Document: draft-ietf-mipshop-transient-bce-pmipv6-06
Reviewer: Spencer Dawkins
Review Date: 24 August 2010
IESG Telechat date: 26 August 2010

Summary: This specification is ready for publication as an Experimental RFC.

Comments: I have a small number of nits, forwarded for the convenience of 
any downstream editors.

Abstract

  This document specifies a mechanism which enhances Proxy Mobile IPv6
  protocol signaling to support the creation of a transient binding
  cache entry which is used to optimize the performance of dual radio
  handover, as well as single radio handover.  This mechanism is
  applicable to the mobile node's inter-MAG handover while using a
  single interface or different interfaces.  The handover problem space
  using the Proxy Mobile IPv6 base protocol is analyzed and the use of
  transient binding cache entries at the local mobility anchor is
  described.  The specified extension to the Proxy Mobile IPv6 protocol
  ensures optimized forwarding of downlink as well as uplink packets
  between mobile nodes and the network infrastructure and avoids
  superfluous packet forwarding delay or even packet loss.

Spencer (nit): "or even packet loss"? maybe there's a qualifier missing? :D

1.  Introduction

  According to the PMIPv6 base specification, an LMA updates a mobile
  node's (MN) Binding Cache Entry (BCE) and switches the forwarding
  tunnel after receiving a Proxy Binding Update (PBU) message from the
  mobile node's new MAG (nMAG).  At the same time the LMA disables the
  forwarding entry towards the mobile node's previous MAG (pMAG).  In
  case of an inter-technology handover, the mobile node's handover
  target interface must be configured according to the Router
  Advertisement being sent by the nMAG.  Address configuration as well
  as possible access technology specific radio bearer setup may delay
  the complete set up of the mobile node's new interface before it is
  ready to receive or send data packets.  In case the LMA performs
  operation according to [RFC5213] and forwards packets to the mobile
  node's new interface after the reception of the PBU from the nMAG,
  some packets may get lost or experience major packet delay.  The
  transient BCE extension, as specified in this document, increases
  handover performance (optimized packet loss and forwarding delay)
  experienced by MNs, which have multiple network interfaces
  implemented while handing over from one interface to the other.  The
  transient BCE extension increases also handover performance for

Spencer (nit): s/increases also/also increases/

  single radio MNs, which build on available radio layer forwarding
  mechanisms, hence re-use existing active handover techniques.

3.1.  Handover using a single interface

  In some active handover scenarios, it is necessary to prepare the
  nMAG as handover target prior to the completion of the link layer
  handover procedures.  Packets sent by the LMA to the nMAG before the
  completion of the link layer handover procedure will be lost or need
  to be buffered.

Spencer (nit): "will be lost unless they are buffered"?

  In some systems, the nMAG will be the recipient of uplink traffic
  prior to the completion of the procedure that would result in the
  PBU/PBA handshake.  These packets cannot be forwarded to the LMA.

3.3.  Need for a common solution

  This document specifies transient BCEs as an extension to the PMIPv6
  protocol.  Set up and configuration of a transient BCE can be
  performed by means of extended PMIPv6 signaling messages between the
  MAG and the LMA component using a new Transient Binding mobility
  option.  The transient BCE mechanism supports three clearly
  distinguished sequences of transient states to suit various handover
  scenarios and to improve handover performance for both, inter- and

Spencer (nit): s/both,/both/

  intra-technology handover.  As a result of using transient BCEs,
  excessive packet buffering at the nMAG during the MN's handover
  process is not necessary and packet losses and major jitter can be
  avoided.

4.8.  Protocol Stability

  Lost connection with pMAG during late path switch:  In case an MN
     looses connectivity to its pMAG during a transient BCE phase with

Spencer (nit): s/looses/loses/

     late path switch and the nMAG fails to initiate turning a
     transient BCE into an active BCE to perform the path switch to the
     nMAG, in a worst case downlink packets are lost until the chosen
     TIMEOUT_1 expires.  After TIMEOUT_1 seconds, the protocol
     operation has been recovered successfully.  However, this case is
     very unlikely for two reasons: If the connectivity to the pMAG is
     lost, the pMAG will send a deregistration PBU for the MN to the
     LMA, which results in turning the transient BCE into an active BCE
     and in a path switch.  Furthermore, the nMAG will initiate turning
     the transient BCE into an active BCE as soon as the set up of the
     data link between the MN and the nMAG has been completed
     (Section 4.4).  Note that this case in particular affects downlink
     packets, whereas uplink packets can be sent through the new
     connection after a broken link to the pMAG has been detected.