The Fibre Channel protocol has defined five levels of functions. FC-0, FC-1, FC-2, FC-3 and FC-4, each containing functions as described in Figure 1 below.

Figure 1: The Fibre Channel protocol has defined five levels of functions—the FC-0, FC-1, FC-2, FC-3 and FC-4.

The ANSI INCITS 373-2003 (FC-FS) standard specifies the functions for FC-1, FC-2 and FC-3 levels.For 10Gbit Fibre Channel, minor changes are made to FC-1 functions as defined in FC-FS.

The major change in 10Gbit Fibre Channel is the creation of the ANSI INCITS 364-2003 (10GFC) standard, which specifies the physical layer requirements for 10Gbit Fibre Channel interfaces. In addition, the arbitrated loops topology defined for lower rates is not supported by the 10Gbit Fibre Channel protocol.

Figure 2 below describes the protocol components within a 10Gbit Fibre Channel port as defined in the 10GFC standard. Besides ANSI, ISO/IEC also has documents that define the Fibre Channel protocol.

10GFC standard
The 10GFC standard describes the signaling and physical interface requirement to transport data at a rate in excess of 10Gbps over a family of FC-0 physical variants. Optional port management functions are introduced at the FC-3 level as well.

The standard has defined two formats of the four quarter-speed lanes optical physical variants and the one full-speed lane over one fiber variant. This article focuses on the one full-speed lane over one fiber variant, because it is the most popular among the three formats.

Statements made hereafter may not apply to the first two variants.Aside from the higher rate, the physical layer design for 10Gbit Ethernet (10GE) is adopted into the 10GFC standard.

Figure 2: A 10GFC level is created to provide translations between FC-1 functions defined in FC-FS and XGMII functions defined in 10GE

The 64B/66B transmission code is used in place of the FC-1 8B/10B transmission code described in FC-FS for 1Gbit and 2Gbit Fibre Channels. Although the 8B/10B code seems a straighter evolution to many existing Fibre Channel users, the 64B/66B code has higher bandwidth efficiency and leverages existing 10G technologies.

The 10Gbit Media Independent Interface (XGMII), the physical coding sublayer (PCS) where the 64B/66B coding/ decoding functions reside, the physical medium attachment (PMA), and the physical medium dependent (PMD) layers as shown in Figure 2 above, are defined in IEEE Standard 802.3ae -2002 for 10GE and expanded in 10GFC - such that they are capable of operating at 10.518Gbps.

It should be noted that a special jittery signal is introduced in the 10GE standard to evaluate the performance of the receiver in a worst case scenario.

Within the 10GFC standard, a 10GFC level is created to adapt the FC-1 information defined in FC-FS to the XGMII. This permits standard operations of the FC-1 functions, as defined in FC-FS and XGMII functions defined in 10GE, to remain unchanged.

With single-lane 10Gbit Fibre Channel, the 8B/10B transmission coding is no longer part of FC-1 functions as defined in FC-FS. Primitive Signals, Primitive Sequences and port state machines remain within the FC-1 functions.

10GFC level's functions
The 10GFC level provides the necessary translations between the FC-1 and the XGMII. There is no need to translate user data that come from FC-2, as XGMII will pass them on unchanged. However, FC-1 ordered sets -such as frame delimiters, primitive signals and primitive sequences - are defined differently in FC-FS and XGMII.

For example, all FC-FS ordered_sets start with a leading K28.5 special character followed by 3bytes that determine the meanings of the ordered_sets. However, in 10GE, there is one control code defined for each ordered_set. Therefore, an ordered_set from FC-1 must be translated into the format that is recognized and supported at the XGMII for transmission.

Likewise, an ordered_set received from the XGMII needs to be translated into the format that can be delivered to the FC-1 functions. The 10GFC level also qualifies primitive sequences received from XGMII before delivering to the FC-1 functions.

The NOS ordered_set defined in FC-FS does not appear on XGMII; it is mapped by the 10GFC level to the RF ordered_set. Qualified LF received from XGMII is converted to the out-of-band signal "loss_of_sync" to the FC-1 level.

Although 10GFC uses the XGMII defined in 10GE, rules governing the information flow that can appear on XGMII for 10GFC and 10GE are different. For example, the two technologies have different rules on the generation of interframe gaps (IFG), primitive sequences and primitive signals. Detailed requirements on XGMII, PCS, PMA and PMD can be found in IEEE Standard 802.3ae—2002.

Testing the channel
Testing of 10Gbit Fibre Channel includes physical layer tests and protocol tests (FC-2 and above). PHY layer tests evaluate the ability of a DUT to carry information error-free from one place to another.

Protocol tests evaluate the DUT's ability to exchange information to establish and release a connection, and its ability to forward and switch data frames in accordance with given recommendations, specifications or standard.

Before protocol testing can be performed, PHY layer performance requirements must be satisfied. The 10Gbit Fibre Channel PHY layer includes the FC-1, XGMII, PCS, PMA and PMD. Evaluation of the PMD requires the use of optical instruments for the measurement of transceiver characteristics such as waveform, clock and sensitivity.

It is more difficult to find instruments for receiver testing than for transmitter testing; as special requirements for the input optical signal are not easily satisfied by most products in the market.

Testing the PCS and the XGMII require specialized tools that provide analysis of the 64B/66B code transmitted by the DUT. The ideal instrument should be able to report PCS errors and statistics, and capture and display the received 64B/66B code in a readable format.

This allows for examination of compliance with the rules of IFG, primitive signals, primitive sequences and link fault signaling as specified in the standard, since this information is embedded in the 64B/66B code stream.

The instrument should also be able to generate the appropriate 64B/66B code, allow injection of error conditions, and allow editing of transmitted bits to force the DUT receiver into or out of specific states, to verify implementation in accordance with the standard. Client data performance can be determined by evaluating the BER of the payload once the FC-1 level and below are tested.

Once the transport capability of the DUT is validated, a 10GFC protocol tester is used to evaluate its ability to establish and release a connection, handle traffic and map user data to the Fibre Channel signal in accordance with the standard. What must be tested depends largely upon the nature of the DUT and its expected functions.

The major change to the Fibre Channel protocol is the adoption of the 64B/66B transmission code defined in 10GE and the consequent creation of the 10GFC level.

Therefore, specialized tools that can perform PCS analysis are essential in examining compliance with the standard. Moreover, the introduction of stressed receiver conformance testing in the 10GE standard also constitutes a challenge to the testing of the 10Gbit Fibre Channel receivers.