Signalling Prot

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Tik-109/110.300 Fall 2000 © Hannu H. Kari Page 1

Tik-109/110.300

Telecommunications architectures:Protocols

Hannu H. KARI/Helsinki University of Technology (HUT)

TML-laboratory/CS/HUT




Agenda

Protocol designMultivendor interfaces

Handling protocol error

Handling lost packets

Handling corrupted data

Handling failed network elements

Fault tolerant system design

Protocol examples






Protocol design

• Example protocol stack

Um GbMS BSS SGSN

SNDC SMSGMM

LLC

RLC

MAC

GSM RF

Relay

RLC

MAC

GSM RF

BSSGP

Network

Service

L1

SNDC SMSGMM

LLC

BSSGP

Network

Service

L1




Protocol design

• Basic operation model

4. Confirm1. Request 3. Response 2. Indication

Level - N+1

Level - N




Multivendor interfaces

• Proprietary interfaces• Implementations of different manufacturers won’t

necessarily interwork

• Possible manufacturer extensions, interpretations,

solutions, combined equipments, ...

• Multivendor interfaces

• Well defined protocols

• Strong interoperability requirements• Interoperability testing (type approvals)

• Support for multiple versions




Handling protocol errors

• E.g., in GTP protocol (GPRS Tunneling Protocol), theprotocol layer handles:

• Protocol has version numbers

• Handling too short packets

• Unknown and erroneous headers• Unexpected message

• Missing or invalid mandatory elements

• Unknown information element

• Out of sequence information elements

• Repeated information elements

• Incorrect optional information elements

• TLV, TV, V formatting (T=Type, L=Length, V=Value)




Handling lost packets

• In principle, data packets at any protocol layer may belost

• Methods to cope lost packets

• Acknowledges

• Timers• Retries

• State machines




Handling corrupted data

• Methods to cope corrupted data• CRC checks (RLC, LLC, L2 under IP, …)

• Sanity checks of data

• State machines




Handling failed network

elements

• Network elements with permanent data (HLR failure)• After restart, inform all MSC/VLRs and SGSNs that have MSs of that HLR

• Network elements with non-permanent data (SGSN

failure)• Inform associated neigboring element

• VLRs

• Inform MS next time when it next time sends uplink message

• Inform GGSN next time when GGSN sends MT data. MS may bepaged

• MT SMSs are rejected

• CS page is sent to entire MSC/VLR area or to MSC/VLR specifiedarea




Handling failed network

elements

• Simpler network elements (GGSN failure)

• Inform SGSN when SGSN sends MO data

• Reject data packets MT packets




Fault tolerant systems

• Fault models

• Only knows faults can be handled (i.e., if you are not preparedto handle the faults, you can’t survive those faults)

• Fault prevention

• Fault detection• Fault isolation

• Reduced/Degraded service

• Fault recovery




Example:

Simple procedure, Attach

MS etwork

ATTACH REQUEST

ATTACH ACCEPT

ATTACH COMPLETE




Example:

Signaling chart

7d. Cancel Location Ack

7c. Cancel Location

7b. Update Location

7g. Update Location Ack

7e. Insert Subscriber Data

7f. Insert Subscriber Data Ack

6d. Insert Subscriber Data

6c. Cancel Location Ack

6b. Cancel Location

3. Identity Response

2. Identification Response

2. Identification Request

1. Attach Request

5. IMEI Check

3. Identity Request

4. Authentication

6a. Update Location

7a. Location Updating Request

7h. Location Updating Accept

6f. Update Location Ack

6e. Insert Subscriber Data Ack

MS BSS new SGSN old SGSN GGSN HLR EIR

old

MSC/VLR

new

MSC/VLR

9. Attach Complete

8. Attach Accept

10. TMSI Reallocation Complete




Example:

Signaling chart

• 1) The MS initiates the attach procedure by the transmission of an

Attach Request (IMSI or P TMSI and old RAI, Classmark, CKSN, AttachType, DRX Parameters, old P TMSI Signature) message to the SGSN.IMSI shall be included if the MS does not have a valid P TMSI available. If the MS has a valid P TMSI, then P TMSI and the old RAI associated withP TMSI shall be included. Classmark contains the MS's GPRS multislot

capabilities and supported GPRS ciphering algorithms in addition to theexisting classmark parameters defined in GSM 04.08. Attach Type indicateswhich type of attach that is to be performed, i.e., GPRS attach only, GPRS Attach while already IMSI attached, or combined GPRS / IMSI attach. DRXParameters indicates whether the MS uses discontinuous reception or not.

If the MS uses discontinuous reception, then DRX Parameters also indicatewhen the MS is in a non-sleep mode able to receive paging requests andchannel assignments. If the MS uses P TMSI for identifying itself and if ithas also stored its old P TMSI Signature, then the MS shall include the oldP TMSI Signature in the Attach Request message.




Example:

Signaling chart

• 8) The SGSN sends an Attach Accept (P TMSI, VLR TMSI, P TMSI

Signature) to the MS. P TMSI is included if the SGSN allocates a newP TMSI.

• 9) If P TMSI or VLR TMSI was changed, the MS acknowledges thereceived TMSI(s) with Attach Complete (P TMSI, VLR TMSI).




Example:

Time critical approach

MS Network

ATTACH REQUESTStart T3310

ATTACH ACCEPT

Stop T3310

ATTACH COMPLETEStop T3350

If P-TMSI and/or

TMSI allocatedStart T3350

If P-TMSI and/or

TMSI allocated




Sequence diagramC.1 ATTACH, GPRS only, MS unknown in the network

GMMREG-ATTACH- REQ

[Attach type,

READY-timer, STANDBY-timer ]

START TattachLL-UNITDATA-REQ

[PDU=Attach Req (

IMSI or TLLIplusRAI),

oldTLLI,Cipher=off ]

GRR-DATA-REQ

[LLC-UI,

SAPI=signalling]

GRR-DATA-IND

[LLC-UI, TLLI,

RAI,CI]

LL-UNITDATA-IND

[PDU=Attach Req (

IMSI or TLLIplusRAI),

oldTLLI, CI]

LLGMM-ASSIGN-REQ

[Kc, Algorithm]

START Tauth

LL-UNITDATA-REQGRR-DATA--REQ

STOP Tauth

[ PDU=Auth-Cipher-

Req (Alg, RAND,..),

oldTLLI, Cipher=off ]

[LLC-UI,

DRX, CLM,

SAPI=signalling]

GRR-DATA-IND

[LLC-UI]

LL-UNITDATA-IND

[PDU=Auth-Cipher-

Req (Alg., RAND,…)]

LL-UNITDATA-REQ

[PDU=Auth-Cipher-

Resp (SRES),


GRR-DATA-REQ

[LLC-UI,

SAPI=signalling]

GRR-DATA-IND

[LLC-UI, oldTLLI]

LL-UNITDATA-IND

[PDU=Auth-Cipher-

Resp (SRES),

oldTLLI ]

[Kc, Algorithm]

MS NET

GMMSNDCP LLC RR SM SNDCPLLCRR BSSGPSM GMM

LLGMM-ASSIGN-REQ

START Tident

LL-UNITDATA-REQ

[ PDU=

Identification Req,

oldTLLI, Cipher=off ]

GRR-DATA--REQ

[LLC-UI,

DRX, CLM,

SAPI=signalling]

GRR-DATA-IND

[LLC-UI]

LL-UNITDATA-IND

[PDU=

Identification Req]

STOP Tident

LL-UNITDATA-REQ

[PDU=Identification-

Resp (IMSI),


GRR-DATA-REQ

[LLC-UI,

SAPI=signalling]

GRR-DATA-IND

[LLC-UI, TLLI]

LL-UNITDATA-IND

[PDU=Identification-

Resp (IMSI),

oldTLLI ]

The oldTLLI may be a

Local TLLI, or a

Foreign TLLI, or a

Random TLLI

IMSI fetched if

- No GPRS MM Context exists, and- Attach Request without IMSI

The network starts theauthentication together with setting

the ciphering mode.




Example:

Service primitives

PRIMITIVE PARAMETER

(message,info elements

of message,

other

parameters)

REFERE

GMMREG-ATTACH-REQ attach-type, READY-timer, STANDBY-timer 6.6.1.1

GMMREG-ATTACH-CNF PLMNs MT-caps, attach-type. 6.6.1.2

GMMREG-ATTACH-REJ cause 6.6.1.3

GMMREG-DETACH-REQ detach-type, power-off/normal-detach 6.6.1.4

GMMREG-DETACH-CNF detach-type 6.6.1.5

GMMREG-DETACH-IND detach-type 6.6.1.6




Example:

Service primitives

• 6.6.1.1 GMMREG-ATTACH-REQ

• MS initiates the GPRS and/or IMSI attach. GMM is requested

to send an ATTACH REQUEST message to the network. The

attachment is registration pending in the MS.

• 6.6.1.2 GMMREG-ATTACH-CNF

• The attach (either GPRS-attach or IMSI-attach or both) was

successful. The network confirmed the attach, i.e.the ATTACH

ACCEPT message was received by the MS. The LLC and RR

sublayer will be informed by GMM about the TLLI to be used.

• 6.6.1.3 GMMREG-ATTACH-REJ

• The attach (either GPRS-attach or IMSI-attach or both) has

failed. The network rejected the attach attempt, i.e. the

message ATTACH REJECT was received from the network.




Example:

Information exchange

• Attach request

I Information Element Type/Reference Presence Format Length

Protocol discriminator Protocol discriminator 10.2

M V 1/2

Skip indicator Skip indicator 10.3.1

M V ½

Attach request message identity Message type10.4

M V 1

MS classmark MS classmark 410.5.5.12

M LV 4 - 6

Attach type Attach type10.5.5.2

M V ½

GPRS ciphering key sequencenumber

Ciphering key sequence number 10.5.1.2

M V ½

DRX parameter DRX parameter 10.5.5.6

M V 2

Force to standby Force to standby10.5.5.7

M V ½

Spare half octet Spare half octet10.5.1.8

M V ½

P-TMSI or IMSI Mobile station identity10.5.5.13

M LV 6 - 10

MS Radio Access capabili ty MS RA capability10.5.5.12.a

O TLV 5-12

Old P-TMSI signature P-TMSI signature10.5.5.8

O TV 4

Old routing area identification Routing area identification10.5.5.15 O TV 7

Requested READY timer value

Timer 10.5.5.16

O TV 2

Requested STANDBY timer value Timer 10.5.5.16

O TV 2

MS classmark MS classmark 110.5.1.5

O TV 2




Example:


• 9.5.1.0 MS Radio Access capability

• This IE may be included by the MS in order to provide its radio access capabilities.

• 9.5.1.1 Old P-TMSI signature

• This IE is included if a valid P-TMSI and P-TMSI signature are stored in the MS.

• 9.5.1.2 Old routing area identification

• This IE is included if the MS has stored the old RAI and an associated valid P-TMSI.

• 9.5.1.3 Requested READY timer value

• This IE may be included if the MS wants to indicate a preferred value for READY timer.

• 9.5.1.4 Requested STANDBY timer value

• This IE may be included if the MS wants to indicate a preferred value for STANDBY

timer.




Example:


• Attach accept



M V 1/2

Skip indicator Skip indicator 10.3.1 M V 1/2

Attach accept message identity Message type10.4

M V 1

Attach result Attach result10.5.5.1

M V 1/2


M V 1/2

Routing area identification Routing area identification10.5.5.15

O TV 7

Periodic RA update timer Timer value10.5.5.16

M V 1

P-TMSI signature P-TMSI signature10.5.5.8

O TV 4

Negotiated DRX parameter DRX parameter 10.5.5.6

O TV 3

Negotiated READY timer value

Timer 10.5.5.16

O TV 2

Negotiated STANDBY timer

value

Timer

10.5.5.16

O TV 2

Allocated P-TMSI Mobile station identity10.5.5.13

O TLV 7

MS identity Mobile identity10.5.1.4

O TLV 6 - 11

GMM cause GMM cause10.5.5.14

O TV 2




Example:


• Sample information elements

• attach result

• routing area identifier

8 7 6 5 4 3 2 1

Routing Area Identification IEI octet 1

MCC digit 2 MCC digit 1 octet 2

1 1 1 1 MCC digit 3 octet 3

MNC digit 2 MNC digit 1 octet 4

LAC octet 5

LAC cont’d octet 6

RAC octet 7

8 7 6 5 4 3 2 1

Attach resultIEI

0spare

Result ofattach

octet 1

Result of attach (octet 1)Bits3 2 1

0 0 1 GPRS only attached0 1 1 Combined GPRS/IMSI attached

All other values are reserved.




Example:


• Attach complete



M V 1/2


M V 1/2

Attach complete messageidentity

Message type10.4

M V 1


M V 1/2

Spare half octet Spare half octet10.5.1.8

M V 1/2




Example:


• Attach reject



M V 1/2


M V 1/2

Attach reject message identity Message type10.4

M V 1

GMM cause GMM cause10.5.5.14

M V 1




Example:

Exception cases

• If the attach request cannot be accepted by the network, an ATTACH REJECT message

is transferred to the MS. The MS receiving the ATTACH REJECT message stops timer T3310 and takes one of the following actions depending upon the reject cause:

• # 3 (Illegal MS)# 6 (Illegal ME)# 7 (GPRS services not allowed)

• The MS shall set the GPRS update status to GU3 ROAMING NOT ALLOWED (and shall store itaccording to section 4.1.3.2.9) and shall delete any P-TMSI, P-TMSI signature, RAI and GPRSciphering key sequence number. The SIM shall be considered as invalid until switching off orthe SIM is removed. The new state is GMM-DEREGISTERED.

• # 11 (PLMN not allowed)

# 12 (Location area not allowed)# 13 (Roaming not allowed in this location area)




Example:

Exception cases

• The MS shall delete any RAI, P-TMSI, P-TMSI signature and GPRS ciphering

key sequence number stored, shall set the GPRS update status to GU3ROAMING NOT ALLOWED (and shall store it according to section 4.1.3.2.9)and shall change to state GMM-DEREGISTERED.

• The MS shall store the LAI or the PLMN identity in the appropriate

forbidden list, i.e. in the “forbidden PLMN list” for cause #11, in the list of “forbidden location areas for regional provision of service” for cause #12 orin the list of “forbidden location areas for roaming” for cause #13. In casecause #11 or #13 was received, the MS shall perform a PLMN selectioninstead of a cell selection.




Example:

Abnormal cases

a) Access barred because of access class control

• The GPRS attach procedure shall not be started. The MS stays in the currentserving cell and applies normal cell reselection process. The GPRS attachprocedure is started as soon as possible, i.e. when access is granted or because of a cell change.

b) Lower layer failure before the ATTACH ACCEPT or ATTACH REJECT message isreceived

• The procedure shall be aborted, the MS shall keep, if any, the stored P-TMSI, RAI,and GPRS ciphering key sequence number and shall proceed as described below.

c) T3310 time-out

• On the first expiry of the timer, the MS reset and restart timer T3310 and shallretransmit the ATTACH REQUEST message. This retransmission is repeated untilthe timer has expired four times, i.e. on the fiftth expiry of timer T3310, the GPRSattach procedure shall be aborted and the MS shall proceed as described below.




Example:

Abnormal cases

d) ATTACH REJECT, other causes than those treated in section 4.7.3.1.4

e) Change of cell into a new routing area

• If a cell change into a new routing area occurs before an ATTACH ACCEPT or ATTACH REJECT message has been received, the GPRS attach procedure shallbe aborted and re-initiated immediately. If a routing area border is crossedwhen the ATTACH ACCEPT message is received but before an ATTACHCOMPLETE message is sent, the GPRS attach procedure shall be aborted andthe routing area updating procedure shall be initiated. If a P-TMSI was allocatedduring the GPRS attach procedure, this P-TMSI shall be used in the routing areaupdating procedure. If a P-TMSI signature was allocated together with the P-TMSI during the GPRS attach procedure, this P-TMSI signature shall be used in

the routing area updating procedure.

f) Power off

• If the MS is in state GMM-REGISTERED-INITIATED at power off, the GPRSdetach procedure shall be performed.

E l




Example:

Abnormal cases

g) Procedure collision

• If the MS receives a DETACH REQUEST message from the network in stateGMM-REGISTERED-INITIATED, the GPRS detach procedure shall be progressedand the GPRS attach procedure shall be aborted. If the cause IE, in the DETACHREQUEST message, indicated a “reattach request”, the GPRS attach procedureshall be progressed and the DETACH REQUEST message shall be ignored.




Example:

State machine

• General state machine

idle

attached

context

active

attach

detach

activate

context

deactivatecontext

detach

mobility

management

send/receive

SMS

mobility

management

send/receive

SMS

send/receive

data




Example:

State machine

• Simple state machine

IDLE

REGISTRA-

TION PEND.

GMMREG-ATTACH-REQ

GMMREG-ATTACH-CFN

GMMREG-

ATTACH-REJ

GMMREG-DETACH-CFN

REGISTERED

GMMREG-DETACH

-IND

GMMREG-DETACH-REQ (power off)

GMMREG-DETACH-REQ

(not power off)

DE-

REGISTRA-

TION PEND.




Example:

State machine at MS

NULL RA-UPDATING-

INITIATED

DEREGISTERED

Enable

GPRS

DETACH requested

(not power off)

REGISTERED

Any state

DEREGISTERED-

INITIATED

ATTACH

requestATTACH rejected

DETACHrequested

(power off)

Network init. DETACH

requested

Lower layer failureATTACH

accept

RAU rejected

Network init. DETACH

implicit DETACH

DETACH accepted

Lower layer failureRAU

requested

RAU accepted

RAU failed

REGISTERED-

INITIATED

Disable

GPRS




Example:

State machine at network

GMM-DE-REGISTERED

- Network initiatedDETACH requested

GMM-REGISTERED

GMM-COMMON-PROCEDURE-INITIATED

GMM-DE-REGISTERED-

INITIATED

- COMMON procedurefailed

- Lower layer failure

- ATTACH proceduresuccessful

- MS initiated

DETACH requested- RAU rejected

- Iimplicit DETACH

- DETACH accepted- Lower layer failure

- COMMON proceduresuccessful

- ATTACH proceduresuccessful

- COMMON procedurerequested

- COMMON procedurerequested




Links

• In English

• http://www.ee.umanitoba.ca/~blight/telecom.html

• In Finnish

Documents

Signalling Prot