1 K. Salah Module 2.1: QA – Putting it all together What is the max number of users/connections/sessions a particular network can support for handling a new connection? Delay Types Analyzing Delay Analyzing Throughput

2 K. Salah Delay Types Propagation Delay: This is the delay which is caused by distance. According to Einstein, who’s views on the subject are still accepted today, communication across a distance cannot take place faster than the speed of light. Much of the communication we undertake today is carried by light. Electrical signals carried on wires also travel at approximately the speed of light. Fast as it is (300 million meters per second), the delay due to a pulse of light traveling from one side of the earth to the other is still significant. Around 15micro second. Usually, this is negligible, unless going through satellite links. Transmission Delay: Transmission delay is much more significant than propagation delay over short distances. It is the delay caused by the fact that it takes time to feed a signal onto the communication line. For example, suppose the line is transmitting at 10 Mbit/s, and the user wishes to send a file of 10 Mbytes. 10 Mbytes is 80 Mbits, so, all things being equal, the transmission will take 8 seconds. This is the transmission delay. Queueing Delay: This, the most interesting delay is caused by storage and retransmission of bits, bytes, and packets, in equipment lying in the network between the origin and the destination of a transmission. Buffering can take place at the origin, and at any point along the way where retransmission takes place. Packetization/Processing Delay: In packet networks, one more factor affects the end-to- end and round-trip delay for voice: the delay inherent in storing up a whole packet of digital audio data in a packet. Others: This may include: Echo Cancellers (10ms), Codec for compressing speech (75ms for 2 ends). There also delays an the NIC and ports about 15micro second (negligible).

3 K. Salah Analyzing Delay Get idea of the new rate and packet size for one connection/user end-to-end. Show the Analytical model of two way traffic flow. –In VoIP and Videoconferencing we assume the traffic in both ways is symmetric. Also, session can take place between two different parties (multimedia PCs). Point-to-point VoIP/Vieoconferencing. Calculated the delay for one session (VoIP or Videoconferencing). Plot delay for multiple sessions. As you add more sessions, network delay will start going up. The max sessions that the network can handle is when the delay goes beyond an acceptable delay value.

4 K. Salah Analyzing Throughput The capacity of the network can also limit the number of connections/users it can handle for a particular type of service. This is determined by finding out the narrowest available bandwidth in the path. This is the network bottleneck. The narrowest bandwidth can be a router, switch, or link.

5 K. Salah Network effective BW is the narrowest link

6 K. Salah Network Capacity and Available Bandwidth

7 K. Salah Example: Multicast and Interactive Video Streaming An videostreaming server is connected through a 100Mbps Ethernet link to a switch. Switch processing is 2 million pps, and we assume it has unlimited number of ports. All links to the switch are full duplex. Link speed to all multimedia PCs is 10 Mbps. The video server has a video processing rate of 200Mbps. The multimedia PC can process incoming and outgoing video packet to the application at rate of 25Mbps How many simultaneous sessions can such a network support, maintaining high QoS?

8 K. Salah First Multicast Video Streaming

9 K. Salah Second Interactive Video Streaming