Long time I haven’t blogged, I was so busy in some new projects that burned my time.
I will blog about a topic I wanted to blog about it long time ago, applying the correct QoS for OCS 2007 traffic over the WAN, this has been a hot topic (at least for me) as I believe that all of voice traffic requires over WAN links.
I will introduce some QoS terminology in this post, and later will tell you how to apply QoS for OCS traffic.
Quality of Service Models
There are 3 service models:
· Best Effort · No QoS policies are implemented
· Integrated Services (IntServ) · Resource Reservation Protocol (RSVP) is used to reserve bandwidth per flow across all nodes in a path, uses the Resource Reservation Protocol (RSVP) to reserve network resources in advance of the data actually traveling across the network. Once the end-to-end bandwidth reservation is in place, the data is transmitted.
· Differentiated Services (DiffServ) · Packets are individually classified and marked; policy decisions are made independently at each node in a path, DiffServ doesn't use RSVP, but instead uses hop by hop Behavior or per hop behavior (PHB) to allow each router/hop across the network to examine the packet and decide what service level it should receive.
IP QoS Markings
We currently use 2 QoS marking methods:
· Precedence · The first three bits of the IP TOS field are evaluated; compatible with Ethernet CoS and MPLS EXP values
· DSCP · The first six bits of the IP TOS are evaluated to provide more granular classification; backward-compatible with IP Precedence
The following table contains the Precedence Values
| | Binary | Application |
| 7 | 111 | Reserved |
| 6 | 110 | Routing |
| 5 | 101 | Voice |
| 4 | 100 | Streaming Video |
| 3 | 11 | Call Signaling |
| 2 | 10 | Transactional |
| 1 | 1 | Bulk Data |
The following table lists the DSCP marking values:
| Likely to be dropped | AF Class | Drop Probability | DSCP Value |
| Low | AF Class 1 | AF11 (low) | 001 01 0 |
| AF12 (medium) | 001 10 0 | ||
| AF13 (high) | 001 11 0 | ||
| Medium | AF Class 2 | AF21 (low) | 010 01 0 |
| AF22 (medium) | 010 10 0 | ||
| AF23 (high) | 010 11 0 | ||
| High | AF Class 3 | AF31 (low) | 011 01 0 |
| AF32 (medium) | 011 10 0 | ||
| AF33 (high) | 011 11 0 | ||
| Very High | AF Class 4 | AF41 (low) | 100 01 0 |
| AF42 (medium) | 100 10 0 | ||
| AF43 (high) | 100 11 0 |
How to reserve the Bandwidth:
You can use any of the following methods:
· Policing · Creates an artificial ceiling on the amount of bandwidth that may be consumed; traffic exceeding the cap and be remarked or dropped
· Shaping · Similar to policing but buffers excess traffic for delayed transmission; makes more efficient use of bandwidth but introduces a delay
Mahmoud
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