Cisco Cisco ASR 5000
Serving GPRS Support Node (SGSN) Overview
Features and Functionality ▀
SGSN Administration Guide, StarOS Release 18 ▄
The SGSN conforms to the DiffServ model for QoS by handling the 3GPP defined classes of traffic, QoS negotiation,
DSCP marking, traffic policing, and support for HSDPA/HSUPA.
DSCP marking, traffic policing, and support for HSDPA/HSUPA.
QoS Classes
The 3GPP QoS classes supported by the SGSN are:
Conversational
Streaming
Interactive
Background
The SGSN is capable of translating between R99 and R97/98 QoS attributes.
QoS Negotiation
On PDP context activation, the SGSN calculates the QoS allowed, based upon:
Subscribed QoS - This is a per-APN configuration, obtained from the HLR on an Attach. It specifies the highest
QoS allowed to the subscriber for that APN.
Configured QoS - The SGSN can be configured with default and highest QoS profiles in the configuration.
MS requested QoS - The QoS requested by the UE on pdp-context activation.
DSCP Marking
The SGSN performs diffserv code point (DSCP) marking of the GTP-U packets according to allowed-QoS to PHB
mapping. The default mapping matches that of the UMTS to IP QoS mapping defined in 3GPP TS 29.208.
mapping. The default mapping matches that of the UMTS to IP QoS mapping defined in 3GPP TS 29.208.
The SGSN also supports DSCP marking of the GTP control plane messages on the Gn/Gp interface. This allows QoS to
be set on GTP-C messages, and is useful if Gn/Gp is on a less than ideal link. DSCP marking is configurable via the
CLI, with default = Best Effort Forwarding.
be set on GTP-C messages, and is useful if Gn/Gp is on a less than ideal link. DSCP marking is configurable via the
CLI, with default = Best Effort Forwarding.
Traffic Policing
The SGSN can police uplink and downlink traffic according to predefined QoS negotiated limits fixed on the basis of
individual contexts - either primary or secondary. The SGSN employs the Two Rate Three Color Marker (RFC2698)
algorithm for traffic policing. The algorithm meters an IP packet stream and marks its packets either green, yellow, or
red depending upon the following variables:
individual contexts - either primary or secondary. The SGSN employs the Two Rate Three Color Marker (RFC2698)
algorithm for traffic policing. The algorithm meters an IP packet stream and marks its packets either green, yellow, or
red depending upon the following variables:
PIR - Peak Information Rate (measured in bytes/second)
CIR - Committed Information Rate (measured in bytes/second)
PBS - Peak Burst Size (measured in bytes)
CBS - Committed Burst Size (measured in bytes)
The following figure depicts the working of the TCM algorithm: