packet core interfaces

Interfaces, Protocols, Procedures Siemens

TM2110EU01TM_00031

Contents

1 Overview: Interfaces & Protocols 3

1.1 Signaling in GSM Phase1/2 4

1.2 Transmission in the GSM/GPRS-PLMN 6

1.3 GPRS Transmission Plane 8

1.4 GPRS (Signaling Plane) in the GPRS 16

2 The Radio Interface (Layer 1) 21

2.1 Layer 1 of the GSM-/GPRS-Radio Interface Um 22

2.2 Channel Bundling, Sharing of Channels 24

2.3 Channel Coding 26

2.4 Logical GPRS Radio Channels 30

2.5 Multiframes in GPRS 34

3 Activation of GPRS Services 37

3.1 Mobility Management States 40

3.2 Packet Data Protocol PDP States 42

3.3 GPRS Packet Data Transmission 44

3.4 Combined GPRS & IMSI Attach 46

3.5 PDP Context Activation Procedure 48

3.6 Start of Mobile Originated Packet Transfer 50

Interfaces, Protocols, Procedures

Siemens Interfaces, Protocols, Procedures

TM2110EU01TM_00032


TM2110EU01TM_00033

1 Overview: Interfaces & Protocols

Overview:

Interfaces & Protocols

GPRS:

Interfaces,

Protocols & Procedures

Fig. 1


TM2110EU01TM_00034

1.1 Signaling in GSM Phase1/2

In GSM-PLMN phase 1/2 the Signaling System No. 7 SS7 is used for the transmis-sion of signaling information between the components of the network switching sub-system NSS (interfaces B-G), as well as between MSC and BSC (A-interface) and indirection of the external ISDN networks.

SS7 comprises 4 levels, of which the lowest 3 layers are combined to form the mes-sage transfer part MTP whereas level 4 contains different user parts depending onthe tasks to be performed. Level 1 serves for the physical transmission (physicallayer) of data and for the provision of the requested equipment. (e.g. cable connec-tion, radio relay links, ...). In the GSM-PLMN PCM30/PCM24 (E1/T1) is used for therealization of level 1 functions.

Level 2 serves for the safe transmission of signaling information (link layer). Its func-tions include fault location and clearance across a sub-part of the transport.

Level 3 determines the entire transport link (network layer) including the transport ofinformation in the event of faults in individual signaling points (e.g. overload).

The Mobile Application Part MAP is the most important User Part UP (layer 4). Itregulates the mobility aspects in the GSM-PLMN between the MSCs as well as be-tween MSCs and registers. Its functions include amongst others: updating and clear-ance of location information in the VLR, storing of routing information in the HLR, up-dating and supplementing of user profiles in the HLR&VLR, Inter-MSC handover, ...

The ISDN user part ISUP handles the connection-oriented signaling between MSCsand external networks.

GSM-specific signaling between MSC and BSC is defined in the BSS ApplicationPart BSSAP. The BSSAP is subdivided into the Direct Transfer Application PartDTAP used for the BSC-transparent transport of signaling (call control CC and mobil-ity management MM) between MS and MSC, and the BSS Management ApplicationPart BSSMAP used for radio resource management RR.

The signaling connection control part SCCP and transaction capabilities applicationpart TCAP are user-neutral user parts which serve for the support of complex MAPapplications. SCCP can be used also for the support of ISUP and BSSAP.

Layer1 and layer 2 tasks (Link access Protocol for D-channel) on the Asub and Abisinterfaces have been slightly modified as compared to SS7. The radio interface Um inthe GSM-PLMN is set up of three layers.

Layer 1 serves for the physical transmission and includes the implementation of thelogical signaling channels (FDMA/TDMA, multiframes, channel coding, etc.)

Layer 2 functions on Um are performed by a modified LAPD unit (LAPDm).


TM2110EU01TM_00035

Layer 3 on the Um radio interface is subdivided in three sublayers: radio resourcemanagement RR (channel administration, cell selection, power control and hando-ver), mobility management MM and connection management CM (set-up, operationand clear-down of services). The connection management consists of three phases:call control CC, supplementary services support SS and short message servicesSMS support.

Signaling in the GSM-PLMN:(Phase 1 / 2)

HLR AC VLR EIR

ISDNBTS

MS

OMC-B

MSC

OMC-B

L1

L2

L3

MTP

SCCP

TCAP

MAP

MTP

ISUPSCCP

MTP

SCCP

BSSAPDTAPBSSMAP

L1

LAPDm

RR

MM

CM

CC SS SMS

xL1

LAPD

Signalling System

No. 7

SS7RR

LAPD(m)

BSC

Fig. 2 Signaling in the GSM-PLMN based on LAPD(m) and SS7


TM2110EU01TM_00036

1.2 Transmission in the GSM/GPRS-PLMN

Beside the interfaces in the classical GSM PLMN, a number of new interfaces aredefined for the implementation of GPRS services based on the introduction of thenew network elements SGSN and GGSN.

The interfaces Gi (external PDN-GGSN), Gn (GSN-GSN), Gb (SGSN-BSS) and Gd(SGSN-SMS/IWMSC) serve for the transport of both signaling data and of user data.

Interfaces Gp (GSN-GSN in external PLMNs), Gf (SGSN-EIR), Gc (GGSN-HLR), Gs(SGSN-MSC/VLR) and Gr (SGSN-HLR) serve exclusively for the transfer of signalingdata.


TM2110EU01TM_00037

MS BSS SGSN GGSN PDN TE

GGSN

other PLMNs

SMS-GMSC

SMS-IWMSC

MSC/VLR HLR/(GR)

SMS-SC

EIRSGSNGp Gf

Gi

GrGc

Gn

GbUm

Gs

Gd

E C

A

D

Transmission in

the GPRS-PLMN Signalling

Signaling &

user data

Gn

Packet switched

Also for

user data

transmission

Protocolsabove

Layer 1 !!

Fig. 3 Transmission and interfaces in the GPRS PLMN


TM2110EU01TM_00038

1.3 GPRS Transmission Plane

The transmission plane has a layered protocol structure for the transfer of user infor-mation. It includes the control procedures associated with the information transfer,e.g. flow control, fault detection and fault clearance.

The bird's-eye view on the protocols reveals the intention of this structure:

If the application is internet access for example the GPRS MS (WWW client) and thePDN (WWW server) will exchange IP packets. This is the IP protocol below the appli-cation in the stack of the MS and the IP on top of the stack of the GGSN. The rec-ommendations have defined that X.25 protocol is possible too. In case of IP the MShas to be part of the IP world and needs to be identified by an IP address which canbe either temporary or static. This IP address has to remain the same as long as thePDP which is related to this application is active. This is necessary because the PDNis not able to handle the mobility of the subscriber. If the GPRS MS is moving to cellin the service area of another SGSN the GPRS network has to solve the problem bythe IP layer on the Gn interface above the L2 layers. In consequence the fact that theGPRS user is a mobile user is not to be seen by the PDN, the user data is tunneledtransparently.

The air interface makes it necessary to introduce protocols which adopt the size ofthe packets. They perform segmentation/re-assembly depending on the direction ofthe packets to be able to send IP packets via an air interface which consists of burstswhich a fixed bit structure.

One of the main advantages of GPRS compared to HSCSD is that it is packetswitched. This can only be done by introducing new network elements using newhardware/protocols and by changes in the protocol structure on Um to enable packetswitching. The latter is done by the MAC protocol.


TM2110EU01TM_00039

GPRS transmission plane

MAC

GSM RF

RLC

LLC

SNDCP

IP / X.25

Application

MAC

GSM RF

RLC

FR

L1bis

BSSGP

Relay

FR

L1bis

BSSGP

LLC

SNDCP

L1

L2 L2

IP IP

UDP /

TCP

UDP /

TCP

GTP GTP

Relay

IP / X.25

MS BSS SGSN GGSNUm Gb Gn Gi

L1

SNDCP: SubNetwork Depentent Protocol

LLC: Logical Link Control

RLC: Radio Link Control

MAC: Medium Access Control

BSSGP: BSS GPRS Protocol

FR: Frame Relayl

GTP: GPRS Tunnelling Protocol

UDP: User Datagrm Protocol

TCP: Transmission Control Protocol

IP: Internet Protocol

Fig. 4 GPRS protocol layers for data transmission


TM2110EU01TM_000310

Protocol Structure for the interfaces Gi and Gn

The following protocols are needed to pass the user data from the PDN to the SGSN(or vice versa) during GPRS transmission in the GSM-PLMN:

L2, L1: L2 and L1 are the link layer and physical layer of the external networksconnected via the Gi-interface to the GSM-GPRS-PLMN. As such, L2 and L1 aresituated outside the GPRS definition area. However, there has to be an agreement interms of these layers functions between the different network operators (GSM-PLMNand PDN) interconnected via the Gi-interface, or between the GSM network operatorand a transit network.

GTP (GPRS Tunneling Protocol)The GTP task is to tunnel user data and user signaling between the GPRS supportnodes GSN of the GPRS backbone network. The data packets (protocol data unitsPDUs) supplied by different packet data protocols PDPs, e.g. X.25 or IP, have to beencapsulated / de-capsulated by the GTP prior to tunneling. GTP is specified inRec.09.60.

UDP / TCP (User Datagram Protocol / Transmission Control Protocol): UDP andTCP respectively are used for the transfer of data packets encapsulated by the GTPacross the GPRS backbone network. The protocol needed for this is called UDP. Ithas to be supported by all GSNs as minimum solution since it transports data pack-ets (GTP PDUs) of protocols which require a safe data connection (e.g. IP). UDPalso protects transmission against data corruption/mutilation. TCPs have to be sup-ported in the GSNs whenever data packets of protocols have to be transported, re-quiring safe data connections (e.g. X.25). TCP ensures the flow control and providesprotection against loss of data and data corruption.

IP (Internet Protocol): is used in the GPRS backbone network for the routing of userdata and network information. At the beginning, the GPRS backbone network can bebased on the IP version 4. However, the objective envisaged is IP version 6.

L2, L1: L2 and L1 are GPRS-internal link and physical layer. L2 and L1 are situatedoutside the area of GPRS definition. Operator-specific solutions are used here.


TM2110EU01TM_000311

GGSNGn GiSGSNPDN

(e.g. X.25, IP)

En-/De-capsulation PDUs (IP,X.25) tunneling of user data & signalling

data between GSNs

transmit encapsulated GTP data packets protect against data corruption

UDP / TCP Protocols for unreliable / reliable data link (z.B. IP / X.25)

UDP: minimum solution for each GSN TCP includes flow control & data protection

Operator specific

L2Link Layer

IPInternet

Protocol

UDPUser

DatagramProtocol

TCPTransmission

ControlProtocol

GTPGPRS

TunnellingProtocol

L1Physical

Layer

L2Link Layer

L1Physical

Layer

IP / X.25

Relay

GPRS backbone networkIP V4 / V6

extern arrangement PLMN

-PDN necessary

Protocolsvia

Gi, GnGPRS-

transmission plane

Fig. 5 Protocols via Gi and Gn, "Ip over IP"


TM2110EU01TM_000312

Protocol Structure for the interface(s) Gb (and Um)

SNDCP (SubNetwork Dependent Convergence Protocol):The SNDCP supports the following functions: compression/segmentation and joining,multiplexing and de-multiplexing of data packets onto one or several LLC SAPs(service access points). The compression function is applied to the user data of thedata packet and (if applicable) to the packet header. Segmentation is required to limitthe size of the data packets which is transferred by the LLC as one single unit via theradio interface. The SNDCP is specified in the GSM Rec. 04.65.

LLC (Logical Link Control): The LLC layer realizes a highly reliable ciphered logicalconnection and thus provides the basis for maintaining communication between theSGSN and the MS. From the point of view of the LLC layer, there is a complete con-nection between SGSN and MS, even if the RLC/MAC do not support a physicalconnection, i.e. even if no data packets are transferred at that point in time. A physi-cal connection is set-up by the RLC/MAC layer only if the LLC layer supplies the datarequired for transmission. LLC layer has several access points to be able to transportvarious types of data; also, it distinguishes between several quality of service QoSclasses. The LLC layer is also responsible for carrying out the ciphering function inthe GPRS network. LLC is specified in GSM Rec. 04.64.

BSSGP (BSS GPRS Protocol): The BSSGP transports the LLC frames as well asrouting and QoS-related information between the BSS (PCU) and the SGSN. TheBSSGP does not carry out fault correction. It is specified in GSM Rec. 08.18.

FR (Frame Relay): The Network Service (NS) layer transports the BSSGP datapackets. NS is based on frame relay, which thus represents the link layer protocol forthe connection between SGSN and PCU (Gb interface). NS is specified in GSM Rec.08.16.

L1bis: Physical Layer of the Gb-interface. L1bis is realized through E1/T1(PCM30/PCM24)technology.


TM2110EU01TM_000313

RLC

MAC

SNDCPSubNetwork

Dependent

Convergence

Protocol

SGSNGb Gn

transmit LLC frames

& Routing & QoS - Infos

no error correction

Unreliable transport

BSSGP PDUs

FRFrame Relay

IP

UDP /

TCP

GTP

L1bisPhysical

Layer

L2

L1

Relay

BSSGPBSS

GPRS

Protocol

LLCLogical Link

Control

BSS (PCU)

L1bisPhysical

Layer

FRFrame Relay

GSM RF

BSSGPBSS

GPRS

Protocol

Relay

UmE1 / T1 (PCM30/24)

logical connection (even

without physical connection)

different SAPs (SNDCP,

GMM/SM, SMS), QoS,..

Ciphering

Compression

(user data + maybe header)

Segmentation / Re-assembly

Multiplexing / De-Multiplexing

different PDPs

Protocols via

Gb, (Um)GPRS-

transmission plane

SAP: Service Access Point

Fig. 6 Protocols via Gb (and Um)


TM2110EU01TM_000314

Protocol Structure for Um

RLC (Radio Link Control) / MAC (Medium Access Control): RLC and MAC are thelayers used for the implementation of a reliable physical connection via the radio in-terface on which data packets are transported. RLC and MAC are closely associatedwith each other and are defined in GSM Rec. 04.60.

RLC (Radio Link Control): The RLC function supplies a reliable connection (pro-vides BEC) via the radio interface. The physical connection depends on how the ra-dio transmission is realized in each case (L1-dependency). RLC segments LLCframes and re-assembles them respectively. In addition, the RLC carries out sub-multiplexing in order to place more than one MS on a physical channel and to bundleup to 8 physical channels for one MS.

MAC (Medium Access Control): The MAC function controls the signaling proce-dures via Um which are required to obtain network access (access signaling proce-dures), e.g. request and grant of radio resources (packet data channel PDCH). Fur-thermore, the MAC function controls the mapping of LLC frames to the physicalchannels of the radio interface. The identifiers (TFI "Temporary Flow Identifier, USF"Uplink State Flag") which are used by the MAC protocol enable the sharing of physi-cal channels by several MSs. Different mechanisms of allocation of radio resourcesmay be used, dynamic or fixed allocation (to be explained in the next chapter).

GSM RF (Radio Frequency): GSM RF is the physical channel used to transferpacket data via the GSM radio interface Um.


TM2110EU01TM_000315

RLCRadio Link

Control

MAC Medium Access

Control

SNDCP

SGSN

Gb

LLC

BSS (PCU)

L1bis

FR

BSSGP

Relay Segmentation / Re-assembling

LLC-frames RLC radio blocks Backward Error Correction BEC

Protocols via UmGPRS

transmissions plane

GSM RF

UmMS

RLCRadio Link

Control

MAC Medium Access

Control

GSM RF

IP / X.25

Application

GGSN

TE

Access Signalling Procedures

(Requests, Grants)

Sub-Multiplexing:

different MSs 1 physical channel

channel combining 1 MS (1..8 TS)

RLC/MAC:enable reliable

physical connection

via Um

Physical RF-channel

for packet data transmission

Fig. 7 Protocols via Um


TM2110EU01TM_000316

1.4 GPRS (Signaling Plane) in the GPRS

The signaling plane consists of protocols for the control and support of transmissionplane functions:

Control of GPRS network access, e.g. attaching and detaching

Control of the data elements (attributes) of an established network connection andactivation of the packet data protocol PDP (e.g. X.25 / IP) addresses.

Control of the routing path of an established connection in terms of subscriber mobil-ity support.

Support of the network resource allocation to account for various user requests.

Supplementary services implementation

Signaling Plane MS-SGSN:

In addition to the protocols of the transmission plane a further plane, based on thefunctions GSM FR, RLC/MAC and LLC, is required:

GMM/SM (GPRS Mobility Management and Session Management): The GMM/SMprotocol supports mobility management functions such as GPRS attach, GPRS de-tach, safeguarding functions, routing area & location update), and session manage-ment functions as PDP context activation & deactivation & modification.


TM2110EU01TM_000317

MAC

GSM RF

RLC

LLC

GMM/SMGPRS MobilityManagement

& SessionManagement

MAC

GSM RF

RLC

FR

L1bis

BSSGP

Relay

FR

L1bis

BSSGP

LLC

GMM/SMGPRS MobilityManagement

& SessionManagement

MS BSS SGSNUm Gb

GPRS signaling plane

MS-SGSN

Mobility Management functions GPRS attach / detach

security functions Update Location (CGI, RAI) PDP context (de-) activation / modification

Fig. 8 GPRS signaling plane, GMM/SM


TM2110EU01TM_000318

Signaling SGSN - HLR / EIR / SMS-GMSC, GGSN - HLR:

For signaling via Gr-, Gf-, Gd- and Gc-interface, i.e. between SGSN and HLR, EIR,SMS-GSMC and between GGSN and HLR the same protocols of Signaling SystemNo. 7 (SS7) are used as in the NSS of GSM-PLMN (Phase1/2). The realization of theMessage Transfer Parts MTP (L1 L3), of the Signaling Connection Control PartSCCP as well as of the Transaction Capabilities Application Parts TCAP are identi-cal.

MAP (Mobile Application Part): The MAP used in GSM (Phase1/2) needs to be ex-panded by mobility management functions particularly in view of the information ex-change between SGSN and GGSN and between SGSN and HLR respectively (GSMRec. 09.02.)

The information flow between GGSN and HLR can also flow across further GSNsand is tunneled in this case by using the GPRS tunneling protocol GTP between theGSNs (Gn-interface).

Signaling plane SGSN MSC/VLR

Signaling via the Gs interface, i.e. between SGSN and MSC/VLR, uses the sameprotocols of the SS7 as the ones used via the A-interface of the GSM-PLMN (GSMRec. 09.16).

BSSAP+ (BSS Application Part+): Signaling is performed via a subset of theBSSAP functions used on the A-interface (GSM Rec. 09.18).

Signaling plane GSN-GSN:

The exchange of signaling information between the different GPRS Support NodesGSN (Gn-interface), i.e. via the IP-based GPRS backbone uses the correspondingtransmission plane protocols: L1, L2 (operator-specific), IP (V4, later V6), UDP (UserDatagram Protocol) and GTP (GPRS Tunneling Protocol). The GTP tunnels bothuser and signaling data between the various SGSN and GGSN.


TM2110EU01TM_000319

L1

SCCP Signalling Connection

Control Part

TCAP Transaction

Capabilities

Application Part

MAP Mobile

Application

Part

MTP L2

MTP L3

L1

SCCP

TCAP

MAP Mobile

Application

Part

MTP L2

MTP L3

L1

SCCP

MTP L2

MTP L3

L1

SCCP

MTP L2

MTP L3

BSSAP+BSS Application

Part +

BSSAP+ BSS Application

Part +

SGSN HLR, EIR, SMS-GMSCGr,f,d

GPRS Signaling plane

SGSN MSC/VLRGs

GGSN HLRGc

MAP enhanced for GPRS Subset of BSSAP functions

Fig. 9 GPRS signaling plane, protocol stack for CSS7-interfaces


TM2110EU01TM_000320


TM2110EU01TM_000321

2 The Radio Interface (Layer 1)

The Radio Interface Um

(Layer 1)

GPRS:

Interfaces,


Fig. 10


TM2110EU01TM_000322

2.1 Layer 1 of the GSM-/GPRS-Radio Interface Um

By introducing GPRS services into the GSM-PLMN, world-wide modifications arenecessary also in the area of physical transmission (layer1) via the air or radio inter-face Um. The tasks of layer 1 radio interface relate to the transmission of user andsignaling data as well as to the measuring of receiver performance, cell selection,determination and updating of the delayed MS transmission (timing advance TA),power control PC and channel coding.

In the GPRS, a decisive difference to the realization of the connection-oriented serv-ices (circuit-switched services) relates to the fact that a physical channel and a so-called packet data channel can be used by several mobile stations at the same time.One packet data channel is allocated per radio block, i.e. for four consecutive TDMAframes and not for a specific time interval. This means that signaling and the packetdata traffic of several mobile stations can be statistically multiplexed into one packetdata channel. Furthermore, the packet data channel can be seized asymmetrically.

On the other hand it is also possible for a mobile station to use more than one packetdata channel at the same time, i.e. to combine several physical channels of one radiocarrier. In principle, up to 8 packet data channels can be seized simultaneously. Thenumber of channels that are combined for reception (DL) and transmission (UL) canbe different to achieve asymmetric data rates for certain applications (e.g. file transferprotocol FTP, internet surfing).

The assignment of radio resources can be done dynamically or in a fixed allocation.In case of the fixed allocation a message with a bit pattern is sent downlink to indi-cate which channels can be used by this MS for UL transmission.

If dynamic allocation is applied the MS will be receive a temporary flow identifier (TFI)and an uplink state flag (USF) for each of the time slots it is allowed to use. The TFIis part of the control information in the DL packet and identifies the "owner" of thepacket. Each packet also includes an USF that indicates which of the MSs (that hasbeen assigned to use this time slot UL) is allowed to transmit the next radio block UL.


TM2110EU01TM_000323

GSM RF:

GPRS Layer 1 (Um)

L1-

tasks

Transmission

of user &

signaling data

determinate &

actualise

Timing Advance

Cell SelectionMeasure

signal strength

Power Control

functionsResource optimisation:

1 physical channel to be used

by many MSs simultaneously !!

asymmetrical trafficUL / DL possible !!

High data rate trafficup to 171.2 kbit/s:

combining 1..8 PDCH for 1 MS !!

Allocation of physical channel(Packet Data Channel PDCH)

dynamically: 1 or 4 Radio Blocks

(1 Radio Block = 4 Normal Burst

in 4 consecutive TDMA-frames)

User & signalling data of several MSs statistically to be multiplexed into 1 PDCH

(also fixed allocation possible)

Fig. 11 Tasks of the GSM air interface, layer 1 (GSM RF)


TM2110EU01TM_000324

2.2 Channel Bundling, Sharing of Channels

Sharing of Resources in a Cell: GSM circuit switched (CS) users will share the timeslots in a BTS with the GPRS packet switched (PS)users. A physical channel can ei-ther be used for GSM CS or GPRS PS traffic but not for both at the same time. De-pending on the traffic load in the cell there will be more or less channels available forGPRS, CS connections are dealt with priority.

Sharing of Physical Channels: It is a characteristic of a CS connection that thephysical resource (the time slot) is reserved for one subscriber. Therefore theGSM CS users cannot share their channels with others. In contrast GPRS PS sub-scribers can share physical channels. The handling of the channels, the multiplexingof subscribers onto the same time slots is done by software (protocol, MAC) andhardware (PCU). Packet oriented connections are not only carried out through thecore network by usage of an appropriate hardware (ATM switches) and software(protocols) but also on the air interface. This is an important feature of GPRS with re-gard to an optimized usage of resources on Um which is the limiting bottleneck in thePLMN.

Multislot Class: The subscribers for GPRS will have different needs (applications,data rates) and therefore the MS will have more or less capabilities. The network(PCU) will have to identify these different MSs by their multislot class which indicateshow many time slots (channels) can be bundled by the MS uplink and downlink. Acheap GPRS mobile will be a GSM mobile that is able to handle the protocols andcoding schemes of GPRS. This will be multislot class 1: one time slot UL and onetime slot downlink can be "bundled". The other extreme is multislot class 29 whichwill be able to receive and to transmit in eight time slots UL and DL simultaneously. Inconsequence such a MS has to have two synthesizers, and a high battery capacitybecause this is more or less continuous transmission and reception. The MS willsend its multislot class and the PCU will only assign time slot combinations which canbe handled by this equipment.


TM2110EU01TM_000325

Channel Bundling, Sharing of Channels

e.g. BTS with 2 RFCs => 2 TRX = 16 channels

RFC 1

RFC 2

UL

RFC 1

RFC 2

DL sharing of physicalchannels

=> packet switching

on UmTDMA frame = 8 time slots

multislot classes29 classes defined

assignment of

channels by PCU

according to

capabilities of MS

identifying high

end and low cost

MS

e.g. 6 GSM

CS users

e.g. 4 GPRS

PS users

Signaling:

BCCH,

SDCCHs,...

time

slot

Fig. 12 Channel Bundling, sharing of channels, multislot classes


TM2110EU01TM_000326

2.3 Channel Coding

Channel coding was modified substantially for GPRS purposes (GSM Rec. 03.64).

Channel coding starts with the division of digital information into transferable blocks.These radio blocks, i.e. the data to be transferred (prior to encoding) comprise:

a header for the Medium Access Control MAC (MAC Header)

signaling information (RLC/MAC Signaling Block) or user information (RLC DataBlock) and

a Block Check Sequence BCS.

The functional blocks (radio blocks) are protected in the framework of convolutionalcoding against loss of data. Usually, this means inserting redundancy.

Furthermore, channel coding includes a process of interleaving, i.e. different ar-rangement in time. The convolutional radio blocks are interleaved to a specific num-ber of bursts/burst blocks. In the case of GPRS, interleaving is carried out across fournormal bursts NB in consecutive TDMA frames and, respectively, to 8 burst blockswith 57 bit each.

Four new coding schemes were introduced for GPRS (Rec. 03.64): CS-1 to CS-4.These can be used alternatively depending on the information to be transferred andon the radio interfaces quality.


TM2110EU01TM_000327

Channel Coding

collectuser datasignaling

RLC Data Block BCSMAC Header

RLC/MAC Control Block BCSMAC Header

Convolutional

coding

(not CS-4)

Radio Block

Radio Block

BCS: Block Code Sequence

(for error recognition)

Radio Block

(Redundancy !)rate 1/2 convolutional coding

Radio Block (456 Bits)

puncturingPuncturing(only CS-2, CS-3)

4 new Coding Schemes:

CS-1, -2, -3, -4

MAC: Medium Access Control

RLC: Radio Link Control

Interleaving 57 Bit 8 Burst-blocks

57 Bit 57 Bit 57 Bit57 Bit

Um: Allocation of PDCH for 1 / 4 Radio Blocks = 4 / 16 Normal Bursts

Fig. 13 Channel Coding, RLC/MAC blocks, redundancy


TM2110EU01TM_000328

Coding Schemes:

CS-1: CS-1 uses the same coding scheme as specified by Rec. 05.03 for theSDCCH. It comprises a half rate convolutional code for FEC forward error correction.CS-1 corresponds to a data rate of 9.05 kbit/s.

CS-2 and CS-3 are punctured version of the same half rate convolutional code asCS-1. The coded bits are numbered starting from 0 and certain punctured bits areremoved.

CS-2: With CS-2 the punctured bits have numbers 4 i + 3 with i = 3,...,146 (excep-tion: i = 9, 21, 33, 45, 57, 69, 81, 93, 105, 117, 129, 141). This means that none ofthe first 12 bits is punctured. CS-2 corresponds to a data rate of 13.4 kbit/s. Remark:For CS-2 the puncturing pattern must be adapted to the future new TRAU frame for-mat in order to be used via the Abis interface (e.g. more bits must be punctured tomake space for RLC signaling).

CS-3: With CS-3 the punctured bits have numbers 6 i + 3 and 6 i + 5 with i =2,...,111. CS-3 correspond to a data rate of 15.6 kbit/s.

CS-4: CS-4 has no redundancy (no FEC) and corresponds to a data rate of 21.4kbit/s.

By bundling up to 8 packet data channels of one carrier into one MS, transmissionrates up to 171.2 kbit/s are possible.


TM2110EU01TM_000329

9,05 kbit/s 13,4 kbit/s 15,6 kbit/s 21,4 kbit/s

CS-1 CS-2 CS-3 CS-4 differentredundancy

(FEC) Quality Um

Coding

Scheme

Code

Rate

Radio

Block*

Coded

Bits

Punctured

Bits

Data Rate

kbit/s

CS-1 1 / 2 181 456 0 9,05

CS-2 2 / 3 268 588 132 13,4

CS-3 3 / 4 312 676 220 15,6

CS-4 1 428 456 0 21,4

common

coding & interleaving

for 4 Normal Bursts:456 Bit coded user

data

bundling

1..8 TS

max. 171,2 kbit/s

Channel Coding: Coding Schemes

* Radio Block without

Uplink State Flag USF &

Block Check Sequence BCS

Fig. 14 Coding schemes of GPRS, CS1 with high redundancy, CS4 no redundancy, radio blocks


TM2110EU01TM_000330

2.4 Logical GPRS Radio Channels

Use of "classical" logical channels for GSM-CS

A Logical channel is used for a special purpose/contents. For example the MSs haveto find out if this cell is a suitable one (operated by the "right" network operator),which features are offered (e.g. HR/FR/EFR, GPRS, ...), what is the structure of Um(channel combination), ... This is provided by the BCCH which is naturally onlytransmitted in the downlink. Some resources have to be given for initial access for theMS (RACH). For these reasons logical channels have been defined to fulfil all taskswhich are necessary in a GSM network on the air interface (see figure 13).

The GPRS subscribers will share the air interface with the circuit switched users. Onthe other hand the protocol structure of GPRS is different from "classical" GSM-CS.Therefore the user traffic and (part of) the signaling will have to be separated. Beforethis separation can take place the different MS (GPRS/non-GPRS) have to be han-dled by signaling procedures for access (channel assignment. There are two solutionof this problem. The first one is to use (some of) the logical channels for GSM-CS:

The GPRS-MS detects the BCCH of this particular cell and looks for the system in-formation to find out if GPRS is available. If this is a cell belonging to the same rout-ing area the MS can choose this cell and wait for paging or for the user to use theRACH for activating a PDP. In case that the user wants to run an PS application theGPRS MS will use an access burst (RACH) which indicates that this is a GPRS MSand the request will be answered by the PCU assigning resources for packetswitched traffic (time slots reserved for GPRS). Signaling (e.g. for authentication) willthen take place using these resources indicated by the message in the AGCH.

So GPRS uses some of the logical channels of GSM-CS. On one hand this can bean advantage if the resources are sufficient. On the other hand if in the future moreand more GPRS traffic has to be handled, separate logical channels reserved forGPRS MS will have to be given. This is the second solution. In any case the GPRSMS will have to look for the BCCH of the cell to find out if GPRS is available. If thesecond solution has been chosen the GPRS MS will also read information where aPBCCH (Packet Broadcast Control Channel) is to be found (which time slot). Thissecond solution will be explained in figure 14.


TM2110EU01TM_000331

Allocation of dedicated signaling channel

Dedicated signaling MS BTSE (CallSetup, LUP, Security, SMS, CBCH,...)

Signaling

Traffic

User Data

DL

DL

UL

UL + DL

DL

UL

+

BCCH

FCCH

SCH

PCH

AGCH

RACH

SDCCH

SACCH

FACCH

TCH/F

TCH/H

CGI, FR/EFR/HR, GPRS available frequency hopping, channel combination,...)

frequency synchronization

Time synchronization + BSIC, TDMA-No.

Paging / Searching (MTC)

Request for access

Measurement Report, TA, PC, cell parameters,...

Signaling instead of TCH

BCH

CCCH

DCCH

User traffic (Full Rate)

User traffic (Half Rate)

Logical channel(for GSM Circuit Switched)

Synchronisation Channel

Frequency Correction Channel

Access Grant Channel

Random Access Channel

Paging Channel

Broadcast Control Channel

Stand Alone Dedicated

Control Channel

Broadcast Channel

Slow Associated

Control Channel

Fast Associated

Control Channel

Traffic Channe/Fl

Traffic Channel/H

Dedicated Control Channel

Common Control Channel

Fig. 15 "Classical" logical channels of GSM may be used by GPRS users too


TM2110EU01TM_000332

Use of new logical channels for GPRS

In addition to the nine existing logical radio channels used for signaling (BCCH, SCH,FCCH, PCH, RACH, AGCH as well as SDCCH, SACCH and FACCH) and the TrafficChannel (TCH) for circuit switched user information, a new set of logical channelswas defined for GPRS.

Packet traffic is realized by means of the Packet Traffic Channel (PTCH) which in-cludes the following :

Packet Data Traffic Channel PDTCH.

Packet Associated Control Channel PACCH

The PDTCH is temporarily assigned to the mobile stations MS. Via the PDTCH, userdata (point-to-point or point-to-multipoint) or GPRS mobility management and sessionmanagement GMM/SM information is transmitted.

The PACCH was defined for the transmission of signaling (low level signaling) to adedicated GPRS-MS. It carries information relating to data confirmation, resource al-location and exchange of power control information.

New GPRS signaling channels are mainly specified analogously to GSM Phase1/2.

The Packet Common Control Channel PCCCH has been newly defined. It consistsof a set of logical channels which are used for common control signaling to start theconnection set-up:

Packet Random Access Channel PRACH

Packet Paging Channel PPCH

Packet Access Grant Channel PAGCH

Packet Notification Channel PNCH

PRACH and PAGCH fulfil GPRS-MS functions which are analogue to the classicallogical channels RACH and AGCH for non-GPRS-users. The PNCH is used for theinitiation of point-to-multipoint multicast (PtM multicast).

For the transmission of system information to the GPRS mobile stations, the

Packet Broadcast Control Channel PBCCH

was defined analogue to the classical BCCH.

In a physical channel all different types of logical channels can be contained (noseparation into traffic and signaling channels respectively as is done in conventionalGSM). The differentiation of channel contents is carried out per radio block using theMAC header, i.e. contents are specified for the four normal bursts of a radio blocksent in each case.

The MAC function, which distributes the physical channel to the various mobile sta-tions and allocates radio resources to an MS can also use the conventional logicalchannels in GSM.


TM2110EU01TM_000333

Packet-

Signaling

PacketTraffic Channel

PTCH

DL

DL

UL

UL & DL

PDTCHPacket Data

Traffic Channel

PACCHPacket AssociatedControl Channel

System informationfor GPRS-MS

Packet

Common Control

Channels

PCCCH

New logical channel

for GPRSPBCCH

Packet Broadcast

Control Channel

PPCHPacket

Paging Channel

PAGCHPacket AccessGrant Channel

PNCHPacket

Notification Channel

PRACHPacket RandomAccess Channel

Paging

GPRS-MS

Resource Allocationfor Setup of

Packet-Transfer

Notification

for GPRS-MS inPtM Multicast

access request for UL

packet data transmissionDedicated signaling MS-network

e.g.: Acknowledgements,

Power Control, Resource(Re-)Assignment

Transmission of user packet data;Multislot operation:

1 MS - many PDTCH simultaneously

Fig. 16 New logical channels for GPRS


TM2110EU01TM_000334

2.5 Multiframes in GPRS

The GPRS packet data traffic is arranged in 52-type multiframes (GSM Rec. 03.64).52 TDMA frames in each case are combined to form one GPRS traffic channel multi-frame which is subdivided into 12 blocks with 4 TDMA frames each. One block(B0-B11) contains one radio block each (4 normal bursts, which are related to eachother by means of convolutional coding). Every thirteenth TDMA frame is idle. Theidles frames are used by the MS to be able to determine the various base stationidentity codes BSIC, to carry out timing advance updates procedures or interferencemeasurements for the realization of power control.

For packet common control channels PCCH, conventional 51-type multiframes canbe used for signaling or 52-type multiframes. The GPRS users can use "classical"common control channels of GSM before they will be directed onto their PTCHs. TheBCCH will be read by all mobiles anyway. Either in case of GSM mobiles to fulfil thesame tasks as before and for GPRS equipment this logical channel will indicateweather GPRS service is available and if extra logical channels (PBCCH, PPCH, ...)are used.

GSM CS traffic and GPRS subscribers are clearly separated so that there is no con-flict due to different signaling or multiframe structure.

It is important that there are no "visible" changes for "GSM only mobiles" due to theintroduction of GPRS. GSM CS connections will use for example the same 26 multi-frame structure for TCH an the 51 multiframe structure for signaling.


TM2110EU01TM_000335

iB0 B1 B2 B3 B4 B5 i B6 B7 B8 i B9 B10 B11 i

52 TDMA Frames = PDCH Multiframe

4 Frames 1 Frame

New multiframe

for GPRS PDCH follows 52 multiframe structure

52 Multiframe: 12 Blocks 4 TDMA-frames

PCCCHs: classical 51er Multiframes

or 52er Multiframes

B0 - B11 = Radio Blocks (Data / Signaling)

i = Idle frame

BCCH indicates PDCH with PBCCH (in B0)

DL: this PDCH bears PDCCH & PBCCH

PBCCH in B0 (+ max. 3 further blocks; indicated in B0)

PBCCH indicates PCCCH blocks & further PDCHs with PCCCH

UL: PDCH with PCCCH: all blocks to be used for PRACH, PDTCH, PACCH

PDCH without PCCCH: PDTCH & PACCH only

Idle frame: Identification of BSICs

Timing Advance Update Procedure Interference measurements for Power Control

Fig. 17 Multiframes for GPRS consist of a certain time slot in 52 consequent TDMA frames


TM2110EU01TM_000336


TM2110EU01TM_000337

3 Activation of GPRS Services

Activation of

GPRS services

GPRS:

Interfaces,


Fig. 18


TM2110EU01TM_000338

States of the GPRS services

With regard to point-to-point PtP packet data transmission the GPRS service oper-ates in two independent state models/circles. One circle describes the mobility man-agement behavior whereas the other is assigned to the activation of a packet dataprotocol PDP.

The circle related to mobility management states in the MS and the associated SGSNconsist of the :

"Idle" state

"Standby" state

"Ready" state

The circle related to a specific packet data protocol has the:

"Inactive" state

"Active" state


TM2110EU01TM_000339

Packet Data

Protocol

PDP

States of

GPRS services 2 circlesregarding:

Inactive

State

Active

State

Idle

State

Ready

State

Standby

State

Mobility

Management

Fig. 19 States of GPRS services with regard to mobility management and packet data protocols


TM2110EU01TM_000340

3.1 Mobility Management States

"Idle" state

A mobile station MS in the idle state is detached from the GPRS. Only GPRS sub-scription data is available in the HLR. No further information exists in other networkunits such as SGSN and GGSN. It is not possible to activate a packet data protocolPDP or to maintain a PDP in its active state. The GPRS MS must monitor the BCCHto determine the availability of cells which support GPRS services. Accordingly, theGPRS MS can carry out PLMN and cell selection procedures. To exit idle state, theMS must execute the attach procedure. Upon successful completion of this proce-dure, the MS changes to ready state.

"Standby" state

In the standby state the GPRS MS is attached to the GPRS network. The GPRS andthe SGSN have a mobility management context comparable to the circuit switchedconnections. The MS monitors the broadcast channel to determine the availability ofcells offering GPRS services and also the paging channel PCH, to be informed aboutpaging requests. The SGSN recognizes/stores the routing area RA of the GPRS-MS.The routing area is a sub-unit of the location area LA, in other words a more detaileddetermination of the GPRS-MS location. The GPRS-MS informs the SGSN aboutchanges of the routing area and answers paging requests.

"Ready" state

In the ready state, the SGSN detects the current cell of the GPRS-MS beyond therouting area RA of the GPRS-MS. If the GPRS-MS changes cells, it informs theSGSN. Paging is thus superfluous in the ready state. The DL packet data transfercan be performed any time. Ready state does not mean that a physical connection isestablished between SGSN and MS. Only in the ready state, SGSN and MS cantransfer data packets. MS and SGSN exit ready state upon expiry of a ready timer orin case of a faulty packet data transmission and change to standby state. Upon log-off, i.e. execution of a detach procedure, MS and SGSN exit ready state and changeto idle state.


TM2110EU01TM_000341

Mobility Management

States

IDLE

state

READYstate

STANDBY

state

GPRS

detach

expire

STANDBY Timerexpire READY Timer /

Transmission errors

GPRS

attach

SGSN: Paging /

MS: initiates Transfer

SGSN & GGSN without

MS information only HLR contains subscription data no PDP context can be activated

MS observes BCCH PLMN- & Cell Selection

SGSN knows Routing Area & cell !!

UL & DL packet transmission possible

SGSN MS: MM-Context SGSN knows Routing Area

MS observes BCCH, PCH initiates RA-Update reacts to Paging Request

MS initiates Cell Update

Fig. 20 Mobility management states


TM2110EU01TM_000342

3.2 Packet Data Protocol PDP States

There are separate state circles for every authorized PDP of a GPRS-MS

"Inactive" State

The inactive state of a PDP means that this PDP is not operating at that moment.There is no routing context in the MS, SGSN and GGSN. A transition in the activestate is only possible if there is a mobility management connection and if MS andSGSN are in the standby or ready state.

No data transfer is possible in the inactive state. Data packets which reach the GPRSnetwork are either rejected or ignored.

"Active" State

In the active state the MS, GGSN and SGSN are in a routing context. Data can betransmitted or received by the MS. The active state is ended explicitly if the MS de-activates a certain PDP. With GPRS detach and expiry of the standby timer, all theactivated PDP are deactivated, too.


TM2110EU01TM_000343

PDP States

INACTIVE

state

ACTIVE

state

De-activation PDP context /

GPRS detach

expire STANDBY timer

Activation

PDP context

PDP not activated

no Routing-context

for MS, SGSN & GGSN

no data transmission possible !

Transition to Active State

only if MM-context exists( MS & SGSN: STANDBY / READY)

Routing context

for MS, SGSN & GGSN

Data transmission possible !

Fig. 21 States of a Packet Data Protocol


TM2110EU01TM_000344

3.3 GPRS Packet Data Transmission

The transmission of GPRS packet data presupposes the execution of

GPRS Attach Procedure as well as of the

PDP Context Activation Procedure.

In the case of a mobile packet data transfer, a one or two phase packet access isadded. This access procedure is necessary for packet data transfer.

Common Mobility Management / MS-Location

To reduce the signaling load via the radio interface during GPRS and non-GPRS op-eration, important mobility management MM procedures are carried out jointly (com-mon MM). This regards the procedures for : attachment / detachment, location &routing area update and paging.

The result of a GPRS routing area update procedure is stored in the SGSN. Therouting area represents a more exact indication of the MS location, than is actuallyneeded for non-GPRS services. Triggered by the MS ( in the framework of a RA up-date) the SGSN informs the MSC/VLR via the Gs interface of a change in the loca-tion areas which has taken place simultaneously.

Further mobility management procedures are also executed via GPRS procedures. Ifpossible , all messages containing mobility management information, are transferredthrough signaling data packets. The MM procedures are defined in the GGM/SM(GPRS Mobility Management & Session Management).


TM2110EU01TM_000345

GPRS Packet data transfer

GPRS Attach

Procedure

PDP Context

Activation

Procedure

One / Two Phase

Packet Access

RLC Data

Transmission

Common Mobility Management

MS:

GPRS &

Non-GPRS

operation

Reduce Signaling load via Um

Attachment

Detachment

Location Update

Routing Area Update

CS-Paging

GPRS Procedures

MS, SGSN

(GMM/SM)

adjust with

HLR, MSC/VLR

Fig. 22 GPRS packet data transfer, one/two phase access


TM2110EU01TM_000346

3.4 Combined GPRS & IMSI Attach

A first prerequisite for the GPRS data transfer to be carried out is the registration ofthe MS in the GPRS network, i.e. the execution of an attach procedure. If an MS isdesigned for common GPRS & non-GPRS operation, a common procedure for IMSIand GPRS attach is carried out.

Attach Request (1)

Start of the combined attach procedure. In the attach request transmission the MSindicates, which attach (only GPRS or also IMSI) is requested. The MS indicates itsidentities (IMSI or packet TMSI: P-TMSI) and also the routing area identity RAI.

Identification Request / Response (2)

This is needed in case of SGSN change. The old SGSN (determined by the newSGSN via P-TMSI) hands over to the new SGSN the IMSI as well as existing authen-tication triples.

Security procedures (3)

The attach procedure can also contain security functions. The SGSN may request anauthentication of the MS and then initiate ciphering. Furthermore, the MS equipmentnumber in the EIR can be checked, too (IMEI check).

Update Location / Cancel Location & Ack / Insert Subscriber Data & Ack / Up-date Location Ack (4)

In the event of SGSN change or first attach, routing area update procedures areperformed. The HLR is updated, the old SGSN released. The HLR delivers theGPRS subscriber profile to the new SGSN which stores this profile for future PDPcontext activation. The SGSN can then establish a mobility management context forthe MS.

Location Updating Request & Accept (5)

The IMSI attach is effected via SGSN in the framework of a combined routing areaRA /location area LA procedure (location updating request / accept). The SGSN ne-gotiates the IMSI attach procedure with the MSC/VLR. From this, MSC/VLR derivethat the MS is also GPRS-attached and marks the MS accordingly.

Attach Accept & Complete / TMSI Reallocation Complete (6)

If the attach procedure was successful, the SGSN sends an attach accept informa-tion to the MS. Optionally, a P-TMSI re-assignment takes place.

Upon successful completion of the attach procedure, MS and SGSN change to readystate. The MS can now transmit SMS, receive point-to-multipoint PtM messages oractivate a PDP context.


TM2110EU01TM_000347

MS new SGSN old SGSN MSC/VLR HLR

Attach Request

Identification Request

Identification Response

Security functions(if necessary)

Update Location (SGSN-Id.)

Cancel Location

Cancel Location Acknowledge

Insert Subscriber Data

Insert Subscriber Data Acknowledge

Update Location Acknowledge

Location Updating Request

Location Updating Accept

normal LUP with HLR,

maybe with MSC/VLR change

Attach Accept

Attach Complete

only if P-TMSI re-allocation TMSI Reallocation Complete

Common GPRS &

IMSI Attach

Signaling message transferredby conventional signaling channel

by Packet Data Channel PDCH

only for TMSI Reallocation

MS & SGSN: Ready State

1

2

3

4

5

6

(GPRS/IMSI, P-TMSI, RAI,..)

Fig. 23 The combined GPRS/IMSI attach procedure is used to save resources on the air interface


TM2110EU01TM_000348

3.5 PDP Context Activation Procedure

For packet data to be transferred, an attach procedure must be followed by a PDPcontext activation.

Activate PDP Context Request (1)

Normally, the mobile station starts a request to the network in order to activate thedesired PDP context (PDP type, e.g. Internet Protocol, PDP address) with theneeded Quality of Service QoS.

This request can also be started by a network and is then called network request.

Security functions (2)

Here, too, authentication / ciphering / IMEI can be carried out.

Create PDP Context Request & Response (3)

The SGSN checks the authorization of the data delivered in the activate PDP contextrequest, i.e. their agreement with the subscription data stored in the SGSN. The QoSrequests can be limited (network capacity, current load state). The routing context isactivated in the GGSN. Hereby, it is possible to transmit (tunneled) packet data be-tween SGSN and GGSN.

Activate PDP Context Accept (4)

The complete routing context from MS until GGSN is established, activation is com-pleted successfully. Packet data can now be transmitted.

Network Requested PDP Context Activation Procedure

PDP context activation can also be initiated by the network.

(A) If a new PDP Packet Data Unit PDU reaches the GGSN, the latter checkswhether a PDP context is activated.

(B) If there is no PDP context, the GGSN needs routing information (IMSI, SGSNaddress, Mobile Station Not Reachable Reason) from the HLR.

(C) The GGSN contacts the SGSN (IMSI, PDP type, PDP address).

(D) The SGSN request the MS to activate the corresponding PDP context. Then thePDP context activation procedure (see above) is carried out.


TM2110EU01TM_000349

MS SGSN GGSN

Activate PDP Context Request

Security functions(if necessary)

Create PDP Context Request

Activate PDP Context Accept

PDP Context Activation

1

2

3

4

Create PDP Context Response

HLR

PDP PDUSend Routing

Info for GPRS

Send Routing Info forGPRS Ack (SGSN Address,

IMSI, MS Not Reachable Reason)

PDU NotificationRequest

PDU Notification Response

RequestPDP Context Activation

Network Requested

Normal / MS Requested

A

B

C

D

Fig. 24 PDP context activation procedure may be either requested by the MS or by the network


TM2110EU01TM_000350

3.6 Start of Mobile Originated Packet Transfer

An MS initiates a packet data transfer in a One or Two Phase Packet Accessmethod. If the GPRS subscriber uses a RACH to send a channel request only 8 bitare usable to indicate which service is requested. In case of a random access carriedout on a PDCH 11 bit are reserved for the identification of the request. This speedsup the call set-up by avoiding two phase packet accesses.

One Phase Packet Access

(1) Packet Channel Request: this serves as a starting point of the packet data trans-fer in an activated MS and is realized via random access channel RACH or viapacket RACH. The message contains a brief information about the resources neededfor the transfer.

(2) Packet Immediate Assignment: is used for allocation of UL resources to one /several packet data channel(s) PDCH(s) for a number of radio blocks. The packetimmediate assignment message is realized via an access grant channel AGCH orpacket AGCH (PAGCH). The timing advance derived from the received PRACH andRACH respectively and an information about the MS power control are communi-cated to the MS as well.

Two Phase Packet Access

If the allocated resources do not have the requested quality of service, (e.g. only 1time slot allocated), the MS can end the one phase access and initiate a two phaseaccess. Upon (1) and (2) the MS sends to the network message a complete descrip-tion of the resources needed for the UL transfer with the

(3) packet resource request.

(4) packet resource assignment: The network confirms the resource request. Themessage contains information about the resources allocated in each case. (3) and (4)are realized via the packet associated control channels PACCH.

The data transfer, i.e. transport of RLD blocks, can now begin. The RLC data is real-ized as packet data traffic channel PDTCH.


TM2110EU01TM_000351

MS Network

Start Packet data transfer

1

2

Packet Channel Request

Packet Immediate Assignment (TA, PC)

3

4

Packet Resource Request

Packet Resource Assignment

One Phase

Packet Access

Two Phase

Packet Access(optional)

RLC Data Transfer

4RLC block

RLC block

PRACH or RACH

PAGCH or AGCH

PACCH

PACCH

PDTCH

Fig. 25 Start of packet data transfer


TM2110EU01TM_000352

Interfaces, Protocols, ProceduresOverview: Interfaces & ProtocolsSignaling in GSM Phase1/2Transmission in the GSM/GPRS-PLMNGPRS Transmission PlaneGPRS (Signaling Plane) in the GPRS

The Radio Interface (Layer 1)Layer 1 of the GSM-/GPRS-Radio Interface UmChannel Bundling, Sharing of ChannelsChannel CodingLogical GPRS Radio ChannelsMultiframes in GPRS

Activation of GPRS ServicesMobility Management StatesPacket Data Protocol PDP StatesGPRS Packet Data TransmissionCombined GPRS & IMSI AttachPDP Context Activation ProcedureStart of Mobile Originated Packet Transfer

packet core interfaces

Documents