E3Switch LLC High-Speed Ethernet to Single/Dual DS3/E3 Network Extender V5.4 Operating Information Manual - page 15
Chapter 5: Operating Modes and Configuration
LAN Port Speed
1000Mbit/s LAN speeds are only available if firmware enabling the SFP port option or 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)).
1000Mbit/s LAN port speed may be desireable when one LAN port is configured to monitor the other LAN
port in addition to receiving incoming DS3/E3 data. In such a case, the data rate that the LAN port is
expected to transmit (the sum of all ports that could be a data source for the LAN port) may be greater than
100Mbit/s. The HTTP management statistics screen will show overflow errors if a port's data rates are
exceeded.
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 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.
SFP Second LAN Port
The SFP LAN Port 1 hardware exists on all converters shipped and may be enabled as purchased or enabled
by purchasing an upgrade password. This upgrade enables out-of-band management, through either LAN
port, or fiber-optic LAN connections of 10km or more. Refer to interoperability section of this document
for compatible SFP transceivers.
Dedicated Management/Data LAN Ports
If the SFP Second LAN Port has been purchased and enabled, then either LAN port may be configured to
pass all packets to DS3/E3 or, selectively, to pass only management or only data packets when such can be
determined.
LAN-to-LAN forwarding 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.
If a LAN port is configured for data-only packets, the unit will drop incoming management packets destined
for an E3Switch MAC address. This provides a moderate level of security. These packets and
management broadcast/multicast packets may not be forwarded to the second LAN if LAN-to-LAN traffic
is configured.
If a LAN port is configured for management-only packets, the unit will not forward, to the DS3/E3, unicast
packets destined for non-E3Switch MAC addresses. Broadcast and multicast packets will be forwarded.
LAN-to-LAN forwarding may occur if so configured.
VLAN
The converter passes all VLAN information, unaltered, between ports. VLAN configuration settings shown
at the HTTP management page apply only to communication with the converter's management entity.
15