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Chapter 6: Interoperability
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
In certain firmware, 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 allows
the "high" CoS level to be configured.
Telecom/WAN
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.
Certain firmware allows subrate/fractional WAN connectivity.
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 WAN units to "loop" may alleviate problems.
Routers and Switches
The configuration of routing tables of the PPPoE equipment attached to the E3Switch converter is beyond
the scope of this document.
Chapter 7: Telecom Connections
Framing and Physical Link
The converter can transmit the LAN data over a variety of E3, T3/DS3 links (with the appropriate media
converter) such as fiber optic, microwave radio, laser, copper, satellite, or a combination. The converter
may be used with a standard (i.e., M13, M23, clear-channel, C-Bit or G.751) framed or unframed, E3 or
T3/DS3 link with AMI and HDB3 or B3ZS encoding. The link must be unchannelized, i.e., not subdivided
into T1/E1 channels. C-Bit framing is recommended for DS3 links. Newer firmware supports PMDL
Circuit ID on C-Bit links.
Certain firmware supports sub-rate/fractional WAN.
Each converter generates the timing clock of its transmitted bit-stream, within E3 and T3/DS3 standards,
either locally, or locked to either port's received bit-rate. The incoming clock rates are displayed at the
unit's HTTP management page.
Telecom Cabling
For the E3 or T3/DS3 connection, two 75-ohm coaxial cables (one transmit and one receive) with BNC
connectors are required at each end. It is important that 75-ohm cable be used and not 50-ohm cable. For
long connections or in electrically noisy environments it may be important to use a high-quality 75-ohm
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