Chapter 6: Interoperability
direction at a rapid, consistent periodic rate, which is proportional to the difference in clock speeds of each
TDM direction.
Chapter 7: Telecom Connections
Framing and Physical Link
The gateway can transmit the LAN data over a variety of E3, T3/DS3 links (with the appropriate media
gateway) such as fiber optic, microwave radio, laser, copper, satellite, or a combination. The gateway may
be used with a standard (i.e., M13, M23, clear-channel, C-Bit or G.751) framed or unframed, fractional or
full-rate E3 or T3/DS3 link with AMI and HDB3 or B3ZS encoding. C-Bit framing is recommended for
DS3 links. The gateway will report PMDL Circuit ID present on C-Bit links.
Each gateway regenerates the timing clock of the remote, received TDM bit-stream, within E3 and T3/DS3
standards. The receive and transmit 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
cable which will have more consistent shielding and conduction. The maximum length of each cable shall
be 440 meters for E3 or 300 meters for T3/DS3, but the acceptable cable lengths of equipment attached to
the gateway must be met as well. For lengths over 135 meters, testing in field should be used to determine
whether bit error rates are acceptable. Long cable lengths also require careful selection of cable type and
attention to sources of external noise.
Third-party fiber to copper media gateways can be used with the E3Switch gateway to implement fiber-
optic DS3/E3 links; however, refer to the interoperability section of this document for vendors to avoid.
Chapter 8: LAN Connections and Performance
LAN Ports
Each LAN port implements the following features to maximize LAN compatibility and link utilization and
minimize packet loss:
•
autosense/autoconfiguration/autonegotiation with the attached LAN.
•
100Mbit/sec data rates (1000Mbit/s via SFP or if GbE upgrade purchased).
•
full-duplex LAN connection.
•
data buffering.
•
1650-byte packet acceptance (1350 for mgmt and 9600 for jumbo).
These features and their ramifications are discussed below in more detail.
Autonegotiation
The network equipment attached to the LAN port of the gateway should be set for autonegotiation
mode in order to allow the gateway to negotiate a 100Mbit full-duplex connection.
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 gateway and the attached LAN equipment, with both
forced to 100BaseTX full-duplex. Autonegotiation interoperability and standards were not well understood
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