Layer3 Messages

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BSSAP

GSM 08.06http://www.etsi.fr

The MTP and the SCCP are used to support signalling messages between the Mobile Services SwitchingCenter (MSC) and the Base Station System (BSS). One user function of the SCCP, called BSSApplication Part (BSSAP) is defined. In the case of point-to-point calls the BSSAP uses one signallingconnection per active mobile station having one or more active transactions for the transfer of layer 3messages. In the case of a voice group or broadcast call there is always one connection per cell involvedin the call and one additional connection per BSS for the transmission of layer 3 messages. There is anadditional connection for the speaker in a broadcast call or the first speaker in a voice group call up to thepoint at which the network decides to transfer them to a common channel. Additional connections mayalso be required for any mobile stations in the voice group or broadcast call which the network decides toplace on a dedicated connection. The BSSAP user function is further subdivided into two separatefunctions:

The Direct Transfer Application sub-Part (DTAP), also called GSM L3, is used to transfermessages between the MSC and the MS (Mobile Station); the layer-3 information in thesemessages is not interpreted by the BSS. The descriptions of the layer 3 protocols for the MS-

MSC information exchange are contained in the 04- series of GSM Technical Specifications.

The BSS Management Application sub-Part (BSSMAP) supports other procedures between theMSC and the BSS related to the MS (resource management, handover control), or to a cell withinthe BSS, or to the whole BSS. The description of the layer 3 protocol for the BSSMAP informationexchange is contained in Recommendation GSM 08.08.

Both connectionless and connection-oriented procedures are used to support the BSSMAP. Rec. GSM08.08 explains whether connection oriented or connectionless services should be used for each layer 3procedure. Connection oriented procedures are used to support the DTAP. A distribution function locatedin BSSAP, which is reflected in the protocol specification by the layer 3 header, performs thediscrimination between the data related to those two subparts.

BSSAP messages include the following fields:

DiscriminationDistribution between the two sub-protocols: BSSMAP and DTAP.

DLCIOnly for DTAP. Used in MSC to BSS messages to indicate the type of origination data link connectionover the radio interface.

LengthSubsequent Layer3 message parameter length.

BSSMAP

The BSS Management Application Part (BSSMAP) supports all of the procedures between the MSC and the BSSthat require interpretation and processing of information related to single calls, and resource management. Some ofthe BSSMAP procedures result in, or are triggered by, Radio Resource (RR) management messages defined in GSM04.08.The format of the BSSMAP protocol is as follows:

1 byte

Message type
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Information Element

BSSMAP structure

Message TypeA one octet field defining the message type. This mandatory field uniquely defines the function and format of eachBSSMAP message.

Information ElementEach IE has an identifier which is coded as a single octet. The length of an IE may be fixed or variable and may ormay not include a length indicator.

GSM L3 (DTAP Direct Transfer Application Part )


Global System for Mobile Communications (GSM) is a cellular radio system. The signalling layer 3 provides thefunctions to establish, maintain and terminate circuit-switched connections across a GSM PLMN and other networksto which the GSM PLMN is connected. It provides the necessary supporting functions related to supplementaryservices control and short messages service control. Furthermore it includes the functions necessary for mobilitymanagement and radio resource management.

The layer 3 is composed of three sublayers comprising:

Radio Resource Management (RR)

Mobility management (MM)

Connection Management (CM)

The Connection Management (CM) sublayer is composed of:

Call Control (CC)

Sort Message Support (SMS)

Supplementary Services Support (SS)

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Protocol Distriminator Transaction ID / Skip Indicator

Message Type

Common Information Elements (variable length)

L3 structure

Protocol discriminatorIdentifies the L3 protocol to which the standard layer 3 message belongs. Values may be as follows:0000 Group call control0001 Broadcast call control

0010 PDSS10011 Call control; call related SS messages0100 PDSS20101 Mobility Management Messages0110 Radio resources management messages1001 SMS messages1011 Non-call related SS messages1110 Extension of the PD to one octet length1111 Tests procedures described in TS GSM 11.10


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Transaction ID / Skip identifierThe value of bits 5 to 8 depends on the protocol used.

Message typeUniquely defines the function and format of each GSM L3 message. The message type is mandatory for allmessages. The format of the message type is as follows:

8 7 6 - 1

0 N(SD) Message type

Message type IE

N(SD)For MM and CM, N(SD) is set to the value of the send state variable. In other level 3 messages, bit 7 is set to 0 bythe sending side. Messages received with bit 7 set to 1 are ignored.Message typeThe message type determines the function of a message within a protocol in a given direction. The meaning of themessage type is therefore dependent on the protocol (the same value may have different meanings in differentprotocols) and direction (the same value may have different meanings in the same protocol, when sent from theMobile Station to the network and when sent from the network to the Mobile Station).

RR


RR (Radio Resource) management procedures include the functions related to the management of the commontransmission resources, e.g., the physical channels and the data link connections on control channels. The generalpurpose of Radio Resource procedures is to establish, maintain and release RR connections that allow a point-to-point dialogue between the network and a Mobile Station. This includes the cell selection/reselection and thehandover procedures. Moreover, Radio Resource management procedures include the reception of the uni-directional BCCH and CCCH when no RR connection is established. This permits automatic cellselection/reselection.

4 4

Protocol Distriminator Skip Indicator

Message Type


RR structure

Protocol discriminator0110 identifies the RR Management protocol.Skip identifierValue of 0000.

Message typeUniquely defines the function and format of each RR message. The message type is mandatory for all messages. RRmessage types may be:

00111--- Channel establishment messages:011ADDITIONAL ASSIGNMENT111 IMMEDIATE ASSIGNMENT001 IMMEDIATE ASSIGNMENT EXTENDED010 IMMEDIATE ASSIGNMENT REJECT


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00110--- Ciphering messages:101 CIPHERING MODE COMMAND010 CIPHERING MODE COMPLETE

00101--- Handover messages:110 ASSIGNMENT COMMAND001 ASSIGNMENT COMPLETE111 ASSIGNMENT FAILURE

011 HANDOVER COMMAND100 HANDOVER COMPLETE000 HANDOVER FAILURE101 PHYSICAL INFORMATION

00001--- Channel release messages:101 CHANNEL RELEASE010 PARTIAL RELEASE111 PARTIAL RELEASE COMPLETE

00100--- Paging messages:001 PAGING REQUEST TYPE 1010 PAGING REQUEST TYPE 2100 PAGING REQUEST TYPE 3111 PAGING RESPONSE

00011--- System information messages:000 SYSTEM INFORMATION TYPE 8

001 SYSTEM INFORMATION TYPE 1010 SYSTEM INFORMATION TYPE 2011 SYSTEM INFORMATION TYPE 3100 SYSTEM INFORMATION TYPE 4101 SYSTEM INFORMATION TYPE 5110 SYSTEM INFORMATION TYPE 6111 SYSTEM INFORMATION TYPE 7

00000--- System information messages:010 SYSTEM INFORMATION TYPE 2bis011 SYSTEM IN FORMATION TYPE 2ter101 SYSTEM INFORMATION TYPE 5bis

110 SYSTEM INFORMATION TYPE 5ter00010--- Miscellaneous messages:

000 CHANNEL MODE MODIFY010 RR STATUS

111 CHANNEL MODE MODIFY ACKNOWLEDGE100 FREQUENCY REDEFINITION101 MEASUREMENT REPORT

110 CLASSMARK CHANGE011 CLASSMARK ENQUIRY

MM


The main function of the Mobility Management (MM) sub-layer is to support the mobility of user terminals, such asinforming the network of its present location and providing user identity confidentiality. A further function of the MMsub-layer is to provide connection management services to the different entities of the upper Connection

Management (CM) sub-layer.

The structure of the MM sub-layer is the same as that ofRR.

Protocol discriminator0101 identifies the MM protocol.
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Message typeMM message types may be as follows. Bit 8 is reserved for possible future use as an extension bit. Bit 7 is reservedfor the send sequence number in messages sent from the mobile station.

0x00----Registration messages:0001 IMSI DETACH INDICATION0010 LOCATION UPDATING ACCEPT

0100 LOCATION UPDATING REJECT1000 LOCATION UPDATING REQUEST

0x01---- Security messages:0001 AUTHENTICATION REJECT0010 AUTHENTICATION REQUEST0100 AUTHENTICATION RESPONSE1000 IDENTITY REQUEST1001 IDENTITY RESPONSE1010 TMSI REALLOCATION COMMAND1011 TMSI REALLOCATION COMPLETE

0x10---- Connection management messages:0001 CM SERVICE ACCEPT0010 CM SERVICE REJECT0011 CM SERVICE ABORT0100 CM SERVICE REQUEST1000 CM REESTABLISHMENT REQUEST1001 ABORT

0x11---- Miscellaneous messages:0001 MM STATUS

CC


The call control (CC) protocol is one of the protocols of the Connection Management (CM) sublayer. Every mobilestation must support the call control protocol. If a mobile station does not support any bearer capability at all then itmust respond to a SETUP message with a RELEASE COMPLETE message. In the call control protocol, more thanone CC entity are defined. Each CC entity is independent from each other and communicates with the correspondentpeer entity using its own MM connection. Different CC entities use different transaction identifiers.

Certain sequences of actions of the two peer entities compose elementary procedures. These elementary proceduresmay be grouped into the following classes:

Call establishment procedures.

Call clearing procedures.

Call information phase procedures.

Miscellaneous procedures.

The terms "mobile originating" or "mobile originated" (MO) are used to describe a call initiated by the mobile station.

The terms "mobile terminating" or "mobile terminated" (MT) are used to describe a call initiated by the network.

The CC structure is shown here:

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Protocol Distriminator Transaction ID

Message Type


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CC structure

Protocol discriminator0011 identifies the CC protocol.Transaction IdentifierThe format of the transaction identifier is as follows:

8 7 - 5 4 - 1

TI flag TI value - - - -

Transaction Identifier

TI flagIdentifies who allocated the TI value for this transaction. The purpose of the TI flag is to resolve simultaneousattempts to allocate the same TI value.

TI value

TI values are assigned by the side of the interface initiating a transaction. At the beginning of a transaction, a free TIvalue is chosen and assigned to this transaction. It then remains fixed for the lifetime of the transaction. After atransaction ends, the associated TI value is free and may be reassigned to a later transaction. Two identicaltransaction identifier values may be used when each value pertains to a transaction originated at opposite ends of theinterface.

Message typeCC message types may be as follows. Bit 8 is reserved for possible future use as an extension bit. Bit 7 is reservedfor the send sequence number in messages sent from the mobile station.

0x000000 Escape to nationally specific message types0x00----Call establishment messages:

0001 ALERTING1000 CALL CONFIRMED

0010 CALL PROCEEDING0111 CONNECT1111 CONNECT ACKNOWLEDGE1110 EMERGENCY SETUP0011 PROGRESS0101 SETUP

0x01---- Call information phase messages:0111 MODIFY1111 MODIFY COMPLETE0011 MODIFY REJECT0000 USER INFORMATION1000 HOLD1001 HOLD ACKNOWLEDGE1010 HOLD REJECT1100 RETRIEVE

1101 RETRIEVE ACKNOWLEDGE1110 RETRIEVE REJECT

0x10---- Call clearing messages:

0101 DISCONNECT1101 RELEASE1010 RELEASE COMPLETE

0x11---- Miscellaneous messages:

1001 CONGESTION CONTROL1110 NOTIFY1101 STATUS0100 STATUS ENQUIRY


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0101 START DTMF0001 STOP DTMF0010 STOP DTMF ACKNOWLEDGE0110 START DTMF ACKNOWLEDGE0111 START DTMF REJECT1010 FACILITY

SMS


The purpose of the Short Message Service (SMS)is to provide the means to transfer messages between a GSMPLMN Mobile Station and a Short Message Entity via a Service Center, as described in TS GSM 03.40. The terms"MO" - Mobile Originating - and "MT" - Mobile Terminating - are used to indicate the direction in which the shortmessage is sent.

The SMS structure is as follows for control messages:

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Protocol Distriminator Transaction ID

Message Type


SMS CP structure

Protocol discriminator1001 identifies the SMS protocol.

Transaction IdentifierSeeCCfor the format of the Transaction ID.

Message type

The message type, together with the protocol discriminator, identifies the function of the message being sent.Messages may be of the following:00000001 CP-DATA00000100 CP-ACK00010000 CP-ERROR


The SMS structure is as follows for relay messages:

8 - 4 3 - 1

0 0 0 0 0 MTI

Message Reference


SMS structure

MTIMessage type indicator. Values are as follows:
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Bit Value (3 2 1) Direction RP-Message0 0 0 ms -> n RP-DATA0 0 0 n -> ms Reserved0 0 1 ms -> n Reserved0 0 1 n -> ms RP-DATA0 1 0 ms -> n RP-ACK0 1 0 n -> ms Reserved

0 1 1 ms -> n Reserved0 1 1 n -> ms RP-ACK1 0 0 ms -> n RP-ERROR1 0 0 n -> ms Reserved1 0 1 ms -> n Reserved1 0 1 n -> ms RP-ERROR1 1 0 ms -> n RP-SMMA1 1 0 n -> ms Reserved1 1 1 ms -> n Reserved1 1 1 n -> ms Reserved

Message ReferenceUsed to link an RP-ACK message or RP-ERROR message to the associated RP-DaATA or RP-SMNA message.


Mobile IP

RFC2002: http://www.cis.ohio-state.edu/htbin/rfc/rfc2002.html

Mobile IP enables nodes to move from one IP subnet to another. Each mobile node is always identified by its homeaddress, regardless of its current point of attachment to the Internet. While situated away from its home, a mobilenode is also associated with a care-of address, which provides information about its current point of attachment to theInternet. The protocol allows registration of the care-of address with a home agent. The home agent sendsdatagrams destined for the mobile node through a tunnel to the care- of address. After arriving at the end of thetunnel, each datagram is then delivered to the mobile node. It can be used for mobility across both homogeneous andheterogeneous media. Mobile IP defines a set of new control messages, sent with UDP, Registrat ion Request andRegistration Reply.

The IP packet consists of the IP source address and IP destination address, followed by the UDP source port anddestination port followed by the Mobile IP fields. Mobile IP packets can be either Registration Request or RegistrationReply. The format of the Mobile IP Registration Request header is shown in the following illustration:

8 16 32 bits

Type S B D M G VRsv

Life Time

Home Address

Home Agent

Care-of Address

Identification

Extensions

Mobile IP registration request

TypeType=1 specifies a registration request.
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SSimultaneous bindings. If the S bit is set, the mobile node is requesting that the home agent retain its prior mobilitybindings.

BBroadcast datagrams. If the B bit is set, the mobile node requests that the home agent tunnel to it any broadcastdatagrams that it receives on the home network.

DDecapsulation by mobile node. If the D bit is set, the mobile node will itself decapsulate datagrams which are sent tothe care-of address. That is, the mobile node is using a co-located care-of address.

MMinimal encapsulation. If the M bit is set, the mobile node requests that its home agent use minimal encapsulation fordatagrams tunneled to the mobile node.

GGRE encapsulation. If the G bit is set, the mobile node requests that its home agent use GRE encapsulation fordatagrams tunneled to the mobile node.

VVan Jacobson. The mobile node requests that its mobility agent use Van Jacobson header compression over its linkwith the mobile node.

RsvReserved bits (2) are sent as zero.

Life TimeLife Time. The number of seconds remaining before the registration is considered expired.

Home AddressIP address of the mobile node.Home AgentIP address of the mobile node's home agent.

Care-of AddressIP address for the end of the tunnel.

IdentificationA 64-bit number, constructed by the mobile node, used for matching Registration Requests with Registration Replies,and for protecting against replay attacks of registration messages.

ExtensionsThe fixed portion of the Registration Request is followed by one or more Extensions. The Mobile-Home

Authentication Extension must be included in all Registration Requests.

The format of the Mobile IP Registration Reply header is shown in the following illustration:

8 16 32 bits

Type Code Life Time

Home Address

Home Agent


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Identification

Extensions

Mobile IP registration request

Type

Type=3 specifies a registration reply.

CodeA value indicating the result of the registration request. The following values are defined for use within the Code field.

Registration successful:0 Registration accepted1 Registration accepted, but simultaneous mobility bindings unsupported

Registration denied by the foreign agent:64 Reason unspecified65 Administratively prohibited66 Insufficient resources67 Mobile node failed authentication68 Home agent failed authentication69 Requested Lifetime too long

70 Poorly formed Request71 Poorly formed Reply72 Requested encapsulation unavailable73 Requested Van Jacobson compression unavailable80 Home network unreachable (ICMP error received)81 Home agent host unreachable (ICMP error received)82 Home agent port unreachable (ICMP error received)88 Home agent unreachable (other ICMP error received)

Registration denied by the home agent:128 Reason unspecified129 Administratively prohibited130 Insufficient resources131 Mobile node failed authentication132 Foreign agent failed authentication133 Registration Identification mismatch

134 Poorly formed Request135 Too many simultaneous mobility bindings136 Unknown home agent address

Life TimeLife Time. If the Code field indicates that the registration was accepted, the Lifetime field is set to the number ofseconds remaining before the registration is considered expired. A value of zero indicates that the mobile node hasbeen deregistered. A value of 0xffff indicates infinity. If the Code field indicates that the registration was denied, thecontents of the Lifetime field are unspecified and must be ignored on reception.

Other fields are as in registration request.

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