Communication(including Networks)

Pervasive Intelligent EnvironmentsSpring 2004

Copyright © 2004 Charles J. HannonAll rights Reserved.

Why do we need communication in a smart environment? Allows sensor input to be collected, fused

and used by a controller or processor Allow controllers and processors to effect

the environment via actuators Allows controllers and processors to work

together Allows the environment to talk to other

environments Allows the remote access to the

environment by its owner

Is there a one size fits all solution to communication? Short answer, NO Each level has different needs

sensors controller actuators low data rate with little or no overhead

controllers controllers processors medium to low data rate with little overhead

processors processors high data rate with higher overhead

processors WAN medium data rate with higher overhead

Some Basic Concepts Data transmission Clock/control signals Data framing Synchronous vs. asynchronous

transmission Serial vs. parallel P-to-P, hierarchies and broadcast Addressing (fixed and virtual) A network

Some Other Concepts A reference model

with a quick overview of the layers Collisions and collision avoidance Data rate control

admission control flow control congestion control

Quality of Service (QoS)

Some Standards I2C RS-232/449 IEEE-488 (GPIO) TCP/IP (802.3, 802.u, 802.z) Wireless Ethernet (802.11) Broadband (ATM, 802.16, etc.) Others (VoIP, etc.)

Data Transmission Given two devices capable of

generating and receiving a digital signal (high=1, low=0) on a data line with respect to a common ground If A is the sender and B is the

receiver, A can send one bit of information to B by setting the data line to either a high or a low

A Bdata

Now, Some Control Add a second line (for control)

that can be set high, if A is sending to B low, if B is sending to A

Now, A/B can send one bit of information to B/A by setting the correct direction

voltage on the control line then, setting the data line to either

a high (1) or a low (0)

A Bdata

control

Now, Some More Control(a hardware handshake)

Add three more control lines that can be set high when

A and B see each other A/B is ready to send B/A is ready to receive

Now, A/B can send one bit of information to B/A by

see if the connect line is high set the RTS line high see if the RTR line is set set the correct direction voltage set the data line to either a high (1) or a low

(0)

A B

data

direction

connect

RTS

RTR

Now, some distance

If we want to add some distance between the two devices, we need to do two things Add one or more ground lines to

ensure that the devices have the same idea about the voltage level of ground

Increase the voltage level (above or below ground) of the control and data lines so they are less affected by the resistance of the transmission lines

A B

data

direction

connect

RTS

RTR

GND

Why so much work just to send a bit?

First, A/B can be sure that B/A is really there

Second, A/B knows that B/A is ready to use the information being sent

Third, A/B can send a bit, and then, do another handshake to send a another bit

Of course, there is a better way

A B

data

direction

connect

RTS

RTR

GND

Bi-directional Communications

The direction control line is currently kind of a waste, so let us replace it with a second data line

we will need it back a littler later, but … Of course, now we need two sets of

RTS/RTR lines but you never get something for nothing

For this approach the handshake is the same as before except there is no direction to set

And, of course you can send and receive at the same time

A B

data

connect

RTS (2)

RTR(2)

data

GND

Enough control already, can we send some useful data?

For the simple approach, we need another control line called the clock Sends out alternating ones and

zeros at twice the rate we want to send data over the data lines

This allows us to send serial data over the data line

Example:

A B

data

connect

RTS (2)

RTR(2)

data

clock

1 1 0 1

GND

The Problem with a Clock Signal (1)

A clock signal is basically a square wave

In EM transmission, the only things that really exist are sine and cosine waves

So if you try to transmit a square wave, you end up transmitting a bunch of sine waves at difference frequencies and amplitudes

But, transmission lines have an impedance (AC resistance) which is proportional to the frequency being transmitted

The Problem with a Clock Signal (2)

So, the longer the transmission line the more the high frequency

components of the clock signal get attenuated

and, the less the clock signal looks like a square wave

Since the leading (or sometimes the trailing) edge of the clock pulse

is used to figure out when the data bit is changing

a clock pulse that not longer has an identifiable edge is not exactly the most useful thing to be trying to use

OK, now what do we do? For long distances, a clock line is clearly not the

solution Is there another way to clock?

Yes, it is called a frame The problem with clocking off the data line is that

nothing forces the data to transition from 0 1 or 1 0 at any given time in the signal

If we were to insert a forced transition at a given rate

we could use this framing signal to clock the data

1 1 0 1 1 1 1 1F=1/0 F=1/0 1 1 1

Framing The good news

As longs as all the data is being transmitted on a signal line, it allows us to get rid of a clock signal

The bad news It adds ‘overhead’ (a non-data part of the

signal) to the transmission The more transitions, the better

so it works best when we use something like a framing nibble

A Definition (sort of) A transmission approach that uses a clock

line is called synchronous data transmission

A transmission approach that uses some type of framing is called asynchronous data transmission

Like everything else in networking the term synchronous and asynchronous are

overloaded Later, we will see a different meaning when we

cover STM and ATM

Serial vs. Parallel(increasing speed) We can increase the data transmission

speed by adding more (parallel) data line increasing the speed at which we send serial data

we will cover this method later A parallel data transmission method is

just a group of serial data lines that have been synchronized to send their data in lock step

So, the same method for increasing the speed at

which we send data should help both, right?

Serial vs. Parallel(the limits of parallel) One might think that the reason things like the

Ethernet are serial is simply due to the cost of wiring

after all, a parallel line must contain more wires, so be more expensive to run

True, but that is not the real problem first, framing only clocks a single line, so a parallel line

normally must contain a clock line second, thanks to the way EM works, data lines that

run at high voltage right next to each other tend to share their information (called cross-talk)

This means that parallel lines are inherently bad for running data any further than about 50 feet

Topologies (Point-to-Point) Every device is connected to

every other device Good points

simplest approach no addressing needed everyone is your neighbor you can always talk to your neighbor

Bad points number of ports/lines grow relatively

quickly with the number of devices

A B

C D

Topologies (Hierarchy) Devices are connected via hubs to

other devices If everyone is connected to a single hub,

it is called a Star topology Good points

fewer connections devices can have neighborhoods

Bad points you need an address (defined later) you may have to wait to talk to a

neighbor asymmetric communication with some

devices

A

B

C

D

Topologies (Broadcast) All of the devices are connected to

a single wire Good points

single wire everyone is your neighbor

Bad points you need an address you may have to wait to talk to anyone collisions can occur communication times become

statistical

A

B

C

D

Physical Addresses If more than two devices are on the same wire

(bus), you will need an address to send and receive data

Approaches separate vs. combined data/address lines hardwired vs. selectable address

Issues as the number of devices increase, the address

space (size of the address) must increase hardwired addresses may tell you nothing about

the network topology addresses will be used up by devices that might

not be on-line so your address space may be too big, causing too

much overhead

A

B

C

D

0001

1111

1000

1100

Virtual Addresses A solution to some physical address

problems is a virtual address the address space (size of the address) can be

reduced by only giving addresses to on-line devices

addresses can be set up to support network topology

Approaches fixed vs. run-time addresses universal vs. p-to-p addresses

Issues how to assign them their relationship to the physical address

A

B

C

D

00

01

10

11

A Network (A Basic Definition)

A group of computer devices connected together using a common protocol

Most networks physically use One or more serial data lines Little or no hardware-based control (i.e., no control lines) A combined address/data transmission scheme A fixed hardware-based address scheme

Built on this, the network protocol Allows an easy way to connect devices to the network Tries to reduce transmission errors Handles transmission problems as they occur Makes it easy for software applications to talk over the

network

The Reference Model(Overview)

Network protocols are now built in layers

These layers and their boundaries are defined using something called a reference model

The most general of these reference models is the OSI model which defines seven layers

Most of what we have talked about up to this point is in the physical layer

The Reference Model(A Software View)

Network software is written to handle each layer containing software (2 and above) It uses the API (or SAP)

from the layer below Provides an API (or SAP)

for the layer above A SAP provides a virtual

connection at that layer

Reference Model(Message View [1])

At each layer the data from the layer above

is viewed as the message this message is provided with

a header (and/or trailer) which allows the virtual

connection of that layer to share connection information

Above the bottom S/W layer the result is called a packet

Reference Model(Message View [2])

However, the bottom layer is special because it has to really

send the message it may break the message

into pieces to better transmit it

it almost always adds a header, trailer and flags

the result being called a frame or a cell if just a header is

used

The Physical Layer Make up of hardware (standards)

Nodes controllers NIC: PCs, servers, etc. hubs, Ethernet switches routers circuit/packet/cell switches

Connection wire: twisted pair, co-ax fiber optics: NB and BB wave guides wireless RF

Physical Layer - Connections

The first two components of a medium’s ability to carry information are base

frequency range

bandwidth range

Connection Examples Typical Fiber Optics

very high base frequency: 5 x 1014 Hz low relative bandwidth: 10%

Cat 5e cable (twisted pair) lower base frequency: 2.5 x 108 Hz very high relative bandwidth: 100%

Typical Satellite Slightly higher base frequency: 5 x 109 Hz very low relative bandwidth: 5%

Network Components Local Area Network

Within a building (or maybe a complex) May have one or more pieces (subnets)

Wide Area Network Example: one type of WAN is the Internet Components

The ‘Last Mile’ or ‘Digital Last Mile’ connects LANs to the WAN Internet Service Providers (ISPs) handle the protocol level

connection over the Last Mile The Telco network handles the ‘backbone’ which connects

ISPs

The LAN

Processing nodes are connected using Broadcast networks (called a LAN in the figure) Hubs/switches (do much the same thing) Bridges (and routers)

but technically a LAN cannot contain a router

Example: Cable as the (Analog) Last Mile

Example: ADSL as theDigital Last Mile

Telco Switching

A Sign Post We have spent a great deal of time covering the

physical layer Because this will directly help you understand how a smart

environment is physically connected when we get around to that Now we are going to cover the high points of the other

layers first, because this will also help but more importantly, it will give you some idea of just how

much you are asking a network enabled smart device to do when you assume it is going to provide something like a web interface

The moral (before the story) is don’t demand user friendliness, unless you are wiling to pay for

it

The Data Link Layer

Messages are ‘framed’ using character stuffing, bit stuffing or header matching

Message pieces are reordered and reassembled Collisions (of they are possible) are resolved Many other things (like error correction, location

detection, message encoding, etc.) are handled

The Framing Problem

If you allow variable size frames You cannot just use length to frame

A Partial Solution Add a flag at the beginning and end of

every frame You need both to be able to deal with dead

air Pretty much any byte length sequence

with some ones and zeros will do But a common flag is 01111110

OK, now the problem What if that byte sequence just happens to

be the message you are sending?

A Pretty Dumb Solution (to the Problem our Solution Caused)

It is called character stuffing

It works just like the way you print special

characters in UNIX by putting yet another special character in front of them

Only problem It a terrible solution Half of your message ends

up being stuffed bytes

A Better Solution (Bit Stuffing)

Just add a zero anytime you see the flag pattern in the message

Believe it or not This is actually relatively easy to do and to recover

from doing

Reordering Frames This is not an easy

problem Hard to detect

Sequence numbers have to repeat sometime

Acknowledging every message waste bandwidth

Hard to recover from without wasting either

time (resending), or Space (save out of

sequence messages)

Collisions (and non-collision) There are some protocols that do not

allow collisions Bit Map Binary Countdown Token Ring and Token Bus

And some that go out of their way to avoid them Adaptive Tree Walk, etc.

But, most of the important ones being used today do

What causes a collision? Just because a device looks

to see if someone else is transmitting before sending does not mean its message

will get through the reason: it takes time for a

signal to travel down a wire The longer the wire, the

worse the problem gets which is why a broadcast LAN

can be only so long

Two Statistical Solutions to a Statistical Problem If you are using

a wireless medium with a great deal of distance between

stations there is basically nothing you can do to

avoid collision But if you are using a wire, you can

Carrier Sense (CSMA) by making sure the channel is free (idle) before sending

Collision Detect (CSMA/CD) by listening to what you send

Carrier Sense(without the two or three days of math)

p-persistent means you wait for the channel to become idle and when it does you have a probability of p of choosing to seize it

nonpersistent means if the channel is idle you send, but if it is not idle you go away for some random time before trying again

Collision Detection

Good News The concept is absurdly simply

If what I am hearing is not what I am sending, there must have been a collision

Bad News This is an analog comparison which requires special (but fairly

simple) hardware Even if I am an using a full-duplex line (like with a hub), I

cannot send and receive at the same time

Some Ethernet Details The Data Link layer is where the Ethernet

MAC address (EA) lives the 48 bit number that come with your NIC

Example: EA = 00:50:04:A4:5F:84 There is one special EA called a broadcast

address EA = FF:FF:FF:FF:FF:FF

The Ethernet header looks like

DIX

802.3

The Network Layer Routers live here

The things that drive the WAN ARP and DHCP lives here

APR is the thing that allows you to figure out the EA of the computer assign an IP address

like 138.237.123.12 so you can send it a message DHCP is the thing that allows you to

provide network information from a server And, most of data rate control lives here

Stuff that try to keep the network from getting overloaded

Routing(without the graph theory)

Routers are basically IP switches they map output paths to a range of IP addresses

But unlike LAN devices, routers live in a world where not only do theyhave to figure out how to get a packet from

point A to B you have to worry about the effects of picking one path

over another

Routing Algorithms

You need a routing algorithm, unless you want to Set up the network by hand (hardcode all the paths) Never deal with dynamic equipment changes

Network routing R&D is not going anywhere There is always a need for better and better specialized

routing algorithms (many papers a year) Complexity is a routing algorithm’s middle name

But, almost all algorithms are some combination of

Bellman-Ford’s distance vector (1957) Link state (1979)

Routing Issues

When and how do you update the network topology? How large a view of the whole network does each router

need? Should a route be

Connection-oriented (all of the packets following the same route) Connectionless (each packet is free to get there the best way it

can) How do you router the same packet to multiple places? What if the devices being routed to are free to move?

called mobile hosts What do you do if the routers are free to move around?

called an Ad Hoc networks

Address Resolution Protocol

ARP is what allows you to give a computer an IP address without

having to worry about telling every other computers on the LAN its EA-IP mapping

The beauty of ARP is that it is fully distributed very simple almost foolproof

ARP (how it works [1]) Every computer on a LAN keeps an ARP table with all

known EA to IP mappings If it wants to talk to another computer, it looks to see

if it already knows the EA If so, it puts the EA in the level 2 and the IP in the level 3

header and sends the message If not, it broadcasts an ARP request using the EA

broadcast address Who owns 192.168.2.2 ?

All computers on the LAN get the request, but only the computer with that IP responds and all it has to say is

I own 192.168.2.2

ARP (how it works [2])

Since the reply message is not broadcasted (sent p-to-p), the level 2 header already contains the EA address of the requestor and responder

Then the requestor can update its ARP table with the responder’s EA to IP mapping

Over a period of time a table entry times out so if you replace a NIC, all the devices on the LAN quickly learn about the change

ARP and the WAN An EA broadcast never leaves a LAN

routers do not forward EA broadcast But WAN magic happens because

a router connected to a LAN responds to ARP requests just like any other computer

Each computer is setup either statically or by something like a DHCP server

to know the IP address of the gateways (ways out of the LAN for a given set of IP addresses)

The computer uses ARP to find the gateway’s EA and then sends the message to it

Reversing the ARP Process Why?

Allows a computer’s IP address (and other things like gateways’ IPs, host names, etc.) to be configured from a central location

Better utilization of IP addresses A historic overview

RARP BOOTP DHCP

A More Detailed History Reverse Address Resolution Protocol (RARP)

Used EA broadcast (just like ARP) Simple process

A computer broadcast: what IP belongs to EA = x? A RARP server responds to x with: IP= y

Problem: could not cross router boundaries BOOTP

Uses UDP messages (IP broadcast) Requires a manual setup of the EA-IP mapping

DHCP Extends BOOTP to allow the server to provide more information Adds the concept of leases which allows an automatic

assignment of IPs while providing some EA-IP mapping stability

Tunnels and Private LANs(the problem) Computers on the same LAN can share

information using EA-based services like ARP IP-based services blocked at the router

(firewall) done for security, speed, etc.

Routers do not preserve anything below the network layer

So, two computers on separate LANs cannot normally be as ‘connected’ as two computers on the same LAN

Tunnels and Private LANs(the tunnel concept)

Any packet can be wrapped by another packet/frame/cell this is how the layered concept of networking

works If you wrap a packet/frame/cell

in a packet/frame/cell at the same network layer using either the same or a different protocol you create something called a tunnel

Since the internal packet is wrapped before transmission tunnels can preserve LAN-based information

Tunnels and Virtual LANs(virtual private networks)

Tunnels can be used to do a lot of things but we will address only VPNs

Say you want to allow a remote computer to use a service (like PostgreSQL) without running the risk of everyone seeing the database

Using either the server’s built-in access control or the firewall’s port control

you can open a port in your firewall for the service while controlling which remoter computers can access the database

however, you are still passing your data through a public network Solution:

set up a VPN between your firewall and the remote computer now you can tunnel your data via an encrypted link

Transport Layer

Forms the link between network applications running on different machines Setup the connection Get the data packet to/from

the NIC and application who wants it

Figure out when a connection is no longer operating

Ports (TSAPs) Ports are ID numbers used to keep track of

application connections ‘well known’ ports (0 - 1023) ‘registered’ ports (1024 - 49151) dynamic or private ports (49152-65535)

A complete connection consists of two ports (one on each machine) these are sent in the transport level packets

Ports point to the ‘socket name’ data structure contains information about how the application is

using the port

Sockets Uses the analogy of wall plug

A socket is what you plug your application into to get connected to the network

A socket is the mapping between the name socket name structure using be the

transport layer, and the stream/datagram structures used by OS’s

system call to support IPC In UNIX, socket numbers are just file

descriptors with a Non-NULL socket name pointer in their file descriptor structure

Transmission Control Protocol (TCP) TCP is the protocol for setting up a bi-

directional pipe between two sides of a networked application

Good points More secure connection

both sides know who each other are (or at least claim to be)

Guaranteed delivery Flow control is built in

Bad points Slow

User Datagram Protocol (UDP) UDP is the protocol for setting up a

datagram transport between two sides of a networked application

Good points Fast Better handles dynamic connections

Bad points Less secure connection No guaranteed delivery No flow control

Client/Server TCP-based applications are built on the

client-server model The Server

sets up a listening port (and socket) accepts (or rejects) client connections

Adds a new socket for each connected client The client

attempts to connect to a server Once connected the path is

normally bi-directional can be shut down from either side

The Gory Details

Session thru Application Layer The session and presentation level

of the OSI model are rarely used The Application layer supports

network enabled applications These applications use their own

protocol Examples: HTTP, SMTP, etc.

Little or no network related activity happen above the transport level

An Example: DNS The Domain Name Service (DNS)

maps between IP addresses and domain names

It is supported by DNS servers which use their own protocol

Other Common Applications E-mail

SMTP, POP3, IMAP, etc. WWW

HTTP, HTML, XML, etc. Other Important Classes

RPC-based (NFS, etc.) UDP-based (RPC, etc.) Tunnels (ssh, cipe, etc.)

Hierarchy of Control Admission Control

supports something called QoS tries to prevent the conditions for a

problem Flow Control

tries to stop the problem at the source Congestion Control

tries to fix problems when they happen

Admission Control (just the basics)

Tries to statistically determine what you want

average latency, average and peak bandwidth, etc. what you can stand

maximum latency, jitter rate, etc. what you can have

Total bandwidth available Priory of traffic (how much you are willing to spend)

your willingness to play by the rules Three steps

negotiate (renegotiate) for QoS monitor your adherence to the rules take action when things do not work out

Flow Control Tries to throttle a dataflow at

the source or the problem called forward flow control reduces traffic directly

destination of the problem called backwards flow control reduces traffic by reducing request

Forward works better, but backward is easier to do reason is on the next slide

Congestion Control Two step

Start dumping packets to fix the immediate problem

Dumb: First in, first dumped Smart: Priority dump Smarter: Priority & percent of problem dump

Inform someone so flow control can take over

Dumb: forward inform in related packets Smart: backward inform in related packets

Backward works better, but forward is much much easier to do

Smart Home, Office & Car Communication/Network Issues

Installation Homes and offices last 100s of years

need a way to be upgraded to smart environments without sacrificing power

Cars are normally replaced every few years intelligent systems must be integrated to other

components from the start Cost

A solution needs to cost under the ‘threshold of pain’ last long enough to return on the investment

Safety and reliability The more you control, the harm you can do

Smart Homes and OfficesThe Current Model

NIC

I/O

AI S/W

Net S/W

S Ctrl S/W

OS S/W

LAN

WAN

NIC

I/O

NIC

NIC

Digital Modem

Net S/W

Firewall S/W

OS S/W

ApplianceAppliance

A Ctrl S/W

AI S/W

Net S/W

S Ctrl S/W

OS S/W

A Ctrl S/W

ApplianceSensor Appliance

Appliance

X10, IR/RF RS232/USB

Smart Homes and OfficesThe Future Model

NIC

Appliance

NIC

Appliance

NICMobility S/WAgent S/W

Sensor

NIC

Sensor

Mobility S/WAgent S/W

Mobility S/WAgent S/W

Mobility S/WAgent S/W

wireless, wire or fiberLAN Interface WA

N

Smart Car (One view) Main Processor will

have the power of a modern home PC

Talks to the engine & chassis systems using existing standards

CAN, LIN J1850 PWM & VPM,

Keyword 2000 Talks to the other

systems using MOST, FlexRay USB, 1394, Ethernet

The Supporting Standards Serial:

RS232 USB IEEE 1394 Ethernet:

802.3 802.u 802.z Wireless:

802.11 & Bluetooth Controller:

I2C, CAN, LIN, X-10 Others:

FlexRay, MOST, VoIP

RS-232 Very old (and reliable) standard for direct

connection of devices to a computer Specs

P-to-P connection (master-slave) no addressing supported

11 to 6 wire used depending on application

Can support speeds up to 56 kbps 9600 bps is the most common flow rate used

Features Built-in support for things like analog modems The most widely used I/O standard in the history of

computing

USB Designed to replace RS-232 for computer device

I/F Specs

127 devices in a tiered star using hubs hot swappable devices

Control main processor acts as controller controls who can transmit

Speed full-speed – 12 Mbps; high-speed – 480 Mbps

Features inexpensive enough for general control

IEEE 1394 (Firewire/i.Link) Designed to support the LAN-based video Specs

64K nodes in a peer-to-peer topology 63 nodes per network, 1024 networks, 1394 bridges hot swappable nodes

Control 1 device per node acts as bus manager all nodes get equal access

Speed 1394a – 400 Mbps; 1394b – 800 to 3200 Mbps

Features high speed too expensive for many control applications

TCP/IP (802.3, 802.u, 802.z)

802.3 (10 Mbps) 10baseT: twisted pair (4-wires of CAT5) 10base2 (and others): co-ax based

802.u (100 Mbps) 100baseT: twisted pair (4-wires of CAT5 or CAT5e) 100baseF (FDDI): single fiber

802.z (1 Gbps) 1000baseT: twisted pair (8-wires of CAT5e or

CAT6) 1000baseF: single fiber

Wireless Ethernet (802.11)

We will only cover 802.11b (the most common) Data rate varies with the SNR

at maximum SNR, transmits at 11 Mbps Uses

fixed Access Points (APs) that work like bridges the same frequency band as FRS radios (2.4GHz) spread spectrum encoding (79 channels)

Features allows hand-off between Access Points vendors supported encryption

Problems vendors tend to modify things, so single vendor solution is

best

Bluetooth Supports an Ad Hoc network

for PDA-type devices 64Kbps (each way) per hop

Uses Bridge slaves to extend the

network The same FRS transmission

standard as 802.11b Is basically an experimental

network

I2C (Inter-Integrated Circuit)

One of the oldest controller buses Philips (1980s)

Low-cost chip-to-chip communication link uses two wires to form a clocked serial bus

one called Clock (SCL) and the other Data (SDA) the SDA carries address, selection, control,

and data Overview

multi-master bus (up to 1024 devices) can run at speed up to 3.4 Mbps can be used as a SAN

but normal ranges are on the order of 14 cm

Automotive Inspired Busses

LIN (Local Interconnect Network) Designed for European cars (still

used) Very simple

single wire single mastered bus

Overview 1 master, up to 16 Slaves uses a message-based protocol maximum distance of 40 m Two data rates

9,600 and 19.2 Kbps

CAN(Controller Area Network )

CAN was designed to support emission control system in European cars

but became a general automation control bus Capable of

high-speed (1 Mbits/s) data transmission over short distances (40 m)

low-speed (5 kbits/s) transmissions at lengths of up to 10,000 m

Overview a multi-master bus highly fault tolerant

Built-in support for error detection and handling

MOST(Media Oriented System Transport)

An inexpensive automotive and appliance network 25 Mbps fiber-

optic bus for real-time data

transfer used in surround-

sound systems and CD and DVD players

FlexRay Designed to replace LIN, CAN and MOST

as a ‘by wire’ solution for future cars It is a fiber-optic bus (like MOST) Current speed

10 Mbps But it is designed to go much higher

could run faster than 100 Mbps But remember

that is faster than most current micro-controller’s internal bus speed

X10 Has been around for 20 years Uses

AC power lines to transmit control information from a transmitter to up to 16 receivers

the address scheme allows for 256 devices but top 4 bits of the address are reserved for a home code (A-P)

Problems was designed as a manual control system

very little control information can be sent the data signal can be easily confused

by things like fluorescent lamps, motors, etc.

VoIP (Voice over IP)

This is simply a way to send voice over a computer network details are not that important

In a WAN, VoIP allows you to move from sending data over voice lines to sending voice over data lines

In a LAN, VoIP allows you to combine cable, phone and your computer

network into a single line a very important thing to do

if we move to a totally fiber network

Some Other Issues Compression

MPEG as an example Mobile Agents

What they are How they work

Security The challenge of moving from where

we are into an ubiquitous future

Compression using MPEG(Moving Picture Experts Group)

MPEG are a group of standards for compressing audio and video data

MPEG-1 was designed to support CD-ROMs data rates of about 1.5 Mbps

MPEG-2 was designed to Support DVDs data rates of about 4-8 Mbps

Currently, almost every piece of digital video transmitted or

stored uses MPEG compression including this class

MPEGA Very Simple Explanation

Between frames of a moving picture, most of the picture does not change

So a simple way to compress video is to

compare the frames find the smallest box (or set of boxes) that

outline the things that did change instead of sending the whole second frame,

send only those boxes Of course, the real process needs to

worry about things like transmission errors, and thus, is much more complex

but that is just the details

Mobile vs. Fixed Code Some Basic Facts

A program (agent) is made up of code (native or VM) data state

All network enabled programs (agents) must support some form of network enabled IPC fixed programs send data mobile programs send themselves

Mobile vs. Fixed Code What is Mobility

For a program (agent) to migrate it must (at least)

be cloned (forked) on another machine send some part of its data to that machine be shut down on the first machine

It would be nice if it also could pass its state so it can take up where it left off however, this must be supported by either the OS, a

VM, or a middleware program To be truly mobile, a program (agent) must also

send its code, which requires that all machines are totally homogeneous, or some type of VM is used

Mobile vs. Fixed Code The Trouble with Mobility

No current OS or VM truly supports state-based program restart

VMs are inherently slow Have to interpret instructions Have to provide their own interface to

threads and sockets Unless programs (agents) rarely

move, sending code greatly increases network message traffic

Ubiquitous Computing SecuritySome Basic Facts Most current methods use

port-blocking firewalls SSL message interface

These methods are based on privilege LANs (i.e.)

us firewall them ownership of physical devices

a few visible powerful nodes that have little or no problem supporting

encryption are easy to monitor

Ubiquitous Computing SecurityThe Death of the Firewall

The concept of ownership will need to change You may still ‘own’ some of the computational

resources in your house and transportation However, these will have to be seamlessly connected to

other resources The real ownership will be in the number and type of

agents working for you These agents will need to provide their own

bubble of security Analogy #1: as people become adults, they learn what

is safe behavior Analogy #2: communities develop and maintain

organizations (made up of individuals) that enforce laws

Ubiquitous Computing SecurityClever Secure Messaging Message traffic between many-to-

many small nodes will need to be Authenticated Encrypted Tracked

These node will need to rely on Fast approaches to methods used today

This can be done using special hardware New approaches

Quamtum-based Brain models: dumb messages, smart end-nodes