Category: Technology


QoS overview

The most helpful overviews I’ve found to date on QoS for VoIP:

http://www.ciscopress.com/articles/article.asp?p=357102

http://www.networkworld.com/community/node/37507 (You can browse through the preceding several posts until you arrive at the initial discussion on the QoS byte. Interesting reading.)

The key is to tag your VoIP traffic as DSCP class EF (Expedited Forwarding; the numeric value for EF is 46, binary is 101110(00), ToS 184).

The DSCP classes were created by Cisco and are the default markings applied to VoIP traffic. They are the evolution of the IETF’s ToS byte, which allowed the first bits to be used to specify a rough QoS (called “IP Precendence”). The other bits were never used, so Cisco used several of them to create a more granular set of QoS markings. EF 46 is one of them. EF 46’s first bits indicate IP Precedence 5, which is the class for voice traffic on the older IP Precedence system. So, if you mark traffic as DSCP EF, you’re also marking it as IP Precedence 5. Convenient!

Here’s a helpful tool to assess line quality:

http://myspeed.visualware.com/servers/namerica/iad.php?testtype=-1&codebase=mcsiad.visualware.com&location=USA: Dulles, Virginia&ver=9&cm=&map=namerica&lines=&pps=50&bpp=80&codec=G.726 (32 Kbps)&provtext=Visualware&provtextextra=&provlink=http://www.visualware.com

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If you’re using your company’s SharePoint site, this warning message isn’t really needed, since you already trust it. And the dialog box alarms admins who don’t realize what’s happening. This happens under Windows 7 64-bit, IE 9, Word 2010, SharePoint 2010 running over SSL with a trusted certificate, selecting “Edit in Word” from the drop-down menu.

If you put the site in your “Intranet Zone” and take the security settings slider down to its lowest setting, the problem does not go away. But if you put it in “Trusted Sites” and take the security settings slider down to its lowest level, the warnings do go away. I haven’t taken the time to figure out what setting is to blame. The super-low security settings in this case are not a problem for me, since I only have one site in the Trusted Sites list (the SharePoint site itself).

UPDATE: Office 365 SharePoint Online seems to handle everything much better.

VLAN Management >

Create VLAN > Add > Set up the VLAN you want to be designated as your voice VLAN

Voice VLAN > Properties > Enable/​Pick your new VLAN

Voice VLAN > Telephone OUI > Make sure the leading characters from your phone’s MAC address are listed in there (and make sure your phone is configured to use LLDP, or none of this will work, obviously)

Port to VLAN > Filter > Select your new voice VLAN from the drop-down > Go, Click “Tagged” and for all ports and then “Apply” so that they can use the new VLAN as needed

Admin > Discovery LLDP >

Properties > Enable

LLDP MED Network Policy > Add > Type in the VLAN ID and save it

LLDP Port Settings > Don’t do anything with this

LLDP MED Port Settings > Pick a port and select Edit >

LLDP MED Status > Enable

Available Optional TLVs > Select the Network Policy TLV and click it over to the “Selected Optional TLVs” column

Available Network Policies > Select the network policy you created above and click it over to the “Selected Network Policies” pane

Glad to find this one today: http://inkscape.org/.