effect of qos in mpls

The Effect of QoS Implementation in MPLS Network

Anuar Zamani Othman, Ruhani Ab Rahman, Md Mahfudz Md Zan, Mat Ikram Yusof Faculty of Electrical Engineering

Universiti Teknologi MARA Shah Alam, Selangor, Malaysia

[email protected], [email protected], [email protected], [email protected]

Abstract This paper presents the implementation of Quality of Service (QoS) based on the Class Based QoS IP Precedence in MPLS network. Most of the Internet Service Providers (ISP) need to use QoS since customers nowadays requires more bandwidth to support their network applications. ISP test lab has been used to implement QoS in MPLS network. Results obtained can be used by ISPs and Network Administrators in implementing the QoS and can be enhanced further with other type of queuing mechanism.

Keywords- Multi Protocol Label Switching (MPLS), Virtual Private Network (VPN), Quality of Service (QoS), Border Gateway Protocol (BGP) routing, Class-based Queuing.

I. INTRODUCTION Most of the ISP implement high speed network with varies

types of local access. Most Malaysian subscribers choose network services based on the optimal value of bandwidth requirement without fully considering users demand for higher bandwidth. QoS implementation in the network can help IT Administrators manage their traffic by prioritizing the network traffic. QoS is another method used to save cost rather than using a specific bandwidth management tool.

Quality of service (QoS) is defined in [1] as the capability to provide resource assurance and service differentiation in a network. Users that combine real-time applications, which have a limited tolerance for network latency and packet loss such as voice and video, need to have an IPv4 that is able to handle QoS. Such IPv4 network takes into consideration the following aspects such as delay, throughput and packet drop with enhanced methods such as Weighted Fair Queuing (WFQ), Resource Reservation Protocol (RSVP), and Class Based Weighted Fair Queuing (CBWFQ).

A. Multi Protocol Label Switching (MPLS) VPN MPLS [2] is an advanced forwarding scheme that works

between layer 2 (link layer) and layer 3 (network layer). Most of the worldwide ISP is using MPLS VPN to create a customers dedicated private network environment because of its cost effectiveness and scalability [3]. In this research, the MPLS used is the Layer 3 MPLS VPN in the Internet Service Provider Telekom Malaysia (TM), which has a dedicated core network called IPVPN and running on BGP routing protocol. A Layer 3 MPLS VPN uses VRFs (Virtual Route Forwarding) in isolating one customer from another, ATM Based networks, or IPsec-based VPNs. The customers edge router (CE) is

connected to the MPLS network via a dedicated leased lines or Metro-Ethernet to the nearest exchange, and exchanging routing by either static routing or dynamic routing ranging from MP-BGP, EIGRP, OSPF or RIP [4]. Since MPLS makes the private network transparent from the other customer, the routing from the CE at the Headquarter can be distributed seamlessly to the other branches similar to the dedicated private network. This enables the branch-to-branch communication without worrying to do the conversion or introduce network address translation (NAT) environment, since all the IP addresses is private and dedicated to the customer itself. The selection of MPLS VPN for this research is to emulate the most popular VPN product in Malaysias market, and investigate the effect of QoS in the MPLS network as well as from the customers perspective.

B. IP Precedence and Type of Service (TOS) IP Precedence and the TOS field were first introduced in

IETF RFC 791 (September 1981). The TOS field format in an IP datagram header is shown in Figure 1. The notion of precedence was defined broadly in [5] as an independent measure of the importance of a datagram and the intended use of the Network Control precedence designation is within a network only. Precedence can take one of eight values from 0 ("normal" priority) to 7 ("highest" priority). The actual use and control of that designation is up to each network.

The ToS field provides an indication for the QoS required for this datagram. It is used in selecting the appropriate service parameters at network elements. The main choice is a three-way tradeoff between low delay, high reliability, and high throughput. Bit 3 is used for delay (D) specification. D=0 indicates normal delay, and D=1 indicates low delay. Bit 4 is used for throughput (T). T=0 indicates normal throughput, and T=1 indicates high throughput. Bit 5 is used for reliability (R). R=0 indicates normal reliability, and R=1 indicates high reliability. Bits 67 are reserved for future use (FU).

Figure 1. TOS field in IP datagram.

ToS is simple, and considered to be the first support of QoS on IP Networks. Many of the router vendors support ToS and IP Precedence, and utilise its features as a first aid solution for

2012 IEEE Symposium on Wireless Technology and Applications (ISWTA), September 23-26, 2012, Bandung, Indonesia

978-1-4673-2210-2/12/$31.00 2012 Crown 321

QoS and also other value-added services [3]. TM is using IP Precedence and ToS to provide QoS to its customers due to its simplicity and ease of product development and packaging. TM offers its customers four types of IPVPN packages which are categorized as Multimedia, Mission Critical, Standard Data and Economy Data. Each of the data type is assigned an IP Precedence value which the MPLS process will handle accordingly based on the packet tagged with the specific IP Precedence upon entering the network.

C. Class-based Queuing (CBQ) CBQ is a class of link-sharing scheduling algorithms that

enables a hierarchical division of bandwidth among various classes of traffic for a particular link in times of congestion such as in Fig. 2 [3].

Conn.1

LINK

AgencyB

AgencyA

Agency C

IP Apps RealTime Telnet FTPRealTime Telnet FTP

Conn.n

RealTime Telnet FTP

15% 5% 0%

3% 2% 5%10% 10% 10%

50% 40%

20%

10%

Figure 2. Hierarchical link sharing structure [3].

These algorithms create a sharing tree for all classes to be supported for a link. Both interior and leaf classes should receive its allocated link-sharing bandwidth over a specified time interval. Moreover, any excess bandwidth in the link should be distributed among the classes according to a sharing policy. A link-sharing structure may mark classes as exempt, bounded, or isolated. An exempt class is allowed to have 100% of the total link bandwidth. However, the scheduler and admissions control schemes ensure that the traffic from this class is within the limits of the link sharing goals. A bounded class is not allowed to borrow any excess bandwidth from any of its parent classes in the sharing tree, whereas an isolated class does not allow classes from a different branch to borrow its unused bandwidth and does not borrow from other classes [3].

II. RESEARCH METHODOLOGY

A. Scope of Work In evaluating the performance of the effectiveness of QoS

in the MPLS network, there are researcher using the approach of simulations, [11][14] and some using the network lab setup. In this research, we used the production ISP MPLS network, and dedicated leased lines. The flow of the research is as shown in Figure 3.

Figure 3. Flowchart of the research.

B. Experimental Test Lab Setup In this research, real network devices were used for the

experiments. The network devices were connected to the ISP MPLS IPVPN where one site represents the headquarter and the other site the branch office. The experimental set up is as shown in Figure 4 and details of the setup are shown in Table 1.

Figure 4. Experimental Test Lab setup.

Two MPLS PEs, Brickfield and Jalan Raja Chulan, were used for the experimental setup. The router at HQ and the four PCs are connected to a layer 2 switch. The PCs installed with J-Perf Packet Generator from HQ will produce the source traffic based on class as per Table II. CE HQ is connected to the TM MPLS IPVPN node at Brickfield using a 2Mbps leased line. Static routing was used between CE and PE, and BGP routing protocol was used between PE Brickfield and PE Jalan Raja Chulan. CE Branch router was connected to the PE Jalan Raja Chulan using a 2Mbps leased line. PC E was used as the


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destination host and connected directly to the CE Branch router.

TABLE I. DETAILS OF LAB SETUP.

Equipment/Application/Link Quantity

PCs at HQ to generate traffic 4 PC at Branch to receive traffic from HQ 1

HQ Router Juniper SSG 1 Branch Router Juniper SSG 1

ISP Router in TM IPVPN Brickfield and Jln Raja Chulan

2

2Mbps Leased line with 31 timeslots 2 J-Perf Traffic Generator/Monitoring 5

Each PC at HQ will generate four types of traffic representing four classes of service; Multimedia, Mission Critical, Standard and Economy. This is emulated by using different port numbers to emulate the different types of application. Thus the class of service can be distinguished by applying different type of service matching to the application port.

TABLE II. PC WITH DIFFERENT TYPE OF APPLICATIONS

PC

Generating Traffic with Application

Port

Type of Service

IP Precede

nce

Traffic Allocation

A 5000 Multimedia (mmd)

4 600kbps

B 5001 Mission Critical (mcr)

3 600kbps

C 5002 Standard (std) 2 400kbps D 5006 Economy

(econ) 1 Not set

The CE router is a Juniper SSG router with Screen OS. In Juniper SSG routers, Priority is mapped to the IP Precedence. The mapping between Priority and IP Precedence is shown in Table III. The router was configured with class-based QoS according to the traffic bandwidth allocation shown in Table II.

TABLE III. JUNIPER SSG PRIORITY TO IP PRECEDENCE MAPPING

IP Precedence 7 6 5 4 3 2 1 0 Priority 0 1 2 3 4 5 6 7

The HQ PCs will generate traffic destined for the Branch PC. When any packet arrived at the CE Router, the traffic will be inspected and matched according to the type of class configured in the CE router. For example, if the traffic matches with port 5001, the traffic will be tagged as Multimedia which is priority 3 or IP Precedence 4.

The packets will pass through the PE router, and then transmitted across the MPLS network until it reached the other PE at the destination site. Before delivering the packets to the

CE Router, the IP Precedence of the packets will be inspected and will be queued according to the class of service. The packets will then be delivered to the CE Branch and finally to the destination host. This process is shown in Figure 5.

Traffic generation

QoS marking

QoS classification

Exceedguaranteedbandwidth?

Econ class?

Relegate to Econ class

Exceed leasedline bandwidth?

Pass traffic to branch Drop

Yes

Yes Yes

No

No No

Figure 5. The traffic flow

III. RESULT AND DISCUSSION

A. Before implementing QoS. An initial series of tests was conducted without

implementing the class based QoS which will serve as a reference for later tests. First, a series of packets is generated and injected into the network until the data rate approached the maximum capacity for the 2 Mbps line. After that other miscellaneous traffic is injected into the network and it affected the throughput of the MMD, MCR, STD and ECON traffic as shown in Figure 6, Figure 7, Figure 8 and Figure 9 respectively. Throughout this period, the branch router continuously received total aggregated traffic close to full capacity of 2 Mbps as shown in Figure 10.

Figure 6. The result before implementing QoS for Multimedia


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Figure 7. The result before implementing QoS for Mission Critical

Figure 8. The result before implementing QoS for Standard

Figure 9. The result before implementing QoS for Economy

Figures 6 through 9 show that each of the traffic types, MMD, MCR, STD and ECON, decreased from about 2 Mbps to below 200 kbps after the introduction of other miscellaneous traffic. This indicates that all types of traffic are treated equally without any priority.

Figure 10. Ingress traffic at branch router.

B. After implementing QoS After completing the tests without QoS implementation, a

series of tests was run with QoS configured on the Juniper SSG router. MMD, MCR, STD and ECON packet types were generated and injected into the network as performed for the test without QoS implementation. Figure 11 shows the traffic generated for each traffic type.

Figure 11. The generated traffic from PcA, PcB, PcD & PcD

The traffic received at the branch CE router was recorded

using J-Perf. Figure 12 through 15 are the plotted graphs for each type of traffic. Figures 12 through 14 show that MMD, MCR and STD traffic types stabilized to close the configured QoS allocated bandwidth of 600 kbps, 600 kbps and 400 kbps


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respectively. The ECON traffic will use whatever remaining bandwidth available because no QoS classification was set for this type of traffic.

Figure 12. The result after implementing QoS for Multimedia

Figure 13. The result after implementing QoS for Mission Critical

Figure 14. The result after implementing QoS for Standard data

Figure 15. The result after implementing QoS for Economy

Table IV shows that the average traffic received by the Branch CE router is close to the value of the configured QoS allocation. The traffic for MMD and MCR averaged at 606.15 kbps and 603.65 kbps respectively, as compared to the QoS configured allocation of 600 kbps for each traffic type. The STD traffic recorded an average of 398.94k bps close to the QoS allocation of 400kbps and the ECON traffic averaged at 303.11kbps which equals to the remaining available bandwidth of the 2Mbps line.

TABLE IV. AVERAGE RECEIVED IN PC E.

Type QoS policy

(kb/s) Average Received (kb/s) MMD 600 606.15 MCR 600 603.65 STD 400 398.94

ECON Not set 303.11 The result illustrates that the QoS implementation using IP

Precedence and ToS can provide the desired service level. The simplicity of its implementation makes it very attractive for ISP like TM to develop products that satisfies the need of its customers with the desired QoS.

IV. CONCLUSIONS IP Precedence can be used to prioritize traffic and preserve

QoS. Based on this research, the applications and types traffic generated, bandwidth and priority can be set to each customer application according to the desired IP Presidence. By having prioritized network, the traffic can be assured to get the guaranteed values if the congestion happen or noise happen in the link. The result obtained shows that the bandwidth allocation for specific applications at the access level is guaranteed end to end in this similar VPN network setup. This study suggests that the use other type of QoS mechanism, such as DifServ or DSCP, that have more varieties of options in QoS implementation, and using higher end routers would provide better classification and improved performance.


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REFERENCES

[1] Z. Wang, Internet QoS : architectures and mechanisms for quality of service, San Francisco: Morgan Kaufmann, 2001. [2] E. Rosen, A. Viswanathan, and R. Callon, Multiprotocol Label Switching Architecture, IETF RFC 3031, January 2001; http://www.ietf.org/rfc/rfc3031.txt [3] M. A. El-Gendy, A. Bose, and K. G. Shin, "Evolution of the Internet QoS and support for soft real-time applications," Proceedings of the IEEE, vol. 91, pp. 1086-1104, 2003.

[4] R. Ab Rahman, M. Kassim, and N. Ariffin, "Performance Analysis on Wan Optimizations: Bandwidth Management in Multi Protocol Level Switching (MPLS) Virtual Private Network (VPN)," 2011 International Conference on Future Information Technology, IPCSIT vol.13 (2011), pp. 13-18, 2011. [5] J. Postel, Internet Protocol DARPA Internet Program Protocol Specification, IETF RFC 791, September 1981; http://www.ietf.org/rfc/rfc791.txt


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effect of qos in mpls

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