PWE3%20Sequencing

1
PWE3 Sequencing

• Luca Martini
• 59th IETF Meeting , Seoul, Korea

2
Implementation Issues

• Events which require sequencing number
  resynchronization
• APS switchover
• HW failures and resets
• Switchover events for non-stop forwarding
• Linecard resets
• Label Withdraw only method to resynchronize
• Ideally, algorithms would be run in the data-path
  to expedite sequence number resynchronization.

3
Proposed improved AlgorithmsTransmitter sequence
number training algorithm

• Transmitted sequence number reset
• Initialize start, mid, end sequence numbers.
  Initialize a counter to 0.
• Start 1 (MPLS PW) or 0 (L2TPv3 PW)
• Mid 32768 (MPLS PW) or 8388607 (L2TPv3 PW)
• End 65535 (MPLS PW) or 16777215 (L2TPv3 PW)
• Send the start-seq-
• Send the mid-seq-
• Send the last-seq-
• If count !3, bump count and go back to step 2,
  once count 3, return to normal sequence number
  incrementing, i.e. 2,3,4,5,6,....
• This process should retrain the peers receiver
  sequence number with minimal to no packet loss.
• Patent filed

4
Proposed AlgorithmsReceiver sequence number
force-resync algorithm

• Add the following per-pseudowire counters
• drop_resync_counter
• drop-resync_threshold
• If the received packet is in sequence, reset the
  drop_resync_counter to 0.
• If the received packet is out of order, bump the
  drop_resync_counter.
• if the drop_resync_counter drop-resync_threshol
  d issue label withdraw to reset sequence number.

5
PWE3 Sequencing Counters

• Drop out of order counter maintain the number
  of total packets which have been dropped due to
  sequencing issues
• Gap counter number of packets not received.
  Detects the number of packets which were missing
  between the received sequence number minus the
  expected sequence number.