CH 3 Cisco IP Phone concepts and registration REVIEW Flashcards
Connecting and Powering Cisco IP Phones
- The first item that must be in place is power for the Cisco IP phone.
- This includes technologies such as:
- PoE
- Voice VLANs
- Dynamic Host Configuration Protocol (DHCP)
- Second, Cisco IP phones connect to switches just like any other network device. (Depending on the model of the IP phone, it may also have a built-in switch)
- Third, it must determine its VLAN assignment.
- Because of security risks associated with having data and voice devices on the same network, Cisco recommends isolating IP phones in VLANs dedicated to voice devices.
PoE Power over Ethernet
- Power over Ethernet is a technology, which enables to connect network devices through ethernet cable. Therefore it is not necessary to use two individual lines/1x data, 1x power supply/ for assurance of data connectivity and supplying.
- PoE became an official standard (802.3af) in 2003.
Cisco IP Phone Ethernet Connections
- RS232 – Connects to an expansion module (7914, 7915, or 7916)
- 10/100 SW – Used to connect the IP phone to the network (switch)using a straight through cable.
- 10/100 PC – Used to connect a co-located PC (or other network device) to the IP phone using a straight through cable.
Potential sources of power in a Cisco VoIP network
- Cisco Catalyst Switch PoE (Cisco prestandard or 802.3af power)
- Power Patch Panel PoE (Cisco prestandard or 802.3af power)
- Cisco IP Phone Power Brick (wall power)
Powering IP Phone using Cisco Catalyst Switch PoE
Quick review of Ethernet cable:
- CAT 5 or 6: total of eight wires (4 pairs of wires) to crimp into an RJ-45 connector on each end of the connection.
- 4 of the wires are used to transmit data, the other 4 remain unused and idle … until now.
Terms “inline power” and “PoE” describe two methods to send electricity over the unused Ethernet wires to power a connected device.
- There is now a variety of devices that can attach solely to an Ethernet cable and receive all the power they need to operate.
Cisco Inline Power
Cisco-proprietary, prestandard method of supplying power over an Ethernet cable to attached devices
Advantages of PoE – powering devices through an Ethernet cable
- You have a centralized point of power distribution.
- By using PoE you can connect the switch powering the IP phones to an uninterruptible power supply (UPS) instead of placing a UPS at the location of each IP phone.
- PoE also enables you to power devices that are not conveniently located next to a power outlet.
- PoE eliminates much of the “cord clutter” at employees’ desks.
Note: To power the IP phones without an official PoE standard, some proprietary methods were created, one such method being Cisco Inline Power.
Powering IP Phone using Power Patch Panel PoE or Coupler
- Many companies already have a significant investment in their switched network, to upgrade all switches to support PoE would be expense.
- These org’s may choose to install intermediary devices, such as patch panel, that are able to inject PoE on the line.
- By using the power patch panel, you still gain the advantage of centralized power and backup without requiring switch upgrades.
- However, Cisco switches must also provide QoS and voice VLAN support capabilities, which may require switch hardware upgrades anyway.
Advantages of powering devices through a Power Panel Patch or Coupler
- Inline PoE injectors provide a low-cost PoE solution for single devices (one device per coupler).
- These are typically used to support wireless access points or other “single spot” PoE solutions.
Disadvantages of powering devices through a Power Panel Patch or Coupler
- Using inline PoE couplers for a large IP Phone network would make a mess of your wiring infrastructure and exhaust your supply of electrical outlets (because each inline PoE coupler requires a dedicated plug).
Powering the IP Phone with a Power Brick
Using a power brick to power a device is simple. Most Cisco IP Phones do not ship with power supplies.
- Cisco assumes most VoIP network deployments use PoE.
- If you have to choose between purchasing power bricks and upgrading your switch infrastructure, it’s wise to check the prices of the power bricks.
- The average Cisco IP Phone power brick price is between $30–$40 USD.
- When pricing out a 48-switchport deployment, purchasing power bricks for all the IP phones may very well be in the same price range as upgrading the switch infrastructure.
Note: Some devices exceed the power capabilities of the 802.3af PoE standard. For example, when you add a sidecar module to a Cisco IP Phone (typically to support more line buttons), PoE connections can no longer support the device. These devices will need a power brick adapter.
VLAN Concepts and Configuration
After the IP phone has received power, it must determine its VLAN assignment.
- VLANs allow you to break up switched environments into multiple broadcast domains.
- A VLAN = A Broadcast Domain = An IP Subnet
- Benefits of using VLANs:
- Increased performance – by reducing the size of the broadcast domain, network devices run more efficiently.
- Improved manageability – the division of the network into logical groups of users, apps, or servers allow you to understand and manage the network better.
- Physical topology independence – VLANs allow you to group users regardless of their physical location in the campus network. If depts. Grow or relocate you can simply change the VLAN on their new ports without making any physical network changes.
- VLAN Trunking/Tagging
- Trunk ports are often called Tagged ports because switches send frames between each other with a VLAN “tag” in place.
Understanding Voice VLANs – IP phones support 802.1q Tagging too!
- PCs are often connected to the network using the Ethernet port on the back of a Cisco IP Phone. (f0/1 192.168.1.1 switchport mode access)
- You can assign a switchport to only a single VLAN, it initially seems impossible to separate voice and data traffic. (f0/1,switchport access vlan 10)
- That is, until you see that Cisco IP Phones support 802.1Q tagging.
- The switch built into Cisco IP Phones has much of the same hardware that exists inside of a full Cisco switch.
- The incoming switchport is able to receive and send 802.1Q tagged packets.
- This gives you the capability to establish a type of trunk connection between the Cisco switch and IP phone.
- You might call the connection between the switch and IP phone a “mini-trunk” because a typical trunk passes a large number of VLANs (if not all VLANs).
- In this case, the IP phone tags its own packets with the correct voice VLAN (VLAN 25, in the case of Figure 3-6).
- Because the switch receives this traffic on a port supporting tagged packets (our mini-trunk), the switch can read the tag and place the data in the correct VLAN.
- The data packets pass through the IP phone and into the switch untagged. The switch assigns these untagged packets to whatever VLAN you have configured on the switchport for data traffic.
Note: Keep in mind that Cisco IP phones will be able to receive this voice VLAN configuration from the switch via CDP. After it receives the voice VLAN number, the IP Phone begins tagging its own packets. Non-Cisco IP Phones cannot understand CDP packets. This typically requires you to manually configure each of the non-Cisco IP Phones with its voice VLAN number from a local phone configuration window (on the IP phone).
Understanding the Cisco IP Phone Boot Process
- Phone receives power.
- Phone receives VLAN information via CDP.
- Phone sends DHCP request for IP information.
- The DHCP server responds with an IP address offer. When the Cisco IP Phone accepts the offer, it receives all the DHCP options that go along with the DHCP request.
- Reply should include the phone’s IP address and the IP address of a TFTP server to use (option 150).
- DHCP options include items such as default gateway, DNS server information, and domain name information.
- In the case of Cisco IP Phones, a unique DHCP option is included, known as Option 150. This option directs the IP phone to a TFTP server.
- Phone contacts the TFTP server and downloads configuration file(s) using its MAC address.
- Phone attempts to register with a call processing server.
- If it fails and there is another server in the list, it will attempt to register with the next server. Again, it uses its MAC address.
- If successful, it will receive line numbers, button configuration, and ring tones.
- Once registered, the phone can send and receive calls as the configuration allows.
Create Voice and Data VLANS on a Switch
Switch(config)#vlan 10
Switch(config-vlan)#name VOICE
Switch(config)#vlan 20
Switch(config-vlan)#name DATA
End
Switch#show vlan brief
