Dialogic IMG - Using Differentiated Service (DiffServ or DSCP) rather than TOS
Symptom:
The Dialogic IMG Integrated Media Gateways allow Type of Service (TOS) to be configured in the IP Bearer Profile using the TOS Configuration (IMG 1010 and IMG 1004) or TOS Settings object (IMG 2020) under the IP Bearer Profile, but do not allow Differentiated Services (DiffServ) to be configured.
This article describes how to configure Differentiated Services in the IP Bearer Profile on the IMG Gateways.
Background:
TOS is based on RFC 1349. Another protocol used to define the Type of Service octet in the IP header is known as Differentiated Services, and is based on RFC 4594.
Note that on the IMG Gateways, this only applies to RTP packets, and cannot be configured for VoIP signaling (SIP, or H.323).
TOS uses 7 bits to define the parameters Precedence, Delay, Throughput, Reliability and Cost, whereas DiffServ uses 6 bits to define a Service Class.
Because of this difference there are some TOS settings that do not map to a DiffServ Code Point (DSCP) value.
The quick calculation is TOS = DSCP * 4.
When using TOS to set a DiffServ value the COST parameter should always be set to 'normal' as this maps to the ECN-Capable Transport parameter.
Solution:
Use the following table that maps DSCP (DiffServ Code Point) values to TOS values and then select the TOS settings in the IP Bearer profile in ClientView (IMG 1010 and IMG 1004) or the WebUI (IMG 2020).
Differentiated Services (DSCP) | Type of Service (TOS) | ||
DSCP | Codepoint Name | TOS | TOS description |
0 | CS0 | 0 | Precedence = Routine |
8 | CS1 | 32 (0x20) | Precedence = Priority |
10 (0x0A) | AF11 | 40 (0x28) | Precedence = Priority |
12 (0x0C) | AF12 | 48 (0x30) | Precedence = Priority |
14 (0x0E) | AF13 | 56 (0x38) | Precedence = Priority |
16 (0x10) | CS2 | 64 (0x40) | Precedence = Immediate |
18 (0x12) | AF21 | 72 (0x48) | Precedence = Immediate |
20 (0x14) | AF22 | 80 (0x50) | Precedence = Immediate |
22 (0x16) | AF23 | 88 (0x58) | Precedence = Immediate |
24 (0x18) | CS3 | 96 (0x60) | Precedence = Flash |
26 (0x1A) | AF31 | 104 (0x68) | Precedence = Flash |
28 (0x1C) | AF32 | 112 (0x70) | Precedence: Flash |
30 (0x1E) | AF33 | 120 (0x78) | Precedence: Flash |
32 (0x20) | CS4 | 128 (0x80) | Precedence: Flash Override |
34 (0x22) | AF41 | 136 (0x88) | Precedence: Flash Override |
36 (0x24) | AF42 | 144 (0x90) | Precedence: Flash Override |
38 (0x26) | AF43 | 152 (0x98) | Precedence: Flash Override |
40 (0x28) | CS5 | 160 (0xA0) | Precedence: CRITIC/ECP |
46 (0x2E) | EF | 184 (0xA8) | Precedence: CRITIC/ECP |
48 (0x30) | CS6 | 192 (0xC0) | Precedence: Internetwork control |
56 (0x38) | CS7 | 224 (0xE0) | Precedence: Network control |
Product List
Dialogic IMG 1010 Integrated Media Gateway
Dialogic IMG 2020 Integrated Media Gateway (IMG 2020), formerly referred to as Dialogic BorderNet™ 2020 Session Border Controller
Glossary of Acronyms / Terms
TOS: Type of service
DiffServ: Differentiated Services
DSCP: Differentiated Services Codepoint
ECN: Explicit Congestion Notification