Ethernet Standards

The vast majority of customer have LAN's that employ Ethernet as the network protocol - a few use Token Ring.  At least 90% of these networks are 10BASE-T.  The LAN sits behind the router and  hub or high-speed Ethernet switch, and the workstations are connected in a star topology.  Actually, most networks have replaced the Cat 3 cables with Cat 5.  Both Cat 3 and 5 cables have 4 unshielded, twisted pairs of copper wires and use the RJ-45 connector, as shown below:

• Ethernet 10Base-T uses pairs 2 and 3 (pins 1-2, 3-6) 

• Ethernet 100Base-T4 uses pairs 2 and 3 (4T+) (pins 1-2, 3-6) 

• Ethernet 100Base-T8 uses pairs 1,2,3 and 4 (pins 4-5, 1-2, 3-6, 7-8) 

• Token-Ring uses pairs 1 and 3 (pins 4-5, 3-6) 

• 100VG-AnyLAN uses pairs 1,2,3 and 4 (pins 4-5, 1-2, 3-6, 7-8)

• ATM 155Mbps uses pairs 2 and 4 (pins 1-2, 7-8) 

* Shortwave and Longwave - the boundary between these two wavelengths is 1100 nm.  These were defined originally for dual-wave WDM that used 850 nm for SW and 1310 nm for LW.

More Info

10BaseT over Copper = 100m Cat 3 or better
10BaseFL over Fiber = 2km mulitimode, 25km singlemode
100BaseT over Copper = TX: 100m Cat 5; T4: 100m Cat 3
100BaseFX over Fiber = varies depending on connection type; see below
ATM over Copper = 100m Cat 5 for 155mbps
ATM over Fiber = Varies depending on data rate and fiber type.

This is assuming special gear like extended distance repeaters are not
used.

Here are some Fast Ethernet topology rules illustrated:
---
100BaseT    100m on 2 pair UTP Cat 5
100BaseT4   100m on 4 pair UTP Cat 3
100BaseFX   412m half duplex on MM fiber
100BaseFX   2km full duplex on MM fiber
100BaseFX   15-20km full duplex on SM fiber

Fast Ethernet repeater rules

Class I repeater
    - Relaxed timing constraints within the repeater. <0.7us
      transit delay. Makes media translation, stacking etc.
      possible.
    - One Class I repeater permitted between end stations.

Class II repeater
    - Tighter timing constraints within the repeater. <0.46us
      transit delay.
    - Two repeaters permitted between end systems. If all the links
      combine to <100m, may have 3 repeaters.
    - Normally a 5m UTP or 6m fiber cable length is permitted between
      cascaded repeaters. This link can be longer if end station
      distances are shortened accordingly, such that the total
      system diameter does not exceed 205m and no single copper link
      exceeds 100m.

Repeater rules illustrated:
----  utp (Cat 5 for TX or Cat 3 for T4)
====  mm fiber
[DTE] end station (including Mac entities like routers, bridges and
switches)
[H]   hub (repeater)

Direct connection of end stations (DTE's):
[DTE]--- 100m ---[DTE]
[DTE]=== 412m ===[DTE]

Using one Class I repeater:
[DTE]--- 100m ---[H]--- 100m ---[DTE]
[DTE]=== 136m ===[H]=== 136m ===[DTE]

Using one Class II repeater:
[DTE]--- 100m ---[H]--- 100m ---[DTE]
[DTE]=== 160m ===[H]=== 160m ===[DTE]

Using two Class II repeaters:
[DTE]--- 100m ---[H]-- 5m --[H]--- 100m ---[DTE]
[DTE]=== 111m ===[H]== 6m ==[H]=== 111m ===[DTE]

Topologies can be mixed so long as connection rules are respected.
E.g.,
Using two Class II repeaters:
[DTE]--- 100m ---[H]-- 5m --[H]=== 111m ===[DTE]


Table of Maximum Cable Budgets (meters)
(From 802.3u specification)

Connection Type             TX/T4   Fiber   T4 & Fiber  TX & Fiber
Direct                      100     412     n/a         n/a
One Class I repeater        200     272     231 b       260.8 b
One Class II repeater       200     320     n/a c       308.8 b
Two Class II repeaters      205     228     n/a c       216.2 d

b) Note: Assumes 100 meter copper link and one fiber link.
c) Not Applicable: T4 and FX cannot be linked with typical Class II
repeater.
d) Note: Assumes 105 meters of copper link and one fiber link.

A UTP link should never exceed 100m in length, due to attenuation
(signal loss) rather than timing considerations.

Using full duplex Fast Ethernet, the maximum distances are:
[DTE]=== 2km ===[DTE]       multimode fiber
[DTE]=== 15-20km ===[DTE]   singlemode fiber

---
Gigabit Ethernet transmission distances (pre-standard)

Copper      25m over twinax
1000BaseT   Probably up to 100m using UTP. The 1000BASE-T (UTP)
            work will not be part of the "first wave" of Gigabit
            Ethernet; it is being developed in a separate effort, so
            as not to delay initial standards deployment.
1000BaseF   500m full duplex on MM fiber, 2-3km full duplex on SM
fiber
1000BaseF   100m half duplex on MM fiber, shared LAN

10mbps Ethernet, 100mbps Fast Ethernet and Gigabit Ethernet
distance/timing

                                        10mbps      100mbps     1Gbps
bit time                                100ns       10ns        1ns
collision diameter (bit times)          512         512         4096
slot time (bit times)                   512         512         4096
maximum round-trip delay                51.2us      5.12us      4.09us
maximum repeater-free diameter          4000m       412m        400m
minimum packet size                     64 bytes    64 bytes    64
bytes*
maximum packet size                     1518 bytes  1518 bytes  1518
bytes
maximum throughput, minimum packets     14,880pps   148,800pps
maximum throughput, maximum packets     812pps

* must be padded to 512 bytes on half duplex links (in order to get a
useful network diameter)