Example: Configuring Dynamic Shaping Parameters to Account for Overhead in Downstream Traffic Rates
This topic describes two scenarios for which you can configure dynamic shaping parameters to account for packet overhead in a downstream network.
The RADIUS administrator supplies the initial values on the RADIUS server, and the service activation is performed at subscriber login.
Figure 1 shows the sample network that the examples reference.
Managing Traffic with Different Encapsulations
In this example, the MX Series router shown in Figure 1 sends stacked VLAN frames to the DSLAM, and the DSLAM sends single-tagged VLAN frames to the residential gateway.
To accurately shape traffic at the residential gateway, the MX Series router must account for the different frame sizes. The difference between the stacked VLAN (S-VLAN) frames sent by the router and the single-tagged VLAN frames received at the residential gateway is a 4-byte VLAN tag. The residential gateway receives frames that are 4 bytes less.
To account for the different frame sizes, you configure the frame shaping mode with -4 byte adjustment:
Configure the traffic shaping parameters in the dynamic profile and attach them to the interface.
Enabling the overhead accounting feature affects the resulting shaping rate, guaranteed rate, and excess rate parameters, if they are configured.
[edit] dynamic-profiles { ethernet-downstream-network { interfaces { $junos-interface-ifd-name { unit $junos-underlying-interface-unit { family inet; } } } class-of-service { traffic-control-profiles { tcp-example-overhead-accounting-frame-mode { excess-rate percent $junos-cos-excess-rate guaranteed-rate $junos-cos-guaranteed-rate overhead-accounting $junos-cos-shaping-mode bytes $junos-cos-byte-adjust shaping-rate $junos-cos-shaping-rate; } } interfaces { $junos-interface-ifd-name { unit "$junos-underlying-interface-unit" { output-traffic-control-profile tcp1; } } } } } }Table 1 lists the initial values defined by the RADIUS administrator for the shaping rates.
Table 1: Initial Shaping Values at Subscriber Login For Traffic With Different Encapsulations Predefined Variable
RADIUS Tag
Value
$junos-cos-shaping-rate
T02
10m
$junos-cos-guaranteed-rate
T03
2m
$junos-cos-excess-rate
T05
50
$junos-cos-shaping-mode
T07
frame-mode
$junos-cos-byte-adjust
T08
–4
Verify the adjusted rates.
user@host#show class-of-service traffic-control-profile Traffic control profile: tcp-example-overhead-accounting-frame-mode, Index: 61785 Excess rate 50 Shaping rate: 10000000 Guaranteed rate: 2000000 Overhead accounting mode: Frame Mode Overhead bytes: —4
Managing Downstream Cell-Based Traffic
In this example, the DSLAM and residential gateway shown in Figure 1 are connected through an ATM cell-based network. The MX Series router sends Ethernet frames to the DSLAM, and the DSLAM sends ATM cells to the residential gateway.
To accurately shape traffic at the residential gateway, the MX Series router must account for the different physical network characteristics.
The administrator does not need to configure a byte adjustment value to account for the downstream ATM network, but has the option of configuring a byte adjustment value to account for different encapsulations or decapsulations.
To account for the different frame sizes, configure cell shaping mode:
Configure the traffic shaping parameters in the dynamic profile and attach them to the interface.
Enabling the overhead accounting feature affects the resulting shaping rate, guaranteed rate, and excess rate parameters, if they are configured.
[edit] dynamic-profiles { atm-downstream-network { interfaces { $junos-interface-ifd-name { unit $junos-underlying-interface-unit { family inet; } } } class-of-service { traffic-control-profiles { tcp-example-overhead-accounting-cell-mode { excess-rate percent $junos-cos-excess-rate guaranteed-rate $junos-cos-guaranteed-rate overhead-accounting $junos-cos-shaping-mode shaping-rate $junos-cos-shaping-rate } } interfaces { $junos-interface-ifd-name { unit "$junos-underlying-interface-unit" { output-traffic-control-profile tcp1; } } } } } }Table 2 lists the initial values defined by the RADIUS administrator for the shaping rates.
Table 2: Initial Shaping Values at Subscriber Login For Downstream Cell-Based Traffic Predefined Variable
RADIUS Tag
Value
$junos-cos-shaping-rate
T02
10m
$junos-cos-guaranteed-rate
T03
2m
$junos-cos-excess-rate
T05
50
$junos-cos-shaping-mode
T07
cell-mode
Verify the adjusted rates.
user@host#show class-of-service traffic-control-profile Traffic control profile: tcp-example-overhead-accounting-cell-mode, Index: 61785 Shaping rate: 10000000 Excess rate 50 Guaranteed rate: 2000000 Overhead accounting Cell Mode Overhead bytes: 0
To account for ATM segmentation, the MX Series router adjusts all of the rates by 48/53 to account for ATM AAL5 encapsulation. In addition, the router accounts for cell padding, and internally adjusts each frame by 8 bytes to account for the ATM trailer.