521262S Computer Networks 2 (fall 2007) Laboratory exercise #4: Multimedia, QoS and testing

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1 521262S Computer Networks 2 (fall 2007) Laboratory exercise #4: Multimedia, QoS and testing Name Student ID Signature In this exercise we will take a little look at the multimedia and Quality of Service and try some testing methods in network. Multimedia and QoS will mostly be theory and demonstrations while testing part should be more practical. This exercise will be done in the groups of one, two or three persons, so that we get a maximum of ten groups. Each student shall mark their name, student ID and signature in this paper which will be left for the assistants when you leave. There are few questions at the end of this document in which you should find answers during the exercise. Please fill in the answers to the questions before leaving the paper. All kind of feedback is also very welcome. Hardware Every group has five LinksysWRT54gl wireless routers which all have OpenWRT linux installed so that they can be used to various different functions. Each Linksys device has a sticker in front panel to indicate its function and IP-address. All Linksys devices have a build-in 5-port switch. Internet port of the Linksys devices should not be used until told so. Groups also have color-coded cables to connect the devices. Name IP Function AP 10.x.y.z Connection from Internet to LAN DHCP 10..x.y.2 DHCP-server Switch 10.x.y.3 5-port switch Client dhcp client for testing Gateway 10.x.y.1 gateway to other LANs, also a router We also have two Cisco 2600 series routers, HP Procurve VLAN capable switch and NexGate NSA1086 with OpenBSD OS inside. With these devices we should be able to create fully functional internet. In exercise #4 we also have one Cisco LRE switch and Cisco 575 CPE to provide Long Reach Ethernet connections. All these devices are installed in a small rack. Network topology

2 Command glossary Command ssh ping ifconfig tcpdump control+c arp nslookup traceroute ettercap Purpose Take secure remote connection from host to another use ICMP echo request to find out if the other device answers typical unix-command to show information about network interfaces capture traffic flowing through network interface usually stops running program (for example tcpdump) find out information about mac-addresses resolved by host DNS lookup utility trace a route to host man in the middle tool Building up an internet 1. task Connect your devices to make a working LAN. Test LAN with ICMP echo requests. 2. Task Write down the IP addresses of the devices in you LAN:

3 3. task Connect your gateway to the HP Procurve switch in port dedicated for your group. Group number is same as the third number in your IP addresses in Linksys devices. For example if your gateways address is , you should connect to port 1 on a HP switch. Groups 1, 2, 3, 4, 5 are connected to one Cisco router and groups 6, 7, 8, 9, 10 to another Cisco router. When told to connect to neighbor group s host, use the one connected to same router as you are. Use gateways Internet/Wan port when connecting to HP. Multimedia Multimedia is a medium which uses different kinds of content to provide full media experience. Multimedia can contain video, images, audio, and so on. Usually multimedia is first created (or recorded) and then viewed with some processing devices. Multimedia can be seen for example in almost every webpage nowadays. Also streaming video has become very popular along with IPTV. This all means growing requirements for network bandwidth and latency. Basically multimedia can be first retrieved and then played locally, streamed straight from webpage or streamed from media server via webserver. Multimedia can be streamed using different kinds of protocols such as RTP or RTSP. The underlying transfer protocol can be either TCP or UDP although UDP is mostly used. Multimedia requirements Multimedia is usually using quite a lot of network resources. Especially high quality video transfers can take a large amount of bandwidth and can consume network resources quite quickly. Good thing is that latency or packet loss usually doesn t matter that much unless in some real-time video meeting. Usually media is buffered anyway. There is also quite a few different ways to recover from packet losses with redundant information of the media send to the client. UDP is mostly used as underlying connection protocol because it doesn t have latency caused by retransmissions or client starvation caused by rate averaging. 4. task Demos 5. task There can be found captures of the different kinds of network traffics in Save the captures in your home directory in STEKT terminal and open them with ethereal. Analyze captures. 01 HTTP - find out the user-agent of the client, http version used, two possible charsets used in http.

4 02 Telnet - what is username and password for this telnet session? - what version of the OpenBSD is used in server? 03 SIP - what is the user-agent of the client? - what is the user-name registering to system? - what is the type of media and protocol used (check SIP/SDP packets)? 04 -? - protocols, ports, mode 05 h223 - what kind of media parameters are described in SIP INVITE request? - what protocol is used for streaming media? 06 WLAN - What is the SSID of the network? - What is maximum supported rate? - What channel is used? - What security method is used? Quality of Service Sometimes if one doesn t have enough bandwidth to satisfactory use for example multimedia streaming and file transfer simultaneously, we need to use priorities for different kinds of traffics to ensure function of services. Basic idea is to offer some applications better service than for the others. For example if we have file transfer and multimedia stream open at the same time, we can give multimedia better priority to go through network. Priority can be implemented in various different ways. Usually packets are given some weight values and they are routed through network according the weights and some scheme. Problem with QoS is that the given priorities have to go through the whole network meaning every router and switch between communicating parties. This can be very hard or even impossible to implement. Scheduling mechanisms FIFO: First in, first out. Packets leave the queue in same order that they have arrived. Priority Queuing:

5 Packets get priority classes when they arrive and they leave the queue in some defined order. Priorities can be based on e.g. protocols, port numbers or IP addresses. Round Robin and Weighted Fair Queuing: Packets get weight values which are then output with bandwidth of R*Wi/sum(W). 6. task Consider network with links of 4Mbps, 5Mbps and 100Mbps. Is it possible to stream two videos which need 3Mbps bandwidth each over the network using QoS? Is it possible to have ftptransfer and one stream at the same time? Do you need QoS on that? 7. task What would be the best solution to make sure that all applications get enough bandwidth? Testing the bandwidth and latency Quite often you don t know what kind of links there are in the network between communicating parties. Even in your own network you can t always tell how much bandwidth or latency there really is available. For example in wireless networks, the throughput in the network can vary quite much depending on e.g. weather, transmission powers or number of others using the same frequency. Even more variable is a wireless mesh network where topology keeps changing dynamically. At least in these cases the network functionality should be tested to find out failing parts of the network and develop it further. There are quite a few different tools for testing but here we will use only few. name wget iperf dna downloadtest function transfer data over http test bandwidth using different parameters downloadtest.suomi.net 8. task Try to get 10Mb file from with wget from your gateway and from NSA. Write down the speeds and also latencies of the links. TIP: redirect output of wget to /dev/null. Use c and O options. Use time command to get transfer time. 9. task Use wget in NSA to retrieve 10Mb file from Write down average speed and latency. 10. task

6 Use downloadtest with lynx from NSA and from Write down the average speeds. 11. task has an iperf server running. Test the bandwidth from NSA with iperf. Write down the results. Try with different window sizes. TIP: Use iperf w <window size> p c d. NOTE: This should be done by one group at a time so inform assistants when you are doing this.

7 Questions 1. Explain briefly what are RTP and RTSP. 2. Why could UDP be better transport protocol than TCP in regard of multimedia? 3. What is jitter? What is causing it? How can you remove jitter at the receiver for audio? 4. What is the basic idea of FEC (Forward Error Correction)? 5. What is a purpose of SIP proxy? 6. What causes client starvation with TCP? 7. Name at least three key components of SIP. 8. What is the aim of the QoS? 9. How would you implement QoS in our network? Which devices should support QoS? 10. Have you learned anything in these four laboratory exercises? If you have, name two things. 11. Any feedback: