As with the DSL product line, Cisco caters to the head end and the remote installation. At the
central office, Cisco provides the uBR10012 and uBR7100/7200 series Universal Broadband
routers. The uBR10012 product combines the Cisco 10000 Edge Services Router with the
uBR7200 product, which can support up to 8,000 terminations.
For remote installations, the product line contains two products: the uBR905 and the uBR925.
Both support VPN tunnels (IPSec) and firewall services in addition to routing, but the uBR925 adds
support for voice over the cable network and a USB port.
Unlike the DSL product line, Cisco does not currently support a cable modem interface for
the higher end routers, including the 1700, 2600XM, and the 3600 series. This will likely
change in the future, but administrators should note that cable television is not as prevalent in
business parks and commercial buildings as compared to residential settings.
IT Certification CCIE,CCNP,CCIP,CCNA,CCSP,Cisco Network Optimization and Security Tips
DOCSIS
The primary purpose of DOCSIS was to ensure interoperability between vendors’ equipment.
Different versions provide standards for security, encapsulation, management, QoS, and services.
There are three versions of the DOCSIS specification, as outlined in Table 28.1.
TABLE 2 8 . 1
DOCSIS Specifications
Version Features
DOCSIS 1.0 This was the original specification and provided for standardization
between vendors.
DOCSIS 1.1 This version of DOCSIS is commonly used today and provides basic
quality of service and security functions. This is very important for most
users, and cable networks leverage these features to protect user traffic
in transit from being intercepted. Please note that this does not protect
user machines from attack; the specifications are not firewalls, but rather
a switched emulation over the shared infrastructure. The specification is
backward compatible. DOCSIS 1.1 adds voice and streaming services.
This version also takes steps to prevent theft of service from the provider.
In previous specifications, a user with cable service could remove the filter
in the street and have data service for free.
DOCSIS 2.0 This new standard will provide six times the upstream capacity of DOCSIS 1.0
(three times the capacity of 1.1). The channel is increased to 6.4MHz for greater
capacity and efficiency. It is also backward compatible.
NOTE:DOCSIS specifies the connection between only the CMTS and the cable
modem or cable modem router. The PC, network router(s), and other network
elements are not involved. Readers wanting to study the DOCSIS 2.0 standard
should visit
www.cisco.com/en/US/netsol/ns469/networking_solutions_
event_and_seminar_home.html
, where a number of DOCSIS white papers are
available.
Different versions provide standards for security, encapsulation, management, QoS, and services.
There are three versions of the DOCSIS specification, as outlined in Table 28.1.
TABLE 2 8 . 1
DOCSIS Specifications
Version Features
DOCSIS 1.0 This was the original specification and provided for standardization
between vendors.
DOCSIS 1.1 This version of DOCSIS is commonly used today and provides basic
quality of service and security functions. This is very important for most
users, and cable networks leverage these features to protect user traffic
in transit from being intercepted. Please note that this does not protect
user machines from attack; the specifications are not firewalls, but rather
a switched emulation over the shared infrastructure. The specification is
backward compatible. DOCSIS 1.1 adds voice and streaming services.
This version also takes steps to prevent theft of service from the provider.
In previous specifications, a user with cable service could remove the filter
in the street and have data service for free.
DOCSIS 2.0 This new standard will provide six times the upstream capacity of DOCSIS 1.0
(three times the capacity of 1.1). The channel is increased to 6.4MHz for greater
capacity and efficiency. It is also backward compatible.
NOTE:DOCSIS specifies the connection between only the CMTS and the cable
modem or cable modem router. The PC, network router(s), and other network
elements are not involved. Readers wanting to study the DOCSIS 2.0 standard
should visit
www.cisco.com/en/US/netsol/ns469/networking_solutions_
event_and_seminar_home.html
, where a number of DOCSIS white papers are
available.
A cable modem installation
HFC/CMTS HFC/CMTS
Router
Broadcast
Video
Internet
Note that cable modems have a perceived disadvantage of shared bandwidth for all users
on a particular link—there are two distinct shared domains shown in Figure 28.1. As noted in
Chapter 27, this is not a significant issue from a bandwidth perspective. It could be a security concern
however, as data from one home is viewable from all other homes within that domain. This
is addressed by the
Data Over Cable Service Interface Specification (DOCSIS)
ratified by Cable-
Labs, a nonprofit organization composed of cable service providers in the Americas. DOCSIS is
described in the following section; it provides customer data protection over the shared medium.
The biggest advantage to cable modems is their capability to provide high per-user bandwidth
over long distances, often significantly greater than DSL. Although the cable is capable
of providing up to 40Mbps of downstream bandwidth, the network is provisioned so that each
user can obtain only a predefined rate—typically less than 2Mbps. For consumer installations,
this is sufficient and leads to a very economical solution. However, the provider could easily
increase the bandwidth to an individual user, although they would need to have a dedicated
coax connection to attain the full capacity.
Router
Broadcast
Video
Internet
Note that cable modems have a perceived disadvantage of shared bandwidth for all users
on a particular link—there are two distinct shared domains shown in Figure 28.1. As noted in
Chapter 27, this is not a significant issue from a bandwidth perspective. It could be a security concern
however, as data from one home is viewable from all other homes within that domain. This
is addressed by the
Data Over Cable Service Interface Specification (DOCSIS)
ratified by Cable-
Labs, a nonprofit organization composed of cable service providers in the Americas. DOCSIS is
described in the following section; it provides customer data protection over the shared medium.
The biggest advantage to cable modems is their capability to provide high per-user bandwidth
over long distances, often significantly greater than DSL. Although the cable is capable
of providing up to 40Mbps of downstream bandwidth, the network is provisioned so that each
user can obtain only a predefined rate—typically less than 2Mbps. For consumer installations,
this is sufficient and leads to a very economical solution. However, the provider could easily
increase the bandwidth to an individual user, although they would need to have a dedicated
coax connection to attain the full capacity.
What Is a Cable Modem?
The
cable modem
is the industry’s response to DSL and other broadband network services from
competitors. It provides remote access connectivity by establishing a shared data channel across
the existing cable television network. In fact, it’s apt to call it a channel—the bandwidth provided
to customers is actually taken from one of the 6MHz channels that would normally be
used for a video feed such as CNN or ESPN.
This 6MHz channel (NTSC—the North American standard from the National Television
System Committee) can provide up to 40Mbps of downstream (to the user) bandwidth and
12Mbps of upstream bandwidth. This bandwidth, as noted in Chapter 27, “Remote Access
with Digital Subscriber Line,” is shared by all the customers within a specific area. As such, due
to the normal installation and design model, in addition to bandwidth rate limiting by the provider,
a typical user should expect less than 2Mbps downstream and 128Kbps to 256Kbps
upstream. The typical cable modem installation is illustrated in Figure 28.1.
As shown in this figure, each home is connected to the coax (coaxial cable) that is running
through the neighborhood and providing video services. At the head end, or cable service provider,
this cable is connected to a hybrid fiber-coax (HFC) device that might also provide the
cable modem termination system (CMTS). This device is connected to the router that links to
the Internet and to the video streams (greatly simplified in this figure). The CMTS is the electronic
engine that processes cable modem feeds comparable to the digital subscriber line access
multiplexer (DSLAM) in DSL.
The installation at the home requires the installation of a filter to service all the televisions
on the premises. An unfiltered connection is provided to the cable modem itself. Note that for
customers without cable modems, the filter is typically placed in the street. In residences with
cable data services, the filter can be installed anywhere between the head end and the televisions
that will be using the cable signal. Many customers, as a result, never have to concern themselves
with the filter, but it does complicate the installation of a cable modem, just as the splitter
complicates DSL installations.
cable modem
is the industry’s response to DSL and other broadband network services from
competitors. It provides remote access connectivity by establishing a shared data channel across
the existing cable television network. In fact, it’s apt to call it a channel—the bandwidth provided
to customers is actually taken from one of the 6MHz channels that would normally be
used for a video feed such as CNN or ESPN.
This 6MHz channel (NTSC—the North American standard from the National Television
System Committee) can provide up to 40Mbps of downstream (to the user) bandwidth and
12Mbps of upstream bandwidth. This bandwidth, as noted in Chapter 27, “Remote Access
with Digital Subscriber Line,” is shared by all the customers within a specific area. As such, due
to the normal installation and design model, in addition to bandwidth rate limiting by the provider,
a typical user should expect less than 2Mbps downstream and 128Kbps to 256Kbps
upstream. The typical cable modem installation is illustrated in Figure 28.1.
As shown in this figure, each home is connected to the coax (coaxial cable) that is running
through the neighborhood and providing video services. At the head end, or cable service provider,
this cable is connected to a hybrid fiber-coax (HFC) device that might also provide the
cable modem termination system (CMTS). This device is connected to the router that links to
the Internet and to the video streams (greatly simplified in this figure). The CMTS is the electronic
engine that processes cable modem feeds comparable to the digital subscriber line access
multiplexer (DSLAM) in DSL.
The installation at the home requires the installation of a filter to service all the televisions
on the premises. An unfiltered connection is provided to the cable modem itself. Note that for
customers without cable modems, the filter is typically placed in the street. In residences with
cable data services, the filter can be installed anywhere between the head end and the televisions
that will be using the cable signal. Many customers, as a result, never have to concern themselves
with the filter, but it does complicate the installation of a cable modem, just as the splitter
complicates DSL installations.
Remote Access with Cable Modems and Virtual Private Networks
THE CCNP EXAM TOPICS COVERED IN THIS
BLOG INCLUDE THE FOLLOWING:
Understand cable modem technologies.
Know how to configure cable modem technologies.
Understand how to troubleshoot cable modem
technologies.
Understand VPN technologies including IPSec.
Know how to configure VPN technologies.
In this blog, we discuss two increasingly important technologies
in remote access: cable modems and virtual private networks
(VPNs). Although Cisco has finally added these topics to the
Remote Access exam, they have not attained the prominence that one might expect compared
to legacy technologies such as ISDN. Cable modems, like DSL, provide high data rates at low
cost, and don’t suffer from the call setup and bonding issues that ISDN includes. In addition to
providing an overview of cable modem and VPN technologies, this chapter also covers the configuration
of IPSec, one of the most common VPN technologies.
BLOG INCLUDE THE FOLLOWING:
Understand cable modem technologies.
Know how to configure cable modem technologies.
Understand how to troubleshoot cable modem
technologies.
Understand VPN technologies including IPSec.
Know how to configure VPN technologies.
In this blog, we discuss two increasingly important technologies
in remote access: cable modems and virtual private networks
(VPNs). Although Cisco has finally added these topics to the
Remote Access exam, they have not attained the prominence that one might expect compared
to legacy technologies such as ISDN. Cable modems, like DSL, provide high data rates at low
cost, and don’t suffer from the call setup and bonding issues that ISDN includes. In addition to
providing an overview of cable modem and VPN technologies, this chapter also covers the configuration
of IPSec, one of the most common VPN technologies.
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