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Serial ip port redirector8/19/2023 Network connections through proxy servers.network packetization and Nagle's algorithm. The timing effects of the TCP protocol stack, e.g.Data rate limiting of the application data stream to provide the performance expected for the baud rate currently in effect on the virtual COM port, which is slower than the maximum speed of the network connection to the server.(This is not the same as hardware/software flow control of the serial device itself.) Flow control of the network data stream to prevent overrun of the server.Accepting inbound connections initiated by device servers running in client mode and routing the data stream to a waiting application.Initiating the network connection to a device server and determining that server is ready to relay application data. Device servers for certain applications, such as those that use wireless networks, use UDP instead of TCP to gain performance at the risk of network reliability. Several of the larger server manufacturers use proprietary protocols in addition to, or instead of, public protocols. The majority of server manufacturers use public TCP protocols (raw, Telnet, or Telnet with RFC 2217 extensions). Most device servers are accessed with TCP connections (raw or using the Telnet protocol) to gain reliable delivery of the application's data stream in order of transmission. Network protocol support that is compatible with the device server.Redirectors address a number of issues related to the network connection, including: The equivalent software for a Unix/ Linux operating system is commonly called a tty port redirector and most of the information on this page also applies to it. Compatible networked device servers are currently available from a large number of manufacturers, with a heavy concentration of revenue in the top players, who are based in the North America and Asia/Pacific regions. Network packet loss or excessive packet times have dramatic effects on redirector operation and must be avoided.ĬOM port redirector software products have been offered by at least 30 vendors dating back to the early 1990s. The performance drawbacks of simple redirector implementations can be largely addressed by kernel-level drivers that avoid context switches. The performance of a COM port redirector is determined by both its implementation and the network it uses to reach device servers. The redirector GUI typically also includes displays of virtual COM port activity and various diagnostic aids. The COM port redirector then begins relaying the application data stream between the virtual COM port and the device server.Ī redirector will typically permit creation of many (at least 256) virtual COM ports, but simultaneous use of hundreds of ports is often practically limited by a number of factors, including the memory and processor requirements of the redirector, limits on operating system resources, and the performance of the network stack.Ī redirector for the Windows operating system is typically configured using a control-panel style graphical user interface for creating virtual COM ports, configuring settings for individual COM ports, and configuring global settings affecting all COM ports. When the application opens the virtual COM port, the redirector makes an IP network connection to the device server at the specified IP address and TCP/UDP port number that corresponds to the remote device on the server. These issues are described in the Technology section below.Īpplications use a COM port redirector through one or more virtual COM ports that the redirector creates, as configured by the user. The main challenges arise in two other areas: the network connection to the device server and the behavior of the device server. A virtual COM port itself is a relatively simple software mechanism that can be implemented by driver software similar to that of a conventional COM port driver. The purpose of the redirector is to make the virtual COM port exhibit behavior that closely resembles that of a "real" COM port, i.e., a COM port driver for local serial port hardware.
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