Sip trunking - future of tomorrow communications

SIP TRUNKING [future of tomorrow communications]
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SIP Trunking
“future of tomorrow communications”
IP Telephony & Contact Center Architect
mail@ranjitpatel.com
SIP
SIP
SIP

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Table of Contents
1. SIP Trunking Introduction ..............................................................................................................................3
1.1. Introducing Enterprise PBX Trunking ....................................................................................................3
1.2. Types of Enterprise PBX Trunking .........................................................................................................3
1.3. What is SIP World?................................................................................................................................4
1.3.1. How SIP Trunking Works?.................................................................................................................4
1.3.2. Components of SIP Trunking.............................................................................................................5
1.3.2.1. IP PBX............................................................................................................................................5
1.3.2.2. Session border controller .............................................................................................................5
1.3.2.3. Session Management System.......................................................................................................6
1.3.2.4. ITSP/SIP Trunk Service Provider ...................................................................................................6
2. Benefits of SIP Trunking.................................................................................................................................7
2.1. PSTN Trunking Vs SIP Trunking..................................................................................................................7
3. SIP Trunking Considerations ..........................................................................................................................8
3.1. Planning Enterprise SIP Trunk Architecture ..............................................................................................8
3.2. Internet Telephony Service Provider.........................................................................................................8
3.3. Pricing & Services ......................................................................................................................................8
3.4. Considering Session Boarder Controller....................................................................................................9
3.5. DID and Local Numbers .............................................................................................................................9
3.6. Over The Top - OTT....................................................................................................................................9
3.7. Quality of service.......................................................................................................................................9
4. SIP Trunk Service Provider Overview...........................................................................................................10
4.1. Service Provider Infrastructure...........................................................................................................11
4.2. Service Plan & Design for Customer:...................................................................................................11
4.3. Service Implement & Manage for customer:......................................................................................12
4.4. Reporting/Billing/Monitoring..............................................................................................................12
5. SIP Trunk Service Design..............................................................................................................................12

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1. SIP Trunking Introduction
Enterprises of all kinds are dealing with two big trends when it comes to their real-time communications needs. First,
they’re trying to save money in an era when just about every business is tightening its belt. Second, they’re trying to figure
out how to support a host of new unified communications applications in an era where new devices, mobile connections,
and more sophisticated users are demanding change right now.
A technology being considered by many enterprises that meets both of those goals: Session Initiation Protocol (SIP)
Trunking. First, I discuss enterprise Private Branch Exchange (PBX) Trunking in general and then the difference between
circuit-switched and SIP trunking.
“SIP trunking allows your enterprise to connect its IP-PBX and IP communications systems directly to a SIP service provider,
reducing and sometimes eliminating the need for conventional PRI, BRI, ISDN or PSTN gateway connections. SIP trunking
supports transport of all media types (voice, video, text) which makes it ideal for enterprises wishing to implement a unified
communications solution”
A SIP trunk has been used to describe all of the following.
A service provided by service providers to enterprises, used for the purpose of interconnection to the PSTN, as a
replacement for circuit based connectivity.
A SIP port on an enterprise server, for the purposes of interconnection to other server-based systems, such as
voicemail servers, call centers, and application servers.
A SIP-based interconnection between IP-PBXs, for the purposes of replacing traditional TDM tie lines.
1.1. Introducing Enterprise PBX Trunking
Many enterprises — in fact, I’d say most medium and large enterprises — use a PBX telephone system to provide voice and
other communications services to their employees. You know what I’m talking about if you dial “9” or “#” or “” first to get
an outside line or if you can dial a coworker with just a few of the digits of her phone number.
The telecommunications network connections that connect the PBX to a telephone service provider are known as trunks.
The name implies a tree analogy that explains what a trunk is: all of the individual lines (phones on peoples’ desks) are the
branches of the tree, connected to a bigger line (the trunk), which connects back to the network. Trunking is a big deal
because it lets an enterprise pay for fewer phone “lines” than it has users with phones — the PBX lets a larger number of
users and stations effectively share a smaller number of connections to the outside world.
The thing to remember about enterprise voice trunking is that it’s an efficient and cost-effective alternative to buying an
individual phone line for every person in the enterprise.
1.2. Types of Enterprise PBX Trunking
PBX trunks were traditional analog circuit switched voice lines just like the ones you may buy from your local phone
company for your home/office.
For example, a small business may purchase three lines from the phone company, connect them to a small business phone
system (essentially mini-PBX, sometimes called a key system) and then share those lines among the six or seven people
(extensions) in the office.
Another option for connecting a PBX to a telephone carrier is known as a Primary Rate Interface (PRI) line. PRI is a Time
Division Multiplexing (TDM) interface, provided over standard telecommunications copper or fiber lines. PRI uses a T1
interface in North America or an E1 interface in other parts of the world.

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T1 and E1 lines are carved into 23 or 30 individual voice lines, respectively. Essentially, a T1 or E1 is a souped-up phone line
that can carry multiple voice lines over a single pair (or pair of pairs, in some cases) of copper phone lines, by using some
digital trickery to divide the voice signals up by time slots. All the extensions in the office connect to the PBX, which then
connects to one or more PRIs and on to the phone company network.
1.3. What is SIP World?
SIP trunking is a method of delivering telephone and other unified communications services over the Internet to customers
that have SIP enabled private branch exchange (IP-PBX) solutions. SIP utilizes both Voice over Internet Protocol (VoIP) and
Session Initiation Protocol (SIP) and it replaces traditional telephone lines or PRIs (Primary Rate Interface).
The PRI system worked well for a long time, but a more efficient (in terms of both bandwidth utilization and cost) and
modern system has begun to replace circuit switched voice:
SIP trunks, which utilize Voice over IP (VoIP) and the SIP. SIP trunking uses a data connection — the same connection that
a business uses for Internet access, for connecting to cloud services, or for hosting its e-commerce site — to carry voice
signals as VoIP to a service provider who can handle that kind of voice signal.
A carrier who can offer VoIP services is called an Internet Telephony Service Provider (ITSP). An ITSP could do just that, or it
could be your familiar local and long distance carrier who offers VoIP services in addition to more traditional circuit-
switched voice services.
1.3.1. How SIP Trunking Works?
SIP trunking relies on Internet protocols and Internet services instead of old-fashioned circuit-switched voice protocols and
services. With SIP trunking, voice communications can be merged with the data services an enterprise uses. In fact, many
smaller enterprises merge their voice and data onto a single “Internet” data connection while larger enterprises may keep
them separate but save significant amounts of money by using cheaper data services for voice instead of TDM trunking. In
other words, voice (and related communications services such as video, which I discuss in Chapter 2, when I talk about
Unified Communications, or UC) is just another data service being delivered over an enterprise’s data network. A good way
to understand this concept is to think about the phone functionality on your Android, Windows, or iPhone smartphone. It’s
just another one of the apps on the phone, instead of a dedicated hardware device. When you want to check Facebook
comments, you click the Facebook app, and when you want to make a call, you click the Phone app (or the Skype app, for
that matter).
A SIP trunk is a virtual connection between an Internet Protocol Private Branch Exchange (IP PBX) and a telephone service
provider providing SIP-based voice and UC services, connected over an enterprise’s data network connections.

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1.3.2. Components of SIP Trunking
Some of the components needed to implement SIP trunking are hardware devices that you need installed on your network,
while another component is the service itself, provided by a third-party service provider. I cover those components in this
section, but Figure 1-1 shows some of the necessary components in a typical deployment.
1.3.2.1. IP PBX
The key element to SIP trunking is a phone system that can convert voice calls into VoIP calls for transmission across the
SIP trunk. While there are other devices out there that can do this job — various VoIP gateway type devices, for example —
the most common and cost-effective mechanism is an IP PBX.
1.3.2.2. Session border controller
A key element of a SIP Trunking solution is Session Border Controller (SBC). The SBC is the device that sits on the border
between an enterprise’s private network and the public network provided by data and telephony service providers.
The SBC is essentially the traffic cop and doorman of SIP trunking. In its first role (traffic cop), the SBC looks at each
individual session crossing between the internal enterprise network and the external ITSP network and determines where
and when that session should go — in other words, where the session should be routed and what priority the session will
be assigned when the network is busy.

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1.3.2.3. Session Management System
An optional but often very useful addition to a SIP trunking implementation is a Session Management System. Without
session management, many or even most UC applications will have their own servers, their own management systems,
their own policy enforcement, and their own policy database systems — each of these elements individually controlled and
managed. Session management brings all these elements under a single system’s control, saving time and money.
Session management has an additional benefit: It provides intermediation and federation (in the computing sense, not the
political one) between different platforms, different networks, and different geographies. So a session management
system makes it easy for a UC application to be deployed one time and then provided to users (based on policies) no
matter where they are, what device they are using, what kind of IP PBX is installed in their office, and so on. This ability to
centrally and quickly deploy new applications is a big deal for enterprises with heterogeneous network infrastructures —
like companies who’ve merged or with subsidiaries who “did their own thing” when they built their networks.
Session management isn’t a “must have” for SIP trunking, but it’s a problem solver for complex UC deployments.
Session management is something you definitely should consider as you move from a simple voice-centric UC deployment
and start adding new multimedia apps.
1.3.2.4. ITSP/SIP Trunk Service Provider
Your SIP sessions, whether they’re voice calls, video conferences, and multimedia sessions need a public network provider
to get to where they’re going if they’re not internal calls handled on your own enterprise network. That’s the role of a
service provider just as it was with traditional circuit-switched voice.
A service provider that provides transport and termination of SIP calls is the ITSP also called a SIP service provider. You can
really think of an ITSP as just a “phone company,” with the difference being their interface with your network (through
your SBC and onto your IP PBXs) is a data connection using SIP to control the flow and routing of sessions.
Traditional phone companies are beginning to offer SIP trunking services to their enterprise customers.

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2. Benefits of SIP Trunking
SIP Trunking provides some concrete and measurable benefits for most enterprises, by simplifying network elements,
enabling new services, and reducing expenses.
SIP Trunking lets you combine your voice and data network onto a single, unified data connection. When you
eliminate PRIs and all their related equipment and standardize on data networks for voice and Unified
Communications (UC), as you do with SIP trunking, you make the network easier to administer and manage.
o Create centralized dialing plans that apply to every location in your enterprise (instead of creating custom
dial plan for each individual PBX).
o Use a single carrier (your ITSP/SIP service provider) rather than contracting with multiple local and long
distance carriers in each location.
o Set your security and application policies one time — in your centralized policy management database and
apply them to users whenever needed.
o Centralize your billing and cost accounting — so you know exactly what you’re spending where and can
charge or rebill your costs accurately and easily
SIP Trunking makes it a lot easier to add capacity to your VoIP and UC network when needed.
Adopting SIP trunking and SBCs — especially when combined with a session management solution — facilitates the
adoption of new SIP-based UC services and applications like
o Audio and video conferencing
o Audio recording
o Presence (determining the availability and communications preferences of a user on the network)
o Instant messaging (IM)
o Online collaboration (whiteboarding)
Redundancy with multiple service providers and links
2.1. PSTN Trunking Vs SIP Trunking
PSTN Trunking SIP Trunking
PRI (Primary Rate Interface) is a physical connection
to the PSTN over a dedicated line that only serves
voice transmission.
PRI uses a circuit switched model for making voice
connections between people
PRI has a guaranteed Quality of Service (QoS)
Scaling up requires the installation of new circuits and
additional termination hardware at specific
increments.
Providing sufficient backup circuits to remote sites in
an IPT-distributed architecture can negatively impact
the ROI.
Additional capacity must be planned well in advance
since considerable lead time may be required for the
ordering and installation of new circuits and
termination hardware.
Disaster Recovery / Business Continuity - While
possible, diverting calls to alternate locations can be
complex and expensive.
SIP (Session Initiating Protocol) Trunking is a virtual
connection to the PSTN over a physical line that is
often shared over your existing data connection.
SIP Trunking uses a packet switched model for making
voice connections between people
SIP Trunking is typically Best Effort
Scales up or down easily and quickly (a software
configuration change) and can offer automatic and
on-demand burst capabilities.
Automatic IP re-routing capabilities allow practical
geographic distribution of PSTN connectivity to sites
with limited or network redundancy.
While capacity planning is still important, adding
additional capacity can be as simple as a software
change. Additionally, providers are likely to offer
burst capabilities to accommodate brief periods of
higher than anticipated utilization.
The technology allows for automatic call rerouting to
pre-define locations should the location go offline (a
huge business continuity benefit).

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3. SIP Trunking Considerations
The reasons why you should consider implementing Session Initiation Protocol (SIP) Trunking in your enterprise voice and
Unified Communications (UC) network.
3.1. Planning Enterprise SIP Trunk Architecture
The deployment of SIP trunks allows more flexibility and choice than TDM in designing the network architecture. There are
three basic SIP trunk deployment models to choose from:
Distributed - SIP trunks are terminated at each enterprise site. In a distributed SIP trunk deployment, each
corporate site that has routed connectivity to the corporate private WAN also has direct SIP session connectivity
to the IP PSTN.
Centralized - SIP trunks are consolidated into central data centers. In a centralized SIP trunk deployment, only the
central hub–usually the headquarters or data center site of the organization–has direct SIP session connectivity
to the IP PSTN & all external calls to or from remote sites of the business go through this central hub.
Hybrid – SIP trunks are terminated at each enterprise site as well as center data center. Hybrid SIP trunk
deployment, some of the businesses’ sites conform to a distributed SIP trunk deployment model. In this model
each site has direct SIP session connectivity to the IP PSTN, and other sites conform to a centralized SIP trunk
deployment, accessing the IP PSTN through a central hub, which has SIP session connectivity to the IP PSTN
3.2. Internet Telephony Service Provider
A big part of any SIP trunking deployment is, of course, the company that actually provides you the service — your Internet
Telephony Service Provider (ITSP). Maybe hundreds — of companies offer SIP trunking services these days, and the
number keeps growing. You may be offered SIP trunking by the following vendors:
Your traditional Time Division Multiplexing (TDM) telephone service provider (the company you’re buying your
Primary Rate Interface [PRI] TDM trunks from today)
The data service provider who offers you your Multiprotocol Label Switching (MPLS) Wide Area Networking
(WAN) service.
A “pure play” SIP trunking provider, focused solely on SIP trunking
You may end up picking more than one provider. For example, you may choose one provider for your primary service and
another as a backup, or one for domestic calls and another for international. You don’t have to limit yourself to just one.
3.3. Pricing & Services
Most enterprises choose SIP trunking because of its cost savings benefits, figuring out the price you’re going to end up
paying is pretty important.
On-net traffic – how ITSP handle your on-net traffic, like one enterprise center to multiple enterprise center.
Pricing structure – For the off-net traffic you do have to pay for. Is that flat rate or bundles minutes? Local rate?
Domestic long distance calls?
International calls - look closely at your usage to see which countries you call most frequently, typically are
charged at different rates on a per-country basis.

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3.4. Considering Session Boarder Controller
The SBC plays a number of vital roles in SIP trunking, primarily by being the gatekeeper between your internal network and
the external WAN that carries sessions to and from your ITSP. The SBC, as the name implies, controls the border between
these networks, and determines which sessions are let in or out.
The SBC also provides security for the network, deals with the routing of SIP signals, and does a whole lot of intermediation
to make sure things just plain work right like dealing with transcoding and translating and providing SIP normalization.
Check out some of the basic criteria while buying SBC
Security features
SIP normalization/interoperability
Transcoding/translating support
NAT Traversal
Availability/Performance/scalability
Manageability
Quality
SLA Assurance - resiliency, survivability
Cost Management
3.5. DID and Local Numbers
Direct Inward Dialing (DID) is simply the series of numbers that customers and partners use to dial into your network and
Private Branch Exchange (PBX).
Ask following two things regarding DID when you evaluate an ITSP.
Number portability
Local number availability
3.6. Over The Top - OTT
This is a phrase that got started with data carriers and companies like Netflix who stream movies over the Internet.
The carrier provides access to the Internet and the content provider streams the movie over that circuit. So, two different
providers, providing two different services.
In the SIP trunking world, an Over the Top (OTT) provider delivers SIP trunking over a separate data carrier’s circuit.
3.7. Quality of service
Your service provider should assure you that the quality of service you get from your SIP trunking providers meets quality
of service of your existing TDM trunking.
You are trying to save some money, but you’re probably not trying to have poor voice quality etc.
You’re SIP Trunking Service Provider which codecs it supports and uses.
Service Level Agreement (SLA) for your SIP trunking service, Uptime, Latency and Jitter etc.

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4. SIP Trunk Service Provider Overview
A growing number of enterprises are migrating to SIP Trunking, which connects the enterprise’s IP PBX directly
to the SIP Trunk service provider IP network. The two key network components to an effective service provider
implementation of SIP Trunking are the network-based Session Border Controller and the Unified
Communications platforms.
One of the major issues to address when offering SIP Trunking services is the interoperability with multiple IP PBX vendors
on the market and the interworking between the multiple protocols and codecs in use.
The SIPconnect Technical Recommendation is an industry-wide, standards-based approach to direct IP peering between
SIP-enabled IP PBXs and VoIP service provider networks.

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4.1. Service Provider Infrastructure
While designing the service provider sip trunking network, we have to keep this in mind traffic aggregation point.
Geographical distributed point of presence of the traffic aggregations is always better for network resiliency and
availability point.
It also helps us for better geographical peering with other service providers/PSTN and save network uses.
Application Server operates at the core of services and is responsible for the execution of all enhanced personal and group
features, SIP trunking capabilities extend UC-One to PBX users allowing the business to take advantage of UC without
incurring the cost of changing their existing infrastructure until the time is right.
4.2. Service Plan & Design for Customer:
Carefully consider the benefits and challenges of the centralized or distributed SIP trunk designs for customer, Identifying
initial provisioning and configuration needs while including .
IP Planning
Dial Plan
Numbering Plan, Inbound/Outbound Calling, Off Net Calling, OnNet calling.
Template for local routing and element configuration requirements.
Network Design & Redundancy
Protocols and Codecs
Security

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4.3. Service Implement & Manage for customer:
Managed services include Fault Management, Trouble Ticket Management etc
Successful completion of the implementing templates & element configuration as per customer need.
Provisioning of the services
Performs verification, testing in the customer environment,
Ensuring the environment is ready for service.
Maintenance is an integral part of the service.
Provides 24x7x365 support.
Fault detection/isolation
Customer alarm/notification
Coordination with customer engineering team and equipment vendors
Remote fault repair and network element maintenance
Onsite repair where necessary
Repair status updates
Event escalation (where required)
Verification of successful fault resolution
4.4. Reporting/Billing/Monitoring
As a service provides service reporting, billing & monitoring is very important part for service continuity and capacity
argumentations.
Real time alert with customer thresholds.
Historical Reporting.
Resource Utilization Reposts
Service availability reports.
Capacity Monitoring.
CDR for Billing.
5. SIP Trunk Service Design
“Service design is the activity of planning and organizing people, infrastructure, communication and material components
of a service in order to improve its quality and the interaction between service provider and customers.”
The design of appropriate and innovative IT services, including their architectures, processes, policies and documentation,
to meet current and future agreed business requirements.
There are five individual aspects of service design. These are:
New or changed services
Service management systems and tools, especially the service portfolio, including the service catalogue
Technology architecture and management systems
The processes required
Measurement methods and metrics
The service design stage of the lifecycle starts with a set of new or changed business requirements and ends with the
development of a service solution designed to meet needs of the business. This developed solution is then passed to
service transition to evaluate, build, test and deploy the new or changed service.
Other objectives include:
Design services to satisfy business objectives, based on the quality, compliance, risk and security requirements,
delivering more effective and efficient IT and organization solutions and services aligned to organizational needs.
Design services that can be easily and efficiently developed and enhanced within appropriate timescales and
costs and, wherever possible, reduce, minimize or constrain the long term costs of service provision.
Design efficient and effective processes for the design, transition, operation and improvement of high quality IT
services, together with the supporting tools, systems and information, especially the service portfolio, to manage
services through their lifecycle.

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Design secure and resilient IT infrastructures, environments, applications and data/information resources, and
capability that meet the current and future needs of the organization.
Design measurement methods and metrics for assessing the effectiveness and efficiency of the design processes
and their deliverables.
Produce and maintain IT plans, processes, policies, architectures, frameworks and documents for the design of
quality IT solutions, to meet current and future agreed organization needs.
Assist in the development of policies and standards in all areas of design.
Develop the skills and capability within IT by moving strategy and design activities into operational tasks, making
effective and efficient use of all IT service resources.
Contribute to the improvement of the overall quality of IT service within the imposed design constraints,
especially by reducing the need for reworking and enhancing services, once they have been implemented in the
live environment.
The scope of Service Design is not limited to new services. It includes the changes and improvements necessary to increase
or maintain value to customers over the lifecycle of services, the continuity of services, achievement of service levels and
conformance to standards and regulations.

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Ranjit Patel
He is a Son, Brother, Husband, Father, Friend, Student & IP Telephony Architect.
He carries more than 14+ years of domain expertise & experience for voice managed services, unified communications, contact center
technology, premise-based, hosted & cloud-based solutions.
He likes working on new technologies and pushing existing ones to their limits.

Sip trunking - future of tomorrow communications

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