Design and Planning

How to design a business phone system.

NOTE - This is a work in progress. Send an email to if something is missing and you need it ASAP.

Step 1: Will this be cost effective?

The first thing anyone should do when choosing or changing his/her phone system is to ask the question: Will this be cost effective? A little homework up front can save you hundreds of dollars. Below is a simple Operating Costs Analysis worksheet. Print this sheet out and read the notes below for answering the questions. If this is a new phone system, use this sheet for comparing different Service Providers and Equipment Operating costs.
Operating Costs Analysis

Here are some notes to help fill out the Operating Cost Analysis form.
  1. Current Phone System
    1. Trunks - Types include POTS lines, PRI, ISDN, SIP etc..
    2. Trunk Circuits - Number of lines or number of concurrent calls available. For example: 2 POTS lines = 2 Trunk Circuits, PRI = 23 Trunk Circuits.
    3. Costs per Circuit - If you don't know what the Costs per Circuit are, just put total costs minus LD or Local charges.
    4. Long Distance Calling Minutes - This is needed for comparing service providers. Most "non-contract" Service Providers charge per minute.
    5. Long Distance Costs - This is important to know and probably one of the reasons for changing your phone system.
    6. Local Calling Minutes - This is needed for comparing service providers. Most "non-contract" Service Providers charge per minute.
    7. Local Calling Costs - This is usually "free" for most businesses getting service from the monopoly phone company. But consider, how many times have you called across town and have been charged for a LD call? Or, do you pay extra for an "extended calling area"?
    8. E911 Costs - There is usually a fee for E911.
    9. Total Costs per Month - This total should add up to your monthly phone bill minus equipment charges.
  2. Current PBX - Fill in this information if you are renting/leasing your phone system and phones. Or, if you have some sort of service contract or monthly maintenance fees related to your phone equipment.
  3. Current ISP - This your current Internet Service Provider information and will be needed for the Site Survey.
    1. Internet Connection Speed - Duplex - use the smallest number (usually the "up" speed). This is your duplex bandwidth available. Ex: If your Internet access speed is 1 Mbps up and 3 Mbps down then your duplex speed (bandwidth) is 1 Mbps.
  4. New Phone System
    1. Since you will be purchasing the Micro PBX, there will be no monthly fees associated with it.
    2. Phone Costs Per Month - These will also be purchased so the there is no monthly fees for these, either.
  5. VoIP Service Provider - To assist with this form, I will use an example Insurance Agency. See the form below.
    1. Long Distance Calling Minutes per Month: This will probably be your biggest savings area.
    2. Pay special attention to Local Calling Minutes per Month. With our example VoIP Service Provider, Junction Networks, they charge a flat $0.03 per minute for local or long distance and a very, very small monthly fee for 25 lines. This is great for long distance but can be pricey if your business makes large number of local calls. There are several solutions to this including: using a different VoIP Service Provider that charges more per month but less (or free) per minute for local calls or, buying additional POTS lines from the local monopoly phone company and using the POTS lines for local calling and the VoIP for Long Distance.
Operating Costs Analysis Example

Step 2: Site Survey

Once you've determined what phone system and Service Provider you want, it becomes a matter of how much and where.

Example office drawing by Dan Designs - Houston, TX

The Site Survey is very important for a seamless integration into your office.
Site Survey

The Site Survey is fairly self explanatory. Below are some notes:
  1. Current Phone System information is not needed for new installations. If your boss is used to using a certain feature and you buy a PBX that doesn't support it, you will soon be replacing your PBX and possibly your job!
  2. Current Network Infrastructure: This is where you collect all the information you will need to integrate your new Micro PBX into your business.
    1. Gateway Router: Must support VLANs and QoS.
    2. Ethernet Switch: Must support VLANs and QoS.
    3. Ethernet Hubs: There MUST not be any in the network that carry voice or fax traffic since these are simplex devices.
    4. Firewall: This will need to have policies adjusted to allow traffic for SIP signaling and RTP voice traffic.
    5. DHCP Server: This may be used to boot the phones and point them at the Micro PBX with OPTION 66; for businesses that have a large number of phones. I prefer to use static IP addresses so I know which phone is at which IP address when I want to do maintenance.
    6. Email Server: This will be where the Micro PBX sends voice mail to users or errors if something fails.
    7. UPS Availability: Enterprise Micro PBXs come with their own battery backup (UPS). However, having a UPS on the Micro PBX and not on the Gateway router or modem will only allow for FXO dialing to the PSTN.
    8. Backup Solution: All Micro PBXs backup their DBs to an external drive. However, this does not include Voicemail or other programs that might have been installed on the Micro PBX.
    9. Remote Users: These are folks that work from home and want a business phone at their house.
  3. Branch Offices: These are offices in different cities, states or countries. One Micro PBX can be the central phone switch for all branch offices. The best part is, calling between the branch offices will always be FREE!
  4. New Phone System: Number of VoIP Phones and Lines: Using the Example Office Layout above, fill in who, what, where and how many lines, for the VoIP phones.
    1. Receptionist: Do they need a side-car to support 6 to 50 phone lines?
    2. Conference Rooms: Does it need video capabilities or a speaker phone specifically designed for Conference Rooms?
    3. Lobby: Is a single line phone sufficient to save money?
    4. Executive Phones: Do they want HD voice, video, or other non-standard features?
    5. Kitchen Phones: Is a single line phone sufficient to save money?
    6. Fax Machines: How many and where. This will determine the number of FXS ports needed on the Micro PBX.
  5. New Phone System: Features: List all the features as either "R" for required or "D" for desired. This will be useful when comparing IP PBXs and VoIP Service Providers.
    1. Call Flows: This is very important. What do you want your customer's experience to be? Do you want an Automated Attendant to answer the phone with a menu of options or a real person? How are calls going to be transfered after answering? Are employees going to have an outside telephone number so customers can dial them directly?

Site Survey:Sizing the network:

  1. Ethernet Switches: Count the number of Ethernet ports needed and mark their location(s) on the Layout.
    1. Required muPBX 10/100/1000 PoE ports = Add number of VoIP Phones desired. One PoE port per phone. Most VoIP phones come with an A/C power supply but they will not be on the muPBX's battery backup in the event of a power failure.
    2. Required muPBX 10/100/1000 BaseT Ports = Add 1 for the muPBX + 1 for port monitoring (recommended if the Ethernet switch supports it). These ports do not need to be PoE ports and should have PoE disabled if on a PoE Eswitch.
    3. Remote Eswitch(es) and Number of 10/100/1000 PoE ports: Sometimes it is better to split a Micro PBX into two or more pieces where cable runs may become too long for individual phones lines. A battery backup system may be attached to the PoE switch to supply power to the remote phones in case of a power outage. Otherwise, a cheaper non-PoE Eswitch may be used.
    4. Remote Eswitch(es) and Number of 10/100/1000 ports: Sometimes it is better to split a Micro PBX into two or more pieces where cable runs may become too long for individual phones lines. These phones will not have access to the phone network in a power outage scenario.
    5. If a VoIP phone will be next to a PC that is already connected to the existing network, an added Ethernet connection for the VoIP phone may not be necessary. Most VoIP phones have a port to plug the PC into. Therefore, you can plug the existing Ethernet cable into the phone's network port and plug the PC into the phone's PC port.
    6. The Total Required Ethernet Ports should be less than the number of available ports on your existing Ethernet switch. If not, you'll need an additional or larger Ethernet switch.
  2. Fax:
    1. FXS Ports: Each fax machine will need 1 FXS port unless it supports multiple lines. Then, it will need one FXS port per line.
    2. Remote FXS Ports: If you have fax machines close to a Remote Ethernet switch, then it might be cheaper to use a remote FXS port connected to a Remote Ethernet Switch rather than running a cable from the muPBX.
    3. T.38: Number of FoIP fax machines that you want running T.38. Note - your VoIP Service Provider must support T.38.
  3. Voice Codecs:
    1. G.711 standard PCM and the best for interoperability with other VoIP equipment.
    2. G.722 is used for HD voice.
    3. G.729 is compressed and uses less bandwidth than G.711 but can NOT be used for faxing.
  4. QoS:
    1. Referring to the Service Provider Internet access speed, use the smallest number (usually the "up" speed). This is your duplex bandwidth available. Ex: If your Internet access speed is 1 Mbps up and 3 Mbps down then your duplex speed (bandwidth) is 1 Mbps.
    2. Using the duplex bandwidth number, subtract the desired amount of bandwidth you want to reserve for data traffic. Data traffic is WWW access, email, file transfers, etc.. Note: This is important if your business accesses outside websites to conduct business or if your customers are accessing a website inside your network. Ex: 1M minus 256K reserved for data = 750K bandwidth available for voice traffic.
    3. Tag the Data traffic with DSCP type 0.
    4. Using available bandwidth for voice traffic, divide that by 87.2 Kbps (G.711 bandwidth requirement) = Total number of concurrent voice calls possible. Ex: 750K divided by 87.2K is approximately 8 concurrent calls possible.
    5. If the number of concurrent calls possible is less than the number of concurrent calls desired then, you will need to add additional bandwidth or use a codec like G.729 that compresses the voice into 8K. Note: I have not tested the muPBX using the G.729 codec. I would recommend using G.711 until I have thoroughly test the G.729 codec negotiation, voice quality, and upspeed capabilities.
    6. Tag the Voice RTP traffic with DSCP type EF
    7. Tag the Voice Signaling traffic with DSCP type AF3x
  5. PSTN Media Gateway: This will be the number of POTS lines connected to the Local Service Provider. Local Service Providers are your friendly local monopoly phone company and can provide for local services like 911, 411, and Operator Service. Plus, POTS lines can provide for lower cost local phone calling if your business makes many, many local calls.

Step 4: Layer 1 - Physical connectivity and power.


  • A drawing is optional but I find it easier to organize all the information associated with the network. You can draw the drawing by hand or use a drawing program; I use either MSWord or a CAD program depending on the complexity.
  • Verify there are no hubs in the VoIP path and all cables are pinned correctly; see pinnout below. Note:The colors don't matter as long as they match up on both ends the same as the image below. Ex: if brown is in pin 1 on the right then it needs to be in pin one on the left.

  • Power: Where are the phones going to get power? Here are a few design considerations:
    • The Grandstream GXP-2000 comes with a power supply and supports POE (Power Over Ethernet).
    • If a phone is going to be in a lobby or reception area where there is no power, using an Ethernet switch with POE might be cheaper than hiring an Electrician to run a new 110V socket.
    • Will the VoIP phones be used for E911? If so, you need to consider using a backup power supply for the phones and the muPBX in case of a power failure during an emergency. Unless you want to buy a backup power supply for each phone, I would highly recommend using POE. Then, all that is needed is one backup power supply to keep power on the muPBX and Ethernet switch. The DSL provider should already have a backup power supply on their equipment for E911.

  • Fax: Is there an existing telephone line off of the DSL modem for fax? If so, I would suggest keeping it. Fax over VoIP can be tricky, especially if you decide to use a compression codec like G.729 in your muPBX.
  • Fax using the FXS ports on the muPBX.
  • Fax using an ATA off of the muPBX.

Step 5:

If this is a new business and/or a new network installation then there are additional design considerations:
    • Router: - I currently use a Cisco 871W router running the 12.4.11.XJ2 Advanced IP Services software. It's stability is great and price a little expensive but, it has all of the features (Firewall, QoS, Wireless, VPN) that I wanted.
    • Ethernet Switch: I currently use the SMC GS8P-Smart running software load V1.40. The SMC has been very stable and the price is good ($275) for an 8 port POE switch. The GS8P supports port monitoring/miroring, POE, VLANs and Trunking. It doesn't have a fan so it does get a little warm but it is blessedly silent!
    • Future:Router design consideration - Layer1, Layer2, and Layer 3.
    • Future:Ethernet design consideration - Layer1 and Layer2.
    • Future:Updated drawing showing router and Ethernet design layout.


Make sure you review the Micro PBX Testing results to ensure there are not any test cases that failed that will prevent your successful integration and operation of you phone system.

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