16-15
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
The following describes how MLP implements fragmentation and interleaving:
•
Delay-Sensitive, Real-Time Packets—On transmit, MLP encapsulates the packets as PPP over ATM
(PPPoA) and sends the packets to a special transmit queue to enable the router to transmit the
real-time packets earlier than other packet flows. The router interleaves the real-time packets
between the fragments of the larger, nonreal-time packet over a single point-to-point link to the
remote address. Upon receipt, the receiving fragmentation peer processes the real-time packets as
PPPoA packets.
•
Delay-Insensitive, Nonreal-Time Packets—On transmit, MLP fragments the large data packets to a
size small enough to satisfy the delay requirements of real-time traffic. MLP encapsulates the
packets as MLP packets and sends the packets to a transmit queue to enable the router to transmit
the fragments at the same time over multiple point-to-point links to the same remote address. The
receiving fragmentation peer reassembles the fragments to the original packet and then processes it
as Point-to-Point Protocol over ATM (PPPoA). The underlying PPP encapsulation conforms to
RFC 1661. All outbound MLP packets with a payload larger than the specified fragment size are
fragmented. The minimum fragment size depends on the AAL5 encapsulation type and whether or
not protocol compression is enabled (see
Table 16-2 on page 16-15
).
When configuring single-VC MLP over ATM-based LFI, you must configure a virtual template interface
for the MLP bundle. However, the virtual template does not need to be unique for each bundle—multiple
MLP bundles can share the same virtual template.
For more information about MLP, see the
“Multilink PPP-Based Link Fragmentation and Interleaving”
section on page 16-11
and the
Cisco 10000 Series Router Broadband Aggregation, Leased-Line, and
MPLS Configuration Guide
.
Feature History for Single-VC MLP Over ATM-Based LFI
Fragment Size Calculation for MLP Over ATM-Based LFI
For MLP over ATM-based LFI, the ideal fragment size should allow the fragments to fit into an exact
multiple of ATM cells.
Table 16-2
lists the minimum fragment sizes for Single-VC and Multi-VC MLP
over ATM-based LFI. As shown in the table, the minimum fragment size depends on the AAL5
encapsulation type used and whether or not protocol compression is enabled.
Cisco IOS Release
Description
Required PRE
Release 12.2(27)SBB
The single-VC MLP over ATM-based LFI feature was
introduced on the router for the PRE2.
PRE2
Release 12.2(31)SB2
This feature was introduced on the PRE3.
PRE3
Table 16-2
ATM Minimum Fragment Size
AAL5 Encapsulation Type
Protocol Compression
Minimum Fragment Size
AAL5 MUX
OFF
82 Bytes
AAL5 SNAP
OFF
78 Bytes
AAL5 Cisco
OFF
80 Bytes
AAL5 MUX
ON
83 Bytes
AAL5 SNAP
ON
79 Bytes
AAL5 Cisco
ON
81 Bytes