ng. EIR (excess information rate). The EIR bandwidth is considered "excess" and it improves the network's goodput. The excess traffic is dropped at congestion nodes in the network. CBS/EBS (committed burst size/excess burst size, two parameters which are expressed in bytes). Typically, higher burst size gives better performance. Color mode. The carrier Ethernet can be "Color Aware" or "Color Blind." When set as "Color Aware" this parameter governs discard eligibility, with marking usually done at ingress network nodes. The defined colors are: Green: used for forwarded frames and CIR conforming traffic. Yellow: used to mark for discarding of eligible frames, which are over CIR but within the given EIR. Red: used for marking of discarded frames which exceed the given EIR. Coupling flag (it is set to either 1 or 0). This parameter governs which frames are classed as yellow. Bandwidth profiles are used to divide the available bandwidth per EVC over a single UNI. There are multiple services over the same port (at UNI), and CoS markings provide the possibility for the network to determine the required QoS. Overall, there are several phases in the development of Metro Ethernet (i.e. Carrier Ethernet) CoS. In CoS phase 1 the MEF specifies a three-CoS model and allows 4.4 QoS in Ethernet and Metro Ethernet for subsets and extensions. Also, it provides possibilities for interconnections of Carrier Ethernet networks with implementation of CoS models. In that manner priority code point/differentiated services code point (PCP/DSCP) values are used as part of the CoS ID. The PCP values are mandatory at ENNI (for the purposes of interconnection), while they are only optional at UNIs. The further CoS phases (e.g. phase 2 and phase 3) further extend and specify the QoS details via CoS performance objectives (CPOs). They also include new performance tiers. In general, the performance objectives apply to qualified frames in EVC or OVC. An Ethernet frame which arrives at an external interface (EI) may have different delay in cases w