DiffServ
DiffServ (Differentiated Services)
DiffServ is a QoS
(Quality of Service) protocol for managing bandwidth allocation for Internet media connections (e.g. a VOIP voice connection).
- Nice overview here
- IETF Diffserv page
With low bandwidth lines, such as ADSL, users may feel jittering.
Try to allow full upload bandwidth to eMule and do a phone call in
G.711 in the same time, and you will surely understand what I mean.
Regarding Cisco docs, and others as well, the correct DiffServ value is EF (Expedited Forwarding)
. The EF DiffServ also contains the ToS Low Delay bit
,
which is treated by many routers without any configuration. This is
called PFIFO (Priority Fist In First Out, or FIFO with Priority).
The values you must know:
- EF DiffServ decimal: 184
- EF DiffServ hexadecimal: 0xb8
- EF DiffServ binary: 101110 00 (in red: DSCP field)
- EF DSCP decimal: 46
- EF DSCP hexadecimal: 0x2e
- EF DSCP binary: 101110
Remark: The DSCP field is contained within the 6 first bits of the DiffServ byte.
Here is the part where we getting crazy. Each constructor requires a different DiffServ or DSCP value.
- Alcatel OmniPCX Office - EF DiffServ binary : 10111000 DIFFSERV_PHB_EF
- Asterisk 1.0.9 (ie sip.conf) - EF DiffServ hexadecimal : tos = 0xb8
- Grandstream (requires FW 1.0.6.3 and older) - EF DSCP decimal : 46
- ZyXEL - EF DiffServ decimal : 184
- TELES - EF DiffServ decimal : 184
If any doubt, use a sniffer such as Wireshark
(formerly Ethereal). If settings are correct, it will show the Differentiated Services Field
in any of the RTP packets, whith a value of 0xb8 (DSCP 0x2e: Expedited Forwarding: ECN: 0x00)
.
See also:
