f2000 tik 109 300 protocols - tkk - · pdf filegsm rf relay rlc mac gsm rf bssgp network ......

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

Tik-109/110.300Telecommunications architectures:

Protocols

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

TML-laboratory/CS/HUT


Agenda

Protocol designMultivendor interfacesHandling protocol errorHandling lost packetsHandling corrupted dataHandling failed network elementsFault tolerant system designProtocol examples


Protocol design:architecture

Local areanetwork

Server

Router

Local areanetwork

Server

Router

Corporate 2

Corporate 1

Serving GPRSSupport Node(SGSN)

Gateway GPRSSupport Node(GGSN)

Gateway GPRSSupport Node(GGSN)

GPRS INFRA-STRUCTURE

HLR

MSC/VLR

Other GPRSoperators Border

gateway

Gb

Gr Gd

Gi.IP

Gi.X.25

Gi.IP

��

��

Firewall

Firewall

Firewall

Firewall

UmR/S

SMS-GMSC

Gr Gd

Gs

GcGp

Gn, Gp

Gn, Gp

EIRGf

Gf

BSCBTSPSTN

GPRSbackbone

Datanetwork(Internet)

Datanetwork(X.25)

Datanetwork(Internet)

SS7Network


Protocol design

• Example protocol stack

Um GbMS BSS SGSN

SNDC SMSGMM

LLC

RLC

MAC

GSM RF

Relay

RLC

MAC

GSM RF

BSSGP

NetworkService

L1

SNDC SMSGMM

LLC

BSSGP

NetworkService

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 networkelements

• 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 (SGSNfailure)• 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 be

paged• MT SMSs are rejected• CS page is sent to entire MSC/VLR area or to MSC/VLR specified

area


Handling failed networkelements

• 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 prepared

to 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 Network

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 HLREIR

oldMSC/VLR

newMSC/VLR

9. Attach Complete

8. Attach Accept

10. TMSI Reallocation Complete



• 1) The MS initiates the attach procedure by the transmission of anAttach 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. Ifthe 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 multislotcapabilities 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, GPRSAttach 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.



• 8) The SGSN sends an Attach Accept (P�TMSI, VLR TMSI, P�TMSISignature) 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 ACCEPTStop T3310

ATTACH COMPLETEStop T3350

If P-TMSI and/orTMSI allocatedStart T3350

If P-TMSI and/orTMSI 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), oldTLLI,Cipher=off ]

GRR-DATA-REQ


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), oldTLLI,Cipher=off ]

GRR-DATA-REQ


GRR-DATA-IND

[LLC-UI, TLLI]

LL-UNITDATA-IND

[PDU=Identification- Resp (IMSI), oldTLLI ]

The oldTLLI may be aLocal TLLI, or aForeign TLLI, or aRandom TLLI

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

The network starts theauthentication together with settingthe ciphering mode.


Example:Service primitives

PRIMITIVE PARAMETER(message,info elementsof message,otherparameters)

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 requestedto send an ATTACH REQUEST message to the network. Theattachment is registration pending in the MS.

• 6.6.1.2 GMMREG-ATTACH-CNF

• The attach (either GPRS-attach or IMSI-attach or both) wassuccessful. The network confirmed the attach, i.e.the ATTACHACCEPT message was received by the MS. The LLC and RRsublayer 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) hasfailed. The network rejected the attach attempt, i.e. themessage ATTACH REJECT was received from the network.


Example:Information exchange

• Attach request

EI Information Element Type/Reference Presence Format LengthProtocol discriminator Protocol discriminator

10.2M V 1/2

Skip indicator Skip indicator10.3.1

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 number10.5.1.2

M V ½

DRX parameter DRX parameter10.5.5.6

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

X MS Radio Access capability 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 timervalue

Timer10.5.5.16

O TV 2

Requested STANDBY timer value Timer10.5.5.16

O TV 2

MS classmark MS classmark 110.5.1.5

O TV 2



• 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 STANDBYtimer.



• Attach acceptEI Information Element Type/Reference Presence Format Length

Protocol discriminator Protocol discriminator10.2

M V 1/2


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 parameter10.5.5.6

O TV 3

Negotiated READY timervalue

Timer10.5.5.16

O TV 2

Negotiated STANDBY timervalue

Timer10.5.5.16

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



• 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 10 0 1 GPRS only attached0 1 1 Combined GPRS/IMSI attached

All other values are reserved.



• Attach complete


10.2M 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



• Attach reject


10.2M 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 messageis transferred to the MS. The MS receiving the ATTACH REJECT message stops timerT3310 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 cipheringkey 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 appropriateforbidden 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 ofa 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.



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 orATTACH 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 inthe 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.



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

contextactive

attach

detach

activatecontext

deactivatecontext

detach

mobilitymanagement

send/receiveSMS

mobilitymanagement

send/receiveSMS

send/receivedata


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

EnableGPRS

DETACH requested

(not power off)

REGISTERED

Any state

DEREGISTERED-INITIATED

ATTACHrequest

ATTACH rejected

DETACHrequested

(power off)

Network init. DETACHrequested

Lower layer failureATTACHaccept

RAU rejected

Network init. DETACHdimplicit DETACH

DETACH accepted

Lower layer failureRAUrequested

RAU accepted

RAU failed

REGISTERED-INITIATED

DisableGPRS


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 initiatedDETACH 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

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