http://en.wikipedia.org/wiki/IEEE_802.1Q

an example will read later.

cisco info

The two most commonly used QoS labels in the Layer 3 IP header are the IP precedence field and the DSCP field. The QoS label in the Layer 2 frame header is called Class of Service (CoS). Catalyst switch QoS tools can provide the preferential treatment based on either Layer 3 QoS labels or Layer 2 QoS labels.

MLS is Multilayer Switching.

mls qos trust device  = configure the port to trust a Cisco phone tagged packet. (COS or DSCP)

ToS/differentiated services code point (DSCP)

This apply the trust boundary up to the phone.

This is used for QoS config later, when you have to trust COS or DSCP flag in you LAN, and apply priority queuing or policy or shapping or whatever you dream to do

Type of Service (ToS), cisco info

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http://en.wikipedia.org/wiki/Asynchronous_Transfer_Mode

ATM operates as a channel-based transport layer, using virtual circuits (VCs). This is encompassed in the concept of the Virtual Paths (VP) and Virtual Channels. Every ATM cell has an 8- or 12-bit Virtual Path Identifier (VPI) and 16-bit Virtual Channel Identifier (VCI) pair defined in its header. The VCI, together with the VPI, is used to identify the next destination of a cell as it passes through a series of ATM switches on its way to its destination. The length of the VPI varies according to whether the cell is sent on the user-network interface (on the edge of the network), or if it is sent on the network-network interface (inside the network).

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