Multiple Client Server Program In C Using Udp

It is defined by RFC 768 written by John Postel. So finally I have put together an example for you people. Share serial devices over a network (or even the internet) Use TCP/Com as a Virtual Serial Port Splitter Cable. - the example sketch. Hello Adi, Well, you can either use one different port to each client you have. There are many C# example codes on TCP/IP Multiple Client but I couldn't find to connect Multiple Server on One Client (Window 7 PC in my case). Just use the Java interpreter and specify the Server class name. The properties and methods of the UdpClient class abstract the details of creating a Socket for requesting and receiving data using UDP. cgi, using the client code and sending the arguments 1, 5, 1000, and 0, use the command client royal21. I have a Java server and a Java client running on the same network and the applications are not to be used outside a private network (not over internet). I am coding a real-time, network program with UDP protocol using SFML libraries. Example of Client Server Chat Program in java using TCP/IP Source Code for Server. This example provides more complete sockets’ APIs usage. The next chapter will cover in detail the server side of socket programming, and it will go into detail about asynchronous socket operations. High Performance. Package net provides a portable interface for network I/O, including TCP/IP, UDP, domain name resolution, and Unix domain sockets. Server will replay to the query. Send and Socket. Main reasons for doing so is because some languages tend to have available libraries / already written co. Server-Client Chat application using UDP That chat app is created using UDP and not TCP. I created a shiny new file 'server. Then: This WebClient will download a page and the server will think it is Internet Explorer 6. If requested by the RTSP client, the server will stream its RTP (and RTCP) packets over TCP. Help w/ Multiple Client Socket Programming (UDP) Hi guys, I need some help with socket programming using UDP. In this guide, we will cover how to set up a basic firewall for your server and show you the basics of managing the firewall with firewall-cmd, its command-li. Since UDP is connectionless, it’s more often used for streaming-services, since it just mows out a bunch of data, and hopes all of it goes according to plan, whereas TCP requires an active connection to the client, using a lot more resources. TCP (Transmission Control Protocol): TCP (Transmission Control Protocol ) is a standard that defines how to establish and maintain a network conversation via which application programs can exchange data. Server receives this number and multiplies it by 2. UDP is the abbreviation of User Datagram Protocol. FTP Connect, Examine Server Certificate, and then Authenticate FTP Set Remote File Date/Time Equal to Local File's Last-Modified Date/Time FTP Download Text File to a Stream. Because this example uses asynchronous methods, the server application does not use threads to communicate to multiple clients (although internally the. In the following program, the user sends a message with the help of the Client application. Type ping and the computer name of the management server, and then press Enter. NET framework provides two classes specifically for TCP: TcpClient and TcpListener. Not really getting anywhere with this, i'll post ode for both client and server below. The position listed below is not with Rapid Interviews but with Baxter International Our goal is to connect you with supportive resources in order to attain your dream career. Click Allow a program through Windows Firewall. One is for server and other is for client. java – this will create a TCPClient. This is the second version of my client/server program. The language also facilitates declaration of user-defined classes. This is a 12 month contract position. UDP Server-Client implementation in C. The system calls send(), sendto(), and sendmsg() are used to transmit a message to another socket. net 2005 winsock simple client server chat; TCP/IP simple client server socket program; Simple Client Server Instant Messaging Java code using UDP datagrams; Simple client server chat program using socket; Simple Client Server program. Share TCP SOCKETS CHAT APPLICATION(SERVER & CLIENT) USING C. Example: UDP multicast client. In the main method, we create objects of two classes and call their methods. If both are running in different machines , then in the client side we need to specify the. The difficulty is that you can use sockets to program network applications using different protocols. There is no "session" established using a long-lived socket. In this module, we will learn about client-server programming, and how distributed Java applications can communicate with each other using sockets. This is the most common type of connection. You can see , the function connection_handler from server take a socket_desc as paramater, so when you accept is beeing called you can for example create a struct representing a client with all information like IP, FD etc. These two are very important topics when you want to build a network application and I want to ensure that all students have the basics before we start to code Client – Server applications. Example: UDP multicast client. bye", the client and the server will both quit. Everytime you are going to make or receive a connection, you are going to use a socket (on both client and server side). The following is the output sample when we run it both as a receiver and as a sender. The properties and methods of the UdpClient class abstract the details of creating a Socket for requesting and receiving data using UDP. Modbus is used in multiple master-slave applications to monitor and program devices; to communicate between intelligent devices and sensors and instruments; to monitor field devices using PCs and HMIs. Server applications using the API normally do not need to know client port numbers. tcp socket, socket programming, tcp buffer, raw socket, chat c#, how to, chat room, mobile, android, iOS, iPhone, c#, c# socket, web development How to C# Socket Programming using Visual Studio. I have no problem with usage the threads. Anyway, I have multiple copies of the preferences. 0 - Do not use an RD Gateway server. Because of this minimal design, UDP has considerably less overhead than TCP. In other words, TCP establishes a continuous open connection between a client and a server, over which. These socket programs need to be run from two separate terminal/command prompts. Now lets make a simple server-client program to see all of this in action and hopefully it will make your concepts more clear. Corba program to Write a Echo server and client with UDP server and client : Feb 22: Corba program of Count Client Applet, IDL,Server, Client: Feb 23: chat client GUI problem: Feb 20: TCP/IP program to create a passive socket for use in a UDP server: Feb 22: TCP/IP program to create a passive socket for use in a TCP server: Feb 22. Pls help me. When I get a connection over TCP I create a new Client object and use BeginRead() on the NetworkStream. Suppose that you wish to write a server that implements the UDP-based variant of the Daytime Protocol, as defined by RFC 867. now open new File write second program Client1. In this tutorial, we will learn how to create a simple HTTP Server in Java, which can listen HTTP request on a port let's say 80 and can send response to client. It uses two values, client and server, to establish a connection as the client or the server. cpp), and the UDP server should be named CalcServerUDP. Client allocates a local port number and sends it to server at well-known port. And run the client program (on the same computer): java QuoteClient localhost 17 Both the client and server are running in an infinite loop, so you have to press Ctrl + C to terminate. Depending on how complicated things get, multiple server programs may eventually exist, but for now there's just one. Concurrent Server handling Multiple Clients Code in C in Linux Platform //TCP SERVER Concurrent: multiple clients can be handled by this server //Now second client no need to wait for first client to close by finishing its task. Together, TCP and IP are the. Use stream operations to communicate with the client. The following is the output sample when we run it both as a receiver and as a sender. TCP Client and Server sample example with source code for Beginners in C#. World of Warcraft(WoW) game client utilizes TCP while the Voice Chat features use UDP. Understanding the Multiple-Client Problem : Overview of Server Functions : Using fork(2) to Service Multiple Clients : Designing Servers That Use select(2) Applying select(2) to a Server : What's Next : 12. The program can be run either in interactive mode or controlled using command line arguments. [C#] Reflection Examples – examples how to use dynamically loaded assembly [C#] Get Method Names using Reflection – get names of methods of any class [C#] Get Property Names using Reflection – get property names of any class [C#] Get Calling Method using Reflection – how to get name of calling method. To use an alternate codec, use ServeCodec. cfg; SQL- LIBRARY MANAGEMENT SYSTEM; Java - Blowfish Encryption Algorithm. The number of si multaneously open UDP ports depends on the operating system. The objective of this article is to demonstrate a socket-based client/server application that will allow two-way asynchronous communication between a server and multiple client applications. Accepting Multiple Clients. You should already know your destination server, and for basic uses of port forwarding, you can usually use the port numbers in Wikipedia's list of TCP and UDP port numbers. I want to clear some doubts in server. A simple way to build a TCON_IPv4 DB is to place, in your program a block TSEND_C, and use the properties of the block to create and configure the DB. Until next time, cheers! About the Author Hannes DuPreez. In particular, with UDP our client uses a DatagramSocket whereas with TCP our client used a Socket. This chapter highlight the difference between TCP and UDP connection. Therefore, when ccnahub's Hosting Server receives multiple requests from the same client device using multiple Applications (Web, FTP, and Email), Multiplexing Logic kicks in (Regardless what is used TCP or UDP), all requests will be managed and respond to without any problems. Example of Client Server Chat Program in java using TCP/IP Source Code for Server. The SMTP application on the mail server will then request authentication from the client, such as the email address and password. This implies asymmetry in establishing communication between the client and server, which has been examined in the ``Basics'' section. The files and directories in /home will now be available on client, in the /mnt directory. But now I want to make it more practical by handling multiple clients for a single Server. CLIENT SPECIFIC OPTIONS-c,--client host run in client mode, connecting to the specified server. Figure 1 depicts a possible scheme for a client-server image processing system. Every message is a discrete chunk of data, opaque to the broker. Bind socket to a port 3. The Help menu in the IDE provides access to extensive information about using the IDE. ssl_server. To mount /home on server to the /mnt mount point on client: # mount server:/home /mnt. The end product will be a server that listens for all connections and messages over a specific port and prints out any messages to the console. cpp - Function to handle a single client connection for the echo servers. Click here for a complete server program which includes this change. Connecting a TCP server and client. A thread is a single sequential flow of control within a program. UDPTunnel can be run in two modes: a client mode and a server mode. The caller typically invokes ServeConn in a go statement. The following is a simple example that illustrates the different portions of a server/client pair. C is a statically typed, structured, general purpose computer programming language which has formed the basis for many other programming languages. Provides fast and lightweight data transmission for local packet broadcasts and remote multicasting. ” This example is from my sandbox. I want the control to respond to each client's request, but it does not seem to be doing that. Firstly, we run the program as a receiver from the C:\. /client" can be used only if the name of the executable file generated on compiling the program is "client" Delete. CoAP Client and CoAP (Embedded) Server Examples Take a look at how to set up and use Mongoose Embedded Web Server's CoAP client and server, complete with code blocks and explanations. client) and Web server (HTTP server) " TCP connection closed HTTP is “stateless” " server maintains no information about past client requests ! cookies an exception protocols that maintain “state” are complex! " past history (state) must be maintained " if server/client crashes, their views of “state” may be. From one DOS prompt, first, run the server program and from the other DOS prompt run the client program. Hi, trying to make a chat system with multiple servers. Next section is a client program, clientprog. In the following program, the user sends a message with the help of the Client application. Just use the Java interpreter and specify the QuoteServer class name. That's all. In this in-depth tutorial you'll learn how to build a socket server and client with Python. The sigaction() code is responsible for cleaning the zombie processes that appear as the forked child processes. The server program. Net framework. It is possible to act as server and/or client and transmit textstrings, arrays of any datatype, files or MATLAB variables. I have different MAC and IP on both Servers but I could connect only 1 Server at a time from my PC (Client). Once the server has started, you can run the client. The main difference is the server loop. Using the -P or --parallel option in the client, you can run multiple parallel tests from the client to a single server. Then, we run the same program from other path as a sender. The code is based on the singlethreaded server desbribed in the text on Singlethreaded Servers. So for this installment I will cover how to use Dart to send and receive data over UDP. The ntpq can also obtain and print a list of peers in a common format by sending multiple queries to the server. UDP CSocket Examples UDPEchoClient. Alternative types of sockets This example showed a stream socket in the Internet domain. Java program that finds the area of a circle using Client-Server network; C program to Implement Morse code to text conversion and vice-versa. Establish. The next chapter will cover in detail the server side of socket programming, and it will go into detail about asynchronous socket operations. The server must run a third program and pipe it to the client (I already did this app with TCP and Named Pipes, and I just 'dupped' the file descriptors of the fifo or socket to the child running the third program). Specifies if and how to use a Remote Desktop Gateway (RD Gateway) server. Net namespace. The language also facilitates declaration of user-defined classes. And Java can run on any server and that solve that server part of equation. Each has its own benefits and disadvantages. Tags for File Transfer Using TCP in C. First I’m going to explain the server code, and when it’s already running we jump into our client, which in this case I’ll consider only one, but nothing prohibits you to connect more than one client to you server. The server end is much more complicated. Some popular applications built around UDP are DNS, NFS, SNMP and for example, some Skype services and streaming media. Like most of distributed applications, daytime is composed of a client and a server programs. Creating multiple UDP sockets in a 'C' program How do I create two UDP sockets in a single code? I want to to write a forwarder that is connected to a client and a server such that a message from the client to the server passes thro' the forwarder and vice-versa. In this article, let us discuss how to write Perl socket programming using the inbuilt socket modules in Perl. Both classes have their constructors and a method. Now lets make a simple server-client program to see all of this in action and hopefully it will make your concepts more clear. What is the default server port for Murmur? The default server port for Murmur is UDP and TCP 64738. This is a 12 month contract position. User Datagram Protocol (UDP) is a simple protocol that makes a best effort to deliver data to a remote host. This call typically blocks until a client connects with the server. I haven't managed to read all the posts here, but the behaviour you describe in this post is normal for a UDP server. Microsoft's updated DNS server is said to preallocate 2,500 UDP ports to use for these random queries, and for discussion we'll round this down to an even power of two: 2 11 = 2,048. The server side binds to a port and publishes data. The QUdpSocket class can be used to send and receive UDP datagrams. Send method sends data from your buffer to a connected Socket. By the end of this tutorial, you'll understand how to use the main functions and methods in Python's socket module to write your own networked client-server applications. With UDP datagrams, the remote port is supplied with the TSENDTO request. In the following program, the user sends a message with the help of the Client application. Be aware though that all connections are from server to client. In this case, we use UDP. Prevent downtime and data loss from complex IT infrastructures. Server will replay to the query. As such, I made sure to set an socket operation timeout such that if no messages were received (ie, I forgot to start the Node. 1998 Writing Client/Server Programs in C Using Sockets (A Tutorial). Go is a compiled, statically typed programming language developed by Google. event-driven programming or select()-based multiplexing, it's a solution to a network programming problem: How do I talk to bunch of different network connections at once, all within one process/thread? Let's say you're writing a database server that accepts requests via a tcp connection. The sigaction() code is responsible for cleaning the zombie processes that appear as the forked child processes. ProxyChains allows to run any program through HTTP or SOCKS proxy. The connection establishment phase comprises a three-way handshake during which time the client and server exchange their initial sequence numbers (ISN) and acknowledge the other host's ISN. For this, we'll create the following two separate modules. Be aware though that all connections are from server to client. It provides a best-effort datagram service to an End System (IP host). Below you’ll find the code of a simple server-client program in C using UDP sockets for the transmission. UDP is the abbreviation of User Datagram Protocol. To stop fopen or to stop listening for connections, and restore the use of MATLAB, type Ctrl+C at the MATLAB command line. In this case, we use UDP. We learned how to send and receive datagram packets using UDP sockets and also, how to set a proper socket timeout. The program can be run either in interactive mode or controlled using command line arguments. Client allocates a local port number and sends it to server at well-known port. Corba program to Write a Echo server and client with UDP server and client : Feb 22: Corba program of Count Client Applet, IDL,Server, Client: Feb 23: chat client GUI problem: Feb 20: TCP/IP program to create a passive socket for use in a UDP server: Feb 22: TCP/IP program to create a passive socket for use in a TCP server: Feb 22. 3 with gcc) and Windows (tested under Win2K with Visual C++ 6. Connecting a TCP server and client. This example works using localhost, which corresponds to the default local computer IP address of 127. Basically i have written a simple multithreaded server and client program where the client will send cstrings to the server and the server will just echo out the message received. The UDP packet can be viewed using Ethereal capture. One of the major changes is the move to an new hardware-based shader design for their 3D graphics display. One of the most basic network programming tasks you’ll likely face as a Java programmer is performing socket functions. Then send()instead of sendto()can be used. I haven't managed to read all the posts here, but the behaviour you describe in this post is normal for a UDP server. Message Queue in Unix Using C Programming. UDP sockets are used by protocols like DNS etc. This is an fine example for Scoket Programmin in java. The RTMFP protocol communicates over UDP. If you are prompted for an. Server-based processing Using SQL Server in a client/server configuration reduces network traffic by processing database queries on the server before sending results to the client. The goal of the language is to allow web developers to write dynamically generated pages quickly. A TCP server is created and set to listen to a specific port. You can use the script in link below to confirm whether or not the message in tcpdump are displaying as malformed or not ( they are not in my case). Here comes the example of the UDP multicast client. The following line in a configuration file sets the connection port so that client and server always. The ntpq utility program is used to query NTP servers which implement the recommended NTP mode 6 control message format about current state and to request changes in that state. The programs include a simple TCP/UDP server (simples), a TCP-only server (simples_ioctl) that uses the select function in a Win32 console application to support multiple client requests, and a client TCP/UDP program (simplec) for testing the servers. Server¶ Server sockets proceed by: uv_tcp_init the TCP handle. Languages like C++ have derived from it and have an extended application, thanks to their OOP concepts such as encapsulation and inheritance. The most commonly used paradigm in constructing distributed applications is the client/server model. By default, Library Server advertises its presence on the local network, so that clients may connect without knowing the address of the server. In this tutorial, we'll review the process of running a WebSocket server in PHP, and then building a client to send and receive messages to it over the WebSocket protocol. CoAP Client and CoAP (Embedded) Server Examples Take a look at how to set up and use Mongoose Embedded Web Server's CoAP client and server, complete with code blocks and explanations. The server is even simpler, as no waiting is required. The advantages to adopt SoftEther VPN Server instead of old OpenVPN Server program are as follows: SoftEther VPN Server has easier configuration than OpenVPN Server by OpenVPN Technologies, Inc. The client now has everything it needs to mount a remote file system. Create a client-server program in C using Makefile. Socket is the endpoint of a bidirectional communications channel between server and client. tcp-echo-server/main. In this article we will use DD-WRT as an example. py) in two separate files. It works fine for single server and single client. Learn about TCP and UDP ports used by Apple products such as macOS, macOS Server, Apple Remote Desktop, and iCloud. Specifies if and how to use a Remote Desktop Gateway (RD Gateway) server. Starting from OpenVPN 2. Bind socket to a port 3. Client/Server Computing You can use the Java language to communicate with remote file systems using a client/server model. It uses two values, client and server, to establish a connection as the client or the server. # # See the "easy-rsa" directory for a series # of scripts for generating RSA certificates # and private keys. For example “iperf 3 -c 192. In this lab, we learned he basics of socket programming for UDP in Python. How to make Client Server Chat Program in java using TCP/IP. Sample Applications. Apart from that, the client must know the IP address of the server and which port the server is listening on. Client Process. The tutorial programs in this section show how to use asio to develop simple client and server programs. Multiple Client Server Program in C using fork | Socket Programming The server is a simple echo sever that can handle multiple client using fork. TCP-Com is a software based serial port to TCP/IP + UDP Redirector, that can act as either a TCP/UDP client or server. C has been a solid programming language for nearly 50 years now and is still in demand. Client systems use TCP 1433 to connect to the database engine; SQL Server Management Studio (SSMS) uses the port to manage SQL Server instances across the network. Hercules SETUP utility is useful serial port terminal (RS-485 or RS-232 terminal), UDP/IP terminal and TCP/IP Client Server terminal. By default, clients use port 1935 and ports 19350-65535 to communicate with Adobe Media Server over the RTMFP protocol. But I still have one problem. Bookmark the how i wont to show message from UDP server ? Reply. Socket Programming in C/C++: Handling multiple clients on server without multi threading. now open new File write second program Client1. TCP and UDP are used for different purposes and both have unique constraints:. In other words, TCP establishes a continuous open connection between a client and a server, over which. In this in-depth tutorial you'll learn how to build a socket server and client with Python. At least that's the approach I've taken for my 747 project. c in the Linux kernel before 2. TCP was split into TCP and IP to allow applications that didn't need TCP's complexity to bypass it, using the much simpler UDP instead as a transport layer protocol. LightweightM2M is principally a device management protocol, but it should be designed to be able to extend to meet the requirements of applications. fork() rexec. A client process initiates contact with. c Chapter 17: Sharing Messages with Multicast, Broadcast, and Mbone. In Windows Azure, we have the concept of endpoints, which give us the possibility to open TCP or UDP ports on the WEB. First, the FTP Client opens two dynamic ports - a command port (for example port 1025) and a data transfer port (the command port +1 = port 1026). ” This example is from my sandbox. In this mode, a client does not have to wait for the server to finish serving other clients. Two Gui will be shown as in below. Server-Client Communication using ESP8266 Serial WiFi Module (ESP-01) In realterm software you can change it in the port settings. The order in which the server and client start generally does not matter. As such, I made sure to set an socket operation timeout such that if no messages were received (ie, I forgot to start the Node. xml That second location contains the options that drive the connection interface, btw. Internet of Things project – Communication between ESP8266 modules | ESP8266 Arduino Tutorial What people don’t know is the real benefits of making two ESP8266 talk each other. Since UDP is conectionless, you do not have to worry about handshaking or other stuff like that, just "copy/paste" your clients and connect them to your sever. Readers of this document are assumed to be proficient in the C and C++ programming languages including template classes and be comfortable using a Unix operating system to develop programs. Host Name: The host name to query Port Number: The client UDP port that was used to send the DNS query. Following are the sample socket programs available:. However, before you read the descriptions and look at the code, you should compile and run the two programs to see what they do. NET (part 1) sending and receiving messages with multiple clients on 2/18/2014 9:07 AM HI, do you have an example where the server sends message to all clients connected in the same port?. World of Warcraft(WoW) game client utilizes TCP while the Voice Chat features use UDP. I am learning java, I am doing file transfer using UDP protocol, my problem is I can not create a new file server, please help me this is my code clie transfer files from client to server using the UDP protocol (Sockets and Internet Protocols forum at Coderanch). Client creates socket binds to SENDER_PORT_NUM and sends data to Server. Example of Client-Server Program in C (Using Sockets and TCP) Below you’ll find an example of a very simple client-server program in C. Tags for File Transfer Using TCP in C. [C#] Reflection Examples – examples how to use dynamically loaded assembly [C#] Get Method Names using Reflection – get names of methods of any class [C#] Get Property Names using Reflection – get property names of any class [C#] Get Calling Method using Reflection – how to get name of calling method. Client-Server Model. Java Sockets and Client/Server Programming. UDP is an unreliable, datagram-oriented protocol. If it fails then the udp protocol is not concerned. Use the UDP Open function to open a UD P socket on a port. The server had been on Server 2016 until last night when it was upgraded to 2019. c Mani Radhakrishnan and Jon Solworth Socket Programming in C/C++. c and (2) net/ipv6/udp. cpp', and stuck in a bog-standard main function which will be the entry point of the server program. Because this example uses Asynchronous methods, threads are not necessary to communicate to multiple clients (though internally the asynchronous communication mechanism uses threads at the OS level). Call uv_listen on the handle to have a callback invoked whenever a new connection is established by a client. Updated Wednesday, June 26, 2019 by Linode Contributed by Mihalis Tsoukalos Use promo code DOCS10 for $10 credit on a new account. Accept new connection b. Streaming to multiple clients is implemented using a ZeroMQ Pub-Sub pattern. That’s the lesson about how to develop a network client/server application relying on UDP protocol. Next, we’ll describe how the behavior of the SMB client can help distribute the load for a file server with multiple NICs. Detailed knowledge of network standards or Unix I/O is not required. Read RAW Socket in Unix Using C Programming. Launch SteamCMD on your host and use it to download the server files. The code is based on the singlethreaded server desbribed in the text on Singlethreaded Servers. The openRTSP command-line RTSP client (which receives/stores stream data, without playing it) Notes: The server can transmit multiple streams (from the same, or different files) concurrently By default, the server transmits its streams as RTP/UDP packets. Cary, NC Feb. Peer-to-peer systems such as this, that must operate in the presence of firewalls, are really client-server architectures. Many applications are running concurrently over the Web, such as web browsing/surfing, e-mail, file transfer, audio & video streaming, and so on. The program UDPClient. At the end of the test, Iperf will tell you the amount of jitter as well as the amount of dropped packets in the transmission. TCP Client and Server sample example with source code for Beginners in C#. Sockets Programming in C Using UDP Datagrams Below you'll find the code of a simple server-client program in C using UDP sockets for the transmission. 3 - Use the default RD Gateway settings. Server-Client chat program or two way chat using TCP connection is a common problem for java practical labs or networking labs. edu 2003 "/output. A TCP based client/server system consisting of a server which responds to multiple clients and allows them to issue "ls" and "more" commands to view the directory information and view a file on the server machine. The connection establishment phase comprises a three-way handshake during which time the client and server exchange their initial sequence numbers (ISN) and acknowledge the other host's ISN. This example provides more complete sockets’ APIs usage. One of the coolest new features of HTML5 is WebSockets, which let us talk to the server without using AJAX requests. NET is a simple yet very powerful and high performant open source library for the. You will learn about the client-server model that is in use for the World Wide Web, E-mail and many other applications. A server is a pr ocess that is continuously running and waiting to be contacted by a client process. Basically i have written a simple multithreaded server and client program where the client will send cstrings to the server and the server will just echo out the message received. TCP Client Server sample example, that waits for any clients to connect. That being said, sometimes you need to use UDP, e.