der is 24 bytes in the payload data message. The size of the IP header depends on what version of the IP stack is used, IPv4 or IPv6. The length of the IPv4 header can vary from between 20 and 60 bytes; 20 bytes is the length of the basic IP address in IPv4 while the remaining 40 bytes is the length of the option field. Options are not commonly used BSSAP RANAP M3UA (24 bytes) SCTP (28 bytes) IP (20 IPv4, 40 IPv6) Ethernet (38 bytes) Figure 4.17 SIGTRAN generic protocol stack 3GPP Release 4 Circuit Core Network H.248 SCTP/TCP Ethernet Figure 4.18 MEGACO protocol stack in IPv4. The length of the IPv6 header is 40 bytes + option fields. Usually some of those option fields are included in the message when it is using IPv6. Including the IPv4 protocol overhead, transferring an upper layer payload message would introduce 72 bytes of overhead. H.248 (MEGACO) Protocol - Mc Interface H.248 or MEGACO is the protocol used by the MSS/GCS to instruct the MGW about the actions to perform in relation to a call (see Figure 4.18). H.248 or MEGACO has been developed by IETF MEGACO workgroup in cooperation with the ITU-T. The MEGACO protocol was standardised by the ITU and is used to perform the following tasks: reserve and connect terminations; connect or release echo canceller to terminations; connect or release tones and announcements to terminations; send/receive DTMF tones. The dimensioning of the bandwidth needs between a given MGW and its controller (MSS or GCS) is based on the total number of calls, at the MGW, during the busy hour, the estimated signalling messages needed per call and average message size. (The BHCA load of the element is obtained from the NetAct tool. In case a MGW is handling transit traffic by means of the AAL2 nodal function, this transit traffic should not be considered for the MEGACO calculation as it does not require any interaction between the MSS and MGW.) The H.248 messaging load per call is difficult to estimate as it depends partly on the implementation (i.e. how transactions are packed into t