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.
Symmetric DSL
Symmetric DSL (SDSL)
is a variant of HDSL; however, it runs over a single copper pair. HDSL
requires two pairs of copper. The data rate is 1.544Mbps in each direction.
is a variant of HDSL; however, it runs over a single copper pair. HDSL
requires two pairs of copper. The data rate is 1.544Mbps in each direction.
High Bit-Rate DSL
High bit-rate DSL (HDSL)
requires two pairs of copper for service, unlike most other DSL
offerings. In exchange, it provides a T-1-like presence of 1.544Mbps in each direction. It’s
important to note that this service does not support analog voice.
requires two pairs of copper for service, unlike most other DSL
offerings. In exchange, it provides a T-1-like presence of 1.544Mbps in each direction. It’s
important to note that this service does not support analog voice.
G.lite
G.lite
, which is sometimes called
splitterless
DSL
, is quickly dethroning ADSL for the most common
DSL variant, although technically it is only a subspecification of ADSL itself. As the
splitterless
nickname
infers, this technology does not require a splitter to be installed at the customer location. In this
splitterless installation, the provider isolates voice from data in the central office by controlling the
frequency of the voice channel.
The advantage to this type of installation is significant. In a splitter (ADSL) type of deployment,
the provider needs to visit the customer location and install a splitter on the line in addition to a
second jack—one jack is for the DSL router, and the other jack is for the telephone. The cost of
this is very high compared to the alternative of encoding the data and voice so the end equipment
can isolate the voice traffic where no splitter installation is required. G.lite installations can be
completed at the central office, and the user can simply plug their router into the jack as they
would a telephone.
G.lite is further described in ITU-T standard G.992.2.
, which is sometimes called
splitterless
DSL
, is quickly dethroning ADSL for the most common
DSL variant, although technically it is only a subspecification of ADSL itself. As the
splitterless
nickname
infers, this technology does not require a splitter to be installed at the customer location. In this
splitterless installation, the provider isolates voice from data in the central office by controlling the
frequency of the voice channel.
The advantage to this type of installation is significant. In a splitter (ADSL) type of deployment,
the provider needs to visit the customer location and install a splitter on the line in addition to a
second jack—one jack is for the DSL router, and the other jack is for the telephone. The cost of
this is very high compared to the alternative of encoding the data and voice so the end equipment
can isolate the voice traffic where no splitter installation is required. G.lite installations can be
completed at the central office, and the user can simply plug their router into the jack as they
would a telephone.
G.lite is further described in ITU-T standard G.992.2.
Oversubscription and Bandwidth Contention
A discussion of consumer DSL, of which ADSL is a common offering, necessitates a discussion
of vendor claims regarding oversubscription and bandwidth contention. As you might know,
oversubscription occurs when the network is provisioned with greater potential demand than
could be serviced at any one time, under the reasonable assumption that use patterns and the
quantity of bandwidth demanded will never be 100 percent.
This assumption is very reasonable in many networks. Consider your network for a moment.
You might have 100 workstations connected to a switch with a single 100Mbps uplink to the
core. If each of the 100 workstations is connected at 100Mbps, the network would be oversubscribed
100:1. Consumer DSL network vendors commonly oversubscribe at ratios between 3
and 10 to 1, or 10:1.
Let’s suspend discussion of oversubscription for a moment and consider bandwidth contention.
DSL providers quickly point out that cable modem networks provide shared bandwidth from the
head end to a population of users. Think of this as shared Ethernet. They then add that their DSL
technology is more akin to switched Ethernet, where each user has no contention for bandwidth
from their router to the DSLAM.
On the surface it would appear that DSL is the superior technology, as many networkers have
migrated from the old shared network model to the superior switched network in Ethernet.
The marketing folks for DSL providers enjoy that analogy and relish in users choosing the
dedicated technology.
However, all is not as it appears. Although it is true that DSL dedicates bandwidth from the end user
to the head end at the Physical layer, we must return to oversubscription. I might have a dedicated
100Mbps Ethernet connection to my workstation, and Piper might have 100Mbps to her workstation,
but if we have a single 100Mbps uplink from the switch to our resource, we could expect
only 50 percent, or 50Mbps in this example, of throughput. So long as we have that consideration,
shared bandwidth is always a factor, even if the hop from my router to the head end is dedicated.
As such, cable modem’s shared technology (presented further in Chapter 28, “Remote Access with
Cable Modems and Virtual Private Networks”) is less of a concern than DSL providers would like.
Cisco contends that ADSL is best suited to video on demand and video conferencing; however,
in practice we would recommend against this generalization. The asymmetric nature of
ADSL is such that quality upstream video conferencing is unlikely if there is concurrent load.
Because video conferencing is typically a bidirectional experience, it would be overgeneralizing
to conclude that ADSL is the best solution. We justify their answer by simplifying the
scope and comparing ADSL to ISDN, analog (POTS), and other remote access technologies.
In this light, ADSL is the best solution. However, HDSL and other DSL flavors, discussed
later, might be better for your installation.
of vendor claims regarding oversubscription and bandwidth contention. As you might know,
oversubscription occurs when the network is provisioned with greater potential demand than
could be serviced at any one time, under the reasonable assumption that use patterns and the
quantity of bandwidth demanded will never be 100 percent.
This assumption is very reasonable in many networks. Consider your network for a moment.
You might have 100 workstations connected to a switch with a single 100Mbps uplink to the
core. If each of the 100 workstations is connected at 100Mbps, the network would be oversubscribed
100:1. Consumer DSL network vendors commonly oversubscribe at ratios between 3
and 10 to 1, or 10:1.
Let’s suspend discussion of oversubscription for a moment and consider bandwidth contention.
DSL providers quickly point out that cable modem networks provide shared bandwidth from the
head end to a population of users. Think of this as shared Ethernet. They then add that their DSL
technology is more akin to switched Ethernet, where each user has no contention for bandwidth
from their router to the DSLAM.
On the surface it would appear that DSL is the superior technology, as many networkers have
migrated from the old shared network model to the superior switched network in Ethernet.
The marketing folks for DSL providers enjoy that analogy and relish in users choosing the
dedicated technology.
However, all is not as it appears. Although it is true that DSL dedicates bandwidth from the end user
to the head end at the Physical layer, we must return to oversubscription. I might have a dedicated
100Mbps Ethernet connection to my workstation, and Piper might have 100Mbps to her workstation,
but if we have a single 100Mbps uplink from the switch to our resource, we could expect
only 50 percent, or 50Mbps in this example, of throughput. So long as we have that consideration,
shared bandwidth is always a factor, even if the hop from my router to the head end is dedicated.
As such, cable modem’s shared technology (presented further in Chapter 28, “Remote Access with
Cable Modems and Virtual Private Networks”) is less of a concern than DSL providers would like.
Cisco contends that ADSL is best suited to video on demand and video conferencing; however,
in practice we would recommend against this generalization. The asymmetric nature of
ADSL is such that quality upstream video conferencing is unlikely if there is concurrent load.
Because video conferencing is typically a bidirectional experience, it would be overgeneralizing
to conclude that ADSL is the best solution. We justify their answer by simplifying the
scope and comparing ADSL to ISDN, analog (POTS), and other remote access technologies.
In this light, ADSL is the best solution. However, HDSL and other DSL flavors, discussed
later, might be better for your installation.
Asymmetric Digital Subscriber Line
The most common DSL variant is
asymmetric digital subscriber line (ADSL)
, and this is often
used for home and business users. It is called
asymmetric
because the bandwidth is not equal in
the upstream and downstream directions. Upstream traffic is sent from the user, and downstream
traffic is sent from the direction of the DSLAM.
When discussing a DSL circuit without specifying the type of DSL being used,
it is common to refer to xDSL.
This unequal traffic flow is well suited to Internet surfing and centralized data storage, as
would be found in many tele-worker applications. For example, many users download graphics,
documents, and other large files from the remote network, while only sending small e-mail messages
or requests for information. As such, the network needs to provide only a small amount
of bandwidth to service these smaller datagrams from the user, and it’s preferable to provide
larger amounts of bandwidth to support the greater volume of data from the network.
ADSL requires the use of a splitter to isolate the voice traffic from the data stream on the
copper pair.
asymmetric digital subscriber line (ADSL)
, and this is often
used for home and business users. It is called
asymmetric
because the bandwidth is not equal in
the upstream and downstream directions. Upstream traffic is sent from the user, and downstream
traffic is sent from the direction of the DSLAM.
When discussing a DSL circuit without specifying the type of DSL being used,
it is common to refer to xDSL.
This unequal traffic flow is well suited to Internet surfing and centralized data storage, as
would be found in many tele-worker applications. For example, many users download graphics,
documents, and other large files from the remote network, while only sending small e-mail messages
or requests for information. As such, the network needs to provide only a small amount
of bandwidth to service these smaller datagrams from the user, and it’s preferable to provide
larger amounts of bandwidth to support the greater volume of data from the network.
ADSL requires the use of a splitter to isolate the voice traffic from the data stream on the
copper pair.
The Different Flavors of DSL
You learned in Chapter 26, “Integrated Services Digital Network (ISDN),” that there are a couple
of different flavors to that technology—specifically BRI and PRI. We will discuss six different
flavors of DSL in this chapter, although there are many more. These include:
Asymmetric digital subscriber line
G.lite
High bit-rate DSL
Symmetric DSL
ISDN DSL
Very-high data rate DSL
The different flavors of DSL typically alter the bandwidth available and the range—or
distance—between the DSLAM and the end point. There can be other differences as well,
such as the need for a
splitter
to separate voice traffic from the circuit.
of different flavors to that technology—specifically BRI and PRI. We will discuss six different
flavors of DSL in this chapter, although there are many more. These include:
Asymmetric digital subscriber line
G.lite
High bit-rate DSL
Symmetric DSL
ISDN DSL
Very-high data rate DSL
The different flavors of DSL typically alter the bandwidth available and the range—or
distance—between the DSLAM and the end point. There can be other differences as well,
such as the need for a
splitter
to separate voice traffic from the circuit.
What Is Digital Subscriber Line?
Digital subscriber line (DSL)
is the result of demand for cheaper and higher bandwidth services
over the already existing copper phone-line network. As with ISDN, there was, and is, a great
deal of installed and widely available sub-Category 3 cable that, with a new encoding method,
could provide high-bandwidth services.
Within this chapter the terms
DSL
and
xDSL
are used. By convention, both
mean the same thing, although
xDSL
is a generic term that means all DSL technologies,
including ADSL and HDSL. These variants of DSL are described later
in this chapter.
DSL
is typically used to describe the base technology.
However, this existing cable currently supports analog voice services, so the new technology,
again like ISDN, needs to support legacy voice services in addition to providing the new data
service. So DSL is a voice and data service that supports multi-megabit data rates over the same
cable that previously supported only voice.
The
digital subscriber line access multiplexer (DSLAM)
provides the cornerstone of the
DSL infrastructure. This device provides two important functions in the DSL network: First,
it separates voice and data traffic from each line, and, second, it terminates each connection
to the residence or business. Figure 27.1 illustrates a typical DSL residential installation with
an access terminal (DSLAM) extending the link from the central office. Note that a remote
access terminal is not required and that a one-mile copper connection could extend directly
from a central-office-located DSLAM.
As an overview, DSL provides the following benefits:
Voice and data services over the same copper pair
Significantly greater bandwidth than ISDN or analog services over comparable physical media
Unfortunately, DSL also has some negatives, including these:
Significant distance limitations at higher data rates
Low tolerance for low-quality copper wiring
Complex, labor-consuming installation procedures for some versions
An inability to work with legacy line-conditioning equipment, including load coils
This chapter covers the flavors of DSL that are available to the administrator for remote
access solutions, in addition to covering configuration and troubleshooting of this technology.
is the result of demand for cheaper and higher bandwidth services
over the already existing copper phone-line network. As with ISDN, there was, and is, a great
deal of installed and widely available sub-Category 3 cable that, with a new encoding method,
could provide high-bandwidth services.
Within this chapter the terms
DSL
and
xDSL
are used. By convention, both
mean the same thing, although
xDSL
is a generic term that means all DSL technologies,
including ADSL and HDSL. These variants of DSL are described later
in this chapter.
DSL
is typically used to describe the base technology.
However, this existing cable currently supports analog voice services, so the new technology,
again like ISDN, needs to support legacy voice services in addition to providing the new data
service. So DSL is a voice and data service that supports multi-megabit data rates over the same
cable that previously supported only voice.
The
digital subscriber line access multiplexer (DSLAM)
provides the cornerstone of the
DSL infrastructure. This device provides two important functions in the DSL network: First,
it separates voice and data traffic from each line, and, second, it terminates each connection
to the residence or business. Figure 27.1 illustrates a typical DSL residential installation with
an access terminal (DSLAM) extending the link from the central office. Note that a remote
access terminal is not required and that a one-mile copper connection could extend directly
from a central-office-located DSLAM.
As an overview, DSL provides the following benefits:
Voice and data services over the same copper pair
Significantly greater bandwidth than ISDN or analog services over comparable physical media
Unfortunately, DSL also has some negatives, including these:
Significant distance limitations at higher data rates
Low tolerance for low-quality copper wiring
Complex, labor-consuming installation procedures for some versions
An inability to work with legacy line-conditioning equipment, including load coils
This chapter covers the flavors of DSL that are available to the administrator for remote
access solutions, in addition to covering configuration and troubleshooting of this technology.
Remote Access with Digital Subscriber Line
Understand digital subscriber line technologies.
Know the differences in digital subscriber line technologies.
Know how to configure digital subscriber line technologies.
Understand how to troubleshoot digital subscriber line
technologies.
In this chapter we will examine the remote access technologies
encompassed in digital subscriber line (DSL) services. This set of
newer remote connectivity access methods provides residential
and business locations with high-speed, low-cost connections that can surpass T-1 in some
instances. In addition to the basics of DSL, we will also compare the different flavors of the technology
and the troubleshooting methodologies employed.
Know the differences in digital subscriber line technologies.
Know how to configure digital subscriber line technologies.
Understand how to troubleshoot digital subscriber line
technologies.
In this chapter we will examine the remote access technologies
encompassed in digital subscriber line (DSL) services. This set of
newer remote connectivity access methods provides residential
and business locations with high-speed, low-cost connections that can surpass T-1 in some
instances. In addition to the basics of DSL, we will also compare the different flavors of the technology
and the troubleshooting methodologies employed.
Subscribe to:
Posts (Atom)