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Graceful restart - why

Graceful restart - why. A graceful restart mechanism for ANCP needs to be defined as per ANCP framework and it is also referred to in the ANCP draft. ANCP runs on TCP and the ANCP session is brought down whenever TCP session resets. This wipes out all the session data on both AN and NAS.

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Graceful restart - why

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  1. Graceful restart - why • A graceful restart mechanism for ANCP needs to be defined as per ANCP framework and it is also referred to in the ANCP draft. • ANCP runs on TCP and the ANCP session is brought down whenever TCP session resets. This wipes out all the session data on both AN and NAS. • The quicker the AN detects the loss of adjacency, the faster it can connect with a NAS. • We present the above problems and their initial solutions.

  2. What data is transported and built in ANCP sessions • Capabilities : four categories of capabilities are exchanged for the session and are fixed for the session • Topology data : NAS discovers the topology of DSL ports on AN and builds a topology database • Multicast flow data: This data on NAS consists of how many S,G sessions are active per subscriber on AN, what is the bandwidth usage of each flow, etc

  3. What have we identified as issues to address • Topology Discovery: After a fresh adjacency is established the topology information that NAS builds is not complete • AN doesn’t send port-up data about all active ports after a new session is established • NAS may have lost all of its topology information as a result • Detection of Adjacency Loss: The AN needs to wait till the ANCP Hellos expire to detect adjacency loss • Multicast: Upon a restart of the adjacency the multicast flow information on the NAS may not be synchronized with that of AN.

  4. How to solve them… • Topology Discovery: Have the AN send port-up for all active ports upon a fresh session establishment. • Needs very little change in the protocol operation on AN and doesn’t need any new messages. NAS can correctly rebuild the topology information. • Detection of Adjacency Loss: TCP Socket state can be used to detect ANCP transport failure more quickly. • Multicast: NAS can request an all flow report from AN using existing messages to recover flow info. • Other multicast cases (like which ones need re-authentication and which don’t need re-authentication)TBD in future revisions.

  5. Summary • Solve existing protocol issues in line with protocol framework • Use existing message types with minimal changes to protocol mechanism. • Doesn’t rely on TCP HA for correct protocol operation – doesn’t make assumptions about whether TCP state-full HA is present or not

  6. Proposal • Soliciting feedback….

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