GPRS for Mobile Internet
2.4 Quality of Service
The network associates a certain quality of service (QoS) with each data transmission in GPRS packet mode. The appropriate QoS is characterized according to a number of attributes negotiated between the MS and the network. Figure 2.2 characterizes the application in terms of error tolerance and delay requirements.
Figure 2.2: Applications in terms of QoS requirements. ( From - [1].)
A first list of attributes is defined in Release 97/98 of the 3GPP recommendations. It was replaced in the release 99 by new attributes.
2.4.1 Attributes in Release 97/98
In Release 97/98 of the 3GPP recommendations, QoS is defined according to the following attributes:
-
Precedence class. This indicates the packet transfer priority under abnormal conditions, as for example during a network congestion load.
-
Reliability class. This indicates the transmission characteristics; it defines the probability of data loss, data delivered out of sequence, duplicate data delivery, and corrupted data. This parameter enables the configuration of layer 2 protocols in acknowledged or unacknowledged modes.
-
Peak throughput class. This indicates the expected maximum data transfer rate across the network for a specific access to an external packet switching network (from 8 to 2,048 Kbps).
-
Mean throughput class. This indicates the average data transfer rate across the network during the remaining lifetime of a specific access to an external packet switching network (best effort, from 0.22 bps to 111 Kbps).
-
Delay class. This defines the end-to-end transfer delay for the transmission of service data units (SDUs) through the GPRS network. The SDU represents the data unit accepted by the upper layer of GPRS and conveyed through the GPRS network. Table 2.1 shows the delay classes.
Table 2.1: Delay Classes Delay (Maximum Values)
SDU size : 128 octets
SDU size: 1,024 octets
Delay Class
Mean Transfer Delay (s)
95 Percentile Delay (s)
Mean Transfer Delay (s)
95 Percentile Delay (s)
1. (Predictive)
< 0.5
< 1.5
< 2
< 7
2. (Predictive)
< 5
< 25
< 15
< 75
3. (Predictive)
< 50
< 250
< 75
< 375
4. (Best Effort)
Unspecified
From: [2].
The delay class for data transfer gives some information about the number of resources that have to be allocated for a given service. Predictive value in delay class means that the network is able to ensure an end-to-end delay time for the transmission of SDUs; best effort means that the network is not able to ensure a value for an end-to-end transfer delay; in this case transmission of SDUs depends on network load.
2.4.2 Attributes in Release 99
The attributes of GPRS QoS were modified in Release 99 of the 3GPP recommendations in order to be identical to the ones defined for UMTS. The attributes described below apply to both GPRS and UMTS standards. Table 2.2 gives the characteristics of the different classes.
| Traffic Class | Real-Time Conversational | Real-Time Streaming | Interactive Best Effort | Background Best Effort |
|---|---|---|---|---|
| Fundamental Characteristics | No transfer delay variation between the sender and the receiver; stringent and low delay transfer | No transfer delay variation between the sender and the receiver | Request response pattern; preserve pattern content | No time constraint; preserve pattern content |
| Example of Applications | Conversational voice and videophone | One-way video, audio streaming, still image, and bulk data | Web browsing, voice messaging and dictation, server access, and e-commerce | E-mail, SMS, and fax |
Four classes of traffic have been defined for QoS:
-
Conversational class. These services are dedicated to bidirectional communication in real time (e.g., voice over IP and videoconferencing).
-
Streaming class. These services are dedicated to unidirectional data transfer in real time (e.g., audio streaming, one-way video).
-
Interactive class. These services are dedicated to the transport of human or machine interaction with remote equipment (e.g., Web browsing, access to a server, access to a database).
-
Background class. These services are dedicated to machine-to-machine communication that is not delay sensitive (e.g., e-mail and SMS).
Table 2.3 lists the expected performance for conversational services.
| Key Performance Parameters and Target Values | ||||||
|---|---|---|---|---|---|---|
| Medium | Application | Degree of Symmetry | Data Rate | End-to-End One-Way Delay | Delay Variation Within a Call | Information Loss |
| Audio | Conversational voice | Two-way | 4-25 Kbps | <150 ms preferred <400 ms limit Note 1 | < 1 ms | < 3% of frame error rate |
| Video | Videophone | Two-way | 32-384 Kbps | < 150 ms preferred < 400 ms limit Lip-synch: <100 ms | < 1% of frame error rate | |
| Data | Telemetry - two-way control | Two-way | <28.8 Kbps | < 250 ms | N/A | Zero |
| Data | Interactive games | Two-way | < 1 KB | < 250 ms | N/A | Zero |
| Data | Telnet | Two-way (asymmetric) | < 1 KB | < 250 ms | N/A | Zero |
| From: [1]. | ||||||
Table 2.4 lists the expected performance for streaming services.
| Key Performance Parameters and Target Values | ||||||
|---|---|---|---|---|---|---|
| Medium | Application | Degree of Symmetry | Data Rate | One-Way Delay | Delay Variation | Information Loss |
| Audio | High-quality streaming audio | Primarily oneway | 32-128 Kbps | < 10 s | < 1 ms | <1% FER |
| Video | One-way | One-way | 32-384 Kbps | < 10 s | <1% FER | |
| Data | Bulk data transfer/ retrieval | Primarily oneway | < 10 s | N/A | Zero | |
| Data | Still image | One-way | < 10 s | N/A | Zero | |
| Data | Telemetry-monitoring | One-way | <28.8 Kbps | < 10 s | N/A | Zero |
| From: [1]. | ||||||
Table 2.5 lists the expected performance for interactive services.
| Key Performance Parameters and Target Values | ||||||
|---|---|---|---|---|---|---|
| Medium | Application | Degree of Symmetry | Data Rate | One-Way Delay | Delay Variation | Information Loss |
| Audio | Voice messaging | Primarily no way | 4-13 Kbps | < 1 sec for playback < 2 sec for record | < 1 ms | < 3% FER |
| Data | Web browsing-HTML | Primarily oneway | < 4 sec/page | N/A | Zero | |
| Data | Transaction services - high priority (e.g., e-commerce and ATM) | Two-way | < 4 sec | N/A | Zero | |
| Data | E-mail (server access) | Primarily oneway | < 4 sec | N/A | Zero | |
| From: [1]. | ||||||
The Release 99 of 3GPP recommendations defines attributes for QoS such as traffic class, delivery order, SDU format information, SDU error ratio, maximum SDU size, maximum bit rate for uplink, maximum bit rate for downlink, residual bit error ratio, transfer delay, traffic-handling priority, allocation/retention priority, and guaranteed bit rate for uplink and guaranteed bit rate for downlink.
-
Traffic class indicates the application type (conversational, streaming, interactive, background).
-
Delivery order indicates if there is in-sequence SDU delivery or not.
-
Delivery of erroneous SDUs indicates if erroneous SDUs are delivered or discarded.
-
SDU format information indicates the possible exact sizes of SDUs.
-
SDU error ratio indicates the maximum allowed fraction of SDUs lost or detected as erroneous.
-
Maximum SDU size indicates the maximum allowed SDU size (from 10 octets to 1,520 octets).
-
Maximum bit rate for uplink indicates the maximum number of bits delivered to the network within a period of time (from 0 to 8,640 Kbps).
-
Maximum bit rate for downlink indicates the maximum number of bits delivered by the network within a period of time (from 0 to 8,640 Kbps).
-
Residual bit error ratio indicates the undetected bit error ratio for each subflow in the delivered SDUs.
-
Transfer delay indicates the maximum time of SDU transfer for 95th percentile of the distribution of delay for all delivered SDUs.
-
Traffic-handling priority indicates the relative importance of all SDUs belonging to a specific GPRS bearer compared with all SDUs of other GPRS bearers .
-
Allocation/retention priority indicates the relative importance of resource allocation and resource retention for the data flow related to a specific GPRS bearer compared with the data flows of other GPRS bearers (useful when resources are scarce ).
-
Guaranteed bit rate for uplink indicates the guaranteed number of bits delivered to the network within a period of time (from 0 to 8,640 Kbps).
-
Guaranteed bit rate for downlink indicates the guaranteed number of bits delivered to the network within a period of time (from 0 to 8,640 Kbps).