A virtual port (VPort) is a data object that represents an internal port on the NIC switch of a network adapter that supports single root I/O virtualization (SR-IOV). Each NIC switch has the following ports for network connectivity:
One external physical port for connectivity to the external physical network.
One or more internal VPorts which are connected to the PCI Express (PCIe) Physical Function (PF) or Virtual Functions (VFs).
The PF is attached to the Hyper-V parent partition and is exposed as a virtual network adapter in the management operating system that runs in that partition.
A VF is attached to the Hyper-V child partition and is exposed as a virtual network adapter in the guest operating system that runs in that partition.
There are two types of VPorts:
Default VPort
The default VPort provides network connectivity to the networking components that run in the management operating system. The default VPort has an identifier of NDIS_DEFAULT_VPORT_ID.
When the PF miniport driver creates and configures the default NIC switch, the driver implicitly creates the default VPort and attaches it to the PF. The default VPort cannot be attached to a VF.
The default VPort is always in an activated state and cannot be explicitly deleted. The PF miniport driver implicitly deletes the default VPort only when it deletes the default NIC switch.
For more information on how to create a NIC switch and the default VPort on the switch, see Creating a NIC Switch.
Nondefault VPort
Nondefault VPorts are not created implicitly when the NIC switch is created. An overlying driver, such as the virtualization stack, explicitly creates these ports by issuing OID method requests of OID_NIC_SWITCH_CREATE_VPORT. Nondefault VPorts may be attached to the PF or to a VF, and can only be created after the NIC switch has been created.
A nondefault VPort that is attached to a VF provides network connectivity to the networking components that run in the guest operating system. After it is created and attached to the VF, the nondefault VPort is in an activated state.
Hume tumse pyar kitna drama. A nondefault VPort that is attached to the PF provides additional network offload capabilities to the networking components that run in the management operating system. For example, nondefault VPorts on the PF could be used to provide offload capabilities similar to the virtual machine queue (VMQ) interface.
Note Nondefault VPorts can only be created after the NIC switch has been created.
An overlying driver issues an object identifier (OID) method request of OID_NIC_SWITCH_CREATE_VPORT to create a nondefault VPort on a specified NIC switch. This OID request also attaches the created VPort to the network adapter's PF or a previously allocated VF.
The InformationBuffer member of the NDIS_OID_REQUEST structure contains a pointer to theNDIS_NIC_SWITCH_VPORT_PARAMETERS structure. After a successful return from the OID_NIC_SWITCH_CREATE_VPORT request, the VPortId member of the NDIS_NIC_SWITCH_VPORT_PARAMETERS structure has a VPort identifier that is unique across the VPorts on the NIC switch.
The overlying driver initializes the NDIS_NIC_SWITCH_VPORT_PARAMETERS structure with the configuration information about the nondefault VPort to be created. The configuration information includes the PCIe function to which the nondefault VPort is attached and the number of queue pairs for the nondefault VPort.
When it initializes the NDIS_NIC_SWITCH_VPORT_PARAMETERS structure, the overlying driver must do the following:
The SwitchId member must be set to the identifier of a NIC switch that was previously created on the network adapter through an OID method request of OID_NIC_SWITCH_CREATE_SWITCH.
Note Starting with Windows Server 2012, the SR-IOV interface supports only one NIC switch on the network adapter. This switch is known as the default NIC switch. When creating a nondefault VPort, the overlying driver must set the SwitchId member to the NDIS_DEFAULT_SWITCH_ID identifier.
The VPortId member must be set to NDIS_DEFAULT_VPORT_ID.
The AttachedFunctionId member must be set to the identifier of the VF or PF on which the nondefault VPort is to be attached.
A value of NDIS_PF_FUNCTION_ID specifies the PF. Otherwise, the value must be set to the identifier of a VF whose resources were previously allocated through an OID method request of OID_NIC_SWITCH_ALLOCATE_VF.
Note The attachment of a nondefault VPort to a VF or PF cannot be changed after the nondefault VPort has been created.
The overlying driver can also specify the number of queue pairs assigned to the VPort. A queue pair is a transmit and receive queue on the network adapter that is assigned to the VPort. If the network adapter supports asymmetric queue pairs for nondefault VPorts, the overlying driver may specify a different number of queue pairs for each VPort that the driver creates. For more information, see Symmetric and Asymmetric Assignment of Queue Pairs.
The overlying driver calls NdisOidRequest to issue the OID_NIC_SWITCH_CREATE_VPORT request to the underlying PF miniport driver. Before NDIS forwards the OID method request to the miniport driver, it does the following:
NDIS validates the parameters within the NDIS_NIC_SWITCH_VPORT_PARAMETERS structure. If the parameters are in error, NDIS fails the OID method request and does not pass the request to the PF miniport driver.
NDIS assigns an identifier for the nondefault VPort within the range from one to (NumVPorts– 1), where NumVPorts is the number of VPorts that the miniport driver has configured on the network adapter. The driver specifies this number in the NumVPorts member of the NDIS_NIC_SWITCH_INFO structure. The driver returns this structure through an OID query request of OID_NIC_SWITCH_ENUM_SWITCHES.
Note A VPort identifier of NDIS_DEFAULT_VPORT_ID is reserved for the default VPort that is attached to the PF on the default NIC switch.
The assigned VPort identifier uniquely identifies the nondefault VPort on the NIC switch of the network adapter.
- NDIS sets the VPortId member of the NDIS_NIC_SWITCH_VPORT_PARAMETERS structure with the assigned VPort identifier.
When the PF miniport driver is issued the OID request, the driver allocates the hardware and software resources associated with the specified nondefault VPort. After all of the resources are successfully allocated, the PF miniport driver completes the OID successfully by returning NDIS_STATUS_SUCCESS from MiniportOidRequest.
If the OID_NIC_SWITCH_CREATE_VPORT request is completed successfully, the PF miniport driver and the overlying driver must retain the VPortId value of the nondefault VPort for successive operations. The VPortId value is used during these operations:
NDIS and the overlying drivers use the VPortId value to identify the nondefault VPort in successive OID requests related to this VPort, such as OID_NIC_SWITCH_VPORT_PARAMETERS and OID_NIC_SWITCH_DELETE_VPORT.
During send operations, NDIS specifies the VPortId value to identify the VPort from which a packet was sent. This value is specified within the out-of-band (OOB) NDIS_NET_BUFFER_LIST_FILTERING_INFO data of the NET_BUFFER_LIST structure.
During receive operations, the PF miniport driver specifies the VPortId value to which a packet is to be forwarded. This value is also specified in the OOB NDIS_NET_BUFFER_LIST_FILTERING_INFO data of the NET_BUFFER_LIST structure. List of xfinity nascar drivers.
The following points apply to the creation of nondefault VPorts:
Usb Virtual Comm Port
Receive filters for media access control (MAC) and virtual LAN (VLAN) identifiers are configured on the VPort after it has been created. Overlying drivers dynamically set these receive filters by issuing OID method requests of OID_RECEIVE_FILTER_SET_FILTER. Receive filters can also be moved from one VPort to another through OID set requests of OID_RECEIVE_FILTER_MOVE_FILTER.
A nondefault VPort attached to the VF is in an activated state when it is created. The VPort cannot be deactivated if it is attached to the VF.
A nondefault VPort attached to the PF is in a deactivated state when it is created. An overlying driver, such as the Hyper-V extensible switch module, explicitly activates the nondefault VPort attached to the PF after the VPort has been created successfully. This is done by issuing an OID method request of OID_NIC_SWITCH_VPORT_PARAMETERS to the PF miniport driver.
When the overlying driver issues this OID request, it passes an NDIS_NIC_SWITCH_VPORT_PARAMETERS structure with the VPortState member set to NdisNicSwitchVPortStateActivated.
After a nondefault VPort is in an activated state, the PF miniport driver can allocate shared memory for the VPort by calling NdisAllocateSharedMemory. The driver must set the VPortId member in the NDIS_SHARED_MEMORY_PARAMETERS structure to the VPort's identifier value.
Note When a nondefault VPort is in an activated state, it is only set to a deactivated state when it is deleted through an OID set request of OID_NIC_SWITCH_DELETE_VPORT.
Just like we can check COM ports in windows 7 or lower , by going to
Control Panel >> Device Manager >> Ports
How should we check it in Windows 10?
2 Answers
I had the same question and I found this page. And the answer is in @zipzit's comment. So I post it as answer here:
To see 'Com Ports' in Device Manager in Windows 10 you should select 'Show hidden devices' in View menu.
The Device Manager still exists in Windows 10 and should show this. It has not really changed at all between versions.
Open your Start Menu
and just type in Device Manager
, and it will come up.
protected by Community♦May 31 '17 at 22:07
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Inability to locate some devices and drivers on your computer may continue to happen due to a corrupted system file and incompatible drivers. To further address your concern in locating the COM ports, we suggest running the System File Checker. This tool will allow you to scan and diagnose any corrupted files in your system and enhance its performance. Check this article: Use the System File Checker tool to repair missing or corrupted system files for the procedures.
Additionally, we recommend performing a clean boot. To do so, kindly access this link: How to perform a clean boot in Windows and follow the steps. This process gets rid of software conflicts and identifies any third party applications that can block the process of installing the drivers. Verify if you encounter the same behavior afterwards.
Disclaimer: After troubleshooting, refer to this section: 'How to reset the computer to start normally after clean boot troubleshooting' on the same article to boot the computer in normal startup once the issue has been resolved.
Feel free to provide any updates and feedback about your query.
A COM port redirector (tty port redirector under Unix/Linux) is specialized software (often including device driver and user application) that includes the underlying network software necessary to access networked device servers that provide remote serial devices or modems.
- 2Variants
- 2.1Virtual serial port
Overview[edit]
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. 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 main challenges arise in two other areas: the network connection to the device server and the behavior of the device server. These issues are described in the Technology section below.
Applications use a COM port redirector through one or more virtual COM ports that the redirector creates, as configured by the user. 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. The COM port redirector then begins relaying the application data stream between the virtual COM port and the device server.
A 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.
A 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. The redirector GUI typically also includes displays of virtual COM port activity and various diagnostic aids.
The performance of a COM port redirector is determined by both its implementation and the network it uses to reach device servers. The performance drawbacks of simple redirector implementations can be largely addressed by kernel-level drivers that avoid context switches. Network packet loss or excessive packet times have dramatic effects on redirector operation and must be avoided.
COM port redirector software products have been offered by at least 30 vendors dating back to the early 1990s. 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.
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.
Redirectors address a number of issues related to the network connection, including:
- Network protocol support that is compatible with the device server.
- 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. The majority of server manufacturers use public TCP protocols (raw, Telnet, or Telnet with RFC 2217 extensions). Several of the larger server manufacturers use proprietary protocols in addition to, or instead of, public protocols. 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.
- Initiating the network connection to a device server and determining that server is ready to relay application data.
- Accepting inbound connections initiated by device servers running in client mode and routing the data stream to a waiting application.
- Flow control of the network data stream to prevent overrun of the server. (This is not the same as hardware/software flow control of the serial device itself.)
- 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.
- The timing effects of the TCP protocol stack, e.g. network packetization and Nagle's algorithm.
- Network connections through proxy servers.
- Management of the IP routing table to avoid loss of an IP route to the device server.
- Detection and handling of network interruptions, possibly with an automatic attempt to reconnect to the device server to resume application data flow.
Redirectors must also deal with the feature differences of networked device servers related to:
- Visibility and control of serial line signals such as DSR, DCD, CTS, DTR. The redirector may be able to sufficiently emulate these signals.
- Relay of BREAK signals.
- Settings for hardware or software flow control.
- Handling of the network connection when serial devices or modems disconnect.
Because COM port redirectors emulate COM ports on the operating system abstraction level, rather than hardware serial ports, old software which is not written to utilize the operating system, but instead interface directly with a serial microcontroller (hardware ports 0x3F8 to 0x3FF for COM1, for example) will not function with COM port redirectors.
Variants[edit]
Specialized types of redirectors have been offered to meet the needs of certain applications.
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A redirector may support back-to-back operation, in which two computers run copies of the redirector and an outbound connection from one results in an inbound connection to the other. In effect, this technique creates a serial communications tunnel through a network connection. In practice, this configuration works only for certain applications but offers potentially lower costs and higher performance using the Internet to carry serial communications instead of modems between two computers.[citation needed]
A redirector may include a modem emulator that allows the application to use 'AT' modem commands even though no physical modem is present. The 'number' dialed is an IP address, and the connection is a TCP network connection instead of a modem telephone call. This type of redirector is generally used by applications in originating client software needs to use a modem but the destination for the connection is a network endpoint. Back-to-back operation of this type of redirector can, in some cases, function as a replacement for modems on two computers for some applications. Network effects on timing of the data stream generally preclude the use of this method for transmitting faxes. Additionally, this method is also not reliable if used for PPP connections (such as dial-up networking) due to architectural limitations of TCP, a topic discussed in technical literature related to TCP-over-TCP.
Virtual serial port[edit]
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One variant of a COM port redirector is a virtual serial port. A virtual serial port is a redirector without network software support which is usually used to create a pair of back-to-back virtual COM ports on the same computer. Two legacy applications can then communicate using virtual serial ports instead of conventional inter-process communication mechanisms such as named pipes.
Virtual.com Port
This type of software is capable of emulating all serial port functionality, including Baud rate, data bits, parity bits, stop bits, etc. Additionally, it allows the data flow to be controlled, emulating all signal lines (DTR / DSR / CTS / RTS / DCD / RI) and customizing pinout.
Serial port emulation[edit]
- Serial port emulation is useful especially when there is a lack of available physical serial ports. Communication between software and/or devices which would otherwise require extra physical connections, can be benefited by using a virtual COM Port emulator.
- Virtual serial ports let you send or receive data over a TCP/IP port using any serial communication program. This facility allows creating a full-fledged client-server architecture which provides multiple connections and data sharing possibilities between different applications. Such a connection is the best way to allow use of rare and expensive serial devices by different users simultaneously.
- Using serial port emulation one can split a real COM port between a number of virtual serial ports. This makes it possible to supply data from a single serial device to a number of different applications. Such necessity arises when several applications compete for a single GPS connection and the user must close one program to allow another to access a single GPS device.
- A virtual serial port may have the same name as physical one. This facility allows real serial port overlapping (mapping) and receiving data from a physical port through virtual port. In other words, you can map any serial port or virtual port to any other existing port in your system. In this case applications will work with virtual ports, but, in fact, they will receive data from overlapped real ports.
Specification[edit]
- RFC 854 - Telnet protocol specification
- RFC 2217 - Telnet Com Port Control Option
See also[edit]
References[edit]
SerialToIP - open source Terminal Server software
Further reading[edit]
- Serial Port Complete: COM Ports, USB Virtual COM Ports, and Ports for Embedded Systems; 2nd Edition; Jan Axelson; Lakeview Research; 380 pages; 2007; ISBN978-1-931-44806-2.
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