A Novel Software-Based H.323 Gateway with

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1 A Novel Software-Based H.323 Gateway with Proxy-TC for VoIP Systems Presenter : Wei-Sheng Yin Advisor : Dr. Po-Ning Chen Institute of Communications Engineering National Chiao Tung University Agenda Introduction Motivation Proposed System Architecture System Architecture Proxy-Transcoder (Proxy-TC) The GW-TC GW-TC Procedure The Handoff Mechanism The Error Recovery Procedure Data Structures Simulation Model and Results Conclusions 1

2 Introduction Due to the constant growth of transmission bandwidth, real-time applications such as VoIP gradually become feasible on the Internet. VoIP can bring us advantages like toll-by-pass, coexistence of voice and data services, and easy deployment of telephony network between two branch offices. In techniques, VoIP carries voice traffic as data packets over a packet-switched network, instead of as a synchronous stream of binary sampled data over a circuit-switched, time-division multiplexed (TDM) network. Introduction - VoIP Protocols Features of the VoIP protocols, call control, and media transport Existing protocols for VoIP Recommendation H.323 by ITU-T Session Initiation Protocol and Session Description Protocol (SIP/SDP) by IETF Media Gateway Control Protocol (MGCP) by IETF Media Gateway Control (MEGACO) by IETF Been submitted to ITU-T SG-16 for decision as Recommendation H.248 Of the protocols above, H.323 is perhaps the most widely deployed; hence, our design is based on H.323 protocol stack. 2

3 Introduction - H.323 components Gatekeeper Manage a zone (i.e., a collection of H.323 devices). Required Functionality: Address translation, admissions control and bandwidth control. H.323 Terminal An endpoint on a LAN. Support real-time, 2-way communications with another H.323 entity. Must support voice (audio codec) and signaling (Q.931, H.245, RAS). Gateway Provide interoperability between different networks, and convert signaling and media. E.g., IP/PSTN gateway. Multi-point controller (MC), multi-point processor (MP) and Multi-point control Unit (MCU) are used to support conference calls. Introduction Gateway protocol stack Interworking Call Control (H.246) Gateway Call Manager Audio Codec G.723 G.729 RTP Video Codec H.261 H.263 RTCP H.225 RAS Control H Layer H.225 Call Control H.245 Control SCN Call Control Layer e.g., Q.931 SCN Link Control Layer e.g., LAPD Transport Protocols & Local Area Network Interface SCN Physical Interface 3

4 Motivations The telephony links maintained by a software-based gateway at times suffer short interrupts due to the possible uneven switching of PC platforms among several computation-bound tasks. We observe that the computation powers of the desktop PCs in use for general employees are sometimes not in full utilization. This leads us to the idea of gathering these excessive computation powers to share the load of the softwarebased gateway, and hence, reduce the number of computation-bound tasks on it. In such case, one may further increase the gateway capacity without introducing additional hardware cost. Proposed System Architecture Server PC1 Office Extension PC Telephone PBX PC2 R* Internet / Intranet PSTN / ISDN PC3 PC4 LAN Note: *The edge router must support QoS functionality. PC Telephone 4

5 Proposed System Architecture Office Extension G.711 Q.931 PBX PSTN / ISDN GW-TC GW TC2 TC3 G.711 TC1 G.723 or G.729 H.225 Call Control TC4 R* PC Telephone Internet / Intranet LAN Note: *The edge router must support QoS functionality. PC Telephone Proposed System Architecture - Modified Gateway Protocol Stack Interworking Call Control Gateway Call Manager GW-TC Payload (RTP/RTCP) GW-TC Control Audio Codec G.723 G.729 RTP Video Codec H.261 H.263 RTCP H.225 RAS Control H Layer H.225 Call Control H.245 Control SCN Call Control Layer e.g., Q.931 SCN Link Control Layer e.g., LAPD Transport Protocols & Local Area Network Interface SCN Physical Interface 5

6 Proposed System Architecture - Proxy-Transcoder (Proxy-TC) The Observer monitors local resource condition on PCs, such as available CPU power, and periodically updates the information for use by Controller. GW-TC proxy-tc Observer Controller Transcoder LAN/Gateway Internet/ RTP Logical Channel H.323 Endpoint G.711 G.723/G.729 RTCP Logical Channel CPU Proposed System Architecture - Proxy-Transcoder (Proxy-TC) The Controller maintains the communication between a proxy-tc and its associated gateway by using GW-TC signaling procedures. These control messages include: GW-TC proxy-tc Observer Controller (1) informing the gateway that LAN/Gateway Transcoder Internet/ the proxy-tc is still active RTP Logical Channel H.323 Endpoint upon the request of its G.711 G.723/G.729 associated gateway, RTCP Logical Channel receiving the request of the transcoding service from the gateway; and (3) updating the information of the CPU utilization. CPU 6

7 Proposed System Architecture - Proxy-Transcoder (Proxy-TC) The Transcoder is responsible for voice stream transcoding between different speech coding algorithms, such as G.711, G and G.729. GW-TC proxy-tc Observer Controller Transcoder LAN/Gateway RTP Logical Channel G.711 G.723/G.729 RTCP Logical Channel CPU Internet/ H.323 Endpoint Proposed System Architecture - The GW-TC (1/2) The major goal of the GW-TC signaling is to enable the cooperation between the gateway and the proxy-tcs. There are six commands in the GW-TC signaling, which are described below: Register: The proxy-tcs send this command manually to the gateway (through web-browsing activity) to register to the gateway so that the gateway can create corresponding proxy-tc record. Setup: This command is used by the gateway to request one of the proxy-tcs to perform the transcoding service upon the occurrence of a new call. Release: The gateway uses this command to release the transcoding service either (1) upon the end of a call or (2) upon the receipt of the Emergency command from a proxy-tc. 7

8 Proposed System Architecture - The GW-TC (2/2) : Proxy-TCs use this command to update their latest statuses kept on the gateway. Query: If the update timer expires the gateway will send Query command to request the proxy-tc to update its status. Emergency: This command is sent by proxy-tcs to notify the gateway of their (sudden) shortage of transcoding resources. Acknowledge (): This command may be sent by either the gateway or proxy-tcs to inform the other side that the previous command has been successfully received. Proposed System Architecture - The GW-TC Procedure Normal call setup Normal call clearing procedure 8

9 Proposed System Architecture - The Handoff Mechanism Hard Handoff PSTN/ISDN Terminal Gateway proxy-tc1 proxy-tc2 H.323 Endpoint Voice stream transmitted through PC1 Emergency Release Voice stream communication interrupted (about 60~200ms) Close Logical Channel Setup Close Logical Channel Voice stream transfer to PC2 Open Logical Channel Open Logical Channel H.245 GW-TC Proposed System Architecture - The Handoff Mechanism Soft Handoff PSTN/ISDN Terminal Gateway TC1 TC2 H.323 Endpoint Emergency Setup Voice stream continued through PC1 Close Logical Channel Open Logical Channel Close Logical Channel Open Logical Channel Voice stream transfer to PC2 Release H.245 GW-TC 9

10 Proposed System Architecture - Error Recovery Procedure Situations concerned Setup Emergency Release Proposed System Architecture - Error Recovery Procedure -- Setup Gateway proxy-tc1 proxy-tc2 Successful Setup procedure Setup G.711 voice packet Setup Timer expiry Setup Setup Setup to another TC G.711 voice packet 10

11 Proposed System Architecture - Error Recovery Procedure -- Gateway TC timer reset timer expiry Query timer reset timer expires three times Query Query Discard TC Record Proposed System Architecture - Error Recovery Procedure -- Emergency Gateway TC1 TC2 Emergency Setup G.711 voice packet Gateway TC1 TC2 Emergency Emergency Emergency Setup G.711 voice packet 11

12 Proposed System Architecture - Error Recovery Procedure -- Release Gateway TC Release Release Release Release Proposed System Architecture - Data Structure The gateway needs to maintain two tables: The first one records the periodic update information of CPU utilization from each proxy-tc CPU utilization time The number of serving users The second one keeps the call information in the system The active proxy-tc Occupied port numbers Call party information 12

Simulation Model and Results - The Simulation Model Register (Web based) TC1 Arrival GW Setup Release TC2 Emergency TC record: TC1: TC resource : 169MHz num_custs_insys : 2 time of update : 11:05:22

13 Simulation Model and Results - The Simulation Model Register (Web based) TC1 Arrival GW Setup Release TC2 Emergency TC record: TC1: TC resource : 169MHz num_custs_insys : 2 time of update : 11:05:22 TC2 : TC resource : 210MHz num_custs_insys : 1 time of update : 11:05:23 Call information record: Customer1: Active TC : TC2 Customer2 : Active TC : TC1 Customer3 : Active TC : TC2 TC3 We assume that both the call inter-arrival time and the call duration are exponentially distributed. Simulation Model and Results - CPU utilization records GW Average = TC1 Average = TC2 Average = TC3 Average =

14 Simulation Model and Results - Proxy-TC selection schemes Definition: Ri : available resource of i th proxy-tc Token(i) : selecting i th proxy-tc NR : necessary TC resource per call N : the number of proxy-tcs First-Fit-Round-Robin (FFRR) initial: i = 0 while( R { Token( i) } Maximum Available Resource R j = max { R } Token ( j ) i < NR) i = ( i + 1)mod( N i + i 1) Simulation Model and Results - Performance Indices (1/2) Definitions of call events Blocked call When upon receipt of a new call, the individual CPU resources of the gateway and all registered proxy-tcs are less than 25MIPS. Dropped call When the serving proxy-tc is occasionally running out of resources for at least one second and no other proxy-tc can take over this call. 14

15 Simulation Model and Results - Performance Indices (2/2) Definitions of probabilities The new call blocking probability Pb Number of blocked calls = Pr [ blocking ] = Total arrival calls The active call dropping probability Number of dropped calls Pd = Pr[ droping ] = Total served calls The handoff frequency Number of handoff calls Ph = Pr[ Handoff ] = Total served calls Simulation Model and Results - The Simulation Results (1/5) Case 1 : The relation between the number of registered proxy-tcs and the probabilities of call blocking and call dropping, when no handoff mechanism is implemented. Dropp The mean duration of each call is 3 minutes. 15

16 Simulation Model and Results - The Simulation Results (2/5) Case 2 :The probabilities of call blocking and call dropping, when the gateway cooperates with only one proxy-tc and handoff mechanism is implemented. Dropp The mean duration of each call is 3 minutes. Simulation Model and Results - The Simulation Results (3/5) Case 2 : The handoff frequency, when the gateway cooperates with only one proxy-tc and handoff mechanism is implemented. Handoff Frequency 16

17 Simulation Model and Results - The Simulation Results (4/5) Case 3 : The performance comparison between the two call placement schemes (i.e., FFRR and MAR) under the condition that the gateway cooperate with 10 proxy-tcs and handoff mechanism is implemented. Dropp The mean duration of each call is 15 minutes. Simulation Model and Results - The Simulation Results (5/5) Case 3 : The performance comparison between the two call placement schemes (i.e., FFRR and MAR) under the condition that the gateway cooperate with 10 proxy-tcs and handoff mechanism is implemented. Handoff Frequency 17

18 Conclusions We conclude that the proposed architecture achieves higher capacity and lower blocking probability with respect to the arrival calls, and the employment of the handoff mechanism leads to a drastic decrease in the active call dropping probability at the expense of a little increase in the new call blocking probability. Along this research direction, an interesting future work will be to find a method to predict the CPU utilization, as well as a good call placement approach to reduce the handoff frequency. 18

Introduction. H.323 Basics CHAPTER

Introduction. H.323 Basics CHAPTER CHAPTER 1 Last revised on: October 30, 2009 This chapter provides an overview of the standard and the video infrastructure components used to build an videoconferencing network. It describes the basics