RGMII,SGMII,XAUI

MII   - Media Independent Interface - 100 Mbps
GMII  - Gigabit MII - 1 Gbps (24 pins) (8TX - 8RX)
RGMII - Reduced GMII - 1 Gbps (12 pins) (4TX - 4RX)
SGMII - Serial GMII - 1 Gbps (8 pins) (2TX - 2RX)
XAUI  - XGMII Extender - 10 Gbps (XY pins) (8TX - 8RX)
SPI-4.2 - System Packet Interface Level 4, Phase 2 (16TX - 16RX)

The Media Independent Interface (MII) is a standard interface used to connect a Fast Ethernet (i.e. 100Mb/s) MAC-block to a PHY. The MII may connect to an external transceiver device via a pluggable connector or simply connect two chips on the same printed circuit board. Being media independent means that any of several different types of PHY devices can be used without redesigning or replacing the MAC hardware.

Gigabit Media Independent Interface (GMII) is an interface between the Media Access Control (MAC) device and the physical layer (PHY). The interface defines speeds up to 1000 Mbit/s, implemented using an eight bit data interface clocked at 125 MHz, and is backwards compatible with the Media Independent Interface (MII) specification.

Reduced Gigabit Media Independent Interface (RGMII) specifies a particular interface between an Ethernet MAC and PHY. RGMII uses half the number of pins as used in the GMII interface. This reduction is achieved by clocking data on both the rising and falling edges of the clock, and by eliminating non-essential signals (carrier-sense and collision-indication). Thus RGMII consists only of: RXC, RD[3:0], RX_CTL, TXC, TXD[3:0], and TX_CTL (12 pins, as opposed to GMII's 24).

The Serial Gigabit Media Independent Interface (SGMII) is a sequel of MII, a standard interface used to connect an Ethernet MAC-block to a PHY. It differs from GMII by its low-power and low pin count serial interface (commonly referred to as a SerDes).

XAUI is a standard for extending the XGMII (10 Gigabit Media Independent Interface) between the MAC and PHY layer of 10 Gigabit Ethernet (10GbE). XAUI is pronounced "zowie", a concatenation of the Roman numeral X, meaning ten, and the initials of "Attachment Unit Interface".

Reference:
http://uiway.blogspot.sg/2009/03/rgmiisgmiixaui.html
http://www.altera.com/technology/high_speed/protocols/spi_42/pro-spi_4.2.html

automatic proxy configuration for your pc

A proxy auto-config (PAC) file contains a JavaScript function "indProxyForURL(url, host)". This function returns a string with one or more access method specifications.

The URL of the PAC file is either configured manually or determined automatically by the Web Proxy Autodiscovery Protocol.

A very simple example of a PAC file is:

function FindProxyForURL(url, host)
{
   return "PROXY proxy.example.com:8080; DIRECT";
}

The Web Proxy Auto-Discovery Protocol (WPAD) is a method used by clients to locate a URL of a configuration file using DHCP and/or DNS discovery.

Before fetching its first page,
- a web browser sends the local DHCP server a DHCPINFORM query, and uses the URL from the WPAD option in the server's reply. [option 252 ("auto-proxy-config")]
- If the DHCP server does not provide the desired information, DNS is used. [A Web server must be configured to serve the WPAD file with a MIME type of "application/x-ns-proxy-autoconfig"]

c:\> nslookup wpad
On success check for "http://wpad/wpad.dat"

Reference:
http://en.wikipedia.org/wiki/Proxy_auto-config
http://en.wikipedia.org/wiki/Web_Proxy_Autodiscovery_Protocol

802.11n deployment strategie

To achieve maximum output, a pure 802.11n 5 GHz network is recommended. The 5 GHz band has substantial capacity due to many non-overlapping radio channels and less radio interference as compared to the 2.4 GHz band. An 802.11n-only network may be impractical for many users because they need to support legacy equipment that still is 802.11b/g only. Consequently, it may be more practical in the short term to operate a mixed 802.11b/g/n network until 802.11n hardware becomes more prevalent.

In a mixed-mode system, an optimal solution would be to use a dual-radio access point and place the 802.11b/g traffic on the 2.4 GHz radio and the 802.11n traffic on the 5 GHz radio. This setup assumes that all the 802.11n clients are 5 GHz capable. A technique called "band steering" is used to send 802.11n clients to the 5 GHz band, leaving the 2.4 GHz band for legacy clients. Band steering works by responding only to 5 GHz association requests and not the 2.4 GHz requests from dual-band clients.

802.11n protection mechanisms kick in as soon as an access point hears a legacy device transmitting on the same channel. The legacy device does not have to be associated to the 802.11n access point; the access point just needs to hear it on the same channel. 802.11n standardized support for increased data rate, short guard interval (800us to 400us), 40 MHz channels etc...

MIMO techniques:
- Spatial Multiplexing - this requires MIMO client capable of receiving and de-multiplexing N spatial streams. a 3x3:2 MIMO access point can transmit and receive 2 data streams on its 3 antennas.
- Maximal Ratio Combining (MRC) - MRC is a receive-side MIMO technique that takes RF signals from multiple receive antennas and combines them within the radio to effectively boost the signal strength.
- Transmit Beamforming (TxBF) - focus RF energy toward the target receiver (only supported for 802.11n clients). client send special frequency characteristics and channel response information to the access point. This information is used by the AP in calculating the phase adjustment for its next transmission.

Frame Aggregation Techniques:
- MSDU Aggregation (A-MSDU) - The maximum A-MSDU size allowed by 802.11n is 8192 bytes. The disadvantage of aggregating A-MSDU is that each frame is only protected by a single checksum and the overhead of having to retransmit the entire A-MSDU again.
- MPDU Aggregation with Block ACKs - MPDU (MAC Protocol Data Unit) aggregation gathers 802.11 frames, which each already have an 802.11 header for the same destination and transmits them as a single frame. One of the disadvantages of MPDU aggregation is that each 802.11 frame needs to be encrypted separately, adding encryption overhead.
- Reduced Interframe Spacing (RIFS)

Reference:
http://en.wikipedia.org/wiki/IEEE_802.11n-2009#Deployment_strategies
http://mcsindex.com/
http://www.motorola.com/web/Business/_Documents/White%20Paper/_Static%20files/802%2011nDEM_WP_v4_0209.pdf