Afar NX-2E1, Operator'S Manual

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NetCrossing Gateway NX-2E1/T1 Operator’s Manual
2-3
A gateway that receives a connect request packet responds with a positive acknowledge or with a
negative acknowledge packet depending on whether its configuration is “compatible” with the
requesting gateway. The compatibility requirements are as follows:
•
The peer address setting of each unit must identify the other as its peer. Alternatively, in
bridge mode, one gateway may have its peer address unspecified (set to zero).
•
Both units must not be presently connected.
•
The wan network-type parameter must match in both units ( bridge or route )
•
The serial-port setting for the clock source of one gateway must be r emote and the other must
be either internal or external .
•
If the clock source is external at one gateway, the TDM serial stream into that gateway must
be running.
•
In fractional TDM mode the time slots selected at each end must add up to the same data rate.
Once a gateway that issued the connect request receives a positive acknowledge, the connection is
established and the units start exchanging serial data.
In bridge mode you can leave the peer address set to zero. In this case the gateway does not transmit
connect request packets. It will, however, accept connect requests from any other gateway as long as
the other parameters are compatible. In route mode the peer IP addresses in each unit must identify
the other unit as its peer.
The two TDM ports are connected between the same two gateways, with line A connected to line A
of the remote gateway and line B connected to line B.
If the connection is not established, the command show gateways will help you in determining the
reason. In response to this command the gateway sends a probe request packet into the network,
causing all visible gateways to respond and include their configuration in the response. The
command then displays all visible gateways and indicates which parameters are incompatible.
During the first ten seconds of the connection, the gateways enter a training mode, tuning the amount
of serial data stored at each end of the link in order to avoid an “underrun” condition. During this
training period the front panel Gateway-Link LED flashes green. When that LED turns into a steady
green, it indicates that the training period is over and the link is established.
2.3.2 Serial Data Encapsulation
Once a connection is established, a gateway collects a fixed number of frames of TDM data before
creating a wan packet. In E1 mode each wan packet contains 32 frames (two multi-frames). In T1
mode , unframed, each packet contains 32 frames while in T1 framed mode each packet contains 24
frames (two Superframes).