Specifications

Technical Concepts Nur für den internen Gebrauch
A31003-H3580-M103-2-76A9, 01-2009
9-10 HiPath 3000/5000 V8 - HG 1500 V8, Administrator Documentation
hg-09.fm
Quality of Service (QoS)
HG 1500 uses various different procedures to implement Quality of Service.
On layer 2 (in accordance with OSI, Ethernet), you can activate an extension (IEEE 802.1p) to
the standard Ethernet format (DIX V2). This adds more information to the Ethernet header in-
cluding 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 un-
derstood; the format can be selected for all packets that are sent from the board to the LAN.
You should check whether all components in the network support this format before this param-
eter 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 (e. g. IS-
DN). 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 case of the QoS procedure, either three bits
(IP precedence based on RFC 791, older standard) or six bits (Differentiated Services or Diff-
Serv, based on RFC 2474) are evaluated for the creation of various classes. HG 1500’s IP rout-
er provides various bandwidths for these classes, so that voice packets can be processed first.
For the DiffServ parameter, various so-called codepoints ("Basic Settings > AF/EF Code-
points") are defined, and based on these codepoints two different procedures are used for pro-
cessing 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 band-
width 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 ex-
tended period of time (this only increases the delay). In the case of secure data transfer (e. g.
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 (low priority) , AF2x, AF3x and AF4x
(high priority), where "x" stands for one of three dropping steps: 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 PSTN peer or LAN interface. When the de-