ZyXEL Communications Prestige 941 Información técnica descargar pdf (Pagina 7)

Navas Cable Modem/DSL Tuning Guide http://cable-dsl.home.att.net/

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(1) downlink speed (see "How to check your connection speed") and (2) latency:

Minimum TCP Receive Window Needed

Downlink speed in kilobits per second

500 1000 1500 2000 2500

Latency

(end to end)

as measured

by 'ping' in

milliseconds

50 2K 5K 7K 10K 12K

100 5K 10K 15K 20K 24K

150 7K 15K 22K 29K 37K

200 10K 20K 29K 39K 49K

250 12K 24K 37K 49K 61K

Windows 95/98/NT default 8K

Windows Me/2000/XP default 16K

Navas recommended setting 32-63K

This TCP Receive Window tweak is needed because Windows 95/98/Me/NT/2000/XP do not do a proper

job of automatically adjusting the TCP Receive Window size to accommodate different network speeds

and latencies. (Other operating systems may do a better job and not need this kind of tweaking; in this

author's tests, for example, Red Hat Linux 6.0 performed as well without tweaking as Windows 98 with

tweaking, even though Linux was running on much slower hardware.)

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Dealing with latency, packet loss, and/or upload speed

Latency and packet loss can be measured with the 'ping' command. Open a Command window and type

"ping remotesite" where remotesite is the domain name or IP address of the remote server (e.g., "ping

www.yahoo.com"). For more information, see "How to find out what's slowing you down".

Latency

In basic terms, latency is the time needed for a round trip over the Internet between two points (e.g., your

computer and remote host). Latency is usually not a problem with a proper TCP Receive Window (see

"Why TCP Receive Window matters"), but high latency can adversely affect interactive applications such

as on-line real-time gaming. High latency is usually caused by Internet routing and/or congestion issues.

There's usually not much you can do about such issues other than complaining or even switching service

providers. However, if your latency is is higher due to "interleaved mode" then it may be possible to get

some improvement. See "What is 'Interleaved Mode?'"

Packet Loss

Data is transmitted over the Internet in blocks known as packets. Packets usually reach their destination,

but may be lost due to such things as network congestion. When a packet is lost, it takes a significant

amount of time for: the receiver to notice that a packet has been lost; the receiver to notify the sender to

resend the lost packet; and packet(s) to be retransmitted. Ideally zero, packet loss should be less than 1%;

packet loss over 5% is generally considered severe. There's usually not much you can do about packet loss

other than complaining or even switching service providers. There is no adjustment that you can use to

decrease packet loss. However, if you are suffering from packet loss, the adverse effects may be reduced

by decreasing the TCP Receive Window. See "Why TCP Receive Window matters".

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