Chapter 6: Interoperability
If LAN equipment appears to disable a port connected to the converter, be aware that “sophisticated”
routers and switches will often disable a LAN port if data being sent appears similar to data or MAC
addresses being received, as is the case in telecom loopback.
Autonegotiation problems
There are rare cases with older LAN equipment in which it may be necessary to disable autonegotiation. If
crc-errors or short packet errors are seen in the management statistics of the LAN port, the attached LAN
equipment has probably configured itself to half-duplex mode and colliding packets are being lost. In such
a case, autonegotiation should be disabled on both the converter and the attached LAN equipment with both
forced to 100BaseTX full-duplex. Autonegotiation interoperability and standards were not well understood
by the industry at the inception of 100BaseTX, resulting in some older LAN equipment not understanding
the converter's autonegotiation advertisement of strictly full-duplex capability.
It is highly desireable to leave autonegotiation enabled so that changing attached LAN equipment does not
result in the new equipment defaulting to half-duplex if set to autonegotiate.
SFP LAN Port 1
This port is designed to be compatible with inexpensive, high-quality, copper or fiber-optic, SFP
transceivers from Finisar, which allows LAN connections of 10km or more. Most other industry-standard
SFP transceivers will work as well; however, fiber-optic features such as temperature and optical
transmit/receive power and alarms will only be available if using Finisar transceivers. Non-Finisar copper,
RJ45 SFP transceivers may only operate in 1000Base-T mode, while recommended transceivers from
Finisar, and possibly Avago or 3Com will operate in 100Base-TX mode as well.
Pause Frames
Unless disabled in the settings or through autonegotiation, the converter sends pause command frames to
attached LAN equipment when the converter's incoming LAN buffers become nearly full. The converter
ignores pause command frames sent to it.
VoIP / Video or High-CoS Priority Frames
Receive queue space is reserved in the converter to allow frames with high 802.1p class-of-service (CoS)
priority settings to bypass existing frames waiting to be transmitted to the DS3/E3. This allows voice, video
and other high-priority traffic to experience low-latency transmission. Firmware shipped since July 2008
allows the “high” CoS level to be configured. Prior firmware has the high-CoS level set at >=6.
Telecom
The converter can transmit over a variety of E3 or T3/DS3 links (with appropriate media converters) such
as fiber optic, microwave radio, laser, copper, satellite, or a combination; however, the attachment interface
is always via 75-ohm copper coaxial rather than optical. The point-to-point telecom link must be
unchannelized, i.e., not subdivided into T1 or E1 channels. The telecom link may be either framed or
unframed and supports both M13, M23, clear-channel, C-Bit, and G.751 framing. C-Bit framing is
suggested for DS3 links.
Be aware that during loopback testing, “sophisticated” routers and switches will often disable a LAN port if
data being sent appears similar to data or MAC addresses being received. This can cause confusion.
Fiber/Copper Media Converters
Transition Networks DS3/E3 Coax to Fiber Media Converter, SCSCF3014-100 has been reported to lack
the ability to properly maintain separate DS3/E3 transmit clock speeds in each direction and are not
recommended. This problem typically manifests itself as frame slips or loss of telecom signal lock in one
direction at a rapid, consistent periodic rate, which is proportional to the difference in clock speeds of each
telecom direction. If such media converters are already in use, setting the DS3/E3 transmit clock source of
one
of the E3Switch units to “loop” may alleviate problems.
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