dit Efficiency Issues in MPLS Transport for the UMTS Access Network E. Vázquez, M. Álvarez-Campana, A. B. García

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1 Efficiency Issues in MPLS Transport for the UMTS Access Network E. Vázquez, M. Álvarez-Campana, A. B. García Dept. of Telematic Engineering Technical University of Madrid, Spain 1

2 Outline in the access network of efficiency model and results s QofIS'04 - Barcelona 30/9/2004 2

3 UMTS (Release 99) IP IP B B B Uu B ATM connection ATM ATM connection Iub interface RNC RNC IuPS IuCS UMTS Radio Access Network (UTRAN) IP tunnel SGSN MSC Packetswitched (PS) Circuitswitched (CS) GGSN GMSC circuits IP network Core Network (CN) Telephone network QofIS'04 - Barcelona 30/9/2004 3

4 Protocol stack in Iub interface Non-access Layer Higher layers IP/PPP Circuitmode voice Circuit-mode and packetmode services Radio Network Layer (RNL) PDCP Radio Link Control Medium Access Control Frame Protocol New UMTS protocols, standardized by 3GPP Transport Network Layer (TNL) AAL2 ATM Layer 1 SSSAR CPS Iub interface (user plane) Reuse of existing protocols Release 99: ATM Release 5 (2002): ATM or UDP/IP QofIS'04 - Barcelona 30/9/2004 4

5 AAL2/ATM transport option Node B Radio Network Controller (RNC) Segmentation Multiplexing Quality of Service Frame Protocol Radio Network Layer Frame Protocol SSSAR Transport Network Layer AAL2 AAL2 SSSAR CPS CPS ATM ATM ATM ATM L1 L1 L1 L1 ATM switch SSSAR (Service Specific Segmentation and Reassembly) ITU-T I CPS (Common Part Sublayer) ITU-T I QofIS'04 - Barcelona 30/9/2004 5

6 Example of IP transport option Node B RNC Frame Protocol Radio Network Layer Frame Protocol UDP Transport Network Layer UDP Multiplexing Segmentation IP header compression PPPmux MC/ML-PPP HDLC framing IP header compress. PPPmux MC/ML-PPP HDLC framing IP L2 IP L2 L1 L1 L1 L1 These protocols may also be terminated in the RNC by using a tunnel between Node-B and RNC Edge IP Router DiffServ may be used for QoS QofIS'04 - Barcelona 30/9/2004 6

7 AAL2 over MPLS Keep AAL2 for segmentation and multiplexing (easy migration and interworking with AAL2/ATM nodes) Replace ATM cells and switches by MPLS (less overhead and cost) MPLS Label Switched Paths (LSPs) instead of ATM VCC/VPP Node B RNC Frame Protocol Radio Network Layer Frame Protocol SSSAR AAL2 CPS MPLS L2 L1 Transport Network Layer MPLS MPLS L2 L2 L1 L1 SSSAR AAL2 CPS MPLS L2 L1 SSSAR does not change CPS optimized for encapsulation without ATM cells Traffic engineering and QoS with MPLS-TE and DiffServ ATM switch Label-Switching Router (LSR) No header compression QofIS'04 - Barcelona 30/9/2004 7

8 AAL2 over MPLS Node B RNC overhead per packet Channel identifier and segment length in CPS header (3 bytes) Packets to be transported, segmented if necessary by SSSAR overhead per group of packets payload payload payload Layer 2 overhead (ej. 5 bytes for PPP/HDLC) MPLS label (4 bytes) Limited by maximum waiting time ( Timer_CU ) and maximum frame length (Lmax) QofIS'04 - Barcelona 30/9/2004 8

9 Performance analysis Different transport options analyzed to determine protocol header overheads per packet (H) and per group (Hg) Parameters Packet length (P) Number of packets per group (N) Conions Packet segmented if P+H > Lmax N x (P+H) Lmax Timer_CU not considered Efficiency = bytes from RNL / bytes passed to layer 1 QofIS'04 - Barcelona 30/9/2004 9

10 Transport efficiency Transport efficiency (%) AAL2/MPLS/PPP/HDLC cudpip/pppmux/hdlc cudpip/pppmux/ip tunnel AAL2/ATM MPLSx2/PPP/HDLC P = 40 bytes Active voice calls Transport efficiency (%) cudpip/mcml-ppp/hdlc MPLSx2/MCML-PPP/HDLC AAL2/MPLS/PPP/HDLC cudpip/mcml-ppp/ip tunnel AAL2/ATM Lmax = 1000 bytes Packet size (bytes) AAL2/MPLS gives an efficiency between 90-95% in most cases is the most efficient option for packets smaller than 160 bytes MPLS efficiency is very sensitive to the packet length (75-98%) QofIS'04 - Barcelona 30/9/

11 model overview Transmission Timing Interval (TTI) RNC Node-B Results: delay, loss, link utilization = f(n) Frame Protocol PDUs high high... TTI Two applications: - Voice at 12.2 kbps - Web at 64 kbps low low 1... N TNL protocol stack 1.92 Mbps Q (frames or cells depending on TNL stack) Parameters: - H and Hg, different values for each TNL stack - Lmax and Timer_CU, same values for all stacks QofIS'04 - Barcelona 30/9/

12 Traffic parameters high low Based on 3GPP TR and [5] TTI (ms) TTI values fixed by UMTS radio interface Packet size (bytes) Mean duration (s) Transm. rate (kbps) Packet size (bytes) Mean duration (s) Transm. rate (kbps) Average traffic (kbps) Voice 12.2 kbps Silence Insertion Descriptors Web 64 kbps ,65 66, Includes RNL protocol overhead Mean file size 13.2 kbytes Mean reading time QofIS'04 - Barcelona 30/9/

13 Transport parameters Protocol overheads H and Hg, same values as before QoS requirements in Iub interface obtained from end to end UTRAN requirements (Radio Access Bearer), see [5] Iub Loss Delay (ms) Voice < < 10 (99%) Web < < 15 (95%) Values obtained from pilot simulations, see [24] Maximum waiting time (Timer_CU): 1 ms Maximum length (Lmax): 500 bytes Buffer size (Q): frames QofIS'04 - Barcelona 30/9/

14 results (1): voice Delay (ms) 0.99-quantile M PLSx2/M CM L-PPP/HDLC AAL2/ATM cudpip/mcml-ppp/hdlc AAL2/MPLS/PPP/HDLC Number of voice users AAL2/MPLS gives the lowest delay and loss MPLS alone is the worst option for short packets Loss probability 1,E+00 1,E-01 1,E-02 1,E-03 1,E-04 1,E-05 1,E-06 Link utilization (%) Number of voice users MPLSx2/MCML-PPP/HDLC cudpip/mcml-ppp/hdlc AAL2/ATM AAL2/MPLS/PPP/HDLC MPLSx2/MCML-PPP/HDLC AAL2/ATM cudpip/mcml-ppp/hdlc AAL2/MPLS/PPP/HDLC Number of voice users QofIS'04 - Barcelona 30/9/

15 results (2): web Delay (ms) 0.95-quantile Number of web users AAL2/ATM AAL2/MPLS/PPP/HDLC MPLSx2/MCML-PPP/HDLC cudpip/mcml-ppp/hdlc Smaller differences among transport options Now MPLS is a good option because packets are longer Smaller link utilizations Loss probability 1,E+00 1,E-01 1,E-02 1,E-03 1,E-04 1,E-05 Link utilization (%) AAL2/ATM AAL2/MPLS/PPP/HDLC MPLSx2/MCML-PPP/HDLC CUDPIP/MCML-PPP/HDLC Number of web users AAL2/ATM AAL2/MPLS/PPP/HDLC MPLSx2/MCML-PPP/HDLC cudpip/mcml-ppp/hdlc QofIS'04 - Barcelona 30/9/2004 Number of web users 15

16 AAL2/MPLS similar to AAL2/ATM, but No ATM switching needed More efficient (10-15% improvement) more users served For long packets AAL2 is not needed (a) (b) AAL2 - SSSAR AAL2 - CPS MPLS LSP 1 Each group of concatenated packets carries 1 MPLS label for packet forwarding between RNC and Node-B AAL2 - CPS LSP 1 LSP 2 Each packet carries 2 labels Multiplexing label Forwarding label QofIS'04 - Barcelona 30/9/

17 Thank you E. Vázquez, M. Álvarez-Campana, A. B. García Dept. of Telematic Engineering Technical University of Madrid, Spain 17