Windows sdk pgm Article 3 PGM sender options

PGM sender options

PGM senders are provided with certain default settings that affect the performance of data transmission, and how long data is buffered to account for packet loss and associated PGM client retransmission requests. the following paragraphs describe these default settings.

Window Size and transmission rate

The capability to set window size and transmission rate enables applications to control the amount of data the transport buffers for retransmission, and the rate at which the byte-stream is transmitted.

Retransmission data is stored in a file, therefore the maximum window size is limited by disk space usable by the transport. the default window size is 10 MB. although it is possible for a send or message size to exceed the window or buffer size, the data stream remain uninterrupted; The send is pended until the all the data has been sent out.

NoteThe maximum buffer space is limited by the maximum number of packets that can be held in the window at any given time, which is equal to 2 ^ 31-1.

The transmission rate is the combined outflow of original data packets (odata), retransmitted data packets (RDATA) and transport-specific bookkeeping packets (spms), expressed per second. if the rate limit is set to 56 kilobits per sec by default. the default window size is 10 megabytes, with a default rate of 56 kilobits per second. due to the relationship between the three members ofRm_send_windowStructure, the default window size is therefore 1428 seconds. SeeRm_send_windowFor more information.

Window advance rate

The window advance rate is set byRm_sender_window_adv_rateSocket option. this option enables applications to specify the increment at which the PGM sender's window is advanced, expressed as a non-zero percentage value of the window size. the default value is 15%, and the maximum rate is 50%. if the PGM sender has repair data pending that falls in the space of the increment window, the window is advanced partially as each repair packet in the window is sent out.

Forward Error Correction (FEC)

Forward error correction is set through use of the rm_use_fec socket option. this socket option enables the PGM sender to send repair packets as parity packets instead of regular data packets. doing so minimizes the number of repair packets sent to repair different sequences lost by multiple receivers from within the same data group. enabling FEC is only set on the PGM sender. PGM receivers automatically follow the policy set by the sender. for a detailed discussion on FEC, refer to the pgm rfc located onIETFWebsite.

PGMSending options

PGMThe default setting of the sender can affect the data transmission performance, the cache time for packet loss retransmission, And the retransmission request of the relevant client. The following sections describe3Default options.

Window Size and transmission rate

ApplicationProgramYou can set the window size and transmission rate to control the cache size and data transmission rate for the re-transmission.

The retransmitted data is stored in a file, so the maximum size of the window is limited to the maximum disk space available for transmission. The default window size is10 MB. Although it is possible to send packets larger than the window size, the data stream will not be interrupted; the sender will suspend until all data is sent.

Note: at any time, the maximum number of packages that the cached space can accommodate in the window is equal2 ^ 31-1.

Raw data packets transmitted per second (Odata), Re-transmits the data packet (RDATA) AndTransport-specific bookkeeping packets (spms)Combined transmission rate. If the rate limit is set56kb/Seconds. The default window size is1000x1000x10Bytes (approximately10 m), And the default transmission rate is56kb/Seconds. BecauseRm_send_windowThere is a relationship between the three parameters of the structure, and the calculated default window data cache time is about1428Seconds. ViewRm_send_windowTo understand the relationship between the three parameters.

Window advanced rate

Window advanced rate passedRm_sender_window_adv_rateSocketOption. This option allows the application to specifyPGMThe pre-growth mode of the sending window, which is a non-zero proportional value of the window size. The default value is15%, The maximum proportion cannot be set to exceed50%. IfPGMThe sender fixes the loss of suspended data packets within the increasing window size range,If the PGM sender has repair data pending that falls in the space of the increment window, the window is advanced partially as each repair packet in the window is sent out.

Forward Error Correction (FEC)

Forward Error Correction passedRm_use_fec socketOption. This option allowsPGMThe sender sends the remedial data packet just like a normal data packet.Doing so minimizes the number of repair packets sent to repair different sequences lost by multiple receivers from within the same data group.FECOnlyPGMSender settings.PGMAutomatically used by recipientPGMPolicy of the sender. Need to know aboutFECFor more information, seeIETFWebsitePGM RFC.

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