Big Picture: Lab 3

ECE 354 © Moritz 2009, some slides modified from Koren, Burleson, UMass and Wolf, Computers as Components, Morgan Kaufman, 2005

Big Picture: Lab 3Networks

Csaba Andras Moritz

physicaldata linknetworktransport

presentationapplication

session

physicaldata linknetworktransport

presentationapplication

session

physicaldata linknetworkIP

2ECE 354 © Moritz 2009, some slides modified from Koren, Burleson, UMass and Wolf, Computers as Components, Morgan Kaufman, 2005

Readings

Textbook Chapter 8


Outline - Networking for Embedded Systems Why we use networks. Network abstractions. Embedded Networks and TCP/IP. Example networks. Networks programming with sockets.


Technical background Moore: number of transistors/mm2 doubles every 18

months• processing power and memory capacity become

abundant Metcalfe: the “value” of a network is proportional to the

square of the number of nodes• adding a node benefits existing nodes• the larger the network the larger the benefit

Gilder: Internet bandwidth triples every 18 months


Embedded Systems evolution

Hardware replaces software• functionality• features

Digitization and manipulation of signals

Configuration/programming of systems from outside

Completely networked systems

increase in networking


time

standalone fully networked

network aware

network connected

network central


network aware

network connected

network central

Network central: Adapt product design withrespect to the network connection

• Integrate network functions with embedded hardware and software

• Standardisation of connections, protocols

Advantage:• service: access to embedded software:

debugging, replacement, sell features• owner: standardisation, new software

Standalone: embeddedhardware and software:• invisible• are, in fact, an

implementation aspect of the product

Fully networked: the functionality is definedby the network

• Devices controlling each other• Intelligent environments, all equipment in the

background (Philips: “ambient intelligence”)

•

Advantage: http://www.research.philips.com/generalinfo/special/ambintel/index.html

• service: new markets• owner: ease of use, comfort, integration

Network connected: On-line connection withthe system

• Put control hardware/software next to the embedded system

• Interaction!

http://aquarium.eesi.tue.nl

Advantage:• service: diagnostics, leasing of appliances• owner: remote monitor & control, security,

production-control, fleet maintenance

Network aware: Information retrievalfrom the system in a rudimentary fashion

• Status information: errors, wear, use• Using existing connections and resources

already available within the system• Off-line analysis of data• Transport: telephone, Internet

Advantage: • remote diagnosis

Evolution of embedded networking


Networks in embedded systems

PEPE sensor

PE actuator

initial processing

more processing


Networking for Embedded Systems

Why we use networks. Network abstractions. Embedded Networks and TCP/IP. Example networks. Networks programming with sockets


Network abstractions

International Standards Organization (ISO) developed the Open Systems Interconnection (OSI) model to describe networks:• 7-layer model.

Provides a standard way to classify network components and operations.


OSI model

physical mechanical, electrical

data link reliable data transport

network end-to-end service

transport connections

presentation data format

session application dialog control

application end-user interface


Hardware architectures

Many different types of networks:• topology;• scheduling of communication;• routing.


Point-to-point networks

One source, one or more destinations, no data switching (serial port):

PE 1 PE 2 PE 3

link 1 link 2


Bus networks

Common physical connection:

PE 1 PE 2 PE 3 PE 4

header address data ECC packet format


Bus arbitration

Fixed: Same order of resolution every time.Fair: every PE has same access over long periods.

• round-robin: rotate top priority among PEs.

A,B,C A,B,C

fixed

round-robin

A B C A B C

A B C AB C


Ethernet

Dominant non-telephone LAN. Versions: 10 Mb/s, 100 Mb/s, 1 Gb/s, 10Gb/s. Goal: reliable communication over an unreliable

medium.


Ethernet topology

Bus-based system, several possible physical layers:

A B C


Ethernet packet format

preamblestart

framesourceadrs

destadrs

datapayload

length padding CRC


Ethernet performance

Carrier sense multiple access with collision detection (CSMA-CD)• sense collisions;• exponentially back off in time;• retransmit.

Quality-of-service tends to non-linearly decrease at high load levels.

Can’t guarantee real-time deadlines. However, may provide very good service at proper load levels.





Internet Protocol

Internet Protocol (IP) is basis for Internet. Provides an internetworking standard: between

two Ethernets, Ethernet and token ring, etc. Higher-level services are built on top of IP.


IP in communication

physical

data link

network

transport

presentation

application

session

physical

data link

network

transport

presentation

application

session

physical

data link

network

node A router node B

IP


Another look at TCP/IP for Embedded Devices

Application Layer

PresentationLayer

Session Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Application Layer

Transport Layer

InternetLayerLink

Layer

OSI ModelLayers

TCP/IPLayers

Physical Layer

Telnet FTP SMTP DNS POP3 SNMP

TCP UDP

IP802.2LLC

PPP SLIP

Ethernet Serial Port

TCP/IP Protocol Suite


TCP/IP Basics : Data Encapsulation

Application Data

TCP Header

IP Header

Ethernet Header

Application Data

Application Data

Application Data

TCP Header

TCP HeaderIP Header Ethernet Trailer

Application Data

App Header

App Header

App Header

App Header


IP addresses

32 bits in early IP, 128 bits in IPv6. Typically written in form xxx.xxx.xxx.xxx.

Each group ranges from 0 to 255

Names (foo.baz.com) translated to IP address by domain name server (DNS).





Embedded protocols and software

Remote user

Request connection

Program code

HTML browser

AppletES-Server

HTTP server HTTP(applet code)

UDP

sensors

actuators


Components HTTP server:

• standardized access: URL • code download: Java applet

ES server: provide “driver interface” for embedded system

HTTP browser (client): • setup contact• run machine-independent code• “programmable interactive remote control”

Applet: • interface to user





Networked systems programming

Distributed systems programming is needed in many of today’s applications• Web servers, web caches, client-server applications, network

devices, …From low level to services

• Sockets (low-level API) • RPC, RMI (higher-level API)• CORBA (also adds services, component model) LATER!• EJB, J2EE, (Java version); .net (Microsoft)• Jini (Java’s answer to networked services and devices)


Sockets

Low-level communication interface (API) Network Programming Defined 1981Bolt, Beranek and Newman (BBN) Originally developed for the C language TCP/IP version with Unix called BSD sockets To some extent similar to file IO


Sockets

What is a socket?• It is a peer-to-peer communication “endpoint” abstraction• Hides details of network for programming communication

situations• Interfaces to some common network protocols (e.g. TCP, UDP,

XNS, NetBIOS, IP, etc.)

Many high level APIs are based on sockets• 1985 Sun introduced RPC and NFS (Network File System) over

sockets.


Socket Ports

On TCP/IP networks:• Socket = Internet Address(IP) + Port Address

• Port is an “entry point” to an application that resides on a host.


Socket Ports cont.

Typically a communication is assigned to a port, a process can request/assign to access a port-number.

TCP and UDP protocols (most common TCP/IP transport protocols) use port numbers 1-1023 that are reserved.

Standard Internet apps (FTP, TELNET, TFTP, SMTP, SNMP,..) use ports between 1-255.

> 1023 can be used for new user-level servers


Socket types

Three types: • Stream (e.g. interface to TCP),

• session based reliable service that takes care of connection maintenance, packet reassembly, etc.

• Mimics UNIX file system semantics

• Datagram (e.g. interface to UDP, NetBIOS), • handles independent packets. • Unreliable; 5% of datagrams don’t make it. • Needs higher level acknowledgement service.

• Raw (e.g. interface to IP, etc.), • Programming interface to lower-level protocols


Sockets

To initiate a connection one must fix the roles: client or server

A network connection can be connection-oriented or connectionless• With a connectionless protocol there is nothing like an “Open”

communication; every network IO operation can be with different process/host

• In a connection based operation a peer-to-peer channel is opened


Connection-oriented use

Connection is first established between client and serverSystem Calls at server side

• socket() // creates endpoint, specify protocol (TCP, UDP, XNS, etc.), specify type (i.e. stream, datagram, etc.) Returns a small integer similar to file descriptor.

• bind() // register and bound network address to socket• listen() // signal willingness to receive connections• accept() // accept a connection• read(), write() // transfer data


Connection-oriented protocol

Client side• socket() // same meaning as in server• connect() //establish contact between local-remote

site• read() write() //transfer data


Example, connection-oriented sequence

socket()

bind()

listen()

accept()

read()

write()

socket()

connect()

write()

read()

SERVERCLIENT

Connection establishment

Data(request)

Data (reply)

BlocksUntilconnect


System calls connectionless case

sendto(addr,) // send datagrams (data packets)recvfrom(addr,..) // receive datagrams

Compared to the connection-oriented read() and write() these calls have arguments for remote protocol-specific addresses.


Example 2, connectionless sequence of calls

socket()

bind()

recvfrom(addr1,…)

sendto(addr2,…)

socket()

bind()

sendto(addr1,…)

recvfrom(addr2,…)

SERVERCLIENT

Data(request)

Data (reply)

BlocksUntil data received from client


Summary Sockets

Abstraction for network programming. Advantage:

• Best performance in distributed embedded applications, fine-tuning opportunities.

• Many known high-level protocols use sockets as underlying communication mechanisms.

Disadvantages: • lots of details to address, many parameters to control.• Requires understanding of system issues and network

protocols.


What's next ?

Lab 3 details by TA


BACKUP


Internet-enabled embedded system

Internet-enabled embedded system: any embedded system that includes an Internet interface (e.g., burglar alarm system).

Internet appliance: embedded system designed for a particular Internet task (e.g. email).• UMASS ECE SDP Internet-connect Refrigerator

Laser printer. Personal digital assistant (PDA). Home automation system.


time


network aware

network connected

network central


network aware

network connected

network central

The effect of Internet

• Data transport (large distance)

• Standards: ftp, email, ...• Distributed access

Interoperability• Standards for

offering services: Jini, UPnP, OSGi

• Platform for • data exchange• integration

..... + information exchange!!

• Standards for• software architectures• communication: HTTP, Java,

TCP, UDP, ....• visualisation: browsers

• Global addressing


Remote user

Request connection

Program code

Example: A coffee maker

Switch and heat control not networked individually


Example: Javacam

Hardware platform:• parallel-port camera;• National Semi NS486SXF;• 1.5 Mbytes memory.

Uses memory-efficient Java Nanokernel.


Javacam architecture

Web browser

QuickCam

486

Java nanokernel

Java VM

HTTPQuickcamserver

QuickCamapplet


Fully networked devices Separate user interface and driver functions It must be simple to attach to the network

• lightweight • easy to handle

Zero configuration connection • builds a logical network automatically• peer to peer in absence of server

Zero configuration interoperable • service publication and discovery • devices control each other• no fixed identification


Differences connectionless vs. connection-oriented

Connection establishing not required• Blocks until data is received as opposed until connection is

established• Note: Client could also use connect() and read() write() in the

connectionless case, but not “real connect” as it returns immediately, i.e. does not block as there is no connection established.

Use of the sendto() and recvfrom() as opposed to the read() and write() system calls

The client registers an address for itself with the bind() to be able to receive messages back (this address is sent with data automatically)


More on the differences

Connectionless is often useful • Lower overhead, no session creation required• Discovery type of situations: broadcasting queries to

the network and learning who is out there…• Quick messages (e.g. heartbeat, “I am alive”)• Can send to 500 nodes, would need 500 sessions

with the connection-oriented model• If one of the messages are not received no problem…


To Sum Up

TCP/IP is close to 20 years old, but it has outlasted more modern protocols and has become the de-facto standard for the internet

Proliferation of internet enabled devices is predicted in the next wave of the internet

As developers try to get their embedded devices on the net, they face the issue of the networking problem exceeding the application problem

Practical solutions are currently available to connect embedded devices to the internet in a cost effective manner

Proper selection of methodology is important to make a successful enabled Internet Appliance


IP packet

Includes:• version, service type, length• time to live, protocol• source and destination address• data payload

Maximum data payload is 65,535 bytes.


Embedding TCP/IP – The Advantages

Internet

� Provides a universal, flexible, User Interface for the Device� UI can be exposed using a standard browser� Opens possibilities of remote diagnostics and software upgrade


Embedding TCP/IP – The issues

� Resource Limitations– Code Size– Data Size– CPU Processing capacity

� Operating System Services– Timer Services– Memory Management– Network Drivers

� Processing Latency– Layer to layer buffering


Sockets and Java

Before RMI and CORBA support has been designed for Java this was the only way to do network programming

Java.net package contains• Set of classes that let you download and manipulate URL

objects• A native Java implementation of Berkeley (BSD) sockets


Java sockets

Semantics the same as we discussed earlier Java.net contains most of the classes needed Java.io contains socket related stream classes

• A socket may be associated with a “stream” in Java (provided by the Socket class implementation)

• Streams are fun as they hide devices, its like a data pipe• You can use OutputStream, InputStream, and other stream

classes derived from these with sockets. Somewhat similar to file access.

Documents

Big Picture: Lab 3