er relay receives a packet from the Internet destined to a host behind a MAP enabled CPE. The border relay has the following FMR and BMR configuration: Rule IPv6 prefix 2001 : db8 : 0000 : : /40. Rule IPv4 prefix 192.0.2.0/24. PSID offset 4 and length 8. Rule EA-bits length 16 bits, which means 8 bits suffix from the rule IPv4 prefix is used. Border relay prefix 2001 : db8 ffff::/64. The subscriber is assigned with a /56 prefix. When a packet is received from the Internet with a source address 12.13.14.15 (0x0c0d0e0f) and port 80 destined to an address 192.0.2.18 . (0xc0000212) and port 9030 (0x2346), then the FMR destined to the CPE becomes: EA-bits will be 0x1234; the 8-bit suffix of 192.0.2.18/24 is 0x12 and the PSID of 9030 is 0x0034. IPv6 prefix is 2001 : db8 : 0000 : : / 40. IPv6 Transition Mechanisms for 3GPP Networks When put together the FMR is: 2001 db8: 00 + 12 + 34 + 00 + IID and remembering the specific formulation of the IID the final FMR IPv6 address is: 2001 db8 0012 3400 0002 1200 :3400/128. Similarly, the source address of the border relay becomes: 2001 db8: ffff: 0000 + IID and based on the specific formulation of the IID in the case of DMR the final IPv6 address is: 2001 db8 ffff 0000 000c 0d0e: 0f00: 0000/128. Summarizing: IPv6 source address: 2001: db8 ffff:0:c:d0e:f f00:0000. IPv6 destination address: 2001:db8:12:3400:c0:2:1200:3400. IPv6 source port: 80. IPv6 destination port: 9030. 5.3.7 Other Tunneling or Translation Based Transition Mechanisms Application Proxies As described previously, NAT64 provides a generic mechanism to translate between IPv4 and IPv6. However, sometimes a generic solution is not desirable for certain reasons. These reasons include performance, manageability, and protocol incompatibility with middle-boxes like NAT64. An alternative can be provided by application specific proxies. An application specific proxy can be an explicit proxy where the client is configured to support a proxy. This category includes web (HTTP) proxies [44] that are used in many enterprises a