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Fibre Channel Over MPLS

2. Topics. FCoMPLS congestion management modelInterworking between TFRC and LAPBRate shaping Selective retransmission FC credit management . 3. PWE3 Provider Edge reference model. Native service processing termination for Fibre Channel is handled by FC-BB-4 in T11PW termination is handled by

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Fibre Channel Over MPLS

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    1. Fibre Channel Over MPLS IETF/T.11 interworking draft-ietf-pwe3-fc-encap-01.txt Tuesday, July 11, 2006 Moran Roth – Corrigent Ronen Solomon – Corrigent Munefumi Tsurusawa – KDDI LABs

    2. 2 Topics FCoMPLS congestion management model Interworking between TFRC and LAPB Rate shaping Selective retransmission FC credit management

    3. 3 PWE3 Provider Edge reference model Native service processing termination for Fibre Channel is handled by FC-BB-4 in T11 PW termination is handled by PWE3 in IETF Including LAPB and interworking with TFRC

    4. 4 FC PW Congestion Control – Introduction FCoMPLS may be used in controlled and non-controlled environment where CIR and EIR are service attributes. Rate adaptation based on TFRC throughput equation. Selective Retransmission (SR-LAPB) mechanism provides reliable transport of FC traffic, for faithful emulation of FC service. (LAPB ISO standard ISO/IEC 7776:1995) SR also indicates congestion conditions to the TFRC mechanism for throughput calculation.

    5. 5 General architecture – TFRC/LAPB Interworking Rate Shaping - TFRC Rate shaping (to avoid traffic bursts) Adopt to available bandwidth Selective retransmission - LAPB Reliable LAPB protocol for retransmission of lost frames. FC Credit Manager (NSP function) Ingress queue management

    6. 6 FC PW encapsulation

    7. 7 General architecture – RS Reference to TFRC (TCP friendly rate control ) RFC 3448 Rate shaper Performs rate shaping to transmitted frames Reduces frame drop probability by low pass filtering traffic burst Assures minimum bandwidth guarantee (CIR) Adaptive shaper control Interworking with LAPB Works in conjunction with Selective Retransmission mechanism Monitors SR frame loss (congestion indication), and thereby adaptively configures the rate shaper Frame loss monitored – reduce shaper rate No Frame loss – increase shaper rate

    8. 8 General architecture – SR Selective Retransmission (LAPB) Re-use the exiting protocol for FC over ATM w/o modification as in FC-BB Reliable protocol Sequencing and re-sequencing mechanism Acknowledgments - to the sender Frame loss retransmission Very low protocol overhead (4 bytes total) Uses fixed window size Thereby allowing bandwidth control via rate shaper. Efficient for FC application

    9. 9 Summary Reuse SR (Selective Retransmission) as described in T.11 FCoATM. Document in draft-ietf-pwe3-fc-encap-01.txt the interworking between LAPB/TFRC. Assign new PW Type “Fibre Channel port mode”

    10. Congestion control for FC PW Interworking between TFRC and LAPB details

    11. 11 Rate Control – Protocol Mechanism CIR and EIR are configured per FC service and FCoMPLS frames are marked accordingly. Throughout [Bytes/Sec] – actual sending rate is a function of loss event rate and round trip time (RTT). Loss event – one or more frames dropped within a single LAPB window. Protocol mechanism overview The sender measures RTT as defined in FC-BB-3. Receiver identifies lost frames and feeds this information to the sender. The sender uses the feedback and RTT to calculate loss event rate and throughout. The sender adjusts its transmission rate to match the calculated throughout.

    12. 12 Rate Control – Sender Protocol Sender initialization Rate initialization to guaranteed bandwidth (CIR). SR mechanism initialization (resetting the sequence numbers). The sender calculates the loss event rate based on feedback frames generated by the receiver. Based on the calculated loss event rate and RTT the sender calculates the throughput for the rate shaper.

    13. 13 Rate Control – Throughout Equation Throughput equation is defined in RFC 3448. CIR and EIR are service attributes. Throughput equation should conform to CIR and PIR (PIR = CIR+EIR) boundaries to support controlled and un-controlled environment. The throughput equation controls the excess transmission rate (as CIR is guaranteed). Throughput [Bytes/Sec] = CIR + X X is the excess throughput equation result.

    14. 14 Rate Control – Throughout Equation Equation parameters: Packet size (s) – replaced by the SR window size (K). Retransmission timeout (t_RTO) – replaced by T1 timer of the SR mechanism. Number of acknowledged frames (b) – in accordance with RFC 3448 and SR, b = 1. Frame loss probability is calculated by the sender. RTT is measured by the sender as defined in FC-BB.

    15. 15 Rate Control – no feedback timer LAPB defines the no feedback timers as follows: T1 timer [msec] – define the number of milliseconds the sender awaits for an acknowledgement. Following T1 expiration the sender issues a recovery procedure by sending a supervisory frame (i.e S-frame) to the receiver. N2 counter – the number of times the sender initiates a recovery procedure. No feedback = When 2*T1 timer expires The sender halves its X sending rate. LAPB stops transmission upon end of window transmission and resumes when feedback arrives. When N2*T1 expires The sender shall issue a LAPB link reset.

    16. 16 FC PW Congestion Control – Feedback Frames Uses LAPB S-frame (supervisory frame) encapsulation. RR ( Receiver Ready) – includes the N(R) counter to acknowledge sender frames. RNR ( Receiver Not Ready) – includes the N(R) counter to acknowledge sender frames and stop the transmitter. SREJ (Selective REJect) – indicates sequence numbers of dropped frames to feed the transmitter. Recommended to send S-frames as high-priority (EF).

    17. 17 Frame Format – Data and Feedback Frames Date frames – uses LAPB I-frame (information frame) encapsulation.

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