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APPLICATION NOTE - Deploying IP Telephony with EX Series Ethernet Switches

Introduction

Juniper Networks

EX Series Ethernet Switches offer a number of features for optimizing IP telephony deployments.

This application note describes how voice over IP (VoIP) phones can be deployed in conjunction with endpoint hosts

such as desktop or laptop computers; provides background information on Link Layer Discovery Protocol (LLDP) and

LLDP-Media Endpoint Discovery (LLDP-MED); and describes the interaction between VoIP phones and EX Series

Ethernet Switches.

Scope

While this document can’t cover all of the physical configurations that are possible on the EX Series, it does present

configuration examples for the most common applications seen today. In particular, this document addresses

configurations relating to:

• VoIP phones and endpoint hosts sharing the same switch port

• Using separate ports for VoIP phones and an endpoint host

This application note applies to the Juniper Networks EX2200, EX3200, EX3300, EX4200, EX6200 and EX8200

Ethernet Switches as solutions for existing and new enterprise IP telephony deployments.

Description and Deployment Scenario—Method 1: VoIP Phones and End Hosts Sharing Ports

The most common enterprise VoIP edge deployment consists of VoIP phones and end-host machines connected in

series and attached to a single switch port. This physical layout reduces switch port requirements by allowing multiple

end user devices to share a connection rather than occupy their own individual switch ports, thereby reducing the total

number of switches deployed, as well as capital and operational expenses.

However, when VoIP phones and end hosts share a switch port, sound quality on an IP phone call will suffer when

large bursts of data traffic create network congestion that leads to packet loss or delay. To overcome this problem, it is

desirable to provide voice traffic with a higher level of service due to its susceptibility to jitter, delay and packet loss.

Figure 1: VoIP phone and end-host machine sharing a switch port

This is accomplished by separating voice and data traffic into separate broadcast domains or VLANs—an essential

capability for any robust VoIP solution. The EX Series offers a Voice VLAN feature that enables otherwise standard

access ports to accept both untagged (data) and tagged (voice) traffic from directly connected VoIP phones, and

separate these traffic streams into separate VLANs (namely data-VLAN and voip-VLAN).

The EX Series can separate data and voice traffic on the switch port where Voice VLAN is implemented. However, the

phone is still vulnerable to large bursts of data from the attached end host on its own phone port, depending on the

phone’s ability to prioritize its own voice traffic over the end-host data traffic before forwarding both streams to the

switch. To solve this problem, the user can take the “separate port” approach in which the phone and the end host are

connected to separate ports on the switch. This solution is covered in the “Method 2” section of this paper.

VoIP Phones with LLDP-MED Support

Before exploring the actual interaction between VoIP phones and the EX Series, it’s important to understand the

fundamentals of two industry-standard protocols: Link Layer Discovery Protocol (LLDP) and LLDP-Media Endpoint

Discovery (LLDP-MED). This section will provide a brief overview covering the basics of these two protocols.

Data

VoIP

EX Series

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