Analysis of IP Network for different Quality of Service

Transcription

1 2009 International Symposium on Computing, Communication, and Control (ISCCC 2009) Proc.of CSIT vol.1 (2011) (2011) IACSIT Press, Singapore Analysis of IP Network for different Quality of Service Ajith Kumar V. 1 and Sheela Ganesh Thorenoor 2+ 1 Associate Consultant, Talent Transformation, Wipro Technologies 2 Consultant, Talent Transformation, Wipro Technologies, Abstract. Quality of Service defines a set of criteria used to classify the level of service allotted to a consumer or application. These criteria include, but are not limited to, data rate, round trip delay, jitter and packet loss. Quality of Service is the ability to provide different priorities to different applications, users, or data flows, or to guarantee a certain level of performance to a data flow. For example, a required bit rate, delay, jitter, packet dropping probability and/or bit error rate may be guaranteed. QoS guarantees are important if the network capacity is insufficient, especially for real-time streaming multimedia applications such as voice over IP and IPTV, since these often require fixed bit rate and are delay sensitive and in networks where the capacity is a limited resource, for example in cellular data communication. Keywords: Quality of Service, Differentiated Service, Queuing discipline, Integrated Service, Traffic Shaping, Traffic Policing. 1. Introduction The ultimate goal of QoS is to provide adequate service levels [1] for certain heterogeneous applications without reducing the service experienced by other applications. Early work on QoS for the Internet used the "IntServ" [2] philosophy of reserving network resources. In this model, applications used the Resource reservation protocol (RSVP) to request and reserve resources through a network. While IntServ [3] mechanisms do work, it was realized that in a broadband network typical of a larger service provider, core routers would be required to accept, maintain, and tear down thousands or possibly tens of thousands of reservations. It was believed that this approach would not scale with the growth of the Internet. The second and currently accepted approach is "DiffServ" or differentiated services. In the DiffServ model, packets are marked according to the type of service they need. In response to these markings, routers and switches use various queuing strategies to tailor performance to requirements. (At the IP layer, differentiated services code point (DSCP) markings use the 6 bits in the IP packet header. At the MAC layer, VLAN IEEE 802.1Q and IEEE 802.1D can be used to carry essentially the same information) Routers supporting DiffServ use multiple queues for packets awaiting transmission from bandwidth constrained (e.g., wide area) interfaces. Router vendors provide different capabilities for configuring this behavior, to include the number of queues supported, the relative priorities of queues, and bandwidth reserved for each queue. In practice, when a packet must be forwarded from an interface with queuing, packets requiring low jitter (e.g., VoIP or VTC) are given priority over packets in other queues. Typically, some bandwidth is allocated by default to network control packets (e.g., ICMP and routing protocols), while best effort traffic might simply be given whatever bandwidth is left over. + Corresponding author. address: ([email protected],[email protected]). 79

2 In this paper we use Opnet (the leading network R&D) tool to examine both IntServ (RSVP) and DiffServ (PQ, CQ, FIFO, RED, and WRED) mechanisms and their impact on the network. QOS refers to traffic control mechanisms that seek to differentiate performance based on application or network operator requirements and also provide predictable or guaranteed performance to applications sessions. QoS is an issue because the default service in many packet switched networks is to give all applications the same service and does not consider any service requirements to the network. This is also referred to as best-effort service. IP service is best effort service and it is different from probabilistic model. In case of probabilistic service there is a chance factor for success or failure. IP packets sometimes never reach the destination, the reason is that they take the best path from source to destination. IP packets are routed and routing is connectionless. Sometimes IP packets are discarded by the routers, hence they will not be able to reach the destination. IP packets are dropped by the router for some reason. Router cannot unscrupulously discard the packet. Router should state the valid reason for dropping the packet that is why it is known as best effort. It is very difficult to support QoS in a pure IP network; there is no single definition for the term QoS. QoS requirements are different for Audio and video application, QoS requirements are different for the interfaces and the network elements. Even at system level, QoS requirements are different and also vary from user to user. Perceptual parameters are translated to System QoS, for example picture detail is a perceptual parameter defined in terms of pixel resolution, picture color accuracy maps to color information per pixel, video rate maps to frame rate, video smoothness maps to frame rate jitter and audio quality depends up on sampling rate and quantization. 2. Components of QoS Framework QoS has to be implemented at various places in the network. IP network comprises of Nodes, Switches, Routers and Gateways. One has to implement packet classification and scheduling at the Router level, traffic conditioning at the network entrance, admission control at routers or somewhere in the network and there is a need for signaling between host and the routers. Admission control is the first line of defense against attacks on QoS. Network should not commit any guarantee if available resources are not sufficient to support the request. Admission control functions must examine both traffic and QoS parameters carefully before accepting or rejecting a new request for QoS Traffic Policing Users violating the traffic policies can jeopardize the QoS of other connections, the network must protect well behaving users against such traffic violations. We can make sure that all entering traffic is subjected to policing. Policing functions are deployed at the edge of the network. If arriving traffic conforms to the traffic norms then it will be allowed inside the network and non-conforming traffic is dropped by the traffic policing entity Traffic Shaping Traffic shaping entity will not drop the non-conforming traffic instead it will be more interested in smoothening the traffic. Arriving traffic might be having undesirable characteristics but Traffic shaping entity will buffer the input traffic to smoothen it so that out going traffic will be having desirable characteristics QoS Management Goals of the QoS management are sharing the bandwidth requirements, fairness to competing flows, meeting bandwidth, packet loss, delay guarantees and reducing the delay variations. 3. QoS Architecture for the Internet 80

3 Two QoS architectures have been defined for Internet. Integrated Services (IntServ) and Differentiated Services (DiffServ) 3.1. Integrated Services This architecture was proposed in 1994, and support Per-flow Quality of Service. In this scheme Resource reservation/admission control is implemented and can support delay guarantees. IntServ specifies two types of services, Guaranteed Service and Controlled Load Service Guaranteed Service This service is characterized by having guaranteed bandwidth, End-to-end delay bounds and no loss due to buffer overflows Controlled Load Service Controlled Load Service provides a service that is equivalent to a best effort service in a lightly loaded network and is characterized by low loss, low delay and no absolute guarantees Integrated Service is having the advantage of having strong guarantees (bounded delays) but suffers from the following disadvantages that it requires all routers to be implemented with IntServ. Scalability concerns since routers must maintain state information, charging and authentication of reservations must be solved and Inter domain issues are difficult to resolve Differentiated Services (DiffServ) This architecture was proposed in 1998 and supports Class-based QoS. In this scheme Resource reservation is not always needed DiffServ specifies two types of services, Assured Forwarding and Expedited Forwarding. In Assured Forwarding service, customers sign service agreements with ISPs and edge routers mark packets as being in or out of profile, core routers run RIO, RED with in/out. This service distinguishes different classes. Expedited Forwarding has hard guarantee on the delay and delay variants. DiffServ has the following advantages. There is no per-flow processing in network core and per-flow processing only at the network edge. This service is simpler to implement than IntServ, because there is no requirement of a signaling protocol. DiffServ has the following disadvantages; Assured Forwarding has weaker service guarantees and Expedited Forwarding service raises same issues with charging and authentication as IntServ services. 4. Packet Scheduling To support QoS we need a facility for packet classification and marking. We have CoS bits (Class of Service) at layer 2 for classifying the traffic and TOS (Type of Service) bits at Network Layer First in, first out (FIFO) FIFO queuing is the most basic queue scheduling discipline. In FIFO queuing, all packets are treated equally by placing them into a single queue, and then servicing them in the same order that they were placed into the queue. FIFO queuing is also referred to as First come, first served (FCFS) queuing Priority Queuing Priority Queuing used in QoS, Priority queuing supports some number of queues, usually from high to low. Queues are serviced in strict order of queue priority, so that high queue always is serviced first, than the next-lower priority and so on. If a lower-priority queue is being serviced and a packet enters a higher queue, that queue is serviced immediately. This mechanism is good for important traffic, but can lead to queue starvation 4.3. Custom Queuing Custom Queuing (CQ) assigns a certain percentage of the bandwidth (denoted as byte count) to each queue to assure predictable throughput for other queues. It is designed for environments that need to guarantee a minimal level of service to all traffic. 81

4 4.4. Weighted Fair Queuing: Weighted Fair Queuing (WFQ) allocates a percentage of the output bandwidth equal to the relative weight of each traffic class during periods of congestion 5. Analysis of QOS for IP Networks using OPNET In this simulation model, we have used OPNET IT Guru to build a small IP network and apply QoS policies, to analyze the performance of the network in terms of packet loss and delay for different kinds of video streaming applications.. Figure 1. Basic IP Network Here we are connecting two different LAN networks, one consisting of different video streaming clients and the other consisting of the corresponding video servers. Here there are four clients connected to Router A through the switch. There are four servers connected to Router B again through another switch and clients are accessing the servers through IP network. The bottleneck has been created in the link between router A and router B. Figure 2. IP Router interface with no QoS configuration In this scenario IP Router interfaces not configured for any QoS as shown in the figure. In the Opnet simulation model, profile confiigurator describes the activity patterns of a user or group of users in terms of the combination of applications defined through application confiigurator, used over a period of time Application configuration Application Config is used to specify applications that will be used to configure user profiles. Even though there are different possible applications which can be configured, like database access, , file transfer, file print, telnet session, video conferencing, we have chosen different types of video conferencing applications for individual clients Figure 3. Application configuration. 82

5 We have then customized the application requirements by setting the parameters for the selected application. Like this a baseline model has been built in which case all the profile, application and other interface parameters have been set as mentioned above, but without configuring any of the router interfaces for QoS. Figure 4. QoS configuration on the Router s interface For Discrete Event Simulation (DES), those parameters which need to be verified are to be selected, like IP, IP interface Video called party, video calling party, video conferencing., end to end packet loss, delay, jitter etc. These settings are done by choosing the respective parameters under global and node statistics of DES parameter settings. Now the simulation engine is run and the different parameters under observation are noted 5.2. Priority Queuing configuration As a second scenario, router interfaces are configured for QoS parameters and are set to priority queuing as ToS Figure 5. QoS configuration set to Priority Queuing. Figure depicts the QoS configuration parameters of priority queuing that s set to the priority of ToS. Then the network is simulated for these conditions are the results are noted. Similarly for the same network QoS configurations are set to custom queuing and Weighted Fair Queuing as another two different scenarios and the corresponding results are noted after running the simulation engine. Then we compared the effect of different QoS configuration settings in terms of queuing delay at the router, end to end delay, packet loss., jitter etc on all different types of video conferencing signals already defined. You can also verify the QoS configuration, in this scenario we have configure Custom Queuing as the QoS settings on the router s interface. 6. Results After successfully running the simulation, we can compare the results as plotted in the following two graphs It can be noticed that in all the four types of video application, the number of packets sent were the same, but the number of packets received has varied based on the type of configuration, as this would affect the 83

6 buffer size and thereby the packets that are going to be lost at router B and in turn the packets received at the receiving node. Also end to end delay variation is different for different applications and is also corresponding to the different QoS settings. Figure 6. Packets sent Figure 7. Packets received under four different QoS Settings Figure 8. End to end delays being different for different video conferencing applications We can measure the QOS parameters fro various settings, such as end to end delay and packet loss, these parameters give an indication regarding the performance of the network for a given Quality of Service. 7. Conclusion In conclusion, it can be mentioned that for a given condition of a QoS, among the four different video streaming applications like background, standard, excellent effort and streaming multimedia, the delay is highest for background and the lowest for streaming multimedia, thus proving the different queue delays and sizes will in turn decide upon the packet loss and also end to end delay. 8. References [1] Cormac Long. IP Network Design, Tata McGraw- Hill Publishing Company, New Delhi. 200 [2] Behrouz and A. Forouzan, Data Communications and Networking, Ed. New York: McGraw-Hill, [3] Alberto Leon-Garcia and Indra Widjaja, Communication Networks, Ed. New York: McGraw- Hill,