![]() ![]() This forwarding treatment is called the packet's Per-Hop Behavior (PHB). This is a very common way to implement QoS policy-such as, dropping low-priority traffic over a backup circuit, for example.ĭSCP denotes the forwarding treatment a packet should receive. ![]() Both are defined in RFC791- These are used in a similar way as DSCP-to mark traffic to influence per hop behavior throughout the network.Īn IP ACL can match packets that have been marked by any of these QoS values. The DSCP field superseded the IP Precedence value (3 bits can represent values from 0 to 7) and the type of service (TOS) field (4 bits ranging from 0 to 15). The DSCP value is 6 bits and can range from 0 to 63. Once marked, the packet can be treated (queued, dropped, and so forth) differently from other packets based on a QoS policy defined by administrators. This field (defined in Request for Comments (RFC) 2474 and RFC2475- is used to mark a packet to ensure it is handled correctly by each device in the network, without each having to individually evaluate the contents of the packet. The Differentiated Services Code Point (DSCP) is a field in the header of an IP packet. Luigi DiGrande, in Cisco CCNA/CCENT Exam 640-802, 640-822, 640-816 Preparation Kit, 2009 QoS Information In the next section, we will look at and describe the various rules of traffic shaping.ĭale Liu. It is entirely possible to grind your network to a halt with a bad traffic-shaping configuration, so it is important to consider all aspects of it before implementing traffic shaping. Off This turns it off regardless of other configurations. On This turns on DiffServ mapping regardless of whether there is a policy or not. Mode You can define three different modes for DiffServ traffic shaping on your firewall: ▪Īuto This turns on DiffServ mapping if there is a policy that uses ingress or egress traffic shaping. If you leave it at default, priority 7 (bits 111) will be mapped to queue 0 (highest priority) all the way down to priority 7 (bits 000), which is the lowest value (shown in Table 5.1). The firewall will map them to the appropriate queues that you define in the IP precedence fields. IP Precedence You can set the eight different DiffServ values in the ToS bits of the IP packet. DiffServ on the system has the following properties: ▪ĭSCP Class Selector Enabling this option will allow DSCP Class selection on your system. ![]() Solution: Use the following table that maps DSCP (DiffServ Code Point) values to TOS values and then select the TOS settings in the IP Bearer profile in ClientView (IMG 1010 and IMG 1004) or the WebUI (IMG 2020).You can configure DiffServ on your firewall systemwide and also mark packets that travel through a policy configured to do so. When using TOS to set a DiffServ value the COST parameter should always be set to 'normal' as this maps to the ECN-Capable Transport parameter. Because of this difference there are some TOS settings that do not map to a DiffServ Code Point (DSCP) value. TOS uses 7 bits to define the parameters Precedence, Delay, Throughput, Reliability and Cost, whereas DiffServ uses 6 bits to define a Service Class. Note that on the IMG Gateways, this only applies to RTP packets, and cannot be configured for VoIP signaling (SIP, or H.323). Another protocol used to define the Type of Service octet in the IP header is known as Differentiated Services, and is based on RFC 4594. This article describes how to configure Differentiated Services in the IP Bearer Profile on the IMG Gateways. Symptom: The Dialogic IMG Integrated Media Gateways allow Type of Service (TOS) to be configured in the IP Bearer Profile using the TOS Configuration (IMG 1010 and IMG 1004) or TOS Settings object (IMG 2020) under the IP Bearer Profile, but do not allow Differentiated Services (DiffServ) to be configured. ![]()
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