IPv4. In the table AMR mode 7 (12.2 kbps) has been used. If a different mode is used, refer to the AMR modes to get the bit rates. If the G.711 codec is used, then the Nb user plane does not introduce any header, while for the AMR a header of 3-4 bytes is added. Ethernet overhead bytes: 12 gap + 8 preamble + 14 header + 4 trailer = 38 bytes/packet w/o 802.10 12 gap + 8 preamble + 14 header + 4 trailer = 38 bytes/packet w/o 802. 1q Example 1. If the G.711 codec is used on top of the IPv4 backbone, then the data bit rate for one call is calculated as: Data bit rate (kbps) = 64 kbps + [20 bytes (IPv4) + 8 bytes (UDP) + 12 bytes (RTP)] X 8 bits/20 ms = 80 kbps If an Ethernet header is added, then Data bit rate (kbps) = 64 kbps + [42 bytes (Ethernet) + 20 bytes (IPv4) + 8 bytes (UDP) + 12 bytes (RTP) X 8 bits/20 ms = 96.8 kbps Example 2. If an AMR mode 7 (12.2 kbps) codec is used on top of an IPv4 backbone, then the data bit rate for one call is calculated as: Data bit rate (kbps) = 12.2 kbps + [20bytes (IPv4) + 8bytes (UDP) + 12bytes (RTP) +4 bytes(Nb-UP)) X 8 bits/20 ms = 29.8 kbps (approximately 30 kbps) 3GPP Release 4 Circuit Core Network Table 4.10 Data bit rates in the ATM backbone G.711 AMR VAD Nb-UP Bit rate [kbps] Cells/s If an Ethernet header is added, then Data bit rate (kbps) = 12.2 kbps + [42 bytes (Ethernet) + 20 bytes (IPv4) + 8 bytes (UDP) + 12 bytes (RTP) + 4 bytes(Nb-UP)] X 8 bits/20 ms = 46.6 kbps ATM Backbone (AAL2) The AAL2 specifies bandwidth-effective transmission of variable length packets over a single ATM VC. Up to 248 AAL2 connections can be multiplexed on a single VC. The AAL2 adaptation layer consists of two parts: a common part sublayer (CPS) (ITUT specifications 1.363.2) and a service specific convergence sublayer (SSCS) (ITUT specifications I.366.1). The CPS specifies a format for CPS-PDU, which consists of a CPS-PDU start field and a CPS packet. The CPS packet has a 3 byte CPS packet header followed by 1, , 45 octets payload. The start field is one octet long, followed by a CPS-PDU pay