GatesAir Intraplex NetXpress, Installation And Operation Manual

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2—Functional Design Intraplex NetXpress IP Multiplexer
Version 3.05
GatesAir, Inc. 2-19
Intraplex Products
2.8 NetXpress System and FEC
The NetXpress system maintains uninterrupted audio transport by supporting Forward Error Correction
(FEC). Specifically, the NetXpress system supports RFC 2733 framework. Basically, forward error
correction is an error control process in data transmission where the source (transmitter) sends
redundant data and the destination (receiver) accepts only the data that contains no apparent errors.
An FEC packet is a special type of RTP packet. It is constructed by placing an FEC header and FEC
payload in the RTP payload.
In the NetXpress system versions 2.2 or higher, up to 32 streams (16 in each direction) can be
designated as FEC streams. For each of the FEC streams, you can specify either of two techniques for
forward error correction: FEC LOW or FEC HIGH (Section 4.4.5.1 –
Stream Creation ). This specification
affects the sender only. The receiver processes all FEC packets.
FEC LOW (appropriate for most low packet loss conditions)
Single error correction is engaged. This scheme introduces a 50% overhead (increased bandwidth
required) and can correct all single packet losses – consecutive packets are not lost.
FEC HIGH (used in more serious packet loss conditions)
Triple error correction is engaged. This scheme introduces a 100% overhead (increased bandwidth
required) and can correct one, two, or three consecutive packet losses. In this scheme, the sequence
of packets sent is critical if it is to protect against consecutive packet losses.
Table 2-3 shows NetXpress rate loss for both FEC low and FEC high options.
Table 2-3. NetXpress FEC Performance Data
Network Loss
Rate (%)
High FEC
Loss (%)
Low FEC
Loss (%)
1 0.0017 0.027
2 0.0023 0.085
3
4
5 0.0168 0.507
6
7
8
9
10 0.14 2.1
11
12
13
14
15 0.597 4.87
% High FEC Loss ((Lost packets / Rx packets) x 2) x 100
% Low FEC Loss ((Lost packets / Rx packets) x 1.5) x 100
2.9 Power
The NetXpress system supports redundant power supplies. You can install a main power supply and a
redundant supply in case the main supply fails. The system runs on either AC or DC power supplies,