See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/230867584 Characterizing the Control Delay For RIP and OSPF Routing Protocols Article · October 2008 CITATIONS READS 0 132 1 author: Sherine M. Abd El-Kader Electronics Research Institute 77 PUBLICATIONS 429 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: An Efficient Monitoring System Exploiting Wireless Sensor Network Technology View project 5g project View project All content following this page was uploaded by Sherine M. Abd El-Kader on 20 May 2014. The user has requested enhancement of the downloaded file. 160 The Mediterranean Journal of Computers and Networks, Vol. 4, No. 4, 2008 Copyright © 2008 SoftMotor Ltd - United Kingdom CHARACTERIZING THE CONTROL DELAY FOR RIP AND OSPF ROUTING PROTOCOLS S. M. Abd El-Kader * Electronics Research Institute, Computers and Systems Dept.,Cairo, Egypt Published - Authors’ electronic copy - For information only - Not for distribution ABSTRACT C ic on ctr Ele rs’ tho Au There is no doubt that the control messages for any routing protocol are critical parameters that have great effect on the performance of the entire network. Studying the delay effect of these control information will help in innovating or adapting a control delay formula for different routing protocols. This paper mathematically studies the performance of RIP and OSPF, which are the most widely deployed routing protocols, from the delay point of view. It studies the impact of the number of routers, the router forwarding rates, the link rates and the network topology on the control delay for both RIP and OSPF routing protocols. Finally, this paper concludes that the control delay of the OSPF is approximately double the control delay of the RIP in case of the pipeline network topology whereas in tree topology case the RIP control delay is approximately less by 10% than OSPF. Keywords RIP, OSPF, Tree Topology, Pipeline Topology and Control Delay. 1. INTRODUCTION In dynamic routing, a router is configured to automatically generate routing information and share the information with neighboring routers. The routing tables of the dynamic routers are updated automatically based on the exchange of routing information with other routers. The most common dynamic routing protocols are Distance vector routing protocols (DV) and Link state routing protocols (LS) [4-7]. DV algorithms are based on distributed Bellman Ford [5, 6], such as Routing Information Protocol (RIP). Each node maintains a table giving the distance from itself to all other destinations of which it is aware. Each node periodically broadcasts this information to each of its neighboring node, and uses similar broadcasts from its neighbors to update the values of its own table. By comparing the distances received for each destination from each of its neighbors and knowing its distances to its neighbors, a node can determine the neighbor through which the best route can be obtained to any destination. Although DV algorithm is simple in implementation and consumes a very little bandwidth, it suffers from slow convergence and not suitable for large networks. y op There are several routing mechanisms that could be used to assist the routers in building their routing table, depending on how routing information is generated and maintained [1-3]. Routing protocols can be classified to dynamic or static routing protocol [4]. reduce routing problems and routing traffic overhead. For example, static routes could be used in stub networks, where there is only one path available. Another place that static routes could be valuable is in very large networks in which large regions are connected via one or two major links. The isolation characteristics of static routes could help in reducing the load of routing protocols over the entire network and limiting the scope of routing changes problems [2, 3]. In static routing the network administrator enters static routes in the routing table manually by indicating the network ID, IP address of a neighboring router (the next hop) and the router interface through which to forward the packets to the destination. Static routing has significant drawbacks which could be created when the topology changes, so the administrator should change the routing tables of every static router. This does not scale well on large network, manually changing the routing tables when a network problems occurs in a large network would create a tremendous, error-prone, and boring workload. However, static routes applied in a knowledgeable way, at good places in the network, could *Corresponding author: E-mail: sherine@eri.sci.eg All Rights Reserved. No part of this work may be reproduced, stored in retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise - except for personal and internal use to the extent permitted by national copyright law - without the permission and/or a fee of the Publisher. Copyright © 2008 SoftMotor Ltd. ISSN: 1744-2397 In LS algorithms, such as the Open Shortest Path First (OSPF), each node floods the entire network with link-cost information about its adjacent links. Each node in the network then builds a complete picture of the entire network using link cost information from each node. It then employs Dijkstra’s single shortest path to get routes to all nodes in the network. LS algorithm has fast convergence time so it is suitable for large networks but it needs complex algorithm to be implemented, which consumes memory and lead to high bugs probability [2]. Previous efforts on RIP routing protocol have largely focused on speeding up routing convergence and preventing routing loops. These approaches tend to achieve loop-free routing through delaying routing update propagation [8, 9]. The authors in [10] simulated the convergence behaviors of several routing protocols, then measured the convergence time, number of routing messages, and the routing loops after node failures. Paper [11] studied the end-to-end traceroute measurements collected in 1994 and 1995. The author detected a few transient loops and conjectured that these transient loops were caused by link failures. While paper [12] maximized the packet delivery during routing convergence by having alternate path always ready at the routing table. On the other 161 CHARACTERIZING THE CONTROL DELAY FOR RIP AND OSPF ROUTING PROTOCOLS hand the previous studies of the OSPF routing protocol have been either modeled or simulated [13, 14], or concentrated on measuring OSPF implementation behavior on a single router or in a small test bed environment [15]. The only exception is found on papers [16, 17] in which the authors in [16] analyzed OSPF instability for a regional ISP network, and [17] which analyzed the OSPF LSA traffic, provided a realistic networkwide modeling parameters and simulation scenarios of greatest interest. But all of these works concentrated their efforts on the convergence time only; in case of RIP, or on instability in case of OSPF, no one of them studied the effect of the control messages in both RIP and OSPF on the performance of the entire IP network, or either studied the effect of varying the router forwarding rates, the link rates, the number of routers and the network topology on the control messages in both RIP and OSPF routing protocols. In general, the control messages of any routing protocol consume bandwidth or reduce the total bandwidth, although running real-time multimedia applications over packetswitched networks like the Internet is very attractive, the Internet is often heavily loaded. So the quality of the Real-time applications such as video on demand and chatting will not be acceptable if the available bandwidth drops below a certain minimum bandwidth or when transit times vary so much that interactivity is impossible [18-20]. In this paper the control messages of the Routing Information Protocol (RIP) and the Open Shortest Path First (OSPF) have been studied to indicate the effect of them on the delay. This paper is organized as follows: Section 2 describes the Dynamic Routing Protocols (DRP), Section 3 describes different network configuration scenarios for both RIP and OSPF, and Section 4 provides the results and a performance analysis for both RIP and OSPF. Finally, Section 5 concludes this paper and proposes the future work. 2. DYNAMIC ROUTING PROTOCOLS Dynamic Routing Protocols (DRP) not only perform path determination and route table update functions, but they also determine the next-best path if the best path to a destination becomes unusable. The capability to compensate for topology changes is the most important advantage dynamic routing offers over static routing [6]. In this section a brief review for two dynamic routing protocols will be provided, in Section 2.1 the RIP operation along with its packet format has been presented whereas Section 2.2 demonstrates the OSPF operation along with its packet format. 2.1 Routing Information Protocol RIP is a DRP based on the distance vector algorithm [6, 27]. This algorithm has been used for routing computations in computer networks. RIP calculates the shortest path distance to a destination by the number of hops it takes. In order for the router to accomplish this task it must keep its routing table updated. Each router sends its information to its neighbors, upon receiving distance information from its immediate neighbors, a router could then develop a table of destination addresses, distances, and associated neighboring routers, and from this table then select the shortest route to the destination [2]. Metrics contain two components: hop count, and throughput, which, can be measured as 10 LogC ten times the decimal logarithm of the maximum link data rate in Kbps selected path with largest throughput [22, 23]. One of the biggest problems with RIP is the hop count; the maximum hop count is 15. This restriction is due to the count to infinity problem that comes with using RIP. This scales down the size of network that RIP can function on. The updating of the routing tables can use an excessive amount of bandwidth, but it needs small amount of memory. Whereas RIP has very little overhead in terms of used bandwidth, configuration and management time in a small network. RIP is also very easy to implement [2]. RIP is UDP based protocol, small regular messages, no need for windowing, handshaking or retransmission. Frames received and transmitted on UDP port number 520 (RIPv1 and RIPv2) and it supports from 1 to 25 RIP routing entries [21]. RIPv1 header has maximum datagram size of 512 bytes (IP or UDP header not counted). Every 30 seconds, the output process is instructed to generate a complete response to every neighboring. Regular routing update is occurred every 30 seconds. Triggered update is used whenever the metric for a route is changed which do not need to include the entire routing table [21]. RIP header is indicated in Fig. 1. Figure 1. RIP Header Packet Format RIP is transmitted in UDP segment format with 520 bytes as the maximum size and this size support from 1 to 25 RIP routing entries [22]. It consists of common part as indicated in fig. (1) and RIPv1 entry. The common part includes 4 bytes and the RIPv1 entry includes 20 bytes. Every 30 seconds, the output process is instructed to generate a complete response to every neighboring. Mathematically, RIP header can be described as follows: H RIP = ( command ) + ( version ) + ( zero ) + ( RIPv1 entry table ) From Fig. 1, H RIP = 4 bytes + (20 bytes × number of entries ) Where command indicates whether the RIP packet was generated as a request or as a response to a request, version contains the version of RIP, RIPv1 entry table are fields from address family (AFI) to metric called entry, and H RIP is the RIP header size (bytes). 2.2 Open Shortest Path First OSPF is link state routing protocol in which, it routes IP packets based solely on the destination IP address found in the IP packet header [24]. IP packets are routed without any modifications they are not encapsulated in any further protocol headers. The period of convergence is short and involves a minimum of routing traffic [2, 25]. In OSPF protocol each router has to keep a partial map of the network. In case of a new router joins a network, it should learn the identity of all neighboring routers. Then each router 162 CHARACTERIZING THE CONTROL DELAY FOR RIP AND OSPF ROUTING PROTOCOLS constructs a message containing the identities and costs of the links attached to that particular router. These messages are called Link State Advertisements (LSA) [25, 26]. Whenever a link changes its state, an LSA is flooded throughout the network. All the routers will notice the change, and recomputed the routes accordingly. The collection of all LSAs is called the link state database; each router has an identical link state database. Fig. 2 demonstrates the OSPF packet format, All OSPF packets have a common 24-byte header that contains all information necessary to determine whether OSPF should accept the packet or not. Some of these information are listed below. 3. CONTROL DELAY The Control Delay (CD), in general, can be classified to four components: the transmission time, the processing time, the propagation time, and the queuing time which can be calculated according to the used queuing technique. So, the CD could be divided to two parts fixed part, which consists of both the propagation and queuing times, and variable part which is the transmission and processing times. In this paper we concentrate only on the variable part of the control delay assuming that the other part can be considered as a fixed value. Then the packet control delay resulting from sending one control packet using RIPv1 will be equals to the delay resulting from both the Transmission delay (Tr, in sec.) and the Processing delay (Pr, in sec.) and they could be calculated as shown in Eq. (1) and (2). ⎛ Length of frame ⎞ ⎟ ⎝ Data rate of link ⎠ Tr = ⎜ Figure 2. OSPF V2 Header Where, (Version) specifies the OSPF version number, (Type) specifies the OSPF packet types, (Packet length) the length of the protocol packet (bytes) including the standard OSPF header, (Router ID) the router ID of the packet's source, (Area ID) is 32 bit number identifying the area that this packet belongs to, (Checksum) the standard IP checksum of the entire contents of the packet, (AuType) identifies the authentication scheme to be used for the packet, (Authentication) a 64-bit field for use by the authentication scheme. The main OSPF operations are establish router adjacencies, select Designated Router (DR), Backup Designated Router (BDR), discover routes, select appropriate routes to use, and maintain routing information. Internal metrics: cost associated with output side of router interfaces. External metrics: denote externally derived routing data. Type 1; treated the same as internal metrics. Type 2; it is always greater than cost of any internal path. Both external metric types can simultaneously exist in an AS [25]. The size of an OSPF link state database can get quite large so it consumes a large memory size, especially in the presence of many external LSAs. This imposes requirements on the amount of router memory available. CPU usage: In OSPF, this is dominated by the length of time it takes to run the shortest path calculation. This is a function of the number of routers in the OSPF system [26, 27]. There are basically 6 types of OSPF packets: “Hello” packet which establishes and maintains neighboring relationships. It consists of 44 bytes in addition to 4 bytes for the address of each neighbor, database description packets which describes the contents of the topological database, link-state request which is used for requesting pieces of the topological database from neighbor routers, link-state update which considered as responds to a link-state request packet, these messages also are used for the regular dispersal of LSAs, Several LSAs can be included within a single link-state update packet, and link-state advertisement which acknowledges link-state update packets [28-30]. Length of frame ⎛ ⎞ ⎟ ⎝ Packets forwarding rate × Avg . packet size ⎠ Pr = ⎜ (1) (2) It should be noted that all of the scenarios assume that the average packet size equals to 64 bytes, the header size of IPv4 is typically 20 bytes, the UDP header size is 8 bytes, the RIP header size is 24 bytes, and all the packets are transmitted without any fragmentation [22]. 4. RESULTS AND DISCUSSIONS This section demonstrates the results obtained by applying the mathematical Eq. (6) and (8) in case of RIP and OSPF respectively and varying the number of routers, forwarding rates, data link rates and the network topology on both RIP and OSPF routing protocols. 4.1 Network Configurations In this section, 46 scenarios have been considered; 23 scenarios for RIPv1 and 23 scenarios for OSPFv2 [27]. In each scenario the network topology has been considered first as pipe line then as tree. Four types of routers have been taken into consideration for control delay measurements: Cisco 2620 (C2620), Cisco 3640 (C3640), Cisco 3700 (C3700) and Cisco 7301 (C7301) with forwarding rates: 25000, 70000, 225000 and 1000000 packets/sec respectively [29]. The number of routers are increased by one each iteration until it reaches 15 (where the maximum RIP usable number of hops is 15). Also the used data link rates are: 2 Mbps, 4 Mbps, 6 Mbps, and 8Mbps. Figs. 3, 4 demonstrate the pipe line and the tree network topologies for the fifteen routers of both RIPv1 and OSPFv2 respectively. Figure 3. Pipeline network topology for fifteen routers 163 CHARACTERIZING THE CONTROL DELAY FOR RIP AND OSPF ROUTING PROTOCOLS The number of neighbors for two routers equal to 1, but for 3 to 15 routers the number of neighbors will be equal to 2 (assuming that the edge routers do not make a request and make update only) (Update ) packets = (Rint × ORIP × (( H UDP ) + ( H IP ) +( H RIP )+( E RIP + (Re × ORIP × (( H +( H Figure 4. Tree network topology for fifteen routers 4.2 RIP Scenarios These scenarios study the effect of different parameters on the packet control delay for the IP networks that use RIP as their routing protocol. This work concentrates on the router forwarding rates, the link rates, the number of routers and the network topology. 4.2.1 Scenarios’ Description Our calculations are based on two types of control messages; request and update messages, which are updated every 30 seconds whether there are any changes in the network or not. Although the RIP request messages are sent under special circumstances, i.e., these messages are sent when a router provided with immediate routing information [22]. The most common example of this is when a router is first powered on. After initializing, the router will typically send an RIP request on its attached networks to ask for the latest information about routes from any neighboring routers. A router receiving an RIP request will process it and send an RIP response containing its entire routing table. Under normal circumstances, however, routers do not usually send RIP request messages asking specifically for routing information. Instead, a special timer is used on each RIP router that goes off every 30 seconds. 4.2.2 Scenarios’ Assumptions The number of control messages concerned with RIP messages could be implemented with two types of packets which are the update and the request packets. Eq. (3) demonstrates the size of these control messages. MS RIPv1 ( = Request ) packets + (Update) packets ( Request ) packets = ( H UDP ) + ( H IP ) + ( H RIP ) +( E RIP (3) (4) × Ni ) Where MS RIPv1 is the number of control messages for RIP (bytes), ( Request ) packets are RIP request packets, ( Update ) packets are RIP update packets, H RIP the header of RIP (equals to 24 bytes), H IP the header of IP (equals to 20 bytes), H UDP the header of UDP (equals to 8 bytes), E RIP the entry size of RIP v1 (equals to 20 bytes), and N i the number of neighbors for Ri routers, RIP )+( E × (Ri - 1)))) UDP RIP )+( H (5) IP ) × (Ri - 1)))) Where R int is the number of intermediate routers (in case of 2 routers = 0), O RIP the number of update occurrence (equals to 15), R e the number of edge routers (equals to 2), R i the number of routers, and R i – 1 is the number of routes for router i. Due to the fact that the number of routers in IP networks which use RIP will not exceed 15 hops and the period of routing table update in RIP is 30 sec, we assume that the frequency of iterations will be 15 (hops) by 30 sec (update period) equal to 450 sec. i.e., For two routers, the number of updates during 450 sec is 15 and this packet will have one route entry for the next hop and one request during 450 sec. Then the packet control delay resulting from sending one control packet using RIPv1 will be equals to: CD RIPv1 MS ⎛ MS RIPv1 ⎞ ⎛ ⎞ RIPv1 ⎟+⎜ ⎟ ⎝ ( dr ) ⎠ ⎝ ( fr × Avg. packet size ) ⎠ =⎜ (6) Where CD RIPv1 is the control delay for RIP (sec), dr the data rate (Mbps), f r the forwarding rate (packet /sec). Eight figures will be shown in the following section, four figures for the network pipeline topology will be presented in Section 4.2.3, and four for the tree network topology in Section 4.2.4, each figure contains control delay bars for different forwarding rates (25000, 70000, 225000 and 1000000 packets/sec respectively) for one data link rates (2 Mbps, 4 Mbps, 6 Mbps, and 8 Mbps respectively). 4.2.3 Pipeline topology Results Fig. 5-8 demonstrate the effect of changing the number of routers, forwarding rates, and data link rates on the RIP control delay. From Fig. 5, it is obvious that the RIP control delay increases by increasing the number of routers i.e., increases by increasing the distance between source and destination. Also it is clear that the RIP control delay decreases by increasing both of the data link rate and the forwarding rate. It has been found from Fig. 5, 6 that increasing the data link rate from 2 Mbps to 4 Mbps decreases the RIP delay by 47%, and increasing the data link rate from 4 Mbps to 6 Mbps, as shown in Fig. 6, 7 decreases the RIP delay by 30%, finally from Fig. 7, 8, increasing the data link rate from 6 Mbps to 8 Mbps decreases the RIP delay by 22%. So, it could be concluded that increasing the data link rate by great value decreases the delay, but it should be noticed that the decreasing percentage decreases by increasing the data link rate. This is logically because of the processing delay effect. CHARACTERIZING THE CONTROL DELAY FOR RIP AND OSPF ROUTING PROTOCOLS 164 4.2.4 Tree topology Results From Fig. 9-12, it could be concluded that at the same forwarding rate the percentage of incremental in RIP control delay is reversely proportional with both of the link data rate and the forwarding rate. Also, as mentioned in Section 4.2.3, it is obvious that increasing the data link rate by great value decreases the delay, but this decreasing percentage decreases by increasing the data link rate from 2, 4, 6, to 8 Mbps due to the added effect of the processing delay. Figure 5. RIP delay for 2 Mbps data link rate The results obtained from Fig. 5-12 have lead to the fact that the RIP control delay in tree topology is 1.8 times the control delay in the pipeline topology for the four studied CISCO routers. This behavior happened because the number of neighbors (Ni) in pipeline topology is small fixed number which is one neighbor in the edge routers or two neighbors in the intermediate routers while in tree topology it is variable number and greater than that of the pipeline topology, so, as a result of this fact the number of control messages in tree topology is higher than that of the pipeline topology. Figure 6. RIP delay for 4 Mbps data link rate Figure 9. RIP delay for 2 Mbps data link rate Figure 7. RIP delay for 6 Mbps data link rate Figure 10. RIP delay for 4 Mbps data link rate Figure 8. RIP delay for 8 Mbps data link rate It is clear that the size of the RIP control messages is calculated by substituting with Eq. (4) and (5) in Eq. (3), then the control delay is calculated by substituting in Eq. (6). Figure 11. RIP delay for 6 Mbps data link rate 165 CHARACTERIZING THE CONTROL DELAY FOR RIP AND OSPF ROUTING PROTOCOLS Table 1. OSPF parameters value Figure 12. RIP delay for 8 Mbps data link rate MS 4.3.1 OSPF Scenarios’ Description When everything is first turned on, OSPF routers detect which networks are directly accessible. They also try to determine who their neighboring routers are. Routers identify neighboring routers by transmitting “Hello” packets on all their ports. In these packets, each router identifies itself [26]. Once the designated router is selected; all other routers establish a relationship with it to exchange database information. The database exchange process uses OSPF request and response messages to exchange data. Once the databases are fully exchanged and synchronized, the routers are said to be in a full state. After they are synchronized, the routers run the shortest path algorithm. Each router constructs a tree structure from itself to all known destinations. By building this structure, the routers are able to determine how to best forward a packet to any destination across the network. A similar database relationship is also established with the backup router; however, this is only used in case of the designated router's failure. Once the network is up and running, the routers periodically send “Hello” packets on their interfaces. This is done to verify that all links are still active and also to make sure of the neighboring routers' status. In our scenarios the “Hello” packet is sent to all of the neighbors every 10 seconds, i.e., it will be sent for 15 times. After that Database Description Packet (DDP) is exchanged between routers, then the Link State Request (LSR) and Link State Update (LSU) is transferred between the new router and its neighbors. The Link State Advertisement (LSA) is held by the router that sent its local routing information to its neighbors only. It should be noticed that the main difference between the tree and the pipeline topologies is in the number of neighbors. 4.3.2 OSPF Scenarios’ Assumptions The OSPF scenarios assume that the network is non-broadcast point-to-point network, the routers are related to the same area, there is no designated router, only one router is incremented for every iteration, and the used topologies are applied on to Cisco routers only. Table 1 demonstrates the assumed OSPF parameters values. = (2× Rint × OOSPF × H N ) + (Rint N i × DDP) + (Rint × N i × LSA) + ( Re × OOSPF × H N ) 4.3 OSPF Scenarios This scenarios study the effect of the router forwarding rates, the link rates and the network topology on the packet control delay for the IP networks that use OSPF as their dynamic routing protocol. OSPF ( ) ( + (Re × (Ri - 1)× DDP) + LSR + LSU ( + Re × LSA ) (7) ) Where MS OSPF is the number of control messages for OSPF (bytes), H N the Hello packet length for N neighbor, DDP the Database Description Packet, LSR the Link State Request, LSU the Link State Update, LSA the router Link State Advertisement packet length, O OSPF the number of update occurrence (equals to 45), and R i – 1 the number of routes for router i. and The packet control delay for N routers using the OSPF routing protocols is equal to Eq. (8). MS OSPF ⎛ MS OSPF ⎞ ⎛ ⎞ ⎟+⎜ ⎟ ⎝ ( dr ) ⎠ ⎝ ( fr × Avg. packet size ) ⎠(8) CD OSPF = ⎜ 4.3.3 Pipeline topology Results Fig. 13-16 demonstrate the effect of changing the number of routers, forwarding rate, and link data rate on the control delay. It is clear from these figures that the OSPF control delay increases by increasing the number of routers and decreasing both of the link and the forwarding rates. But by comparing these figures with their corresponding figures in Section 4.2.3 Fig. 5-8 for RIP, it could be concluded that for different data link and forwarding rates the RIP control delay is lower than the OSPF control delay by approximately 0.5 in the pipeline network topology case. In pipeline configuration the maximum number of neighbors will not exceed two neighbors therefore, for each trial the control delay is calculated according to Eq. (8). CHARACTERIZING THE CONTROL DELAY FOR RIP AND OSPF ROUTING PROTOCOLS 166 mentioned in Section 4.2.3, it is obvious that increasing the data link rate by great value decreases the delay, but this decreasing percentage decreases by increasing the data link rate from 2, 4, 6, to 8 Mbps due to the added effect of the processing delay. Figure 13. OSPF delay for 2 Mbps data link rate Figure 17. OSPF delay for 2 Mbps forwarding rate Figure 14. OSPF delay for 4 Mbps data link rate Figure 18. OSPF delay for 4 Mbps forwarding rate Figure 15. OSPF delay for 6 Mbps data link rate Figure 19. OSPF delay for 6 Mbps forwarding rate Figure 16. OSPF delay for 8 Mbps data link rate 4.3.4 Tree topology Results From Fig. 17-20 and 13-16, it is obvious that the increasing rate of the OSPF control delay bars in case of tree topology is higher than that of the pipeline network topology. Also, as Figure 20. OSPF delay for 8 Mbps forwarding rate By comparing Fig. 17-20 with their corresponding Fig 9-12, in Section 4.2.4, it could be concluded that for different data link 167 CHARACTERIZING THE CONTROL DELAY FOR RIP AND OSPF ROUTING PROTOCOLS and forwarding rates the RIP control delay is lower than the OSPF control delay by approximately 0.9 in the tree network topology case. It should be clear that the OSPF control delay is higher than the RIP control delay due to two factors: First, the OSPF protocol relays on several control messages, as presented in Eq. (7), while the RIP had only two types of messages. Second, the occurrence of the update messages in RIP are done every thirty seconds, while the occurrences of the HN update message only in OSPF are repeated for forty five times. 5. CONCLUSIONS This paper studied the impact of the control messages that are generated from the most widely deployed routing protocols; RIP and OSPF on delay. Four performance parameters have been considered in the analysis; link rate (2 Mbps, 4 Mbps, 6 Mbps, and 8Mbps), forwarding rate (25000, 70000, 225000 and 1000000 packets/sec), number of hops (The number of routers are increased by one each iteration until it reaches 15 hops), and topology type (pipeline and tree topologies). The analysis phase have led to three majors conclude remarks, first, it have been found that the control delay for RIP and OSPF increases by increasing the number of routers and decreases by increasing both of the data link rate and the forwarding rate. Second, the network topology had great impact on the delay; the control delay in case of the tree topology is always greater than the control delay in pipeline topology for both RIP and OSPF protocols. This behavior happened because the number of neighbors (Ni) in pipeline topology is small fixed number (1 neighbor in edge routers or 2 neighbors in intermediate routers) while in tree topology it is variable number and greater than that of the pipeline topology, so, the number of control messages in tree topology is higher than that of the pipeline topology. On the average bases, the control delay of the tree topology is approximately 1.8 the pipeline topology in case of the RIP and 1.1 in case of the OSPF, for the four studied CISCO routers. Third, the RIP control delay is lower than OSPF control delay, this behavior has been occurred due to the fact that OSPF includes several messages; HN, DDP, LSA, LSR, and LSU, whereas the RIP had only two types of messages; request and update messages, Moreover, the occurrence of the update messages in RIP were assumed to be done every 30 seconds, while the occurrences of the HN update message only in OSPF will be repeated for 45 times, therefore, the overhead messages in the OSPF is greater than that of the RIP. So, for the four studied CISCO routers, the control delay of the OSPF is approximately double the control delay of the RIP in case of the pipeline network topology whereas in tree topology case the RIP control delay is approximately less by 10% than OSPF. [3] Jeff Doyle, “Routing TCP/IP Volume I (CCIE Professional Development)”, Cisco Press, 1st edition, 2001. [4] Andrew S. Tanenbaum, “Computer Networks”, Fourth Edition, Prentice Hall, 2002, ISBN: 9780130384881. 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Garcia-Luna Aceves, “Dynamics of Distributed Shortest-Path Routing Algorithms”, Proceedings of ACM Sigcomm, August 1991. [11] V. Paxson, “End-to-End Routing Behavior in the Inthernet”, IEEE/ACM Transactions on Communications, 1997, pp. 610- 615. [12] Z. Wang, J. Crowcroft, “Shortest path first with emergency exits”, Proceedings of ACM Sigcomm, 1990, pp. 166-176. [13] Anindya Basu, Jon G. Riecke, “Stability Issues in OSPF Routing”, Proc. ACM SIGCOMM, August 2001. [14] Aman Shaikh, Mukul Goyal, Albert Greenberg, Raju Rajan, and K. K. Ramakrishnan, “An OPSF Topology Server: Design and Evaluation”, IEEE J. Selected Areas in Communications, Vol. 20, No. 4, May 2002. [15] Aman Shaikh, Albert Greenberg, “Experience in Black-box OSPF Measurement”, Proc. Internet Measurement Workshop (IMW), ACM SIGCOMM, November 2001, pp. 113-125. [16] Craig Labovitz, Abha Ahuja, and Farnam Jahanian, “Experimental Study of Internet Stability and Wide-Area Network Failures”, Proc. International Symposium on FaultTolerant Computing, June 1999. In the future, we could apply the same methodology on different routing protocols to evaluate the effect of routing overhead on the Internet traffic performance from the throughput, latency, path length points of view. [17] Aman Shaikh, Chris Isett, Albert Greenberg, Matthew Roughan, Joel Gottlieb, “Case Study of OSPF Behavior in a Large Enterprise Network”, Internet Measurement Workshop (IMW), ACM SIGCOMM, November 2002, pp. 217-230. REFERENCES [18] D. Ghosh, V. Sarangan, R. Acharya, “Quality of Service Routing in IP Network”, in IEEE transaction on Multimedia, Vol. 3, No. 2, June 2001, pp. 200-208. [1] Christian Huitema, “Routing in the Internet”, Prentice Hall, April 1995, ISBN: 0131321927. [2] Terry Slattery, William Burton, “Advanced IP Routing in Cisco Networks”, McGraw-Hill, New York, 1999, ISBN: 0-07-058144-4. [19] Ira M. Weinstein, “Real-World IP Network Convergence for Conferencing, Considerations for Hosting IP Video on the Enterprise Data Network”, Wainhouse Research, July 2005, available at: http://www.wainhouse.com/files/papers/wripconv4conf.pdf, last date accessed 30/1/2008. CHARACTERIZING THE CONTROL DELAY FOR RIP AND OSPF ROUTING PROTOCOLS [20] “Voice over IP, Per Call Bandwidth Consumption”, Cisco Systems, May 2005, available at: http://www.cisco.com/warp/public/788/pkt-voicegeneral/bwidth_consume.pdf, last date accessed 30/1/2008. [21] C. Hedrick, “Routing Information Protocol”, RFC 1058, Network Working Group, June 1988, available at: http://www.ietf.org/rfc/rfc1058.txt, date accessed 30/1/2008. [22] G. Malkin, “RIP Version 2 - Carrying Additional Information”, RFC 1723, Xylogics, November 1994, available at: http://www.faqs.org/rfcs/rfc1723.html, last date accessed 30/1/2008. [23] G. Malkin, “RIP Version 2,” RFC 2453, IETF, Network Working Group, November 1998, available at: http://www.ietf.org/rfc/rfc2453.txt, last date accessed 30/1/2008. [24] John T. Moy, “OSPF: Anatomy of an Internet Routing Protocol”, Addison-Wesley, January 1998, ASIN: 0201634724. [25] Huitema, C., Moy, John, editor, “OSPF Protocol Analysis”, Westborough, MA, RFC 1245, July 1991, available at: http://www.unix.com.ua/rfc/rfc1245.html, last date accessed 30/1/2008. [26] Moy, John, editor, “Experience with the OSPF Protocol”, Westborough, MA, RFC 1246, July 1991, available at: http://www.unix.com.ua/rfc/rfc1246.html, last date accessed 30/1/2008. [27] J. Moy, “OSPF Version 2", RFC 2328, IETF, Network Working Group, April 1998, available at: http://www.ietf.org/rfc/rfc2328.txt, last date accessed 30/1/2008. [28] G. Apostopoulos, R. Guerin, S. Kamat, “Implementation and Performance Measurements of QoS Routing Extensions to View publication stats 168 OSPF”, Proceedings of INFOCOM'99, New York, March 21-25, 1999. [29] Scott M. Ballew, “Managing IP Networks with Cisco Routers”, O'Reilly, 1st Edition October 1997, ISBN: 10: 1-56592-320-0. [30] Aman Shaikh, Albert G. Greenberg, “OSPF Monitoring: Architecture, Design, and Deployment Experience”, 1st Symposium on Networked Systems Design and Implementation (NSDI 2004), San Francisco, California, USA, March 29-31, 2004, pp. 57-70. Biographies Sherine M. Abd El-kader has her M.Sc., & Ph.D. degrees from the Electronics & Communications Dept. & Computers Dept., Faculty of Engineering, Cairo University, at 1998, & 2003. Dr. Abd El-kader is an Assistant Prof., Computers & Systems Dept., at the Electronics Research Institute. She is currently supervising one Ph.D. student, and 8 M.Sc. students. Dr. Abd El-kader has published more than 10 papers in computer networking area. She is working in many computer networking hot topics such as; Wi-MAX, Wi-Fi, IP Mobility, Active Queue Management, QoS, Wireless sensors Networks, Ad-Hoc Networking, real-time traffics, Bluetooth, and IPv6. She is heading the Internet and Networking unit at ERI from 2003 till now, this unit supports the seven departments of the ERI. Dr. Abd El-kader is supervising many automation and web projects for ERI. She is supervising many Graduation Projects from 2006 till now. She is also a technical member at both the ERI projects committee and at the telecommunication networks committee, Egyptian Organization for Standardization & Quality (EOS) since February 2007 till now. Finally, Dr. Abd El-kader is the main researcher at two US-EG joint funded projects with University of California at Irvine, CA, USA from 2001 till now.