(figure 2), it pulls open a trap door, which causes the arriving packet to be dropped and stops its water from entering the bucket; in shaping (figure 3), it pushes up a flap, which delays the arriving packet and prevents it from delivering its water, until the water level in the bucket falls below τ. The difference between the descriptions given by Turner and the ITU-T/ATM Forum is that Turner's is specific to traffic policing, whereas the ITU-T/ATM Forum is applicable to both traffic policing and traffic shaping. Also, Turner does not state that the contents of the counter should only be affected by conforming packets, and should only be incremented when this would not cause it to exceed a limit, i.e. Turner does not explicitly state that the bucket's capacity or counter's maximum value is finite. To make Turner's description clearly aligned with ITU-T, the statement "If the counter exceeds a threshold upon being incremented, the network discards the packet" would have to be changed to something like "If the counter would exceed a threshold [equivalent to the bucket depth, T + τ, in the ITU-T description] upon being incremented, the network discards the packet and the counter is not incremented", i.e. it is only incremented when it is less than or equal to the limit value, τ, or at least T less than the bucket depth in the ITU-T description. While the description given by Turner does not state that the counter should only be affected by conforming packets, it is given in terms of a traffic policing function, where overzealousness in limiting a connection containing nonconforming packets may not be an issue. Indeed, in some contexts, such as variable bitrate (VBR) transmissions, the loss of any one packet may corrupt the entirety of a higher layer message, e.g. an OSI Network Layer PDU. In which case, discarding all the following packets of that corrupted PDU sheds an unnecessary network load. However, it would be entirely unacceptable in traffic shaping for a packet that fails the conformance test to affect how long before conformance can next occur, i.e. if the act of testing a subsequent packet for conformance would change how long a packet currently waiting to conform has to wait. This is exactly what would happen if the water from nonconforming packets were to be added to the bucket, as any subsequent nonconforming packets would raise the