The shift from traditional telephony, based on circuits, to Unified Communications (or VoIP) began a number of years ago and continues to dominate the voice landscape today. While simply learning the details and mechanics of this "new world order" may sound like the most logical place to begin, many important logical concepts can get left out without an understanding of traditional telephony. This vital area of Cisco's advanced technology portfolio is rich with learning opportunities as well as demand for that skillset in the marketplace. Gaining experience in this cutting-edge subject can effectively carve out a great niche for any ambitious network professional.
When Alexander Graham Bell invented the first telephone in March 1876, he could hardly have conceived the impact he would create. Today, nearly a century and a half later, human being communicate verbally over land-line phones (e.g., traditional home telephone), cellular telephones using radio com`munications, and access data along these very same lines as well. Bell's original device made use of analog technologies of the day, which was transitioned to digital transmission in the Public Switched Telephone Network (PSTN) core. Voice conversations in this proverbial world took place through a series of physical electrical circuits, and thus named circuit-switched. The next progression and/or transition of telephony came in the form of packet-switched telephony, giving way to the all too familiar term VoIP - Voice over Internet Protocol. In positioning its technologies for this next-generation methodology, Cisco pioneered a number of critical elements that paved the way for practical, affordable telephony that we will examine in this white paper.
Cisco has classified a number of specific technology areas that require additional knowledge beyond the foundational routing and switching level itself. Each of these areas typically has additional certification requirements, normally mapping to the CCNA, CCNP, and CCIE levels. These are as follows:
Cisco Telepresence
Data Center
Optical Networking
Security
Unified Communications
Wireless
Service Provider
These advanced technologies carry a great deal of additional value in terms of employer demand and desirability, particularly if they have been paired with relevant experience. In some cases, the ability to sell and support the devices involved may be restricted to Cisco partners who possess additional certifications, usually based on staff engineering and sales roles.
You need to have an understanding of - and appreciation for - the critical importance of a solid network foundation and the corresponding skills necessary to support it. On a personal note, I have worked with many very intelligent and skilled advanced technology engineers who inadvertently impacted both customers and their own credibility by lacking the foundational skills referred to here.
Using an analogy in this regard, technology professionals can legitimately have great regard for the proverbial magic of the advanced technologies, and rightly so - data center, voice, security, wireless, and other areas have great desirability attached to them. Even so, each and every one of them depends directly on an optimal network infrastructure---routing and switching---in order to function at all. For example, using VMware virtualization products to simplify an enterprise data center will produce no business/technical benefit whatsoever if the switching environment is inefficient or non-functional. Hence, if the "plumbing" doesn't work, neither will the "magic" of advanced technologies.
Cisco carefully architected the Career Certification Program (see Figure 2, above) to correspond to this inevitable dependence on routing and switching technologies. In the newly announced changes to the CCNA certification, more emphasis has been placed on foundational technologies at the CCENT level, which a student must pass before moving on to the various CCNA specialization tracks. This serves as yet another reminder of the importance of knowing the fundamentals before adding on deeper skills in a particular advanced technology area.
Cisco Voice Technologies - now typically referred to as Unified Communications Technologies - not only depend on a solid network foundation, but also use conceptual building blocks from the world of traditional telephony. The reasons for this include:
Capability to interconnect the Unified Communications Environment to the PSTN
Creating "new world" equivalent logical functions that mimic "old world" methodologies
Understanding the basic elements utilized in older telephony can help in knowing how these same functions are created in Unified Communications networks. The basics of an analog telephone call (see Figure 3, above) are mapped out in the following paragraphs.
When an individual wishes to have a voice conversation with someone at another physical location, he/she typically will initiate the conversation using an analog telephone. This device receives power from the RJ-11 wall jack, and the initiating caller (the "calling" party) picks up the handset ("off hook"), receiving a dial tone indicating the network is ready. The next step involves entering a series of digits, which indicates where the intended party is located. In the United States, the values and format of the number typically follows ten digits, and is referred to as the North American Numbering Plan (NANP). These digits are transmitted to the telephone company Central Office, where the analog line terminates.
