16-16
Cisco 10000 Series Router Quality of Service Configuration Guide
OL-7433-09
Chapter 16 Fragmenting and Interleaving Real-Time and Nonreal-Time Packets
Multilink PPP-Based Link Fragmentation and Interleaving
To calculate the fragment size, do the following:
Step 1 Calculate the nominal fragment size (link weight) by using the following formula:
(Link Bandwidth * Fragment-Delay) / 8
Step 2 Determine the number of whole ATM cells the nominal fragment size represents.
If the number of ATM cells is less than two, then use two ATM cells in Step 3. The minimum number of
ATM cells you can have is 2.
Step 3 Calculate the total bytes per fragment, including the MLP header bytes and AAL5 trailer bytes, by
multiplying the number of ATM cells you calculated in Step 2 by 48:
Number of Cells * 48
Step 4 Subtract the MLP header bytes and AAL5 trailer bytes.
The AAL trailer is 8 bytes.
The number of MLP header bytes depends on the AAL5 encapsulation and whether or not protocol
compression is enabled (see
Table 16-3).
Table 16-3 lists the number of bytes in the MLP header, depending on the AAL5 encapsulation type and
whether or not protocol compression is used.
MLP Bundle Interface and Service Policies
The router applies a service policy, attached to a multilink interface, to only the MLP bundle interface.
The QoS actions defined by the service policy are applied to the outbound nonreal-time packets before
the packets reach the bundle first-in first-out (FIFO) queue. The nonreal-time packets are fragmented in
the FIFO queue and then the real-time packets are interleaved between the fragments as the real-time
packets exit their priority queue.
Ta b l e 16-3 MLP Header Bytes and AAL5 Trailer Bytes
AAL5 Encapsulation
Type
Protocol
Compression
No. of MLP Header
Bytes
No. of AAL5 Trailer
Bytes
AAL5 MUX OFF 6 Bytes 8 Bytes
AAL5 SNAP OFF 10 Bytes 8 Bytes
AAL5 Cisco OFF 8 Bytes 8 Bytes
AAL5 MUX ON 5 Bytes 8 Bytes
AAL5 SNAP ON 9 Bytes 8 Bytes
AAL5 Cisco ON 7 Bytes 8 Bytes
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