Comtech EF Data CDD-562AL - Manual (Page 58)

CDD-562AL/564A/L Multi-Channel Demodulator Revision 0
IP Module Ethernet Interface MN-CDD562AL564AL
4–4
Ethernet 2.0 + VLAN-tag
Ethernet 2.0 + MPLS
802.3-raw
802.3-raw + VLAN-tag
802.3 + 802.2
802.3 + 802.2 + VLAN-tag
802.3 + 802.2 + SNAP
802.3 + 802.2 + SNAP + VLAN-tag
802.3 + 802.2 + SNAP + MPLS
Supported Layer 3&4 Headers
IP
TCP
UDP
RTP (Codec Independent)
Header Compression reduces the required VoIP bandwidth by 60 percent. Example: A G.729a voice
codec, operating at 8 kbps, will occupy 32 kbps once encapsulated into IP framing on a LAN. Using
IP/UDP/RTP Header Compression, the same traffic only needs 10.8 kbps total WAN satellite bandwidth
to cross the link. A total maximum of 64 simultaneous VoIP calls can be compressed. Normal Web/HTTP
traffic can be reduced an additional 10% via IP/TCP header compression.
4.2.2.1 Header Decompression Configuration
Header Decompression requires one configuration change. Make sure the Header Compression and
Decompression feature is enabled on both the sending and receiving IP modem and demodulator.
Packets with a Header Decompression header are identified automatically for decompression.
You might want to change only one configuration parameter: the Header Decompression Refresh Rate.
This rate is how many decompressed header packets are sent before a single, full header packet is sent.
Sometimes, compressed header traffic can be lost during poor satellite link conditions. Sending a full
header packet allows the traffic stream to return. You can increase the Refresh Rate for poor satellite link
conditions, or decrease the Refresh Rate to reduce overhead.
4.2.3 Payload Decompression (future)
Traffic optimization through Payload Decompression is another optional feature of the demodulator.
• FAST feature to upgrade
• Compression algorithm applied to all data (HDLC header excluded) on the transmit side
• Compression algorithm not applied to RTP streams because this traffic is already compressed and
would only increase the satellite bandwidth if compressed again.