Converting Voice Signal Into VoIP

For the transmission of the voice signal over IP network, the analog voice signal must be converted to the digital VoIP packets. For that the voice signal must be pass through following steps in order: Sampling, Quantization, Encoding, and optionally Compression. 

Sampling

Sampling is the process of chopping analog signal into regular intervals.Harry Nyquist prove that if the signal is sampled at the rate of twice the highest frequency (2*4000 kHz), the samples will contain sufficient information to accurately reconstruct signal at the receiver end.The figure below shows the sampling of an analog signal.

Sampling

• The human ear can sense sounds from 20 to 20,000 Hz
• Human speech uses frequencies from 200 to 9000 Hz
• The telephone channel was designed to operate at frequencies of 300 to 4000 Hz

Quantization 

Quantization divides  an analog signal sample into a set of discrete steps that are closest in value to the original analog signal.

The amplitude range is divided into 16 segments (0 to 7 positive, and 0 to 7 negative). Starting with segment 0, each segment has less-granular intervals than the previous segment, which reduces the signal-to-noise ratio (SNR) and makes the segment uniform.The sample value ranges from +127 to -127.

Quantization

Encoding

Encoding convert decimal values in the binary expressions of either 1 and 0. After sampling the signal next step to encode samples for the transmission over the telephony network.This process is called pulse-code modulation(PCM).  The PCM process, as shown in Figure below.

Coding

•  The first bit (MSB) identifies polarity
•  Bits two, three, and four identify segment
•  Final four bits quantize the segment

In the United States, Canada, and Japan, mu-law is used. The rest of the world uses a-law.

Compression

Signal compression is used to reduce the bandwidth usage per call. The most common codec algorithms are presented in the table below.

Compression

Summery

These four steps are performed by the DSP {Digital Signal Processor} at the originating gateway.The VoIP packets are then traveled to the destination gateway. DSPs on the destination side decodes the payload and reverse the process performed on the originating gateway.

Exam Resources and Books for CCNA Collaboration

In the world of Cisco the main resources for exam preparation for  CCNA collaboration is Cisco's Official Certification Guide.I have shared some links from where you get and download PDF copy of books.You will also find the topics for both exams.

CICD Exam Topics

The official study guide helps you master topics on the CCNA Collaboration CICD 210-060 exam, including the following:

• Cisco Unified Communications components
• Cisco Unified Communications Manager Express administration, end user management, dial plans, and telephony features
• Cisco Unified Communications Manager administration, end point management, dial plan elements and interactions, and telephony and mobility features
• Cisco Unity Connection voicemail
• CM IM and Presence support
• CME and CUCM management and troubleshooting
• Monitoring Cisco Unity Connection

You can also download  topics from Here.

CICD Books

• CCNA Collaboration CICD Official Cert Guide available Here.
• You can also buy from Amazon.
• You can also download PDF which I have shared Here.

CIVND Exam Topics

The official study guide helps you master topics on the CCNA Collaboration CIVND 210-065 exam, including the following:

• Cisco Collaboration components and architecture
• Cisco Digital Media Suite, Digital Signs, Cisco Cast, and Show and Share
• Cisco video surveillance components and architectures
• Cisco IP Phones, desktop units, and Cisco Jabber
• Cisco TelePresence endpoint portfolio
• Cisco Edge Architecture including Expressway
• Multipoint, multisite, and multiway video conferencing features
• Cisco TelePresence MCU hardware and server family
• Cisco TelePresence management
• Cisco WebEx solutions

You can also download  topics from  Here.

CIVND Books

• CCNA Collaboration CIVND Official Cert Guide available Here.
• You can also buy from Amazon.
• You can also download PDF which I have shared Here.

My Approach to CCNA Collaboration Certification

In this my first blog I'll drive you straight to how to make your self ready for getting Cisco Collaboration certificate in  you first attempt.

Cisco Collaboration has two exams to pass.

1.   210-060 CICD
2.  210-065 CIVND

You will find exam topics and policies over there.

For getting certified you should have basic knowledge of CCNA R&S.It will helpful to get this smoothly done. VLAN, DHCP, Switching ,Subnetting concepts are need to be more clear before you jump in Collaboration world ,though Cisco does not require to have any prerequisite.

For the preparation I recommend to use Cisco official Cert Guides for both CICD and CIVND. These two books are enough to get certified.

First you have to pass CICD and then go for CIVND.Each Exam contains 55-65 questions.But mostly 60 questions are there.Exam passing score is 860 for now it may vary timely.You will be given 90 minutes to finish exam.The questions are of multiple choice,drag n drop.You can book your exam from Pearson Vue. 

The exam cost 250 USD.This amount is for single time exam.If you unable to clear exam you have to pay fees again.So be careful and have your exam when your are confident enough.

Only theory knowledge is not enough to crack exam you'll also need to have strong practical knowledge of CUCM. There also comes few other components like CME CUC,Jabber.Talk on these components in my upcoming blogs.CUCM is the king in Collaboration world.

In my next blog You will find available resources for certification and more toward CICD topics.If you have any question please write in comment.