iMportant parametres to be known

Maximum Transmission Unit (MTU) This is the default packet size that Windows uses to negotiate with. When a connection is opened between two computers, they must agree on an MTU. This is done by comparing MTUs and selecting the smaller of the two. If the MTU is set too large for routers that are between the computers, these routers then fragment this information into a packet size that the router can handle. This fragmentation can double the amount of time it takes to send a single packet. Windows has a built-in MTU Discovery that will adjust for this by sending out a packet that is marked as "Not Fragmentable". Then the router sends back an error to the computer saying that the packet was too large, and Windows then lowers the MTU until there are no more errors. If your ISP uses an MTU of 576, then every time you start a connection, Windows must adjust down to this value. Even though Windows automatically adjusts the packet size, it still takes it time to negotiate an acceptable MTU. By setting this value manually, you greatly reduce the amount of work that Windows must do to negotiate. Maximum Segment Size (MSS) Maximum Segment Size defines the largest segment of data that the TCP stack is prepared to receive. When a connection is established, the two ends agree to use the smaller of each end's value. MSS is generally 40 bytes less than Maximum Transmission Unit, because 40 bytes are used for the TCP and IP headers. TCP Receive Window Size (RWIN) The TCP Receive Window Size is the amount of receive data (in bytes) that can be buffered at one time on a connection. The sending host can send only that amount of data before waiting for an acknowledgment and window update from the receiving host. A value that's too large will result in greater loss of data if packets are lost or damaged, and a value that's too small will slow down data transfer considerably, as each packet will have to be acknowledged before the next packet is sent. Matching the receive window to even increments of the MSS increases the percentage of full-sized TCP segments utilized during bulk data transmission. Time To Live (TTL) This parameter specifies the default Time To Live (TTL) value that is set in the header of outgoing IP packets. The TTL determines the maximum time that an IP packet can live in the network without reaching its destination. It is effectively a limit on the number of routers an IP packet can pass through before it is discarded. Keep Alive Time Specifies how often to send session keepalive packets on active sessions. This will keep connections that have stalled during a particular download session from timing out. The minimum is 1 minute (60000 ms). Recommended setting is 10 minutes (600000 ms). Path MTU - Enable Black Hole Detect This specifies whether the stack will attempt to detect Maximum Transmission Unit (MTU) routers that do not send back ICMP fragmentation-needed messages. ICMP (Internet Control Message Protocol) is defined in STD5, RFC 792. With this feature enabled, TCP will try to send segments without the Don't Fragment bit set if several re-transmissions of a segment go unacknowledged. If the segment is acknowledged as a result, the MTU will be decreased and the Don't Fragment bit will be set in future packets on the connection. Enabling black hole detection increases the maximum number of re-transmissions performed for a given segment. Setting this parameter when it is not needed can cause performance degradation. However, if the router is not sending back the ICMP messages, then PMTU Discovery will not work. This can cause an even greater loss of performance. PMTU Black Hole Detect is recommended to be disabled. Path MTU - Enable Auto Discovery Enabling this setting causes TCP to attempt to discover the Maximum Transmission Unit (MTU or largest packet size) over the path to a remote host. By discovering the Path MTU and limiting TCP segments to this size, TCP is supposed to be able to eliminate fragmentation at routers along the path that connect networks with different MTUs. This requires implementation of the corresponding server side algorithm, however, and presupposes all of the servers on the entire Internet only running MSFT server software with server-side optimization features accessible from MSFT web-browser client software. Needless to say, this is rather unlikely. Nevertheless, it is not recommended to disable this setting as it would then cause an MTU of 576 bytes to be used for all connections that are not to machines on the local subnet. Disabling this setting can cause severe performance degradation because fragmentation may not be compensated for. PMTU Auto Discovery is recommended to be enabled.

Enable Selective Acknowledgements (SACK) This parameter controls whether or not Selective Acknowledgment (SACK) support, as specified in RFC 2018, is enabled. Selective Acknowledgement (SACK) is an optimizing feature that lets you acknowledge receipt of individual blocks of data in a continuous sequence, rather than just the last sequence number. The recipient can tell the sender that one or more data blocks are missing from the middle of a sequence, and the sender can retransmit only the missing data. Max Duplicate ACKs This parameter determines the number of duplicate ACKs that must be received for the same sequence number of sent data before fast retransmit is triggered to resend the segment that has been dropped in transit. TCP Window Scaling (RFC 1323) Receive window scaling permits TCP to negotiate a scaling factor for the TCP receive window size, allowing the use of a very large TCP receive window size (RWIN). This option must be enabled in order to use a receive window size (RWIN) larger than 64 KB. Timestamps (RFC 1323) Timestamps help TCP to measuring round trip time (RTT) accurately in order to adjust retransmission timeouts. The Timestamps option provides two four-byte timestamp fields in the TCP header, one to record the time the initial transmission is sent and one to record the time on the remote host. Since this option increases packed header overhead and don't provide much of an improvement, it is recommended to be disabled. This option is specified in RFC 1323. Session Keep Alive This value determines the time interval between keepalive transmissions on a session. Recommended value is 60000 ms (10 minutes). Internet Explorer: MaxConnectionsPerServer This value limits the number of concurrent connections to a web server. Quality and Type Of Service : DisableUserTOSSetting This parameter can be used to allow programs to manipulate the Type Of Service (TOS) bits in the header of outgoing IP packets. LAN Settings : LAN Request Buffer Size This parameter can be used to reduce local area network delays. LAN Settings : Increase LAN Browsing Speed This option disables the network task scheduler leading to faster browsing of network folders. Host Resolution Priority This option group allows settings the priority level for LocalPriority (local names cache), HostsPriority (the hosts file), DnsPriority (DNS) and NetbtPriority (NetBT name resolution, WINS). NetBIOS over TCP/IP: BcastNameQueryCount This value determines the number of times NetBT broadcasts a query for a particular name without receiving a response. NetBIOS over TCP/IP: BcastQueryTimeout This value determines the time interval between successive broadcast name queries for the same name. NetBIOS over TCP/IP: CacheTimeout This value determines the time interval (in miliseconds) that names are cached for in the remote name table. DNS Cache Parameters MaxNegativeCacheTTL limits the negative DNS query answer cache time. NegativeSOACacheTime limits the negative answer to SOA DNS query cache time. NetFailureCacheTime value determines the time to stop sending DNS queries if no answer is received.