encapsulation overhead varies, but is typically either 6 or 8 bytes on serial links. This
overhead causes smaller packets to be less efficient and result in serial data requiring
more bandwidth.
Calculate the bandwidth required for a serial bit stream as follows:
IP Bandwidth = [Packet Size (bytes) + 20 (bytes) + 2 (bytes) + Encapsulation
Overhead (bytes) x [Packet Rate (pps)] x 8
Packet Creation Delay
Serial data received at the CTP interface must be buffered long enough to allow a packet
to be created. The delay to create the packet increases as either the size of the packet
increases or as the rate of the serial interface decreases. Generally, this delay is minimal
except when the rate of the serial interface is low and the packet size is large. We
recommend that you set the packet size to a smaller value for lower-speed serial
interfaces. Table 3 on page 9 provides examples of serial interface packet creation delay
in milliseconds.
Table 3: Packet Creation Delay for Serial Interfaces
Serial Interface Delay (msec)
Packet Size (bytes)
14001024768512256128
Interface Rate
(Kbps)
175.0128.096.064.032.016.064
87/564.048.032.016.08.0128
43.832.024.016.08.04.0256
10.98.06.04.02.01.01024
7.35.34.02.71.30.71544
5.54.03.02.01.0.52048
Performance of the IP Network
The number of packets created (packet rate) is inversely related to the packet size
configured. For example, smaller packets result in a greater packet rate. When you
configure the packet size, consider the packet-forwarding performance of the attached
router and network. Table 4 on page 10 provides examples of packet rates for various
packet sizes and serial interface rates.
9Copyright © 2018, Juniper Networks, Inc.
Chapter 1: Overview of CTP Bundles
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