PWE-71 Slide 1

1
PWMUX

• PWE 71st IETF
• 10 March 2008

Yaakov (J) Stein
2
ACs and PWs

• RFC 3985 states that PWs connect forwarders
• The ingress forwarder selects into which PW to
  inject traffic based on
• the AC
• payload content
• configured forwarding information
• Thus the forwarder function can be used for
• PW protection
• AC protection
• PW load balancing and inverse mux
• When the mapping of PW to AC is not one-to-one
• we will call the forwarder function - a PW MUX

3
Are there enough labels?

• There are only 220 unique PW labels
• If we assign multiple PW labels for each AC
• won't we run out of labels ?
• This question is ill-posed
• When using multiple PWs for protection or load
  balancing
• these PWs will not be in the same tunnel
• RFC3985 mentions that the PW label MAY be unique
  per PE
• but it only MUST be unique per tunnel
• In theory, we could even use the same PW label
• for all the PWs associated with the same AC
• So using multiple PWs does not lead to label
  space exhaustion

4
11 PW Protection
active PW
PW MUX needs to map the AC to the appropriate PWs
PW set up protocol associates multiple PW labels
with the single AC Ingress forwarder needs to
replicate packets Egress forwarder needs to
detect and reject duplicate packets
5
11 PW Protection
active PW
backup PW
PW MUX needs to map the AC to the appropriate
PW(s) PW set up protocol associates multiple PW
labels with the single AC Ingress forwarder
labels traffic with label of the active PW Egress
forwarder extracts traffic from active PW Use
VCCV to monitor continuity of active PW Use LDP
status message to trigger switch from active to
backup PW May revert to original PW when fault is
rectified
6
11 AC Protection
PW MUX needs to map one PW to multiple ACs PW
setup protocol associates multiple ACs with a
single PW label Ingress forwarder needs to select
highest quality AC and encapsulate Egress
forwarder needs to map PW label to both ACs
7
11 AC Protection
PW MUX needs to map one PW to multiple ACs PW
setup protocol associates multiple ACs with a
single PW label Ingress forwarder needs to
extract traffic from active AC and encapsulate
with the PW label Egress forwarder needs to copy
PW traffic to active AC Native OAM needs to
monitor active AC Native protection mechanisms
used to switch between ACs
8
PW load-balancing and inverse mux
balancing PW
AC
AC
PSN
PW MUX
PW MUX
PW MUX needs to map the AC to the appropriate
PW(s) PW set up protocol needs to associate
multiple PWs with the single AC Ingress forwarder
makes a per-packet decision as to which PW to
use Egress forwarder needs to collect packets
from all PWs in use
9
Proposal

• PWE3 should select a single method for handling
• PW protection
• AC protection
• Load balancing and inverse mux
• This means a unified mechanism should be used for
  
• associating PW labels to AC identifiers
• designating PW status (active, backup, balancing)
• signaling between forwarders (when needed)