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Chapter 2
GPRS protocolsContents:2.1 Signalling Protocols used in GSM 2.2 Control Plane and User Plane in GPRS overview
1. User Data and Signalling2. GPRS User plane (Rel 99)3. Protocol used on the air-summary4. Protocols used on GB and Gn summary5. User data handling6. GPRS control plane (Rel 99)
2.3 Other Interfaces1. The Abis interface2. Nokia solution for the Dynamic Abis3. SS7 Interfaces in GPRS CN
2.4 GPRS protocols Rel 51. Evolved user plane for PS (Rel 5)2. Evolved control plane for iu PS (Rel 5)
2.5 The GPRS Service1. QoS Parameter (Rel 97/98)2. QoS Parameter (Rel 99) 3. QoS Parameter comparison
2.1 Signalling Protocols used in GSM
HLR AC VLR EIR
BTS
MS
MSC
MTP
ISUP
SCCP
MTP
SCCP
BSSAP
DTAPBSSMAP
L1LAPDm
RR
MM
CMCC SS SMS
L1
LAPD
RSL/O&M/L2ML
BSCISDN
L1
L2
L3
MTP
SCCP
TCAP
MAP
Abis
A
In GSM-PLMN phase 1/2 the Signaling System No. 7 (SS7) is used for the transmission of signalling information between the components of the network switching sub-system NSS (interfaces B-G), as well as between MSC and BSC (A-interface) and in direction of the external ISDN networks.
There are three layers defined for signalling on Um in GSM:Layer 1 serves for the physical transmission and includes aspects as e.g. logical channels, FDMA, TDMA, multiframes, channel coding, etc.)Layer 2 functions on Um are performed by a modified LAPD protocol (LAPDm).Layer 3 on the Um radio interface is subdivided into three sublayers: radio resource management RR (channel administration, power control and handover), mobility management MM and connection management CM. The connection management consists of: call control CC, supplementary services SS and short message services SMS
Um
Chapter 2
GPRS protocols2.2 Control Plane and User Plane in GPRS overview
1. User Data and Signalling2. GPRS User plane (Rel 99)3. Protocol used on the air-summary4. Protocols used on GB and Gn summary5. User data handling6. GPRS control plane (Rel 99)
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.
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.
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.•providing supplementary services.
Control plane
User Plane
GPRS User plane (Rel 99)
MS BSS SGSN ExternalUm Gb Gn Gi
MAC
GSM RF
RLC
LLC
SNDCP
IP v 4/6
ApplicationTCP/UDP
MAC
GSM RF
RLC
NS
FR
L1
BSSGP
Relay
NS
FR
L1
BSSGP
LLC
SNDCP
L1
L2 L2
IP IP
UDP /TCP
UDP /TCP
GTP GTP
Relay
L1
SNDCP: SubNetwork Dependent Convergence ProtocolLLC: Logical Link ControlRLC: Radio Link ControlMAC: Medium Access Control
BSSGP: BSS GPRS ProtocolNS: Network ServiceFR: Frame Relay
GTP: GPRS Tunnelling ProtocolUDP: User Datagram ProtocolTCP: Transmission Control ProtocolIP: Internet Protocol
L2
IP v 4/6
L1
ApplicationTCP/UDP
GGSN
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.
Protocols used on GB and Gn summary
FRFrame 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). NSThis 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.
BSSGPThe 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.
NS NetworkService
BSSGPBSS
GPRSProtocol
NS
BSSGP
GTP GTP
GbGn
User data handling in MS (UL)
SNDCP PDU (SN-PDU)
LLC-PDU
RLC Block
MAC Block
Network PDU (NPDU)e.g. IP-packet
LLC-PDU
RLC Block
Burst Burst Burst Burst
channel codingMAC
GSM RF
RLC
LLC
SNDCP
IP v 4/6
Application
LLC segmentation
compression/segmentation
GPRS control plane (Rel 99)
MS BSS SGSNUm Gb
MAC
GSM RF
RLC
LLC
GMM/SM/SMS
MAC
GSM RF
RLC
NS
FR
L1
BSSGPRelay
NS
FR
L1
BSSGP
LLC
GMM/SM/SMS
SGSN GGSNGn Gi
L1
L2 L2
IP IP
UDP /TCP
UDP /TCP
GTP-C GTP-C
L1
GTP-C (GPRS Tunneling Protocol-Control) to separate from GTP-U (user plane)
In LLC heade
r
Distinction between signalling and user data coming from the MS is done finally in the SGSN with the
help of the LLC protocol
Chapter 2
GPRS protocols2.3 Other Interfaces
1. The Abis interface2. Nokia solution for the Dynamic Abis3. SS7 Interfaces in GPRS CN
The Abis interface
GSM RF
MAC
RLC
GSM RF PCM
PCU Frames Dynamic
Abis
BSS
MAC
GSM RF
RLC
NS
FR
L1
BSSGPRelay
The functional part of the BSS has to be split up into functions performed by the BTS and the PCU. In between the two a vendor specific format is used. The PCU frames. RLC/MAC functions are performed by the PCU , Channel coding and RF generation are performed by the BTS. The increased throughput of especially CS 3 and 4 and EGPRS compared with GSM requires a new solution, a dynamic Abis. That means the resource on demand principle is as well realized on abis. In most vendors cases concatenated PCU frames can be found.
MS BTS SGSNUm Gb
MAC
RLC
PCM
PCU Frames
NS
FR
L1
BSSGP
Relay
NS
FR
L1
BSSGP
LLC
SNDCP
BSCAbis
Nokia solution for the Dynamic Abis
Abis PCM allocation
fixed poolCoding Scheme Bit rate (bps)
CS-1 8,000
CS-2 12,000
CS-3 14,400
CS-4 20,000
MCS-1 8,800
MCS-2 11,200
MCS-3 14,800
MCS-4 17,600
MCS-5 22,400
MCS-6 29,600
MCS-7 44,800
MCS-8 54,400
MCS-9 59,200
Slave Groups
GMSK
8-PSK
GMSK
EDGE
GPRS
9 TCH:TRX:5:1 TCH:TRX:5:2 TCH:TRX:5:3 TCH:TRX:5:410 TCH:TRX:5:5 TCH:TRX:5:6 TCH:TRX:5:7 TCH:TRX:5:811 TCH:TRX:6:1 TCH:TRX:6:2 TCH:TRX:6:3 TCH:TRX:6:412 TCH:TRX:6:5 TCH:TRX:6:6 TCH:TRX:6:7 TCH:TRX:6:813141516
EDGE Dynamic Abis Pool
1 2 3 4 5 6 7 8
TRXSIG:TRX:1 TRXSIG:TRX:2
In this solution each TS on the TRXs gets its fixed subslot on the PCM, a group of other subslots gives the Dynamic Abis Pool (DAP). Depending on the availability of subslots and the throughput on the air additional subslots (slaves) are allocated to the TS temporarilly.
Gc (GGSN-HLR) Interface is optional and usually not implemented. It would be required for an external networks initiated “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.
SS7 Interfaces in the GPRS CN
HLR AC EIR
Gs (SGSN-MSC) is optional:
-Combined GPRS/IMSI attach and detach -Combined RA/LA update-Circuit switched services paging via GPRS network-Non-GPRS alerts-Identification procedure-MM information procedure
SGSN GGSN
MSC/VLR
Based on BSSAP+ Based on MAP Gr Gc GfGs
L1
L2
L3
MTP
SCCP
TCAP
MAP
GsL1
L2
L3
MTP
SCCP
BSSAP+
MTP may be replaced by
IP
Chapter 2
GPRS protocols2.4 GPRS protocols Rel 5
1. Evolved user plane for PS (Rel 5)2. Evolved control plane for iu PS (Rel 5)
Evolved user plane for PS (Rel 5)
PHY
RLC
PDCP
LLC
SNDCP
PHY
RLC
PDCP
SNDCP
LLC
BSSGP
NetworkService
Iu-ps
GbUm
Relay
/Ack UnackRLC
MACMAC
/Ack UnackRLC
FRIP
L2FR
BSSGP
NetworkService
IP
L2
L1L1L1
GTP-U
L2
UDP/IP
L1
GTP-U
L2
UDP/IP
Iu modeGb mode
PDCP Packet Data Convergence ProtocolRLC Radio Link ProtocolRANAP Radio Access Network Application Part
For Iu mode:Compression, Ciphering, celll level Mobility, buffer management
Common protocolsIu influenced protocolsGb Gb influenced protocols
IP option Rel 4
Layer 1,2, not further specified,IP option, ATM option
MS GERANGERAN SGSN
Evolved control plane for iu PS (Rel 5)
RLC RLC
RRC NetworkService
Iu-ps
MS
Relay
GERAN
MAC
Common protocolsIu influenced protocolsGb
FR FR
NetworkService
L1
IP
LAPDm LAPDm
RRC
RLC
PHY
RLC
RRC
NetworkService
GbUm
GERAN SGSN
MACMAC
Gb influenced protocols
FR
Se
LAPDm LAPDm
RRRRC
L2
L1
RANAP
SCCP
As Definedin Iu Specs
L3
L2
L1
RANAP
SCCP
As Definedin Iu Specs.
L3
Layer 1,2, 3 not further specified,IP option, ATM option
L1PHY
BSSGP
RR
LLCLLC
GMM/SMGMM/SM
BSSGP
IP
L2 L2
RLCAck/NACK RLC
Ack/NACK
Chapter 2
GPRS protocols2.5 The GPRS Service
1. QoS Parameter (Rel 97/98)2. QoS Parameter (Rel 99) 3. QoS Parameter comparison
Precedence Class1: high priority2: normal priority3: low priority
Delay Class mean transferdelay (sec)
95% delay(sec)
mean transferdelay (sec)
95% delay(sec)
1 < 0,5 < 1,5 < 2 < 72 < 5 < 25 < 15 < 753 < 50 < 250 < 75 < 3754 (Best Effort) unspecified unspecified unspecified unspecified
Delay Class
SDU size: 128 Byte 1024 Byte
Reliability Class1 - 5 (lowest):
• data loss probability• out of sequence probability
• duplicate probability• corrupt data probabilityprobabilities 10-9 - 10-2
peak throughput Class1 - 9: > 8 kbit/s - >2048 kbit/s
maximum data rateno guarantee for this data rates
over a longer period of time
mean throughput Classmedium, guaranteed data rate; Class 1 - 19:
1: best effort100 Byte/h (0,22 bit/s) / 200 / 500 / 1000 / ... /
50 Mio. Byte/h (111 kbit/s)
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.
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.
QoS Profile Rel 99SDU Error Ratio
Residual Bit Error Ratio
Delivery of erroneous
SDU’s
Max Bitrate
Deliveryorder
Guaranteed bitrateTransfer delay
Traffic HandlingPriority
Allocation /Retention
Priority
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.
Guaranteed bitrate (kbps) It indicates the guaranteed number of bits delivered by network within a period of time (provided that 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.
SDU error ratioIt indicates the fraction of SDUs lost or detected as erroneous. For Conversational and 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.
Delivery of erroneous SDUs
Is used to decide whether error detection is needed and whether packets with detected errors shall be forwarded or not. 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 without considering error detection.
Transfer delay (ms)It indicates maximum delay for 95th percentile of the distribution of delay for all delivered SDUs 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.
Allocation/Retention PriorityIt specifies the relative importance of a PDP context compared to other PDP contexts and can be 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.
QoS Parameter comparison
Yes/No
Yes/No/-
< 2048 kbps
<2048 kbps
<=1500 octets
<100 ms
5*10-2…10-6
10-2…10-5
1, 2, 3
Yes/No
Yes/No/-
< 2048 kbps
<2048 kbps
<=1500 octets
<250 ms
5*10-2…10-6
10-1…10-5
1, 2, 3
Yes/No
Yes/No/-
< 2048 kbps-overhead
<=1500 octets
4*10-3…6*10-8
10-3…10-6
1, 2, 3
1, 2, 3
Yes/No
Yes/No/-
< 2048 kbps-overhead
<=1500 octets
4*10-3…6*10-8
10-3…10-6
1, 2, 3
Conversationalclass
Streamingclass
Interactiveclass
Backgroundclass
Delivery order
SDU formatinformation
Delivery oferroneous SDUs
Maximum bitrate
Guaranteed bitrate
Maximum SDU size
Transfer delay
Residual BER
SDU error ratio
Allocation/retentionpriority
Traffic handlingpriority
GPRS/UMTS R99/R4/R5 QoS parameters
Precedence class
Allocation/retention priority
Delay classInteractiveclass
Backgroundclass
Traffic handlingpriority
Reliability class
Delivery oferroneous SDUs
Residual BER
SDU error ratio
R97/R98 R99/R4/R5
Peak through-put class
Maximum bitrate