Looking for PRI/SIP line in nepal..? Read this first.

PRI and SIP

PRI and SIP Trunking are two different ways of connecting your business to the PSTN (Public Switched Telephone Network). Typically, both methods, PRI and SIP Trunking, require a piece of an equipment in your office called a PBX (Private Branch Exchange). Most PBX and IP PBXs can support both PRI and SIP Trunking connections, either directly or with an adapter.

Primary Rate interface(PRI) is a telecommunication standard that enables traditional phones lines to carry voice, data and video traffic, among others.

• It uses multiplexing/de-multiplexing techniques to carry more than one channel in single circuit.

• There are two common forms of PRI lines. E1(European standard that carry 30 channels) and T1(American Standard which carry 24 channels).
• Technically, a PRI line is a 2 Mbps line, so each channel has a capacity of 64 Kbps. From the service provider POP, it runs on an IP backbone like optical fiber network and various last mile connectivity options like copper, RF, fiber can be used to connect to EPABX.

• Each channels in PRI line provides 64 Kbps for data transmission.

• A PRI line can connect to both Analog/Mixed EPABX systems and also the newer IP PBX systems. A PRI Card / Interface might be required to terminate the PRI circuit on the PBX.
  
  
  
  
  
  
  
  
  
  How does a PRI Line connect to an EPABX ....?
  
  An EPABX refers to the private telephone interconnectivity system usually installed in the customer premises. This system connects all the extensions (phones, fax machines, etc.) to the trunk lines (analog lines, PRI lines, etc.)
  
  Each manufacturer has multiple EPABX models with varying capacities for trunk and extension connections. Some EPABX models have a fixed no. of connections and some PBX models have open slots that can be populated with trunk/extension cards of varying capacities.
  
  While buying an EPABX It is important to size it based on number of PRI and extensions required so that future requirements can be catered without additional costs.
  
  Session Initiation Protocol
  
  
  
  
  
• SIP (Session Initiation Protocol) is a signaling protocol used for initiating, maintaining, and terminating real-time sessions that include voice, video and messaging applications.
• SIP Trunking is nothing more than the virtual connection between your PBX and your carriers SIP network, Over the already existing Physical Data Line.
• SIP is application layer Protocol to start, modify and terminate multimedia sessions. It is independent of lower layer protocols (UDP, TCP, TLS, IPV4, IPV6).In order to complete a call, SIP work with other Protocols like RTP, RTCP, STP etc.
  
  So what is the difference between SIP and PRI…?
  

  PRI	SIP
  1) PRI (Primary Rate Interface) is a physical connection to the PSTN over a dedicated line that only serves voice transmission.	1) 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.
  2) PRI uses a circuit switched model for making voice connections between people	2) SIP Trunking uses a packet switched model for making voice connections between people
  3) PRI has a guaranteed Quality of Service (QoS)	3) SIP Trunking is typically Best Effort

  
  What are telephone Trunk Lines....?Telephone trunk lines are the ones that enable users to make outgoing calls/receiving calls in an organization. I am talking about land line calls,not a cell phones :)
  
  So in an organization there might be many users with either IP Phones or Analog Phones and they connect to the IP PBX or Analog-Mixed PBX. This is on the user end.
  
  On the other side, you can get some trunk lines (Analog Trunks, ISDN Lines/ PRI-E1-T1 Lines, etc) from a Public Telephone Exchange or Telecom Service Provider (PSTN) and terminate them to the PBX as well.
  
  So, when a user makes an outgoing call with his analog phone/ IP phone, the call reaches the PBX and the PBX will connect the call to any of the free Trunk Lines. Similarly, when there is an incoming call, it lands up on the PBX and the PBX routes it to the appropriate extension.
  
  To understand telephone Trunk Lines deeply we can more divide trunk lines in different ways.
  
  Analog Trunk Lines:The phone line (land-line) that you get in your home is an example for an analog trunk line. At homes, one line would suffice. But in organizations, multiple such lines might be required (as the number of telephone users are more). These analog trunk lines carry a single channel of voice call per line (meaning, one person can make or receive a phone call from outside at any given point of time).
  
  For terminating the analog trunk lines in a PBX, special analog trunk cards (12 ports, 24 ports, etc) are used. In an IP PBX, Analog Terminal Adapters (ATA) or PCI based Analog Cards may be used. These devices convert the analog calls into IP so that an IP PBX can understand them and transmit them over the network.
  
  Separate rental / call charges needs to be paid for each analog trunk. Analog trunk lines are sufficient for small organizations which require a few lines.
  
  PRI/E1/T1 Lines:
  For larger organizations that require a lot of trunk lines, procuring additional analog trunks might not be a practical idea as they need to buy separate (perhaps multiple) analog trunk cards to terminate these lines in their PBX (and) they need to pay separate rental for each line where the free call capacity for some individual lines might never be reached!
  
  So, these organizations can procure a digital line called as PRI/ E1 (In Europe/ Asia) or T1 (In America). Each PRI / E1 line can carry up to 30 channels of voice communications simultaneously. They can do this by using multiplexing/ de-multiplexing techniques (at the public telephone exchange end -and- the customer PBX end). A T1 line, similarly can carry up to 24 channels of voice communications simultaneously.
  
  At the customer end, they need to procure a PRI / E1/ T1 Card, to terminate this PRI/ E1/ T1 line in their PBX. Just imagine – One line coming into your organization but thirty people can simultaneously make or receive calls through it! And add to it a single consolidated rental / billing package from the Telecom company.
  
  VOIP /SIP Trunks:VOIP service providers have become very popular. They use the Internet backbone (mostly) to transmit the call as IP packets to the destination. They have gateways (where required) to convert the IP calls to analog calls before passing them on to the local telephone exchanges so that people can reach normal landline/ cell phone numbers using the VOIP Service