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

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.


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


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.


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.


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 network architectures

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


Point-to-point networks

One source, one or more destinations:

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


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.


Ethernet topology

Bus-based system

A B C


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 – 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.


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


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.


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).


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


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.


What’s next ?

Lab 3 details


Backup


Ethernet packet format

preamblestart

framesourceadrs

destadrs

datapayload

length padding CRC


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


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


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

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

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