13.6.17  
Quality of Service in HG 1500 
 
Quality of Service encompasses various methods for guaranteeing certain transmission properties in packet-oriented 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. If multiple applications with equal rights are operating via IP, then the available bandwidth for the transmission path (for example an ISDN B channel, 64 Kbps) is split. In this case, a voice connection may experience packet losses which can reduce voice quality.
HG 1500 uses various different procedures to implement Quality of Service.
On layer 2 (in accordance with OSI, Ethernet), you can activate an extension (IEEE802.1p) to the standard Ethernet format (DIX V2). This adds more information to the Ethernet header including a 3-bit data field. This field carries priority information on the data packet. For all packets that reach the board from the LAN, both Ethernet formats (IEEE 802.1p and DIX V2) are understood; for all packets that are sent from the board to the LAN, the format can be selected via "Basic Settings > IEEE 802.1p". You should check whether all components in the network support this format before this parameter is activated. Otherwise, it may not be possible to access HG 1500 from the LAN anymore.
The Ethernet header is not transported when switching to another transport medium (for example, ISDN). An IP router (like the HG 1500`s router) can, however, use the information contained in the IP header for prioritization. Straightforward IP routers that connect two network segments, for example, can use the IP level prioritization. In the "Type of Service" field, either three bit (IP precedence based on RFC 791, older standard) or six bit (Differentiated Services or DiffServ, based on RFC 2474) are evaluated for the creation of various classes. HG 1500`s IP router provides various bandwidths for these classes, so that voice packets can be processed first. The procedure adopted by HG 1500 can be set under "Basic settings > QoS procedures" (Autodetect is set by default).
For the DiffServ parameter, various so-called codepoints ("Basic Settings > AF/EF Codepoints") are defined, and based on these codepoints two different procedures are used for processing the payload of different marked data flows:
The "Expedited Forwarded (EF)" procedure (based on RFC 2598) guarantees a constant bandwidth for data in this class. If this defined value is reached, all packets that exceed this bandwidth are rejected. A separate class is defined for EF on HG 1500. For this class, the bandwidth can be defined as a percentage for every ISDN peer (QoS bandwidth for EF).
The "Assured Forwarding (AF)" procedure (based on RFC 2597) guarantees a minimum bandwidth for the data of one (of many) classes. Lower priority classes share the bandwidth not used by EF or the classes with higher priority. In addition, the speed at which packets are rejected if the system is unable to forward them fast enough can be defined for every class by means of the Dropping Level setting. Nothing is thus to be gained by buffering voice packages for an extended period of time (this only increases the delay). In the case of secure data transfer (for example, file transfer), on the other hand, a large buffer is advantageous as packets are otherwise sent repeatedly between the two terminals.
Four classes are reserved for AF on the HG 1500: AF1x (high priority), AF2x, AF3x and AF4x (low priority), where "x" stands for one of three dropping levels: low (1), medium (2) and high (3). In the case of "low", packets are buffered over an extended period, in the case of "high", packets are promptly rejected if they cannot be forwarded. Unmarked IP packets (ToS field=00) are handled in the same way as the lowest priority.
If a routing partner can only work with one of the two standards (DiffServ or IP precedence, for example an older router that only works with IP precedence), then HG 1500 can translate the ToS field accordingly. This can be set for each ISDN partner or DSL/LAN2/PPTP interface via "QoS Capability". When the default value is set ("identical"), nothing is translated; with the values "DiffServ" or "IP Precedence", translation is performed on the basis of the table below, if data is not entered in the field in accordance with the standard set.
In the case of IP data traffic, the IP packets that generate HG 1500 are split into five groups (for example, the H.323 gateway). You can set which codepoint is to be used for marking the packets for four of these groups. This is configured under "Basic Settings > QoS priority classes":
 •   Voice Payload for H.323 telephony (Voice over IP)
 •   Call Signaling for connection setup in H.323
 •   Data Payload, for example, for IP networking with fax or modem
 •   Network Control, for example, SNMP traps
The remaining data traffic is marked "disabled", that is 00.
The following table shows the relationship between the various codepoints of DiffServ, IP precedence and the "User Priority" field in the Ethernet header.

 Table 13-4   Codepoint Implementation
 IP header  
 Ethernet header  
 DiffServ  
 vs.  
 IP Precedence  
 IEEE802.1p  
 Codepoint  
 Default (can be changed)  
 Drop level  
 Assignment (fixed)  
   
   
 Binary (bit field)  
 ToS field (hex)  
 high  
 med  
 low  
 Binary (bit field)  
 ToS field (hex)  
 User Priority
(binary, bit field)  
 CS7  
 111000  
 E0  
   
 x  
   
 <->  
 111  
 E0  
 111  
 AF 11  
 001010  
 28  
   
   
 x  
 ->  
 110  
 C0  
 110  
 AF 12  
 001100  
 30  
   
 x  
   
 <->  
 110  
 C0  
 110  
 AF 13  
 001110  
 38  
 x  
   
   
 ->  
 110  
 C0  
 110  
 AF 21  
 010010  
 48  
   
   
 x  
 ->  
 101  
 A0  
 101  
 AF 22  
 010100  
 50  
   
 x  
   
 <->  
 101  
 A0  
 101  
 AF 23  
 010110  
 58  
 x  
   
   
 ->  
 101  
 A0  
 101  
 AF 31  
 011010  
 68  
   
   
 x  
 ->  
 100  
 80  
 100  
 AF 32  
 011100  
 70  
   
 x  
   
 <->  
 100  
 80  
 100  
 AF 33  
 011110  
 78  
 x  
   
   
 ->  
 100  
 80  
 100  
 AF 41  
 100010  
 88  
   
   
 x  
 <->  
 011  
 60  
 011  
 AF 42  
 100100  
 90  
   
 x  
   
 <->  
 011  
 60  
 011  
 AF 43  
 100110  
 98  
 x  
   
   
 <->  
 011  
 60  
 011  
 EF  
 101110  
 B8  
   
   
   
 <->  
 110  
 C0  
 110  
 DE
(default)  
 000000  
 00  
   
   
   
   
 000
001
010  
 00
20
40  
 000  
The "vs." column shows the relationship between the DiffServ and IP precedence standards. Since DiffServ offers more variants, the codepoint is permanently selected when translating IP precedence into DiffServ: for example, the codepoint for the IP precedence "100", for example, becomes "AF31". In the case of packet that leave HG 1500 in the direction of the LAN, the user priority specified in the last column is set when IEEE 802.1p is active.
QoS can be activated for the second LAN interface as well as for the ISDN partner. For this interface, the interface is extended by an additional transmission rate limitation. The function of the quality evaluation corresponds to the ISDN peer procedure. The average transmission rate is set in configuration data.

HiPath 3000/5000 V9, Service Documentation, Issue 7   up Top
Disclaimer & Copyright   ID: P31003H3590S100017620   2012-06-25