WWTC LAN and VoIP Design


WWTC has a technical goal that LAN speeds be equivalent or exceed a speed of 100 MB for local communications and at least 54 MB for Internet speed. An outside consultant has already tested the existing network infrastructure and reported that it is capable of gigabit speeds.  Appropriate network devices, such as switches and routers, have been chosen that support these speeds and allow for future growth.  All switches chosen are capable of at least one gigabit speeds to account for scalability as well as to ensure that data and voice can be easily transmitted through the same devices at the same time.

WWTC also requires a network that is consistently available.  Therefore, strategically placed redundancies at all layers of the network will be required to maintain availability. WWTC cannot support sustained profit growth if the network is intermittently unavailable. The switches chosen will provide a dedicated port for each device on the network while also provisioning for future growth. Additionally, switches implemented in different parts of the network may require additional capabilities. Switches in the server farm will need to be able to handle more traffic at higher speeds than the access layer switches that connect regular network hosts. This will ensure that customer usage is not limited by the speed or throughput of WWTC’s network.

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WWTC Equipment List

Table 1 below lists the minimum devices required to implement the network at WWTC’s New York office. The devices were carefully chosen based on the requirements for the network like speed, capacity, redundancy, and security.  The quantity of each device also represents the minimum number of devices required to get the network up and running safely and securely, while also allowing for future growth and scalability.

WWTC LAN and VoIP Design Case Study

Table 2 below details the naming convention and device placement for each device on the network.  Here, complexity is not WWTC’s friend. An easy, standard naming convention for devices will allow the network administrators to easily identify what type of device is being described.

There is no need for a complex naming convention that will confuse someone looking for a specific device on the network. Along with names, this table identifies the other devices with a direct connection. This can save time from having to look through a detailed diagram for a specific device or path.

Table 3 describes the IP address, subnet, and VLAN assignments for the WWTC New York office network. A class B private addressing scheme has been chosen because this will meet the number of IP addresses per subnet required while leaving room for the required 100% growth scenario.

This means that if a subnet requires a minimum of 100 IP addresses to support the existing devices, it will have at least 200 IP addresses available. Subnets and VLANs will be segmented based on the organizational structure of the WWTC New York office. This will help ensure that members of each VP office will be logically separate from the other offices. For instance, the VP OPR office will be logically separate from the VP NW office, yet still reside within the same physical network and utilize the same network resources.

Along with organizational segregation, network device segregation has also been implemented.  The wireless networks for the conference rooms and reception areas will be on their own subnets as well as each office within the organization.  The server farm will also be on its own subnet and have dedicated, redundant switches to separate it from regular host to host network traffic. Departments have been grouped together to share the access switches. The VP OPR and NE, VP NW and SE, VP SW and Mid have separated into these three groups as seen in Figure 2. This will save from having to implement a separate access switch for each department and will still allow room for growth and VLAN implementation.

Network Link IP Addresses

Link addresses connect two devices point-to-point. It is best practice to limit the amount of IP addresses to only what is needed on a single subnet. This also helps with communication between devices because there will not be multiple devices to choose from when deciding how to forward information. A /30-bit subnet only allows four IP addresses on that specific subnet.  However, one of those IP addresses is used by the network address and another for the broadcast address. This means that there are only two usable IP addresses on that /30 subnet.  This is ideal when connecting WAN links or network infrastructure devices such as switches and routers.

Table 4 shows the link IP addresses between the routers, to the distribution switches, and then to the access and server switches.

High Level Network Diagram

As seen in Figure 1, WWTC’s New York office network diagram shows redundancies at the core, distribution level, and access level switches. This is done so that if a distribution switch went down, there is a working backup available. This may slow down some traffic, but will not bring the entire network down. A single point of failure in a network this size could be detrimental to operations .

There are also switch redundancies at the access level for the same reason. If one of the access or sever switches were to fail, there is another switch available to keep operations flowing. Not pictured are the core routers, which are also directly connected to both distribution switches for redundancy in a core mesh environment. Additionally, the wireless LAN controller for the wireless network is also connected to both distribution switches in the event that one of them fails.  This modular design allows future scalability for WWTC if the New York office expands.

Figure 1. WWTC New York Office High Level Diagram

Wireless Network Design

The WWTC wireless network requires at least 54 mbps of bandwidth and only be available in the two large conference rooms and reception areas.  The reception area wireless network should be available for guests to connect to the Internet while they wait.  The wireless in the conference rooms are for employees to connect to during meetings or while making presentations. Wireless in the conference rooms are required so that employees do not have to physically connect to the network while mobile. This would be extremely inefficient to require employees to plugin to connect in the conference rooms. However, employees should not be able to wirelessly connect at their workstations, so special considerations should be made to reduce to amount of WiFi spillage outside of these specific areas. To control the WiFi area, certain types of antennas should be used depending on the room shape and size.

For the WWTC conference rooms and receptions areas, a single omnidirectional WAP will suffice. If WiFi spillage is noticed, the transmission power for each WAP can be adjusted accordingly to reduce the WiFi footprint. Most WLC and WAP products offer the ability to provide a secure channel and also have the capability of enabling a guest channel. This should be sufficient for WWTC and would decrease the amount of hardware required. Different sets of rules can also be applied to the main channel and the guest channel. Guests can be forced to agree with a privacy or usage policy prior to being allowed to connect.

This will keep the guests off of the main channel but still allow them to connect to the Internet if required. Figures 2 and 3 show the WAP layout placement throughout office and the wireless network diagram.

Figure 2. WWTC Wireless Network Diagram

Figure 3. WWTC WAP Locations

VoIP Network Design

WWTC’s VoIP network will reside on the same physical network as the data and will utilize the same network resources. However, VoIP will be on its own VLAN (180) to keep it separate from the data traffic. Also, by putting voice on its own VLAN, it is easier to allocate bandwidth and make adjustments more manageable. The current network hardware throughput exceeds the minimum required LAN speed which helps to prevent packet loss that causes choppy voice connections.

The redundancies throughout the network will also enable VoIP traffic to avoid bottlenecks that can cause poor voice connectivity.

The VoIP network will have outside dialing capability and provide for 100% connectivity while minimizing the number of outside lines required at any given time. This VoIP solution will require hardware such a unified communications manager, end user IP phones, and existing network infrastructure devices. As a redundancy, access to the Public Switched Telephone Network (PSTN) will also be provided should a WAN link fail. This will allow for outside phone calls to still be made. With that, PSTN channels are required for redundancy if the WAN link fails. To ensure 100% connectivity to the PSTN, a 5:1 ration is best practice for users per channel on a heavily used network. This means that five users can communicate over a single PSTN channel to maintain outside communication.

Considering that not everyone needs an outside line, the VPs, managers, and brokers should always have the ability to call out so that business operations continue. Considering this, between 35-40 employees would require dedicated outside lines. Going by the 5:1 ratio, WWTC would need at least eight PSTN channels to maintain connectivity in the event the WAN link failed.

When implementing VoIP, it is important to know the average VoIP call bandwidth required. Low bandwidth degrades the quality of the call and could cause communication errors. To determine the bandwidth required, multiply the sum of packet overhead and size by the packet rate.

This gives the minimum bandwidth required for VoIP calls and allows administrators to adjust resource allocation to meet these requirements. Figure 4 shows a high-level diagram of the WWTC VoIP network in which it uses the existing network with the addition of the unified communications manager.

Figure 4. WWTC VoIP Network Diagram

Table 5 shows the bandwidth requirement calculation for WWTC. As previously stated, bandwidth is determined by multiplying the sum of packet overhead and size by the packet rate.


The preceding tables and figures provide a visual representation of the LAN, VoIP and wireless networks for the WWTC New York office.  All of these elements work together in a modular environment to meet and exceed the requirements, which provides scalability for the future. For WWTC, constant communication is key to achieving their business goals of increasing revenue, decreasing overhead costs, and providing their products and services to their clients. The combination of network availability, consistency, and security provided by this network infrastructure will enable WWTC to be profitable while continually growing and providing its services to clients all over the world.