Re: Sliding windows on XP and 2K don't???

From: Steve Alpert (sra_at_newsgroups.nospam)
Date: 07/14/04 

Date: Wed, 14 Jul 2004 12:14:25 -0400

Chris P. [MVP] wrote:
> Steve Alpert wrote:
>
>>We've been trying to speed up an application and have looked at a few
>>sniffs and have found that when we're talking to a host (apparently
>>with Nagle enabled), Windows XP will not transmit a second packet
>>until a first packet has been ack'ed! We send a packet of about 30
>>bytes followed almost immediately by a send of another packet of
>>about 300 bytes and the second always waits until the server has
>>ack'ed the first one? How come?
>>
>>These packet sizes are certainly small enough that the sliding window
>>should come into play.
>
>
> This is TCP, so don't think in terms of packets, it's a stream. At the
> lowest level things are transmitted as packets obviously, and in your case
> with Nagle turned on these two sends would get sent out as a single packet.
>
>
but the real issue is (regardless of Nagle) that on NT, Win2K, and XP
that we've tested, a second packet is not transmitted until the remote
machine ACKs the first one. The TCP wire protocol suggests that the
transmitter is allowed to send data up to the limit of the tcp sliding
window size without receiving a prior ACK but that doesn't seem to
happen! As soon as the ACK is received (about 40 mSec later), the
wintel box seems quite willing to send the next packet almost
instantaneously.

/steveA 

-- 
Steve Alpert
my email Fgrir_Nycreg @ vqk.pbz is encrypted with ROT13 (www.rot13.org) 
and spaces

Relevant Pages

  • Re: Bandwidth
    ... >They communicte using TCP sockets ... you might have to add in the transmit time. ... Processing in the TCP stack takes time. ... the packet by air courier from Dallas to Houston. ...
    (comp.unix.programmer)
  • Inter-thread communications
    ... The read thread must input the packet, ... It must also forward any ACK or NAK received to the transmit ... There is no chance of an ACK or NAK embedded in the packet, ...
    (perl.beginners)
  • =?UTF-8?Q?problem=20with=20OWN=20bit=20when=20writting=20driver=20?= =?UTF-8?Q?for=20rtl8139
    ... For several weeks I have been writing kernel driver for network card based on ... there is a bit in Transmit Status Descriptor of RTL8139c which after clearing(It must be cleared to ... /**function called by kernel when kernel wat to transmit packet which is ... unsigned int physical_addr_len; ...
    (Linux-Kernel)
  • Serial ISDN to VMS system
    ... DS700-16 which is partial modem control. ... I fell over a description of the Circuit Timer parameter on the ... not up to the "transmit" size. ... I believe that a PPP packet ...
    (comp.os.vms)
  • help required on writing Network device driver
    ... In the transmit side the device the device has transmit FIFO OF SIZE ... pending queue descriptor is linked list of one or more transmit packet ... As the hdlc controller processes transmit pending queue descriptor ...
    (freebsd-hackers)