E3Switch DS3 Operating Information Manual - page 13
Chapter 5: Operating Modes and Configuration
Port to Port Packet Flow
LAN-to-LAN
Full LAN-to-LAN packet flow can be enabled on a unit, if desired. This might be useful if it was desirable
for incoming SFP management packets to exit the copper LAN Port 2 of the unit, along with the packets
carrying TDM data, in order to reach and manage the remote gateway. LAN-to-LAN unidirectional flow
for monitoring may also be configured if desired.
LAN-to-LAN should be used cautiously in combination with management or data-only LAN port settings.
The blocking of a subset of traffic can result in network and spanning tree topologies which can be
inappropriate or difficult to diagnose.
Loopback
C-Bit T3 TDM ports will respond to FEAC loopback requests. A TDM port can also be put into loopback
via appropriate DS3-MIB SNMP commands.
LAN Port Settings
The hardware for two LAN ports exist on all gateways shipped; however, entry-level models ship with only
100Base-TX mode on LAN Port 2 enabled. See upgrades section of this manual to enable these additional
features if required:.
●
GbE, GigE 1000Base-T for the RJ-45 LAN Port 2
●
jumbo frames (9600 bytes)
See the “Interoperability” section of this manual for information on packet lengths and detailed port
connection/autonegotiation discussion.
The autonegotiation mode of the gateway must match the autonegotiation mode of attached LAN
equipment. If autonegotiation is enabled on the gateway it must be enabled on the attached equipment. If
disabled on the gateway, it must be disabled on the attached equipment. This requirement is necessary to
fulfill 802.3 standards which mandate a fallback to half-duplex operation if an autonegotiation mismatch
exists. The gateways require full duplex LAN connections to operate.
LAN Port Speed
1000Mbit/s LAN speeds are only available via the SFP port or if GbE LAN has been purchased.
100Mbit/s is generally preferred over 1000Mbit/s, which generates significantly more power-requirements,
heat, and radiated noise even in the absence of packet flow. 1000Mbit/s may slightly reduce path latency,
as an incoming LAN packet must be fully received before being forwarded to an outgoing port. The latency
savings to receive or transmit a 1500-byte packet at 1000Mbit/s vs 100Mbit/s speed is 0.108 milliseconds
(1500bytes/packet x 8bits/byte / (100Mbits/s) - 1500bytes/packet x 8bits/byte / (1000Mbits/s)).
Setting more than one LAN port to 1000Mbit/s is not recommended and may result in
underflow/overflow errors in certain high packet load, memory-intensive cases.
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 gateway 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 gateway's autonegotiation advertisement of strictly full-duplex capability.
13