ESI 24-Key Digital Feature Phone Specifications download pdf (Page 10)

ESI Communications Servers Product Overview

• ESI additionally supports SIP-compliant hardware

endpoints — i.e., SIP “phones.” However, due to

limitations with SIP itself, not all of the ESI feature

set is available via a SIP phone. The following SIP

hardware endpoints have been tested with ESI

Communications Servers:

– Aastra 9133i

– Grandstream BudgeTone 101

– Grandstream HandyTone 286

Note: Each compatible ESI IP Phone [IP Feature Phone II,

IP Cordless Handset (Local or Remote), or VIP

Softphone] or SIP endpoint requires an available

IVC port and the activation in the system of either a

local or remote license before the IVC will connect

to the IP Phone. When an IP Phone is programmed

in the system, a license is consumed.

Quality of Service (QoS) support

Quality of Service is an important component in any

converged or pure IP telephone system. It increases

the likelihood for IP voice communications to be clear,

and free of dropped calls and delayed audio.

QoS is defined as providing the means for specific data

streams in a network to be prioritized over other types

of traffic. In the case of a voice over IP application,

the IP packets carrying the voice conversation are

given priority over data packets. When using the built-in

two-port data switch to connect the IP Phone and

customer’s computer to the same Ethernet port, it is

highly advisable for the customer’s network to support

QoS so that large downloads do not affect the quality of

voice communications to the IP Phone.

Benefits of QoS

Networks that are designed to support QoS are best

suited for IP deployment since quality of voice is judged

by the end-to-end experience of the user. It is not

sufficient for ESI’s IP applications to support QoS if all

network components used in the transport of voice over

the customer’s LAN are not properly configured for

QoS support.

The benefits of end-to-end QoS in any IP telephony

application are many, and when absent, quite

noticeable to the user:

• Available bandwidth is optimized by ensuring that

voice packets are sent and delivered at a higher

priority than “regular” data traffic on the LAN. This may

allow the customer to delay upgrading the speed of

transmission of his network. He may be able to

defer this expense until other applications are added

or IT changes in the business dictate it is necessary.

• The quality of the IP conversation is improved by

ensuring that voice packets are delivered and

“reassembled” at the other end of the conversation

in order. This eliminates garbled conversation,

hollowness, and noticeable gaps in speech.

• Unlike data packets, voice packets cannot be resent

if they are dropped. Jitter

is reduced for voice

packets by QoS. This improves the likelihood that all

voice packets will not be dropped before being

delivered at the other end of the IP conversation, as

happens when the amount of jitter of a packet

exceeds an acceptable level.

• The latency with which voice packets are delivered is

minimized in a network employing QoS. This results

in more natural-sounding speech patterns for both sides

of an IP conversation.

802.1p and 802.1q standards for VLANs

Virtual LANs (VLANs) provide a method of separating data

streams to make a local area network appear to be two or

more networks. A VLAN is likely to be implemented in a

business where IP telephony is heavily used. The VLAN

segregates the voice packets onto their own network to

prevent the degradation of voice quality, loss of packets,

and late delivery of voice packets (latency).

Two standards are concerned with VLAN. Both are

required to be supported in order to adequately support

VLAN operation. These are:

• 802.1p — Provides for the prioritization of voice

packets. This standard establishes eight levels of

priority, 0 through 7, with 7 being the highest priority.

Level 7 is reserved for those applications and packets

that are considered network-critical. Levels 5 and 6

identify packets that are delay-sensitive. Priority levels

below 5 are used for “loss-eligible” data, meaning that

if a packet is lost and must be retransmitted, nothing

is affected. This is not the case with voice, where if a

packet is lost, portions of words will be missing or

unintelligible. ESI defines its prioritization field at 5.

• 802.1q — Dictates how the prioritization level (or

“tag”) is attached to each packet. Without this

tagging of voice packets, prioritization would not be

possible because there would be no differentiation

between types of packets.

By compliance to the 802.1p and 802.1q standards,

ESI’s local IP Phones have built-in prioritization to

simplify managing traffic and QoS over a LAN.

The variation from packet-to-packet in transit time, expressed in

milliseconds. For a more detailed explanation, see the Esi-Link

Product Overview (ESI # 0450-0214).

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ESI 24-Key Digital Feature Phone Specifications Page 10

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