ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

Big Picture: Lab 3

Networks (OSI-view)

physicaldata linknetworktransport

presentationapplication

session

physicaldata linknetworktransport

presentationapplication

session

physicaldata linknetworkIP

2ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

Networking for Embedded Systems

Why we use networks. Network abstractions, OSI. Embedded Networks and TCP/IP.

3ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

Metcalfe’s Rule 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

4ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

Networks in embedded systems

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-connected Refrigerator

Laser printer. Home automation system.

5ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

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. It is a conceptual model only.

6ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

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

7ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

Hardware network architectures

Many different types of networks based on• topology;• scheduling of communication; and• routing.

8ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

Point-to-point networks

One source, one or more destinations:

PE 1 PE 2 PE 3

link 1 link 2

9ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

Bus networks

Common physical connection:

PE 1 PE 2 PE 3 PE 4

header address data ECC packet format

10ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

Ethernet – a Physical Layer

Dominant non-telephone LAN. Versions: 10 Mb/s, 100 Mb/s, 1 Gb/s, 10 Gb/s,

100Gb/s. Goal: reliable communication over an unreliable

medium.

11ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

Ethernet topology

Bus-based system

A B C

12ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

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.

13ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

Internet Protocol – a Network Layer

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.

14ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

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

15ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

IP packet

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

Maximum data payload is 65,535 bytes.

16ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

IP addresses

32 bits in early IP, 128 bits in IPv6. Typically written in form xxx.xx.xx.xx. Names (foo.baz.com) translated to IP address by

domain name server (DNS).

17ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

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

18ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

Software Abstractions - Message-based

Transport layer provides message-based programming interface:• send_msg(adrs,data1); Data must be broken into packets at source,

reassembled at destination.

19ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

What’s next ?

Lab 3 details

20ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

Backup

21ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

Ethernet packet format

preamblestart

framesourceadrs

destadrs

datapayload

length padding CRC

22ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

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

23ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

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

24ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

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

25ECE 354 Copyright ECE Department, some slides modified from W. Wolf, Computers as Components, Morgan Kaufmann, 2005

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 may exceed the application problem

Practical solutions are currently available to connect embedded devices to the internet