Speed/Duplex. Avaya IP Telephony

This 50-second delay is not necessary and not desired on ports connected to IP hosts (non-network devices). Enable a fast start feature on these ports to put them into the Forwarding state almost immediately. Avaya P550 calls this fast-start and Cisco calls it portfast. If this feature is not available, disabling STP on the port is an option that should be considered. Do not disable STP on an

entire switch or VLAN.

- Enable Rapid Spanning Tree and configure host ports as edge ports – As the name implies, Rapid

Spanning Tree Protocol (RSTP) is a faster and more advanced replacement for STP. RSTP is preferred over STP when all network devices in a L2 domain support it. Even if they don’t, there are ways to combine RSTP and STP (depending on the network equipment), though certainly not as clean as having RSTP throughout the L2 domain. When running RSTP, configure the host ports as edge ports, which is equivalent to enabling fast-start or portfast in a STP domain.

- Disable Cisco features – Cisco features that are not required by Avaya endpoints are auxiliaryvlan

(except for IP phones in a dual-VLAN setting as described in appendices A and B), channeling, cdp,

inlinepower, and any Cisco proprietary feature in general. Explicitly disable these features on ports connected to Avaya devices, as they are non-standard mechanisms relevant only to Cisco devices and can sometimes interfere with Avaya devices. The CatOS command set port host <mod/port> automatically disables channeling and trunking, and enables portfast. Execute this command first, and then manually disable cdp, inlinepower, and auxiliaryvlan. For dual-VLAN IP telephone implementations, see Appendices A and B for more information and updates regarding auxiliaryvlan

and trunking.

- Properly configure 802.1Q trunking on Cisco switches – If trunking is required on a Cisco CatOS switch connected to an Avaya device, enable it for 802.1Q encapsulation in the nonegotiate mode (set

trunk <mod/port> nonegotiate dot1q). This causes the port to become a plain 802.1Q trunk port with no Cisco auto-negotiation features. When trunking is not required, explicitly disable it, as the default is to auto-negotiate trunking.

Speed/Duplex

One major issue with Ethernet connectivity is proper configuration of speed and duplex. There is a significant amount of misunderstanding in the industry as a whole regarding the auto-negotiation standard. The speed can be sensed, but the duplex setting is negotiated. This means that if a device with fixed speed and duplex is connected to a device in auto-negotiation mode, the auto-negotiating device can sense the other device’s speed and match it. But the auto-negotiating device cannot sense the other device’s duplex setting; the duplex setting is negotiated. Therefore, the auto-negotiating device always goes to half duplex in this scenario. The following table is provided as a quick reference for how speed and duplex settings are determined and typically configured. It is imperative that the speed and duplex settings be configured properly.

Device1

Configuration auto-negotiate

Device2

Configuration auto-negotiate

Result auto-negotiate auto-negotiate auto-negotiate

100/half

10/half

100/full

100/full expected and often achieved, but not always stable. Suitable for user PC connections, but not suitable for server connections or uplinks between network devices. Suitable for a single VoIP call, such as with a softphone or single IP telephone. Not suitable for multiple VoIP calls, such as through a MedPro/MR320 board.

100/half stable. Device1 senses the speed and matches accordingly.

Device1 senses no duplex negotiation, so it goes to half duplex.

10/half stable. Device1 senses the speed and matches accordingly.

Device1 senses no duplex negotiation, so it goes to half duplex.

Device1 goes to 100/half, resulting in a duplex mismatch – undesirable. Device1 senses the speed and matches accordingly.

Device1 senses no duplex negotiation, so it goes to half duplex.

KW Avaya IP Telephony Implementation Guide 17