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The GPRS Core Network is also called GSS (GPRS Sub-System). It is an IP network, and therefore contains routers (machines handling the packet switching function.)
▼ Routing Function
Data transmission between GPRS Support Node (GSN), may occur across external data networks that provide their own internal routing functions, for example X.25 [34], Frame Relay or ATM networks.
▼ IP interworking
The GPRS Core Network supports interworking with networks based on the Internet protocol (IP). The GPRS Core Network may provide compression of the TCP/IP header when an IP datagram is used within the context of a TCP connection.
▼ X.25
X.25 PDP Type have been removed from the standard sinc e R99.
� Type 1 are simplex MS, i.e. without duplexer: they are not able to transmit and receive at the same time
� Type 2 are duplex MS, i.e. with duplexer: they are able to transmit and receive at the same time
▼ Rx
� Maximum number of received timeslots that the MS can use per TDMA frame. The receive TS shall be allocated within window of size Rx, but they need not be contiguous. For SIMPLEX MS, no transmit TS shall occur between receive TS within a TDMA frame. This does not take into account measurement window (Mx).
▼ Tx
� Maximum number of transmitted timeslots that the MS can use per TDMA frame. The transmit TS shall be allocated within window of size Tx, but they need not be contiguous. For SIMPLEX MS, no receive TS shall occur between transmit TS within a TDMA frame.
▼ SUM
� Maximum number of transmit and receive timeslot (without Mx) per TDMA frame
▼ Meaning of Ttb, Tra et Trb changes regarding MS type s.
� For SIMPLEX MS (type 1):
� Ttb Minimum time (in timeslot) necessary between Rx and Tx windows
� Tra Minimum time between the last Tx window and the first Rx window of next TDMA in order to be able to open a measurement window
� Trb same as Tra without opening a measurement window
� For DUPLEX MS (type 2):
� Ttb Minimum time necessary between 2 Tx windows belonging to different frames
� Tra Minimum time necessary between 2 Rx windows belonging to different frames in order to be able to open a measurement window
� Trb same as Tra without opening a measurement window
> Use of radio resources in case of packet switching
Radio timeslot
Radio interface
Variable Rate
▼ Benefits of Packet Switching
� Variable bit rate becomes possible
� One MS uses several RTSs. The maximum number of RTSs is given by the Operator (O&M parameters) and MS capabilities (MS multislot class)
� One RTS is shared by several MSs. The maximum number of MSs per RTS is given by the Operator (O&M parameters) and 3GPP specifications (limitation due to addressing availability)
> Radio resource assigned according to requirement
• Radio resource shared between users
• Various radio channel coding schemes are specified to allow bit rates from 9 to more than 150 kb/s per user (according also to the quality of radio transmission and the modulation used)
• High bit rates if several channels are assigned to one MS
• Low bit rates if one channel is shared by several MSs.
> Optimized use of the radio resource
• Use of the radio resources only when data is transferred
• Uplink and downlink resources reserved separately
▼ Radio resource sharing
The radio resources are shared by statistical multiplexing. As in GSM, no subscriber has their own permanent radio resource.
▼ Bit rate
Maximum instantaneous bit rate provides 171,2 kb/s by the allocation of eight RTSs to one subscriber. The stated maximum bit rates are different, because different coding schemes are used, which impacts the bit rate over a RTS. (see Annex)
▼ Up link (UL) and downlink (DL)
It is possible to use a different bit rates in each transmission direction, whereas in CS (Circuit Switching) mode, there is a maximum limit of 9.6 kb/s, in both directions and at all times.
> Dynamic allocation and sharing of radio resources
User 1User 2User 3User 4User 5
1 RESOURCE SHARED BY X USERS (PDCH)
User 1
USER1 USES 3 RESOURCES (3 PDCH)
1 RESOURCE USED BY ONE USER NOT SHARED TCH
User 1
Number of resources according to the capability of the MS
▼ Caution: Animated slide that does not make sense if not in the slide-show mode.
▼ Optimized use
A radio resource (set of Radio Blocks over one or several RTS) is allocated only when data is being transferred, by establishing and releasing Temporary Block Flow (TBF), that can be presented as micro-connections, each time a data transfer has to be sent over the radio interface.
▼ Radio resource sharing
One TS can be shared by several MSs, by dynamic time multiplexing under control of the BSS.
– and new coding schemes (MCS-1 to MCS-9) in the MS and the BSS.
> The same set of services provided by GPRS is available in EGPRS.
▼ Shared = in other words: "the radio resources are shared by statistical multiplexing". As in GSM, no subscriber has their own permanent radio resource.
▼ High or low bit rates = more than one time slot per MS or conversely, more than MS on the same TS (one TDMA frame occupies 4.615 ms and is divided into 8 TS or channels).
▼ Maximum instantaneous bit rate provided = 171,2 kbps through the allocation of eight TSs to one subscriber. The stated maximum bit rates are different (according to the BSS release), because different ways of encoding the data, or "coding schemes", are used, which impacts the bit rate over a TS. (cf Annex)
▼ Optimized use:refer to Radio resource allocation in the slides to come + radio resource management in the BSS Chapter.The radio resource allocation is suitable for variable, bursty traffic (downloading Web pages).
▼ Up link (UL) and downlink (DL): It is possible to use a different bandwidth (bit rate) in each transmission direction, whereas in CS (circuit switching) mode, there is a maximum limit of 9,6 kbps, in both directions and at all times.
▼ QoS: Henceforth, QoS parameters are part of subscription data, according to the wide range of services provided to a subscriber.
Precedence Classrelative importance of service under congestion3 classes
Delay Classtotal delay measured between R or S point and Gi4 classes
Reliability Classacknowledgement of packets5 classes
Peak throughput Class
Mean throughput Class
the maximum data rate allowed to the user
maximum data rate during a period
Throughput class
19 classes
9 classes
1 What is GPRS ?1.8 Quality of service profile
▼ Precedence class
According to the class, user data packet can be discarded during the transfer due to a congestion state.
3 classes are defined : any, normal, high
▼ Delay class
The delay class depends on the operator network because a measurement is done between the R or S interface (between the Mobile Terminal and the Terminal Equipment) and the Gi interface. For each operator, delay values are different so delay classes are a reference not a strict value.
4 classes are defined : best effort, 1, 2, 3
▼ Reliability class
The reliability means that user data packets are acknwoledged during the transfer. The reliability classes are defined according to the acknowledgement or not of the packet.
5 classes are defined
▼ Throughput class
The throughput class is defined by the 2 following parameters:
� Mean Throughput : 9 classes are defined (from best effort to 111 Kb/s)
� Peak Throughput : 19 classes are defined (from 8 Kb/s to 2048 Kb/s)
Non physicalNon physicalNon physicalNon physical•on-line Banking•Ticketing•Auction•Gambling….
▼ Retrieval services
Provide the capability of accessing information stored in data base centers. The information is sent to the user on demand only. An example of one such service in the Internet's World Wide Web (WWW).
▼ Messaging services
Offer user-to-user communication between individual users via storage units with store-and-forward mailbox, and/or message handling (e.g., information editing, processing and conversion) functions;
▼ Conversational services
Provide bi-directional communication by means of real-time (no store-and-forward) end-to-end information transfer from user to user. An example of such a service is the Internet's Telnet application;
▼ Tele-action services
Characterized by low data-volume (short) transactions, for example credit card validations, lottery transactions, utility meter readings and electronic monitoring and surveillance systems.
▼ Distribution services
Characterized by the unidirectional flow of information from a given point in the network to other (multiple) locations. Examples may include news, weather and traffic reports, as well as product or service advertisements;
▼ Dispatching services
Characterized by the bi-directional flow of information from a given point in the network (dispatcher) and other (multiple) users. Examples include taxi and public utility fleet services;
▼ Conferencing services
Provide multi-directional communication by means of real-time (no store-and-forward) information transfer between multiple users.
� LLC PDU segmentation / re-assembly into RLC/MAC PDU
� PDCH scheduling (resource multiplexing)
� Channel access control (access requests and grants)
� ARQ function (RLC block Ack / Nak, buffering and retransmission of RLC blocks)
� Radio channel management (power control, congestion control, broadcast control information).
▼ DNS (Domain Name Server) and DHCP (Dynamic Host Convergence Protocol)
▼ NTP server (Network Time Protocol) for GSN synchronization. In general an NTP application does not run on a dedicated server. The OMC-G can play this role.
▼ HLR (Home Location Register) is involved in MS attachment to the GPRS network (authentication + services subscribed to)
Used for network-requested PDP contexts activation (GGSN asks the HLR for SGSN routing information).
▼ Gs interface
Defines the Network Mode of Operation I (NMOI). It allows to perform LA + RA combined Location Update, and PS and CS paging coordination (refer to ANNEX).
▼ Gr interface
Exchange of subscription information at GPRS attachment phase
▼ Additional interfaces
� Gf (to the EIR)
� Gd to deliver the SMS to the mobiles via the GPRS network (SGSN option and subscriber feature)
Autonomous cell reselection NCOOr controled by network NC 2( In paquet transfert mode )
Autonomous cell reselection
▼ IDLE (GPRS) State
In GPRS IDLE state, the subscriber is not attached to GPRS mobility management. The MS and SGSN contexts hold no valid location or routeing information for the subscriber. The subscriber-related mobility management procedures are not performed.
Data transmission to and from the mobile subscriber and the paging of the subscriber is not possible. The GPRS MS is seen as not reachable in this case.
In order to establish MM contexts in the MS and the SGSN, the MS shall perform the GPRS Attach procedure.
▼ STANDBY State
In STANDBY state, the subscriber is attached to GPRS mobility management. Pages for data or signalling information transfers may be received. It is also possible to receive pages for the CS services via the SGSN. Data reception and transmission are not possible in this state.
The MS performs GPRS Routeing Area (RA) and GPRS cell selection and re-selection locally. The MS executes mobility management procedures to inform the SGSN when it has entered a new RA. The MS does not inform the SGSN on a change of cell in the same RA. Therefore, the location information in the SGSN MM context contains only the GPRS RAI for MSs in STANDBY state.
The MS may initiate activation or deactivation of PDP contexts while in STANDBY state. A PDP context shall be activated before data can be transmitted or received for this PDP context.
▼ READY State
In READY state, the SGSN MM context corresponds to the STANDBY MM context extended by location information for the subscriber on the cell level. The MS performs mobility management procedures to provide the network with the actual selected cell. GPRS cell selection and re-selection is done locally by the MS, or may optionally be controlled by the network.
An identifier of the cell, the Cell Global Identity including RAC and LAC, is included in the BSSGP header of the data packet from the MS; see GSM 08.18 [21].
The MS may send and receive PDP PDUs in this state. The network initiates no GPRS pages for an MS in READY state. Pages for other services may be done via the SGSN. The SGSN transfers downlink data to the BSS responsible for the subscriber's actual GPRS cell.
The MS may activate or deactivate PDP contexts while in READY state.
2 GPRS Operation2.3 MS Radio Resource Operating Modes
Packettransfer mode
Packetidle mode
Packetidle mode
Ready Standby
RR
MM
> Packet transfer modeIn packet transfer mode, the mobile station is allocated radio resource providing a Temporary Block Flow (TBF) on one or more physical channels. Continuous transfer of one or more LLC PDUs is possible. Concurrent TBFs may be established in opposite directions. Transfer of LLC PDUs in RLC acknowledged or RLC unacknowledged mode is provided.
> Packet idle modeIn packet idle mode no Temporary Block Flow . Upper layers can require the transfer of a LLC PDU which, implicitly, may trigger the establishment of TBF and transition to packet transfer mode.
> MS RR operating modes vs MS MM states
▼ Packet idle mode
While operating in packet idle mode, a mobile station belonging to GPRS MS class A may simultaneously enter the different RR service modes. A mobile station belonging to either of GPRS MS class B or C leaves both packet idle mode and packet transfer modes before entering dedicated mode, group receive mode or group transmit mode.
▼ Packet transfer mode
When selecting a new cell, mobile station leaves the packet transfer mode, enters the packet idle mode where it switches to the new cell, read the system information and may then resume to packet transfer mode in the new cell.
While operating in packet transfer mode, a mobile station belonging to GPRS MS class A may simultaneously enter the different RR service modes. A mobile station belonging to either of GPRS MS class B or C leaves both packet idle mode and packet transfer modes before entering dedicated mode, group receive mode or group transmit mode.
▼ GTP (GPRS Tunnelling Protocol) tunnels user data between GPRS Support Nodes in the backbone network. The GPRS Tunnelling Protocol shall encapsulate all PDP PDUs.
▼ UDP (User Datagram Protocol) carries GTP PDUs for protocols that do not need a reliable data link (e.g., IP), and provides protection against corrupted GTP PDUs.
▼ IP (Internet Protocol) is the backbone network protocol used for routing user data and control signalling. The backbone network may initially be based on the IPv4. Ultimately, IPv6 shall be used.
▼ SNDCP (SubNetwork Dependent Convergence Protocol ) maps network-level characteristics onto the characteristics of the underlying network.
▼ LLC (Logical Link Control) provides a highly reliable ciphered logical link. LLC shall be independent of the underlying radio interface protocols in order to allow introduction of alternative GPRS radio solutions with minimum changes to the NSS.
▼ Relay. In the BSS, this function relays LLC PDUs between the Um and Gb interfaces. In the SGSN, this function relays PDP PDUs between the Gb and Gn interfaces.
▼ BSSGP (Base Station System GPRS Protocol) conveys routing and QoS-related information between the BSS and the SGSN. BSSGP does not perform error correction.
▼ (NS) Network Service transports BSSGP PDUs. NS is based on the Frame Relay connection between the BSS and the SGSN, and may - multi-hop and traverse a network of Frame Relay switching nodes.
▼ RLC/MAC (Radio Link Control / Medium Access Control ). The Radio Link Control function provides a radio-solution-dependent reliable link. The Medium Access Control function controls the access signalling (request and grant) procedures for the radio channel, and the mapping of LLC frames onto the GSM physical channel.
Data compression, segmentation of large packets, recognition of PDP-PDU sessions (according to their NSAPI), inclusion of QoS (use of SAPIs on the LLC link).
▼ NSAPI (Network Service Access Point Identifier)
This is used for a particular MS to distinguish different PDP contexts (= sessions)
� by the PDP-type: X.25 or IP, or mainly by
� the APN to be reached, or by
� the required QoS.
▼ LLC (Logical Link Control)
Provides a safe link, encrypted and independent of the physical bearer, independent to BSS brand.
▼ TLLI (Temporary Logical Link Identity)
Identifies a logical link with the MS (one TLLI per MS)
Almost always empty. The network then dynamically assigns (using a DHCP server) an IP address to the subscriber when he activates his PDP context (seen later).
▼ PDP contexts
Each PDP context can be considered as a BS (basic service = telephony, fax, etc). A PDP context is a dialog session with an external IP network, identified with an APN. It is not always mandatory to subscribe (in the HLR) to PDP contexts, access to some networks is free. For a user, the traffic of his different sessions will be recognized in the messages by the use of different NSAPIs. A user can declare one of his PDP contexts as the default.
▼ APN (Access Point Name)
The APN represents an IP network. An APN has two parts: the APN-Network Id (example: wanadoo.fr) and the APN-operId (example: mnc...gprs)
� Examples of APN: wanadoo.fr.mnc001.mcc208.gprs,
� APN = * (wildcard) potentially authorizes the MS to activate any APN.
▼ Valid APN
Boolean, if YES, indicates that this APN can be reached through the GGSN of the visited FPLMN.
In case of IP PDP_type access with no additional mobile authentication procedure, the MS IP address is provided by the PLMN, using either the subscription data, or the backbone DHCP server. No additional user authentication is needed on top of the GPRS authentication mechanisms (i.e. using IMSI and authentication triplets)
▼ PDP Context Activation
� ➀ MS requests for a PDP_context activation, providing the name of target Packet Data Network (PDN2 parameter).
� ➁ SGSN queries the backbone Name Server (here DNS) to identify the GGSN giving access to the Data Network PDN2 (here GGSN2).
� ➂ SGSN sends a Create_PDP message to the corresponding GGSN2, in order to setup a GTP tunnel.
� ➃ GGSN2 allocates an IP address to the MS (@IP_MS), using the backbone DHCP server.
� ➄ GGSN2 acknowledges the Create_PDP message to the SGSN, returning the @IP_MS allocated to the MS.
� ➅ SGSN acknowledges the Activate_PDP message to the MS, with the allocated @IP_MS.
IP PDP_type access with mobile authentication via a RADIUS. The address allocation server (i.e. DHCP) and/or authentication server (i.e. RADIUS) may be located within the PLMN or in the ISP/Intranet network. Non-transparent access is aimed for corporate intranet access, where additional user authentication is often required.
▼ PDP Context Activation
� The authentication data are piggybacked in the Protocol Configuration Options (PCO) field of the PDP context activation messages ➀ and ➆.
� ➀ , ➁ , ➂ same as for IP PDP_type in transparent access.
� ➃ GGSN performs the user authentication towards a RADIUS server.
� ➄ GGSN allocates an @IP to the MS using the intranet/ISP DHCP server.
� ➅, ➆ same as for a PDP context in transparent access.
In order to achieve a proper transfer of User Data, two main protocols are used: GTP (between GGSN and SGSN) and LLC (between SGSN and MS), and two types of logical connections are established:
� MS <-> SGSN. Logical Link used for signaling and data transfer, created at GPRS attach (unique per MS), identified by a TLLI value;
� SGSN <-> GGSN. Created with the activation of PDP context = when opening a session (several per MS), identified each by a TID value.
▼ TLLI (Temporary Logical Link Identity)
Identifies uniquely a MS attached to the GPRS core network (Standby or Ready state).
▼ TID (Tunnel Identity)
Identifies a logical connection ("tunnel") between GGSN and SGSN (for each session of each MS). TID= IMSI+NSAPI.
Data are transferred from header translation, then encapsulation in underlined protocol data unit.
At the GGSN, the IP address of the MS is used to retrieve a PDP context and therefore a TID and the address of the current SGSN.
At the SGSN, the TID is used to work out the NSAPI and the IMSI (therefore the TLLI). If the MS is ready, no need for paging because the MS is located to the exact cell.
1- Secured network access• Authentication of MSs and confidentiality of their identity• Possibility of encrypting user data• Possibility of verifying IMEI with an EIR (Gf)
2- Secured backbone IP networkFirewall = application-level filteringFiltering by access lists (in the GGSNs)
GPRS Network
3- Secured intranet accessAPN with mandatory subscriptionAPN with access lists APN with tunneling on Gi (IPsec)
▼ Authentication and confidentiality
As in GSM, by security triplets and the use of the TLLI/P_TMSI instead of the IMSI.
▼ Encryption
The LLC frame is encrypted, so encryption from the MS to the SGSN and not just on Um.
▼ Firewall
Filtering function installed on routers (ex: GGSN). Packets are rejected by filtering at application level (for example: in http, some URLs are barred). Also makes it possible to hide the IP addresses of MSs and backbone entities from external hosts (Network Address Translation function).
▼ Access Lists (IP addresses lists)
A function of Cisco routers (and therefore of GGSNs). Each APN is linked to two lists of IP addresses to be checked during the PDP context activation phase (calling address and called address in both UL and DL directions).
These lists are therefore used to protect access to the operator's backbone IP, but also to filter the access to external PDNs.
At the GGSN, some APNs can be declared "with mandatory subscription" (at the HLR) and therefore inaccessible to other MSs.
▼ Tunneling
Several ways:
� by IPsec (Secured IP) = IP version in which the user data is encrypted (IP datagrams payload but not their header). Or by Generic Routing Encapsulation (GRE)
� by PPTP (Point-To-Point Tunneling Protocol). Refer to ANNEX for PPP Tunneling.
▼ For GPRS TRAFFIC, the BSS simply relays the LLC frames between the MS and the SGSN.
▼ BSSGP = BSS Gprs Protocol. Functions:
� to relay LLC frame over the Gb, with no guarantee of integrity (relaying user data and GMM / SM messages : session, RA_update and paging procedures). Conceals the FR layers for the LLC layer.
� SGSN-MFS signaling = management of Gb interface objects (flush, paging, resume suspend, LLC-discarded and other procedures).
� cell-SGSN traffic management (identified by BssgpVCs): in particular cell update management (in the same RA): the BSSGP header always indicates the current cell so if a "ready" MS moves into a new cell, then the SGSN stores this new cell and sends all the unacknowledged LLC_PDUs to it (DL).
▼ The concept of handover has no meaning in packet switching (GPRS). There is no "circuit" to re-establish!
▼ RLC = Radio Link Control. (Provides a safe link for transporting LLC-PDUs in acknowledged or unacknowledged mode, LLC-PDU segmentation into blocks and reassembly, management of TBF contexts. RLC depends on the physical bearer: data encoding, error control and flow control suited to GSM channels.
▼ MAC = Medium Access Control. Multiplexing of RLC frames onto PDCH (transfer of blocks over the different PDCHi). Including traffic sharing over several TSs or, conversely, the use of one TS for several users.
▼ For GPRS TRAFFIC, the BSS simply relays the LLC frames between the MS and the SGSN.
▼ BSSGP = BSS Gprs Protocol. Functions:
� to relay LLC frame over the Gb, with no guarantee of integrity (relaying user data and GMM / SM messages : session, RA_update and paging procedures). Conceals the FR layers for the LLC layer.
� SGSN-MFS signaling = management of Gb interface objects (flush, paging, resume suspend, LLC-discarded and other procedures).
� cell-SGSN traffic management (identified by BssgpVCs): in particular cell update management (in the same RA): the BSSGP header always indicates the current cell so if a "ready" MS moves into a new cell, then the SGSN stores this new cell and sends all the unacknowledged LLC_PDUs to it (DL).
▼ The concept of handover has no meaning in packet switching (GPRS). There is no "circuit" to re-establish!
▼ RLC = Radio Link Control. (Provides a safe link for transporting LLC-PDUs in acknowledged or unacknowledged mode, LLC-PDU segmentation into blocks and reassembly, management of TBF contexts. RLC depends on the physical bearer: data encoding, error control and flow control suited to GSM channels.
▼ MAC = Medium Access Control. Multiplexing of RLC frames onto PDCH (transfer of blocks over the different PDCHi). Including traffic sharing over several TSs or, conversely, the use of one TS for several users.
▼ For GPRS TRAFFIC, the BSS simply relays the LLC frames between the MS and the SGSN.
▼ BSSGP = BSS Gprs Protocol. Functions:
� to relay LLC frame over the Gb, with no guarantee of integrity (relaying user data and GMM / SM messages : session, RA_update and paging procedures). Conceals the FR layers for the LLC layer.
� SGSN-MFS signaling = management of Gb interface objects (flush, paging, resume suspend, LLC-discarded and other procedures).
� cell-SGSN traffic management (identified by BssgpVCs): in particular cell update management (in the same RA): the BSSGP header always indicates the current cell so if a "ready" MS moves into a new cell, then the SGSN stores this new cell and sends all the unacknowledged LLC_PDUs to it (DL).
▼ The concept of handover has no meaning in packet switching (GPRS). There is no "circuit" to re-establish!
▼ RLC = Radio Link Control. (Provides a safe link for transporting LLC-PDUs in acknowledged or unacknowledged mode, LLC-PDU segmentation into blocks and reassembly, management of TBF contexts. RLC depends on the physical bearer: data encoding, error control and flow control suited to GSM channels.
▼ MAC = Medium Access Control. Multiplexing of RLC frames onto PDCH (transfer of blocks over the different PDCHi). Including traffic sharing over several TSs or, conversely, the use of one TS for several users.
3 The Base Station Subsystem3.5 Radio Interface 3/8
> GMSK / 8-PSK modulations
GMSK
8-PSK
1 0 1 1
001 101 011 001
GMSK270 kb/s
8-PSK810 kb/s
Gross bit rateper carrier1 bit per
Symbol
3 bitS perSymbol
8 PSK has 3times more capacity than GMSK
One TS 142 symbols142 BitsONE TS
One TS 142 symbols426 BitsONE TS
▼ Transmission and reception data flows are the same for GPRS and EGPRS, except for EGPRS MCS-9, MCS-8 and MCS-7, where 4 normal bursts carry 2 RLC blocks (1 RLC block within 2 bursts for MCS-9 and MCS-8).
▼ Radio blocks are transported on the air interface (Um) over 4 consecutive normal bursts of the TDMA frame.
▼ The GMSK normal burst is composed of 156.25 symbols (1 bit for 1 symbol):
� 6 tail symbols,
� 26 training sequence symbols,
� 114 encrypted symbols,
� 2 stealing flags (2 symbols),
� 8.25 guard period (symbols).
� For GMSK, the radio blocks are transported by 114 x 4 = 456 symbols.
▼ The 8-PSK normal burst is composed of 156.25 symbols (3 bits for 1 symbol):
� 6 tail symbols,
� 26 training sequence symbols,
� 116 encrypted symbols (there is stealing flags),
� 8.25 guard period (symbols).
� For 8-PSK, the radio blocks are transported by 116 x 4 = 456 symbols.
INCREASE SECURITY DECREASE USEFUL TRANSMISSION RAT E
Extra capacity Extra capacity
MCS n
Extra capacity Extra capacity
MFSPCU
BTSTRX
BSCrelay
PDCH
Extra capacity Extra capacity
MCS n-1
PDCH
Extra capacity Extra capacity
Extra capacity Extra capacity
MFSPCU
BTSTRX
BSCrelay
Extra capacity Extra capacity
Can be allocated to another PDCH
Can be allocated to other PDCH
3 The Base Station Subsystem3.5 Radio Interface 6/8
▼ When the operator decide that the TRX will run MCS n all the terrestrial resources will be allocated , but if the quality of the radio transmission is bad the PCU decides to increase the security on the air interface, the useful transmission rate on the PDCH will be decreased and less capacity will be needed on the terrestrial transmission .
▼ The resource which is not used a that time can be allocated to another TRX if needed at BTS level
▼ The RLC blocks coming from different are multiplexed on the common resource for all the PDCH in the TRX which is called M EGCH (Multiplexed EGCH)
Packet Resource Assignment (list of PDCHi, token=T,TFIk)
MS starts listening to all DL blocks token value on the allocated PDCHi
SEND on block b+1 (TFIk)
in block b token =T ?
Y
N
Ø Ø T T Ø T Ø T T T ØDL PDCHi
? Ø Ø TFIk TFIk Ø TFIk Ø TFIk TFIk TFIkUL PDCHi
3 The Base Station Subsystem3.5 Radio interface 7/8> UL transfer
PCU
TBF MAC
▼ This slide demonstrate that the radio resources (blocks) are used only when data need to be transferred (LLC-PDU) : dynamic radio resource allocation. As a matter of fact, an MS shall specify its radio resource request at initiation of each TBF for a better optimization of radio resource & MS capabilities.
▼ A TBF (the blue shape) comprises one or more consecutive LLC-PDUs.
▼ Temporary (Block) Flow Identity = TLLI + sequential number, used by the network to recognize data from different MSs. Identifies uniquely a TBF in one direction within a cell.
� The blocks are dynamically allocated upon the use of a token (Uplink State Flag) allocated to the MS at TBF establishment. Any DL block includes a USF in the header.
� The mobile "listens" to the PDCHi assigned, when block b (in DL) contains USF = T, the MS shall send one PDTCH in UL on block b+1 on the UL PDCHi.
▼ The theoretical maximum of 160 kbit/s is given for one MS which would have 8 PDCHs of 21.4 kbit/s each. Those MS are yet to be available on the market place.
MS starts listening to all DL blocks TFI value on the allocated PDCHj
Ø Ø Z Z Ø Z Ø Z ZDL PDCHj
3 The Base Station Subsystem3.5 Radio interface 8/8
> DL transfer
MS IN STANB BYMODE
MS IN READYMODE
▼ In DL, each time an LLC-PDU is received, if there is no TBF in progress, it is essential to “establish" one.
▼ To respond to the paging, the MS needs to send a "paging response" to the SGSN (GMM) encapsulated in an LLC_PDU. This response is carried by an UL TBF.
▼ Upon reception of the Paging response, the SGSN can send the DL PDU (LLC frame) to the MS through the MFS.The MFS shall establish a DL TBF with the MS.
▼ DL TBF: each block of the DL TBF are identified by the DL TFI = TFIz
▼ After completion of the TBF establishment phase, the MS listen to all the DL blocks on the allocated PDCHs and keeps the blocks tagged with the TFIz.
▼ The "Control sub-rack" part is duplex (two DS10 in active/standby modes).
▼ each BSXTU sub-rack contains a maximum of 12 JBGPU boards.The GPRS traffic of one BSC can be handled by several GPUs (up to six are foreseen from the same MFS rack)Since B7, a full MFS contains from 4 to 22 BSS (BSC), due to multi-GPU feature
▼ This platform is a high availability distributed platform composed of blades compliant with the Advanced Telecom Computing Architecture (ATCA) open standard
▼ ATCA has been developed by the PCI Industrial Computers Manufacturers Group (PICMG).
▼ The related specifications are described in the PICMG 3.0 R1.0.
▼ LIU shelf: Multiplexes/demultiplexes and cross connects all E1 external links to/from NE multiplexed links (n E1 over Ethernet) on the TP and the GP board. Equipped with two Mux boards and n LIU boards, depending on capacity.
▼ The LIU shelf hosts Two MUX boards which collect the E1 links from the 16 LIU boards on 16 serial links at 36.864 Mbit/s and build packets sent towards up to 32 directions (125ms each) on a Gigabit Ethernet link.
▼ SSW: it’s an Ethernet switch which allows exchanges between all platform elements and externalIP/Ethernet equipment.
▼ OMCP: these control stations are used to process defense functions and platform Operation, Administration and Maintenance (OAM) generic services..
▼ GP: Manages the user plane packet data flow processing.
▼ Ethernet links on the IP ports of the SSW switch: these links connect the platform to external IP equipment (i.e. OMC-R, external alarm box).
▼ SMS : With GPRS, the 160-character barrier for short messages will be able to be broken (when SMS over GPRS is implemented).
▼ High Speed Circuit-Switched Data : This still involves circuit switching, meaning that, with a continuous use of radio resources, so billed by time. HSCSD is based on the assignment of several traffic channels (TCH) to a single MS to offer a higher bit rate. HSCSD is suited for services requiring a minimum bandwidth guaranteed.
▼ EDGE : (Enhanced data rates for GSM evolution) is a technology previously developed by Ericsson, based on TDMA and offering a maximum theoretical speed of 384 kbit/s (8 channels, each 48 kbit/s, using a new modulation scheme: 8-PSK, eight-phase shift keying, instead of GMSK for GSM and GPRS).
▼ EDGE-specific MTs are required! The BSS remains the same, except for the implementation of EDGE TRX (Evolium product line).Alcatel will offer EDGE from release B8 onwards. This is an important step towards UMTS
▼ UMTS : requires a new Radio Access Network based on W-CDMA technology.The UMTS standard is part of the Third Generation (3G). Together with CDMA 2000 and other systems, they form a set of ITU radio access technologies standardized by IMT 2000.
Blocs which can be used as- PPCH- PAGCH- PDTCH- PACCH
▼ For each cell, it is possible to define the MINIMUM and MAXIMUM number of channels reserved for GPRS + the maximum number of channels reserved for GPRS in case of high traffic load (when the BSC sends "Load indication" to the MFS through BSCGP protocol).
� Higher GPRS signaling capacity, in line with GPRS traffic growth
� Differentiated cell re-selection strategy between GPRS and non GPRS MS. When GPRS attached, a MS listen to PSI broadcast on PBCCH. It allows a finer tuning of GPRS re-selection algorithms, for example in hierarchical networks (C31 and C32 criteria). Otherwise, MS applies the basic Cell-reselection as in GSM Idle-Mode using the C1 and C2 GSM criteria
5 Annex 12 Network Mode of Operation I with Master Channel
BSC
CCCH
PCCCH
PACCH
Um
MSCVLR
SGSN
A
Gb
Gs
CS paging for GPRS-attached MS in idle state (a), o r in data transfer state (b)
CS paging for non GPRS-attached MS GPRS paging
(a)
(b)
▼ In this mode, the Gs interface is present in the core network. As far as GPRS-attached MS are concerned, the BSS receives both GPRS and circuit-switched paging messages from the Gb interface.
▼ There is paging co-ordination because all paging messages towards GPRS-attached mobile stations are sent either on the Master Channel, if present, or on the CCCH otherwise.
▼ In addition, whilst involved in a packet data transfer the GPRS mobiles receive the circuit-switched paging messages via the GPRS traffic channel currently used.
▼ NMO II :
� There is neither Gs interface nor Master Channel. There Paging coordination over the CCCH of GSM. Also, GPRS Mobile Stations operating in Class B may lose CS Paging message if they are not able to monitor CCCH at the same time.
▼ NMO III:
� In this mode, there is no Paging coordination because Gs interface is not present while the Master Channel is. Therefore, CS Paging is transmitted over CCCH when PS Paging is transmitted over PCCCH. Class C Mobile are not able to manage both type of channels.
5 Annex 13MOBILE ONE PHASE ACCESS ON PCCH (Master PDCH)
NETWORK
Packet channel request PRACH
Packet UL assignment + polling indication PAGCH
Usf Scheduling
Packet Control ACK PACCH
RLC data bloc PDTCH
TFIPDCHUSFTA
Packet UL ACK NACK PACCH
▼ "Attach" the MS switches on (GMM protocol):
� MS sends his previous P_TMSI, otherwise a random one. The attach_request message is placed in an LLC frame with its old TLLI if its exists, or a randomly chosen TLLI if not.
▼ TLLI: This is allocated to the subscriber on his attachment to the network. In reality, the SGSN allocates the MS a P-TMSI, from which the MS and the SGSN itself derive the TLLI.
▼ The functions of the HLR:
� to supply the security triplets
� to check roaming restrictions (or ODB)
� to store the address of the current SGSN
� to initiate the deletion of data from the old SGSN
� to send subscriber data to the SGSN
▼ "Detach" proceeds as follow:
� MS to SGSN: Detach request
� SGSN to GGSN: Delete PDP context then Acknowledge
� MS sends his previous P_TMSI, otherwise a random one. The attach_request message is placed in an LLC frame with its old TLLI if its exists, or a randomly chosen TLLI if not.
▼ TLLI: This is allocated to the subscriber on his attachment to the network. In reality, the SGSN allocates the MS a P-TMSI, from which the MS and the SGSN itself derive the TLLI.
▼ The functions of the HLR:
� to supply the security triplets
� to check roaming restrictions (or ODB)
� to store the address of the current SGSN
� to initiate the deletion of data from the old SGSN
� to send subscriber data to the SGSN
▼ "Detach" proceeds as follow:
� MS to SGSN: Detach request
� SGSN to GGSN: Delete PDP context then Acknowledge
� MS sends his previous P_TMSI, otherwise a random one. The attach_request message is placed in an LLC frame with its old TLLI if its exists, or a randomly chosen TLLI if not.
▼ TLLI: This is allocated to the subscriber on his attachment to the network. In reality, the SGSN allocates the MS a P-TMSI, from which the MS and the SGSN itself derive the TLLI.
▼ The functions of the HLR:
� to supply the security triplets
� to check roaming restrictions (or ODB)
� to store the address of the current SGSN
� to initiate the deletion of data from the old SGSN
� to send subscriber data to the SGSN
▼ "Detach" proceeds as follow:
� MS to SGSN: Detach request
� SGSN to GGSN: Delete PDP context then Acknowledge
� MS sends his previous P_TMSI, otherwise a random one. The attach_request message is placed in an LLC frame with its old TLLI if its exists, or a randomly chosen TLLI if not.
▼ TLLI: This is allocated to the subscriber on his attachment to the network. In reality, the SGSN allocates the MS a P-TMSI, from which the MS and the SGSN itself derive the TLLI.
▼ The functions of the HLR:
� to supply the security triplets
� to check roaming restrictions (or ODB)
� to store the address of the current SGSN
� to initiate the deletion of data from the old SGSN
� to send subscriber data to the SGSN
▼ "Detach" proceeds as follow:
� MS to SGSN: Detach request
� SGSN to GGSN: Delete PDP context then Acknowledge
� MS sends his previous P_TMSI, otherwise a random one. The attach_request message is placed in an LLC frame with its old TLLI if its exists, or a randomly chosen TLLI if not.
▼ TLLI: This is allocated to the subscriber on his attachment to the network. In reality, the SGSN allocates the MS a P-TMSI, from which the MS and the SGSN itself derive the TLLI.
▼ The functions of the HLR:
� to supply the security triplets
� to check roaming restrictions (or ODB)
� to store the address of the current SGSN
� to initiate the deletion of data from the old SGSN
� to send subscriber data to the SGSN
▼ "Detach" proceeds as follow:
� MS to SGSN: Detach request
� SGSN to GGSN: Delete PDP context then Acknowledge
▼ RA1: This is the mobile's previous RA The New SGSN retrieves the IP address of the old SGSN from RA1, after request to the DNS which translate RA1 into IP @ of SGSN1.
▼ SGSN_context_req:To obtain any PDP contexts and the MM contexts (IMSI, RA, cell, IMEI, etc) = all the data stored in the old SGSN concerning the MS, including the address of the GGSN related to each PDP context activated.
▼ SGSN_ctxt _ack: This message is sent only if the subscriber has PDP contexts activated. Used to inform the old SGSN that receives and stores datagrams for the MS.
▼ Update_PDP_context_req: Mainly to inform the GGSN of the address of the new current SGSN for this MS. Thus, any new packet arriving from the PDP network is routed to the new SGSN.This operation is carried out in parallel with the retrieval of the old SGSN packets, and not afterwards as the figure above seems to indicate.
▼ The HLR must include the option F_GPRS_002 "Support of SMS-MT over GPRS" to enable transmission of SMs to the MSs (which have this subscription option) via GPRS.
▼ SRI: If the SMS-GMSC supports GPRS, it tells the HLR so.
▼ SRI-res: The HLR sends back the following addresses:
� MS IMSI-attached only: VMSC@
� MS GPRS-attached only: SGSN@
� MS both IMSI and GPRS attached:
� SMS-GMSC does not support GPRS: One address returned according to MS preference option.
� SMS-GMSC supports GPRS: Both addresses returned. The SMS-GMSC first performs transfer through NSS or GSS according to an option. If the transfer to the MS fails (Forward-SM-res), the SMS-GMSC repeats the attempt through the second network.
▼ If the delivery through the GSS fails, the HLR sets the MNRG flag and stores the address of the SMS-GMSC.
▼ Mobile user activity procedure: When the MS is reattached, the HLR indicates this to the SMS-GMSC (conventional GSM "alerting" procedure) and to all the GGSNs which had tried in vain to activate PDP contexts to this MS.
▼ The SGSN sends Ready-for-SM to the HLR before sending the “update location” message.
▼ The SMS-GMSC obviously alerts the SMSC which makes a new attempt to deliver the SM to the mobile (as in the previous slide).
(NSAPI1 + PDP context 1 + @ of GGSN1) IMSI ↔TLLI + current RA+ subscription data (NSAPI2 + PDP context 2 + @ of GGSN2)
SGSN
TID1 + PDP context 1 IMSI ↔ @ current SGSNGGSN
IMSI ↔ @ current SGSNHLR
▼ The SGSN even knows the current cell, if the mobile is in the ready state by looking at the routing over the Gb interface of the PDU originated by the MS. For further explanation, please refer to the sub-chapter “The Base Station Sub-System, The Gb interface”
5 Annex 24 The Gb interface - Frame Relay overview
User connected to the frame relay network through a “synchronous access line”Based on semi-permanent connection, PVC
A PVC is identified on each end by a local connection identity : DLCI possible control of data loss (use of CRC )
User to network signaling is carried by a specific PVC tagged with the DLCI 0
Frame RelayFrame Relay DLCIb
access line
DLCImDLCIp
PVC 1
DLCI=0 (Sig)
DLCIpDLCIm
DLCIa PVC 2
access line
PVC 3
DLCIb
▼ Access Line = any synchronous line would do.
▼ On a FR access line, there can be a large number of PVCs (Permanent Virtual Circuits), identified each by a DLCI, (Data Link Connection Identifier), different on each side + a PVC for signaling (DLCI=0).
▼ Data Loss: all frames have a CRC field used to determine if the data (payload) is correct or not. The network discards any frame with an erroneous payload.
▼ user-to-network signaling is to check the
� local availability of the FR link ("Link Integrity Verification” procedure)
� end-to-end availability of each user's PVC ("Full Status Report" procedure)
▼ Security (redundancy): the user to the right has 2 access lines.
▼ Physical layer = PCM links from the JBGPU boards.
▼ It is best to connect the MFS and the SGSN to the FR network by two PCM links for added protection.
▼ Bearer Channel: This is N x 64 kbit/s over a 2048 kbit/s link
� N time slots on one PCM link
� FR access line.
▼ SGSN end, a BC can recover all the TSs of the PCM link to have the fastest possible access to the FR network.
▼ MFS end, on a BC, only one PVC will be declared (option chosen by Alcatel for simplicity). Therefore, for security: two BCsper BSC, each on a different PCM link (see next slides).
▼ If no FR network, the declarations of the physical and SNS layers must be the same at both ends.
5 Annex 26The Gb interface - SubNetwork Service layer
▼ The FR layer is part of the layer 2 in OSI model = Sub-Network Service layer (2.1). On top of this layer, and for telecom and quality of service purposes was added the Network Service Control layer (2.2).
▼ The "Bearer Channel" object of GPRS corresponds to the notion of FR access line. On a BC, there can be several PVCs(Permanent Virtual Circuits), each identified by a DLCI, which may be different at each end.
▼ Alcatel has set the limit on the BSS (MFS) side, to one PVC per BC.
▼ Several PVCs are needed:
� firstly because a PVC is used for traffic with a given BSC (and therefore several BSCs means several PVCs)
� secondly to provide security at Frame Relay level by introducing redundancy
▼ There is also, on each BC, a virtual link (with DLCI=0) for signaling with the FR switch.
5 Annex 27The Gb interface - Network Service Control layer
Gb SGSN
Physicallayer
SNS
BSSGP
NSC
Gb
Physicallayer
SNS
BSSGP
NSC
PCU1
Physicallayer
SNS
BSSGP
NSC
PCU2
FrameFrameRelayRelay
NS-VCI=12
NS-VCI=13
NS-VCI=14
NS-VC
NS-VCI= 11
BSC1
BSC2
NSEI x
NSEI y
NSE
▼ The Network Service Control layer is used:
� To transport BSSGP frames between MFS and SGSN
� To manage FR virtual circuits (offering in particular a common identifier for the PVCs: these are the NS-VCs (Network Service layer - Virtual Circuit) thanks to a range of standard procedures : (un)block, reset and test.
� To share dynamically the UL/DL traffic (BSC to SGSN) over the existing NS-VCs of the same NSE
▼ Multiplexing scheme: 1 NS-VC = 1 PVC.
▼ NSE = Network Service Entity, identified by its NSEI, representing the packet traffic to/from a given BSC. The NSE = ΣNS-VCs dedicated to the packet traffic for one BSC. NSEI is information included in the messages between SGSN and MFS.
� One BVC for each cell (Point-To-Point BVC) to identify traffic to a particular cell within a NSE.
� One BVC-SIG (identified by BVCI0 : the fine black line) for signaling with the BSC (one per NSE).
▼ The standard also provides for BVC-PTMs. Not implemented.
▼ NSEI and BVCI are information items included in all messages between SGSN and MFS. This information must be consistent on either sides of the Gb interface.
▼ Review of the role of the BSSGP:
� to relay LLC frame (one LLC frame encapsulated into one BSSGP frame) and offer QoS over the Gb
� BVC management = management of packet traffic flow for a cell (DL flow control mechanisms, BVC supervision procedures, etc)
� MFS-SGSN signaling for LLC relay management and MS mobility management
1 High priority Service commitments shall be maintained ahead of precedence classes 2 and 3.
2 Normal priority Service commitments shall be maintained ahead of precedence class 3.
3 Low priority Service commitments shall be maintained after precedence classes 1 and 2.
R e lia b i l i t yC la s s
G T P M o d e L L C F ra m e M o d e
L L C D a taP ro te c t io n
R L C B lo c k M o d e
T ra f f ic T y p e
1 A c k n o w le d g e d A c k n o w le d g e d P ro te c te d A c k n o w le d g e d N o n re a l- t im e tra f fic ,e rro r-s e n s it iv ea p p lic a t io n th a t c a n n o tc o p e w ith d a ta lo ss .
2 U n a c k n o w le d g e d A c k n o w le d g e d P ro te c te d A c k n o w le d g e d N o n re a l- t im e tra f fic ,e rro r-s e n s it iv ea p p lic a t io n th a t c a nc o p e w ith in f re q u e n td a ta lo s s .
3 U n a c k n o w le d g e d U n a c k n o w le d g e d P ro te c te d A c k n o w le d g e d N o n re a l- t im e tra f fic ,e rro r-s e n s it iv ea p p lic a t io n th a t c a nc o p e w ith d a ta lo ss ,G M M /S M , a n d S M S .
4 U n a c k n o w le d g e d U n a c k n o w le d g e d P ro te c te d U n a c k n o w le d g e d R e a l- t im e t ra ff ic , e rro r-s e n s it ive a p p lic a tio n th a tc a n c o p e w ith d a ta lo s s .
5 U n a c k n o w le d g e d U n a c k n o w le d g e d U n p ro te c te d U n a c k n o w le d g e d R e a l- t im e t ra ff ic , e rro rn o n -s e n s itive a p p lic a tio nth a t c a n c o p e w ith d a talo s s .
Peak Throughput Class Peak Throughput in octets per second1 Up to 1 000 (8 kbit/s).2 Up to 2 000 (16 kbit/s).3 Up to 4 000 (32 kbit/s).4 Up to 8 000 (64 kbit/s).5 Up to 16 000 (128 kbit/s).6 Up to 32 000 (256 kbit/s).7 Up to 64 000 (512 kbit/s).8 Up to 128 000 (1 024 kbit/s).9 Up to 256 000 (2 048 kbit/s).
Mean Throughput Class Mean Throughput in octets per hour1 100 (~0.22 bit/s).2 200 (~0.44 bit/s).3 500 (~1.11 bit/s).4 1 000 (~2.2 bit/s).5 2 000 (~4.4 bit/s).6 5 000 (~11.1 bit/s).7 10 000 (~22 bit/s).8 20 000 (~44 bit/s).9 50 000 (~111 bit/s).