why sip makes sense
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White Paper
xo.com
Why SIP Makes SenseEnabling the Evolution to
Unifed CommunicationsWritten by Steven Shepard, President, Shepard Communications Group, LLC
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Why SIP Makes Sense
Contents
Abst ract 3
Introduct ion: The Evolution to Unifed Communications 3
Setting the Stage 3
Enabling the Evolution 4
Signaling the Future 4
Overview o the SIP Signaling Protocol 5
SIP Advantages and Applications 6
1. Intelligence at the Edge 6
2. SIP Is Part o the Overall IP Suite 6
3. Supports Any Network Transport Medium 6
4. Mobility and Presence Support 7
5. Virtual Numbers 8
6. Business Continuity and Disaster Recovery 8
7. Supply Chain Support 9
8. Unied Communications and Conerencing Applications 9
SIP Trunking and Cost Benefts 10
SIP Trunks 10
Reduced Network Service Costs 11
Eliminating PRI Trunks and IP Conversion Devices 12
Evolutionary Migration Path 12
Considerations or Implementation 12
Interoperability 12
Security 12
E911 Requirements 13
Conclusion: Making the SIP Decision 13
The XO Advantage 14
About Steve Shepard 14Appendices 14
About XO Communications 16
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Abstract
Written specically or IT decision makers in medium to large-sized businesses, this white
paper presents an overview o the Session Initiation Protocol (SIP) standard, its drivers,
benets, and barriers to implementation. The paper presents several business applica-
tions or SIP trunking and discusses the advantages o SIP as an enabler or Unied
Communications. Because SIP has become the de acto industry standard or IP telephony
development, the paper concludes that businesses and enterprises o all sizes will be well
served i they consider SIP as part o their evolving network strategy.
Introduction: The Evolution toUnifed Communications
Setting the Stage
Remember the rst mobile phones? You could always tell when someone had one: they
walked hunched over like Quasimodo because o the heavy battery inside. We all coveted
them everybody wanted one. They were so desirous that in the mid-80s the Sharper
Image Company actually sold a ake cell phone that had a suction cup on the end o the
handset cord that could be axed under the dashboard, allowing the owner to drive down
the street looking cool.
Remember the rst laptops? They were equally cool; we all wanted one o those as well.
But Id be willing to bet that very ew people reading this paper today carry a laptop
because its cool. My suspicion is that they carry a laptop because it has theirstuon it.
All the Microsot Word documents, spreadsheets, presentations, images, PDF documents,
sound les, music, movie clips, and other digital paraphernalia that our work and personal
lives require are typically resident on our computers and must, thereore, accompany us
wherever we go.
However, what i the need to have the physical computer were to go away? What i there
was a way to have access to work-related content atanytime, anywhere in the world, on
any network, using any access device over any access technology? Would that not sim-
pliy lie dramatically and make use o the network more ecient and relevant? Well, that is
more than a possibility it is becoming a reality today.
Te growing prolieration
o Unied Communications
(UC) technology in the
workplace is enabling anytime,
anywhere communications.
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Why SIP Makes Sense Enabling the Evolution to
Enabling the Evolution
Three phenomena are making this evolution possible:
Inexorable, steady migration o contentrom the hard drive on the users device (PC or lap-
top) to storage arrays located within the network and managed by the network provider
or hosted by the enterprise.
The growing prolieration o Unied Communications (UC) technology in the workplace,
which is enabling anytime, anywhere communications. UC applications include IP tele-
phony, unied messaging (i.e., voicemail, email, ax), instant messaging, presence, web/
rich media conerencing, document sharing, and the support or Internet Protocol (IP)
applications supported across dierent device types, including smart phones, and sot-
phones, such as laptops. Driving the adoption o UC is the growth o IP telephony, which
has already overtaken TDM in the enterprise. According to industry analysts, 74.2% o
telephony ports shipped worldwide in 2009 were or IP systems, expected to reach over
90% by 2016.1
The extension o the Internet Protocolas an application layer signaling protocol in the
telecommunications network inrastructure, or both wireline and wireless networks. SIP
enables the suite o IP-based Unied Communications applications to be extended rom
PBX systems and/or an IP network across dierent network transport services and end
user devices to support remote sites and mobile workers. In essence, it allows any user on
any network to have access to any content on-demand, regardless o their physical loca-
tion, the device theyre using, or the access modality theyre employing. How important is
SIP in enabling Unied Communications? According to Frost & Sullivan, End-to-end IP
communications that do not require protocol conversion anywhere between the customer
endpoints and the service provider data center will eventually deliver better quality and
greater eciencies to businesses deploying unied communications. SIP trunking, there-
ore, becomes a driver o IP telephony and UC adoption.2
This three-part migration acilitates a number o advantages, including increased enterprise
productivity through improved support or distributed workorces, timelier and higher qual-
ity responsiveness to customers, and reduced capital expenses (CAPEX) and operating
expenses (OPEX) or telecommunications inrastructures. And it gets even better. Using SIP
helps reduce the cost o networking, plus SIP trunks ree the customer rom being locked
into a specic system vendor or network provider now and in the uture.
Signaling the Future
Signaling the process o establishing a call, invoking enhanced services required or the
call (many based on the Caller ID unction), maintaining the call, and tearing it down at the
end is perormed by protocols that are part o the Signaling System 7 (SS7) network,
Driving the adoption o UC
is the growth o IP telephony,
which has already overtaken
DM in the enterprise.
According to industry analysts,
74.2% o telephony ports
shipped worldwide in 2009were or IP systems, expected to
reach over 90% 2016.
1 IP Systems numbers include converged and native IP. Frost & Sullivan, Worldwide Enterpr ise Telephony
Platorm and Endpoint Markets, June 2010.
2 Frost & Sullivan, World Unied Communications Markets: Business Models Evolve as Technologies Mature,
February 2010.
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a unctional adjunct to the Public Switched Telephone Network (PSTN). However, as the
migration to Internet Protocol (IP) continues, SS7 protocols are being replaced with IP pro-
tocols, most notably the Session Initiation Protocol, or SIP.
Service providers have upgraded their network platorms to provide value-added ea-
tures and applications that dierentiate their oerings and complement the SIP standard.
One such eature is virtual numbers, a signicant benet or companies with a distributed
workorce and customer base. Business continuity and network disaster recovery can also
be elements in a SIP environment, aecting not only customer service, but also providing
network managers with additional ways to improve network availability.
This paper presents an overview o the ongoing SIP migration, including an explanation o
what it is, how it works, and why it is important to businesses today.
Overview o the SIP Signaling Protocol
SIP is an application layer protocol that is used to establish, maintain, modiy, and end
communications sessions between two or more parties. As such, it can establish and
manage:
Two-party, multiparty, or multicast sessions
Internet telephony
Distribution o multimedia content
Management o multimedia conerences
SIP is designed to be completely independent o the transport layer and can operate over
the Transmission Control Protocol (TCP), the User Datagram Protocol (UDP), or the Stream
Control Transmission Protocol (SCTP). SIP-based clients (devices) use TCP or UDP proto-
cols to connect to SIP servers.
The primary driving orce behind SIPs development and deployment was the perceived
need to develop a signaling protocol or IP-based networks that can support the standard
call processing unctions ound in the PSTN. The SIP protocol itsel does not dene these
eatures, but enables their creation in network elements, such as proxy servers and user
agents. These eatures include digit collection, call ring, ring back, busy tone, and ast busy
or reorder. And while the manner in which these unctions are delivered in an IP-based SIP
environment is somewhat dierent rom the PSTN, the overall result is identical.
SIP is exible and
extraordinarily dynamic. Its
unctionality can be extended
to any number o applications,
including enhanced signaling
or valueadded services, VoIP,
and XMLtagged applications.
Copyright 2012. XO Communications, LLC. All rights reserved. 5
XO, the XO design logo, and all re lated marks are registered trademarks o XO Communications, LLC.
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Why SIP Makes Sense Enabling the Evolution to
SIP Advantages and Applications
When deployed in a network, SIP o ers distinct advantages that can be used to develop
powerul and compelling end-user applications. For example:
1. Intelligence at the Edge
SIP-enabled telephony systems oer most o the call processing and eature invoca-
tion procedures oered through traditional voice networks but in a dierent way.
Traditional voice networks use a hierarchical, centralized, core-based protocol designed
around the limited requirements o telephone sets which have no innate intelligence.
SIP, on the other hand, is apeer-to-peer protocol, which requires a dierent type o
network core inrastructure (preerably MPLS built on an IP platorm) with a blend o
intelligence located at the edge (i.e., sotware or end-user device hardware or PBX),
complimented by more scalable, granular, and rapidly deployed services oered by
service providers.
2. SIP Is Part o the Overall IP Suite
As part o the overall IP suite, SIP is fexible and extraordinarily dynamic. Its unctional-
ity can be extended to any number o applications, including enhanced signaling or
value-added services, VoIP, and XML-tagged applications. Because XML is used to
structure, store, and send inormation across the network, it works well with SIP in
environments where data needs to be retrieved and used, as in a call center environ-
ment where customer records must be accessed, or in a healthcare environment where
access to customer data is critical. As a lightweight, text-based protocol, SIP relies on
a text-based command structure that uses the now universally amiliar HTTP syntax and
URL addressing, both ideal or delivering telephony over an IP network where the logica
integration o applications (e.g., voice, messaging, conerencing, and Web access) cancreate an enhanced user experience.
3. Supports Any Network Transport Medium
Because SIP is anapplication layer protocol, it can ride seamlessly across any transpor
scheme and be transported across any access modality cable, DSL, private line,
Ethernet, and wireless. Thus, SIP can enable a broad range o applications and remote
session capabilities (such as mobile application delivery and supply chain management)
without the need to provision additional transport services. From an enterprise point-o-
view, this is critical because SIP oers seamless connectivity options or service deliv-
ery or branch locations, remote workers, or trading partners. Since U. S. enterprises
with 500 or more employees have an average o 62 branch oce locations, with anaverage o 53.5 employees per location,3 this is a signicant benet or the enterprise.
3 Frost & Sullivan, Trends in Communication Services and Solutions or Small Businesses and Branch
Oce, 10 Sep 2008.
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4. Mobility and Presence Support
SIP is now incorporated into a range o user devices, including mobile wireless devices
and desktop clients. Using SIP, session establishment requests are not sent to a device
they are sent to the network, which locates the users presence and establishes a
session based on the users current location and usage prole. Because SIP unshack-
les users physical location rom their logical address, they can have ully integrated
corporate communications regardless o location. They can also integrate instant
messaging and desktop collaboration applications.
Presence is a relatively new concept in the networking arena. The users client pub-
lishes his or her availability within the presence application, and all users then have
access to that persons availability via all services oce wireline voice, mobile,
e-mail, chat, etc. Users can customize their availability prole and publish it or the
world to see, thus making communications much more ecient. In short, SIP is the
protocol that supports the universal availability o presence inormation.
Example: An inbound call center might use presence to ensure that a customer has the
ability to get back in touch with a call center agent who was helping them with a techni-
cal support problem. With presence, the agent would not have to be in the call center,
but could be located by the network and have the call routed to them, regardless o
where they actually are, thus making it possible to ulll and exceed customer service
requirements without reliance on a physical call center presence (see Figure 1).
Because SIP unshackles users
physical location rom their
logical address, they can have
ully integrated corporate
communications regardless
o location. Tey can also
integrate instant messaging
and desktop collaboration
applications.
Figure 1. The caller places a call to a specic agent in call center (yellow arrow, lower right), but
because the agent is out o the oce, SIP routes the call to their remote location (blue arrow, lower
let), thus avoiding a service disconnect with the customer.
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Why SIP Makes Sense Enabling the Evolution to
5. Virtual Numbers
A th advantage is the ability to utilize virtual numbers, an assignable telephone num-
ber that has no physical phone line associated with it. In most cases, virtual numbers
are orwarded to either a VoIP account or to an alternate xed or mobile number. For
example, virtual numbers are perect or sales orces, business travelers, small busi-
nesses, and eld service personnel. With virtual numbers, businesses can also create a
local identity in markets that the company serves.
Example: Imagine a business serving customers in multiple, ar-fung locations, such as
Dallas, Los Angeles, and New York City. The company seeks to create a local identity
in these markets by publishing phone numbers with local area codes instead o toll ree
numbers. They would also like to route the call to specic individuals supporting each
market. The company, which is headquartered in Chicago, might purchase virtual Direct
Inward Dialing (DID) numbers rom their service provider with area codes in Dallas, Los
Angeles, and New York City, giving customers the impression that the company has
a local presence in those locations a major element o a customer-riendly contact
strategy (seeAppendix A).
6. Business Continuity and Disaster Recovery
SIP trunks, in concer t with VoIP, can play a major role inbusiness continuity and
disaster recovery. With a SIP-supported IP PBX, many businesses are now able to
design disaster recovery plans using plug and play phones, sotphones, and IP PBX
programmability capabilities. Whats more, automatic reroute in IP environments is
possible, thus reducing the headache o planning or every contingency. For businesses
o any size, SIP trunks provide connections to the PSTN so that outbound calls can
be rerouted and delivered over an Internet connection when the normal connection (or
location o the connection) is unavailable.
Example: Workers can setup their laptop rom home or a remote location as a vir tual
oce, using the sotphone capability that can support presence to detect online sta-
tus o company employees, customers, and trading partners. Additionally, IP PBXs can
be programmed to redirect calls in seconds to dierent phones or locations in the event
o an outage at key company locations.
In addition, business-class service providers build multiple layers o redundancy into
their networks to provide or business continuity. A carrier should provision network
session capacity to support ailover o trac between designated sites. Service provid-
ers also should track session usage or each o their customers sites and implement a
primary/backup arrangement to manage overfow trac. When sessions in one site areully used, the network automatically routes inbound trac, normally delivered to the
rst site, to the second site.
Because as many as 91%
o employees work outside
o headquarters oces,
collaborative applications that
overcome the challenges o
distance are key.
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7. Supply Chain Support
The overall supply chain is enhanced when executed in a SIP environment. By con-
verging its voice, data, and expanding video/rich media applications, businessescan
enhance the end-to-end supply chain, thus measurably improving their eectiveness
and eciency.
Example: Mobile inventory tracking devices not only speed up the overall execution o
supply chain management, but also reduce the errors associated with the logistics o
tracking constantly changing inventory. Supply chains are also early adopters o Unied
Communications applications.
8. Unifed Communications and Conerencing Applications
Because as many as 91% o employees work outside o headquarters oces,4 collabor-
ative applications that overcome the challenges o distance are key. Videoconerencing
has slowly become a part o this equation, but the cost and diculties traditionally
associated with setting it up and the need to go to a specic location to use it have
been showstoppers. Thus, videoconerencing and SIP have combined orces. Not only
do they oer anywhere, anytime video, but they also make it possible to incorporate
presence, screen sharing, Web sharing, and instant messaging.
Example: Customers and suppliers located thousands o miles apart can use vid-
eoconerencing and collaboration tools to review and modiy design specications.
Moreover, training events can be held more requently and e ectively by leveraging rich
media application that can be delivered on-demand or in real-time.
Accelerating the growth o Unied Communications will be the adoption o
Microsots Oce Communications Server (OCS), launched in 2007. OCS is a Unied
Communications client that helps people be more productive by enabling them to com-
municate easily with others, using a range o communication options. Among its key
eatures are support or enhanced presence and enterprise voice capabilities, enabling
users to place computer-to-computer calls and to place outbound calls to (and accept
incoming calls rom) traditional PBX / PSTN phone users.
Whats the Unied Communications orecast? Growth in UC and UC-capable clients is
expected grow rom 15.4 million vendor shipments in 2009 to 25 to 30 million in 2015.
The installed base o ully integrated UC solutions is orecasted to grow rom 2.1 million
users in 2009 to approximately 50 million users by 2015.5
4 Irwin Lazar, Nemertes Research, Leveraging Convergence or Collaboration: Meeting the Challenges O The
Virtual Workplace, 2007.
5 Frost & Sullivan, World Unied Communications Markets: Business Models Evolve as Technologies Mature,
February 2010.
Te installed base o ully
integrated UC solutions is
orecasted to grow rom 2.1
million users in 2009 to
approximately 50 million users
by 2015.5
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Why SIP Makes Sense Enabling the Evolution to
SIP Trunking and Cost Benefts
With these advantages in mind, lets now take a closer look at SIP trunking and the cost
benets that SIP trunks make possible.
SIP Trunks
SIP trunks are one o the more remarkable oshoots o the SIP amily o capabilities and
one o the more important enablers o SIP-dependent applications. SIP trunks are nothing
more than virtual circuits congured and delivered over an Internet connection, typically via
the private IP backbone o a VoIP-enabled carrier, as shown in Figure 2.
SIP trunks are oten used in conjunction with an IP PBX as replacements or evolutionary
next stages rom traditional ISDN PRI or analog circuits. In act, many analysts believe
that SIP trunks will ultimately replace T1 acilities in business networks. SIP trunks not only
make network deployment more fexible, but also make possible the seamless assurance
o operational continuity in the event o a network ailure. Their popularity, which is growing
rapidly, is largely due to a collection o actors, including cost savings and overall reliability.
Some o the more relevant cost benets are as ollows.
Figure 2. SIP trunks enable convergence to one IP connection over a standards-based con-
nection, eliminating the need or TDM-IP gateways.
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Companies that are not
ready to replace their legacy
DM PBXs but wish to
deploy SIP trunks can deploy
media gateways at branch
oces to convert DM voice
communication into IP voice
trac (and vice versa), instead
o installing a brand new IP
system.
Reduced Network Service Costs
Convergence implies that a single connection can serve multiple access requirements.
With SIP trunks:
Voice and data applications ride over one IP connection, instead o separate voice and
data services. According to Gartner, their clients report that savings o more than 40%
can be realized by replacing the Primary Rate Interace (PRI)/T1 and other TDM trans-
ports with SIP trunks. This typically amounts to a savings o more than $4,500 annually
or every PRI/T1 replaced with equivalent SIP trunks throughput, based on gener-
ally available commercial rates in North America, and more savings in other regions.
Furthermore, enabling trunk aggregation at the centralized site can achieve economies
o scale and improve utilization eciency. 6
The connection is highly ecient because unallocated SIP bandwidth is automatically
and dynamically made available or other uses and applications as required (see Figure
3). Added voice compression is available rom some service providers, such as XO
Communications, enabling higher throughput and eciency as well.
On-net dialing plans can be established amongst a companys locations and connected
via SIP trunks, resulting in lower toll costs as well (see Appendix B).
6 Gartner, User Exper iences Reveal Best Practices or Deploying Unied Communications, 21 June 2011.
Figure 3. Real-time IP dynamic bandwidth allocation gives priority to voice trac butmakes additional data bandwidth capacity available when phone lines are not in use.
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Why SIP Makes Sense Enabling the Evolution to
Eliminating PRI Trunks and IP Conversion Devices
SIP trunks eliminate the need or PRI PBX cards and IP conversion devices on the customer
premises, typically reerred to as TDM-IP gateways. This device supports the conversion rom IP
packets to PSTN trac, which is normally transmitted over an ISDN PRI. In addition to hardware
savings, better throughput is also achieved by minimizing a protocol conversion step.
Evolutionary Migration Path
Companies that are not ready to replace their legacy TDM PBXs but wish to deploy SIP trunks
can deploy media gateways at branch oces to convert TDM voice communication into IP voice
trac (and vice versa), instead o installing a brand new IP system. Thus, legacy TDM PBXs
placed in multiple sites are being interconnected via IP networks with the help o gateways that
transorm the PSTN trac into VoIP packets.
Considerations or Implementation
Interoperability
As IP PBXs have come booming into the market, problems o interoperabil ity have arisen with
regard to SIP. Almost all o the rst-generation IP PBXs on the market were designed around pro-
prietary IP signaling stacks because universal agreement on a single protocol had not yet been
achieved. Ultimately, SIP was chosen as that universal protocol, and PBX manuacturers wrote
proprietary interaces or their legacy TDM interaces. This created problems or developers
looking to write interaces or VoIP environments built on media server platorms, as well as com-
plications that required system-by-system interoperability testing or, in some cases, the creationo sotware interaces to perorm a protocol conversion that ensures interoperability beyond very
basic connect-and-disconnect capabilities.
Security
Thanks to new encryption capabilities such as SIP Transport Layer Security (TLS) and Secure Real-
Time Transport Protocol (SRTP), security vulnerabilities are no longer a major issue or SIP imple-
mentations. Just as most enterprise organizations encrypt the data that transverses their network,
they are requesting that VoIP providers encrypt voice and data packets transmitted over their VoIP
networks. Encryption provides customers with an added layer o protection to maintain privacy o
VoIP communications and helps prevent unauthorized access to voice conversations.
Business-grade service providers oer enterprise SIP customers a choice o either or both o the
industry signaling standards or encryption: SIP TLS and SRTP. TLS is based on the earlier Secure
Sockets Layer (SSL) method o encryption and uses cryptography to provide endpoint authentica-
tion and communications privacy over the internet. SRTP was developed by a small team rom
Cisco and Ericsson and denes a prole o RTP, intended to provide encryption, message authen-
tication and integrity, and replay protection to the RTP data.
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E911 Requirements
SIP and Unied Communications extend the mobile nature o VoIP by enabling
communications on a range o wireline and wireless devices that are not tethered to a
physical location address. Todays VoIP-enabled, Internet-based phones oer multiple
eatures or convenience o use that allow callers to use phones rom virtually any Internetconnection. While this technology has many benets or end users, it has created many
challenges or emergency communications call centers that were designed to receive
calls rom landline phone services associated with a xed address. So, how does a
carrier provide E911 services to remote locations; and what are the legal requirements or
providing back up and E911?
Interconnected VoIP service providers are required to comply with enhanced 911 rules
adopted by the FCC that are designed to integrate nomadic interconnected VoIP services
with the existing PSTN emergency 911 system. Careul planning and proper service
provisioning help to ensure phone users in all locations have accurately set up
E911 capabilities.
To provide E911 service to distributed users on a centralized, shared SIP trunk, the callers
telephone number must be provisioned so that the E911 service is programmed to ring
to the caller assigned local emergency dispatch call center, rather than to a center miles
away, across the region or across the country. Nomadic, or wireless 911 users require
a dierent solution rom a xed-IP E911 solution because the VoIP service provider
normally delivers the service to a stationary location. Providers that oer enterprises a
nomadic E911 capability enable employees to move their phones and still get the proper
address inormation transmitted to the Public Saety Answering Point (PSAP), as long as
the nomadic VoIP user keeps their inormation up to date. Updated inormation must be
provided by the user via location update unctionality provisioned by the service provider.
Conclusion: Making the SIP Decision
Like any large-scale technology shit, the move to SIP should be undertaken only ater con-
sidering all options and determining that a SIP migration strategy is the right move or the
enterprise. In most cases it will be but it makes sense to ask the questions. Furthermore, it
is criticalto seek the advice o SIP-seasoned proessionals beore undertaking the migra-
tion. The move to SIP is a relatively straightorward process. However, there is a level o
complexity associated with it that demands the help o a service provider already amiliar
with the overall process. This is what they do use them to your advantage.
SIP is a undamentally important technology in the evolving converged network and will
play an increasingly important role in enterprise and SMB networks in the very near uture.
The advantages listed above and the applications described in this paper are clear indica-
tors o its relevance as a protocol and as an enabler o service provider relevance in the
uture. SIP, like VoIP, is a when rather than aniquestion in todays enterprise. Its time
has come, and businesses o all sizes will be well served i they consider it as part o their
evolving network strategy.
Interconnected VoIP service
providers are required tocomply with enhanced 911
rules adopted by the FCC
that are designed to integrate
nomadic interconnected VoIP
services with the existing
PSN emergency 911 system.
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Why SIP Makes Sense Enabling the Evolution to
XO
SIP
Regional Office
Pittsburgh
XOSIP
NYC212 Nxx-xxxx
Virtual Number
L.A.213 Nxx-xxxx
Virtual Number
Dallas214 Nxx-xxxx
Virtual Number
PSTN
XOSIP
Servers
XOCertified
IP PBX
Data
Phone
CE Router
HQ
Chicago
Servers
XOManaged
IP PBX
Data
Phone
CE Router
Internet
WLAN
WLAN
XO SIP
Network
The XO Advantage
Investigate your SIP trunking options and savings potential. XO Communications o ers
a ull line o IP telephony oerings, including SIP trunks, Managed IP PBX, Cloud
Communications, and VoIP solutions that integrate MPLS IP-VPN and on-net dialing plans.
XO SIP and ESIP provide direct IP access to the XO private, OC-192 IP network, so you
get the most rom your centralized or decentralized IP PBX Solution. Need to serve many
markets rom a single location? XO SIP Service oers vir tual inbound Direct Inward Dial
numbers that allow customers outside your calling area to make local calls to reach you,
giving you a local presence in markets where you want to be one o many reasons why
SIP makes sense in todays evolution to Unied Communications.
About Steve Shepard
Dr. Steven Shepard, Ph.D. is president o the Shepard Communications Group. A proes-
sional writer, educator and industry analyst with more than 25 years o experience in the
technology industry, Dr. Shepard specializes in international telecommunications issues,
the social implications o technological incursion and the analysis o nancial issues
related to technology-dependent businesses. He is the author o 45 books on a wide
variety o topics and regularly speaks to audiences throughout the world, and has clients in
more than 50 countries. Mr. Shepard can be reached at: Steve@ShepardComm.com.
Appendices
XO SIP Service virtual DID numbers enable a company to establish a local identity in
several markets they serve. Additionall y, calls can be routed to the appropriate individual
assigned to each number.
XO Communications ofers
a ull line o IP telephony
oferings, including SIP
trunks, Managed IP
PBX, Enterprise Cloud
Communications and VoIP
solutions that integrate MPLS
IP-VPN and on-net
dialing plans.
Appendix A:
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MPLS IP-VPN Network
Headquarters
Regional Office
Failover
Branch 1
Branch 2
Branch 3
Branch 4
Branch 5
Branch 6Branch 8Branch 7
XO Communications
+
+
+
DIA #1
ILEC#1
PRI
DIA #2
ILEC
#2
PRI
Headquarters
Regional Office
Branch 1
+
+++
Provider
1
Provider
3
Provider
5
Provider
6
Provider8
Provider
4
+
Provider2
Provider
7
+
+
Branch 8Branch 7
Branch 6
Branch 5
Branch 2
Branch 3Branch 4
Appendix B:
Beore Enterprise SIP
Ater Enterprise SIP
BEFORE: Enterprises had to work with more than one local carrier to provide separate Primary Rate
Interace (PRI) lines or IP connections to each location.
AFTER: XO Enterpr ise SIP provides high-capacity SIP trunk ing to one or more pr imary locations,
thereby eliminating lines and equipment, gaining business continuity options and sharing capacity or
sessions across the entire enterprise.
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7/30/2019 Why SIP Makes Sense
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XO911WP-0412
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XO, the XO design logo, and all re lated marks are trademarks o XO Communications, LLC.
About XO Communications
XO Communications is a leading nationwide provider of advanced broadband communications
services and solutions for businesses, enterprises, government, carriers and service providers.Its customers include more than half of the Fortune 500, in addition to leading cable companies,
carriers, content providers and mobile network operators. Utilizing its unique combination of high-
capacity nationwide and metro networks and broadband wireless capabilities, XO Communications
offers customers a broad range of managed voice, data and IP services with proven performance,
scalability and value in more than 85 metropolitan markets across the United States. For more
information, visit www.xo.com.
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