Specifications

Installation and Operation Manual Chapter 1 Introduction
MPW-1 MP-4100 Ver. 2.0 Functional Description 1-23
Redundancy via PSN and TDM (E1) Networks
The dual-cable, parallel transmission redundancy mode supported by
Megaplex-4100 enables protecting traffic over different media. Therefore, a
MPW-1 internal DS1 port can be the redundancy partner of an E1 or PDH port on
another I/O, respectively CL, module. This could be used in two ways, depending
on the application requirements:
• To add protection for selected E1 links when no TDM transport capacity can
be assigned for redundancy, MPW-1 modules may be used to provide the
protection over the PSN. For purpose, the E1 port to be protected would be
configured as the primary port, and an internal DS1 port of a MPW-1 will be
assigned and configured as the protection (offline) port. This ensures that
unless a fault occurs, the transmission quality is that available over TDM links,
and very little bandwidth is consumed on the PSN.
• When some TDM transport capacity is available, it is possible to add
protection for critical traffic carried by means of MPW-1 modules over the
PSN, without using the same media (PSN) for protection. In this case, MPW-1
internal DS1 ports are configured as the primary ports, and E1 ports are
configured as the protection ports.
Application Guidelines
Bandwidth Utilization Considerations
When selecting parameters for a new pseudowire, one of the critical parameters
is the payload size, which is determined by the number of TDM bytes per packet.
This parameter affects several important performance aspects:
• Bandwidth utilization: because of the relatively short payload (especially
relevant for TDMoPSN and HDLCoPSN), the bandwidth utilization efficiency
depends on the overhead that must be transmitted to the network in order
to support the transmission of a certain amount of payload.
 The overhead depends on the packet structure: for example, for UDP/IP
networks the overhead is 50 bytes when using VLANs, and 46 bytes
without VLANs
 The payload depends on the number of TDM bytes, and varies between
48 to 1440 bytes.
For example, when using the minimum payload size (48 bytes), bandwidth
utilization efficiency is around 50%.
• Packetizing delay and the associated delay variance. Bandwidth utilization
efficiency increases when using a large payload size per frame. However,
there are additional aspects that must be considered when selecting the size
of the packet payload:
 Packetization time: the packet filling time, which is the time needed to
load the payload into an Ethernet frame, increases in direct proportion to
the number of bytes in the packet payload. This is particularly significant
for pseudowires with few timeslots; for example, a voice channel could be
carried by a single-timeslot pseudowire. Considering the nominal filling
rate (approximately one byte every 0.125 msec), the time needed to fill a
single-timeslot TDMoPSN pseudowire is as follows: