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Characterizing the Control Delay For RIP and OSPF Routing Protocols
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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
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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.
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different routing protocols to evaluate the effect of routing
overhead on the Internet traffic performance from the
throughput, latency, path length points of view.
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Roughan, Joel Gottlieb, “Case Study of OSPF Behavior in a
Large Enterprise Network”, Internet Measurement Workshop
(IMW), ACM SIGCOMM, November 2002, pp. 217-230.
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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.