ZyXEL Communications P-660 series Guia do Utilizador descarregar pdf (Página 157)

Chapter 11 Quality Of Service

P-660R-F1 Series User’s Guide

157

11.5.3 DiffServ

QoS is used to prioritize source-to-destination traffic flows. All packets in the flow are given the

same priority. You can use CoS (class of service) to give different priorities to different packet

types.

Differentiated Services (DiffServ) is a Class of Service (CoS) model that marks packets so that they

receive specific per-hop treatment at DiffServ-compliant network devices along the route based on

the application types and traffic flow. Packets are marked with DiffServ Code Points (DSCPs)

indicating the level of service desired. This allows the intermediary DiffServ-compliant network

devices to handle the packets differently depending on the code points without the need to

negotiate paths or remember state information for every flow. In addition, applications do not have

to request a particular service or give advanced notice of where the traffic is going.

DSCP and Per-Hop Behavior

DiffServ defines a new Differentiated Services (DS) field to replace the Type of Service (TOS) field

in the IP header. The DS field contains a 2-bit unused field and a 6-bit DSCP field which can define

up to 64 service levels. The following figure illustrates the DS field.

DSCP is backward compatible with the three precedence bits in the ToS octet so that non-DiffServ

compliant, ToS-enabled network device will not conflict with the DSCP mapping.

The DSCP value determines the forwarding behavior, the PHB (Per-Hop Behavior), that each packet

gets across the DiffServ network. Based on the marking rule, different kinds of traffic can be

marked for different kinds of forwarding. Resources can then be allocated according to the DSCP

values and the configured policies.

11.5.4 Automatic Priority Queue Assignment

If you enable QoS on the ZyXEL Device, the ZyXEL Device can automatically base on the IEEE

802.1p priority level, IP precedence and/or packet length to assign priority to traffic which does not

match a class.

The following table shows you the internal layer-2 and layer-3 QoS mapping on the ZyXEL Device.

On the ZyXEL Device, traffic assigned to higher priority queues gets through faster while traffic in

lower index queues is dropped if the network is congested.

Table 60 Internal Layer2 and Layer3 QoS Mapping

DSCP (6 bits) Unused (2 bits)

PRIORITY

QUEUE

LAYER 2 LAYER 3

IEEE 802.1P USER

PRIORITY

(ETHERNET

PRIORITY)

TOS (IP

PRECEDENCE)

DSCP

IP PACKET

LENGTH (BYTE)

0 1 0 000000

2 0 0 000000 >1100

1 2 ... 152 153 154 155 156 157 158 159 160 161 162 ... 267 268

Comentários a estes Manuais

Sem comentários

ZyXEL Communications P-660 series Guia do Utilizador Página 157

Comentários a estes Manuais

Manuais e produtos relacionados com Routers ZyXEL Communications P-660 series