ECE 424 Embedded Systems

Design

Networking ConnectivityChapter 12Ning Weng

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Networking Overview• Goal: key concepts and system details to

integrate network connectivity into embedded systems

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Global Internet Bandwidth

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UDP Packet Sender

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UDP Packet Sender in C

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Socket API

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Protocol Layers

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IP Layer Packet Headers

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Comparison: IPv4&6 header

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Transport Layer Headers

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TCP connections

This diagram shows the start of a TCP connection.

A sends packet X withSYN. “Hello I would like to talk”.B sends a SYN, ACKpair “I got yourmessage. I wouldalso like to talk”A sends an ACK (andsome data) “Igot your message,here is some data.”

TCP Window Increase/Decrease

Transmission no

Threshold

Threshold

Congestion window

The initial doubling of thewindow size is called “slowstart”.

Timeout

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Encapsulation

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Example of Switched Ethernet LAN

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Ethernet Frame Format

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Ethernet Controller

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WI-FI• Short of wireless fidelity

─ Dominant wireless LAN technologies─ Relying on availability of unlicensed radio frequency

• High f -> affected by various medium• Security: dos, unauthorized access and etc.• Wireless medium access control

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IEEE 802.11 Data Frame

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Basic Security Strategies• Block your Service Set Identifier (SSID) from being

broadcast.─ Wireless beacon so PCs can easily find the access point.

• Change the default network name in the access point.

• Change the default access point password.• Center the access point in the middle of the

building/house.

Media Access Control (MAC) Filtering

• Every network device has a unique MAC address─ Allocated by the manufacturer.

• MAC Filtering only allows certain addresses access.

• Mostly for home use.─ Tedious to implement on a large scale

Wired Equivalency Protocol (WEP)

• Basic encryption technology.─ Uses an RC4 stream cipher.

• Pseudo-random bytes.─ Two versions: 64-bit and 128-bit versions.

• Built into Wi-Fi certified equipment.─ Implemented at the MAC level.

• Protects radio signal between device and access point.─ Does not protect data beyond the access point.

• Uses static encryption keys.─ Easy to crack.

• Still better then nothing.

Wi-Fi Protected Access (WPA)• Designed to replace WEP.

─ Firmware update. ─ 128-bit Temporal Key Integrity Protocol (TKIP)

encryption. • Uses a master key that is regularly changed.

─ User authentication.─ Data Integrity.

• Protects radio signal between device and access point.

• Built into Wi-Fi certified equipment.─ Implemented at the MAC level.

• Available in two versions:─ WPA2 Personal.─ WPA2 Enterprise.

Wi-Fi Protected Access 2 (WPA2)

• Designed to replace WEP.─ 128-bit Advanced Encryption Standard (AES).

• Based on the IEEE 802.11i standard.• Provides government level security.• Also available in two versions:

─ WPA2 Personal.─ WPA2 Enterprise.

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Wireless Media Access Control

• MAC protocol: shared media scheduling• maximize number of communications• Ensure fairness among all transmitters

• CSMA – carrier sensing multiple access• CD – collision detection

─ If (Transmitted_Signal != Sensed_Signal) Sender knows it’s a Collision ABORT

• Wireless problem─ Can not send and listen ─ Signal not same at same

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Bluetooth Overview• Bluetooth is a global, RF-based (ISM

band: 2.4 GHz), short-range, connectivity solution for portable, personal devices─ it is not just a radio, it is an end-to-end solution

• The Bluetooth spec comprises─ a HW & SW protocol specification─ usage case scenario profiles and interoperability

requirements

• IEEE 802.15.1 is working on standardizing the PHY and MAC layers in Bluetooth

• More Info:─ http://www.bluetooth.org ─ http://ieee802.org/15/pub/TG1.html

Bluetooth - Piconet• A collection of devices connected via

Bluetooth technology in an ad hoc fashion. • A piconet starts with two connected

devices, and may grow to eight connected devices.

• All Bluetooth devices are peer units and have identical implementations. However, when establishing a piconet, one unit will act as a Master and the other(s) as slave(s) for the duration of the piconet connection.

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Application Framework and Support

Link Manager and L2CAP

Radio & Baseband

Host Controller Interface

RF

Baseband

AudioLink Manager

L2CAP

Other TCS RFCOMM

Data

The Bluetooth protocols

• A hardware/software description• An application framework

SDP

Applications

Control

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Linux Networking• Networking utilities

─ Ipcofig─ Netstat

• Socket implementations

• Networking kernel structures

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Linux Network Stack

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Struct SK_buff

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