PDN Gateway Overview
Features and Functionality - Base Software ▀
Cisco ASR 5x00 Packet Data Network Gateway Administration Guide ▄
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DHCPv6 Support
The Dynamic Host Configuration Protocol (DHCP) for IPv6 enables the DHCP servers to pass the configuration
parameters, such as IPv6 network addresses to IPv6 nodes. It offers the capability of allocating the reusable network
addresses and additional configuration functionality automatically.
The DHCPv6 support does not just feature the address allocation, but also fulfills the requirements of Network Layer IP
parameters. Apart from these canonical usage modes, DHCPv6's Prefix-Delegation (DHCP-PD) has also been
standardized by 3GPP (Rel 10) for “network-behind-ue” scenarios. P-GW manages IPv6 prefix life-cycle just like it
manages IPv4 addresses, thus it is responsible for allocation, renew, and release of these prefixes during the lifetime of a
call. IPv6 prefixes may be obtained from either local-pool, AAA (RADIUS/DIAMETER) or external DHCPv6 servers.
Stateless DHCPv6 procedures are used to supply higher layer IP parameters to the end host.
DHCPv6 support for P-GW covers the following requirements:
RFC 3633, prefix delegation and Stateless services (primarily via the INFORMATION-REQUEST) mechanism
RFC 2132, DHCP Options and BOOTP Vendor Extensions
RFC 4039, Rapid Commit Support
Important:
For more information on DHCPv6 service configuration, refer to the
DHCPv6 Configuration
section
of the
PDN Gateway Configuration
chapter.
Direct Tunnel Support
When Gn/Gp interworking with pre-release SGSNs is enabled, the GGSN service on the P-GW supports direct tunnel
functionality.
Direct tunnel improves the user experience (e.g. expedited web page delivery, reduced round trip delay for
conversational services, etc.) by eliminating SGSN tunnel “switching” latency from the user plane. An additional
advantage of direct tunnel from an operational and capital expenditure perspective is that direct tunnel optimizes the
usage of user plane resources by removing the requirement for user plane processing on the SGSN.
The direct tunnel architecture allows the establishment of a direct user plane tunnel between the RAN and the GGSN,
bypassing the SGSN. The SGSN continues to handle the control plane signalling and typically makes the decision to
establish direct tunnel at PDP Context Activation. A direct tunnel is achieved at PDP context activation by the SGSN
establishing a user plane (GTP-U) tunnel directly between RNC and GGSN (using an Update PDP Context Request
toward the GGSN).
A major consequence of deploying direct tunnel is that it produces a significant increase in control plane load on both
the SGSN and GGSN components of the packet core. It is therefore of paramount importance to a wireless operator to
ensure that the deployed GGSNs are capable of handling the additional control plane loads introduced of part of direct
tunnel deployment. The Cisco GGSN and SGSN offer massive control plane transaction capabilities, ensuring system
control plane capacity will not be a capacity limiting factor once direct tunnel is deployed.
Important:
For more information on direct tunnel support, refer to the
Direct Tunnel
appendix in this guide.
DNS Support for IPv4/IPv6 PDP Contexts
This feature adds functionality in P-GW for PDN type IPv4v6. in StarOS Release 15.0. Previously, if an MS requested
an IPv4 DNS address, P-GW did not send the IPv4 DNS address.
