QoS refers to 'Quality of Service'.
After 'PDP context activation' procedure completes, a 'PDP context' shall exist on the MS, the SGSN, and the GGSN. In addition, the GGSN assigns a QoS for this 'PDP context'.
This QoS describes the priority that the nodes shall give to traffic belonging to this 'PDP context'.
The subscription data of the MS exist in the HLR, contains the QoS subscribed for this MS.
During 'PDP activation' procedure, the SGSN will compare the requested QoS from the MS against the subscription data. This is done in order to guarantee the MS doesn’t request privilege more than it should have.
Difference between QoS 'Subscribed', 'requested', and 'Negotiated'
- Subscribed, the one that exist in user subscription data in the HLR.
- Requested, the one the MS requests in 'Activate PDP context' message.
- Negotiated, the one assigned to the 'PDP context' after negotiation is finished between network nodes.
Attributes exist in Qos Profile,
There are four different classes,
- Conversational class;
- Streaming class;
- Interactive class; and
- Background class.
The main distinguishing factor between these classes, is how delay sensitive is the traffic. As example,
- Conversational class is suitable for traffic which is very delay sensitive, like 'Skype' as example.
- While Background class is the most delay insensitive traffic class, like downloading files as example.
Maximum bitrate (kbps)
- Defines the maximum bit rate that is available to the 'PDP context'.
Guaranteed bitrate (kbps)
- Defines the minimum bit rate that is available to the 'PDP context'.
Traffic handling priority (THP)
- THP is the relative importance for handling data belonging to one PDP context compared to other PDP contexts.
- Priorities between 1 and 14 are ordered in decreasing order , '1' is the highest priority, while '14' the lowest.
Allocation/Retention Priority (ARP)
- When network resources are limited, and the network will not be able to establish PDP contexts for all the requesting MSs. In this case, the network uses the ARP value to decide it should establish the contexts for which MSs.
- ARP values range from 1 to 3, where 1 corresponds to the highest priority, while 3 corresponds to the lowest priority.
Evolved Allocation/Retention Priority
This puts additional information to the ARP value. Those information are,
- Pre-emption capability, determines if the PDP context with high ARP value should be created, even if the network should drop another context.
- Pre-emption vulnerability, determines if the context with low ARP value will be dropped, in case resources are needed to establish another context with high ARP.
Maximum SDU size (octets)
- SDU refers to 'Service Data Unit'.
- Maximum SDU is the maximum data packet size for which the network shall satisfy the negotiated QoS.
- Handling packets with size bigger than the 'maximum SDU size' is implementation specific, the network may drop them, or forward them with lower QoS.
QoS Attributes unrelated to specific PDP context
The MS may have more than one PDP context established. Below QoS are related to the aggregate PDPs for one MS,
- The 'APN-Aggregated Maximum Bit-rate', limits the aggregate bit rate that can exist across all PDP contexts of the same APN.
- The 'UE Aggregated Maximum Bit-rate', limits the aggregate bit rate that can exist across all PDP contexts of an MS.