Introduction to GPRS 1 o GPRS n General

Introduction to GPRS

1. 簡介 o GPRS n General Packet Radio Service n 一般封包式無線電服務 o GPRS標準 n 制訂於 1994年 n 制訂單位ETSI/SMG (European Telecommunications Standards Institute / Special Mobile Group) n 主要內容於 1997年由SMG#25通過 n 完成於 1999年

Circuit Switched vs. Packet Switched Circuit Switched Packet Switched

Circuit and Packet Support

o 設計GPRS協定時，盡可能讓channel的配置 有彈性，以增加系統容量 n 以timeslot為基本傳送packet的單位，最多可將同 一carrier的8個timeslots都分配給同一個MS n 手機傳送封包的channel o 以符合像web、file transfer之asymmetric flow 的特性，分別分配uplink與downlink的channel n 提供fast reservation，可在 0. 5到 1 sec�動資料傳 輸

n 四種channel coding schemes (CS 1、CS 2、CS 3、 CS 4) o CS 1 n user data rate： 9. 05 Kbps n correction capability：highest n max cell range： 450 m o CS 2 n user data rate： 13. 4 Kbps n max cell range： 390 m

o CS 3 n user data rate： 15. 6 Kbps n max cell range： 350 m o CS 4 n user data rate： 21. 4 Kbps n max cell range： 290 m n correction capability：none

o 安全機制：GPRS與GSM相同 o 編碼演算法：GPRS調整GSM編碼演算法以 適合packet data的傳輸 o GPRS系統方面 n GPRS元件中由舊的GSM元件加以修改(software upgrade)而得 o MS、BSS、MSC/VLR、HLR o 例如：HLR會加上GPRS subscriber information

TRAU：Transcoder and Rate Adaptation Unit

1. 2 GPRS Implementation o GPRS phase 1 implementation n 標準封包傳送服務(point to point packet bearer service) n 達成CS-1及CS-2通道編碼技術 n 建置下列介面 o Gn (SGSN ↔ SGSN) o Gb (SGSN ↔ BSS) o Gp (SGSN ↔ GGSN (other PLMN)) o Gs (SGSN ↔ MSC/VLR)

n 彈性的無線電資源配置 n Class B與Class C手機的規範 o Class A：上網時可同時接聽電話 n can be connected to GPRS service and GSM service (voice, SMS), using both at the same time n such devices are known to be available today o Class B：上網時不可同時接聽電話 n can be connected to GPRS service and GSM service (voice, SMS), but using only one or the other at a given time n during GSM service (voice call or SMS), GPRS service is suspended, and then resumed automatically after the GSM service (voice call or SMS) has concluded n most GPRS mobile devices are Class B

o Class C：只可上網不可接聽電話 n are connected to either GPRS service or GSM service (voice, SMS) n must be switched manually between one or the other service n n GPRS計費，如以封包計費及Qo. S計費 提供靜態及動態IP address配置 匿名存取(anonymous access) 安全性(security)

o GPRS phase 2 implementation n 加強GPRS的Qo. S支援 n 無格式化位元組資料流(unstructured octet [八位 元組] stream)的GPRS PDP (Packet Data Protocol) type n 對ISP及Intranet的接取 n GPRS預付機制(prepaid)

n GPRS收費建議(Advice of Charge，Ao. C)機制 o Ao. C service provides the mobile subscriber with an estimate of the call charges o two types of Ao. C information n provides the subscriber with an estimate of the bill n used for immediate charging purposes (hot billing) n 群體通話(point-to-multipoint services) n 點對多點的multicast服務

Logical Architecture：Interfaces 註：公 眾 行 動 電 話 網 路 (Pulbic Land Mobile Network, PLMN)

o 在此GPRS網路內，GSM定義一種新的邏輯 網路節點 n GPRS支援節點(GPRS Support Node，GSN) o GSN依其負責的功能劃分 n GPRS服務支援節點(Serving GPRS Support Node， SGSN) n GSN閘道(Gateway GPRS Support Node，GGSN)

o GPRS attach n SGSN會為MS建立一個MM context (關於MS的 mobility及security) o PDP context activation n SGSN會為每個session建立一個PDP context用於 儲存轉送封包等資訊

o Case 3：GPRS手機與PDN上的PC n [步驟 1] MS首先會做GPRS-attached，以開始� 動GPRS的服務，此後MS與SGSN建立起一個 session

n [步驟 3] GGSN 1向DHCP server要到一個IP address，透過SGSN 1送給MS，建立起PDP context o 註：DHCP (Dynamic Host Configuration Protocol)

GPRS手機與PDN上的PC DHCH Server

o 在Internet上，DNS server會把domain name轉 成IP address，在GPRS network上的DNS server，會將此APN轉成GGSN的IP address

透過APN存取GPRS Service的步驟 o [步驟一] 使用者�動一個 service，MS會送 request給SGSN o [步驟二] SGSN比較HLR中的用戶資料，檢 �此 service是否有授權給該user o [步驟三] SGSN向local GPRS DNS server�詢 負責此APN的GGSN的IP address

o [步驟四] 如果在local DNS找不到APN相對應 的IP address n case 1：user在自己的home network，此request會 被拒� n case 2：user在foreign network，SGSN會向MS的 home network的DNS�詢 o [步驟五] 當找到GGSN的IP address n SGSN會藉助GTP (GPRS Tunneling Protocol)建立 起與GGSN間的tunnel

2. 7 MS IP Address Allocation o 要建立起MS與external network間的連結(PDP context)，MS必須要有IP address o GPRS有兩種分配MS IP address的方式 n fixed addressing n dynamic addressing

o Fixed addressing n 永遠分配給MS相同的IP address，此IP address存 在HLR中 n 當MS想要開�一個 PDP context到某一個APN， HLR將IP address送到SGSN再送到MS n 此種方式是搶迫MS一定要使用network分配的IP address

o Dynamic addressing n 當MS開� PDP context時，GGSN會分配一個IP address，並透過SGSN傳送給MS n 當關閉PDP context時，SGSN收回此IP address

2. 8 GGSN取得IP Address的四種方 式 o 四種方式 n n from a local address pool on the GGSN via RADIUS form an external RADIUS server via DHCP from the customer network via an L 2 TP tunnel from the GGSN

o From a local address pool on the GGSN n 運作方式類似PSTN dialup server o GGSN有一個IP address pool o 當有MS需要IP，GGSN從pool分配一個IP給 MS n 如客戶端選擇由operator分配IP，這是所有方式 中最簡單的方式

o Via RADIUS form an external RADIUS server n 通常RADIUS server會在customer network n RADIUS server認證user terminal，給予一個fixed IP address o 註：RADIUS (Remote Access Dial In User Service) Protocol n 提供authentication機制，用來辨認使用者的身份與密碼 n 確認通過後，經由authorization授權使用者登入網域使用 相關資源 n 提供accounting機制，保存使用者的網路使用記錄，以提 供系統服務業者完整認證收費機制的一個基礎

o Via DHCP n GGSN向DHCP server要一個IP address n 可把DHCP server設定成fixed IP address，則MS 每次都會取得相同的IP address

o From the customer network via an L 2 TP tunnel from the GGSN n L 2 TP是Layer 2的tunneling protocol o 通常用於PSTN dial-up到一個Remote Access Server n 對GPRS而言，L 2 TP在GGSN與customer network 的router間建立一個安全的連結

Footnote：Layer 2 Tunneling Protocol (L 2 TP) o A tunneling protocol used to support virtual private networks (VPNs) o It does not provide any encryption or confidentiality by itself; it relies on an encryption protocol that it passes within the tunnel to provide privacy o Although L 2 TP acts like a Data Link Layer protocol in the OSI model, L 2 TP is in fact a Session Layer protocol

2. 9 GPRS Billing

o GPRS的計費資訊是由SGSN及GGSN收集 n SGSN收集MS的radio resource usage n GGSN收集MS的network usage n 如MS到其它GPRS network使用資源 o 若到訪的GPRS network使用dynamic address 連到MS，則計費資料會送到home GPRS network

o SGSN所搜集的計費相關資訊 n location information o 指出MS是在home network還是在visited network o cell location n mobile origination及mobile termination的資料傳輸量 o 資料量在SGSN的SNDCP (Sub Network Dependent Convergence Protocol) level測得 n 使用者指定的Qo. S profile n 使用的通訊協定

o GGSN所搜集的計費相關資訊 n destination和source的addresses n MS與external data network間所使用的資料傳輸 量(資料量在GGSN的GTP level所測得) n MS使用到PDP address的整段時間

Call Detailed Records (CDRs) o SGSN與GGSN收集到的計費資料會轉成call detailed records (CDR) o Call detailed record分成 n S-CDR (SGSN PDP context generated-CDR) o 由SGSN�生，記錄 MS無線電資源的使用量 n G-CDR (GGSN generated-CDR) o 由GGSN�生，記錄 MS所使用GGSN的外部網路 n M-CDR (Mobility Management generated-CDR) o 由SGSN�生，記錄 MS行動管理的相關資料

o S-CDR的欄位包含 n mobile originating (MO) data volume：手機撥出 資料量 n mobile terminating (MT) data volume：手機接收 資料量 n location information：手機的位置資訊 n SMS MO：SGSN mobile originated SMS record n SMS MT：SGSN mobile terminated SMS record n associated Qo. S：相關的Qo. S資訊 n record duration：相關record存在SGSN中的時間

o G-CDR的欄位包含 n n n source address destination address 收到外部網路的資料量 送到外部網路的資料量 相關的Qo. S資訊 record duration：record存在GGSN中的時間

o 每位使用者的PDP context，會�生一個 CDR n �動 (activate) PDP context時，會開始�生相對 應的CDR n 每個PDP context可能�生數筆 S-CDRs及G-CDRs

o CDR可依下列三種方式�生 n end-of-call accounting schedule：通話結束時�生 n time-of-day accounting schedule：一天中的某時 刻�生 n inter-SGSN routing area update：跨SGSN RA (Routing Area)移動時�生 o 當手機在通訊狀態下移動到不同GSN，數個 CDRs可由不同的GSNs及外部資料網路�生

o Charging gateway function (CGF) n 控制charging data record (CDR)的收集 o CDR被送到GPRS Billing Mediation (調停) n 組成billing record，再送到billing system，做為 計費的依據

o GPRS的幾種billing方式 n flat-rate billing (ex：月租費 800元) n per-packet billing (ex： 0. 2元/128 kbytes) n volume-based billing (PDP activate到deactivate的 時間) n value-based billing (加�服務， depend on context)

o 影響上述rate的因素 n Quality of Service n time of day (如減價時段，off-peak time/peak time) n day of week (如weekend，weekday，holiday) n content, call type, services used (ex： 0204、圖形 下載) n source or destination (如國外電話，用戶是員 、 員警等屬性)

Billing by Quality of Service o Service precedence class o Reliability class n n n loss ratio (for each layer) out of order (失序率) corrupted ratio (誤碼率) duplicate ratio (重覆率) reliability (1 -5 levels) o Peak throughput class (吞吐量) o Mean throughput class o Delay class (傳輸延遲)

3. GPRS介面(Interface)

o GPRS架構於GSM上，盡可能不動原先GSM 的運作，除air interface及與SGSN、GGSN相 連的介面外，基本上都延用GSM的protocol o 新的protocol也都遵循GSM MAP架構 n n Gs (SGSN ↔ MSC/VLR) Gr (SGSN ↔ HLR) Gc (GGSN ↔ HLR) Gf (SGSN ↔ EIR)

3. 1 GPRS Transmission & Signaling Planes o GPRS延用OSI 7 -layer概念，每個interface定義的協定都 具layered structure o 使用的protocol stack分為 n transmission plane o 傳送使用者資料及與此資訊傳送相關的控制程序 o 例如：流量控制、錯誤偵測、更正與回覆 n signaling plane o 其它用於控制transmission plane functions所用到 的控制訊號

3. 1. 1 GPRS Transmission Plane

o GPRS protocol n 參考ISO/OSI (International Organization for Standardization/Open Systems Interconnection)架構所 建議的GPRS傳輸協定架構 o 在手機與終端主機的網路層之上，可根據應用程式需求， 採用不同協定 n 例如：在應用程式下可使用TCP (Transmission Control Protocol)來傳送，至於是架在X. 25或IP上， GPRS並不限制

3. 1. 2 GPRS Signaling Plane

o 在MS與SGSN間 n GMM/SM layer提供GPRS行動管理(GMM)及會 期管理(SM)功能 o SGSN↔GGSN之Gn interface與transmission plane的不同 n 只採用UDP傳送控制訊息

o GGSN↔HLR的Gc interface的MAP n 將GSM的MAP延伸成能支援GPRS行動管理的能 力 o SGSN↔MSC/VLR的Gs interface n 上層採用extended BSSAP，而非使用TCAP

3. 1. 2. 1 MS ↔ BSS o MS與BSS間實體層(physical layer) n 實體無線電子層(physical RF sub. Layer，RFL) o 負責GSM無線電相關規範，執行 modulation/demodulation n 實體連結子層(Physical Link sub. Layer，PLL) o 負責在實際連結上資訊的傳輸

Note：Aloha o A system for coordinating and arbitrating access to some shared communication channel o A medium access method is supposed to prevent two or more systems from transmitting at the time on a shared medium

o In the Aloha system n a station transmits whenever data is available to send n if another station transmits at the same time, a collision occurs and the frames that were transmitted are lost n however, a station can listen to broadcasts on the medium, even its own, and determine if the frames were transmitted

Aloha

o Slotted Aloha n distinct time slots are created in which systems can transmit a single frame n one system emits a signal at the start of each slot to let all other systems know when the slot is available n by aligning frames on slots, overlaps in the transmissions are reduced

n however, systems must wait a fraction of a second for the beginning of a time slot before they can transmit n also, data may be lost if stations contend for the same slot n tests have shown that slotted Aloha has a performance advantage

Slotted Aloha

Note：Selective ARQ o Automatic Repeat-re. Quest (ARQ) n an error control method for data transmission which uses acknowledgments and timeouts to achieve reliable data transmission o an acknowledgment is a message sent by the receiver to the transmitter to indicate that it has correctly received a data frame o a timeout is a reasonable point in time after the sender sends the data frame; if the sender does not receive an acknowledgment before the timeout, it usually re-transmits the frame until it receives an acknowledgment or exceeds a predefined number of re-transmissions

o Selective (Repeat) ARQ n a specific instance of the Automatic Repeat-re. Quest (ARQ) Protocol n it may be utilized as a protocol for the delivery and acknowledge of message units, or it may be utilized as a protocol for the delivery of subdivided message sub-units n the sending process continues to send a number of frames specified by a window size even after a frame loss n the receiving process will continue to accept and acknowledge frames sent after an initial error

n the receiver process keeps track of the sequence number of the earliest frame it has not received, and sends that number with every ACK it sends n if a frame from the sender does not reach the receiver, the sender continues to send subsequent frames until it has emptied its window n the receiver continues to fill its receiving window with the subsequent frames, replying each time with an ACK containing the sequence number of the earliest missing frame n once the sender has sent all the frames in its window, it resends the frame number given by the ACKs, and then continues where it left off

3. 1. 2. 2 BSS ↔ SGSN o NS (Network Service) n 利用下層frame relay建立起BSS與SGSN間的 virtual connection (NS-VC) n NS是在管理NS-VC以提供上層BSSGP傳送 BSSGP PDU

o 基地台GPRS協定(BSS GPRS Protocol， BSSGP) n 負責在BSS與SGSN間傳送路由與Qo. S資訊的 作， 並提供上層LLC傳遞的服務 n 在BSS上，BSSGP的relay function須提供RLC/MAC (MS↔BSS)與BSSGP (BSS↔SGSN)間buffering及 parameter mapping功能，以轉送MS 與SGSN間的 packet

n BSSGP也要執行 o mobility management (MM) n 通知cell去page MS n 指示MS更新Routing Area o network management (NM) n 管理BSS與SGSN n downlink flow control n Qo. S link的相關 作

3. 1. 2. 3 MS ↔ SGSN o 在Layer 2的LLC要提供服務，使MS與SGSN間能有可靠 的第三層連結 n flow control n sequence control n error detection and recovery n ciphered data link n Qo. S delay class n ack/unack mode

o 在transmission plane，LLC上層是收斂協定(Sub. Network. Dependent Convergence Protocol，SNDCP) n 在MS與SGSN間，LLC與上層X. 25或IP的溝通是透過 SNDCP來完成 n SNDCP將上層網路的需求，對應到下層的LLC來達 成協定轉換的 作 n SNDCP的 作包括multiplexing、segmentation、 reassembly、compression

4. 1 Logical Channel Map

o 分封數據邏輯通道 n 分封共同控制通道(Packet Common Control CHannel，PCCCH) n 分封廣播控制通道(Packet Broadcast Control Channel，PBCCH) n 分封時間預先控制通道(Packet Timing advance Control Channel，PTCCH) n 分封傳輸通道(Packet Traffic Channel，PTCH)

4. 1. 3 分封時間預先控制通道(PTCCH) o 分封時間預先控制通道(Packet Timing advance Control CHannel，PTCCH) n PTCCH in the uplink direction (PTCCH/U) o 讓MS傳送random access burst 的通道 o BSS利用此random access burst 便可估計出time advance (TA) n PTCCH in the downlink direction (PTCCH/D) o BSS利用此通道傳送TA updates給MS

4. 1. 4 分封傳輸通道(PTCH) o 分封傳輸通道(Packet Traffic Channel，PTCH) n 可上行與下行 n 分成兩類 o 分封數據傳輸通道(Packet Data Traffic Channel， PDTCH) o 分封相關控制通道(Packet Associated Control CHannel，PACCH)

5. GPRS核心網路 o GPRS核心網路的服務區(service domains) n Circuit-switched service (CS) domain n Packet-switched service (PS) domain o 建立連線傳送packet時須先建立的內容 n Mobility Management (MM) context n Packet Data Protocol (PDP) context n Quality-of-Service (Qo. S) profile

5. 1 Location Tracking o MS可能同時在CS domain與PS domain上運作， 因此會分別有不同的location記錄，分開做 mobility management n 如MS與CS domain連上(i. e. 與GSM MS同)，稱為 IMSI-attached o 此時以LA (Location Area)做為記錄MS位置的 基本單位，記錄於VLR上

5. 2 Mobility Management o 追蹤MS的位置，以傳送data給MS n GPRS自行定義所謂的Routing Area (RA)，是數 個cell所組成的區域，當做是MS location的基本 單位 n 基本上Routing Area是GSM的Location Area的 subarea

o MS要執行GPRS的功能，須支援GPRS MM 功能，儲存 n MM (Mobility Management) context n PDP (Packet Data Protocol) context

o 其他GPRS使用到的參數，但與SIM無關，也 會存在ME中，包括 n n n MM state cell ID ciphering algorithm radio access classmark SGSN classmark PDP type. . .

GPRS MS MM and PDP Context

o 與SIM相關的參數(在上圖SIM欄中標示為∨ 者) n IMSI (International mobile subscriber identity) o 用於存取VLR、HLR與SGSN、GGSN的資料 庫 n P-TMSI (Packet-Temporary Mobile Subscriber Identity) o 是GPRS中與GSM TMSI功能相同的ID

n RA (Routing Area) o 提供MS目前所在位置給GPRS MM n Ciphering key即Kc n CKSN (Ciphering Key Sequence Number) o Kc的相關參數 n P-TMSI Signature o used for identification checking

o 與MM相關參數 n n MM state cell identity ciphering algorithm radio access classmark o 決定radio capabilities n 如multiple time slot capability、power class n SGSN classmark o 決定network-related capability n 如ciphering capability

o 與PDP context相關參數 n n PDP type PDP address PDP state dynamic-address-allowed o 決定MS是否可使用dynamic address n requested and negotiated Qo. S profile

5. 3 MM State o MM state用於描述MS在GPRS網路上目前 mobility的三種狀態(states) n IDLE state：MS尚未與GPRS MM建立起連繫(not GPRS-attached) n STANDBY state：MS已與GPRS MM連繫，但只 保留部份的location資訊(GPRS-attached) n READY state：MS已與GPRS連繫，且有詳細記 錄到MS cell位置的資訊(GPRS-attached)

o 當MS想要傳送data時，就要進行GPRSattached procedure n MS與SGSN會記錄MS進入READY state，分別建 立一份MM context，之後可做authentication/ ciphering n 在GPRS-attached狀況下，MS與SGSN間會存在 邏輯上的連結(data link)

o GPRS的兩種location tracking n READY state o SGSN知道MS所在的cell，當有packet要傳給 MS，paging cost低但location update cost高 o MS每跨一個cell都要做location update

n STANDBY state o SGSN知道MS所在的RA，當有packet要傳給 MS，paging cost高但location update cost低 o MS跨RA時才要做location update

5. 4 Mobility Management (MM) Context o MS及SGSN存放的MM context內含 n MM state n MM-related information o GPRS MS n 只連繫GSM網路(IMSI-attached) n 只連繫GPRS網路(GPRS-attached) n 可同時連繫GSM網路及GPRS網路(IMSI-attached 及GPRS-attached)

o MS在IDLE state時 n 不允許執行任何關於MM的procedure o 當�動 GPRS-attach n 會由IDLE state變成READY state n 此時建立起MM context，分別在MS與SGSN各有 一MM context n 接下來進行authentication及ciphering n MS與SGSN建立起logic link，從MS做GPRS attach (READY，STANDBY)，到GPRS detach ( 進入IDLE)，期間稱為一個session

5. 4. 1 Mobility Management State Machine

o T 1 (IDLE→READY) n MS performs GPRS attach n 可由MS�動 o T 2 (READY→IDLE) n MS is detached from GPRS n 可由MS或SGSN�動此轉變 o T 3 (STANDBY→READY) n MS sends a packet to SGSN n 可由MS�動此轉變，也可能因為 SGSN page MS， 所以MS才send packet

o T 4 (READY→STANDBY) n a READY timer is timeout n 可由MS或SGSN�動此轉變，在 MS與SGSN 都有個READY timer，若在timeout前MS都 未再送出packet，則會轉到STANDBY state o 只有SGSN才可改變READY timer的時間 長度 o 透過Attach Accept和Routing Area Update Accept等訊息，通知MS關於timer的� o 有些方法，在探討SGSN不使用READY timer，而算MS已經移動多少cell，超過 某一設定�才換成 STANDBY

o T 5 (STANDBY→IDLE) n when tracking of MS is lost n 當SGSN無法追蹤到MS，SGSN會� 動state machine，轉成IDLE state n 若HLR送給SGSN 一個cancel location 的訊號(MS移到其它SGSN的管轄範 圍)，也會轉到IDLE state

n 一旦MS要傳送data (PDP context進入ACTIVE)， 或MS被呼叫，就會自動進入READY狀態 n 如果執行GPRS-detach，就會結束MM連接，回 到IDLE狀態 n 對於追蹤MM的位置，SGSN只記錄到MS所在 RA的位置 n 當MS跨越RA時，會執行GMM RA update procedure (GPRS Mobility Management Routing Area update procedure)

5. 4. 1. 2 READY State o MS做GPRS-attached動作，MS進入READY 狀態 n GPRS網路執行GPRS cell selection及re-selection n 當跨越cell時，會執行cell update；跨越RA時， 會執行RA update n 資料封包外層的BSSGP (Base Station System GPRS Protocol) header包含 o GCI (Global Cell Identity) o RAC (Routing Area Code) o LAC (Location Area Code)

o Ready State的其它特性 n 若要傳送資料，可進行PDP context activation n 也可讓已經進入ACTIVE的PDP context回到 INACTIVE n 當READY State的timer結束時，MS會回到 STANDBY狀態

5. 4. 2 SGSN MM Context o 對每個MS使用者，會有一相對應的SGSN MM Context， 包含下列資訊 n IMSI (the main reference key in SGSN) n P-TMSI (Packet-TMSI) n P-TMSI Signature (used for identification checking purposes) n MSISDN n IMEI (International Mobile Equipment Identity)

n MM state (Mobility Management state) o 可以是IDLE、STANDBY或 READY n Routing area o MS目前所在的routing area n Cell identity o 若MS是READY n cell identity是目前所在的cell ID o 若MS是STANDBY或IDLE n cell identity是最後一次READY得到的cell ID

n Cell identity age o 最後一個MS送LLC PDU到SGSN之已經過的時間 n VLR number o 正在負責該MS的VLR號碼 n New SGSN address o the IP address of the new SGSN where buffered and not sent should be forwarded to n Authentication, ciphering parameters, current ciphering key Kc, and the selected ciphering algorithm

n Radio access classmark (MS radio access capabilities) n SGSN classmark (MS network capabilities) n Mobile station Not Reachable for GPRS flag (MNRG) o indicates whether activity from the MS shall be reported to the HLR n Non-GPRS Alert Flag (NGAF) o indicates whether activity from the MS shall be reported to the MSC/VLR n Paging Proceed Flag (PPF) o indicates whether paging for GPRS and non-GPRS services can be initiated

5. 5 PDP (Packet Data Protocol) o 對於每條GGSN與MS間傳送封包的連結，都 會在各個節點建立起相對應的PDP context以 描述該session n MS、HLR、SGSN與GGSN都會有PDP context n 進行資料傳輸前，MS要先做PDP context activation procedure，最後做PDP context deactivation n PDP context有兩種狀態：ACTIVE與INACTIVE o 建立起PDP context，GGSN才會知道MS的存 在，也才能讓MS與外界網路通訊

5. 5. 1 PDP Context o 當MS在STANDBY或READY的MM state時，可開� PDP context，而且令PDP context由INACTIVE改為 ACTIVE n 經過此程序後，GGSN才有MS的記錄，才可傳送資 料到外部網路 o 一個MS可有多個PDP context，分別是不同的session n 雖是同一個MS，但不同PDP context需使用不同IP address，所以terminal要有支援Multiple IP addresses 的功能

o 對ACTIVE PDP context做deactivated時，會由ACTIVE state回到INACTIVE state o 如MS做GPRS-detached，所有PDP contexts都會作廢

5. 5. 2 SGSN PDP Context o 對每個MM context (一個user)，可能會有零或多個 PDP context o SGSN PDP context含有下列資訊 n PDP context identifier (index of PDP context), PDP type (e. g. , X. 25, PPP or IP), PDP address (e. g. , an X. 25 address), PDP state (Active, or Inactive) n Access Point Name (APN) to the external data network n Qo. S profile subscribed, Qo. S profile requested, Qo. S profile negotiated

n GGSN address in use o IP address of the GGSN currently used by the activated PDP context n Charging ID o charging identifier, identifies charging record generated by SGSN and GGSN

5. 6 Qo. S Profile o Qo. S profile中的attributes包括 n precedence class o 有三種傳送等級的優先權，如遇到congestion， 最低等級的封包將最先被丟棄

n delay class o 傳送128位元組，所期望的傳輸速率有四種延 遲等級的優先權 n class 1：delay小於 0. 5 sec n class 2：delay小於 5 sec n class 3：delay小於 50 sec n class 4：best-effort (未指定任何傳輸速度的 限制)

n peak throughput class o 設定期望的最大資料傳輸速率(maximum data transmission rate) 9種等級，從 8 Kbps到 2, 048 Kbps n mean throughput class o 指定平均的資料傳輸速率(average data transmission rate) 19種等級，從best-effort到 111 Kbps

n reliability class o 定訂關於data loss、out-of-sequence、corrupted data等error rates的五種等級 n reliability class 1 § 支援acknowledgement for GTP mode、LLC frame mode和RLC block mode § LLC data受到保護(protection) n reliability class 5 § 全未支援acknowledgement § LLC data未受到保護

Reliability - Qo. S

o 上表格說明五種reliability classes的作業方式 n Ack o 要求acknowledgement n Unack o 不需acknowledgement n Protected o 代表此LLC data受到 保護 n Traffic Type o 說明每種class適合那 類需求的應用