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The way Ethernet works, AFAK, is that if a packet doesn't make it
thru because of congestion or whatever, the sender "backs off" a certain
time delay and resends. The back-off time is increased again if there
is another failure. Repeat as necessary. (I don't have my IP book
handy).
Then again, it could be that the data is broadcast from the sender as
a "datagram", in which case the sender doesn't give a hoot whether it
is received or not ... Best check with the data provider.
Cheers,
Rob Lake
rbl@xxxxxxxxxx
>
> I don't know if the cable modem has a buffer or not - the modem may depend
> upon the ethernet card being as fast as or faster than the modem.
>
> Keep in mind that there are three main components here: the hardware (modem
> & ethernet card), the TCP/IP software, and the application (TradeStation).
> The TCP/IP process obviously has some degree of buffering because it must be
> able to collect all the packets, which may arrive out of order, which
> constitute a "message" and rearrange them into proper order before passing
> the assembled message (not the constituent packets) on to its application.
> TCP/IP does detect missing packets and request resending, but I doubt if the
> application is aware of this.
>
> Also, it is possible that none of the above is applicable in the case of the
> so-called "push" technique in which the server initiates the transmission
> rather than responding to a request from a client. Perhaps someone on the
> list who is knowledgeable about Internet Protocol could enlighten us.
>
> Carroll Slemaker
>
>
> -----Original Message-----
> From: Gerrit Jacobsen <jrt@xxxxxxxxxx>
> To: Carroll Slemaker <cslemaker1@xxxxxxxx>; omega-list@xxxxxxxxxx
> <omega-list@xxxxxxxxxx>
> Date: Sunday, May 23, 1999 7:47 AM
> Subject: Re: PS2k SP2 Update, Tick Counts and Rant
>
>
> > Cable modems connect directly to an ethernet card and do not need a
> > serial port. No serial port that I know of could handle the 10MbPS
> > or better speed of a cable modem!
>
> Brilliant. This brings up another crucial question with IP delivery.
>
> I would be interested to learn whether these cable modems buffer
> data and how data is buffered by the internal drivers since TS cannot
> work the data at 10Mbps.
>
> Furthermore if the data gets through it is hanging in some internal
> IP queue on the IP socket. It seems to happen often that IP queues
> overflow and simply do not accept more packets when they are full and
> the packets are dropped. This could be even more crucial with TS
> since the data has to be stored in the database and to be dispatched
> to the charting application which takes time.
>
> Is there some mechanism that re-requests packets from the tick data
> server if they are lost or is this happening undetected and the data
> ticks are just lost ?
>
> Gerrit
>
>
>
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