1. PAVEL BANKOV
mplementing buffer mechanisms in
FIBRE CHANNEL technology

2. • Define what is Fibre Channel
• Fibre Channel Layers
• Fibre Channel Class of Service (C.O.S.)
• Fibre Channel Flow Control
• Fibre Channel Error Detection and Recovery
• Fibre Channel Protocol Constructs
• Conclusion
Objectives

3. What is FIBRE CHANNEL
• A high-speed transmission technology used as a peripheral channel or
network backbone.
• Up to 16 Gb/s, full-duplex, serial, data communication technology;
variable-length data frames (maximum 2 KB), 32-bit CRC on frames
• It supports several common transport protocols like Internet Protocol
(IP) and SCSI.
• It operates over copper (coaxial/twisted pair) and fiber optic cables
(MM/SM) at distances of up to 10 Kilometers
• Combines best attributes of a channel and a network
• High bandwidth, High data integrity, Highly reliable, Destination paced
(Buffer credits), Scalable, High availability, Shared media,
Circuit/packet, Multiple protocol support, Transport flexibility, 8b/10b

4. What is FIBRE CHANNEL

5. What is FIBRE CHANNEL
• offers point-to-point, switched, and loop interfaces – FC-P2P,
FC-AL, FC-SW
• Standards for Fibre Channel are specified by the Fibre Channel
Physical and Signalling standard, and the ANSI X3.230-1994,
which is also ISO 14165-1
• Fibre Channel Protocol (FCP) is a transport protocol (similar to
TCP used in IP networks) that predominantly transports SCSI
commands over Fibre Channel networks
• Criticism - lack of compatibility, primarily because manufacturers
sometimes interpret specifications differently and vary their
implementations

6. • Port ASIC (FC HBAs, switches, or storage arrays)
What is FIBRE CHANNEL

7. • Fibre Channel does not follow the OSI model layering. It is a
layered architecture with 5 layers: FC-0, FC-1, FC-2, FC-3, and
FC-4. FC-PH is made up of FC-0, FC-1, and FC-2
Fibre Channel Layers

8. • FC-0 defines the physical interface characteristics (signaling
rates, cables, connectors, distance capabilities, etc.)
• FC-1 defines the transmission protocol, including serial
encoding and decoding rules, special characters, and error
control
• FC-2, the signaling protocol, is the transport mechanism of Fibre
Channel. It defines the framing rules of the data to be
transferred between ports, the different mechanisms for
controlling service classes, and the means of managing the
sequence of a data transfer - frames, sequences, exchanges,
login session. Fibre Channel zoning/fabric, RSCN
Fibre Channel Layers

9. • FC-3 defines the common services provided by FC-PH to the
ULPs. These services, which include striping, hunt groups, and
multicast, are not yet implemented. Encryption/RAID
• FC-4 is a protocol-mapping layer, in which application protocols,
such as SCSI, IP or FICON, are encapsulated into a PDU for
delivery to FC2. LUN Masking
Fibre Channel Layers

10. • Fibre Channel defines different delivery options for frame
transmission and these are known as a particular Class of
Service
• Class 1, 2, and 3 are the different services supported by Fibre
Channel and are basically defined with regards to connection,
in-order delivery, confirmation of delivery, and which type of flow
control is used
• These classes of service are independent of the topology used
Fibre Channel C.O.S.

11. • Class 1 is a connection-oriented service that provides a
dedicated connection between two ports allowing them to use
the maximum available bandwidth. Class 1 provides
confirmation of delivery and notification of non-delivery
• Class 2 is a connectionless class of service that provides
confirmation of delivery and non-delivery of frames. No
connection is established between the source and destination
ports and it is up to the fabric to deliver the frames, possibly over
different paths to the recipient. Frames will be transmitted in
order but depending on the fabric may arrive at the recipient out
of order
Fibre Channel C.O.S.

12. • Class 3 is again a connectionless class of service but with no
confirmation of delivery or non-delivery of frames. No connection
is established and, like Class 2 frames, Class 3 frames may
arrive out of order. The biggest difference is that the delivery of
frames is unacknowledged in that the destination port does not
send any link control frame (ACK) on receipt of valid data
frames. The flow control used in Class 3 is Buffer-to-Buffer
• The fact that there is no confirmation of delivery of frames in
Class 3 Fibre Channel means error recovery must be handled at
the Upper Layer Protocol. The confirmation is provided by the
protocol being transported (i.e. SCSI)
Fibre Channel C.O.S.

13. • Class of Service summary
Fibre Channel C.O.S.

14. • When a port wants to send frames to another port the frames are sent
from a buffer at the sending port and received into a buffer at the
receiving end
• If there is no receive buffer space then that port cannot accept any
more frames and this leads to busy responses and the possibility of
frame loss
• Fibre Channel uses two different flow control mechanisms to pace the
rate at which the sender is allowed to transmit frames
• End-to-End and Buffer-to-Buffer - both of these methods of flow
control use a credit-based agreement between nodes to regulate the
flow of frames between them. The credit value is the number of
frames a receiving port has allowed a sending port to transmit to it
Fibre Channel Flow Control

15. • End-to-End credit (EE_Credit) is the maximum number of data
frames a source port can send to a destination port without
receiving an acknowledgement frame (ACK). This credit is
granted during N_Port login and is replenished with the return of
an ACK response frame
Fibre Channel Flow Control

16. • BB_Credit (buffer-to-buffer credit) mechanism for hardware-
based flow control. This means that a port has the ability to pace
the frame flow into its processing buffers. This mechanism
eliminates the need of switching hardware to discard frames due
to high congestion
• It relies on the use of credits that are exchanged at login time
(FLOGI for Nx_Ports, ELP for E_Ports). In the case of an
Initiator or Target (Nx_Port), the port will grant some number of
credits (typically between 8 and 64) to the switch. It does this by
specifying the number of credits to be granted to the switch in
the FLOGI frame
Fibre Channel Flow Control

17. • Login and credit initialization process
Fibre Channel Flow Control

18. • Example - 400 MB/s link with maximum of 200 BB_Credit
Fibre Channel Flow Control

19. • In Fibre Channel, error detection occurs at a number of different
levels
• At the FC-0 level errors associated with signal quality
• At the FC-1 level where it checks for invalid transmission
characters
• At the FC-2 level frames are checked for various conditions
such as CRC error detected, RECEIVE BUFFERS state
• FC-2 Time-outs – 4 different timers used
Fibre Channel Error Detection and Recovery

20. • R_T_TOV (Receiver-transmitter time-out) - used to time
events at the link level (Loss of synchronization), generally
controlled in hardware for all link configurations, default value in
FC Standard is 100ms
• The E_D_TOV (Error Detect time-out) - time-out value is the
timer for transmission of consecutive data frames and
responses at the sequence level. Basically this is a short value
and indicates how long a sequence can take to complete. It is a
time-out value for communicating between two N_Ports that is
negotiated at login time. Typical value for this is 2 seconds
Fibre Channel Error Detection and Recovery

21. • R_A_TOV (Resource Allocation time-out) - time-out value for
how long to hold resources associated with a failed operation
(needed to free shared resources for reuse). Value to determine
how long a port needs to keep responding to a link service
request before an error is detected (typical 10 seconds)
• CR_TOV (Connection Request Time-out) - determines how
long the fabric can hold a class-1 request in the queue during
connection establishment
Fibre Channel Error Detection and Recovery

22. • The next values are provided in microwatts (mW) or dBm and
can be extremely useful when debugging why a link will not
come up (dBM = 10 * LOG mW)
Fibre Channel Error Detection and Recovery

23. • Brocade FOS platforms: using the command sfpshow
[portnumber]
Fibre Channel Error Detection and Recovery

24. • The fundamental protocol structures in the Fibre Channel are
called constructs
Fibre Channel Protocol Constructs

25. • Fibre Channel Frame Structure
• 0–2048 bytes Typical MTU
Fibre Channel Protocol Constructs

26. • From the materials provided, it seems that there is no correlation
between FC buffers (flow control mechanism) and LUN
size/number ratio
Conclusion

27. Thank you!