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Voice Server Modules
Plexus 9000 Planning and Engineering Guide
Issue 2, June 4, 2004
Section 130-120-700
5-172
Telica,
Inc.
5.15.3.3
Voice Processors and Memory
The voice processors are a new generation of voice processing chips, which
integrate highly specialized DSP (Digital Signal Processing) cores for voice
CODEC type processing. The voice processing chips support G.711, G.726,
G.728, and G.729A/B encoding; G.165, G.168 echo cancellation up to
128ms, silence suppression, and comfort noise generation. The 89-0384
module has six voice processors and the 89-0395 has eight. Each voice
processor supports up to 336 full-duplex Pulse Code Modulated (PCM)
channels for a total of 2,016 or 2688 channels per module.
The voice processors are basically two port devices with a bi-directional
TDM interface and a packetized voice interface. Depending on the
configured mode, the packetized voice interface supported is either AAL2 or
IP/UDP/RTP over AAL5. A DS-0, which is routed on the TDM interface
into the voice processor, is processed by the DSP which echo cancels,
compresses, and packetizes the voice content into either AAL2 cells or
IP/UDP/RTP packets encapsulated into AAL5 ATM cells. The ATM cells
are sent to the TSU and routed through the ATM switch fabric to the
network access module. There are two types of network access modules –
ATM or Ethernet. For an ATM network access, it places the ATM cells into
SONET payloads for forwarding over a SONET optical transport. For an
Ethernet network access, it reassembles the ATM cells back into AAL5
frames, strips off the AAL5 overhead fields, and places the IP/UDP/RTP
payload into an Ethernet frame for forwarding over a 10/100/1000Mbps
Ethernet interface.
In the reverse direction, the network access module either removes ATM
cells from the SONET payload (ATM network access) or removes IP
packets from Ethernet frames and places the IP packets into AAL5 ATM
cells (Ethernet network access). The network access module then forwards
the ATM cells over the ATM switch fabric to the FSU on the Voice Server
module which routes the cells to the voice processor. Depending on the
mode, the voice processor extracts the voice payload either from an AAL2
cell or IP/UDP/RTP AAL5 reassembled packet, decompresses, and encodes
it into PCM format. The PCM-encoded voice is placed onto the TDM bus
and sent to the TSU for routing to a TDM IOM.