The specific configuration settings for a DSL installation will depend on the type of router used
and the features desired, but there are common elements.
The key element of a DSL installation is that the technology is fundamentally a physical
transport of ATM cells. As such, we will configure a Cisco 3810 router to terminate multiple
DSL connections (ADSL, in this case). The head end is a T-1 ATM connection. You might realize
that the T-1 is a poor termination choice for ADSL services; however, for this application it
is an appropriate solution. A DS-3 or other ATM connection could provide the termination just
as well.
Configuration of the DSLAM is beyond the scope of the test and this book, but
functionally it is PVC configuration and other parameters. Stated another way,
it is not complicated.
In addition to the typical configuration parameters you might include (such as routing,
logging, security, and management), the DSL configuration requires very little additional
configuration. In this excerpt, we configure the T-1 physical interface with Extended Super
Frame and B8ZS encoding, in addition to setting it for ATM cells. The ATM interface has
no configuration, but is subinterfaced for multiple connections. (Recall that this is a headend,
non-DSLAM connection.) We configure a PVC with unspecified bit rate (UBR) ATM,
and, as an extra service, we configure Operation, Administration, and Maintenance (OAM)
cells to the PVC. OAM provides link monitoring; if any part of the PVC fails, OAM will
detect it and shut down the interface until corrected.
The following configuration also specifies AAL5SNAP, or AAL5 with SNAP headers, for the
encapsulation type. So long as this matches on each side, there is no issue in most cases. For
those not familiar with PVC configurations, interface ATM0.1 has a VPI (virtual path identifier)
of 5 and a VCI (virtual circuit identifier) of 51.
!
controller T1 0
framing esf
linecode b8zs
mode atm
fdl both
description T1 to DSL Cloud
!
interface ATM0
description DSL Headend
no ip address
no ip directed-broadcast
!
interface ATM0.1 point-to-point
description DSL link to Gryffendor
ip address 10.1.1.25 255.255.255.252
no ip directed-broadcast
pvc 5/51
ubr 1500
oam-pvc manage
oam retry 3 5 1
encapsulation aal5snap
!
interface ATM0.2 point-to-point
description DSL Link to Ravenclaw
ip address 10.1.1.33 255.255.255.252
no ip directed-broadcast
pvc 4/51
ubr 1500
oam-pvc manage
oam retry 3 5 1
encapsulation aal5snap
!
NOTE:If there were only one PVC for this circuit, it would be acceptable to use the major
interface and not a subinterface. However, if an installation
might
use more than
one PVC in the future, then the use of a subinterface is recommended.
Other routers might limit various options. The Cisco 827, for example, uses a Bridge Group
Virtual Interface (BVI), which is part of Integrated Routing and Bridging (IRB) services for connectivity
instead of routing in most installations. This bridging solution negates layer 3 and leverages
Network Address Translation (NAT) for those services that are layer 3. The configuration is
not DSL-specific however, because the use of IRB is primarily used to negate the need for remote
configuration. A standard router configuration file can service all end points because DHCP and
NAT hide the Ethernet network, and the DSL side is assigned its address dynamically.
NOTE:IRB, BVI, NAT, and DHCP in this context are beyond the scope of this chapter and
of the exam. Chapter 31, “Network Address Translation (NAT) and Port Address
Translation (PAT),” provides information regarding NAT, and Chapter 25, “Using
Microsoft Windows 95/98/2000/XP,” describes DHCP. If you are interested in learning
more about the 827 router (a common remote DSL platform) and IRB/BVI,
please refer to Cisco’s documentation at
IT Certification CCIE,CCNP,CCIP,CCNA,CCSP,Cisco Network Optimization and Security Tips
Cisco DSL Routers
Cisco’s product line for supporting DSL services is comprised of three classifications of equipment.
The first is the focus of the Remote Access examination, which is primarily made up of the Cisco 800
series of routers and the SOHO (small office, home office) 70 series. The second is comprised of the
xDSL modules for the branch and office routers, including the 2600 and 3600 series. And the third
is the head-end DSLAM switches, including the Cisco 6260 IP DSL switch.
There could be a fourth Cisco DSL product category in their Linksys acquisition.
The Linksys product line includes a wide range of solutions for the SOHO
market and frequently integrates other functions such as print services and
wireless networking.
For the SOHO environment and small remote office, Cisco provides their SOHO line of DSL
routers in addition to the Cisco 800 series. Here is a list of the various DSL platforms in this category:
Cisco 837 ADSL Broadband Router
Cisco 836 ADSL over ISDN Broadband Router
Cisco 828 G.SHDSL Router
Cisco 827 ADSL Router
Cisco 827-4V ADSL Router
Cisco 826 ADSL Router
Cisco SOHO 78 G.SHDSL Router
Cisco SOHO 77 ADSL Router
Cisco SOHO 77 H ADSL Router
Cisco SOHO 76 ADSL Router
There is not much to focus on in this list, other than noting the diversity within the Cisco 827
product line, which includes the 827-4V. This platform provides four voice ports in addition to
ADSL support. The H variant of the 827 provides a four-port hub in addition to DSL termination.
For larger offices, Cisco provides DSL support on the 1700, 2600XM, and 3600 series routers
via a WAN Interface Card (WIC). This allows for the installation of other services, including
network modules (NMs) for content delivery. Voice Interface Cards (VICs) can also terminate
voice services on these platforms.
At the head end, Cisco provides the following switches for terminating DSL connections:
Cisco 6260 IP DSL Switch
Cisco 6160 IP DSL Switch
Cisco 6015 IP DSL Switch
These solutions are targeted toward servicing multi-tenant buildings, telecommunications
service providers, and ISPs. The specifics of these platforms are well beyond the scope of the
Remote Access examination.
The first is the focus of the Remote Access examination, which is primarily made up of the Cisco 800
series of routers and the SOHO (small office, home office) 70 series. The second is comprised of the
xDSL modules for the branch and office routers, including the 2600 and 3600 series. And the third
is the head-end DSLAM switches, including the Cisco 6260 IP DSL switch.
There could be a fourth Cisco DSL product category in their Linksys acquisition.
The Linksys product line includes a wide range of solutions for the SOHO
market and frequently integrates other functions such as print services and
wireless networking.
For the SOHO environment and small remote office, Cisco provides their SOHO line of DSL
routers in addition to the Cisco 800 series. Here is a list of the various DSL platforms in this category:
Cisco 837 ADSL Broadband Router
Cisco 836 ADSL over ISDN Broadband Router
Cisco 828 G.SHDSL Router
Cisco 827 ADSL Router
Cisco 827-4V ADSL Router
Cisco 826 ADSL Router
Cisco SOHO 78 G.SHDSL Router
Cisco SOHO 77 ADSL Router
Cisco SOHO 77 H ADSL Router
Cisco SOHO 76 ADSL Router
There is not much to focus on in this list, other than noting the diversity within the Cisco 827
product line, which includes the 827-4V. This platform provides four voice ports in addition to
ADSL support. The H variant of the 827 provides a four-port hub in addition to DSL termination.
For larger offices, Cisco provides DSL support on the 1700, 2600XM, and 3600 series routers
via a WAN Interface Card (WIC). This allows for the installation of other services, including
network modules (NMs) for content delivery. Voice Interface Cards (VICs) can also terminate
voice services on these platforms.
At the head end, Cisco provides the following switches for terminating DSL connections:
Cisco 6260 IP DSL Switch
Cisco 6160 IP DSL Switch
Cisco 6015 IP DSL Switch
These solutions are targeted toward servicing multi-tenant buildings, telecommunications
service providers, and ISPs. The specifics of these platforms are well beyond the scope of the
Remote Access examination.
DSL Types 2
Type Analog Support
Downstream
Bandwidth Upstream Bandwidth Range
ADSL Yes Up to 9Mbps Up to 640Kbps Up to 18,000 feet
G.lite Yes Up to 1.5Mbps Up to 512Kbps Up to 18,000 feet
HDSL No 1.544Mbps 1.544Mbps Up to 12,000 feet
SDSL No 1.544Mbps 1.544Mbps Up to 10,000 feet
IDSL No 144Kbps 144Kbps Up to 45,000 feet
VDSL Yes Up to 52Mbps Up to 2.3Mbps Up to 4,500 feet
NOTE:You might find that different vendors and sources document range and bandwidth
figures that are not the same as those in Table 27.1. We have used the Cisco
figures, which are sometimes over or under the values included in other specifications.
The variances should not have a significant impact on the test or real-world
deployment—for example, HDSL might have a range of 15,000 feet or 12,000 maximum,
but wire condition, interference, and other factors can greatly influence this,
and a real-world installation might operate correctly at only 7,000 feet. This chapter
covers only DSL basics consistent with the examination.
Downstream
Bandwidth Upstream Bandwidth Range
ADSL Yes Up to 9Mbps Up to 640Kbps Up to 18,000 feet
G.lite Yes Up to 1.5Mbps Up to 512Kbps Up to 18,000 feet
HDSL No 1.544Mbps 1.544Mbps Up to 12,000 feet
SDSL No 1.544Mbps 1.544Mbps Up to 10,000 feet
IDSL No 144Kbps 144Kbps Up to 45,000 feet
VDSL Yes Up to 52Mbps Up to 2.3Mbps Up to 4,500 feet
NOTE:You might find that different vendors and sources document range and bandwidth
figures that are not the same as those in Table 27.1. We have used the Cisco
figures, which are sometimes over or under the values included in other specifications.
The variances should not have a significant impact on the test or real-world
deployment—for example, HDSL might have a range of 15,000 feet or 12,000 maximum,
but wire condition, interference, and other factors can greatly influence this,
and a real-world installation might operate correctly at only 7,000 feet. This chapter
covers only DSL basics consistent with the examination.
Very-High Data Rate DSL
Very-high data rate DSL (VDSL
), sometimes also called
very-high bit-rate DSL
, is exactly
that—a high-bandwidth variant of DSL. Most implementations are capable of downstream
bandwidths in excess of 50Mbps. Consider for a moment that most VDSL deployments are in
residential settings and that the service provides in essence a DS-3 worth of capacity, and you
begin to appreciate the “very-high” aspects indeed.
There are a few installations of VDSL available in large markets, including Denver and Phoenix
in the United States. These services leverage VDSL to provide video, data, and voice services over
the DSL circuit. With over 50Mbps, it’s possible to provide four broadcast-quality video streams
over the connection, while also supporting an always-available Internet data path and analog
voice services—a road to the fully converged network if you will.
Of course, you can’t get something for nothing, and VDSL is no exception. The significant
downside to the technology is its limited range. Stated another way, ADSL technologies can frequently
extend to over 18,000 feet, whereas VDSL is limited to 4,500 feet. The highest data
rates are attainable at only 1,000 feet in most real-world settings.
The DSL types described in this chapter are summarized in Table 27.1.
), sometimes also called
very-high bit-rate DSL
, is exactly
that—a high-bandwidth variant of DSL. Most implementations are capable of downstream
bandwidths in excess of 50Mbps. Consider for a moment that most VDSL deployments are in
residential settings and that the service provides in essence a DS-3 worth of capacity, and you
begin to appreciate the “very-high” aspects indeed.
There are a few installations of VDSL available in large markets, including Denver and Phoenix
in the United States. These services leverage VDSL to provide video, data, and voice services over
the DSL circuit. With over 50Mbps, it’s possible to provide four broadcast-quality video streams
over the connection, while also supporting an always-available Internet data path and analog
voice services—a road to the fully converged network if you will.
Of course, you can’t get something for nothing, and VDSL is no exception. The significant
downside to the technology is its limited range. Stated another way, ADSL technologies can frequently
extend to over 18,000 feet, whereas VDSL is limited to 4,500 feet. The highest data
rates are attainable at only 1,000 feet in most real-world settings.
The DSL types described in this chapter are summarized in Table 27.1.
ISDN DSL
ISDN DSL (IDSL)
provides up to 144Kbps of bandwidth—which is equal to the two B channels
and one D channel of ISDN BRI—by employing the same line coding (2B1Q) as ISDN. It is important
to note that this flavor of DSL does not support analog voice service.
The primary reason for offering IDSL is that the range can be extended to cover virtually any
existing copper path that is devoid of amplifiers or load coils—both of which can be used in very
long analog connections. With repeaters, IDSL can extend to 45,000 feet.
provides up to 144Kbps of bandwidth—which is equal to the two B channels
and one D channel of ISDN BRI—by employing the same line coding (2B1Q) as ISDN. It is important
to note that this flavor of DSL does not support analog voice service.
The primary reason for offering IDSL is that the range can be extended to cover virtually any
existing copper path that is devoid of amplifiers or load coils—both of which can be used in very
long analog connections. With repeaters, IDSL can extend to 45,000 feet.
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