APC IP DSLAM Guia do Utilizador descarregar pdf (Página 35)

EDA 1200 Services

Packet loss Delay Jitter

Voice

Not sensitive Sensitive Very sensitive

Data

Not sensitive Not sensitive Not sensitive

The Very sensitive adjectives in Table 6 indicate which parameter will cause

the perceived quality of the application using the transport to deteriorate. Not

sensitive means that as long as the deterioration is reasonable (there is no

definite definition for limits), the perceived quality will not be changed.

Video applications – As long as the video is only streaming video, only the

packet loss is important for the perceived quality. Delay will only affect the time

elapse when changing a channel. However, if the video service is interactive

video, the delay becomes more important, and should be kept to a time that is

acceptable as response time.

Voice applications – Applications like telephony are very sensitive, especially to

delay and jitter. The jitter is especially important since voice packets may arrive

in the wrong order if they have different delay lengths. Buffering the packets

can help this, but the buffer will then increase the delay. Loss of packets can be

handled by a telephony application without substantial service deterioration,

provided that the loss is limited to a small fraction of the packets, and that the

packets are not lost in bursts.

Data applications – For example, Internet surfing, using the TCP/IP protocol

stack, are generally not very sensitive, neither to packet loss nor delay.

Interactive gaming however, is more sensitive to large packets losses and

unacceptably long delays.

Loss of packets is rare within the EDA 1200 access network, unless the loss is

caused by capacity limitations. In that case it tends to occur in bursts.

Consequently, in order to provide the transport service required for Telephony

over IP there are two main requirements for the QoS function. One is to

minimize the delay of voice packets, the other to minimize the influence of

capacity limitations on voice packets.

In a network carrying a mixture of real-time applications and data packets,

delays are mainly imposed on voice packets when they have to wait for

transmission of often-longer data packets.

3.2.1 Traffic Classification

The classification of the traffic is done by the edge nodes in the network.

The Access Node (IP DSLAM or Ethernet access switch) tags upstream

frames with classification tags (also called p-bit), determined by the origin of

the frame. A frame generated internally by the Access Node is tagged with the

management priority tag. A frame originating from an ATM PVC is tagged with

the priority tag defined for that PVC, or the flow within the PVC, by the operator.

1/1551-LZA 101 464-V1 Uen C 2009-12-17

1 2 ... 30 31 32 33 34 35 36 37 38 39 40 ... 66 67

Comentários a estes Manuais

Sem comentários

APC IP DSLAM Guia do Utilizador Página 35

Comentários a estes Manuais

Manuais e produtos relacionados com Redes APC IP DSLAM