Handbook for Sound Engineers

Digital Audio Interfacing and Networking 1495

If at the end of the autonegotiation process a
10 MBit/s link is established, both devices will send
NLPs when idle. If a 100 MBit connection was estab-
lished, both devices transmit carrier signals.
Autonegotiating devices also utilize parallel detec-
tion. This enables a link to be established with a nonne-
gotiating fixed speed device, and for a link to be
established before a device detects the FLPs. The state
diagram in Fig. 39-33 shows how the different possible
end conditions are reached. Notice that a 100 MBit
device can never parallel detect into a full duplex link.

Fiber optic links do not pass the FLPs needed for
autonegotiation though they do pass the carrier. One
consequence of this is that if full duplex operation over
a fiber link is desired, either manual configuration is
required, or an intelligent media converter is required.
Such a converter includes circuitry to autonegotiate the
link at each end of the fiber.
If a 10/100 NIC were to connect to a 10 MBit/s
repeater hub, the 10 MBit/s hub sends NLPs that are
detected by the NIC. Seeing the NLPs, the 10/100 NIC
goes to 10 MBit/s half duplex operation, and link is
established. This is correct since hubs are half duplex
devices.
If a 10/100 NIC were to connect to a 100 MBit/s
repeater hub, the 100 MBit/s hub sends a carrier that is

detected by the NIC. Seeing the carrier, the 10/100 NIC

goes to 100 MBit/s half duplex operation, and link is

established. This is correct since hubs are half duplex

devices.

If a 10/100 NIC were to connect to a 10/100 MBit/s

switch, the switch sends FLPs that are detected by the

NIC. After interpreting the FLPs, the 10/100 NIC goes

to 100 MBit/s full duplex operation, and link is estab-

lished. This is correct since 100 MBit/s is the highest

common rate, and switches can operate full duplex.

A media converter can be thought of as a two-port

repeater that coverts from one type of media to another.

The most common such conversion is from copper to

fiber. There are two basic types of media converters,

simple and intelligent.

Simple media converters have no intelligence and

just convert electrical signals to light and back. These

simple media converters can’t pass or detect FLPs.

Therefore, they can’t pass the signals needed for autone-

gotiation from one end to the other, nor are they capable

of autonegotiating with the ports at each end on their

own.

Intelligent media converters add electronics at each

end of the fiber link that are able to generate and inter-

pret FLPs. As a result such a converter can either auto-

negotiate with the port at each end, or be manually

configured. They are also capable of both half and full

duplex operation.

39.11.8 Managed Switches

All switches have the capabilities described so far.

Some switches add significant additional capabilities.

Switches with just the basic capabilities are known as

unmanaged switches, and have become very inexpen-

sive. Unmanaged switches operate automatically, and

do not require special settings for their operation.

Managed switches provide the capability to control the

switch’s internal settings.

Common control techniques include a dedicated

serial port for control, and Telnet, Web access using a

normal Web browser, or Simple Network Management

Protocol (SNMP). The last three control methods func-

tion over the network. Some managed switches provide

all four methods of control. The control capabilities

available using each method will often differ. The

methods that work over the network will usually require

that first the switch is accessed via the serial port, and

an IP number assigned to the switch. After that the other

control methods can reach the switch over the network

at the assigned IP address.

Figure 39-33. Ethernet autonegotiation state diagram.
10=10MBit/s, 100=100MBit/s, HD=half duplex,
FD = full duplex. The dashed lines show the parallel detec-
tion that can take place while waiting for the FLPs to be
recognized. Note that if parallel detection sets up a
100 MBit half duplex connection, then a full duplex
connection can never be established.

no

link

Carrier

FLP

LP

100

HD

10

HD

nego-

tiating

100

FD

10

FD