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NetCrossing Gateway NX-2E1/T1 Operator’s Manual

2-2

If the destination address is the gateway own physical address accept and process the packet.

If the destination address is for a station that is reachable in that port, discard the packet.

If the destination address is the reachable on the opposite port or is unknown, queue that packet to
be sent on the opposite port.

The gateway has capacity to store 500 entries in the Ethernet table. Entries are erased after a certain
amount of time to allow for stations to be moved and not show up in two distinct networks. You can
control this time-out with the

bridge

command. If the table ever gets full, entries that have been least

used are erased to make room for new entries. You can use the

show ethernet

command to display

the current list of stations known by the gateway.

The NetCrossing Gateway places the bridged packets from the LAN into a queue. Packets from this
queue are then transmitted into the WAN, but in a controlled fashion such that they never delay the
TDM traffic. Once in the WAN however, the combined traffic from the two TDM ports and the LAN
port might exceed the WAN capacity. If the equipment between the two gateways (bridges or routers
in the WAN) does not distinguish between the LAN and TDM traffic, it will discard packets
indiscriminately. Therefore a burst of LAN traffic could cause errors in the TDM links.

The NetCrossing gateway provides two mechanisms to prevent against such data loss. In a route
network using IP encapsulation you can specify the

type-of-service

for the TDM packets (using the

udp

command). This will tell any routers on the WAN to give priority to the TDM traffic over the

LAN traffic. The second mechanism is to specify a maximum WAN

capacity

(with the

wan

command). In this case the gateway will meter the traffic from the LAN such that the combined
throughput from the TDM and LAN ports never exceeds the specified WAN capacity.

Note that AFAR Radios distinguish between the Gateway LAN and TDM packets. If the offered
traffic exceeds the radio link capacity, the radios delay, and if necessary discard, the LAN packets
before affecting the TDM packets. Therefore, when using the AFAR Radios you do not need to use
the wan capacity parameter to prevent serial data loss.

2.3

Serial (TDM) Ports

The serial TDM ports carry continuous synchronous data streams. Unlike Ethernet traffic, this type
of data is “connection oriented”, i.e. the user serial device gets a “permanent” link to another serial
device that is connected to a remote gateway elsewhere in the WAN. You can establish this point to
point connection between any two gateways connected to the same WAN. Once the connection is
established the serial synchronous data flows continuously between your two serial devices as if they
were connected by wire.

2.3.1

Connection Setup

You must specify the remote

peer

gateway so that a connection setup can be initiated. If the wan

network type is set to bridge, the peer is specified as the serial number of the of the unit with which
you wish to connect (use the

wan

command). If the wan network type is set to route, the peer is

specified as the remote unit IP address using the

udp

command.

A gateway with an assigned peer sends, once a second, a