Selecting DSCP Values
When sending packets, computers add a DSCP value that your network infrastructure can examine to determine how the packet should be prioritized. Although DSCP values can be arbitrary depending on how your network infrastructure is configured, many organizations use a typical DSCP strategy with the following five queues:
- Control traffic Communications transmitted between routers. Typically, these communications require minimal bandwidth, but they should be assigned a high priority because quick transmission can reduce downtime in the event of a hardware failure. You should also use this priority for VoIP control traffic. Use DSCP values of 25 for control traffic.
- Latency-sensitive traffic Traffic, such as VoIP, that must be delivered as quickly as possible. Typically, you should assign this a DSCP value of 46, known as Expedited Forwarding (EF).
- Business critical traffic, also known as Better than Best Effort (BBE) Communications that should receive priority treatment, such as customer service database queries from a line-of-business (LOB) application or streaming video, but that are not highly sensitive to latency. Use a DSCP value of 34.
- Best-effort (BE) traffic Standard traffic, including any traffic not marked with a DSCP number, that should be handled after either of the preceding two queues. This traffic should have a DSCP value of 0, which is the default if no DSCP value is specified.
- Scavenger traffic Low-priority traffic, such as backups, downloading of updates, noncritical file synchronization, and non-work-related traffic that employees might generate. Use a DSCP value of 10 or 8.
Note If you mark traffic from too many applications as high priority, the high-priority queue on routers can grow long enough to add significant latency. This defeats the purpose of QoS. Therefore, you should reserve the highest-priority DSCP marking for real-time communications, such as VoIP.
Table below summarizes these values.
DSCP Interoperability Values
|Purpose||Common Use||DSCP Value|
|VoIP||VoIP traffic, including signaling and control traffic||46|
|Interactive video||Two-way video conferencing||34|
|Mission-critical data||Database queries, LOB communications, video streaming||25|
|Best effort||All other traffic, including e-mail and Web browsing||0|
|Bulk data||Backups, nonbusiness applications, file transfers||10|
Many networks use an even simpler structure with only two priorities: one for latencysensitive traffic and another for BE traffic. However, if you have third-party tools that can use DSCP values to report on network performance for different types of traffic, it is advantageous to define a larger number of DSCP values even if your network infrastructure isn't configured to handle each DSCP value uniquely.
DSCP values might be lost when packets leave your network because most organizations do not trust priorities provided by computers outside the organization. Because sending traffic labeled as high priority can create a denial-of-service (DoS) attack, DSCP values from untrusted computers might be malicious.
Wireless Multimedia (WMM) includes four access categories for prioritizing traffic on 802.11 wireless networks. WMM uses DSCP values to set the priority, so you can take advantage of WMM automatically by specifying DSCP values. Table below shows how DSCP values correspond to WMM access categories.
DSCP Values and WMM Access Categories
|DSCP Value||WMM Access Category|
|24-31, 0-7||Best effort (BE)|
To support fully prioritizing traffic based on DSCP values, your network infrastructure must support the use of multiple queues as defined in RFC 2474.
In this tutorial:
- Configuring Windows Networking
- Usability Improvements
- Network And Sharing Center
- Network Explorer
- How Windows Finds Network Resources
- How Windows Publishes Network Resources
- How Windows Creates the Network Map
- Network Map
- Set Up A Connection Or Network Wizard
- Manageability Improvements
- Network Location Types
- Policy-Based QoS
- Selecting DSCP Values
- Planning Traffic Throttling
- Configuring QoS Policies
- Configuring System-Wide QoS Settings
- Configuring Advanced QoS Settings
- Testing QoS
- Windows Firewall and IPsec
- Windows Connect Now in Windows 7
- Core Networking Improvements
- Networking BranchCache
- How Hosted Cache Works
- How Distributed Cache Works
- Configuring BranchCache
- BranchCache Protocols
- File Sharing Using SMB
- Web Browsing with HTTP (Including HTTPS)
- Efficient Networking
- What Causes Latency, How to Measure It, and How to Control It
- TCP Receive Window Scaling
- Scalable Networking
- Improved Reliability
- IPv6 Support
- 802.1X Network Authentication
- Server Message Block (SMB) 2.0
- Strong Host Model
- Wireless Networking
- Improved APIs
- Network Awareness
- Improved Peer Networking
- Services Used by Peer-to-Peer Networking
- Managing Peer-to-Peer Networking
- Peer-to-Peer Name Resolution
- EAP Host Architecture
- Layered Service Provider (LSP)
- Windows Sockets Direct Path for System Area Networks
- How to Configure Wireless Settings
- Configuring Wireless Settings Manually
- Using Group Policy to Configure Wireless Settings
- How to Configure TCP/IP
- Configuring IP Addresses Manually
- Command Line and Scripts
- How to Connect to AD DS Domains
- How to Connect to a Domain When 802.1X Authentication Is Not Enabled
- How to Connect to a Domain When 802.1X Authentication Is Enabled