21CS637-Advanced-Networks
Cisco DiffServ QoS
Background
Six bits of the DS field are used as the ifferentiated services code point (DSCP) to select the Per-Hop Behavior (PHB) at each interface. A currently unused 2-bit (CU) field is reserved for explicit congestion notification (ECN). The value of the CU bits is ignored by DS-compliant interfaces when determining the PHB to apply to a received packet.
Per-Hop Behavior (PHB) refers to the packet scheduling, queueing, policing, or shaping behavior of a node on any given packet belonging to a Behavior Aggregate (BA), as configured by a service level agreement (SLA) or a policy map.
Default PHB
DSCP value is 000000 (0)
Class-Selector PHB
DSCP value in the form xxx000, where x is either 0 or 1. This is to ensure backward compatibility.
Assured Forwarding PHB
In AF, network traffic can be divided into the following classes:
- Gold: Traffic is allocated 50% of the available BW.
- Silver: Traffic is allocated 30% of the available BW.
- Bronze: Traffic is allocated 20% of the available BW.
DSCP value, xyzab0, where xyz (4 classes) can be 001, 010, 011, or 100, and ab (3 precedence) represents the dP value.dP is the probability for dropping the packet.
dP(AF13) >= dP (AF12) >= dP(AF11)
Expedited Forwarding PHB
Applications such as Voice over IP (VoIP), video, require guaranteed BW robust service.
DSCP value is 101110 (46)
Demo Setup
| Traffic Class | Traffic Type | DSCP Value |
|---|---|---|
| Premium | Voice | 46 |
| Gold | Terminal Access Controller Access Control System (TACACS) | 10 |
| Silver | Telnet | 18 |
| Silver | Simple Mail Transfer Protocol (SMTP) | 20 |
| Silver | File Transfer Protocol (FTP) | 22 |
| Bronze | Hyper Text Transfer Protocol (HTTP) | 26 |
Class-map: a network traffic classification. Policy-map: a series of actions that will be applied to a set of classified inbound traffic.
Config Set in Router
Class Map
Policy Map
Error
Set Config in Router
