Handbook for Sound Engineers

1498 Chapter 39

39.11.13 Core Switching

At its simplest a core switch can be thought of as the
central switch in a star of stars configuration. Data that
needs only to travel between devices local to each other
is switched through the edge switches and never goes
through the core switch. Core switches often run at ten
times the data rate of the edge switches. For example if
the edge switches are fast Ethernet, they will each have
a gigabit uplink port that connects back to the gigabit
Ethernet core switch.
Besides allowing ten times the data traffic, another
reason to use the next higher-speed protocol in the core
switch is that the latency through the higher-speed link
and switch is only as long as if the higher speed was
not used.
Some core switches will be equipped with routing
capabilities to allow easy central control of all the
VLANs using SNMP management.
Core switches are often built to higher-quality stan-
dards than ordinary switches since such a core switch
can be a single point of failure in the network.
To prevent a single point of failure and greatly
increase the fault tolerance of the network, it is possible
to use a pair of core switches, each of which connects to
all of the edge switches. The network will continue full
operation even if one of the core switches or any link to
a core switch was to fail.

39.11.14 Ethernet Wiring

Proper design of an Ethernet cable plant is important for
reliable operation, ease of maintenance, and maximum
performance.

A typical Ethernet network cable path or link is

shown in Fig. 39-37. The items that make up the cable

plant include:

• Cabling connecting nodes—this can be Cat5 or fiber
  optic cable.


• Wiring closet patch panels.


• Station cables—the cable that runs from node to wall
  plate.


• Wall plates—the data or information outlet close to
  the node.

It is considered good design practice to include the

intermediate patch points as shown. This gives the cable

plant operator flexibility in accommodating expansion

and configuration changes.

There are two main types of cables used in Ethernet

networks: Cat5 cable and fiber optic cable. The

following sections will describe these cable types, as

well as the issues associated with each.

39.11.14.1 UTP Cable Grades

Unshielded twisted pair (UTP) cables are graded in

several categories.

• Quad: nontwisted four conductor formerly used for
  telephone premise wiring.


• Category 1: No performance criteria UTP.


• Category 2: Rated to 1 MHz (old telephone twisted
  pair).


• Category 3: Rated to 16 MHz (10Base-T and
  100Base-T4 Ethernet, current FCC required minimum
  for telephone).


• Category 4: Rated to 20 MHz (token-ring).


• Category 5: Rated to 100 MHz—now withdrawn as a
  Standard and replaced by Cat5e.


• Category 5e: Improved Cat5 with tighter tolerances.
  (100Base-TX and 1000Base-T Ethernet).


• Category 6: Rated to 250 MHz.


• Category 7: Shielded cabling mostly used in Europe.

Figure 39-36. Multiple loops around six switches. This is a
typical topology used to increase the fault tolerance of a
network. Spanning tree would disable enough of the links
between the switches to allow the network to be stable.

node

node

node

node

node

node

switch

switch

switch

switch

switch

switch

switch

(^1) » 10
Figure 39-37. Ethernet typical cable plant showing the
entire link from one Ethernet device to another.
Patch cord-
store bought,
stranded CAT5
Patch panel
Main run-field
Terminated, solid
core CAT5
DTE