Sharing of information and resource among different devices require networking. While the networks expanding day by day and increasing number of internet users, IPv6 gaining more and more popularity .So the transition from IPv4 to IPv6 required. Therefore different transition mechanisms have been established and yet a lot of research is to be carried out. Bi-Directional Mapping System (BDMS) is one of the mechanisms reported in the literature to perform IPv4/IPv6 conversion whereas the Dual Stack Transition Mechanism (DSTM) is designed to perform IPv4 to IPv6 transition for IPv6 dominant network. This study analysis of the difference between the BDMS and DSTM. By implement the BDMS and DSTM to analysis their behavior and manner using various performance evaluation metrics such as RTT and Throughput. The OMNet++ simulator is used to implement the BDMS and DSTM mechanisms.
Key Words: IPv6, IPv4, BDMS, DSTM.
1. Introduction
Internet Protocol version 4 (IPv4) is the fourth revision in the development of the Internet Protocol (IP) and it is the first version of the protocol to be widely deployed to provide unique global computer addressing to make sure that two computers (or any two network devices) can uniquely identify one another[4]. The rapidly growth of the network and increase the number of internet users, make a huge amount of unique addresses are needed to overcome the limitations of the existing IP (IPv4) in terms of addresses, routing, and security that led to a new version of Internet protocol to be designed by the Internet Engineering Task Force (IETF) which known as IPv6 [2]. IPv6 -originally known as IPng or IP next generation- has been selected from many proposed alternatives as a suitable successor of the existing Internet Protocol (IPv4) [15]. The main goal for designing the new Internet Protocol (IPv6) is to provider larger address space , IP addresses [3]. The IPv6 address has been designed with a 128-bit (16-bytes) address scheme instead of the 32-bit (4-bytes) address scheme in IPv4, which means The new version of IP can express about 3.4Ã-1038 possible unique addresses compared with 4.3Ã-109 possible unique addresses in IPv4 [4][3].IPv6will have sufficient address to give IP address to every device and internet user around the world because the large number of address (e.g. telephone, cell phone, mp3 player, automobile, etc.) [4]. In addition, IPv6 is designed to support security (IPSec), scalability, multimedia transmissions, easy configuration and simpler packet header. Another key feature of IPv6 is that, its support a new addressing type known as anycast [4].On the other hand, there are several countries have prepared a schedule for implementing the new Internet Protocol (IPv6) to meet their future deployment needs. Due to that, because the IPv4 and IPv6 protocols are incompatible; the next generation transition Working Group (ngtrans WG) [5] in IETF as well as the other researchers have designed several mechanisms transition to ensure level of interactions will happen between those IP versions without any difficulty. In contrast, we still need more study and research to be done on the IPv6 transition in order to remedy many difficulties that are not yet resolved [6].
This paper is structured work as follows. The rest of this section gives a brief description for the transition mechanisms especially the BDMS and DSTM transition mechanisms. Section 2 show comparison between BDMS and DSTM transition mechanisms. Section 3 evaluates BDMS and DSTM using some performance evaluation metrics such as RTT and Throughput. Finally, section 4 conclusions
1.1. Transition Mechanisms
Change from IP version to another IP version need long time and not happen in the near future [4]. So, both Internet protocols (IPv4 and IPv6) need to exist together at the same time during the migration period. a number of transition mechanisms have been developed and identical to execute and managing the transition from IPv4 to IPv6 and vice versa, such as Dual Stack backbone, Tunneling, and Translation mechanisms [7]. a large amount of these transition mechanisms support the communication sessions to enable IPv6-only hosts to reach IPv4 services and to allow individually IPv6 hosts and networks to reach the IPv6 Internet over the IPv4 infrastructure. [13].
This paper shows the implementation results for two different transition mechanisms that are Bi-Directional Mapping System (BDMS) [1] and Dual Stack Transition Mechanism (DSTM) [8] that have been proposed as IPv4/IPv6 transition mechanism. The BDMS has been proposed and designed in order to support the bi-directional communication sessions .which operates when hosts in the native IPv4 network initiate connections with hosts in the native IPv6 network and vice versa[4].
BDMS transition mechanism is based on the following two main components:
(1) V4-V6 Domain Name System (DNS46) server that
Identifies the two public IPv4 and IPv6 addresses statically or dynamically for each IPv4/IPv6 communicating session [1]
(2) V4-V6 Enabled Gateway that performs the address
Mapping between an IPv4 and an IPv6 addresses as
Well as the header conversion process between the
IPv4 and IPv6 packet headers [1].
In contrast, DSTM has been deliberated and submitted as a draft for experimental RFC in the IETF[20].DSTM is applicable for the IPv4/IPv6 hosts that are located in IPv6 network to initiate their communications with IPv4-only hosts that are located in the IPv4 native network. Also,DSTM based on the tunneling method which is needed for encapsulating the IPv4 packets in the IPv6 packets then carry them through the IPv6 network to the DSTM Tunnel End Point (DSTM TEP) that is located at the border of theIPv6 and IPv4 networks (see Figure 4).
1.2. BDMS and DSTM Data Packet Transmission Process
This part shows transmission data packet process in the BDMS and DSTM transition mechanisms in Figures 1 and 2.The BDMS overhead mainly occurs due to steps 2 and 3; while the DSTM overhead occurs due to steps 1, 2, 3, and4. Theoretically, the IPv4-in-IPv6 tunneling process in the DSTM mechanism that includes the encapsulation method (as shown in Figure 2 step 1) and de-capsulation method (as shown in Figure 2 step 3) may cause additional overheads than the IPv6-to-IPv4 translation process (as shown in Figure 1 step 3) in the BDMS mechanism [4].
Step 1: Packet transmission with source IPv6
Step 2: IPv6 to IPv4 address mapping and mapping values calculation
Step 3: Header transmission from IPv6 - to -IPv4
Step 4: Packet transmission with destination IPv4
Fig. 1: BDMS data packet transmission process
Step 1: encapsulation IPv6-in-IPv4
Step 2: encapsulated IPv6 transmission packet
Step 3: IPv4 - in -IPv6 de-capsulation
Step 4: IPv6-to-IPv4 address caching
Step 5: IPv4 transmission packet
Fig. 2: DSTM data packet transmission process
2. Comparison between BDMS and DSTM
Table 1 shows the difference between BDMS mechanism [1] and DSTM mechanism [8]:
BDMS
DSTM
Each communication session uses two types of public IP addresses specified by the DNS46 server [4].
Each communication session Uses only shared of IPv4 addresses in order to assign the public IPv4 address [4].
Two version of IP address (IPv4 and IPv6 addresses) are assumed to be publically unique[4].
Only one version of IP address (IPv4) are assumed to be publically unique [4].
No need to use a tunneling technique [4].
Need tunnel technique to be configured [4].
enable IPv4-only hosts to communicate with
IPv6-only hosts and vice versa. Only translation from IPv4 to IPv6 and vice versa is needed [4].
Encapsulation and De-capsulation
Methods are needed to be used [4].
Applicable for bi-directional communication between IPv6- only nodes and IPv4-only nodes [4].
Not applicable to the IPv6-only nodes that want to communicate with IPv4-only nodes, or vice versa [14].
Lower cost [4].
High cost due to upgrading the required DSTM nodes [4].
Table 1: Comparison between BDMS and DSTM
Furthermore (Table 2) shows comparison between the BDMS and DSTM in terms of applicability and drawbacks.
BDMS
DSTM
Applicability
IPv6-only hosts in the local IPv6 network that need to continue the connectivity with IPv4-only hosts in the local IPv4 network and vice versa (two way transition
Mechanism)[4].
Hosts in the IPv6 network that need
to continue the connectivity with
IPv4-only hosts that can be reached
Only through the local IPv4 network (one way transition mechanism)[4].
Draw backs
-Single point of
disappointment
-Communication
jam
-Single point of
disappointment
-Communication
jam
3. BDMS and DSTM Performance Evaluation Criteria
In this paper two performance evaluation metrics are used: Round Trip Time (RTT) and Throughput using data ranging from 32 to 1024 bytes in order to study the effect of small packet size and the large packet size on the transition and address mapping processes in BDMS mechanism and the encapsulation and de-capsulation processes (tunneling technique) in DSTM mechanism. All the performance measurements are prepared by using the OMNeT++ simulation platform [12]with high bursty traffic where each packet arrival follows a Poisson process with rate λ= 2.The following (Fig. 3 and 4) in the last page show the Network Model for the BDMS and DSTM:
Fig. 3: BDMS Network Model.
Fig. 4: DSTM Network Model
3.1. Round Trip Time (RTT)
The Round Trip Time (RTT) used to find out the time required for communication network from the source host to the destination host and back.RTT is one of the key performance metrics that is computed in OMNeT++ simulation for both transition mechanisms (BDMS and DSTM). While the mean of RTT for a specific size of sequence packets in each communication session is calculated as follows (Eq. 1 and 2)[4]:
MeanRTT= (1)
Whereas,
RTTi = Tri - Tsi (2)
where RTT i is the Round Trip Time of packet "i", Tsi is the generated time of packet "i" at the source host, Tri is the received time of packet "i" at the source host at the end of its trip, N is the number of received packets at the source host, and MeanRTT is the RTT mean value for each communication session [4].Figure 5 shows part of our simulation result over the simulation time 0 to 60 seconds for the RTT for each generated (sent) packet when the packet size is 128 bytes. Also, Figure 6 shows that a comparison between the mean RTT for both transition mechanisms (BDMS and DSTM) using different packet sizes (32 bytes to 850 bytes) [4].
Fig. 5: BDMS and DSTM RTT when the packet size is (128 bytes)
Fig. 6: BDMS and DSTM mean RTT with different packet size
Figure 5 shows the result that BDMS mechanism more performance than DSTM mechanism, due to the encapsulation process in the DSTM that generate more traffic overhead as a result by increasing the packet size during the communicating between the IPv6 and IPv4 hosts [4].Hence, the two previous figures in particular show that, the BDMS mechanism performs better than the DSTM mechanism especially when the small packet sizes (i.e. < 400 bytes) are used [4].
3.2. Throughput
This paper measured the throughput in order to find out the rate of received and processed data in both transition mechanisms (BDMS and DSTM) during the simulation period. While the mean Throughput for a sequence of packets of specific size in each communication session is calculated as follows (Eq. 4 and 5) [4]:
MeanThroghput = (3)
Whereas,
Prec
Thr = *100 % (4)
P gen
In the Eq. 4 Thri is the value of throughput when packet "i" is received by the destination host, N is the total number of received packets at the intermediate device, Prec is the number of received packets at the destination host, Pgen is the number of generated packets by the source host, and the MeanThroughput is the mean throughput value for each communication session [20].
Figure 7 shows the result over time 0 to 420 seconds for the throughput when the packet size is 64 bytes for both (BDMS and DSTM). Also the Fig.7 show that the result approximately 100% but there is decreasing after a particular simulation time to the traffic congestion that occurs that leads for dropping some packets in both (BDMS and DSTM) mechanisms. Also, Figure 8 shows the ratio of Throughput with different packet sizes (32 bytes to 1024 bytes. In Figure 8 also show clearly that the ratio of the Throughput in the BDMS better than the DSTM with small packet sizes (i.e. ≤256 bytes) due to the effect of the DSTM encapsulation method. Also, it is obvious show that the measures become so close for both BDMS and DSTM throughput when their packet sizes are large (i.e. > 256 bytes) due to detract the effect of the IPv4-in-IPv6 tunneling process overhead in the DSTM mechanism [4].
Fig. 7: BDMS and DSTM Throughput when the packet size is 64 bytes
Fig. 8: BDMS and DSTM percentage of Throughput with different packet sizes
4. Conclusions
In this paper, by using different performance metric such as RTT and Throughput. Implemented and evaluated the BDMS and DSTM transition mechanisms. The results showed that the BDMS are better than the DSTM in both RTT and Throughput performance metric. Especially when the packet sizes were used is small [4]. Furthermore, the simulation results in this paper have shown that throughput for both transition mechanisms (BDMS and DSTM) become approximately equal to each other especially when their packet sizes are large. Indeed, the results not show the big difference between transition mechanisms (BDMS and DSTM) especially their throughput results. But, we can consider the BDMS mechanism is better than the DSTM mechanism in terms of the cost, applicability). The OMNeT++ simulator platform is used in this paper for both transition mechanisms [4].
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