The IRM (internal resource manager) calculates only the IP bandwidth required to transport the media payload. It does not take in consideration the overhead added by the Layer 2 (L2) transport protocol, for example, Ethernet, ATM, Frame Relay, and so on. The IRM considers the transport of UDP media packets over Internet Protocol version 4 (IPv4) or IPv6. When IPv6 is present, the IRM is able to consider the additional overhead for the IPv6 header when performing bandwidth calculations.
The IRM does not consider multicast SDP sessions. Nor does it consider any mechanisms that reduce the overhead of IP, UDP and RTP headers, such as RTP header compression, which may be present in the network.
A voice call requires two unidirectional RTP channels. The IRM assumes that the bandwidth required by both channels is always the same, that is, the audio streams are always symmetric.
The IRM does not take silence suppression into consideration for bandwidth calculation.
Unknown static and dynamic payload types are treated, by default, as a 64 kbps codec with a packetization interval of 20 ms. However, both the bit rate and packetization interval for these “unknown” payload types is configurable.
The IRM provides an overload protection mechanism in case of high-traffic volume.
The IRM switches into overload mode when its internal queue of requests reaches a high-threshold limit. In this mode, new call requests are rejected and an alarm will be generated. The IRM switches back to normal mode when the internal request queue depth reaches a low-threshold.
Parent topic: CAC (Call Admission Control)