IP Telephony and VoIP Tutorial-Part 1

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IP Telephony and VoIP Tutorial-Part 1

IP Telephony and VoIP Tutorial-Part 1

Posted: 08 Feb 2010 10:24 AM PST


Although this is a Cisco networks dedicated blog, I decided to start a series of tutorial posts about a general technology which is not directly related to Cisco but it is a field in which Cisco is again a major player. This is IP Telephony and Voice over IP (VoIP). The two terms, IP Telephony and VoIP, are related around the same concept but in my opinion they are not exactly the same thing. Many people refer to these two terms interchangeably but they are not exactly the same. So, before moving on lets clarify the difference between IP Telephony and VoIP.

IP Telephony Vs VoIP

IP telephony has to do mainly with digital telephony systems (LAN based IP PBX systems) which use the IP protocol entirely for voice communication. All components of the IP telephony system use digitized voice which is transferred as IP packets through an IP network (usually the LAN network). The telephone handsets (VoIP phones) translate the analogue voice signal into digital voice (binary voice) which is transferred as IP packets from one phone to another. The call control system is usually a software based (softswitch) server which handles all call signaling, call routing, IP phone management etc, again using IP protocol for transport. So think about IP telephony as a bigger concept.

VoIP on the other hand is a subset of IP Telephony. Basically, VoIP is the technology which is used by IP Telephony as the vehicle to transport phone calls. VoIP is the technology in which the analogue voice signal is digitized (analog to digital conversion) and becomes binary numbers in order to be transferred by the IP protocol. VoIP is the basis for the implementation and functionality of an IP Telephony system. VoIP can also be used by legacy TDM based PBX systems to transport voice calls over an IP WAN network or even over the Internet. Special voice gateways are used to connect to the legacy PBX telephone system on one end and to the IP network on the other end in order to translate the TDM voice stream into IP voice packets.

So to summarize, IP Telephony is the overall concept of the modern form of voice communication which harnesses the power and features of VoIP technology in order to offer the overall experience of communicating effectively and with lots of extra features.

Now that we described the difference between IP Telephony and VoIP, let's see more details about the two concepts:

1. More details about Voice over IP

The term VoIP or Voice over IP refers to the transfer of voice packets over networks based on Internet technology and, more specifically, the IP Protocol. The IP protocol on which the whole Internet is based on was created to implement the transmission of data in the form of data packets. This means that when a data document is transferred over the Internet is cut into small IP packets and sent over the network. When the document reaches its destination, the packets are joined again thus recreating the original document. The same logic applies if the data transferred corresponds to a voice conversation. The voice is digitized, chopped into packets of data transferred over the network via the IP protocol. At the destination the packets are rejoined to recreate the voice stream. Here we should make clear that VoIP refers to the transfer of voice over any IP network. Such a network is the Internet of course, but when considering VoIP it does not necessarily mean that we carry voice over the Internet only. It can be any IP-based network (such as a private corporate WAN network).

2. Packet based (IP Telephony) Vs Circuit Switched Telephone Systems

IP Telephony systems are those using entirely IP packets for voice communication, as explained before. In contrast to packet switched telephone systems (those based on IP protocol), conventional telephone systems apply the logic of direct connection between the two communicating voice parties through a dedicated circuit reserved exclusively for each contact. Thus the term Circuit switched telephone systems. In packet switched systems, however, the same communication line can be used to simultaneously pass different kinds of packets. Thus, the voice packets of one or more conversations may travel through the same route as other packets transferring data, video etc. This is the main difference between traditional telephony which is implemented to the public switched telephone network (PSTN) and telephony implementation on IP networks (or more generally to packet switched networks).

More on IP telephony and VoIP on a future post. Stay tuned.

Related posts:

  1. Cisco ASA QoS for VoIP Traffic
  2. SIP Trunking With Call Manager Express
  3. CCNA 640-802 Tutorial: seven-layer OSI Model

Banning illegal file-sharers could breach human rights

Posted: 08 Feb 2010 08:00 AM PST


Banning web users suspected of illegally downloading from the net could be a breach of human rights, says the Joint Select Committee on Human Rights.

Malwarebytes' Anti-Malware Free

Posted: 08 Feb 2010 08:00 AM PST


You can't depend on just one program to protect you from rootkits, Trojans, viruses, worms, and other malicious code. The job is too important and the villains too numerous for that. So supplement your regular antivirus program (the one you keep running in the background at all times) with an extra malware scanner, such as Malwarebytes' Anti-Malware Free.

An open letter to my public transit company

Posted: 08 Feb 2010 08:00 AM PST


For the last week I have been barraged by phone calls and e-mails from various technology body shops asking what my lowest and best rate was for a six-month PCI project you are looking to staff. I've also received e-mails from a bunch of folks trying to get me to work on a project for you. I have heard various rates of $55 to $70 per hour for this PCI project. Note that these rates are considerably lower than the market rates for qualified PCI professionals, especially in the tri-state area.

How to Configuring Password Encryption

Posted: 08 Feb 2010 01:47 AM PST


As my previous post about How to Configure Privilege Levels for Users on Cisco Router.
Today this post I'd like to show you how to configure Password Encryption on Cisco Router.

Well, It's relatively simple to configure password encryption on Cisco routers. When password encryption is configured, all passwords that are configured on the router are converted to an unsophisticated reversible cipher. Although the algorithm that is used to convert the passwords is somewhat unsophisticated, it still serves a very good purpose. Intruders cannot simply view the password in plain text and know what the password is. To enable the use of password encryption, use the command service password−encryption.

The following example shows a router configuration prior to enabling password encryption. An enable password, a console password, and a Telnet password is configured:

CiscoRouter#show running−config
!
enable password Cisco
!
line con 0
password NetVisa
!
line vty 0 4
password Security
!

The following example shows the command you would use to enable password encryption on the router:

CiscoRouter#config t
Enter configuration commands, one per line. End with CNTL/Z.
CiscoRouter(config)#service password−encryption
CiscoRouter(config)

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