Pseudowire freeze mechanism

draft-jin-pwe3-pw-freeze-00

Lizhong JinBhumip. Khasnabish

Requirements

• Several PW high availability mechanism– Pseudowire redundancy mechanism– PSN tunnel protection technology

• For the PW control plane failure, using above high availability methods will bring:– Additional resources to backup – High provisioning cost – For the case when many PWs are down due to signaling failure

which is coursed by sharing same fate of signaling session:• It is a burden or pressure for the network to switch all affected PWs t

o the backup at the same time.

• MPLS-TP is required that the data and control planes are both logically and physically separated.

Problem statement (I)

• In some network of deploying PW, the signaling path is different from the data transmission path.

• See the figure above, T-LDP session has different path with TE-Tunnel path (setup by strict ERO).

• In this case, the failure of T-LDP session should not influence the pseudowire data traffic.

PE1 PE2CE1 CE2

T-LDP Session

Router

TE-TunnelAC AC

PW

Problem statement (II)• Problem statement

– According to the LDP procedure [RFC5036], if the T-LDP session is DOWN, the corresponding traffic is interrupted.

– When graceful restart [RFC3478] is enabled on this T-LDP session, PE will not interrupt the PW traffic for a time within the time of "reconnect time“.

• The maximum value of "reconnect time" is 4294967.295 seconds, or 49.7 days, not infinite.

– Sometimes, operators need more flexible configuration, and only want some of the PWs not to be influenced by T-LDP session status, so as to provide different availability level of service.

Problem statement (III)

• The PW freeze mechanism aims to:– Provide a function for PW not to be influenced by the

turbulence of control plane.

• When the PW supports “freeze" function and is operational UP:– It will not be influenced by the turbulence of control

plane.

PW freeze status encoding

• PW freeze status is encoded in PW status TLV: 0x00000080 (to be assigned by IANA). – When the PW freeze bit is set,

• it indicates that the PW supports "freeze" function, and will be in "freezed" state.

– When the PW freeze bit is cleared, • it indicates that the PW will be in "unfreeze" state.

• When the PW is configured as "freeze“, PE SHOULD advertise the capability when:– Sending label mapping message carrying the PW status TLV wit

h "PW freeze bit" set– Sending LDP notification message carrying the PW status TLV

with "PW freeze bit" set.

PW freeze status signaling

• When one of the PW endpoint signals PW status with PW freeze bit cleared– both of the two endpoints should unfreeze the PW.

• When PW is already in "freeze" state– the PW status should be transmitted through G-ACH,

as defined in [I-D. draft-ietf-pwe3-static-pw-status-00].

PE operation

• If PW supports "freeze" function through negotiation: – When PW is operational UP

• PW will enter into the freezed state. • The PE should locally store the PW information tha

t received from the peer node, including PW type, PW label and etc.

– When T-LDP session is DOWN, the PE should continue the PW data forwarding.

Next steps

• Need comments from work group

Thank you