HP 600 Series, Услуги и приложения

Страница: 237 / 316

FDDI and the OSI Model
The FDDI standard is made up of four distinct parts:
Physical Layer Medium Dependent (PMD) and
Single Mode Fiber Physical Layer Medium Dependent (SMF-PMD)
Physical Layer Protocol (PHY)
Media Access Control (MAC)
Station Management (SMT).
Although not part of the FDDI standard, the Logical Link Control (LLC) is
required by FDDI to assure transmission of user data. These standards
define the 100-Mbps fiber-optic dual counter-rotating FDDI ring.
The PMD, SMF-PMD, and PHY are equivalent to the physical layer of the OSI
model (see figure 2). The PMD and SMF-PMD correspond to the lower
portion of the physical layer. The PMD defines the media requirements for
multimode fiber, such as fiber-optic cable, connectors, and driver receiver
operation for FDDI stations. (Cables, connectors, and receivers are
discussed below in the “Cabling” section.) The SMF-PMD defines similar
requirements for single-mode fiber-optic media. The PHY corresponds to the
upper portion of the physical layer and defines the symbol set, link states,
encoding/decoding, clocking, and framing.
Figure 2. FDDI Protocol Stack
A
p
p
li
c
a
ti
o
n
N
o
te
s
/
C
a
s
e
S
tu
d
ie
s
3
Shining a Light on FDDI
Technology Overview
3-43