13.1.4  
QoS - Quality of Service 
 

Introduction  
Data transmission in IP networks can encounter:
 •   Time problems due to large e-mail attachments and web surfing
 •   Network bottlenecks as a result of multiple requests for the same web page
 •   Reduced voice quality due to:
   -   Delay (decline in voice quality due to delay)
   -   Variable delays (decline in voice quality due to jitter)
   -   Packet loss (decline in voice quality due to packet loss)
Quality of Service includes various methods which guarantee certain transmission properties in packet-orientated networks (IP).
It is thus important, for example, to ensure a minimum bandwidth for Voice over IP for the entire duration of the transfer operation. When several equal-access applications are operating via IP, the available transmission link bandwidth (for example, an ISDN B channel, 64K bps) is shared between these applications. Consequently, packet loss may occur during a voice connection, causing poor voice quality.

HiPath 3000/5000 QoS  
In HiPath 3000/5000 networks, different types of traffic are transported via a single IP infrastructure. It is the aim of Quality of Service to fulfill the data traffic and voice traffic requirements.
To prevent voice traffic from being suppressed by data traffic, the former must be given high priority. In addition, it must be specified that high-priority traffic is transmitted before traffic with lower priority. This is specified on layers 2 and 3:
 •   The three bits in the 802.1p field, which is part of the 802.1Q tag, are used on layer 2.
 •   On layer 3, the six bits in the DiffServ Code Point (DSCP) field are used in the IP headers' Type of Service (ToS) byte.
It is also essential that sufficient bandwidth is available within the QoS class in use (Codepoint/IEEE802.1p User Priority). The following table lists the QoS values used for DiffServ and the User Priority IEEE802.1p field.

 Table 13-2   Possible QoS Settings
 Traffic type  
 DiffServ Code Point  
 802.1p field  
 (Priority 0 (= lowest) - 7 (= highest)  
 Traffic class  
Voice payload (RTP/RTCP)  
 AF12 (001100)  
 6  
Guaranteed service  
Data payload (fax gateway)  
 AF11 (001010)  
 6  
Guaranteed service  
Signaling (H.225, H.245 and real-time application signaling)  
 AF21 (010010)  
 5  
Controlled Load  
All other traffic types  
 DE (000000)  
 0  
Best effort  
Information on the QoS procedures used for HG 1500 can be found in the HG  1500 Administration Manual.

HiPath 3000/5000 V8, Service Documentation, Issue 10   up Top
Disclaimer & Copyright   ID: P31003H3580S100017620   2011-01-24