2. Qos
Users (applications) need a variety of services
–Guaranteed bit rate (voice)
–High speed throughput (video)
–Priority service (emergency call)
QoS is defined using
QCI (includes GBR/non-GBR, RLC AM/UM, delay and
packet loss)
ARP (allocation retention priority)
GBR, MBR
AMBR, etc.
3. parameters
QoS Class Identifier (QCI)
•Defines packet forwarding treatment at each node, e.g., queuing thresholds, scheduling weight,
admission control priority, etc.
•Nine standardized QCI values with different characteristics – GBR/non-GBR, priority, delay sensitivity,
and packet error loss rate e.g., QCI 1 is defined for a GBR bearer for conversational or voice traffic
Maximum bit rate (MBR, AMBR)
•Maximum allowable bit rate for a GBR bearer or Aggregate Maximum bit rate for all non-GBR bearers
combined
•AMBR defined on per APN and per subscriber basis
Allocation and Retention Priority (ARP)
•“Allocation” dictates control plane behavior during bearer setup, modification procedures, etc.
•“Retention” determines relative priority of a bearer over other bearers in case of congestion
•Fifteen different ARP (priority) levels – 1 being the highest priority
Dedicated / Default Bearers
•Default bearer (one per UE IP) setup on Attach provides basic connectivity – best effort QoS, non-
GBR
•One or more Dedicated bearers setup for specific QoS requirements – can be GBR or non-GBR
5. Bearer
Radio Bearer: DTCH in LTE-Uu interface
S1 Bearer: GTP-U Tunnel over IP/UDP
S5/S8 Bearer: GTP-U Tunnel over IP/UDP
External Bearer: out-side of 3GPP scope
6. EPS Session
Bit rate consumption for GBR bearers is not included in either of these AMBR parameters. UE-AMBR is the upper bit rate
limit provided to UE, and is less than or equal to the total APN-AMBR of all active APNs to which UE is connected.
7. GBR / non-GBR
The channel feedback function maintains the channel state per UE which is utilized by
scheduling function. to prioritize UEs with good channel conditions. This function utilizes the CQI
(Channel Quality Indicator) feedback from UE for estimating downlink channel quality, and SRS
(Sounding Reference Signal) feedback for estimating uplink channel quality.
The Radio Resource Allocation function allocates the actual frequency resources on PDCCH,
PDSCH, and PUSCH channels.
9. Default Bearer
MME -> eNodeB -> UE Activate Default Bearer Request
•The Attach Accept is carried as NAS payload in the Initial Context Setup
Request
•The EPS Bearer id identifies the bearer that needs to be activated
•The EPS QoS carries quality of service information:
QCI to assign session priority
The maximum bit rate for the bearer
Guaranteed bit rate for the bearer
•The Access Point Name (APN) is included in the message
•The PDN IP address assigned by the HSS is passed to the UE
19. Throughput
•eNB limits the DL throughput per bearer not exceeding its MBR.
UL throughput per UE is controlled by eNB Scheduler via sending the UL-Grant.
•Token bucket algorithm is used to control the DL GBR bearer rate.
DL packets will be discarded if no token in the bucket. Token will be added to the
bucket in MBR rate. Bucket volume will afford short-term packet bursts.
•Non-GBR bearers per UE will share the bucket of AMBR rate.
