2
–
Functional Design
NetXpress LX & CM-30R Installation & Operation Manual
Version 1.1
GatesAir, Inc.
2-7
Intraplex Products
information and network bandwidth based upon the user parameters. This table also gives formulas
for how to derive computed parameters for a stream.
Table 2-1. NetXpress LX Stream User and Computed Parameters
User Parameter
Value
Description
Number of TDM
Channels
1
Number of TDM channels to transport in a stream
TDM Frames per
Payload
160
Number of TDM frames per payload (packet)
Jitter Buffer Size
(8
–
128 packets)
64
Configured jitter buffer size in packets
Computed Parameter
Value
Description
Formula
TDM Channel Data Rate
64 kB/S
Calculated TDM channel data rate in kB/S
Number of TDM Channels x 64
Packet Payload Size
160 bytes
Calculated payload size in each packet in
bytes
Number of TDM Channels x
TDM Frames per Payload
Packet Interval
20 mS
Calculated packet interval (time between
packets) in mS
Number of TDM Frames per
Payload ÷ 8
Packet Rate
50
packets/S
Calculated packet rate for a stream in
packets/S
(1 ÷ Packet Interval) x 1000
Jitter Buffer Delay
640 mS
Calculated jitter buffer delay in mS
Note: This delay assumes a receive
queue of half the jitter buffer size
Jitter Buffer Size x Packet
Interval ÷ 2
Ethernet Frame Size
242 bytes
Calculated Ethernet frame size in bytes =
Packet Payload Size + Ethernet overhead
(38 bytes
–
no VLAN) + IP overhead (20
bytes IP + 8 bytes UDP + 16 bytes RTP)
Packet Payload Size + 38 + 44
Ethernet Stream Data
Rate
96.8 kB/S
Calculated Ethernet stream data rate in
kB/S *
Ethernet Frame Size x Packet
Rate x 8 ÷ 1000
IP Packet Size
204 bytes
Calculated IP packet size in bytes =
Packet Payload Size + IP overhead (20
bytes IP + 8 bytes UDP + 16 bytes RTP)
Packet Payload Size + 44
Stream Data Rate
81.6 kB/S
Calculated IP stream data rate in kB/S *
IP Packet Size x Packet Rate x
8 ÷ 1000
* In most instances, Ethernet overhead is stripped before the packet is transported over a WAN link.
However, in certain instances (such as Metro Ethernet networks that transport the entire frame);
the Ethernet overhead is left on the packet.
2.2.9
Stream Statistics
NetXpress LX stream statistics are receiver-based. The time interval for collecting stream statistics is
user-selectable (from 5-10 seconds for each stream). It is a good practice to review your stream
statistics on a regularly scheduled basis (Section 4.3.6.1
–
Stream Statistics
). You may be able to
modify your NetXpress LX system for optimum throughput, bandwidth efficiency, and reduced errors.
As an example, you may wish to alter the size of the jitter buffer if you are experiencing too many
lost, underrun, early, or late packets. Specifically, if you are experiencing too many late packets, you
might need to increase the jitter buffer size.
2.3 System Security
System security is controlled through
●
Logon and password control.