Specifications

Network Configuration Concepts
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into the Expedited Forwarding class with DSCP value 46. Note also that a number of access
Layer 2 switches can overwrite the DSCP value based on the incoming Layer 2 priority
information. Ensure that such ports use a consistent DSCP value, in this case 46.
With a Layer 3 device, such as a router, the packet-per-second (PPS) throughput is also
important. An IP phone with a packet rate of 20 ms means that the phone sends 50 packets
per second and also receives 50 packets per second. Be aware of how vendors specify the
PPS rating. For example, with two phones connected to a router, each port sends and receives
50 PPS—that is, 100 PPS per port, requiring that 200 PPS be handled. However, between the
phones, only 50 PPS goes one way and 50 PPS in the return direction. Throughput is 100 PPS.
In the following figure, the router has a port handling capacity of 15,000 PPS. Throughput is
half this number; i.e. 7500PPS.
Figure 34: Packet-per-second throughput example