FREE TUTORS ON THE FIBRE CHANNEL PROTOCOL STACK COMMON SERVICES Link services: login and addressing and (Fabric services: name server and co)

THE FIBRE CHANNEL PROTOCOL STACK COMMON SERVICES (Fabric services: name server and co)

FC-3 has been in its conceptual phase since 1988; in currently available products FC-3 is empty. The following functions are being discussed for FC-3:

• Striping manages several paths between multiport end devices. Striping could distribute the frames of an exchange over several ports and thus increase the throughput between the two devices.

• Multi patching combines several paths between two multiport end devices to form a logical path group. Failure or overloading of a path can be hidden from the higher protocol layers.

• Compressing the data to be transmitted, preferably realized in the hardware on the host bus adapter.

• Encryption of the data to be transmitted, preferably realized in the hardware on the host bus adapter.

• Finally, mirroring and other RAID levels are the last example that are mentioned in the Fibre Channel standard as possible functions of FC-3. However, the fact that these functions are not realized within the Fibre Channel protocol does not mean that they are not available at all. For example, multipathing functions are currently provided both by suitable additional software in the operating system (Section 6.3.1) and also by some more modern Fibre Channel switches

(ISL Trucking).3.3.6 Link services: login and addressing Link services and the fabric services discussed in the next section stand next to the Fibre

Channel protocol stack. They are required to operate data traffic over a Fibre Channel network. Activities of these services do not result from the data traffic of the application protocols. Instead, these services are required to manage the infrastructure of a Fibre Channel network and thus the data traffic on the level of the application protocols. For example, at any given time the switches of a fabric know the topology of the whole network. Login Two ports have to get to know each other before application processes can exchange data over them. To this end the Fibre Channel standard provides a three-stage login mechanism (Figure 3.20): 1. Fabric login (FLOGI)The fabric login establishes a session between an N-Port and a corresponding F-Port. The fabric login takes place after the initialization of the link and is an absolute prerequisite for the exchange of further frames. The F-Port assigns the N-Port a dynamic

address. In addition, service parameters such as the buffer-to-buffer credit are negotiated. The fabric login is crucial for the point-to-point topology and for the fabric topology. An N-Port can tell from the response of the corresponding port whether it is a fabric topology or a point-to-point topology. In arbitrated loop topology the fabric login is optional. 2. N-Port login (PLOGI) N-Port login establishes a session between two N-ports. The N-Port login takes place after the fabric login and is a compulsory prerequisite for the data exchange at FC-4 level. N-Port login negotiates service parameters such as end-to-end credit. N-Port login

is optional for Class 3 communication and compulsory for all other service classes.3. Process login (PRLI) Process login establishes a session between two FC-4 processes that are based upon two different N-Ports. These could be system processes in Unix systems and system partitions in mainframes. Process login takes place after the N-Port login. Process login is optional from the point of view of FC-2. However, some FC-4 protocol mappings call for a process login for the exchange of FC-4-specific service parameters.

Addressing

Fibre Channel differentiates between addresses and names. Fibre Channel devices (servers, switches, ports) are differentiated by a 64-bit identifier. The Fibre Channel standard defines different name formats for this. Some name formats guarantee that such a 64-bit identifier will only be issued once world-wide. Such identifiers are thus also known as World Wide Names (WWPN). On the other hand, 64-bit identifiers that can be issued several times inseparate networks are simply called Fibre Channel Names (FCN).In practice this fine distinction between WWN and FCN is hardly ever noticed, with all 64-bit identifiers being called WWNs. In the following we comply with the general usage and use only the term WWN. World Wide Names are differentiated into World Wide Port Names (WWPNs) andWorld Wide Node Names (WWNNs). As the name suggests, every port is assigned its own World Wide Name in the form of a World Wide Port Name and in addition the entire device is assigned its own World Wide Name in the form of a World Wide Node Name. The differentiation between World Wide Node Name and World Wide Port Name allows us to determine which ports belong to a common multiport device in the FibreChannel network. Examples of multiport devices are intelligent disk subsystems with several Fibre Channel ports or servers with several Fibre Channel host bus adapter cards.WWNNs could also be used to realize services such as striping over several redundant physical paths within the Fibre Channel protocol. As discussed above (Section 3.3.5,

'FC-3: common services'), the Fibre Channel standard unfortunately does not support these options, so that such functions are implemented in the operating system or by manufacturer-specific expansions of the Fibre Channel standard. In the fabric, each 64-bit World Wide Port Name is automatically assigned a 24-bit port address (N-Port identifier, N-Port ID) during fabric login. The 24-bit port addresses are used within a Fibre Channel frame for the identification of transmitter and receiver of the frame. The port address of the transmitter is called the Source Identifier (S ID) and that of the receiver the Destination Identifier (D ID). The 24-bit addresses are hierarchically structured and mirror the topology of the Fibre Channel network. As a result, it is a simple matter for a Fibre Channel switch to recognize which port it must send an incoming frame to from the destination ID (Figure 3.21). Some of the 24-bit addresses are reserved

for special purposes, so that 'only' 15.5 million addresses remain for the addressing of devices. In the arbitrated loop every 64-bit World Wide Port Name is even assigned only an eight-bit address, the so-called Arbitrated Loop Physical Address (AL PA). Of the 256possible eight-bit addresses, only those for which the 8b/10b encoded transmission word contains an equal number of zeros and ones may be used. Some ordered sets for the configuration of the arbitrated loop are parametrized using AL PAs. Only by limiting thevalues for AL PAs is it possible to guarantee a uniform distribution of zeros and onesin the whole data stream. After the deduction of a few of these values for the control ..., Fibre Channel differentiates end devices using World Wide Node Names (WWPN). Each connection port is assigned its own World Wide Port Name (WWPN). For addressing in the fabric WWNNs or WWPNs are converted into shorter Port IDs that reflect the network topology of the arbitrated loop, 127 addresses of the 256 possible addresses remain. One of these addresses is reserved for a Fibre Channel switch so only 126 servers or storage devices can be connected in the arbitrated loop.

Fabric services: name server and co

In a fabric topology the switches manage a range of information that is required for the operation of the fabric. This information is managed by the so-called fabric services. All services have in common that they are addressed via FC-2 frames and can be reached by defined addresses (Table 3.3). In the following we introduce the fabric login server, the fabric controller and the name server. The fabric login server processes incoming fabric login requests under the address

'0×FF FF FE'. All switches must support the fabric login under this address. The fabric controller manages changes to the fabric under the address '0×FF FF FD'.

N-Ports can register for state changes in the fabric controller (State Change Registration, SCR). The fabric controller then informs registered N-Ports of changes to the fabric (Registered State Change Notification, RSCN). Servers can use this service to monitor their storage devices. The name server (Simple Name Server to be precise) administers a database on N-Ports under the address '0×FF FF FC'. It stores information such as port WWN, node WWN, port address, supported service classes, supported FC-4 protocols, etc. N-Ports can register

their own properties with the name server and request information on other N-Ports. Like all services, the name server appears as an N-Port to the other ports. N-Ports must log on with the name server by means of port login before they can use its services.