PRODUCT BULLETIN
Shielded Twisted-Pair Cabling
Support for Cisco Fast Ethernet
Products
Overview
A significant problem confronting many customers who are migrating their Token Ring networks to Ethernet
and Fast Ethernet is the existing installed shielded twisted-pair (STP) cabling used for Token Ring networks.
Based on testing done on Token Ring STP cabling types 1A, 2A, and 6A, Cisco certifies that the tested set of
Cisco Ethernet products will drive 10/100-Mbps Ethernet transmission rates at distances of up to 100 meters
with no infrastructure rewiring necessary. This capability can save customers tremendous infrastructure costs
and help speed up their deployment of Ethernet solutions.
Background
The Token Ring STP cable was originally developed by IBM during the 1980s and standardized by the IEEE
802.5 committee. The cable is designated by type numbers (for example, Type 1, Type 2, and so on) instead
of the later standardized category numbers (for example, Category 5) now prevalent in most LAN
installations. In addition to the design of the various types of cable, IBM also designed a complete suite of
connectors, patch panels, faceplates, and other hardware needed to construct a complete building wiring
system for the Token Ring network. This set of products and specifications was called the IBM Cabling
System (ICS). The ICS specifications originally supported data rates of up to 20 MHz and were later updated
to support up to 100 MHz. Cables conforming to the updated 100-MHz specification were designated with
an “A” suffix, for example, Type 1A. For those not familiar with the ICS, additional descriptive information
is provided in the ICS Overview section of this document.
In addition to high-quality shielding of individual pairs as well as the entire cable bundle, Token Ring STP
cable has several other important differences from Category 5 unshielded twisted-pair (UTP) cable. Some of
those differences are:
• Cable impedance—STP cable has an impedance of 150 ohms, UTP has100 ohms.
• Connector and connector pin-out—The ICS uses an IEEE 802.5 universal data connector (UDC), whereas
the RJ-45 connector is standard for most Ethernet-based LANs. The UDC is used throughout most Token
Ring networks and has no “male” or “female” version, that is, any UDC will plug into any other UDC.
RJ-45 connectors are also used in some Token Ring networks, but the RJ-45 connector pins used for
Token Ring connections are different from those used for Ethernet.
• Transmit to Receive shorting—The IEEE 802.5 UDC shorts the wires of the Transmit pair to the wires of
the Receive pair when the connector is unplugged.
Each of these three differences is addressed in individual sections later in this document.
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The Solution
Cisco has performed extensive testing of its switch products running 100-Mbps Fast Ethernet over 150-ohm STP cable. The
results of this testing and the actual experience of many customers around the world indicate that, with the proper
precautions, existing Type 1A and 2A cable can be successfully reused by customers migrating their Token Ring networks to
Ethernet. This bulletin discusses the testing performed by Cisco, potential issues, and the previously listed cable differences.
Cable Testing
The products listed in Table 1 have been tested and are supported on Token Ring STP for cable lengths up to the IEEE 802.3u
standard of 100 meters.
Table 1 Testing
Products Tested
WS-X6248-RJ-45
1
Description
Catalyst 6000 48-port 10/100 RJ-45 module
WS-X5224
Catalyst 5000 24-port non-ISL Fast Ethernet 10/100 RJ-45 switching module
WS-X5225R
Catalyst 5000 24-port 10/100 RJ-45 backbone switching module
WS-X5234-RJ45
Catalyst 5000 24-port 10/100 RJ-45 QoS switching module
WS-X5213A
Catalyst 5000 12-port 10/100 BaseTX Fast Ethernet RJ-45 switching module
WS-X4232-GB-RJ
WS-X4148-RJ
1
Catalyst 4000 2-port Gigabit Ethernet (GBIC), 32-port 10/100 Fast Ethernet RJ-45 module
Catalyst 4000 48-port 10/100 RJ-45 auto module
1
WS-C2948G
Catalyst 2948G fixed 48-port 10/100 Fast Ethernet, 2-port 1000BaseX (GBI1C) switch
WS-C2924-XL-A
Catalyst 2924 XL 24-port 10BaseT/100BaseTX autosensing Fast Ethernet switch
WS-C3512-XL
Catalyst 3512 XL 12-port 10/100 switch
WS-C3524-XL
Catalyst 3524-XL 24-port 10/100 switch
WS-C3548-XL
Catalyst 3548-XL 48-port 10/100 switch
WS-C2926T
Catalyst 2926T 24-port 10/100 RJ-45, 2-port 100BaseTX fixed switch
WS-C2924M-XL-EN
Catalyst 2924M 24-port 10/100 switch with two module slots (Enterprise Edition)
WS-C3508G-XL-EN
Catalyst 3508G XL Enterprise Edition
WS-X5013
Catalyst 5000 Ethernet 24-port 10BaseT RJ-45 switching module
WS-X5014
Catalyst 5000 48-port 10BaseT RJ-45 desktop Ethernet switching module
WS-X5203
Catalyst 5000 12-port 10/100TX RJ-45 Fast EtherChannel switching module
WS-X5223
Catalyst 5000 24-port 100TX RJ-45 group switched Fast Ethernet module
WS-X5224
Catalyst 5000 24-port desktop 10/100 RJ-45 switching module
WS-X5225R
Catalyst 5000 24-port 10/100TX Fast EtherChannel, 802.1Q/ISL, RJ-45 backbone switching
module
WS-X6348-RJ-451
Catalyst 6000 48-port 10/100, upgradeable to voice, enhanced QoS
WS-C2950-12
Catalyst 2950 12-port 10/100 autosensing, autonegotiating switch
WS-C2950-24
Catalyst 2950 24-port 10/100 autosensing, autonegotiating switch
WS-C2950C-24
Catalyst 2950 24-port 10/100 switch with two 100Base-FX uplinks
WS-C2950T-24
Catalyst 2950 24-port 10/100 switch with two fixed 10/100/1000Base-T ports
WS-C3550-48-EMI
Catalyst 3550 48-port 10/100 switch with two GBIC-based Gigabit Ethernet ports, enhanced
multilayer image
WS-C3550-48-SMI
Catalyst 3550 48-port 10/100 switch with two GBIC-based Gigabit Ethernet ports, standard
multilayer image
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Table 1 Testing
Products Tested
Description
WS-C3550-24-EMI
Catalyst 3550 24-port 10/100 switch with two GBIC-based Gigabit Ethernet ports, enhanced
multilayer image
WS-C3550-24-SMI
Catalyst 3550 24-port 10/100 switch with two GBIC-based Gigabit Ethernet ports, standard
multilayer image
WS-C2950G-12-EI
Catalyst 2950 12-port 10/100 switch with two fixed GBIC-based 1000BaseX uplink ports,
enhanced image
WS-C2950G-24-EI
Catalyst 2950 24-port 10/100 switch with two fixed GBIC-based 1000BaseX uplink ports,
enhanced image
WS-C2950G-48-EI
Catalyst 2950 48-port 10/100 switch with two fixed GBIC-based 1000BaseX uplink ports,
enhanced image
WS-2950G-24-EI-DC
Catalyst 2950 24-port 10/100 switch with two fixed GBIC-based 1000BaseX uplink ports, DC
version
1. Not recommended for use with non-A-suffix cable without the use of a low-Near End crosstalk (NEXT) or impedance-matching adapter. High-quality adapters
such as the ETS EA-DATA-U-45-L, EB-10/100BaseTX-U-45, or EB-10/100BaseTX-U-45-L should be used when attaching this module to non-A-suffix cables.
For each of the tested products, a variety of Berk-Tek, Belden, and IBM/Montrose cables were used. All tested products
experienced lower error rates on the Token Ring Type 1A, 2A, and 6A cable types than on the Category 5 cable for lengths
up to 170 meters. Traffic was generated with Ganymede Chariot. Traffic simulated was Lotus Notes, File Transfer Protocol
(FTP), Simple Network Management Protocol (SNMP), and Telnet. Line errors were monitored with Network General
Sniffer. Each test loaded the network to more than 90 percent for a five-minute period. All test connections used the IBM
Ethernet over STP Adapter Cable with no impedance matching (IBM P/N 31L3819). For Cisco products that are not listed
in Table 1, customers should contact their Cisco representative for information on specific plans for testing those products.
Observed Bit Error Rate
In all of the tests of the products listed in Table 1, the error rates observed were well below a bit error rate (BER) of 1E-9
with cable lengths of up to100 meters. Based on this testing Cisco is confident that users of these Cisco products can reliably
operate them over Token Ring A-suffix STP cables with lengths of up to 100 meters either with or without impedance
matching. Although it is probable that most Cisco Ethernet products would perform satisfactorily with Token Ring A-suffix
STP cable lengths of more than 100 meters, Cisco does not recommend, and does not support, using more than the IEEE
802.3u standard of 100 meters. Customers who use Token Ring STP cables of longer lengths are potentially exposed to
problems that can be very difficult to diagnose. Cable lengths of more than 100 meters also introduce the potential for
unreliable collision detection of minimum-size frames (see more discussion on this in the Questions and Answers section).
Note: Care must be taken not to mix long lengths of cables that have different impedance (for example, 50 meters of
Category 5 connected to 50 meters of Type 2A). The resulting impedance discontinuity causes reflections that result in higher
than normal error rates. Although the most reliable connection is with the same cable type from end to end, short lengths
such as 90 meters of Token Ring A-suffix STP cable and 5 meters of UTP patch cords on each end should not cause significant
problems.
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Connector and Connector Pin-Out
The connector and connector pin-out differences between 802.5 STP and Ethernet are addressed by the use of any of several
adapter blocks or cables. These adapters or cables have an IEEE 802.5 UDC on one end and an RJ-45 connector on the other.
The wiring of these components map the standard Ethernet pins of the RJ-45 connector to the appropriate pins on the IEEE
802.5 UDC. A description of the wiring is shown in Figure 1.
Figure 1
IBM Fast Ethernet over STP Adapter Cable (P/N 31L3819 and 31L3820)
Simple pin swap adapter blocks, as shown in Figure 2, or impedance matching adapters, as shown in Figure 3, can also be
used to accomplish the pin-out conversion from the IEEE 802.5 UDC to the RJ-45 Ethernet standard. Although either of the
designs shown allows connections that meet the required standard BER on Token Ring A-suffix STP cable, Cisco testing has
shown better results using an adapter that does not do impedance matching. For A-suffix cable, Cisco recommends the use
of an adapter without impedance matching, such as either the IBM adapter cable shown in Figure 1 or the ETS
EA-DATA-U-45-L adapter. Using either of these alternatives allows support of 100 meters on Token Ring A-suffix STP and
should allow a high percentage of existing Token Ring cable plants to be used when those networks are migrated to Ethernet.
Non-A-suffix STP cable, such as Type 1, Type 2, and Type 6, may not work satisfactorily without impedance matching or
the use of a low-NEXT adapter such as the ETS EA-DATA-U-45-L or EB-10/100BaseTX-U-45-L. Customers have
experienced problems using non-A-suffix STP cables, especially when used in conjunction with 48-port switch modules. In
all cases to date, these problems have been resolved by the use of good quality low-NEXT adapters. Because the non-A-suffix
cable was designed many years ago and was only certified by the manufacturer to the early standard of 20 MHz, no
guarantees can be made about its use at 100 MHz. See the Questions and Answers section for more discussion on the reuse
of non-A-suffix cable.
Note: These adapters are often called baluns. This terminology is technically incorrect because the word balun is an
abbreviation for balanced to unbalanced, such as the adaptation of a twisted pair (balanced) transmission line to a coax
(unbalanced) transmission line. Both STP and UTP are balanced transmission lines.
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Figure 2
No Impedance Matching
Figure 3
Impedance Matching Adapter
A number of products are available for this purpose. Following is a list of those of which we are aware; however, there may
be others:
• ETS (for more information, see http://www.etslan.com, and for an excellent technical white paper, “Using the IBM
Cabling System for Fast Ethernet,” see http://www.etslan.com/Pages/jackchat.html)
– EB-10/100BaseTX-U-45 (RJ-45 to UDC 10/100BaseTX adapter/impedance matching)
– EB-10/100BaseTX-U-45-L (RJ-45 to UDC 10/100BaseTX adapter/impedance matching, low NEXT)
– EA-DATA-U-45-L (RJ-45 to UDC 10/100BaseTX adapter/non-impedance matching, low NEXT)
• Lantel Solutions (for more information, see http://www.lantelsol.com, and for a white paper with even more detail, see
http://www.lantelsol.com/pdf_doc/Token_Ring_to_Fast_Ethernet_Migration.pdf)
– SB-LN/VIP-DATA, low NEXT adapter
– SB-LN/VIP-STP, shielded version
– The SB-LN is compatible with Voice over IP (VoIP) and is non-impedance matching
• IBM (for more information, see http://www.ibm.com)
– 31L3819 (Fast Ethernet STP 4-foot cable)
– 31L3820 (Fast Ethernet STP 8-foot cable)
• RIT (for more information, see http://www.rittech.com/ecatalog/index.html)
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– R3712017 ICS to RJ-45 (10/100 Base-T) Adapter
Note: Care should be taken to ensure that the correct adapter block is used. A variety of adapters look very similar to the
ones shown in this document. Adapters for 10Base-T and Token Ring on UTP, for example, either will not work at all or
may give unsatisfactory error rates for 100Base-TX applications. For adapters with part numbers other than those listed, it
is advisable to check with the manufacturer to ascertain the specifications and recommended application.
Transmit Pair to Receive Pair Shorting
The IEEE 802.5 UDC contains shorting bars that cause the Transmit contacts to be shorted to the Receive contacts when the
connector is not plugged in. This “wrap path” is used to maintain the integrity of the ring when ring segments are
disconnected, but it can potentially cause problems when used in Ethernet networks. This type of connector can cause a
full-duplex Ethernet port, for example, to receive its own transmitted frames if the connector is not plugged in. Worse, if the
port is part of a switch with a shared buffer design, these looping frames may adversely affect the entire switch. Fortunately,
this condition can be detected and circumvented by software in most switches.
This problem has been addressed in all Cisco Ethernet switches and, although the switch behavior is somewhat different from
switch to switch, the condition is handled without serious network impact. Users should be aware, however, of an important,
unresolved condition that occurs on Catalyst 4XXX/29XXG/49XXG switches when 1) portfast is enabled and 2) a UDC
connector remote from a switch port (for example, at the workstation end of the cable) is unplugged. During the time the
switch is resolving the resulting loop, packets may be dropped on other ports of the same switch. This problem is currently
unresolved. See bug ID CSCdu24117 for additional details.
Questions and Answers
Q. If I run 100-Mbps Fast Ethernet over Token Ring STP instead of UTP, is this a nonstandard configuration?
A. No. In fact the 802.3u 100Base-T standard (IEEE 802.3u, clause 25) allows for both UTP and STP as specified in ANSI
X3.263 (TP-PMD), which covers both 100-ohm UTP and 150-ohm STP.
Q. Will the Cisco Technical Assistance Center (TAC) now support Fast Ethernet connections over Token Ring STP?
A. Yes, for those products tested, when using the proper adapter and adhering to distance limitations.
Q. Have other vendors performed similar testing?
A. Yes. Both IBM and Intel have tested their products with results similar to the Cisco results.
Q. What about support for products not listed?
A. The decision to test additional products is the responsibility of the Cisco product manager for each product. Customers
should contact their Cisco account manager or systems engineer for information regarding the possibility of testing any
specific product. Cisco field personnel should contact the appropriate product manager for discussions regarding this testing.
Q. Many of my Token Ring cable runs are more than 100 meters. Why does Cisco support only lengths up to 100 meters?
A. Although the Token Ring standard supported cable runs up to 300 meters, Fast Ethernet is a different technology and
does not support this length. Cisco limits support to 100 meters because of the following considerations:
• The IEEE 802.3u 100-Mbps Fast Ethernet standard specifies a maximum length of 100 meters.
• Vendors who design physical layer (PHY) chips use 100 meters as a design criterion for these chips. Although most of the
PHY chips in the past theoretically may have been capable of driving cable lengths of significantly more than 100 meters,
the trend is for chips that have higher densities with significantly lower power output than the older versions. Some
high-density Cisco Fast Ethernet products already use these newer chips and more will inevitably use them in the future.
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• Stations running 100-Mbps Fast Ethernet half-duplex connections over cable lengths of more than 100 meters are
exposed to unreliable collision detection for minimum-size packets (512 bit times). This is because 200 meters (round-trip
for 100 meter connections) can contain approximately 512 bits at 100 Mbps. Therefore, a station connected to a cable
longer than 100 meters could send a minimum-size frame that suffered a collision at the remote end of the link, but it
would not detect the collision itself and would believe the transmission was successful. The probability of this, and
therefore the exposure, would increase as the cable length increased beyond 100 meters.
Q. Why does Cisco recommend using adapters without impedance matching for Type 1A and 2A cable?
A. Although adapters that include impedance matching capability also work satisfactorily, Cisco testing and feedback from
customers has indicated that the adapters without impedance matching (see Figures 1 and 2) experience lower error rates at
longer cable lengths and are typically less expensive. Additionally, some impedance matching adapters contain transformers
that may cause problems with the implementation of IP telephones (see next question).
Q. My plans include running IP telephones over my LAN wiring. Will Token Ring STP support this as well?
A. Yes, the inline power version of each applicable product listed in Table 1 is supported to power Cisco IP telephones.
However, it should be noted that there are only two twisted pairs in the Token Ring STP cables. Therefore, inline power for
IP telephones can be supported, but mid-span power insertion cannot, because this requires more than two pairs. Also, a
potential issue exists if impedance matching adapters are used, depending upon the design of the adapter. Although the
non-impedance matching adapters shown in Figures 1 and 2 and the impedance matching adapter shown in Figure 3 should
not present a problem, adapters that contain transformers may prevent the passing of the DC phantom current used to power
some telephones. This is not always the case and customers with this concern should contact the adapter manufacturer to
ascertain the ability of the adapter to support DC phantom drive current.
Q. Will Token Ring STP cable also be capable of supporting Gigabit Ethernet over copper?
A. No. The current Gigabit Ethernet over copper specification requires four twisted pairs (eight conductors). Token Ring
STP cable contains only two pairs. However, this is only a problem for cable runs where Gigabit Ethernet is likely to be
needed. If Gigabit Ethernet to the desktop is not required for quite some time, the majority of the existing cable may continue
to be useful for many years.
Q. The cabling in my buildings was installed in 1987 and is Type 1, not Type 1A. What is the difference? Will Type 1 cable
also support 100-Mbps Fast Ethernet?
A. When the ICS was introduced in 1984, the electrical specifications for the STP cabling were for testing up to 20 MHz.
These specifications have been adequate for the range of applications found in most office environments. However, when
IBM announced support for 100-Mbps Fiber Distributed Data Interface (FDDI) networks on STP cables, the testing
specifications for Types 1, 2, 6, and 9 cable were extended to subject the same cable designs to more rigorous testing. This
extension ensured suitable operation at higher frequencies and was published in the ANSI X3.263 (TP-PMD) specification
in 1995. The extended testing specification for Type 1A, 2A, 6A, and 9A ensures adequate performance to run 100-Mbps
FDDI and Ethernet networks on Token Ring STP cable.
Because the specification for older Type 1, 2, 6, and 9 cables is a proper subset of the specifications for Type 1A, 2A, 6A, and
9A cables, some (probably most) Type 1, 2, 6, and 9 cables are as suitable as the later A-suffix cables. However, some early
cables do not meet the specification for 100 Mbps and may not work satisfactorily without the use of impedance matching
or low-NEXT adapters. Suitability of this cable may also be affected by the length of individual cable runs, with shorter
length runs less likely to experience problems than longer ones. Users who have concerns about the suitability of their existing
non-A-suffix cables should have the cables tested to determine if they conform to the attenuation and crosstalk parameters
specified in the ANSI X3.263 (TP-PMD) specification (ISO 11801 Class D 150 ohm STP test standard) using an appropriate
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cable tester. Many cabling contractors can perform these tests on installed cables. A few customers have experienced
problems with this early cable but to date all of these have been able to achieve satisfactory performance by using good
quality low-NEXT or impedance matching adapters such as the ones listed earlier in this document.
ICS Overview
This section is included as a brief overview for those who are not familiar with the characteristics and components of the
ICS. IBM designed the ICS during the early 1980s and the essential designs, such as the cable characteristics and the UDC,
were subsequently incorporated into the 802.5 and ANSI X3.263 (TP-PMD) standards. The ICS consists of various cable
types, the UDC, wiring closet accessories (distribution panels, jumpers, cable management hardware, and so on), and
faceplate accessories for mounting data connectors at workstation locations.
Cables
There are a number of cable types specified by the ICS. Table 2 describes the characteristics of these types.
Table 2 Cable Types and Their Characteristics
Cable
Description
1
Type 1
Shield around two individually shielded twisted pairs of
AWG 22 solid copper wire (indoor and outdoor versions
specified)
Type 21
Same as Type 1 cable with the addition of four twisted
pairs of 22 AWG telephone conductors outside of the
shield, but inside the cable’s plastic cladding
Type 3
Specification only, for AWG 22 or 24 telephone twisted pair
Type 5/5J
Two optical fiber conductors (no twisted pairs)
Type 61
Two shielded, stranded twisted pair of AWG 26 wire for use
as patch cables.
Type 8
Under-carpet cable; two shielded AWG 26 pairs of solid
copper wire
Type 9
Two shielded pairs of AWG 26 solid copper wire; lower cost
alternative to plenum grade Type 1
Illustration
1. There is also an A-suffix version of this cable type. A-suffix cables are certified for operation at 100 MHz, whereas non-A-suffix cables are
certified for only 20 MHz.
Connectors
The UDC is an hermaphroditic connector. These connectors directly attach to each other without the necessity of a classic
male/female connector orientation. Figures 4 through 7 show this design. Although many Token Ring networks use RJ-45
connectors, either with ICS cables or with Category 5 cables, most early Token Ring networks were implemented using the
UDC as the common connector for all connections except the connector that plugs directly into the workstation. That
connector was normally a DB9 connector or, later, an RJ-45 connector.
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Figure 4
Token Ring UDC Connectors
The UDC was used on both ends of an ICS cable. In the user’s office, for example, the connector was mounted in a faceplate
as shown in Figures 5 through 7. In the wiring closet, the other end of the same cable was terminated with a UDC mounted
in a distribution panel. A jumper cable with UDCs on both ends was used to connect between the distribution panel and
rack-mounted equipment as shown in the section Token Ring Example. In each case, UDCs were plugged directly into other
UDCs.
Another design feature of the UDC is shorting bars that automatically short the Transmit pair to the Receive pair when the
connector is unplugged. These shorting bars can be seen in Figure 5. Note that the faceplate in Figure 5 has a telephone
connection. This connection is wired to the telephone twisted pair that is included in Type 2 cable. See Table 2 for a
description of Type 2 cable.
Figure 5
Token Ring Faceplate
UDC Connector Mounted in
IBM Token Ring Faceplate
Telephone Connection
Shorting Bars
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Figure 6
How the UDC Is Used in the Token Ring Faceplate
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Figure 7
Token Ring Office Connection
Token Ring Cable with UDC Plugged into
UDC Mounted in Faceplate
Using the ICS for Fast Ethernet
As described earlier in this document, reusing the existing ICS for Fast Ethernet requires adapting the connector type on both
ends of the cable from the UDC to the RJ-45 configuration. This is accomplished with an adapter block as shown in Figure
8. This adapter has a UDC on one end and an RJ-45 on the other that is wired to the pins used for Ethernet. These adapters
are used in both the user office, as shown in Figure 9, as well as in the wiring closet. It is important to make sure that the
correct adapter is used, because adapters also exist that have the RJ-45 receptacle wired to the pins used by Token Ring and
will not operate correctly in Ethernet networks.
Figure 8
Token Ring to Fast Ethernet Adapter
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Figure 9
Token Ring to Fast Ethernet Adapter Plugged into UDC Mounted in Faceplate
When the ICS is used for Ethernet, the RJ-54 connector of the Ethernet Category 5 cable is plugged into the Token Ring to
Fast Ethernet adapter as shown in Figure 10. This connection allows the Ethernet Transmit and Receive pairs to be correctly
mapped to the proper pairs of the ICS.
Figure 10
Token Ring to Fast Ethernet Adapter with Category 5 Cable Plugged into RJ-45 Connector
Token Ring to Fast Ethernet adapters may also be used to adapt Token Ring jumper cables for use with Ethernet by plugging
the adapter directly into the jumper cable as shown in Figure 11.
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Figure 11
Adapting a Token Ring Cable for Use with Fast Ethernet Category 5 Cable
Token Ring to
Fast Ethernet Adapter
Token Ring UDC
Connector Pin Outs
The UDC connector has the following pin assignments:
• Red–Receive +
• Green–Receive • Orange–Transmit +
• Black–Transmit An RJ-45 connector used for Ethernet has the following the pin assignments (colors are Token Ring STP cable colors):
• Pin 1–Red (Receive +)
• Pin 2–Green (Receive –)
• Pin 3–Orange (Transmit +)
• Pin 6–Black (Transmit -)
Adapters such as those shown in Figures 1, 2, and 3 accomplish this mapping of UDC connector pins to Ethernet pins.
Wiring Closet Examples
The following examples show a typical Token Ring wiring closet configuration and how that same wiring system might be
used for an Ethernet network.
Token Ring Example
Figure 12 shows an example of the various components of the ICS as they may be used in a typical Token Ring installation.
Cables from workstations, other racks, and other wiring closets are terminated on the back of distribution panels mounted
in standard racks. Jumper cables are used to connect these cables to Token Ring components, also mounted in the rack, using
the same UDC-type connector. The hermaphroditic design of the UDC allows the jumpers on the front of the distribution
panels to be plugged directly into the cables terminated on the back of the panel. At the workstation end, the cables are
normally terminated in faceplates. Figure 6 shows a detailed view of the faceplate. As in the wiring closet, the UDC is used
on the end of both the cable in the faceplate and the cable from the workstation. Also, as in the wiring closet, these connectors
are plugged directly into each other to make the connection.
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Figure 12
Token Ring Wiring Example
Type 1 or Type 2 Cables
Type 1
Cables Between
Wiring Closets
A
B
C
D
E
F
G H
A
B
C
D
E
F
G H
4
5
6
1
2
3
1
2
3
1
2
3
4
5
4
5
8
7
A
B
C
D
E F
G H
A
B
C
D
E
F
G H
4
5
6
9
7
8
9
6
7
8
9
6
Type 6
Token Ring
MAUs
Wiring Closet A
1
2
3
1
2
3
4
5
6
7
7
8
8
Token Ring Workstations
9
9
Token Ring
MAUs
Type 6
Wiring Closet B
Ethernet Example
Figure 13 shows an example of the network shown in the Token Ring example (Figure 12) after conversion to Ethernet has
been completed. The rack-mounted Token Ring components have been replaced with Ethernet components, and the
workstation NICs have been changed to Ethernet. All the basic cabling remains in place, unchanged. However, the new
Ethernet switches, routers, and so on have RJ-45 connectors. Therefore, the Ethernet pins of these connectors must be
mapped to the UDC connectors in the distribution panels and again between the UDC connector in each faceplate and the
workstation NIC. This mapping is accomplished using the pin-mapping adapters and jumpers described earlier in this
document.
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Figure 13
Ethernet Wiring Closet Example
Type 1 or Type 2 Cables
Type 1
Cables Between
Wiring Closets
A
B
C
D
E
F
G H
A
B
C
D
E
F
G H
4
5
6
3
1
1
1
Loop on this
port because
remote
connector is
shorted
2
2
2
8
7
A
B
C
D
E
F
G H
A
B
C
D
E
F
G H
5
6
9
1
3
3
4
4
5
6
7
8
5
6
7
2
3
2
3
4
9
1
8
Ethernet Workstations
4
7
8
9
9
Ethernet
Switches
Wiring Closet A
Pin Matching
Adapters
Pin Matching
Adapters
Ethernet
Switch,
Router, Etc.
Wiring Closet B
Transmit pair shorted
to receive pair because
connector is unplugged
Figure 13 also shows how the transmit-to-receive shorting occurs when any UDC is unplugged. Because the workstation at
the bottom of the figure is unplugged, the UDC in the associated faceplate shorts the Transmit pair to the Receive pair,
causing a loop on the Ethernet switch port in Wiring Closet A. A discussion of the effect of this loop appears earlier in this
document.
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Cisco Systems has more than 200 offices in the following countries and regions. Addresses, phone numbers, and fax numbers are listed on the
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