 or IPv6 IID followed by IPv4) Figure 4.23 PDN Address Information Element for EPS. IPv6 in 3GPP Networks Octets PDN Type (v4 = 001, v6 = 010, PDN Type IEI (no code point) v4v6 = 011) Figure 4.24 PDN Type Information Element. Octets Protocol configuration options IEI = 0x27 (or 0x84 when in GTP-C) Length of option contents Spare '0000' Config protocol ('000' for PPP) Protocol ID X Length of protocol ID X content Protocol ID X content Protocol ID y or Container ID z... Figure 4.25 Protocol Configuration Option Information Element. zero or more matching PCOs. Figure 4.25 shows the encoding of a PCO. The PCOs are conveyed within NAS protocol messages between the UE and the SGSN/MME, and within GTP-C messages between the MME, the SGW, and the PGW. The only difference in the encoding between NAS and GTP-C transports is the information element code number and the length field. A number of Protocol IDs in a PCO are borrowed as is from PPP, and their use is indicated in the Configuration Protocol field (the 3rd octet in the PCO). In Release- 11, the following PPP-based Protocols IDs are supported: Link Control Protocol (LCP) (0xC023), Challenge-Handshake Authentication Protocol (CHAP) (0xC223), and IPCP (0x8021). The Protocol ID content equals to a 'NCP Packet' [14] that has the 'Protocol' and the 'Padding' octets removed. In addition to PPP-based Protocol IDs, 3GPP has defined a number of its own Content IDs. For instance, a Content ID 0x0003 means a DNS Server IPv6 Address. Containers have their own encoding described in respective 3GPP documents [12]. Figure 4.26 shows a PCO that contains both IPv4 and IPv6 DNS server addresses, and has been sent from network side to UE direction. Tables 4.6 and 4.7 show Content IDs available in Release-11. It should be noted that Content IDs have different encoding depending on whether they were originated by a UE (requesting something) or by a network (providing configuration information). Deploying IPv6 in 3GPP Networks 0000 27 PCO IEI 0001 27 Length = 39 0002 80 Configuration Prot