Frames could be carrying fabric services information, link control information
or upper layer protocol data.
Previously we mentioned two examples of extended link services, fabric login
and port login. Later we are going to look at how they are used.
We also have generic fabric services. These include the name service.
The name service is the directory. During our extended link services we are
going to do a login. So the first thing we will do is talk to the login server to get
an FC_ID. Then we will talk to the Name Server. We will do a Port Login to
the Name Service. This will add us into the directory (this includes our
WWPNs, our FC_IDs and our capabilities). The Name Service then
distributes this information to all of the other switches using the Fibre Channel
Common Transport, FC-CT. The Name Service will be distributed to every
switch. We only need to talk to our local switch and that switch will update all
of the others.
Likewise with zone configuration. We have one active Zoneset. How do we
propagate the Zoneset information to all of the other switches? We use the
Management Services over the Fibre Channel Common Transport protocol.
There is also the authentication service (this checks if you are supposed to be
joining this fabric on this particular port). For an authentication service we
could use DH-CHAP, Challenge Handshake Authentication Protocol or a
digital certificate exchange. The authentication service is already defined in
the Fibre Channel protocol.
We have a key distribution service. If we are using FCsec (Fibre Channel
Security protocol) we can encrypt the payload. We have a choice of
asymmetric or symmetric encryption. A symmetrical encryption key is
something like AES. This is like secret password. This can be distributed
using our key distribution service. It is built into the Fibre Channel protocol.