How do udp sockets work

This method is automatically called by the kernel when the socket is closed or the process terminates, so most apps will never have reason to call this.

If multicastInterface is not specified, the operating system will attempt to drop membership on all valid interfaces. By default, binding a socket will cause it to block the Node. The socket. Returns an object containing the address , family , and port of the remote endpoint. The address parameter now only accepts a string , null or undefined. On success, callback will now be called with an error argument of null rather than 0.

The msg parameter can be an array now. Also, the offset and length parameters are optional now. Broadcasts a datagram on the socket. For connectionless sockets, the destination port and address must be specified. Connected sockets, on the other hand, will use their associated remote endpoint, so the port and address arguments must not be set. The msg argument contains the message to be sent. Depending on its type, different behavior can apply. If msg is a Buffer , any TypedArray or a DataView , the offset and length specify the offset within the Buffer where the message begins and the number of bytes in the message, respectively.

If msg is a String , then it is automatically converted to a Buffer with 'utf8' encoding. With messages that contain multi-byte characters, offset and length will be calculated with respect to byte length and not the character position. If msg is an array, offset and length must not be specified. The address argument is a string. If the value of address is a host name, DNS will be used to resolve the address of the host.

If address is not provided or otherwise nullish, ' If the socket has not been previously bound with a call to bind , the socket is assigned a random port number and is bound to the "all interfaces" address '0.

An optional callback function may be specified to as a way of reporting DNS errors or for determining when it is safe to reuse the buf object. DNS lookups delay the time to send for at least one tick of the Node. The only way to know for sure that the datagram has been sent is by using a callback.

If an error occurs and a callback is given, the error will be passed as the first argument to the callback. If a callback is not given, the error is emitted as an 'error' event on the socket object. Offset and length are optional but both must be set if either are used.

Example of sending a UDP packet composed of multiple buffers to a port on Sending multiple buffers might be faster or slower depending on the application and operating system.

Run benchmarks to determine the optimal strategy on a case-by-case basis. Generally speaking, however, sending multiple buffers is faster. The MTU is the largest size a given link layer technology can support for datagram messages. However, the mandatory minimum fragment reassembly buffer size is octets. The value of 68 octets is very small, since most current link layer technologies, like Ethernet, have a minimum MTU of It is impossible to know in advance the MTU of each link through which a packet might travel.

Sending a datagram greater than the receiver MTU will not work because the packet will get silently dropped without informing the source that the data did not reach its intended recipient. When set to true , UDP packets may be sent to a local interface's broadcast address.

Sets the default outgoing multicast interface of the socket to a chosen interface or back to system interface selection. Datagrams destined to the connected UDP socket's local protocol address e. This limits a connected UDP socket to exchanging datagrams with one and only one peer. Technically, a connected UDP socket exchanges datagrams with only one IP address, because it is possible to connect to a multicast or broadcast address. Asynchronous errors are returned to the process for connected UDP sockets.

The corollary, as we previously described, is that unconnected UDP sockets do not receive asynchronous errors. Figure 8. The application calls connect , specifying the IP address and port number of its peer. It then uses read and write to exchange data with the peer. Datagrams arriving from any other IP address or port which we show as "??? These datagrams could be delivered to some other UDP socket on the host.

In summary, we can say that a UDP client or server can call connect only if that process uses the UDP socket to communicate with exactly one peer. Normally, it is a UDP client that calls connect , but there are applications in which the UDP server communicates with a single client for a long duration e. The DNS provides another example, as shown in Figure 8.

If a single server is listed the leftmost box in the figure , the client can call connect , but if multiple servers are listed the second box from the right in the figure , the client cannot call connect. Also, a DNS server normally handles any client request, so the servers cannot call connect.

A process with a connected UDP socket can call connect again for that socket for one of two reasons:. The first case, specifying a new peer for a connected UDP socket, differs from the use of connect with a TCP socket: connect can be called only one time for a TCP socket.

Mapping Network Resources. Using Network Resources. Chapter 5. Using Serial and Infrared Ports. Serial Communications. Serial Communication Cables. Chapter 6. Remote Access Service. Remote Access Overview. Remote Access Phonebook. Remote Access Devices. Establishing a RAS Connection.

Connection Management. Chapter 7. Connection Manager. Understanding the Connection Manager. Establishing and Maintaining Connections. Connection Service Providers and Proxies. Scheduled Connections. Chapter 8. Pocket PC Phone Edition. Phone API. SIM Manager. Chapter 9. Desktop Synchronization. The ActiveSync Manager. File Conversion File Filters. Synchronization Service Providers. Desktop Connection Notifications. Chapter Pocket Outlook Object Model. The Pocket Outlook Object Model.

Working with Time Zones. Pocket Outlook Folders.