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Configuring an ADSL WAN Interface Card on Cisco 1700 Series Routers
OL-3317-03
Configuring Quality of Service Parameters
!
bundle-enable
dsl operating-mode auto
!
interface ATM0/0.1 point-to-point
description COLLEGAMENTO
ip address 2.0.0.2 255.255.0.0
bundle MMA
class-bundle atm-bundle
pvc-bundle vip 0/33
class-vc vip
pvc-bundle high 0/34
class-vc high
pvc-bundle normal 0/35
class-vc normal
ATM Cell Loss Priority Bit Marking
When congestion occurs in an ATM network, ATM cells are discarded. One way to control which cells
are discarded is to use the cell loss priority (CLP) bit in the ATM header of each cell. The CLP bit may
be set to either 1 or 0. Those cells that have the CLP bit set to 1 are always discarded before any of the
cells with the CLP bit set to 0.
The ATM CLP bit marking feature allows you to control the CLP setting on Cisco routers. The marking
of the CLP bit is implemented on a per-packet basis so that the CLP bit of every ATM cell that belongs
to a particular packet is set to either 0 or 1.
Configuration Example
The following is an example of enabling ATM CLP bit marking using the set atm-clp command and
modular QoS command-line interface. In this example, all output packets that have an IP Precedence
value of 0 are sent with the CLP set to 1. Note that IP CEF must be on when using ATM CLP bit marking.
ip cef
class-map match-all prec0
match ip precedence 0
policy-map ATM_OUT
class prec0
set atm-clp
interface ATM0/0
dsl operating-mode auto
pvc 0/33
service-policy output ATM_OUT
Compressed RTP
The Real-Time Transport Protocol (RTP), as described in RFC 1889, is used to carry real-time data for
voice and video applications. For a typical Voice over IP (VoIP) application, the payload portion of the
packet can be smaller than the header. For instance, using the G.729 codec, the payload is 20 bytes, but
the IP, User Data Protocol (UDP), and RTP header is 40 bytes. It is inefficient to send the IP, UDP, and
RTP header across a slow link without compressing it. The Compressed Real-Time Transport Protocol
(cRTP) feature, as defined in RFC 2508, addresses this inefficiency by making the VoIP packet headers
smaller.
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