HP Fabric OS 7.1.0, Administrator'S Manual

Page: 51 / 666

Fabric OS Administrator’s Guide 51
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Device login
1
Device login
A device can be storage, a host, or a switch. When new devices are introduced into the fabric, they
must be powered on and, if a host or storage device, connected to a switch. Switch-to-switch logins
(using the E_Port) are handled differently than storage and host logins. E_Ports exchange different
frames than the ones listed below with the Fabric Controller to access the fabric. Once storage and
host devices are powered on and connected, the following logins occur:
1. FLOGI—Fabric Login command establishes a 24-bit address for the device logging in, and
establishes buffer-to-buffer credits and the class of service supported.
2. PLOGI—Port Login command logs the device into the name server to register its information
and query for devices that share its zone. During the PLOGI process, information is exchanged
between the new device and the fabric. Some of the following types of information exchanges
occur:
•
SCR—State Change Registration registers the device for State Change Notifications. If a
change in the fabric occurs, such as a zoning change or a change in the state of a device
to which this device has access, the device receives a Registered State Change
Notification (RSCN).
•
Registration—A device exchanges registration information with the name server.
•
Query—Devices query the name server for information about the device it can access.
Principal switch
In a fabric with multiple switches, and one inter-switch link (ISL) exists between any two switches, a
principal switch is automatically elected. The principal switch provides the following capabilities:
•
Maintains time for the entire fabric. Subordinate switches synchronize their time with the
principal switch. Changes to the clock server value on the principal switch are propagated to all
switches in the fabric.
•
Manages domain ID assignment within the fabric. If a switch requests a domain ID that has
been used before, the principal switch grants the same domain ID unless it is in use by another
switch.
E_Port login process
An E_Port does not use a FLOGI to log in to another switch. Instead, the new switch exchanges
frames with the principal switch to establish that the new switch is an E_Port and that it has
information to exchange. If everything is acceptable to the principal switch, it replies to the new
switch with an SW_ACC (accept) frame. The initializing frame is an Exchange Link Parameters (ELP)
frame that allows an exchange of parameters between two ports, such as flow control,
buffer-to-buffer credits, RA_TOV, and ED_TOV. This is not a negotiation. If one or the other port’s link
parameters do not match, a link does not occur. Once an SW_ACC frame is received from the
principal switch, the new switch sends an Exchange Switch Capabilities (ESC) frame. The two
switches exchange routing protocols and agree on a common routing protocol. An SW_ACC frame is
received from the principal switch and the new switch sends an Exchange Fabric Parameters (EFP)
frame to the principal switch, requesting principal switch priority and the domain ID list.
Buffer-to-buffer credits for the device and switch ports are exchanged in the SW_ACC command
sent to the device in response to the FLOGI.