September 23, 2005
VoIP network implementation
VoIP network implementation In order to ensure a high availability of VoIP networks, the following factors must be considered:
Components of call processing: The different components that make up voice systems have different requirements that need to be fulfilled before implementing a VoIP network. The components include voice mail, toll bypass, call center applications, etc. Centralized call processing consists of IP-PBXs, soft phones, etc in centralized locations and the clients can access them through a WAN. Another alternative is on-site call processing, which may be an expensive option if there are too many sites in a WAN. Survivable remote site telephony (SRST) enables centralized call processing but if there is an outage, the phones can still connect via a local router.
Cost: The cost of establishing a network depends upon factors such as the level of redundancy that needs to be incorporated into the network. The network has to be architected keeping the budgetary constraints and ease of use.
Network architecture: WAN and LAN networks are possible. The QoS levels are achieved in different ways for these networks. LANs provide star, bus, and ring topologies. WAN topologies are represented in terms of their technology, examples being Frame Relay, MPLS, etc. LANs use a load-balanced backup circuit in which there are two circuits to share the traffic load. Bandwidth is not a problem with LANs and the load-balancing circuits are relatively inexpensive to install and maintain. WANs use active/passive networks in which the passive network comes into play if the primary circuit experiences an outage. WANs have limited bandwidth to work with and employ expensive circuitry. One has to consider the routes that the circuits will take as these will affect the latency. Network administrators have to ensure that backups provide voice quality similar to that provided by the primary networks. In order to ensure consistent voice quality, the Resource Reservation Protocol should be used for the backup circuit and the utilization of the active circuit should be managed such that in the case of an outage, the increased load on the secondary circuit does not affect the quality of transmission. Another alternative is to route calls over a PSTN network. The choice of backup is a function of costs involved and business considerations.
Cloud Diversity: Carriers such as MPLS, Frame Relay, and ATM are maintained by the carriers. It is safer to have a backup circuit that uses a different cloud than that of the active circuit. This is particularly useful when the entire WAN setup has been provided by a single vendor. Introducing different routings may complicate the network and increase cost but will allow for greater protection against service outages that may happen if a cloud does not work.
Different service layers: Voice and other data traffic should have different access layers. By moving the IP-PBX cluster away from the office network, it is possible to develop an abstracted layer that permits the voice service to continue operating even during maintenance work. The network should be designed after considering the functionalities of the core, access, and distribution layers. Voice virtual LANs provide another layer of abstraction and are often a basic requirement for availing the many proprietary benefits that vendors offer.
DHCP: A Dynamic Host Configuration Protocol (DHCP) provides information regarding the call processing to the VoIP networks. VoIP networks have to strike a balance between the DHCP and DNS service. The DHCP service should be able to cope with an increase in phones in the network.
Subnets: Subnets can sometimes act as points of failure that may affect network performance. Servers and desktops can be given the IP address of the IP gateway either on purpose or by mistake. This can lead to a traffic overflow, which may bring down the subnet. A safeguard is to reduce the size of the subnet, for example one subnet per switch.
Power Consumption: Most networks draw power from the Ethernet (PoE) by using switches. The amount of power drawn should be carefully regulated, especially if large chassis switches are used to provide power to a large number of phones.
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