User guides - VoIP For Dummies

Circuit-switched telephony

Before digital networking took off, everyone had to use the one and only Plain Old Telephone Services (POTS). POTS runs over a network called the Public Switched Telephone Network (PSTN). The PSTN has been around since Mr. Bell invented the telephone. That is why most companies today have POTS-related systems in place. These POTS telephone systems use the old tried-and-true (and more expensive) method of telephone service known as circuit-switched.

Believe it or not, a good illustration of POTS and PSTN is the experiment where your fifth-grade teacher had you take two tin cans and a length of wire to create an archaic telephone system. As strange as it seems, this antiquated method of telephony is the principal means underlying the operation of POTS operating over the PSTN.

What changes in the real POTS-based telephony system is the number, length, diameter, and type of wire or cables used. These elements have grown immensely in variety and type. In addition, the types of telephone equipment have changed dramatically both at the customer end and at the carrier provider end. But POTS telephony continues to use “circuit-switched” rules (or protocols) of operation.

Packet-switched telephony: From POTS to packets

Unlike circuit-switched POTS, which always require use of the Public Switched Telephone Network (PSTN), VoIP technology has enabled telephony and other new and novel features and services to run over dedicated and wireless networks including even your computer network. These newer network types use packet-switched protocols.

Packet-switched VoIP puts voice signals into packets. Along with the voice signals, VoIP packets include both the sender’s and receiver’s network addresses. VoIP packets can traverse any VoIP-compatible network. Along the way, they can choose alternate paths because the destination address is included in the packet. The routing of the packets is not dependent on any particular network route.

In a circuit-switched network, the destination address is not included in the signal; routing directions are determined physically by the actual POTS line. So the routing must follow a specific network line similarly to how a train follows a designated set of railroad tracks. If the line is down, the call cannot go through.

In a packet-switched network, if one of the network lines is down, the packet can switch while in route between locations to another working route to keep the call up. Using VoIP, voice signals can be packetized like computer data packets. This enables companies to consider using the same network infrastructure to support both data and voice applications. Companies can consolidate their physical networks (while maintaining redundancy in their routing patterns) and build an enterprise-class communications network with the latest advanced IP-based features.

VoIP makes possible other services that older telephony systems cannot do. The VoIP protocols, or simply IP, as many have begun to call it for short, are interoperable. This term means that the IP protocols will work well with all kinds of networks. VoIP is valuable because it fundamentally operates the same way in all network types. IP protocols are also highly portable. This means they will work with any IP-enabled end-user device such as an IP telephone, computer, or even a Personal Digital Assistant (PDA). VoIP works everywhere!

Because VoIP is interoperable and portable, it makes possible many new end-user applications that redefine how you can make telephone calls. Because VoIP is highly “networkable,” it is useful to distinguish the two major network types used by most if not all companies.

IP Telephony

IP Telephony enables voice communication over Internet Protocol (IP) networks. It unites an organization’s many locations — including mobile workers — into a single converged network. It promises cost savings by combining voice and data on one network that can be centrally maintained. But more importantly, it brings advanced features and applications that enhance productivity throughout the organization.

A large percentage of calling patterns within corporations indicates that many calls will never leave the LAN. An IP Telephony call to a coworker at the same location would never leave the LAN. Similarly, a call to another department in your building would never leave the LAN. In these examples, the packets remain simply packets that travel over the LAN to the called person. These packets do not need to include other vital data inside them to direct the packet over longer distances to other locations. As a result, IP Telephony calls result in shorter-sized packets when compared to VoIP calling packets that would need to go off the LAN.

IP Telephony works a lot like the computer works on the LAN. But all users do not necessarily need an IP-enabled telephone. Avaya implements IP Telephony in a manner that can protect your investment in preexisting telephone equipment (for example, enabling IP to digital and even IP to analog telephone stations).

You can acquire IP telephones in several different styles. But they all have one important thing in common: The IP telephone has a network interface card (NIC) built into it just like a computer must have a NIC inside of it to connect to the LAN. The NIC is the single most important component for any LAN device because it provides the device with its physical address on the LAN. This address is simply called the MAC address. MAC means media access control. The MAC address uses a standardized 6-OCTET address and is usually represented in hexadecimal. For example, the following is a valid MAC address: 00-0A-E4-02-7B-99.

To support IP Telephony, a server with a MAC address is typically dedicated to load the IPT software that is used to manage all the calls. Servers are just like personal computers except they have more memory, speed, and capacity. Because the server needs a MAC address, it has a NIC inside to provide the MAC address as well as a physical means of connection to the LAN. The managing server stores the database that contains all the MAC addresses, corresponding to all of the IP Telephony telephone extensions that will be assigned to end users. Depending on the size of the LAN and the number of users, other servers may be used. For example, some LANs running IP Telephony dedicate a server just for handling all the voicemail that will be stored and retrieved.

Depending on the size of the LAN, one or more devices known as switches are installed around the LAN to form the core infrastructure of the IP Telephony LAN. These switches are boxes that have a series of ports into which all of the other LAN-addressable devices ultimately connect. Usually the switches are set up in the communications closets around the LAN, and they operate 24 x 7 x 365. All of the cabling typically runs from the user devices (such as the IP Telephony phone, computer, and servers) to the ports on these switches. Older switches supported computer data only.

If you plan to run IP Telephony with your computer data on the same LAN, make sure that you use IPT-compatible switches. As with any addressable device on the LAN, the switches used must also be MAC-addressable.

In a nutshell, all the other addressable devices, including your IP Telephony phone, must physically connect to the LAN via a port on one of the switches. All of the switches are interconnected, usually with fiber-optic cable. When you want to call a coworker at your same location, you dial the phone number corresponding to the person’s name. The signals are packetized and sent to the managing server where the packet picks up the MAC address of the person you are calling. The packet is then forwarded to the switch, the port on that switch, and finally to the IP telephone connected to the port corresponding to the coworker’s MAC address. The coworker’s telephone rings. When the coworker picks up the receiver or answers the call, a virtual connection is established between the coworker and yourself for the life of the call. IP Telephony does all of this at lightning speed.

The process varies a little when you place a call to a coworker located at a different site. This coworker is connected to a different LAN. The call would still initiate the same way. But instead of the managing server sending it to a switch located on your LAN, the call needs to go to the edge device used to connect your IPT LAN to the company’s WAN. This is where IPT becomes VoIP. And this is where that second type of network comes into the picture.

Reaching out with VoIP

From the individual mobile end-user and small single-site LAN to the sophisticated, multi-location WAN that supports domestic and international connectivity, Avaya is a world leader in secure and reliable IP Telephony systems, communications software applications, and full life-cycle services.

Each LAN in a multi-location enterprise network is connected to the larger WAN. If you are located at the headquarters in Pittsburgh, and you call a coworker located at the office in Los Angeles, your call begins as an IP Telephony call on your LAN. It then travels from your LAN through an edge device. Edge devices include products such as the Extreme Networks’ Unified Access enabled switch. The edge device is programmed to re-packetize your call and encode the larger VoIP packet with the additional necessary information such as the address for the destination LAN or the mobile end-user. For a single-location company, other options for the edge include using the Avaya G650 Media Gateway which connects directly to the PSTN.

The process of packetization is referred to as encapsulation by the network gurus. A good analogy for this fancy techno term is like when you put a letter into an envelope for mailing. The difference is that these encapsulated packets contain the content of the telephone conversation in digitized form. You would not be wrong to call it Voice Signals Inside IP Packets.

In order for the LAN to participate in the company’s VoIP WAN, each LAN needs at least one edge device such as a router, level three switch, or a gateway. These devices, like all other addressable devices on the LAN, have a MAC address and a NIC to physically connect them to the LAN. But in addition, they each have an interface card that physically connects them to the company’s WAN or some external network. Depending on the company’s network design, size, and mission, these edge devices can have multiple interfaces that connect them to multiple outside networks. Or you can have multiple separate edge devices. The point is that these edge devices take care of all the IP Telephony traffic going off-LAN by encapsulating the signals into packets, encoding the packets with the correct addressing information, and forwarding the packets out onto the WAN where they make their way in a packet-switched manner to their respective destination LAN.

Unlike the MAC addressing on the LAN side, VoIP traffic on the WAN uses the IP addressing scheme. IP addressing currently uses a 4-OCTET format and represents the address in decimal numbers. For example, 192.168.2.4 is a valid IP address.

When the packets arrive at the destination LAN, the edge device breaks down the VoIP packets and forwards them internally to the server that manages the IP Telephony services on the LAN. From this point, the rest of the process is similar to IP Telephony services. The phone rings. The person being called answers, and a virtual circuit is established between the caller and the person receiving the call.

Instead of maintaining separate networks for computers and telephones, companies can converge both of these networks into one network using IP Telephony and VoIP. The whole new way of doing telephone calling using VoIP is even sometimes called toll bypass.

Say hello to VEMAIL

Before IP Telephony and VoIP, you had to access your voice-mail by telephone and e-mail through computers. With VoIP, you can read your voicemail on your computer screen and listen to your e-mail through an IP-enabled telephone. The new term for this converged feature is VEMAIL. And this is just one of many new uses for IP-enabled telephony.

Surf the Web

Because VoIP operates with the same set of IP rules and protocols that support Web-based applications, it is possible to access the Web with an IP-enabled telephone.

Several flavors of IP telephones are now available. If you have an IP telephone with a large enough screen, you can display any Web page on your telephone, complete with any of your favorite Web links. You can also have the stock exchange ticker displaying your favorite stock symbols and current trading status on your IP telephone. You can even have the current weather for your geographic area of choice displayed on your IP telephone.

You may be wondering how IP Telephony and VoIP can do all these super tricks. If you compare the IP-enabled telephone with any of the POTS telephones, you find a remarkable difference in the quantity and quality of features available with IP-enabled telephones. In an IP Telephony world, the features are available with no monthly recurring charges. Considering that many new features have come about with IP Telephony and VoIP, you’ll want to consider by IP telephone type exactly what features are available.

IP Softphone

The Avaya IP Softphone is designed to operate on a Windows-based computer. It is essentially a piece of software to be loaded on the computer. Imagine dialing a telephone number from your computer by pointing and clicking the on-screen dial pad. Or as an alternative to clicking, you can simply say aloud the speed dial name. Together with a pluggable telephony headset, it enables voice communications and other productivity features, including:

Crystal clear voice communications possible from alternate work locations including home, hotels, Internet hot spots, and customer locations

Integration with Outlook contact lists for autodial support LDAP directory access Phone numbers displayed Incoming calls synchronized with directory look-ups for

simple screen pop applications

Instant messaging and presence tracking

Point-and-click dialing

IP-enabled desktop telephone features accessible from

computer

Multiple call appearances (as opposed to just the one call you are currently on)

Point-to-point video calls application (available with selected versions)

IP Softphone for Pocket PC

The Avaya IP Softphone for Pocket PC is designed to connect a Pocket PC device to the company’s IP Telephony environment — and the best part is that it does so wirelessly. The IP Softphone for Pocket PC is essentially a piece of software that you load on the Pocket PC device. The software connects the Pocket PC (which must be Windows-based) via a Wi-Fi or Wi-MAX network interface to the company’s LAN. It enables voice communications and other productivity features, including:

Multiple call appearances Call transfer Conference calls Point-and-click dialing from directories Outlook contact lists