,
OSI’s equivalent of IP) are supported
—Backbone network of intermediate systems
(IS) provides connectionless packet routing
• IS can be off-the-shelf IP or CLNP
routers
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GPRS - Network Architecture
Internet or other
networks
HLR
SGSN
MSC/
VLR
GGSN
Gateway GSN = packet switch
interworks with other networks
SGSN
Serving GPRS support node
= packet switch with mobility
management capabilities
BSC/PCU
GPRS makes use of existing
GSM base stations
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GPRS , Cont...
SGSN = Serving GPRS Support Node
—Ciphering
—Authentication, IMEI check
—Mobility Management
—Logical Link Management towards mobile
station
—Packet routing and transfer
—Connection to HLR, MSC, BSC and SMSMC
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GPRS , Cont...
GGSN = Gateway GPRS Support Node
— External interfaces
— Routing
GPRS register maintains GPRS subscriber
data and routing information. Normally it is
integrated in GSM HLR
PCU (Packet Control Until) is collocated
with BSC.
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GPRS , Cont...
Three class of mobile terminals
—Class A: Operates GPRS and Circuit
switched service simultaneously
—Class B: Monitors the Control channels of
GPRS and GSM simultaneously but can
operate one set of services at a time
—Class C: Only CS or GPRS capable.
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GPRS , Cont...
For mobility management a new concept is
defined, Routing Area
RAI = MCC +MNC + LAC + RAC
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GPRS Features
Packet data can use up to 8 timeslots to
provide 115.2 kb/s
Suitable for bursty data such as web
browsing
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GPRS Interfaces
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GPRS – Data Connection phases
GPRS attach/detach
PDP context activation
Data Transmission
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Review, 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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Review, Wireless LAN Protocol
 LAN protocol consists of 3 layers
 LLC = Logical Link Control layer
 MAC = Medium Access Control layer
 PHY = Physical layer, which is divided into two
sub layers:
– PLCP= Physical Layer Convergence
Protocol sub-layer
– PMD = Physical Medium Dependent sublayer
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Review, Wireless LAN Protocol, Cont..
There are many type of LAN protocols:
—LBT
—Integrated CSMA-CA and TDMA
—Polling
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Review, Power Management
Strong need to minimize power usage for
wireless modem
Wireless stations have three states
—Sleep
—Awake
—Transmit
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Review, Power Management, Cont…
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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Review, 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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Review, 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
Creating and maintaining the routing table
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Review, 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.
EETS 8316/NTU TC 745, Fall 2003
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Review, 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
EETS 8316/NTU TC 745, Fall 2003
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Review, 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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Review, 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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Review, Frame type and subtypes
Three type of frames
— Management
— Control
— Asynchronous data
Each type has subtypes
Control
— RTS
— CTS
— ACK
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Review, 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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Review, Frame type and subtypes, Cont..
Management…
—TIM (Traffic Indication Map) indicates traffic
to a dozing node
—dissociation
—Authentication
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Review, Mobile IP Principals
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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Review, 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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Review, 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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Review, 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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Review, 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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Mobile IP Registration
FA
HA
Home
Addres
s
FA
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C/o
Addres
s
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Mobile IP Registration, Cont…
A Mobile Host registers with the foreign
agent. Send Home Address
Foreign agent forwards the registration
request to the Home Agent.
If the home agent accepts registration, then
it updates its table associating the home
address of the mobile with its c/o address.
It then informs the foreign agent that the
registration is accepted.
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Mobile IP Registration, Cont…
Foreign agent informs the mobile host that
the registration is accepted.
A tunnel is now created between foreign
agent and home agent.
What if mobile is home? Registration
happens between home agent and the
mobile.
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Mobile IP Registration, Cont…
What if the visiting network does not have a
foreign agent? The registration happened
directly to the home agent, using the
address provided by the visiting network
and the C/O address. This means that the
mobile software should be capable of some
foreign agent functionality
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When to Register?
When entering the new network
When the timer for registration is close to
expire
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Mobile IP Home Agent Options
Home network could be a virtual network
with home agent in the router, a real
network with the home agent in the router
or it can also be a real network with a home
agent as a server connected to the home
network.
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Mobile IP Mobility Management
When moving from one network to another,
a new registration process occurs.
Home agent uses the new C/O address to
forward the packets to the mobile terminal
Packets sent to the old foreign agent has to
be re-transmitted to the new address.
If the mobile moves fast, handling of
mobility becomes difficult.
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Mobile IP, Authentication
Three new authentication is required
—Mobile <-> Home Agent authentication
—Mobile <-> Foreign Agent authentication
—Home Agent <-> Foreign Agent
authentication
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UMTS Architecture
CN
CN : Enhanced GSM/GPRS CN
Iu
UTRAN
RN: UTRAN
Uu
UE
UTRAN
CN
UE
UMTS Terrestrial Radio Access Network
Core Network
User Equipment
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UMTS reference model
Application
services
2G network
Roaming
GW
HLR
IP
CSCF
RAN
Iu
3G
SGSN
3G
GGSN
3G MSC
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PSTN
GW
PSTN
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UMTS reference model
CSCF = Call State Control Function
responsible for call state control functions,
service switching function, address translation,
vocoder negotiation to support VoIP
Call state is a set of states identified in the
process of completing a call. Obvious
examples of call state are: Call attempt, Called
number reception, Called number translation,
Feature Activation, Called party Alert, through
connection, Calling Party Release, etc…
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UTRAN Architecture
Core Network
Iu
Iu
RNS
Iur
RNS
RNC
RNC
Iub
Node B
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Iub
Iub
Node B
Node B
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Iub
Node B
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Functions of UTRAN Components
RNC
— Uplink/downlink signal transfer, mobility,
soft handoff
—Upper outer loop/ downlink power control,
—Common control channels
—Very similar to BSC functions
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Functions of UTRAN Components
Node B:
— Logical node, maintains link with UE
— Responsible for radio transmission for one
or more cells, adds/removes radio links on
demand,
— Mapping logical resources to physical
resources,
— Upper inner loop power control,
— Interconnecting UE from different
manufacturers.
—Similar to BTS function
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UTRAN Interfaces
Uu: Between Node B and UE (WCDMA)
Iub: Between Node B and RNC (ATM)
Iur: Between various RNCs (ATM)
Iu: Between the Core Network and the
RNC (IP over ATM)
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Protocol Model for UTRAN Interfaces
UTRAN consists of
—Radio Network Layer (specific to UTRAN
itself)
—Transport Network Layer (standard
technology: ATM)
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Protocol Model for UTRAN Interfaces
The UTRAN specific protocols include
—Radio Access Network Application Part:
Radio Network Signaling over the Iu.
—Radio Network Subsystem Application Part:
Radio Network Signaling over the Iur.
—Iub interface uses node B application
protocol (NBAP).
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UTRAN Interfaces
Iur Interface (RNC <-> RNC)
—point-to-point open interface,
—macro-diversity support,
—transport signaling for mobility and radio
resource allocation.
Node
B
Iub
RNC
Node
B
Node
B
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Iu
Iur
RNC
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UTRAN Interfaces
Iub Interface (RNC <-> Node B)
— interconnection of equipment from different
manufacturers,
— allows Abis (GSM/GPRS transmission
sharing),
— transports DCH, RACH, FACH and DSCH
data,
— enables negotiation of radio resources
between node B and RNC
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