Enterprise QoS Solution Reference Network Design Guide

Teleworker V3PN QoS Considerations
Broadband-Access Technologies
6-30
Enterprise QoS Solution Reference Network Design Guide
Chapter 6 IPSec VPN QoS Design
In North America, there are four main broadband-access technology options for telecommuter scenarios:
DSL, cable, ISDN, and wireless. DSL and cable are by far the dominant broadband technologies.
Because of per-minute costs, ISDN is used considerably less; however, ISDN flat rate is becoming
available and will make ISDN a good option for areas where DSL or cable is not available. Last-mile
wireless is a new option that is being piloted in certain areas to determine viability.
The minimum recommended broadband data rate for most deployments is 160 kbps (uplink)/860 kbps
(downlink). Data rates below this speed require more troubleshooting by support staff and are less likely
to provide acceptable voice quality. The recommended data rate for V3PN teleworker deployments is
256 kbps (uplink)/1.4 Mbps (downlink) or higher rates. Although V3PN can be deployed at rates less
than 160 kbps/860 kbps, generally the voice quality at that service level is in the cell phone quality range,
and support costs are higher.
Because QoS design for ISDN was discussed in Chapter 3, “WAN Aggregator QoS Design,”, and
because wireless as a last-mile broadband technology has yet to gain wide deployment, this section
focuses only on DSL and cable broadband technologies.
DSL and cable topologies are illustrated in Figure 6-20. Cable is a shared medium between the
teleworker’s cable modem and the broadband provider’s cable headend router. DSL is a dedicated circuit
between the teleworker’s DSL modem (bridge) and the DSL Access Multiplexer (DSLAM). Both cable
and DSL offerings utilize shared uplinks between these aggregation devices and the service provider’s
core network. QoS typically is not provisioned within the broadband service provider’s cloud in either
medium. This lack of QoS within the broadband cloud underscores the requirement of adequate QoS
provisioning at the endpoints of the VPN tunnels.
Figure 6-20 DSL and Cable Topologies
IPSec V3PN
Teleworker
Routers
DSL
Bridge
Cable
Modem
ATM
DSLAM/IP
DSL Switch
ATM
Broadband
Service Provider
Broadband Router
IPSec V3PN
Headend
Routers
DSL (PPPoE) and cable (DOCSIS 1.0) in
service-provider networks are Best-
Effort with no QoS or serialization mitigation.
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