Comtech EF Data CDM-570 - Manual (Page 212)

CDM-570/570L Satellite Modem with Optional IP Module Revision 12
Ethernet IP Module Interface MN/CDM570L.IOM
13–6
13.3.10 Streamline Encapsulation
Streamline Encapsulation is available with Ethernet IP Module V1/MPP-50 FW
Ver. 1.7.# and later, and with Ethernet IP Module V2/MPP-70 FW Ver. 2.2.# and
later.
Numerous encapsulation techniques exist for transporting packetized data including HDLC and
GSM. Many of them perform well on large packet sizes, but produce excessive overhead on
smaller packet sizes such as those found in VoIP or when Header and / or Payload compression
techniques are used. Some, such as HDLC, are data dependent making it impossible to specify the
amount of user bandwidth available and giving a lower bound of 3% in purely random data
regardless of how large the packets are.
The Comtech Streamline Encapsulation method was developed to provide a low overhead method
of transporting any size packetized data. It provides superior performance on small packets and
performs well on large packets, with overhead performance approaching 1%.
As shown in Table 13-1, the three basic encapsulation methodologies are compared and, as this
table shows, the large performance gain of over GSM and HDLC encapsulation on smaller
packets far outweighs the 1% disadvantage on large packets. With respect to HDLC, Comtech
Streamline Encapsulation outperforms the longtime industry standard on all packet sizes.
Table 13-1. Streamline Encapsulation
Packet Size GSM (%) HDLC (%) Comtech Streamline (%)
32 15.6 18.8 7.4
64 7.8 10.9 4.3
128 3.9 7.0 2.7
256 2.0 5.1 2.0
512 1.0 4.1 1.6
1024 0.5 3.6 1.4
2048 0.2 3.4 1.3
Additional advantages of Streamline Encapsulation include:
• HDLC addresses are removed to reduce overhead and deployment configuration
complexity
• HDLC addressing modes have been removed
• Receive Header Compression is now automatically determine from the Streamline
encapsulation information. This removes the need to configure the Rx Header
Decompression feature (these options have been removed)
• The Vipersat STDMA ACK packet (one per burst) is much smaller (42 to 14 bytes)