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
2.1 Signalling Protocols used in GSMThere are three layers defined for signalling on Um inGSM: HLR AC VLR EIRLayer 1 serves for the physical transmission andincludes aspects as e.g. logical channels, FDMA, In GSM-PLMN phase 1/2 theTDMA, multiframes, channel coding, etc.) Signaling System No. 7 (SS7) isLayer 2 functions on Um are performed by a modified used for the transmission ofLAPD protocol (LAPDm). MAP signalling information betweenLayer 3 on the Um radio interface is subdivided into the components of the networkthree sublayers: radio resource management RR TCAP switching sub-system NSS(channel administration, power control and handover), SCCP (interfaces B-G), as well asmobility management MM and connection between MSC and BSC (A-management CM. The connection management L3 interface) and in direction of theconsists of: call control CC, supplementary services L2 MTP external ISDN networks.SS and short message services SMS L1 Um Abis BTS MSC ISDN BSC AMS CM CC SS SMS BSSAP ISUP MM RSL/O&M/L2ML BSSMAP DTAP SCCP RR SCCP LAPD MTP LAPDm MTP L1 L1
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)
User data and “Signalling”GSM is a circuit switched technology. The Resources are split into Signalling Resources (e.g. signalling channelson 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 datalogically but not physically. So user data and high layer signalling use partly common procedures, so the protocolstack should be spitted. Protocols used for user data and for signalling are finally distinguished in the CN. Thisallows a network evolution without the need to redesign the complete system. The high layer signalling is evenreused for 3G.User PlaneA layered protocol structure was designed in GPRS to realize the transfer of user information. Associatedwith 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 theBSS and the radio interface.Control planeThe signalling plane consists of protocols responsible both for control and support of the transmission planefunctions:•controlling the GPRS network access connections, such as „attaching to“ and „detaching from“ the GPRSnetwork.•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.
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 GiMS 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
Protocol used on the air-summaryGSM 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 isresponsible 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 thephysical 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 channelcombining to provide up to eight physical channels to one MS. The RLC layer is strongly associated with theMAC layer and performs additionally signalling tasks.BSSGP The BSS GPRS Protocol is used to transfer the LLC frames together with related information betweenSGSN and PCU. Information as QoS and routing information. Additionally node management information aretransferred by the BSSGP.LLC The Logical Link Control layer provides the service necessary to maintain the communication capabilitybetween the MS and the SGSN. From the point of the LLC layer there is an established connection between MSand SGSN even if the RLC/MAC layer does not provide any physical connection. The physical connection will beestablished by the RLC/MAC layer only if the LLC layer has data available to transmit. The LLC layer providesseveral 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 ofdata which is transferred by the LLC over the air interface as a single unit.
Protocols used on GB and Gn summaryFRFrame Relay is the link layer protocol, which is used to connect the SGSN with the PCU. Alternatively Ethernetconnections 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 betweenBSS 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 andPCU. 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 instanceEthernet/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
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
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 GiMS BSS SGSN GGSN
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
The Abis interfaceThe functional part of the BSS has to be split up intofunctions performed by the BTS and the PCU. In Relaybetween the two a vendor specific format is used. The RLC BSSGPPCU frames. RLC/MAC functions are performed by thePCU , Channel coding and RF generation are NSperformed by the BTS. The increased throughput of MACespecially CS 3 and 4 and EGPRS compared with GSMrequires a new solution, a dynamic Abis. That means FRthe resource on demand principle is as well realized on GSM RF L1abis. In most vendors cases concatenated PCU framescan 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
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.
SS7 Interfaces in the GPRS CN MSC/VLR HLR AC EIR Gs Based on BSSAP+ Gr Gc Based on MAP GfGs (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 L1Gc (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 viaSGSN. For example Security information is provided, the Location in the HLR is updated, … the sameprocedures as known from the the D interface (MSC/VLR-HLR) take place.
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)
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
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
QoS Parameter (Rel 97/98)A GPRS Subscriber profile describes a service in terms of QoS parameters. The GPRS subscription is stored inthe HLR. When a Service is activated the network is requested to provide a bearer with the describedcharacteristics. Corresponding the network will use Ack/Nack mode on the different interfaces for example. Theindicated 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)
QoS Parameter (Rel 99)With the Release 99 the services are categorized according toConversational class (Real Time services e.g. voice over IP, low delay and delay variation, preserved timerelationship)Streaming class (Real Time audio- and video streaming, one direction only)Interactive Background class (request, response pattern, e.g. WWW browsing, telnet applications, RoundTrip 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
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 thatGuaranteed 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 andSDU 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 beAllocation/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.
QoS Parameter comparison R97/R98 R99/R4/R5 GPRS/UMTS R99/R4/R5 QoS parameters Conversational Streaming Interactive Background class class class classPrecedence Allocation/ Allocation/retention 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3class retention priority priority Traffic handling 1, 2, 3 priority InteractiveDelay 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 kbpsReliability 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 informationPeak through- Maximum Delivery of Yes/No/- Yes/No/- Yes/No/- Yes/No/-put class bitrate erroneous SDUs