#1eets 8316/ntu tc 745, fall 2003 engineeringsmu review, aloha aloha —stations starts sending...

#1EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU

Review, 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%

Southern Methodist University Fall 2003

EETS 8316/NTU CC745-NWireless Networks

Review Session

Instructor: Jila Serajemail: jseraj@engr.smu.edu

http://www.engr.smu.edu/~jseraj/tel: 214-505-6303

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)

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

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)

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%

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

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

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.

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

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

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.

Review, Mobitex - common functions

Requires subscription

—individual

—groups of terminals

—host computer

—groups of host computers

Security

—Password based

—ESN

—CUG (Closed User Group)

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.

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

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.

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

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

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

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

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)

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

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)

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

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

BSC/PCU

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

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.

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.

GPRS , Cont...

For mobility management a new concept is defined, Routing Area

RAI = MCC +MNC + LAC + RAC

GPRS Features

Packet data can use up to 8 timeslots to provide 115.2 kb/s

Suitable for bursty data such as web browsing

GPRS Interfaces

GPRS – Data Connection phases

GPRS attach/detach

PDP context activation

Data Transmission

Review, Wireless LAN Architecture

Server

PDA Laptop

LaptopLaptop

Laptop

Access Point Access Point

Ad Hoc

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

Review, Wireless LAN Protocol, Cont..

There are many type of LAN protocols:

—LBT

—Integrated CSMA-CA and TDMA

—Polling

Review, Power Management

Strong need to minimize power usage for wireless modem

Wireless stations have three states

—Sleep

—Awake

—Transmit

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.

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

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

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.

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

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.

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.

Review, Frame type and subtypes

Three type of frames—Management

—Control

—Asynchronous data

Each type has subtypes

Control—RTS

—CTS

—ACK

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)

Review, Frame type and subtypes, Cont..

Management…

—TIM (Traffic Indication Map) indicates traffic to a dozing node

—dissociation

—Authentication

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

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.

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.

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.

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

Mobile IP Registration

Home Address

C/o Address

FARegister

(Home Address)

Register (Host Address, C/O Address)

Registration Accepted

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.

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.

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

When to Register?

When entering the new network

When the timer for registration is close to expire

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.

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.

Mobile IP, Authentication

Three new authentication is required

—Mobile <-> Home Agent authentication

—Mobile <-> Foreign Agent authentication

—Home Agent <-> Foreign Agent authentication

UMTS Architecture

UTRAN UMTS Terrestrial Radio Access NetworkCN Core NetworkUE User Equipment

IuCN : Enhanced GSM/GPRS CN

RN: UTRAN

UMTS reference model

3GSGSN

3GGGSN PSTN

RoamingGW

Application services

2G network

PSTNIu3G MSC

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…

UTRAN Architecture

Core Network

Node B Node B

Iub Iub

Node B Node B

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

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

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)

Protocol Model for UTRAN Interfaces

UTRAN consists of

—Radio Network Layer (specific to UTRAN itself)

—Transport Network Layer (standard technology: ATM)

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).

UTRAN Interfaces

Iur Interface (RNC <-> RNC)

—point-to-point open interface,

—macro-diversity support,

—transport signaling for mobility and radio resource allocation.

Node B

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

#1eets 8316/ntu tc 745, fall 2003 engineeringsmu review, aloha aloha —stations starts sending...

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