Tcpwindowsize
Use the tcpwindowsize option to specify, in kilobytes, the size you want to use for the TCP/IP sliding window for your client node.
The sending host cannot send more data until it receives an acknowledgment and a TCP receive window update. Each TCP packet contains the advertised TCP receive window on the connection. A larger window allows the sender to continue sending data and can improve communication performance.
Supported Clients
This option is valid for all clients.
Options File
Place this option in the client
system-options file (dsm.sys) within a server stanza. You can set this option on the Communication tab, Window Size field of the Preferences
editor.
Place this option in the client
options file (dsm.opt). You can set this option on the Communication tab, Window Size field of the Preferences editor.
Parameters
- window_size
- Specifies the size, in kilobytes, to use for your client node TCP/IP sliding window. The range
of values is 0 through 2048. A value of 0 allows the client to use the operating system default TCP
window size. Values from 1 to 2048 indicate that the window size is in the range of 1KB to 2MB.
If you specify a value less than 1, the
TCP window size defaults to 1. If you specify a value greater than 2048, the TCP window size
defaults to 2048.
- For backup-archive clients, the default value for this parameter is 63 KB.
- For IBM Spectrum Protect™ for Virtual Environments: Data Protection for
VMware, the
default value for this parameter is 512 KB.
- Notes:
- The TCP window acts as a buffer on the network. It is not related to the tcpbuffsize option, or to the send and receive buffers allocated in client or server memory.
- A window size larger than the buffer space on the network adapter might degrade throughput due to resending packets that were lost on the adapter.
- Depending on the operating system communication settings, your system might not accept all values in the range of values.
- The tcpwindowsize option overrides the operating system's default TCP/IP session send and receive window sizes.
- window_size
- Specifies the size, in kilobytes, to use for your client node TCP/IP sliding window. The range
of values is 0 through 2048. A value of 0 allows the client to use the operating system default TCP
window size. Values from 1 to 2048 indicate that the window size is in the range of 1KB to 2MB. If
you specify a value less than 1, the TCP window size defaults to 1. If you specify a value greater
than 2048, the TCP window size defaults to 2048.
- For backup-archive clients, the default value for this parameter is 63 KB.
- For IBM Spectrum Protect for Virtual Environments: Data Protection for
VMware, the
default value for this parameter is 512 KB.
- Notes:
- The TCP window acts as a buffer on the network. It is not related to the tcpbuffsize option, or to the send and receive buffers allocated in client or server memory.
- A window size larger than the buffer space on the network adapter might degrade throughput due to resending packets that were lost on the adapter.
- Depending on the operating system communication settings, your system might not accept all values in the range of values.
- The tcpwindowsize option overrides the operating system's default TCP/IP session send and receive window sizes.
- Windows provides a larger TCP receive window size when communicating with hosts that also provide this support, known as RFC1323. In these environments, a value greater than 63 can be useful.
Examples
- Options file:
- tcpwindowsize 63
- Command line:
- -tcpw=63
This option is valid only on the initial command line. It is not valid in interactive mode.