Transcript ECE 424 Embedded Systems Design

ECE 424
Embedded Systems
Design
Networking Connectivity
Chapter 12
Ning Weng
Networking Overview
• Goal: key concepts and system details to integrate
network connectivity into embedded systems
Ning Weng
ECE 424
2
Global Internet Bandwidth
Ning Weng
ECE 424
3
UDP Packet Sender
Ning Weng
ECE 424
4
UDP Packet Sender in C
Ning Weng
ECE 424
5
Socket API
Ning Weng
ECE 424
6
Protocol Layers
Ning Weng
ECE 424
7
IP Layer Packet Headers
Ning Weng
ECE 424
8
Comparison: IPv4&6 header
9
Transport Layer Headers
Ning Weng
ECE 424
10
TCP connections
 This diagram shows the start of a TCP connection.
A sends packet X with
SYN. “Hello I would
like to talk”.
B sends a SYN, ACK
pair “I got your
message. I would
also like to talk”
A sends an ACK (and
some data) “I
got your message,
here is some data.”
TCP Window Increase/Decrease
Congestion window
Timeout
Threshold
The initial doubling of the
window size is called “slow
start”.
Threshold
Transmission no
Encapsulation
Ning Weng
ECE 424
13
Example of Switched Ethernet LAN
Ning Weng
ECE 424
14
Ethernet Frame Format
Ning Weng
ECE 424
15
Ethernet Controller
Ning Weng
ECE 424
16
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
Ning Weng
ECE 424
17
IEEE 802.11 Data Frame
Ning Weng
ECE 424
18
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.
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
Ning Weng
ECE 424
24
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
25
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.
The Bluetooth protocols
Applications
Other
TCS RFCOMM SDP
Application Framework
and Support
Data
L2CAP
Audio
Host Controller
Interface
Link Manager and L2CAP
Link Manager
Baseband
Radio & Baseband
RF
• A hardware/software description
• An application framework
27
Linux Networking
• Networking utilities
─ Ipcofig
─ Netstat
• Socket implementations
• Networking kernel structures
Ning Weng
ECE 424
28
Linux Network Stack
Ning Weng
ECE 424
29
Struct SK_buff
Ning Weng
ECE 424
30