Understanding VoIP - 1

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Understanding VoIP - 1

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1. Components, Standards and Architectures The Big Picture


Major VoIP Components

Terminals Packetized voice Soft switch Media server Gateway LAN WAN Standards and Protocols


TerminalsFeatures Description

Protocols/Standards

SIP RFC3261, SDP, TCP/IP/UDP, RTP/RTCP, HTTP, ARP/RARP, ICMP, DNS, DHCP, PPPoE, TFTP, NTP, STUN.

Network Interfaces

Dual switched 10/1000Mbps ports with integrated PoE

Voice codec G.711 a/u (64kbps), G.729A/B(8kbps)Telephony Features

Hold, Transfer, Forward, 3-way Conference, Call Waiting, Multiple SIP Accounts, etc.

QoS Layer 2 (802.1Q, 802.1p) and Layer 3 (ToS, DiffServ, MPLS) QoS

Advance Voice Quality Features

Silence Suppression, Jitter Buffer, Voice Activation Detection, Packet Loss Concealment

Operating System

Linux

Example Grandstream, Dlink, Cisco, X-Lite, etc.

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Packetized Voice

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Soft Switches – SIP Servers/Call Managers


Softswitch: A programmable network switch that can process the signaling for all types of packet protocols. Also called SIP Server, SIP Proxy, Call Manager, VoIP Switch, Call Agent, IP Centrex, Hosted PBX, User Agent, Gatekeeper (H.323). According to International Softswitch Consortium, a softswitch should be able to:1. Control connection services for a media gateway and / or native IP

endpoints2. Select processes that can be applied to a call.3. Providing routing for a call within the network based on signaling and

customer database information.

4. Transfer the control of the call to another element .5. Interface to and support management functions such as provisioning,

fault, billing,etc.

The switching technology in a softswitch is in software (hence the name) rather than in the hardware as with traditional switching center technology. This software programmability allows it to support IP telephony protocols (H.323, SIP, MEGACO, etc.). Examples of Softswitch: Asterisk, 3CX, Volcatel, etc.


In Summary, the two main functions of a Softswitch are:1. Terminal Control2. Call Control

•Registration: Authentication, directory entry

•Admission: Permission to make / receive calls

•Status: Call disposition

Terminal Control

•Call Signaling: Address resolution, setup, tear down

•Call routing•Call accounting•Call detail record

Call Control


Media Server or Content Server A computer appliance, ranging from an enterprise class machine with a dedicated software application providing contents such as voice, video, music, text, graphics. Two interesting types of media/content:

1. Integrated Messaging 2. Video Server Integrated Messaging• Voicemail, Email, Fax• Text-to-speech, speech-to-text• Web-style user interface

Video Server• Basic Cable• Video on Demand: Movie “rentals”• Pay-per-view, IPTV• PVR functionality• Game Server

Other Media• Web pages• Digital right management• Music• Google earth• Countless applications


Gateways – Media Gateway Gateways are Protocol Converters Media Gateway converts traditional TDM to RTP stream and vise versa. TDM belongs to the PSTN world. RTP belongs to the IP world. Media and Signaling gateway could be a single device or a separate device.


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Gateways – Signaling Gateway Gateways are Protocol Converters Signaling Gateway converts SIP to SS7 and vice versa. SIP belongs to the IP world. SS7 belongs to the traditional PSTN world.


LANs and WANs LAN: In-building Ethernet: 10 – 1000Mbps Cabling: Cat5, Cat6e twisted pair MAC Address Power Over Ethernet

WAN: Between buildings IP Addresses Access: DSL, Cable, T1, Fiber, Microwave Network Protocol: IP, Frame relay, ATM Carrier Ethernet


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Key VoIP Standards IETF• RFC 3261 SIP• RFC 2327 SDP• RFC 1889 RTP• RFC 0768 UDP• RFC 0791 IP

ITU-T• H.323: Historical• G.700: Voice coding - G.711: 64kbps “PCM” - Many others at lower rates IEEE802.3 TIA Cable Categories


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Broadband IP Dial Tone.IP-PSTN-Internet Protocol – Packet Switch Telephone Network.- IP Packet to any other point > 1Mbps Carrier Ethernet

Where Are We Going?


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2. VoIP Architectures and Implementation Choices Computer-Computer VoIP Over The Internet Requirements: - Computer/Mobile Phone/PDA, …… - Internet Access. - Software: Skype, Nimbuzz, IM, ……. - Directory, call setup/control. - Sound card and headset or USB phone. - Operating system: IP/UDP protocol stack. Considerations: - Free (with internet connection) - Interoperability: Standard? - Less user-friendly than PSTN. - Variable quality of voice


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Skype and IM Proprietary technology - Skype directory is based on Kazaa - It uses P2P file sharing - Good quality voice: Uses 15kbps codec Works through NATs - Communications encrypted - Your computer could relay traffic Good HMI – Human Machine Interface Yahoo, Google, MSN, AOL, Nimbuzz.


Computer to Phone Broadband internet connection at one end. POTs at other end. ITSP/VoIP Service provider in the middle. Variable voice quality. E1 connection to circuit-switch PSTN. Possibly ISP is different from the ITSP. ITSP is located offshore. Softphone required to connect to the ITSP using SIP protocol. Example of softphone: X-Lite, 3CX, etc. Example of ITSP: Skype, Belgacom, etc.


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Phone to Phone over the Internet Broadband internet connection at one end. POTs at other end. ITSP/VoIP Service provider in the middle. Variable voice quality. E1 connection to circuit-switch PSTN. Possibly, ISP is different from the ITSP. ITSP is located offshore. IP phone is required to connect to the ITSP using SIP protocol. Example of IP phone: Grandstream, Cisco, Dlink, etc. Example of ITSP: Skype, Belgacom, etc.


Phone to Phone over the Internet ITSP either supplies the adapter or user verifies compatible off-the-shelf adapter.Broadband internet connection at one end. POTs at other end. ITSP/VoIP Service provider in the middle. Variable voice quality. E1 connection to circuit-switch PSTN. Possibly, ISP is different from the ITSP. ITSP is located offshore. POTs connects to the adapter using the FXS/FXO port. The adapter acts as FX to VoIP gateway. Example of ITSP: Skype, Belgacom, etc.


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Managed-IP Telephone Service Provider All IP end-to-end network. Radio Access Network could be wireless - (WiMAX, Wi-Fi, LTE), cable or fibre. End-to-end Carrier Ethernet Network. IP network QoS methods. Voice quality is guarantee. E1 connection to circuit switched PSTN. ISP and ITSP – same company. Provider connects with upstream ISP for long distance call termination and www. Provider supplies the adapter and modem. Example: ipNX


3. VoIP for Businesses and Organizations VoIP-Enabled PBX PBX provides all VoIP functions.-Call management- Integrated gateway- Integrated voicemail Supports VoIP and traditional phones-Phased implementation of VoIP in-building.


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PBX Replacement Softswitch-General purpose hardware- Proprietary software- Standards-based- Additional applications:Messaging, conferencing, IVR, IM, presence. Availability and Survivability-Redundancy and failover- Distributed Call managers- Distributed call control tables- UPS in closets


Hosted PBX Softswitch at Service Provider-SIP messages over network- Customer configuration via web portal- IVR, ACD hosting too Strategic Advantages-Professional implementation- Scalability, flexibility- Security, reliability Financial advantages-Lease vs. buy: capital, maintenance- Reduce staffing Disadvantages-Lack of control- Feature set? Capacity?


IP Centrex Hosted softswitch service from the Phone Company-Huge Centrex customer base Higher level of trust-Professionalism, longevity Multilocation benefits-Uniform services, support Bundled services-Access circuit plus telephony Seamless services-Home-to-office VPN, telephony Features and pricing-Per user, per month- Local number, DID- Desktop, web collaboration


Open-sourced IP-PBX Software Free code updated by users Asterisk: One of the “Oldest”-IP PBX plus signaling server, media gateway, analog/TDM PBX, IVR, messaging server Supported commercially-30 – 50% cost of proprietary- Asterisk (Digium)- sipX, SIPfoundry (Pingtel)- Others: vovida, Freeswitch Disadvantages-May be difficult to implement- Requires skilled technicians- Lack of management/support tools


SO/HO IP Phone Features and Uses Small / home office All-in-one device-Fast processor, jitter buffer- Linux OS, browser, software- SIP, MGCP- Ethernet switch, PoE, PPPoE- Bluetooth- Router, DHCP, NAT, firewall- VPN, QoS support Dialing features – dial by:- Phone number, SIP address, IP address, directory, voice recognition, softkeys, presence/location notice,…….

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Understanding VoIP - 1