GSM 2.5G Migration

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GSM 2.5G Migration

  1. 1. Course 335 GSM 2.5G Migration: GSM 2.5G Migration: General Packet Radio Service GPRS General Packet Radio Service GPRS 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5-1
  2. 2. What’s GPRS All About? How Does It Fit In? s GSM: Global System for Mobile Communication • The world’s most widely used wireless phone technology – Over 500,000,000 users worldwide! – TDMA-based radio interface, 200 kHz.-wide signals • But very limited data capability – 9,600 or 14,400 bps maximum in circuit-switched mode s WCDMA / UMTS: The Long-Term 3G Data Solution • Uses spread-spectrum CDMA techniques, 4-MHz.-wide signals • Provides both voice and high speed packet data access • But not widely deployed and available until 2003 or later s GPRS: General Packet Radio Service • A packet-switched IP-capable way of using GSM radio infrastructure • Defined in 1996, wide deployment beginning in 2001 • Provides both interim pre-WCDMA and long-term packet access 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5-2
  3. 3. Communications Technology Family History A Story of Births, Weddings and Funerals s Commercial telegraphy gave birth to telephony, then died s Telephony and Land Mobile Radio married, giving IMTS & Cellular s IP networks developed, their usage and bandwidth are increasing s The wedding of IP and Wireless is happening now in 3G! Land Mobile Radio Extinction? HF, VHF, UHF, Trunked IP Networks The Internet Voice over IP Wireless Voice and IP Data IMTS-Cellular-GSM-GPRS-WCDMA Commercial Switched Telephony Extinction? Digital Switching Commercial Telegraphy Extinction! 50 60 70 80 90 10 20 30 40 50 60 70 80 90 10 20 30 40 50 1800s 1900s 2000s 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5-3
  4. 4. GSM and GPRS Background: GSM Technology Background: GSM Technology The Foundation of GPRS The Foundation of GPRS 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5-4
  5. 5. The Beginnings of GSM s 1980’s: Europe used variety of first generation analog cellular systems: TACS, ETACS, NMT450, NMT900, Netz, etc. • Operation was limited to various national boundaries • Poor roaming capabilities, poor economies of scale in mfg. s In 1982, CEPT the Conference of European Posts and Telegraphs created a group to study and define a 2G Pan-European system • Group Spécial Mobile (GSM) • In 1989, administration of GSM was transferred to the European Telecommunications Standards Institute (ETSI) • In 1990, the GSM specification, Phase I, was published s GSM has become very popular due to many positive factors • Non-proprietary: anyone can manufacture networks/handsets • Thorough/integrated standard: well-defined RF air interface, network architecture, call delivery and roaming features 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5-5
  6. 6. GSM World Acceptance s GSM commercial deployment began in 1991 s By 1993, there were 36 GSM networks in 22 countries s In 2000, there were over 200 GSM networks in over 110 countries around the world • Operation in 900 MHz., 1800 MHz., and 1900 MHz. bands s The wide acceptance of GSM has provided tremendous economies of scale in network, handset, and test equipment manufacturing and distribution s Worldwide in 2001, GSM users have passed the 500 million mark • One in 12 human beings uses a GSM phone! s The global dominance of GSM provides a large market for the 2.5G and 3G enhancements GPRS and UMTS WCDMA 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5-6
  7. 7. GSM vs. North American Standards s Two different approaches to wireless technology development! • Americans: Invent cool new stuff driven by market forces, write standards if it works and the market accepts it • Europeans: Study, Plan, build Standards, build Consensus, Plan, Review, build more Consensus, finally Deploy s The differences are visible in the resulting standards • American: multiple interim standards necessary to define functionality • Europeans: single integrated standard covers all functionality North American CDMA GSM Other Features IS-637 IS-683 IS-707 Etc. SMS OTA Data Intersystem Roaming, The GSM Standard IS-41C, D, P Call Delivery, Handoff One coordinated, uniformly structured family of documents Network Architecture IS-634 A-interface Air Interface IS-95/J-Std 008 CDMA RF Architecture 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5-7
  8. 8. GSM Terminology s Some terms have different meanings when used in GSM Sector or North American practice! Cell α α CELL Cell BTS Cell Sector Sector γ β γ β It’s a Sector! It’s a Cell! Sector Sector Cell Cell γ β γ β That was a Handoff! That was a Handover! The frequencies used The frequencies used by each sector are by each cell are its channel set. its allocation. 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5-8
  9. 9. Structure of a GSM Signal s GSM carriers are spaced 200 kHz. apart s In the BTS downlink signal, different 8 Slots Required 1 2 C/I ≅ 9-12 dB timeslots belong to different users - 4 3 a mobile listens only to its recurring timeslots 200 kHz Typical Frequency Reuse N=4 • During unused timeslots, a mobile can measure the signal strength of surrounding BTSs to guide the handover process s The mobile on its uplink transmits only during its assigned timeslots • Mobiles transmit only during BTS their own timeslots • Mobile transmit timeslots occur three timeslots after the corresponding BTS transmit timeslot – This avoids simultaneous mobile TX/RX and the need for duplexer at the mobile 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5-9
  10. 10. The Frequencies Used by GSM Europe and International GSM Uplink GSM Downlink 124 ch. 124 ch. 890 915 MHz. 935 960 North American PCS Licensed Blocks A D B E F C1 C2 C3 A D B E F C1 C2 C3 75 ch. 25 75 ch. 25 25 25 25 25 75 ch. 25 75 ch. 25 25 25 25 25 1850 1865 1885 1900 1910 1930 1945 1965 1975 1990 MHz. s GSM operates in a variety of frequency bands worldwide s GSM carrier frequencies are normally assigned in 200 KHz. Increments within the operator’s licensed block of spectrum s Spectrum is provided in “blocks” • Base stations transmit in the upper block • Mobiles transmit in the lower block s Each cell uses a certain number of carriers, called its “allocation” 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 10
  11. 11. Multiple Carriers in a GSM Cell Time Frequency 6 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS8 Frequency 5 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS8 Frequency 4 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS8 Frequency 3 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS8 Frequency 2 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS8 Frequency 1 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS8 1 timeslot 577 µs 1 frame 4.515 ms s A GSM base station transceiver makes a signal ~240 kHz. wide s The signal is time-divided into a repeating pattern of frames • Each frame is 60/13 = 4.515 ms long, there are ~221.5 frames per second s Each frame is further subdivided into 8 timeslots, each 15/26 ms = 577 µs long • A timeslot can hold the bits of a channel of information – One user’s voice signal, or a signaling/administrative channel s One GSM base station can have several transceivers, each one producing a GSM signal on a different frequency - six carriers in the example above • Various repeating patterns of information can use the timeslots to carry channels of information 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 11
  12. 12. Channels in GSM: Repeating Patterns s Channels of information in GSM occupy physical timeslots of the GSM signal in repeating patterns • Similar to the way that classes and activities of a university occupy the physical classrooms on a defined schedule – Some classes meet daily, some only three days a week – Some labs once or twice a week – Meals daily in the cafeteria, movies on Friday nights – Graduation ceremonies each semester s Dedicated channels (carrying traffic or control information for individual users) occur in a repeating 26-multiframe pattern 120 ms long • 24 frames are used for traffic, one for SACCH, one is unused • Full-rate TCHs occur in each traffic frame • Half-rate TCHs (if used) occur in alternating traffic frames • 1/8 rate dedicated channels are defined for special purposes and are called SDCCHs (Stand-Alone Dedicated Control Channels) 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 12
  13. 13. GSM Traffic Channels: Hyperframes, Superframes, Multiframes, Frames, and Bursts One Hyperframe 2048 superframes 3h 28m 53.760s 0 1 2 3 4 5 2044 2045 2046 2047 51 multiframes of 26 frames each 6.120 s One Superframe 0 1 2 3 4 5 6 47 48 49 50 UNUSED TCHs SACCH TCHs One 26 Used for traffic channels and 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 0 1 2 3 4 5 6 7 8 9 Multiframe associated signaling only 26 frames 120 ms One BP 0 BP 1 BP 2 BP 3 BP 4 BP 5 BP 6 BP 7 Frame 1 frame 60/13 ms ~4.615 ms Stealing Stealing One Burst (156.25 bits) Bit Bit Tail Bits Tail Bits Training Guard Data Bits Data Bits Bits Sequence 3 57 bits 1 26 bits 1 57 bits 3 8.25 bits 15/26 ms Gross Rate 270.833 kbps ~0.577 ms 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 13
  14. 14. GSM Control Channels: Hyperframes, Superframes, Multiframes, Frames, and Bursts One Hyperframe 2048 superframes 3h 28m 53.760s 0 1 2 3 4 5 2044 2045 2046 2047 26 multiframes of 51frames each 6.120 s One Superframe 0 1 2 3 24 25 not used BCCH 1 BCCH 2 BCCH 3 BCCH 4 CCCH0 or FCCH FCCH FCCH FCCH FCCH SYS_INFO CCCH3 or CCCH4 or CCCH5 or CCCH5 or CCCH6 or CCCH7 or SCH SCH SCH SCH SCH 7&8 CCCH 1 CCCH 2 SDCCH SDCCH SDCCH SDCCH SACCH SACCH One 51 0 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 1 2 3 4 5 6 7 8 9 Multiframe 51 frames 235.38 ms Used for control channels only One BP 0 BP 1 BP 2 BP 3 BP 4 BP 5 BP 6 BP 7 Frame 1 frame 60/13 ms ~4.615 ms Stealing Stealing One Burst (156.25 bits) Bit Bit Tail Bits Tail Bits Training Guard Data Bits Data Bits Bits Sequence 3 57 bits 1 26 bits 1 57 bits 3 8.25 bits 15/26 ms Gross Rate 270.833 kbps ~0.577 ms 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 14
  15. 15. Typical Timeslot Allocation in Multiframe Patterns on One GSM RF Carrier TIME S S TimeSlot T T T T T T T T T T T T A T T T T T T T T T T T T T T T T T T T T T T T T A T T T T T T T T T T T T IDLE IDLE C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C 7 H H H H H H H H H H H H C H H H H H H H H H H H H H H H H H H H H H H H H C H H H H H H H H H H H H H H S S TimeSlot T T T T T T T T T T T T A T T T T T T T T T T T T T T T T T T T T T T T T A T T T T T T T T T T T T IDLE IDLE C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C 6 H H H H H H H H H H H H C H H H H H H H H H H H H H H H H H H H H H H H H C H H H H H H H H H H H H H H S S TimeSlot T T T T T T T T T T T T A T T T T T T T T T T T T T T T T T T T T T T T T A T T T T T T T T T T T T IDLE IDLE C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C 5 H H H H H H H H H H H H C H H H H H H H H H H H H H H H H H H H H H H H H C H H H H H H H H H H H H H H S S TimeSlot T T T T T T T T T T T T A T T T T T T T T T T T T T T T T T T T T T T T T A T T T T T T T T T T T T IDLE IDLE C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C 4 H H H H H H H H H H H H C H H H H H H H H H H H H H H H H H H H H H H H H C H H H H H H H H H H H H H H S S TimeSlot T T T T T T T T T T T T A T T T T T T T T T T T T T T T T T T T T T T T T A T T T T T T T T T T T T IDLE IDLE C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C 3 H H H H H H H H H H H H C H H H H H H H H H H H H H H H H H H H H H H H H C H H H H H H H H H H H H H H S S TimeSlot T T T T T T T T T T T T A T T T T T T T T T T T T T T T T T T T T T T T T A T T T T T T T T T T T T IDLE IDLE C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C 2 H H H H H H H H H H H H C H H H H H H H H H H H H H H H H H H H H H H H H C H H H H H H H H H H H H H H Frame 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 1 Number 26 Multiframe Pattern for Traffic Channels 26 Multiframe Pattern for Traffic Channels S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D A A A A A A A A A A A A A A A A TimeSlot C IDLE IDLE IDLE C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C 1 H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H 0 0 0 0 1 1 1 1 2 2 2 2 3 3 3 3 4 4 4 4 5 5 5 5 6 6 6 6 7 7 7 7 0 0 0 0 1 1 1 1 2 2 2 2 3 3 3 3 A A A A A A A A A A A A S S S S S S S S S S S S S S S S S S S S B B B B G G G G G G G G G G G G TimeSlot F C C C C C C C C F C C C C C C C C F D D D D D D D D F C C C C D D D D F A A A A A A A A C S C S S C C C C C C C C S C C C C S C C C C C C C C IDLE C C C C H H H H C C H H H H H H H H C C C C C C C C C C C C B B B B C C C C C C C C C C C C C C 0 C H H H H / / / / C / / / / / / / / C C C C C C C H H H H H H H H H H H H H H H H H H H H H H H H H H P P P P H P P P P P P P P H H H H H H H 1 2 3 4 C C C C C C C C C C C C 0 0 0 0 1 1 1 1 3 3 3 3 0 0 0 0 1 1 1 1 H H H H H H H H H H H H Frame 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 Number 51 Multiframe Pattern for Control Channels 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 15
  16. 16. A GSM Uplink Normal Burst s GSM is a TDMA system and a mobile’s transmission bursts are carefully constructed not to overlap with bursts from other mobiles s Different propagation delays of mobiles near and far mobiles the BTS are compensated by automatically advancing mobile transmit timing s Special training sequences are included in each uplink burst and downlink timeslot to facilitate demodulation s During unused timeslots, a mobile measures the strength of surrounding base stations to guide the handover process (this is called MAHO, Mobile Assisted Hand Over) 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 16
  17. 17. GSM Bursts on the Uplink: 4 Types Frequency Correction Burst or Dummy Burst Guard Tail Tail Fixed ‘0’ or Fill-in Bits Bits 3 142 bits 3 8.25 bits Synchronization Burst Guard Tail Tail Data Bits Training Bits Data Bits Bits 3 39 bits 64 bits 39 bits 3 8.25 bits Access Burst Tail Tail Guard Bits Training Bits Data Bits Bits 8 41 bits 36 bits 3 68.25 bits Stealing Stealing Normal Burst Bit Bit Guard Tail Tail Data Bits Training Bits Data Bits Bits 3 57 bits 1 26 bits 1 57 bits 3 8.25 bits 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 17
  18. 18. GSM Channels DOWNLINK CHANNELS UPLINK CHANNELS BTS identity, channel allocation, BCCH frequency hopping sequences Slotted aloha channel used to FCCH Provides frequency reference request network access RACH Defines burst period boundaries SCH and time slot numbering Carries pages to mobiles, PCH alerting of incoming calls Stand Alone Dedicated AGCH Allocates SDCCH to mobile to Control Channel SDCCH obtain dedicated channel after a request on the RACH Traffic Channel TCH Fast Associated Control BTS Channel FACCH Slow Associated Control Channel SACCH 0 to many F-TRAFFIC Stand Alone Dedicated SDCCH Control Channel Traffic Channel TCH Fast Associated Control Channel FACCH Slow Associated Control Channel SACCH 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 18
  19. 19. The GPRS Timeslot Allocation s In conventional GSM, a channel is permanently allocated for a particular user during the entire call period (whether speaking or silent, whether transmitting data or not) • In GPRS, the channels are only allocated when data packets are transmitted or received, and they are released after the transmission • For bursty traffic this results in much more efficient use of the scarce radio resources • Multiple users can share one channel s GPRS allows a single mobile to transmit and/or receive on multiple timeslots of the same frame (this is called multislot operation) • This provides “bandwidth on BTS demand” in a very flexible scheme • One to eight timeslots per frame can be allocated to a mobile • Uplink and downlink allocations •This GPRS mobile is in “3+1” timeslot mode •3 timeslots assigned on downlink can be allocated separately, •1 timeslot assigned on uplink which efficiently supports asymmetric data traffic (suitable for web browsing, for example) 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 19
  20. 20. Allocation of GPRS Channels s A cell supporting GPRS may allocate physical channels for GPRS traffic s Such a physical channel is denoted a Packet Data Channel (PDCH) • The PDCHs are taken from the common pool of all channels available in the cell • The radio resources of a cell are shared by all GPRS and all non- GPRS mobiles in the cell • The mapping of physical channels to either GPRS or GSM usage can be performed dynamically, based on: – Capacity on demand principle – Depending on the current traffic load, priority of service, and the multislot class s A load supervision procedure monitors the PDCHs in the cell s The number of channels allocated to GPRS can be changed according to current demand • Physical channels not currently in use by conventional GSM can be allocated as PDCHs to increase the GPRS quality of service • When there is a resource demand for services with higher priority, PDCHs can be de-allocated 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 20
  21. 21. GSM, GPRS and WCDMA / UMTS GSM, GPRS, WCDMA GSM, GPRS, WCDMA Coordinated Network Architecture Coordinated Network Architecture 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 21
  22. 22. 3 Steps to 3G: The GSM Transition GSM TODAY PLMN Core Network SIM PSTN MSC BSC BTS Mobile VLR Base Base Gateway Mobile Station ISDN Station Transceiver Switching Controller Stations MSC Mobile HLR Center Equipment Internet 2.5G: GSM + GPRS Core Network VLR MSC PLMN Mobile SIM PSTN Gateway Switching Mobile MSC Center BSC BTS HLR Base Base Station ISDN Gateway Serving Station Transceiver Mobile GPRS GPRS PCU Controller Stations Equipment Support Support Internet node node 3G: UMTS, UTRA Core Network MSC UTRAN RNC Node B UMTS PLMN VLR Mobile PSTN Gateway Switching Radio SIM Network MSC Center Controller Node B User ISDN HLR Equipment Gateway Serving RNC GPRS GPRS Radio Node B Mobile Internet Support Support Network Equipment node node Controller Node B 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 22
  23. 23. Architecture of a Phase-1 GSM Network PLMN Core Network SIM PSTN MSC BSC BTS Mobile VLR Base Base Gateway Mobile Station ISDN Station Transceiver Switching Controller Stations MSC Mobile HLR Center Equipment Internet EIR AuC A Abis Um Interface Interface Interface GSM Functional Entities and Network Elements PLMN - Public Land Mobile Network HLR - Home Location Register PSTN - Public Switched Telephone Network VLR - Visitor Location Register ISDN - Integrated Services Digital Network BSC - Base Station Controller GMSC - Gateway Mobile Switching Center BTS - Base Transceiver Station MSC - Mobile Switching Center SIM - Subscriber Identity Module EIR - Equipment Identity Register ME - Mobile Equipment AuC - Authentication Center MS - Mobile Station s The network elements and interfaces of GSM are standardized s This provides for inter-vendor participation in operators’ networks • Competition improves quality, provides economies of scale 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 23
  24. 24. GSM Network Evolution and History GSM TODAY PLMN Core Network SIM PSTN MSC BSC BTS Mobile VLR Base Base Gateway Mobile Station ISDN Station Transceiver Switching Controller Stations MSC Mobile HLR Center Equipment Internet s The present GSM network architecture emerged from work of the ETSI in the late 1980s s The GSM network can be divided into three main domains • The Network Switching Subsystem (GMSC, VLR, HLR, MSC) • The Operations and Support Subsystem (not shown, includes OMC-R) • The Base Station Subsystem BSS (includes BSCs, BTSs) 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 24
  25. 25. GSM Evolution: General Packet Radio Service s Around 1994, the GSM phase 2 standards were enhanced to include a number of new and improved services. These enhancements became known as GSM Phase 2 Plus. s One of the new features proposed in 1994 was a new bearer service, true packet radio service known as GPRS s GPRS allows a user with suitable mobile station to occupy multiple time slots on a TRX, culminating in the possible occupancy of all 8 timeslots if they are available • Data rates supported per timeslot are 9.06, 13.4, 15.6, and 21.4 kb/s • When all 8 timeslots are available, throughput can reach 8 x 21.4 kb/s = 171.2 kb/s, although realistic expectations are around 115 kb/s due to BCCH and other requirements s GPRS applications are expected to include internet access/web browsing, video and Road Traffic and Transport Informatics (RTTI), and e-commerce and point-of-sale accounting 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 25
  26. 26. GPRS Network Architecture VLR LEGEND PLMN PSTN MSC Existing GSM Core Network elements ISDN A New GPRS elements and interfaces User data & signaling Gs Signaling only SGSN of a HLR EIR SMSC different SIM PLMN Gp Ater Mobile Gc Gr Gf TCU BSC BTS Station Gd Base Abis Base Station Transceiver Mobile Controller Station Eqpm’t PSPDN PCUSN GGSN Gn SGSN Gb Agprs Gi Um Interface s The GSM network architecture was modified to add packet services, through the addition of the new network elements GGSN and SGSN • GGSN Gateway GPRS Support Node – Responsible for routing data packets entering and leaving the radio network; also as a router for packets within the network • SGSN Serving GPRS Support Node – responsible for packet delivery to mobiles in its area – a type of packet switch with capability to interrogate the GSM databases HLR and VLR for location and service profiles of mobiles s Data is “tunneled” from the GGSN to the SGSN using GTP, GPRS Tunneling Protocol, encapsulating packets de-encapsulating on delivery 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 26
  27. 27. Understanding the Backbone Networks VLR LEGEND PLMN PSTN MSC Existing GSM Core Network elements ISDN A New GPRS elements and interfaces User data & signaling Gs Signaling only SGSN of a HLR EIR SMSC different SIM PLMN Gp Ater Mobile Gc Gr Gf TCU BSC BTS Station Gd Base Abis Base Station Transceiver Mobile Controller Station Eqpm’t PSPDN PCUSN GGSN Gn SGSN Gb Agprs Gi FRAME RELAY Um IP or X.25 Interface s Gb between SGSN-PCUSN uses Frame Relay protocols s Gn between SGSN-GGSN uses IP routing, GPRS Tunnel Protocol s Gr between SGSN-HLR is an extension of MAP s Gi between GGSN and PDNs uses IP and X.25 s Gd between SGSN-SMSC delivers SMS messages using MAP s Gc between GGSN-HLR is optional, uses MAP s Gs between SGSN-MSC/VLR is optional, uses BSSMAP 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 27
  28. 28. GPRS Backbone Networks s Two kinds of GPRS backbones: • Intra-PLMN among GSNs of same PLMN (private, IP-based) • Inter-PLMN among GSNs of different PLMNs (roaming agreements) s Gateways between the PLMNs and the external inter-PLMN backbone are called Border Gateways • Border Gateways perform security functions to prevent unauthorized access and attacks s The Gn and GP interfaces are also defined between two SGSNs • This allows exchange of user profiles as mobiles move around s The Gf interface allows a SGSN to query the IMEI of a registering mobile s The Gi interface connects the PLMN to external public or private PDNs • Interfaces to IPv4, IPv6, and X.25 networks are supported s The Gr interface allows an SGSN to communicate with an HLR 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 28
  29. 29. GPRS-GSM Coordination s The MSC/VLR may be extended with functions and register entries for efficient coordination between GPRS packet switched and GSM circuit-switch services • Combined GPRS and non-GPRS location updates s Paging requests for circuit-switched GSM calls can be performed via the SGSN • The Gs interface connects the databases of SGSN and MSC/VLR s The Gd interface allows short message exchanges via GPRS • Gd interconnects the SMS gateway MSC (SMS-GMSC) with the SGSN 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 29
  30. 30. GPRS Services s GPRS bearer services provide end-to-end packet-switched data transfer. There are two kinds: s PTP Point-to-Point Service, available now, has two modes: • PTP Connectionless Network Service (PTP-CLNS) for IP • PTP Connection-oriented network Service (PTP-CONS) for X.25 s PTM Point-to-Multipoint Service (available in future releases) • PTM-M Multicast Services broadcasts packets in certain geographical areas; a group identified indicates whether the packets are intended for all users or for a group • PTM-G Group Call Service addresses packets to a group of users (PTM group) and are sent out in geographical areas where the group members are currently located s SMS Short Message Services s Supplemental Call Services: • CFU Call Forwarding Unconditional, CFNRc Call Forwarding Subscriber Not Reachable, CUG Closed User group s Non-Standard Services may be offered at GPRS service providers • Database access, messaging, e-transactions, monitoring, telemetry 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 30
  31. 31. The Stages of the GPRS Specifications Stage 1 s The GPRS specification is 02.60 GPRS Service Description (overview) built in three stages s Stage 1 describes the basic Stage 2 GPRS Service Description service capabilities 03.60 (System and Architecture) 03.64 Radio Interface Description s Stage 2 describes the specific system and network Stage 3 architectures and the radio 04.60 MS-BSS: RLC/MAC layer descriptions interface description 04.64 MS-SGSN: Logical Link Control 04.65 MS-SGSN: SNDCP s Stage 3 provides details of the 07.60 GPRS Mobile Stations link control layer entities, 08.14 Gb (BSS-SGSN) layer 1 specifications of the mobile 08.16 Gb (BSS-SGSN) network service 08.18 Gb (BSS-SGSN) BSSGP stations, and details of the 09.16 Gs (MSC/VLR-SGSN) layer 2 internal network element 09.18 Gs (MSC/VLR-SGSN) layer 3 interfaces and their protocols 09.60 Gn and Gp GPRS Tunneling Protocol 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 31
  32. 32. GPRS Initial Release Features s All network manufacturers are expected to support IP and interworking with both internet and intranet in their first product release • To support this functionality, some form of server functionality must be provided – Domain Name Server (DNS) is required to translate between domain names and IP addresses – Dynamic Host Configuration Protocol (DHCP) is required to allow automatic reassignment of addresses for mobile hosts s In early networks, a single SGSN will probably be sufficient due to the gradual growth of users and traffic as mobiles become available s The connection between the GGSN and the MSC/VLR, HLR, and SMSC will require a gateway using SS7/IP or SIG to link the IP backbone with the interfaces to these network elements 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 32
  33. 33. GPRS A Closer View of the GPRS A Closer View of the GPRS Internal Interfaces and Elements Internal Interfaces and Elements 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 33
  34. 34. Serving GPRS Support Node (SGSN) Functions s The Serving GPRS Support Node (SGSN) is responsible for the following to and from the mobile stations in its service area: • Packet Routing and Transfer • Mobility management (attach/detach and location management) • Logical Link management • Authentication and charging functions, encryption • Compression (optional) • Location register of SGSN stores location (cell, vlr) and user profiles s A typical PLMN network will start with only one SGSN s Each BSC has a Packet Communications Unit, PCU Several models of the Nortel Passport Switch • Similar hardware provides the for SGSN and PCUSN service PCUSN function 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 34
  35. 35. Gateway GPRS Support Node (GGSN) Functions s The Gateway GPRS Support Node (GGSN) is the interface between external packet data networks and GSM backbone network • Converts GPRS packets from the SGSN into packet data protocol format (IP, X.25) for Nortel’s GGSN: the external networks Bay Contivity Extranet Switch • Converts PDP addresses of CES-4500 incoming data packets to GSM address of destination user, and forwards to responsible s Initial GPRS traffic in a PLMN SGSN network will be low, and a single GGSN will suffice for first service • GGSN stores the current SGSN and an appreciable time address of the user and the thereafter user’s profile in its location register • GGSN performs authentication and charging functions • Performs tunneling 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 35
  36. 36. GSM BTS Changes Required to Support GPRS Three Possible GPRS BSS Configurations s Since GPRS uses new coding Um Gb schemes, a Channel Codec Interface Interface Unit (CCU) is required CCU BTS BSC PCU • The CCU can normally be CCU SGSN implemented within BTS software PCU in BTS Advantage: short Round Trip Delay s Timeslot allocation for GPRS Abis is handled by a new Packet Interface Controller Unit (PCU) which CCU BSC also implements frame relay CCU BTS PCU SGSN connection with the GPRS network PCU in BSC • The PCU function can be Gb physically implemented in Interface the BTS, BSC, or at the CCU BSC SGSN, but is conceptually CCU BTS PCU SGSN part of the BSS PCU at SGSN Advantage: Leverage -- 1 PCUSN can manage multiple BSCs 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 36
  37. 37. Channel Coding Implemented at the BTS GPRS Coding Schemes Pre- Infobits Parity Tail Output Punct Code Data Coding Cod. Without Bits Bits Conv. ured Rate Rate Scheme USF USF BC encoder Bits Kbit/s CS-1 3 181 40 4 456 0 1/2 9.05 CS-2 6 268 16 4 588 132 ~2/3 13.4 CS-3 6 312 16 4 676 220 ~3/4 15.6 CS-4 12 428 16 456 1 21.4 s Channel coding is used to protect the transmitted GPRS data packets against errors • The channel coding in GPRS is very similar to that of GSM – An outer block coding, an inner block coding, and an interleaving scheme are used s Four different coding schemes are defined in the table above s As of mid-2001, network manufacturers were only implementing CS-1 and CS-2 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 37
  38. 38. The MS-SGSN Interface s Packet Controller functions are provided by the PCU, which is implemented in a Physical BSC A VLR physical PCUSN in the BSS TCU Ater MSC • The PCUSN handles the GPRS- specific packet processing using frame Gb relay protocols BSC PCUSN SGSN Agprs • The PCUSN connects to the BSC with network manufacturers’ proprietary Agprs BTS interfaces • The PCUSN connects to the SGSN via the standard-defined Gb interface MS s Although a PCUSN can optionally serve more than one BSC, all channels from one PCUSN and PCU Distinction •A PCUSN (Packet Controller Unit Serving BSC must pass through the same PCUSN Node) is the hardware unit which implements s TRAU frames from the mobile pass through the PCU (Packet Controller Unit) function the BTS to the BSC and on into the PCUSN 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 38
  39. 39. MS-SGSN Logical Link Control (LLC) GMM SNDCP SMS GMM SNDCP SMS LLC LLC Relay RLC RLC BSSGP BSSGP MAC MAC Network Svc Network Service GSM/RF GSM RF L1 L1 MS Um BSS Gb SGSN s LLC provides the reliable link between MS and SGSN s LLC supports these layer-3 Protocols: • SNDCP Sub-Network Dependent Convergence Protocol • GMM/SM GPRS Mobility & Session Management • SMS Short Message Service s Protocols supported by the LLC provide: • Data ciphering for security • Flow control; sequential order of delivery; error detection/recovery • Acknowledged and Unacknowledged data transfer modes s The LLC provides transparency - the lower level radio link protocols are not involved and do not affect the GPRS applications running above 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 39
  40. 40. MS-SGN Service Access Points (SAP) for LLC s The LLC provides six service access points (SAP) to the upper layers • Each SAP has its own Service Access Point Identity (SAPI) s The SAPs include: • GMM/SM - Service for Signaling for Session/Mobility Management • SMS - Short Message Service • QoS1 Packet Transmission SNDCP access • QoS2 Packet Transmission SNDCP access • QoS3 Packet Transmission SNDCP access • QoS4 Packet Transmission SNDCP access s Frames are assembled/disassembled using a multiplex procedure • A logical link management entity (LLME) manages resources 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 40
  41. 41. The Gb Interface: PCU-SGSN SMS-GMSC OTHER SMS-IWMSC GPRS PLMN s The SGSN and the PCUSNs of each BSC Gd Gp GG SN are linked by a backbone network using SG Frame Relay protocol over the Gb interface BTS BSC Gb SN GG Gi • Data rate can be up to 2 Mbps Gf Gn SN BTS Gs Gr PDN • Frame relay protocol implementation is actually simpler than X.25 Gc EIR s Layers at each node of the Gb : MS MSC D HLR • Physical Layer VLR • Network Service Layer (NS) • Base Station Subsystem GPRS Protocol (BSSGP) • Network Management (NM) – GPRS Mobility Management (GMM) – LLC/Relay 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 41
  42. 42. PCU and SGSN Operation over the Gb Interface s BSSGP: Base Station Subsystem GPRS Protocol User Packets User Packets • Provides flow control, manages Via RLC and Via RLC and buffers, provides services for MAC layers MAC layers the higher layers s GMM - GPRS Mobility Management Relay GMM NM LLC GM NM • Manages mobility features for users, such as location updating BSSGP L3 BSSGP and paging L2 s NM - Network Management Network Services Frame Relay Network Services • Manages flow control, buffers, Gb virtual pathways between Physical Physical PCU/SGSN PCU SGSN s Network Services • Implements the communications protocol for the Gb interface (Frame Relay) s Physical Layer • Hardware and physical nature of the interface 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 42
  43. 43. The Gn Interface: SGSN-GGSN SMS-GMSC OTHER SMS-IWMSC GPRS PLMN s The SGSN and GGSN are linked by a Gd Gp GG SN GPRS backbone using IP routing SG BTS BSC s The Gn interface creates and operates Gb SN GG Gi through secure tunnels, using the Gf G SN Gr n GPRS Tunneling Protocol (GTP) BTS Gs PDN s The GTP packet headers include EIR Gc • Tunnel endpoint and group identity MS MSC D HLR • PDU type VLR • QoS parameters • Routing protocol identification – Static, RIP2, OSPF s Beneath IP, any transport architecture can be used • Ethernet, Token-Ring, FDDI, ISDN, ATM 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 43
  44. 44. The Gp Interface: SGSN - Other PLMN GGSN SMS-GMSC OTHER SMS-IWMSC GPRS PLMN s The Gp interface connects an SGSN of Gd Gp GG SN one PLMN with a GGSN of another SG BTS BSC PLMN Gb SN GG Gi Gf Gn SN s This interface forms an inter-PLMN BTS Gs Gr PDN backbone providing mobile IP Gc capability for roaming mobiles EIR MS s Specific configuration of this link MSC D HLR VLR depends on the features intended by the two PLMN operators, as well as dimensioning issues 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 44
  45. 45. More About GPRS Tunneling on Gn and Gp GPRS TUNNELING PROTOCOL (GTP) SMS-GMSC OTHER SMS-IWMSC GPRS PLMN PROTOCOL STACK Gd Gp GG IP SN GMM/SM SNDCP GTP GTP SG IP BTS BSC SN LLC UDP/TCP Gn, Gp UDP/TCP Gb GG Gi BSSGP IP IP Gf Gn SN NS L2 L2 L2 BTS Gs Gr PDN L1B1s L1 L1 L1 Gc EIR SGSN GGSN MS MSC D HLR VLR s GPRS Tunneling Protocol (GTP) is used to carry user packets between nodes • GTP allows various protocols and is adaptable to both inter- and intra-PLMN GGSN interfaces – UDP/IP if reliable link is not required, TCP/IP if required 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 45
  46. 46. The Gn Interface: SGSN-GGSN SMS-GMSC OTHER SMS-IWMSC GPRS PLMN s The SGSN and GGSN are linked by a Gd Gp GG SN GPRS backbone using IP routing SG BTS BSC s The Gn interface creates and operates Gb SN GG Gi through secure tunnels, using the Gf G SN Gr n GPRS Tunneling Protocol (GTP) BTS Gs PDN s The GTP packet headers include EIR Gc • Tunnel endpoint and group identity MS MSC D HLR • PDU type VLR • QoS parameters • Routing protocol identification – Static, RIP2, OSPF s Beneath IP, any transport architecture can be used • Ethernet, Token-Ring, FDDI, ISDN, ATM 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 46
  47. 47. The Gi Interface: GGSN-PDN SMS-GMSC OTHER SMS-IWMSC GPRS PLMN s If the Gi interface is implemented via a Gd Gp GG SN public network, IP Security Protocol SG (IPSEC) can be used to provide link BTS BSC Gb SN GG G authentication and encryption Gf Gn SN i • This allows use of public networks BTS Gs Gr PDN such as the internet while Gc maintaining confidentiality of data EIR MS s The GGSN creates VPN tunnels using MSC D HLR VLR security protocols like IPSEC if needed s Four tunneling protocols are available: • PPTP (client-initiated) • L2F, L2TP (implemented on ISP side) • IPSec (layer-3 secure protocol) s Transparent and Non-Transparent modes are available 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 47
  48. 48. The Gr Interface: SGSN-HLR SMS-GMSC OTHER SMS-IWMSC GPRS PLMN s The Gr interface is an extension of the Gd Gp GG SN GSM-MAP (mobile application part) SG BTS BSC SN s Most network manufacturers use an Gb GG Gi Gf Gn SN SS7 gateway element to provide BTS GsG PDN interworking between the GPRS r Gc network and the SS7-based voice EIR network MS MSC D HLR VLR • This relieves the SGSN from having to do SS7 processing • The SS7 gateway can be a conventional server, usually with redundancy features on both the SGSN (IP) and SS7 sides 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 48
  49. 49. The Gd Interface: SGSN-SMCS GMSC/IWMSC SMS-GMSC OTHER SMS-IWMSC GPRS PLMN s The Gd interface delivers SMS Gd Gp GG SN messages via GPRS in the same SG BTS BSC manner as the GSM-MAP Gb SN GG Gi Gf Gn SN BTS Gs Gr PDN Gc EIR MS MSC D HLR VLR 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 49
  50. 50. The Gf Interface: SGSN-EIR SMS-GMSC OTHER SMS-IWMSC GPRS PLMN s The Gf interface connects the SGSN Gd Gp GG SN and the Equipment Identity Register SG BTS BSC (EIR) Gb SN GG Gi Gf Gn SN BTS Gs Gr PDN Gc EIR MS MSC D HLR VLR 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 50
  51. 51. The Gs Interface: SGSN-MSC/VLR SMS-GMSC OTHER SMS-IWMSC GPRS PLMN s The Gs interface is optional Gd Gp GG SN • Provides simultaneous GPRS and BTS BSC SG SN GSM operation between SGSN and Gb GG Gi Gf Gn SN MSC/VLR (same as BSSMAP but BTS Gs Gr PDN optional) Gc EIR MS MSC D HLR VLR 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 51
  52. 52. The Gc Interface: GGSN-HLR SMS-GMSC OTHER SMS-IWMSC GPRS PLMN s The Gc interface is optional Gd Gp GG SN • Provides the same functions as the BTS BSC SG SN MAP between GGSN and HLR Gb GG Gi Gf Gn SN BTS Gs Gr PDN Gc EIR MS MSC D HLR VLR 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 52
  53. 53. The D Interface: MSC/VLR - HLR SMS-GMSC OTHER SMS-IWMSC GPRS PLMN s The MAP-D interface is used by both Gd Gp GG SN GSM and GPRS networks to SG BTS BSC communicate between the HLR and Gb SN GG Gi the VLR in the MSC Gf Gn SN BTS Gs Gr PDN s This link is specified in the GSM-MAP Gc and is not changed in GPRS EIR MS D HLR MSC VLR 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 53
  54. 54. Quality of Service Reliability Probability of Service Precedence Lost Dupli- Out-of Corrupt- Class High Packet cated Sequence ed Packet Packets Packets Medium 1 109 109 109 109 2 104 105 105 106 Low 3 102 105 105 102 s Mobile packet applications have a wide range of reliability expectations -- real-time multimedia, Web browsing, email transfer s QoS Classes settable per session are a very important feature • Service Precedence – Priority of a service in relation to other services • Reliability – Required transmission characteristics (3 classes defined) • Delay – Maximum values for mean delay and 95-percentile delay • Throughput – Maximum-Peak bit rate and the mean bit rate 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 54
  55. 55. Quality of Service: the Delay Parameter Delay 128 byte packet 1024 byte packet Class Mean 95% Mean 95% Delay Delay Delay Delay 1 <0.5s <1.5s <2s <7s 2 <5s <25s <15s <75s 3 <50s <250s <75s <375s 4 Best Effort Best Effort Best Effort Best Effort s Using these QoS Classes, QoS profiles can be negotiated between the user and the network for each session, depending on QoS demand and currently available resources. • Billing is based on data volume, type of service, and QoS profile 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 55
  56. 56. Mobile Classes and Simultaneous Usage s In a GSM network, two classes of service can run concurrently: • Circuit-Switched Services (speech, data, and SMS) • Packet-Switched Services (GPRS) s Three Classes of Mobile Stations are defined: • Class A mobiles – Support simultaneous operation of GPRS and conventional GSM services, but two separate radio chains are required • Class B mobiles – Able to register with the network for both GPRS and conventional GSM services simultaneously, but can only use one of the two services at a given moment - voice can pre-empt data • Class C mobiles – Able to attach for either conventional GSM or GPRS, manually switched – Simultaneous registration (and usage) is not possible, except for SMS messages which can be received and sent at any time 10-2001 GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter 5 - 56

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