1492 or 1480 question

[lacrosnu123]

I have pppoe with windows xp does one mtu value have more advantages over the other? 1492 and 1480.

[YARDofSTUF]

ya 1492 offers best results for dsl, 1480 doesnt :)

Short for Maximum Transmission Unit, the largest physical packet size, measured in bytes, that a network can transmit. Any messages larger than the MTU are divided into smaller packets before being sent.

Every network has a different MTU, which is set by the network administrator. On Windows 95, you can also set the MTU of your machine. This defines the maximum size of the packets sent from your computer onto the network. Ideally, you want the MTU to be the same as the smallest MTU of all the networks between your machine and a message's final destination. Otherwise, if your messages are larger than one of the intervening MTUs, they will get broken up (fragmented), which slows down transmission speeds.

http://www.webopedia.com/TERM/M/MTU.html

[buster1967]

ive used the TCPOptimizer and restarted the pc but its defaulting to a MTU = 1500.can you help me please to get the best settings for my connection.im using xp prp adsl 2000/256 pppoe


TCP options string = 020405b401010402
MTU = 1500
MTU is fully optimized for broadband.
MSS = 1460
Maximum useful data in each packet = 1460, which equals MSS.
Default Receive Window (RWIN) = 64240
RWIN Scaling (RFC1323) = 0 bits
Unscaled Receive Window = 64240

RWIN is a multiple of MSS
Other values for RWIN that might work well with your current MTU/MSS:
513920 (MSS x 44 * scale factor of 8)
256960 (MSS x 44 * scale factor of 4)
128480 (MSS x 44 * scale factor of 2)
bandwidth * delay product (Note this is not a speed test):

Your RcvWindow limits you to: 2569.6 kbps (321.2 KBytes/s) @ 200ms
Your RcvWindow limits you to: 1027.84 kbps (128.48 KBytes/s) @ 500ms
MTU Discovery (RFC1191) = ON
Time to live left = 125 hops

TTL value is ok.
Timestamps (RFC1323) = OFF
Selective Acknowledgements (RFC2018) = ON
IP type of service field (RFC1349) = 00000000

[Andrzej]

:D 1492 bits
is default MTU value for protocols : PPPoE and or PPPoA
(for both direction transfers ISP to customers)

1480 bits
is default MTU value for native client PPPoE in wXP
(one can ask MS why)

importance of above 12 bits is increased with connection's speed
~0,8% from total data stream (12/1492=0,0080428954423592493297587131367292)
so only connection faster than 10 MBps
and with good the Internet weather
can be noted as differentiation in speed test results
(10000*0,008=80kbps)

BTW also 'Time Stamp' option is 12 bits worth (from MSS size 'useful data')
so one can compare MTU=1492 speed result with 'Time Stamp' on vs. off
OTOH mentioned TS is much more important in same connections
e.g. for retransmissions