Session 5 Topic 4 Benefits from Packet Switching for ETCS

Transcription

1 Session 5 Topic 4 Benefits from Packet Switching for 1

2 Frequency Status GSM-R Air-interface UIC frequency band (paired spectrum MHz Uplink MHz Downlink) hosts 19 potential radio bearers Further radio bearers are available in the Extended UIC band Carrier bandwidth, Multiple Access Scheme, Carrier reuse i.e. C/I are examples of limiting criteria Shunting and simultaneous operation of Level 2 in CS-mode demands more traffic resources! 2

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4 Quantity of typical messages Shares in % operational requirements Frequency of user data packets are relatively low compared to other applications; Varies between 3 and 20 seconds Only 29% of the 21 typical messages are exchanged periodically! 9 66,67% 70,00% ,76% 28,57% Periodically Frequency Typical Messages Uplink (OBU-->RBC) Downlink (RBC-->OBU) Shares in % 60,00% 50,00% 40,00% 30,00% 20,00% 10,00% 0,00% Packet size of data units are relatively small! Onboard to RBC: octets RBC to Onboard: octets / 500 octets Movement Authority 4

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6 Improved Transmission Error Correction Radio media might cause transmission errors in CS-mode applies an E2E error correction; messages can be delayed significantly GPRS/EGPRS will correct erroneous radio blocks at the lower layers; remaining transmission errors shall be corrected by the transport protocol End to End Error Correction for remaining transmission Layer I GSM PS/ CS Error rectification caused by radio BTS GSM-R PCU SGSN GGSN BSC Gb TRAU Um Abis Ater A MSC MSS/MGW Gn/Gp Packet-Switched Domain Gs HLR/ AuC Circuit-Switched Domain Gr D I Fix-PS IP Packet Data Network(s) Gi ISDN Network(s) RBC I Fix-CS End to End Transmission Error Correction 6

7 Message Transfer Delay [ms] Percentage Improved Transmission Error Correction GPRS/EGPRS provide different method of Forward Error Correction than GSM Circuit Switched bearer Transmission errors caused by radio degradation are much faster rectified in GPRS/EGPRS using the acknowledged mode of data link layer EoG Phase 1 testing result demonstrates, radio degradation affects more GPRS radio blocks, but fast retransmission can keep the message transfer delay level ,6% ,1% 1,5% 148 GPRS CS-2 CS-mode 9.6kbps CS-mode 4.8kps percentage of errorneous messages Ø time transfer delay [ms] 30,0% 25,0% 20,0% 15,0% 10,0% Ø time transfer delay caused by radio degradation [ms] 7 5,0% 0,0%

8 Mixed operation of and non- applications CS-mode gets dedicated transmission resources allocated Radio Resource allocation is based on priority! PS-mode shares transmission resources Allocation of the available bandwidth in equal portions within the same traffic class priority based! Consequence: Throughput per user is lowered packet delay increases! Example Priority based resource allocation principle Available Radio Transmission Bandwidth User 1 User 2 User 1 User 1 User 2 User 2 User 3 User 3 User 4 User 4 User 5 Users are belonging to the same traffic class Non- Users Non- Users Non- Users Available bandwidth per user in the cell Number of concurrent users in a cell sharing same bandwidth 8

9 Mixed operation of and non- applications Dedicated resources can be ensured by Guaranteed Bit Rate (GBR) traffic class provisioning together with GBR allocation of e.g. 4kbps for subscribers. Non-Guaranteed Bit Rate traffic class provisioning for non- subscribers. Highest traffic handling priority within Non-Guaranteed Bit Rate Traffic class remains reserved for purposes. Exception handling: If no sufficient resources are available, then the network shall allocate the request to the highest non-gbr traffic class but having most demanding handling priority e.g. user 3. Priority +GBR based resource allocation principle Available Radio Transmission Bandwidth User 1 GBR User 2 GBR Allocated GBR bandwidth User 3 Non- Users Remaining bandwidth Non- GBR Traffic 9

10 Circuit and Packet Mode will coexist during the remaining GSM-R life cycle (CS) Circuit Switched Domain MSC/VLR GSM Backbone MSC/VLR PSTN / ISUP Controller/ ISDN or SIP OTHER CS PS BSC SS7 HLR CS Core PS Core Internet IP NETWORKS Radio Access Network SGSN GPRS Backbone GGSN RBC External Networks (PS) Packet Switched Domain 10

11 GSM-R PS-mode for Increases the number of degrees of freedom! Advantages of GPRS/EGPRS for Multiplexing of sessions per timeslot saves frequency resources improves spectrum efficiency GPRS (Coding Scheme 1&2): 4 sessions (confirmed) up to 7 EGPRS: 4 7; 8-14 sessions (depends on radio conditions and modified resource allocation timer handling) Reliability Transmission errors caused by radio degradations rectified on lower layers retransmission is much faster than in Circuit mode Enhanced transmission error correction techniques in EGPRS Level of Transmission protection i.e. Coding Scheme adaptable on cell level! Higher transmission bandwidth by aggregation of timeslots can keep E2E performance under degraded radio conditions Mixed operation sessions take precedence over non- sessions Appropriate features in the packet access and core network allow an optimum on bandwidth utilisation and delay handling between the two application categories. 11

12 Benefits Packet Switching for Scalability Increases flexibility at trainborne side due to simultaneous operation of various applications e.g. and Online Key Management; Further automation of manuel tasks are possible. CS-mode requires always dedicated Mobile Equipment and dedicated radio resources for each application. GSM-R network: Better resource utilisation due to session multiplexing. Radio Bearer Independence Trackside: RBC becomes radio bearer independent; IP based transport does not require specific interfaces per radio access. CS-mode remains as standalone access. E2E complexity IP based transport reduces system complexity between the communication entities; simplified addressing, routing and redundancy approaches. 12

13 Thank you for the attention! 13