How to use Cisco's Voice VLAN with DBC 422 & 425? 1

[UNN]

This was raised as a question in thread806-1078791 (June 2005). Has anyone heard roumers on Ericsson or/and Cisco efforts to utilize the Cisco switch-interface feature.

interface FastEthernet6/41
switchport access vlan 999
switchport voice vlan 800

The aim would be to minimize efforts in both ends. Connecting an Cisco IP Phone to a switch interface configured for voice as well went quite nicely without any additional tasks required neither on the switch nor on the phone.

I just wondered ,,,,,

 

[fidde]

You can not use it the same way as the cisco phone does.

If you are using Ericsson, I would suggest you to configure your DHCP server to send the the VLAN tag in the DHCP message (option 43). Then when the phone is "out of the box" you connect it to the switch and it sends a untagged DHCP request, then it gets the IP and VLAN tag. It now release the IP address and sends a new DHCP request wiht the VLAN tag that you configured.

This way the user does never have to do anyting....

 

[UNN]

The switch port is then assumed to be dot1q with native VLAN being the access VLAN and the Voice VLAN tagged as such according to the DHCP option 43 field?! Is there an document describing this feature (including DHCP and Ericsson internal switch facilities) ?

 

[ADB100]

I have done this quite a few times now and it isn't pretty....

The only way to get the voice vlan info into a phone is via the webserver the phone contacts as a result of DHCP Vendor Option 43. This must be in the Data VLAN DHCP Scope as the IP Phone initially has no knowledge of the Voice VLAN. This must be entered as a HEX string and is comprised of a length field describing the following text, for an IP Phone this is always 'Ericsson-IP-Phone' so the length field is 17 (11 in HEX). Following this is the value '01', after this is another length field and then the IP address of the webserver. The length field describes the length of the IP address in characters - for example 10.1.1.1 is 8-characters long, whereas 192.168.10.10 is 13-characters long.
So for example your webserver IP address is 172.20.165.1, the Vendor Option 43 value will look like:

Option 43 (Hex)
0x114572696373736f6e2049502d50686f6e65010c3137322e32302e3136352e31

11 45 72 69 63 73 73 6f 6e 20 49 50 2d 50 68 6f 6e 65 01
(17) E r i c s s o n I P - P h o n e

0c 31 37 32 2e 32 30 2e 31 36 35 2e 31
(12) 1 7 2 . 2 0 . 1 6 5 . 1

Once the IP Phone has the Webserver IP address it attempts to load its configuration file via HTTP - depending on the firmware this can be different as well. If the IP Phone has been assigned a DNS suffix it will attempt to locate its configuration file based on the DNS suffix:

http://172.20.165.1/ericsson.com/dbc42201/d4-config.txt

If no DNS suffix was given it MAY try its subnet (this is firmware dependant - newer ones do, older ones don't). The following is based on the subnet that was assigned via DHCP being 10.1.1.0/24:

http://172.20.165.1/10.10.10.0-24/dbc42201/d4-config.txt

They can also use a Telephony Domain Name (dimilar to DNS sort of....). This is sent to the IP Phones via the DHCP Vendor Option 43 but I have never managed to get it to work.....

It is good practise to make your Data & Voice VLAN's mirror each other so you can group the Config files logically. For example if you have one big, flat Data VLAN but you want multiple Voice VLAN's it aint going to work dynamically......

The config file (d4-config.txt) contains the Voice & Data VLAN details as well as LOTS of other stuff. My knowlede stretches as far as the VLAN tags and the QoS settings...

To control the Voice/Data VLAN's the L2QOS section in the config file is used:

[L2QOS]
MIIPort=5,999 ;prio (0-7) ,VID(1-4095)
PCPort=0,1 ;prio (0-7) ,VID(1-4095)
LANPort=1,0 ;MAC based VLAN/802.1Q based VLAN , untagged/tagged PC originating traffic

The MIIPort is the IP Phones port it speaks on (this is the Voice VLAN) - the 802.1p priority (CoS) is set with the first value and the 2nd value sets the VLAN ID.
PCPort sets the VLAN characteristics for the piggy-backed PC - no 802.1p priority and a VLAN tag of 1.
LANPort sets the tagging ON or OFF for both the Voice & Data VLAN's - the 1st value is the MIIPort (Voice) and a '1' tells it to tag (so it uses the MIIPort parameters). The 2nd value is the PCPort and a '0' tells it not to tag (so it DOESN'T use the PCPort parameters).

Finally the Layer-3 QoS is set with the sections DIFFSERVTCP and DIFFSERVUDP. These sections control what DSCP values are used when sending TCP and UDP traffic from the IP Phone.

[DIFFSERVTCP]
TrafficClass=3 ;Class B
DropPrecedence=0 ;Medium drop percentage


[DIFFSERVUDP]
TrafficClass=5 ;Expedited Forwarding
DropPrecedence=3 ;High drop percentage, recommended for EF


The TrafficClass describes the 1st 3-bits of the ToS Field, the DropPrecedence describes bits 4 & 5 of the ToS field. The above example sets the Cisco recommended settings of DSCP EF (46) for UDP and DSCP 24 (CS3) for signalling. Bit 6 of the ToS field is not used (nor are bits 7 & 8)

DSCP 46
101 11 0

DSCP 24
011 00 0


Since Ericsson IP Phones use H.323 some signalling is sent via UDP so unfortunately gets tagged with DSCP EF. What we do here is use inbound policy-maps to re-classify all the traffic anyway.


A bug in the IP Phones (not sure if its still there?) is after the IP Phone has read the config file it immediately starts using the configured 802.1q VLAN tag without releasing the IP address from the Data VLAN and re-requesting another IP address but using the Voice VLAN tag. A reboot is the workaround.

Another pain is once the config file has been read the IP Phone stores the config in NVRAM so it is a pain moving phones as it will use the Voice VLAN Tag constantly until its removed by editing the config file. Cisco & Nortel IP Phones don't retain the config if they are configured for automatic operation.

There has been talk of Ericsson updating the firmware so that the Voice VLAN tag can be discovered directly from DHCP (like the Nortel & Mitel ones do). I haven't seen this yet though.

If all this sounds a bit complicated get an Ericsson partner in (Damovo do this all the time....). I must stress the importance of the design though. You really need to have a nice structured LAN - single access switch, single Voice & Data VLAN etc.

HTH

Andy