1. Chapter 2
GPRS protocols
Contents:
2.1 Signalling Protocols used in GSM
2.2 Control Plane and User Plane in GPRS overview
1. User Data and Signalling
2. GPRS User plane (Rel 99)
3. Protocol used on the air-summary
4. Protocols used on GB and Gn summary
5. User data handling
6. GPRS control plane (Rel 99)
2.3 Other Interfaces
1. The Abis interface
2. Nokia solution for the Dynamic Abis
3. SS7 Interfaces in GPRS CN
2.4 GPRS protocols Rel 5
1. Evolved user plane for PS (Rel 5)
2. Evolved control plane for iu PS (Rel 5)
2.5 The GPRS Service
1. QoS Parameter (Rel 97/98)
2. QoS Parameter (Rel 99)
3. QoS Parameter comparison
2. 2.1 Signalling Protocols used in GSM
There are three layers defined for signalling on Um in
GSM: HLR AC VLR EIR
Layer 1 serves for the physical transmission and
includes aspects as e.g. logical channels, FDMA, In GSM-PLMN phase 1/2 the
TDMA, multiframes, channel coding, etc.) Signaling System No. 7 (SS7) is
Layer 2 functions on Um are performed by a modified used for the transmission of
LAPD protocol (LAPDm). MAP signalling information between
Layer 3 on the Um radio interface is subdivided into the components of the network
three sublayers: radio resource management RR TCAP switching sub-system NSS
(channel administration, power control and handover), SCCP (interfaces B-G), as well as
mobility management MM and connection between MSC and BSC (A-
management CM. The connection management L3
interface) and in direction of the
consists of: call control CC, supplementary services L2 MTP external ISDN networks.
SS and short message services SMS
L1
Um Abis
BTS MSC
ISDN
BSC
A
MS CM
CC SS SMS BSSAP ISUP
MM RSL/O&M/L2ML BSSMAP DTAP SCCP
RR SCCP
LAPD
MTP
LAPDm MTP
L1
L1
3. Chapter 2
GPRS protocols
2.2 Control Plane and User Plane in GPRS overview
1. User Data and Signalling
2. GPRS User plane (Rel 99)
3. Protocol used on the air-summary
4. Protocols used on GB and Gn summary
5. User data handling
6. GPRS control plane (Rel 99)
4. User data and “Signalling”
GSM is a circuit switched technology. The Resources are split into Signalling Resources (e.g. signalling channels
on the air) and resources for user data.
Because GPRS is by its structure a packet switched technology it is possible to separate signalling and user data
logically but not physically. So user data and high layer signalling use partly common procedures, so the protocol
stack should be spitted. Protocols used for user data and for signalling are finally distinguished in the CN. This
allows a network evolution without the need to redesign the complete system. The high layer signalling is even
reused for 3G.
User Plane
A layered protocol structure was designed in GPRS to realize the transfer of user information. Associated
with the information transfer, control procedures were designed in one or more levels such as
•error correction,
•error recovery,
•flow control,
•multiplexing and de-multiplexing, and
•segmentation and re-assembly.
The transmission plane of the NSS is based on a packet switched IP network. It is kept independent from the
BSS and the radio interface.
Control plane
The signalling plane consists of protocols responsible both for control and support of the transmission plane
functions:
•controlling the GPRS network access connections, such as „attaching to“ and „detaching from“ the GPRS
network.
•controlling the attributes of an established network access connection, such as activation of a PDP address.
•controlling the routing path of an established network connection in order to support user mobility.
•controlling the assignment of network resources to meet changing user demands.
5. GPRS User plane (Rel 99)
Application Application
TCP/UDP TCP/UDP
IP v 4/6 IP v 4/6
Relay
SNDCP SNDCP GTP GTP
LLC LLC UDP / UDP /
TCP TCP
Relay L2
RLC RLC BSSGP BSSGP
IP IP
NS NS
MAC MAC L2 L2
FR FR
GSM RF GSM RF L1 L1 L1 L1 L1
Um Gb Gn Gi
MS BSS SGSN GGSN External
SNDCP: SubNetwork Dependent
Convergence Protocol BSSGP: BSS GPRS Protocol GTP: GPRS Tunnelling Protocol
LLC: Logical Link Control NS: Network Service UDP: User Datagram Protocol
RLC: Radio Link Control FR: Frame Relay TCP: Transmission Control Protocol
MAC: Medium Access Control IP: Internet Protocol
6. Protocol used on the air-summary
GSM RF The GSM RF is the physical radio channel used to transfer the data packets.
MAC The Media Access Control layer provides the access to the physical radio resource. That means it is
responsible for the physical allocation of a packet data channel. It is strong associated with the RLC layer.
RLC The Radio Link Control layer provides an reliable link over the air interface that fits the block structure of the
physical channel. Therefore it segments and re ‑assembles the LLC frames.
Additionally it performs a sub-multiplexing to multiplex several MS on one physical channel and a channel
combining to provide up to eight physical channels to one MS. The RLC layer is strongly associated with the
MAC layer and performs additionally signalling tasks.
BSSGP The BSS GPRS Protocol is used to transfer the LLC frames together with related information between
SGSN and PCU. Information as QoS and routing information. Additionally node management information are
transferred by the BSSGP.
LLC The Logical Link Control layer provides the service necessary to maintain the communication capability
between the MS and the SGSN. From the point of the LLC layer there is an established connection between MS
and SGSN even if the RLC/MAC layer does not provide any physical connection. The physical connection will be
established by the RLC/MAC layer only if the LLC layer has data available to transmit. The LLC layer provides
several access points to transfer different kinds of data and to distinguish between different QoS classes.
Additionally the LLC performs the ciphering function.
SNDCP The Sub-Network Dependent Convergence Protocol supports the following tasks:
· compression
· segmentation/re-assembling
· multiplexing/de-multiplexing of data packets to one ore more LLC SAPs.
If applicable user data and the header is compressed. The segmentation is necessary to delimit the amount of
data which is transferred by the LLC over the air interface as a single unit.
7. Protocols used on GB and Gn summary
FR
Frame Relay is the link layer protocol, which is used to connect the SGSN with the PCU. Alternatively Ethernet
connections can be used as link layer protocol on the Gb interface as well (defined in Rel 4).
NS
This layer transports BSSGP PDUs. Network Service is based on the Frame Relay (or IP) connection between
BSS and SGSN, and may be multi-hop and traverse a network of Frame Relay (or IP) switching nodes.
BSSGP
The BSS GPRS Protocol is used to transfer the LLC frames together with related information between SGSN and
PCU. E.g. QoS and routing information. Additionally node management information are transferred by the BSSGP.
On Gn interface the IP payload is transported on behalf of so-called T-PDUs using a GPRS Tunnelling Protocol
(GTP) tunnel. The transport layer for this tunnel can be based on different technologies, for instance
Ethernet/Internet Protocol (IP) or Frame Relay as well. For reliable data transfer User Datagram Protocol (UDP)
provides unacknowledged and Transport Control Protocol (TCP) provides acknowledged transfer services.
The protocol suite on Gi interface is the same as known from the Internet or other kinds of packed data networks.
BSS
Gb BSSGP
BSS
GP GPRS
Gn
Protocol
GTP GTP
NS Network
NS
Service
8. User data handling in MS (UL)
Application
e.g. IP-packet
Network PDU (NPDU)
IP v 4/6
compression/segmentation
SNDCP SNDCP PDU (SN-PDU)
LLC
LLC-PDU LLC-PDU
LLC segmentation
RLC
RLC Block RLC Block
MAC Block
MAC
channel coding
GSM RF
Burst Burst Burst Burst
9. GPRS control plane (Rel 99)
In LLC Distinction between signalling and
user data coming from the MS is
header done finally in the SGSN with the
help of the LLC protocol
GTP-C (GPRS Tunneling Protocol-Control)
to separate from GTP-U (user plane)
GMM/SM/ GMM/SM/
GTP-C GTP-C
SMS SMS
LLC LLC UDP / UDP /
TCP TCP
Relay
RLC RLC BSSGP BSSGP
IP IP
NS NS
MAC MAC L2 L2
FR FR
GSM RF GSM RF L1 L1 L1 L1
Um Gb Gn Gi
MS BSS SGSN GGSN
10. Chapter 2
GPRS protocols
2.3 Other Interfaces
1. The Abis interface
2. Nokia solution for the Dynamic Abis
3. SS7 Interfaces in GPRS CN
11. The Abis interface
The functional part of the BSS has to be split up into
functions performed by the BTS and the PCU. In
Relay
between the two a vendor specific format is used. The RLC BSSGP
PCU frames. RLC/MAC functions are performed by the
PCU , Channel coding and RF generation are NS
performed by the BTS. The increased throughput of
MAC
especially CS 3 and 4 and EGPRS compared with GSM
requires a new solution, a dynamic Abis. That means FR
the resource on demand principle is as well realized on GSM RF L1
abis. In most vendors cases concatenated PCU frames
can be found.
BSS SNDCP
LLC
Relay
RLC RLC BSSGP
BSSGP
MAC MAC NS NS
PCU PCU FR FR
GSM GSM Frames Dynamic Frames
RF RF Abis PCM L1 L1
PCM
MS Um BTS Abis BSC Gb SGSN
12. Nokia solution for the Dynamic Abis
Abis PCM allocation
Coding Scheme Bit rate (bps) fixed pool
CS-1 8,000
CS-2 12,000
GMSK GPRS
CS-3 14,400
CS-4 20,000
MCS-1 8,800
GMSK MCS-2 11,200
MCS-3 14,800 Slave Groups
MCS-4 17,600
MCS-5 EDGE 22,400
MCS-6 29,600
8-PSK MCS-7 44,800
MCS-8 54,400
MCS-9 59,200
1 2 3 4 5 6 7 8
9 TCH:TRX:5:1 TCH:TRX:5:2 TCH:TRX:5:3 TCH:TRX:5:4 In this solution each TS on the TRXs gets
10 TCH:TRX:5:5 TCH:TRX:5:6 TCH:TRX:5:7 TCH:TRX:5:8 its fixed subslot on the PCM, a group of
11 TCH:TRX:6:1 TCH:TRX:6:2 TCH:TRX:6:3 TCH:TRX:6:4
12 TCH:TRX:6:5 TCH:TRX:6:6 TCH:TRX:6:7 TCH:TRX:6:8
other subslots gives the Dynamic Abis Pool
13 (DAP). Depending on the availability of
14 EDGE Dynamic Abis Pool subslots and the throughput on the air
15
16TRXSIG:TRX:1 TRXSIG:TRX:2 additional subslots (slaves) are allocated to
the TS temporarilly.
13. SS7 Interfaces in the GPRS CN
MSC/VLR HLR AC EIR
Gs Based on BSSAP+
Gr Gc Based on MAP Gf
Gs (SGSN-MSC) is optional:
BSSAP+ MAP
-Combined GPRS/IMSI attach and detach TCAP
-Combined RA/LA update
SCCP SCCP
-Circuit switched services paging via GPRS
network L3 L3 MTP may be
-Non-GPRS alerts replaced by
L2 Gs
MTP L2 MTP
-Identification procedure IP
-MM information procedure L1 L1
Gc (GGSN-HLR) Interface is optional and usually not implemented.
It would be required for an external networks initiated SGSN GGSN
“Packet call’ (PDP context activation).
Gf (SGSN-EIR) Interface is optional. It allows the Equipment Identity check to verify the IMEI.
Gr (SGSN-HLR) Interface is mandatory! it is required to allow an MS to register in a GPRS PLMN via
SGSN. For example Security information is provided, the Location in the HLR is updated, … the same
procedures as known from the the D interface (MSC/VLR-HLR) take place.
14. Chapter 2
GPRS protocols
2.4 GPRS protocols Rel 5
1. Evolved user plane for PS (Rel 5)
2. Evolved control plane for iu PS (Rel 5)
15. Evolved user plane for PS (Rel 5)
For Iu mode:Compression,
Ciphering,
celll level Mobility,
buffer management
MS GERAN SGSN
Gb mode Iu mode
SNDCP SNDCP
LLC LLC
Relay
IP
BSSGP BSSGP
option
GTP-U GTP-U
Network Network
Rel 4
PDCP PDCP
Service UDP/IP UDP/IP Service
Ack /Unack Ack / Unack
RLC RLC RLC RLC IP IP
FR FR
MAC MAC L2 L2 L2 L2
Um L1 Gb L1
PHY PHY L1 L1
Iu-ps
Common protocols
PDCP Packet Data Convergence Protocol
Iu influenced protocols Layer 1,2, not further specified,
RLC Radio Link Protocol
Gb influenced protocols RANAP Radio Access Network Application Part IP option, ATM option
16. Evolved control plane for iu PS (Rel 5)
MS GERAN SGSN
GMM/SM GMM/SM
LLC LLC
Relay
BSSGP
BSSGP
RRC RRC RANAP RANAP
RR RR
Network Network
Service SCCP SCCP Se
Service
As Defined As Defined
RLC IP in Iu Specs in Iu Specs. IP
Ack/NACK RLC RLC RLC
LAPDm LAPDm Ack/NACK FR L3 L3 FR
L2 L2
MAC MAC L2 L2
Gb
L1 L1
PHY Um PHY
L1 L1
Iu-ps
Common protocols
Iu influenced protocols Layer 1,2, 3 not further specified,
Gb influenced protocols IP option, ATM option
18. QoS Parameter (Rel 97/98)
A GPRS Subscriber profile describes a service in terms of QoS parameters. The GPRS subscription is stored in
the HLR. When a Service is activated the network is requested to provide a bearer with the described
characteristics. Corresponding the network will use Ack/Nack mode on the different interfaces for example. The
indicated values shall reflect the network performance as seen by the end user.
Delay Class
Delay Class mean transfer 95% delay mean transfer 95% delay
delay (sec) (sec) delay (sec) (sec)
Precedence Class 1 < 0,5 < 1,5 <2 <7
2 <5 < 25 < 15 < 75
1: high priority 3 < 50 < 250 < 75 < 375
2: normal priority 4 (Best Effort) unspecified unspecified unspecified unspecified
3: low priority
SDU size: 128 Byte 1024 Byte
Reliability Class
1 - 5 (lowest): peak throughput Class
• data loss probability 1 - 9: > 8 kbit/s - >2048 kbit/s
• out of sequence probability maximum data rate
• duplicate probability no guarantee for this data rates
• corrupt data probability over a longer period of time
probabilities 10-9 - 10-2
mean throughput Class
medium, guaranteed data rate; Class 1 - 19:
1: best effort
100 Byte/h (0,22 bit/s) / 200 / 500 / 1000 / ... /
50 Mio. Byte/h (111 kbit/s)
19. QoS Parameter (Rel 99)
With the Release 99 the services are categorized according to
Conversational class (Real Time services e.g. voice over IP, low delay and delay variation, preserved time
relationship)
Streaming class (Real Time audio- and video streaming, one direction only)
Interactive Background class (request, response pattern, e.g. WWW browsing, telnet applications, Round
Trip Time sensible)
Background class (best effort, e.g. e-mail, file transfer, SMS, Bit error sensible)
New attributes are used to describe the required Quality of Service in Rel 99.
Max Bitrate Guaranteed
Transfer delay bitrate
Delivery of
erroneous SDU Error Ratio
SDU’s
QoS Profile Rel 99
Allocation /
Retention Traffic Handling
Priority Priority
Delivery Residual Bit
order Error Ratio
20. QoS Parameter (Rel 99)
Maximum bitrate (kbps) The Maximum bit-rate is the upper limit an application can accept or provide. The network does
not guarantee the maximum bitrate.
It indicates the guaranteed number of bits delivered by network within a period of time (provided that
Guaranteed bitrate (kbps)
there is data to deliver), divided by the duration. Guaranteed bitrate is only used for real-time traffic.
Delivery order (y/n) Indicates whether the PDP context shall provide in- sequence SDU delivery or not.
Maximum SDU size (octets) Indicates the maximum allowed SDU size (used for Admission control and policing).
SDU format information (bits) Lists all possible exact sizes of SDUs. Used to achieve better spectral efficiency and reduce delay
when RLC retransmission is not used.
It indicates the fraction of SDUs lost or detected as erroneous. For Conversational and
SDU error ratio Streaming the SDU error ratio performance is independent of the loading conditions, whereas in
Interactive and Background classes SDU error ratio is used as a target value.
Residual bit error ratio It indicates the undetected bit error ratio in the delivered SDUs. If no error detection is requested it
indicates the BER in the delivered SDUs.
Is used to decide whether error detection is needed and whether packets with detected errors shall
be forwarded or not.
Delivery of erroneous SDUs Yes: error detection is employed and erroneous SDUs are delivered together with an error
indication.
No: error detection is employed and erroneous SDUs are discarded.
Not in use: SDUs are delivered 95th percentile of the distribution of delay for all delivered SDUs
It indicates maximum delay for without considering error detection.
Transfer delay (ms) during the lifetime of the PDP context. It is used to specify the delay tolerated by the application.
Traffic Handling Priority (THP)It specifies the relative importance for handling SDUs belonging to one PDP context compared to
the SDUs of other PDP contexts. The THP is only used within the Interactive Traffic Class.
It specifies the relative importance of a PDP context compared to other PDP contexts and can be
Allocation/Retention Priority used by the network when performing admission control and resource allocation. The
Allocation/Retention Priority attribute is a subscription attribute set in the HLR which cannot be
negotiated from the mobile terminal.
21. QoS Parameter comparison
R97/R98 R99/R4/R5
GPRS/UMTS R99/R4/R5 QoS parameters
Conversational Streaming Interactive Background
class class class class
Precedence Allocation/ Allocation/retention
1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3
class retention priority priority
Traffic handling
1, 2, 3
priority
Interactive
Delay class class Transfer delay <100 ms <250 ms
Traffic handling
priority Residual BER 5*10-2…10-6 5*10-2…10-6 4*10-3…6*10-8 4*10-3…6*10-8
Background SDU error ratio 10-2…10-5 10-1…10-5 10-3…10-6 10-3…10-6
class
< 2048 kbps < 2048 kbps
Maximum bitrate < 2048 kbps < 2048 kbps
-overhead -overhead
Residual BER Guaranteed bitrate <2048 kbps <2048 kbps
Reliability class
SDU error ratio Maximum SDU size <=1500 octets <=1500 octets <=1500 octets <=1500 octets
Delivery of Delivery order Yes/No Yes/No Yes/No Yes/No
erroneous SDUs
SDU format
information
Peak through- Maximum Delivery of
Yes/No/- Yes/No/- Yes/No/- Yes/No/-
put class bitrate erroneous SDUs
