IE5.5 TCP ACK Bug @ end of file transfers

[Mark James]

Hi,

I've found a bug in the IE5.5(SP1) browser that manifests
when more than one file is being downloaded simultaneously.
(It is possible that the problem is more general and happens
whenever more than one simultaneous TCP connection is established.)

When download of one file completes, download of the other
file can halt until a TCP timeout restarts transmission.
This is because no TCP ACK is sent for the first packet
received on the uncompleted download after the other
download completes. If the uncompleted connection
has a high retransmission timeout value (due to the
end-to-end flow being slow, congested, or maxi-hop),
the uncompleted download can hang for a minute or more
before a TCP timeout restarts the flow. In other
circumstances the hang is short enough to be difficult
to spot, but I've had hangs of two minutes or more.

By the way, this is on Windows98; and no, this doesn't
happen with Netscape6 downloads, so the problem is
likely to be in IE rather than the TCP stack.

I'd appreciate it if someone could reproduce and
verify the problem on their system. I'll see if
the soon to be released IE6 behaves any differently.

Thanks -- Mark

[Mark James]

Mark James wrote:

> I've found a bug in the IE5.5(SP1) browser that manifests
> when more than one file is being downloaded simultaneously.
> (It is possible that the problem is more general and happens
> whenever more than one simultaneous TCP connection is established.)

> ...

> I'd appreciate it if someone could reproduce and
> verify the problem on their system. I'll see if
> the soon to be released IE6 behaves any differently.

IE6 has the same problem.