I know that SPI plays an important role in IPsec. But I want to know that:
Is it possible to remove SPI from IPSec header and still get it work?
I don´t think that could be possible. But It´s always depends of the kernel´s implementations.
According to the RFC 4301, a SA is identify by three parameters: IP destination, Security Protocol (AH, ESP) and a SPI.
The SPI is unique, if we had a SA with the same IP destination and same Security Protocol (for example, diferent encryption algorithm) the only parameter that could differentiate the SA is the SPI, needed to map the traffic.
https://www.rfc-editor.org/rfc/rfc4301
Related
The INET WirelessHost inherits from the StandardHost which has store-and-forward as its default forwarding behaviour. Is there a way to change that behaviour to cut-through? I did not find any fitting parameters in both the StandardHost and WirelessHost modules.
TL;DR: No, that is not possible and makes no sense.
cut-through is a layer 2 (link layer) device feature i.e. switches can support it. It is impossible to do this on layer 3 (network layer) as IP packets can be fragmented, defragmented and the IP header itself can change during routing. So at most, the question should be: can a wireless access point support cut-through? BUT:
cut-through implies that the interface can receive and send simultaneously. That's an almost impossible feat for a wireless transciever over a radio medium. (unless the transmission is highly directional (like. StarLink laser links, but in that case they could be considered as wired channels)
I'm busy writing a driver for a UART. The, struct uart_port has a field uartclk see this link. According to a slide set I found from free-electrons, this is among the most important fields to initialize. Yet, the Xilinx AXI UART Lite, which I'm writing a driver for, doesn't initialize this member see this link to see.
I'm wondering about the importance of this field. What is this in relation to a UART? Why is it important? What role does it play in the serial core?
Thanks
P.S. I know there's a driver existing. However, this driver assumes the UART Lite is to be used in an embedded environment. In the application I'm writing to, this is not the case.
The UART like any other IP in the system has to have functional and interface clocks. In some IPs it might be same clock, in some it might be more interface or functional clocks. The uartclk field reflects the actual frequency on the input to baudrate generator (don't be confused by the frequency of functional clock which most of the time is constant). When user calls termios to set a desired baudrate the UART driver for actual hardware recalculates uartclk, if needed, and bottom layer, if used, configures the registers. That's how 8250 works. In other cases it might be left unused, if, for example, serial hw driver does everything on its own.
I'm trying to implement S-MAC protocol on waspmote xbee sensors and i know it has its own CSMA/CA. So first of all I need to understand the basic of xBee collision avoidance.
Two senders set up in api mode in libraries and both periodically sending single bytes to a common receiver. I reduce the delay and many changing in libabries to make collision and to see how algorithm works. But when i monitor data at the receiver all looks as expected at the receiver .. byte1, byte 2 .. byte1, byte2.
Do u have any idea how can i make collision?
Are you sniffing the 802.15.4 traffic? That's the only way you'd see a collision.
The XBee module buffers the data you want to send, using the host communication parameters (baud rate, API mode, etc.) and then sends it out over 802.15.4 at 250kbps. The module has all of the collision avoidance built in, and will retransmit as necessary to deliver your message. If it's unable to deliver after some number of transmission attempts, you'll get a Transmit Status frame indicating failure.
On the receiving end, it buffers the data and delivers it to the local host using local serial settings (baud rate and API mode).
If you're trying to implement S-MAC, you need a different radio processor where you have low-level control over the radio. The XBee module provides an application layer and handles the MAC layer itself.
I want to learn and implement CAN BUS protocol. I have implemented UART,SPI,I2C and One Wire Bus protocol using MSP430 Launchpad in software. Now I want to learn about CAN Bus protocol. I have mBed LPC 1768 Cortex M3 Development board. mBed has Can Bus Library but I want to write my own library so that I can learn it in detail, i.e. the way I did for other communication protocols.
I am not able to find suitable resources to start with and the material appears to be scattered on net. Can any one guide how do i write and implement CAN Bus protocol with the development boards available with me.
Thanks
Developing CAN library is relatively easy as compared to I2C or SPI. This is because CAN Controller of your Cortex will take care of most of complex things.
To transmit the data, You have to write ID and Data in designated registers and set bit to transmit data.
This Application note from NXP can be very useful for you.
I would recommend you to implement following functions:
InitCAN - This should set specified Baud Rate of CAN.
SetFilters - Most CAN Controllers come with Acceptance Filters, So it's good to have that
SendData - Make sure you accept Parameters like ID_Type and RTRs etc.
RecieveData - This can be blocking or Interrupt based.
Before beginning, do read CAN Basics to understand. Application notes AN713 and AN754 from Microchip is a good source. Also Vector's site and Wikipedia Article.
Plus, You can always post your doubts here or on Electronics.StackExchange.com :)
Okay so this post is quite old but people may look at it again so:
First of all Can bus is not user friendly protocol like USART or IC2 at all so you have to be very precise about your can bit timing there are tools for that but I suggest you to calculate them by hand. For a microcontroller I would suggest STM32 and be away from PIC series in my opinion. If it's only CAN-BUS without higher level protocols such as SAE J1939, steps are pretty simple and straight forward:
1)Initialize Can
2)Put CAN to configuration mode and remember that you can set baudrate, mask and filters only in configuration mode!
3) Set the baud rate registers.
4) Set the mask and filters. If you need to receive all messages just simply set mask to 0x00. Then filter will be do not care.
5) Set the CAN to the normal or loopback mode. (loopback mode is used for debugging purposes mostly.)
Some remarkable points people try to implement can at the beginning may miss:
*** You need at least 2 working CAN nodes for successfull transmission. (of course with matching baud rate). So if you want to send some data via CAN with 1 node it will not be succesfull. Because your transmitter node will not receive ACK.
*** Most likely you will need a CAN tranciever. Do not forget to put a 100 ohm or similar value resistor between Tx and Rx pins of your tranciever.
I used the software canking to talk to a mcp25050 when I learned how to implement can protocol using an hcs12 dragonboard. It helped a lot because canking will initialize everything for you when u go on the bus and all you have to do is learn how to write and recieve. If you want to learn how to initialize the steps are:
Enables can bus by setting bit on CAN Control Register 1
Enable can initialization Control Register 0
wait until can bus is in initialization mode by checking control register 1 bit
Enables can bus by setting bit on CAN Control Register 1 again and set clock source - Ethier bus clock or eclock
set prescaler baudrate and Tq with Bus timing register
set sample time and prop_seg1, prop_seg2, and phase_seg
set acceptance id on Identifier acceptance register 0-3 or 0-7 - to set your can to recieve everything set those to 00 because when doing a compare the can bus does a ones complement compare with the id coming in
set Identifier mask register 0-3 or 0-7, if you want to not care about any of the bits set them all to FF
set identifier acceptance control register to 32 bit extended or 11 bit - i use 32
set Control Register 0 back to normal mode
wait until bus is normal mode by checking Control Register 1
after this you can start changing registers or reading data to do this you must select the empty can buffer, write your id to write or request data, and then input the address, mask, and value in the 3 transmitter registers if writing and then specify the dlc (3 if writing and 8-1 if reading). to transmit the id and data you then have to set the can transmit flag to equal the can Transmit buffer selection.
** depending on what id you use bit shifting can be tedious so if you are having a problem I would suggest debugging and looking at what your Transmit buffer selection registers are holding. I had this error because i did not shift correctly when i was sending messages to the mcp25050
If your MCU supports CAN Bus, you should start from the related datasheet.
Here is the topology under discussion:
NIC0 NIC0 NIC0
| | |
+-----+-----+ +------+-----+ +------+------+
---NIC1 NIC2---------NIC1 NIC2-----NIC1 NIC2---- . .
+----PC1----+ +----PC2-----+ +-----PC3-----+
I have stack of PC Boxes each having multiple (3) Nic Cards, one to interface with outside world, and others to be used to daisy chain for communication among themselves.
Q(1) Can someone suggest if I can somehow control "multicast traffic" on daisy chained systems without letting that mixed with traffic coming from NIC0(diagram below) Cards?
I am running Linux kernel on each boxes. I can give multicast address in the interface name, but my guess is that it would not guarantee the mixing of traffic if the NIC0 traffic also has same multicast IP, so, is ACL a answer?
Q(2) My application needs subscribe-notify setup, and that's why I need multicast. There are options such as using 0MQ that also use TCP based multicast(PGM). Will that protect me here somehow?
I don't know why you would daisy chain these computers. Before going any further, you should connect these machines with a switch.
Really, though, I don't understand what your questions is...