Only unidirectional communication is possible in

I was just wondering how I could build a private network where it is physically impossible to gain access from outside but still have the option to publish data to some remote server. As an example: Let's say I have a network of devices that controls some kind of critical infrastructure and I don't want anyone to be able to access it except for the people on-site. However, I'd still linke to send diagnostic information without notable delay to a remote server that can be accessed from the internet. Assumptions about the attacker: • can break into any system that is connected to the internet • does not have physical access to the private network So we can't just put a server that acts as a firewall between the public and private network, because every software has flaws and the attacker would gain access to the private network as soon as the firewall has been broken (except if we had a firewall where the rules are embedded in hardware or for some other reason impossible to be modified without physical access. Are there such devices?) What could solve the problem is a device that physically allows only unidirectional communication (in our case from the private to the public network). I don't know if there are any such devices, but I came up with some ideas: • use any kind of write-only media, like CD-ROMs. Issues: high latency and requires specialized hardware to automatically move CDs between machines. • paper printer/scanner setup: Have a printer in your private network th...

We explained OCPP in our 1st post of the EV and OCPP series, you can read that post for the basics of OCPP. In this post, We will understand Websockets and how it used as a carrier protocol in OCPP. What is Websockets? Before going into details of Websockets, lets understand mechanism of HTTP protocol and limitation of same. We know that HTTP is a widely used protocol for client server communications. HTTP is a unidirectional protocol, means client establish connection with server and request for resource always initiated from client end. When you access a web site over HTTP, browser play role of client and request need to be initiated from the client end, any data from the server will always be against some request from the client. HTTP only unidirectional communication can be a roadblock in the application which needs bidirectional communication. In unidirectional communication, if the server has to send some data to the client, the server has to wait for client to get connected first, which means server keep probing if client connected or not. Websockets is the answer where bidirectional communication needed. Client can send data to server and similarly server can also send data to client anytime. HTTP and Websockets both works on TCP, and i would prefer to say that Websocket is an upgrade of HTTP Websocket URL scheme Websocket resource URL use custom scheme ws and wss. ws for plain text communication and wss for secure (TCP+TLS) communication. Example, Here in this exa...

From Data can be written to the file descriptor fildes[1] and read from the file descriptor fildes[0]. A read on the file descriptor fildes[0] shall access data written to the file descriptor fildes[1] on a first-in-first-out basis. It is unspecified whether fildes[0] is also open for writing and whether fildes[1] is also open for reading. As I understand, when you call the pipe syscall like pipe(array), then array[0] is for reading and array[1] is for writing. However, can they both be for read and write? I know I can create another pipe to get write/read in the reverse direction, but can it be done in the same pipe? What the document means with It is unspecified whether ... A pipe is a one-way channel, and though I suppose one could have the same process read and write to itself, that's not really what it's for. If you want another one-way channel, you have to make a second pipe (or: you could use UNIX domain sockets, which are a bidirectional channel that works like a network connection). As I understand, when you call the pipe syscall like pipe(array), then array[0] is for reading and array[1] is for writing. Yes. However, can they both be for read and write? No, the pipe() function does not provide for that, unless as an extension. A standard pipe is a unidirectional communication channel. If great care is exercised, however, then a single pipe may be usable for bidirectional communication. Any number of threads or processes may write to the write end of the pipe, and...

Full duplex (FD) is a communication strategy where each unit transmits and receives at the same time. In principle, FD can be applied to a general multibus DC microgrid. Here, we restrict ourselves to the single-bus system where the effect of the transmission network can be assumed to be negligible and all VSC units connected to the bus observe the same output voltage. Then Eq. ( 11.5) can be rewritten as follows: (11.14) V * = ∑ m = 1 M V m R D , m − I C C + ∑ m = 1 M V m R D , m − I C C 2 − 4 P C P 1 R C R + ∑ m = 1 M 1 R D , m 2 1 R C R + ∑ m = 1 M 1 R D , m , where R CR, I CC, and P CP represent the components of the aggregated load. In addition, to simplify the exposition, we also assume that the units employ the fixed virtual resistance constellation with the same virtual resistances; that is, As already mentioned, in FD power talk all units transmit and receive at the same time. Fig. 11.8A depicts examples of the layout of the detection spaces of a receiving unit in simple single-bus systems with M = 2 and M = 3 VSC units that communicate in FD mode. These two cases expose the main principles of FD power talk communication in single-bus systems. To begin with, observe the case with two VSC units. The same detection principle as in the TDMA case is applied: by observing its local output, the receiving VSC detects the input of the transmitting VSC. The difference from the TDMA case is that the local output depends on the input combination of both VSCs: Consider the ca...

Let me first begin by saying I've looked around, and I haven't found a question asked that pertains to this situation exactly. Essentially my question is this: Is it possible to allow subnet S1to access data from subnet S2, while preventing S2 from accessing data on S1? For further information, let's say that both subnets are a part of Network N1, and that S1 is a staff subnet, while S2 is a student subnet. In this case, we want the teachers to be able to access data on the student computers without allowing the reverse to happen. Is this possible? If so, how would you go about accomplishing it? If there's any confusion, feel free to let me know so I can alleviate it! Yes, this is possible. You need a device (e.g router, firewall, virtual appliance, etc) that does The way in which it works is that it watches traffic that flows from the "trusted" zone to the "untrusted" zone. When "untrusted" devices send traffic in response to "trusted" devices, the firewall will let the traffic through. However, if "untrusted" devices try to initiate a connection to "trusted" devices, the firewall will block it. I wrote a That is the sort of thing firewalls do. A couple of examples: • Users on a network can access resources on the Internet, but Internet users can't access the network. • Test labs are done this way, so that the lab cannot damage the production network, but the testers on the production network can run things in the lab. Just separate the two networks with a firewall, and s...

Cell co-culture serves as a standard method to study intercellular communication. However, random diffusion of signal molecules during co-culture may arouse . It shows that the expression of α-smooth muscle actin (a marker of cancer-associated fibroblast (CAF)) of both MRC-5 fibroblasts and can be up-regulated only by the secreta from invasive MDA-MB-231 cells, but not from non-invasive MCF-7 cells. The proliferation of the tumor cells can be improved by the stromal cells. Moreover, Introduction Intercellular communication is crucial to coordinate cell behaviors and maintain cell functions in multicellular organisms (Kholodenko 2006). Cells communicate by means of signal molecules through Signal-Target-Response activities (Telleen 2018). These signals may include proteins, small peptides, amino acids, nucleotides, fatty acid derivatives, and even dissolved gases such as nitric oxide and carbon monoxide. Most of these signal molecules are secreted from the signaling cell and interact with the receptors in the target cell to trigger a response that alters the behavior of the target cell (Alberts et al., 2002). There are two types of communications between cells: the direct communication between physically connected cells via gap junctions and the indirect communication between non-contacted cells via paracrine and hormonal secretion (Telleen 2018). To study cell communications, cells are isolated from organisms and cultured in vitro so that specific signals can be tested and...