E3Switch DS3 Operating information manual - page 18
Chapter 8: LAN Connections and Performance
efficient network by avoiding time-out requirements for packets that would otherwise be dropped during
bursts of network traffic.
Unless disabled in the settings or during autonegotiation, the converter will transmit pause frames to
attached LAN equipment when its buffer has reached approximately 60% capacity. During autonegotiation,
the converter indicates to the attached equipment that it will ignore received pause frames.
If overflow errors appear for a 1000Mbit/s port at the statistics management page of the converter, confirm
that the pause packet counter shown there is incrementing and that the attached LAN equipment can accept
pause packets. If the overflow errors disappear when the LAN port speed is reduced to 100Mbit/s, it is
possible that the attached LAN equipment is not receiving pause packets in time to interrupt large
1000Mbit/s traffic bursts. It may be necessary to operate at 100Mbit/s in this case, if packet loss during
bursts is unacceptable.
LAN Packet Priority
LAN packets may optionally contain class of service (CoS) information (802.1p information), which may
be used to specify packets that are time critical. In certain firmware, queue space is reserved in the
converter to allow frames with a “high” 802.1p CoS priority setting to bypass existing frames waiting to be
transmitted to the DS3/E3. This allows voice and other high-priority traffic to experience low-latency
transmission.
TCP/IP and General Performance Tuning
In a TCP/IP environment, maximum performance across the E3, T3/DS3 link will be achieved by adjusting
TCP/IP communication parameters of all LAN equipment attached to the converter including equipment
attached indirectly via hubs, switches or bridges. It should be possible to achieve TCP/IP transfer rates
within 5% of the theoretical maximum of 44Mbit/s for T3/DS3 or 34 Mbit/s for E3. The most important
parameter to adjust for maximum performance is the TCP window size. A valuable TCP/IP performance
testing tool called IPERF or JPERF (graphical version) and many excellent documents for setting TCP
parameters are available online.
Chapter 9: DS3 Packets and Link Topology
Link Bit-Errors
The converters at each end of the link will maintain synchronization with each other even at very high DS3
bit-error rates. The converter will count and drop packets with FCS/CRC and length errors.
Chapter 10: Troubleshooting
General
Check the front panel lights and the HTTP log entries at the settings management web page of the unit.
Check for orange status messages at the top of the HTTP status management web page of the unit and
associated orange errored-packet counters.
A great deal of diagnostic information is available by accessing the HTTP management interface of the
converter. Refer to the management section of this document for additional information.
The converter's front panel lights can provide useful information but are often under-utilized. They are
simple to read and can indicate where a data connection is being lost. It can be very helpful to learn their
meaning and monitor flashes as a packet is received at each port.
Incoming Circuit ID is shown at the top of the converter's HTTP management page for C-Bit DS3 links,
facilitating confirmation of the remote data transmitter when presented with a pair of unlabeled BNC cables.
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