Star Microwave SM Cirius LM, Руководство пользователя

Страница: 71 / 79

Cirius LM User Manual 2016 Page 71
6. Native TDM/IP Transport Architecture Overview
6.1. Overview
One of the key benefits of Star Microwave Cirius LM point-to-point microwave radio
Indoor Unit (IDU) is the ability to transport native TDM data along side Ethernet
frame data with minimal latency and without degrading TDM jitter performance.
Latency is indirectly configurable as a function of bandwidth mode (symbol rate),
modulation type and FEC configuration, but is generally well under 1 ms per link.
Jitter tolerance and attenuation are compliant with ITU G.823.
6.2. Native TDM/IP Transport Architecture Description
For a functional block diagram depicting the IDU TDM/IP transport architecture,
refer to Figure 43. TDM data, in this case E1 bit streams, are first conditioned by
E1 line interface transceivers. The data from each separate active E1 port is
separately buffered in individual FIFOs, and “stuff” bytes are added to
accommodate the lack of synchronicity between the symbol rate of the air link and
the bit rate of each incoming E1 bit streams. Incoming Ethernet frames are
separately buffered and GFP framed to account for the difference between the
Ethernet frame and the over-the-air frame size. The individual E1 bit streams are
byte-wise multiplexed together along with GFP framed Ethernet data, assembled
into an over-the-air frame as indicated in Figure 44, then finally coded and
modulated for transmission over the link. On the far-side of the link, the received
signal is demodulated and decoded, and the received data stream is then de-
multiplexed into its constituent E1 and Ethernet data streams. The stuff bytes are
removed from each stream, then each bit stream is separately buffered and rate
smoothed prior to line conditioning in the line interface transceiver. Likewise, the
GFP framing is stripped from the Ethernet data, and whole frames are assembled
prior to ingressing the frame to the internal IDU Ethernet switch for forwarding to
the proper port based on the frames destination address.
In contrast, pseudo-wire techniques employed in other products require buffering
E1 traffic into Ethernet frames and transporting them over the link using an
encapsulation scheme such as GFP. From hop to hop, these frames accumulate
jitter and latency due to Ethernet priority queues. At final destination, a buffer is
required to accommodate the large amount of accumulated jitter, adding
considerable latency to the end-to-end E1 traffic.