Enhancing Network Infrastructure

As we noted for both IP telephony and IP-based video-conferencing, creating an
AVVID-enabled network requires a great deal of new equipment. Depending on
the needs of the network in question you will most likely be adding devices such
as CallManager servers, IP telephones,WebAttendant consoles, video gateways,
gatekeepers, MCUs,VTAs, and endpoints. All of these devices (and more) are very
necessary to make AVVID a reality for your network. In fact, they require even
more additions. Several enhancements also need to be made to your existing
infrastructure, such as specialized router interfaces and specialized switch cards. As
we discussed before, we must blur the line between our voice and data networks.
Here at Layer 2 (the access layer) of the Open Systems Interconnection (OSI)
model and Layer 3 (the network layer), where data has always reigned as the
proverbial king, we must now make our infrastructure voice and data friendly—a
shared kingdom of sorts. Previously, we’ve focused on the upper layers; now we’ll
discuss the Layer 2 and Layer 3 devices that will make our new type of network
a reality.
Using Routers for a Converged Network
As we all know, a router is a Layer 3 device, the primary purpose of which is
path determination and packet switching based on IP or other Layer 3 addresses.
When we introduce a converged network, routers are going to have to be one of
the first places we begin to make enhancements. Cisco has developed several
routers that allow a network to make the change to a converged network. Several
new types of interfaces have emerged, utilizing the modular chassis capabilities of
Cisco’s newer routers. Now both voice and video interfaces are available for these
routers. In the sections that follow, we will discuss these interfaces and the routers
that support them.
Analog Voice Interfaces
Cisco routers utilize analog voice interfaces to interface either directly with telephone
handsets, or to connect to legacy PBX or the PSTN. Because analog technology
is considered a much older and more stable technology, these interfaces
are standardized.There are currently three types of analog interfaces supported by
Cisco routers: Foreign Exchange Station (FXS), Foreign Exchange Office (FXO),
and ear-and-mouth, sometimes known as earth and magneto (E&M). Let’s discuss
these interfaces in more detail.
Foreign Exchange Station
Foreign Exchange Station (FXS) ports use a standard RJ-11 telephone jack to
connect to telephone handsets, modems, or fax machines.This is the common
type of interface found in homes. Cisco routers would most likely use this interface
for phone-to-phone connectivity.
Foreign Exchange Office
Foreign Exchange Office (FXO) ports also utilize a standard RJ-11 telephone
jack. FXS ports are commonly used by businesses to connect their legacy PBX
systems to the service provider’s telephone network. Cisco routers can use an
FXO port to connect to a legacy PBX device or to directly connect to the
PSTN.
Ear-and-Mouth
Ear-and-mouth (E&M) offers a more advanced solution than either the FXO or
FXS ports, as well as several features that the other two do not, such as trunking
and either analog or digital transmission. E&M utilizes an RJ-48 port as opposed
to the RJ-11 used by the others. Cisco routers would most likely use an E&M
port for connection to PBX or PSTN, as well as a connection requiring
trunking.
Digital Voice Interfaces
Digital voice interfaces are provided to Cisco routers by use of digital voice
trunking cards and Digital Voice Processor (DVP) voice compression modules
(VCMs). Digital voice trunking cards interface most commonly with ISDN BRI
and PRI lines. By utilizing the individual channels on each line, it allows for a
single line to support two voice lines using BRI and up to 23 lines using PRI in
the U.S., and up to 30 in Europe. Digital voice processor VCMs allow a router to
take a voice conversation and compress it down to as small as 5.3 Kbps,
depending on the method utilized, as opposed to a 56 Kbps channel.This allows
for a much greater utilization of available bandwidth.
MC 3810 Router
The Multi-Service Access Concentrator 3810 (MC 3810) represents the first
router of its type, offering the full capabilities of a router as well as Voice over
Frame Relay,ATM, and leased lines. It was designed to be an all-inclusive solution
for branch-office deployments. A major disadvantage of the MC 3810 is that
it is expensive and the network modules used in it are not interchangeable with
any other platforms.This is no longer a very popular platform due to the VoIP
capabilities of routers such as the 2600 and 3600.
1750 Multi-Service Series Routers
The 1700 Series of routers provide a small office solution for organizations. As a
member of the 1700 Series family, the 1750 multiservice router series also offers
an IP telephony solution, two analog voice channels, a DSP, and three network
interface module slots for additional voice/data support.The 1750 can share the
same WAN and voice interface cards as the 2600 Series.This router would most
likely serve the small and home office market, due to its small capacity and limited
features—it would not be adequate in the larger branch office role.
2600 Series Routers
The 2600 Series of Cisco’s routers has become one of the most popular connectivity
solutions for branch office connectivity. It offers a modular design, sharing
network modules with the 1600, 1700, and 3600 Series of routers, providing two
WAN interface card (WIC) connections as well as one network module slot.The
2600 router supports 10 Mbps and 100 Mbps Ethernet interfaces as well as token
ring.The 2600 supports VoIP applications and support for up to 48 digital voice
lines (60 in Europe).Voice interface cards (VICs) allow the 2600 Series to support
analog voice interfaces. By using two VIC cards in the WIC card slots, the 2600
can support up to four analog lines.
3600 Series Routers
The 3600 Series bears many resemblances to the 2600 Series, but the 3600 Series is
quite a bit more powerful, offering a great deal more scalability and processing
functions.There are three classes in the 3600 Series: the 3620, 3640, and 3660.The
3620 provides two expansion module slots, the 3640 offers four, and the 3660
offers six.Whereas the 2600 supports the use of WICs, the 3600 Series supports the
use of carrier cards that provide service for WAN, LAN, and voice interfaces; these
cards are interchangeable with the 2600 and 1750 Series routers. LAN support for
the 3600 supports 10 and 100 Mbps Ethernet, as well as token ring.
7200 Series Routers
The 7200 Series is Cisco’s first-level enterprise router. It offers a four- or six-slot
configuration with interfaces including ATM, Synchronous Optical Network
Technologies (SONET), ISDN BRI, ISDN PRI,T1, E1,T3, and E3. It also supports
AVVID applications through use of the multiservice interchange (MIX)
functionality.The MIX allows the 7200 to support digital voice as well as
gateway functionality through the use of two different trunk interfaces, the highcapacity
and medium-capacity T1/E1 trunk interface cards.The primary difference
between the two cards is that the high-capacity card includes an on-board
DSP card for compression.The 7200 Series can support up to 120 voice calls
depending on the module configuration used.This router also supports analog
voice applications through the use of voice interface cards (VICs).
Cisco Switches
Cisco’s Catalyst switch line is a highly-advanced line of switching solutions that
scale to meet various business needs, from small organizations to multinational
corporations. Catalyst switches operate at Layer 2, but Layer 3 switching is also
possible with a Route Switch Module (RSM). All of the switches in the Catalyst
line support AVVID networks, including IP phones, but specific switches within
the product line are designed specifically to meet the needs of IP telephony,
specifically inline power, which we will discuss in the next section, and gateway
functionality.We will discuss three lines that meet this challenge: the 3500, 4000,
and 6000 Series.
3500 Series Switches
The 3500 Series is a scalable, entry-level solution for small- to mid-sized networks.
It is a wholly Cisco-developed switch, which runs a router-like IOS.The
3500 Series of switches are fixed configuration switches, all offering 10/100
Ethernet ports and Gigabit Interface Converter (GBIC) ports.The difference
comes in the number of ports offered and the forwarding rate at which the
switch can process packets. Currently the 3524XL-PWR is the only switch in
the 3500 Series that supports inline power, although other models within the
35xx product line will, in the future, most likely offer inline power as well.The
3524XL-PWR offers 24 10/100 Ethernet ports, 2 GBIC ports, and a packetforwarding
rate of 6.5 million packets per second.
4000 Series Switches
The 4000 Series is a step up from the 3500, offering a modular configuration in
four different switches: the 4003, 4006, 4840G, and 4908G.The 4000 Series also
offers supervisor engine functionality, similar to that of the 5500 Series.Within
the 4000 Series, the 4006 is currently the only switch to offer inline power; by
use of the Catalyst 4000 inline power 10/100BaseT switching module or the use
of an auxiliary power shelf, the 4006 supports up to 240 10/100 ports.The 4003
is also an Ethernet switch, very similar to the 4006, but unfortunately the 4003
cannot offer inline power functionality.The 4840G and 4908G are both gigabit
Ethernet switches.The 4000 Series also offers voice-gateway functionality
through the use of the Series 4000 WS-X4604-GWY module, which provides
support for both H.323 and SSP (in the future it will support MGCP).
6000 Series Switches
The 6000 Series is a highly scalable, enterprise class series of switches.The 6000
Series offers a completely modular design, utilizing supervisor modules, with the
capability for redundant supervisor modules, if necessary.There are five switches
in the 6000 Series family: the 6006, 6009, 6506, 6509, and 6513.The 6006 and
6506 offer six slots while the 6009 and 6509 offer nine slots.The 6513 is the
largest form-factor in the product line, offering 13 slots.The 6000 Series provides
inline power directly through the use of specialized 48-port switching blades.The
6006 and 6506 can support up to 240 10/100 ports, while the 6009 and 6509
can support up to 384 10/100 ports, and the 6513 can support up to 576 10/100
ports. Gateway functionality is provided via the WS-X6608-x1 module.This
module supports SSP and will in the future support MGCP.The 6000 Series also
offers an eight-port voice T1/E1 and services module to provide connectivity to
legacy PSTN or PBX systems, as well as a 24-port FXS module for analog telephone
connectivity.
Exploring Inline Power Options
During our discussion earlier in this chapter concerning IP telephones, we discussed
how second-generation phones were superior to their first-generation
counterparts because they offered support for inline power. First-generation telephones
were limited in that they required an external power source in order to
function. Inline power allows second-generation phones to avoid this pitfall.
There are two ways in which inline power can be offered to second-generation
telephones, either by way of a power patch panel, or through the use of inline
power modules installed directly in the switch. Let’s discuss these different power
options as well as their advantages and disadvantages.
Inline Power Modules
Inline power is currently available for three switches in the Catalyst product line:
the 3524XL-PWR, the 4000 Series, and the 6000 Series.The 3524XL-PWR is a
fixed-configuration 24-port switch. It provides out-of-the-box inline power support.
An important note to make is that the 3524XL-PWR switch offers no
inline power redundancy.
The 4000 Series provides inline power through use of the Catalyst 4000
Inline power 10/100BaseT Switching module and the Power Entry Module
(PEM). Redundancy is provided to the 4006 by use of the WS-P4603 auxiliary
DC power shelf.This allows for an N+1 protection scheme protecting against a
single power supply failure. An important note to make is that the 4003 cannot
interface with the power entry module and therefore cannot utilize inline power
directly from the switch. In order for the 4003 to provide inline power, you must
use the Catalyst inline power patch panel.
The 6000 Series provides inline power by use of a 48-port switching blade.
Inline power is provided to the switch via 2500-watt power supply.Two power
supplies can be used for redundancy. Inline power modules offer a great solution
in environments where space is at a premium.
Because all of the functions are collapsed into one piece of equipment,
administration is simplified. On the down side, this solution may require a forklift
upgrade, as inline power modules are only available for the 3500, 4000, and 6000
Series, which could introduce a great deal of added expense. Even though powerredundancy
is available for these switches, you are still relying on a single point of
failure should the entire switch fail.
Power Patch Panel
The Catalyst inline power patch panel offers an alternative to the forklift upgrade
that might be necessary in order to accommodate inline power.This solution
allows you to utilize your existing switching infrastructure, such as 2900 and 5000
Series Catalyst switches, by providing inline power external to the switch.The
Catalyst inline power patch panel offers 96 ports, for support of up to 48 stations
per panel, one port for the IP telephone and one port for the switch.The major
advantage to this solution is that it helps to protect your existing investment in
switches and helps to keep your options open to future product offerings.The
major disadvantage is that you now have an additional piece of equipment in
order to administer.
Power Cube
Power cubes are an external power supply, used as a sole means of power for the
first-generation telephone offerings. Power cubes can be used by second-generation
telephones as a sole means of power, or more commonly, can be used as a
backup power supply to the inline power patch panel and the inline power modules.
The advantage to this solution is that, when used with inline power, it provides
a redundant power supply for your IP telephone.When used solely as a
means of power, its advantage is that you can deploy IP telephones and not have
to replace your switches or install inline power patch panels for power.The major
disadvantage is that you must provide a power outlet for each cube, and it adds to
the mass of cables around a user’s desk.
Different Queuing for Video/Voice
Queuing is an important design and performance issue that must also be examined
when discussing IP telephony. Queuing has traditionally been a Layer 3
function for WAN connections, but when discussing a converged network, specifically
that dealing with voice or video traffic, attention must also be given to the
LAN. Layer 2 traffic can be classified by type of service using the 802.1Q protocol.
It is recommended that when using this protocol you separate voice and
video traffic from regular data traffic and place this traffic in a higher-priority
queue. 802.1Q specifies seven classes of service (COS), 0 being lowest priority
and 7 being of the highest priority. It is recommended that COS 4–7 be used for
voice and video, and that 0–3 be used for normal data operations. An important
note to make regarding Layer 2 queuing is that once the packet encounters a
router, the Layer 2 information is lost—in other words, 802.1Q is only a LAN
solution. For traffic crossing WAN links, Layer 3 queuing must be incorporated.