#1EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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%
#2EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Southern Methodist University Fall 2003
EETS 8316/NTU CC745-NWireless Networks
Review Session
Instructor: Jila Serajemail: [email protected]
http://www.engr.smu.edu/~jseraj/tel: 214-505-6303
#3EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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
frame A
frame B
frame C
- transmission attempt at time 0
time-T 0 T
- collision if starts in interval (-T,0)
- collision if starts in interval (0,T)
#4EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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
#5EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, Slotted ALOHA
“Vulnerable interval” is reduced by factor of 2 to just T
frame A
frame B
- transmission attempt at time 0
time-T 0 T
- collision if frame B was ready in interval (-T,0)
#6EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, CSMA
Carrier Sense Multiple Access = CSMA
Sense the presence of carrier, sense the channel is free, send data, wait for Ack, re-send if timed-out, if busy back off and try again. Max throughput 60%
#7EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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, Request-
To-Send (RTS) and Clear-To-Send (CTS) .
—Method of choice for wireless LAN
#8EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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
#9EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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.
#10EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, Mobitex - Architecture
Mainexchange
NCC NCC: network Control center
Regionalswitch
Localswitch
Regionalswitch
Localswitch
Base stations use 1-4 frequencies each 8 kb/s
Local switch covers a servicearea, each with 10-30 frequency pairs
FEP
#11EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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
#12EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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.
#13EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, Mobitex - common functions
Requires subscription
—individual
—groups of terminals
—host computer
—groups of host computers
Security
—Password based
—ESN
—CUG (Closed User Group)
#14EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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.
#15EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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
#16EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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.
#17EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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
#18EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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
#19EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, CDPD - Network Architecture
MD-IS MD-IS
Mobile data base station = base station
Mobile data intermediate systems = packet switches with mobility management capabilities
Intermediate systems = generic packet switches in backbone networkIS IS
Internet or other networks
IS
#20EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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
#21EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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)
#22EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, CDPD - Network Architecture , Cont...
Mobile data intermediate system (MD-IS)
—Mobility management: location tracking, registration, authentication, encryption
•Exchange location information by CDPD-specific mobile network location protocol (MNLP)
• “Mobile home function” (MHF) in home network maintains current location info for a mobile end system and forwards packets
#23EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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)
#24EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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
#25EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GPRS - Network Architecture
GPRS makes use of existing GSM base stations
Serving GPRS support node = packet switch with mobility management capabilities
Gateway GSN = packet switch interworks with other networks
Internet or other networks
GGSNMSC/VLR
SGSN SGSN
HLR
BSC/PCU
#26EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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 SMS-MC
#27EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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.
#28EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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.
#29EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GPRS , Cont...
For mobility management a new concept is defined, Routing Area
RAI = MCC +MNC + LAC + RAC
#30EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GPRS Features
Packet data can use up to 8 timeslots to provide 115.2 kb/s
Suitable for bursty data such as web browsing
#31EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GPRS Interfaces
#32EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GPRS – Data Connection phases
GPRS attach/detach
PDP context activation
Data Transmission
#33EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, Wireless LAN Architecture
Server
PDA Laptop
LaptopLaptop
Laptop
Access Point Access Point
Ad Hoc
Pager
DS
#34EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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 sub-layer
#35EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, Wireless LAN Protocol, Cont..
There are many type of LAN protocols:
—LBT
—Integrated CSMA-CA and TDMA
—Polling
#36EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, Power Management
Strong need to minimize power usage for wireless modem
Wireless stations have three states
—Sleep
—Awake
—Transmit
#37EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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.
#38EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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
#39EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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
#40EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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.
#41EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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
#42EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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.
#43EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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.
#44EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, Frame type and subtypes
Three type of frames—Management
—Control
—Asynchronous data
Each type has subtypes
Control—RTS
—CTS
—ACK
#45EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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)
#46EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, Frame type and subtypes, Cont..
Management…
—TIM (Traffic Indication Map) indicates traffic to a dozing node
—dissociation
—Authentication
#47EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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
#48EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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.
#49EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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.
#50EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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.
#51EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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
#52EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Mobile IP Registration
Home Address
C/o Address
FARegister
(Home Address)
FA
HA
Register (Host Address, C/O Address)
Registration Accepted
#53EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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.
#54EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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.
#55EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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
#56EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
When to Register?
When entering the new network
When the timer for registration is close to expire
#57EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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.
#58EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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.
#59EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Mobile IP, Authentication
Three new authentication is required
—Mobile <-> Home Agent authentication
—Mobile <-> Foreign Agent authentication
—Home Agent <-> Foreign Agent authentication
#60EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
UMTS Architecture
UTRAN UMTS Terrestrial Radio Access NetworkCN Core NetworkUE User Equipment
CN
UTRAN
UE
Uu
IuCN : Enhanced GSM/GPRS CN
RN: UTRAN
#61EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
UMTS reference model
3GSGSN
3GGGSN PSTN
GW
RoamingGW
HLR
CSCF
RAN
Application services
2G network
IP
PSTNIu3G MSC
#62EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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…
#63EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
UTRAN Architecture
Core Network
Iub
RNS
RNC
Node B Node B
Iu
Iub Iub
RNS
RNC
Node B Node B
Iub
Iur
Iu
#64EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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
#65EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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
#66EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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)
#67EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Protocol Model for UTRAN Interfaces
UTRAN consists of
—Radio Network Layer (specific to UTRAN itself)
—Transport Network Layer (standard technology: ATM)
#68EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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).
#69EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
UTRAN Interfaces
Iur Interface (RNC <-> RNC)
—point-to-point open interface,
—macro-diversity support,
—transport signaling for mobility and radio resource allocation.
RNC
RNC
Node B
Node B
Node B
Iur
IubIu
#70EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
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