REMS Solutions

H.323 Call Flow

01:15:20:       H225Lib::h225TConn: connect in progress on socket [1]

01:15:20:       H225Lib::h225TConn: Q.931 Call State is initialized to be [Null].

Hex representation of the SETUP TPKT to send.030000660802019E0504038090A36C059138383033700591383830387E0047052080060008914A00020880013C05010000A97BE0D6266A024F000000000044EF6C00450C0700C0A802142BD51100A97BE0D6266A0250000000000044EF6C0100010006800100

01:15:20:

01:15:20:       H225Lib::h225SetupRequest: socket blocking

01:15:20:       Number of octets sent=102, total=102

01:15:20:     H225Lib::h225SetupRequest: Q.931 SETUP sent from socket [1]

01:15:20:     225Lib::h225SetupRequest: Q.931 Call State changed to [Call Initiated].

Hex representation of the received TPKT000000000802819E011E0280883401017E002A0523C0060008914A00020000C0A803142B9D09001100A97BE0D6266A0250000000000044EF6C06800100

01:15:20:

01:15:20:   H225Lib::h225RecvData: Q.931 ALERTING received from socket [1]

01:15:20:       H225Lib::h225RecvData: Q.931 Call State changed to [Call Delivered].

Hex representation of the received TPKT000000000802819E0704038090A37E00410522C0060008914A000200C0A803142B9D0880013C05010000A97BE0D6266A024F000000000044EF6C09001100A97BE0D6266A0250000000000044EF6C06800100

01:15:36:

01:15:36:       H225Lib::h225RecvData: Q.931 CONNECT received from socket [1]

01:15:36:       H225Lib::h225RecvData: Q.931 Call State changed to [Active].

Hex representation of the RELEASE COMPLETE TPKT to send.030000310802019E5A080280107E0021052580060008914A0002011100A97BE0D6266A0250000000000044EF6C06800100

01:15:40:

01:15:40:   H225Lib::h225TerminateRequest: Q.931 RELEASE COMPLETE sent from socket [1]. Call state changed to [Null].

01:15:40:       H225Lib::h225TClose: TCP connection from socket [1] closed

Day 1 Review Questions

1. What key developments have made VoIP possible?
2. What benefit does VoIP bring for PBX to PBX calls within a single organisation?
3. What is the difference between a trunk and a loop/line?
4. When would a VoIP enabled PBX reroute calls via the PSTN/GSTN?
5. When using a collaboration application, such as NetMeeting, what recommendation in H.323 covers the data functions and protocols?
6. What is H.323?

Day 1 Review Questions….cont.

1. G.711 can be used in VoIP. What is it?
2. What is unique about G.711 in H.323?
3. How do ITSP and GSTN charges compare? Why?
4. In a large VoIP carrier network where would billing be undertaken?
5. What is normally carried in a network "control plane"?
6. What is a H.323 zone?
7. What are the key components of a H.323 zone?
8. What is E.164?
9. What defines a H.323 zone?

Day 1 Review Answers

1. DSP’s, Wide spread IP adoption, business case and digital telephony
2. Reduced long distance costs
3. Trunks between exchanges and loops/lines from exchanges to terminals/customer premises
4. Failure/reduced quality or congestion
5. T.120
6. Umbrella recommendation for multimedia conferencing over packet networks
7. 64kbit/s PCM codec
8. Specified that must be supported
9. ITSP’s are typically 20 to 25% cheaper to attract customers
10. By Gatekeeper
11. Signalling
12. H.323 network
13. Gatekeeper, Gateway, LAN, Router, Terminals, MCU and Zone
14. ITU-T recommendation for Telephone numbering
15. Gatekeeper

Day 2 Review Questions

1. How would a carrier stop me using a Quality VoIP service without charge?
2. What Gatekeeper function is used to limit calls and maximise quality?
3. How many bytes in the IP v4 Header?
4. How many bytes in the IP v6 Header?
5. How many bytes in the TCP Header?
6. How many bytes in the UDP Header?
7. How many bytes in the RTP Header?

Day 2 Review Questions….cont.

1. How many phases in the H.323 call signalling procedure?
2. Name the Phases of the H.323 call signalling procedure?
3. Which protocol ensures "error free" signalling in H.323?
4. What is the main information an IP router requires to route a datagram?
5. How does the source H.323 terminal know the interarrival jitter experienced by the receiver?
6. What is jitter?
7. What is H.248 used for?
8. What is the inband signalling most commonly used in analogue networks?
9. How do TCP/UDP identify application running in higher layers?
10. What signalling technique uses a single dedicated channel for signalling purposes?

Day 2 Review Answers

1. Gatekeeper admission control
2. Admission control
3. 20 bytes (to 24bytes)
4. 40 bytes
5. 20 bytes (to 24bytes)
6. 8 bytes
7. 12 bytes
8. 5 phases
9. Call set up
10. TCP
11. DA (Destination Address)
12. RTCP typically sent every 5s but could be up to 5mins
13. Variation in delay
14. Call signalling between H.323 and PSTN networks.
15. DTMF
16. Port Numbers (2 bytes)
17. Common Channel Signalling System 7 (CCSS7)

Day 3 Review Questions

1. Which types of calls experience delay?
2. What is the ITU-T (G.114) recommended maximum one way delay?
3. Why is VoIP delay variable?
4. What is "comfort noise"
5. When is "comfort noise" used?
6. What is G.729?
7. What is the purpose of using compression codecs?
8. How does a linear codec operate?
9. How does an adaptive codec operate to reduce bandwidth?
10. How does a predictive codec operate to reduce bandwidth?
11. What is the impact of silence suppression on a call with an activity level of 30%?
12. If the utilisation of a link is P. How long will the queue length be for transmission over the link in packets?

13. If a service must have no more than one break per annum that takes no more than 4 hours to repair what is the availability?

Day 3 Review Answers

1. All
2. 400mS
3. Network congestion and router buffers/queues
4. Noise played to represent background noise
5. Played during silence
6. 8kbit/s LD-CELP codec
7. Reduce data bits sent
8. Encodes every value from a base line
9. Encodes the difference between the previous value and the current value
10. Encodes the difference between the actual and calculated expect values
11. 70% reduction in network traffic.
12. Q=P/1-P
13. 0.99954