P. Lorenz and P. Dini (Eds.): ICN 2005, LNCS 3421, pp. 202–209, 2005.
© Springer-Verlag Berlin Heidelberg 2005
Quality of Service Routing Network
and Performance Evaluation*
Shen Lin, Cui Yong, Xu Ming-wei, and Xu Ke
Department of Computer Science, Tsinghua University, Beijing, P.R.China, 100084 {shenlin, cy, xmw, xuke}@csnet1.cs.tsinghua.edu.cn
Abstract. In order to provide QoS guarantees for data transmission, we devel- oped the QoS router, which can seek feasible paths subject to QoS require- ments for the IP packets. However, the QoS router cannot be deployed exten- sively in the Internet because the current routers need to be modified. Based on the overlay network, we propose QoS Routing Network (QOSRN), which consists of fewer QoS routers and virtual links. We go further by researching into the impact of the arrangement of QoS routers upon the performance of QOSRN. Extensive simulations show that by adopting reasonable arrange- ment scheme, e.g. deploying border routers first, QOSRN achieves high per- formance without increasing the load of the network excessively. The re- search result can give some guidance to the construction of the overlay net- work that provides QoS guarantees.
1 Introduction
In order to provide QoS guarantees for data transmission, we developed the QoS router to support QoS routing (QOSR)[1]. Compared with traditional routers, the QoS router has the following characteristics: (1) It gathers dynamical local link state information (e.g. available bandwidth, delay, loss ratio) by means of interface statis- tics, (2) QoS-aware routing protocols are used to exchange the gathered information between QoS routers, (3) Multi-constrained QoS routing algorithms[2][3] are em- ployed to compute the routing table.
Although the QoS router can provide QoS guarantees for data transmission, it is not practical to transform all the routers into QoS routers at present. The only feasible scheme is to deploy a few QoS routers in the Internet, but it is also exposed to some problems. Firstly, QoS router needs to exchange the special measurement packets with neighbors to measure local links state (e.g. loss ratio). However, if the neighbor is a traditional router, the measurement cannot be carried out because the traditional router does not support the measurement protocol. Secondly, QoS-aware routing information cannot be exchanged by QoS routing protocol between QoS router and traditional router. Finally, for the above two reasons, QoS router cannot acquire the enough network state information, so it cannot compute the routing table by multi- constrained QoS routing algorithms.
* Supported by (1) the National Natural Science Foundation of China (No. 60403035, 60473082); (2) the National Major Basic Research Program of China (No. 2003CB314801).
To solve these problems, we use overlay network for reference and propose QoS Routing Network (QOSRN), which consists of a few QoS routers and virtual links that connect all the QoS routers together. In QOSRN, each QoS router measures the QoS metrics of connected virtual links, exchanges with each other using QoS-aware routing protocol and computes paths consisting of virtual links by multi-constrained QoS routing algorithms.
In order to evaluate the performance of QOSRN, we conduct the simulation based on a 200-node hierarchical network topology generated by GT-ITM, from which a number of nodes are chosen to be QoS routers to construct the QOSRN. Two metrics (Improvement Ratio and Failure Ratio) are introduced to evaluate the performance of QOSRN. In the simulation, we research further into the arrangement of QoS routers in QOSRN and find that the rule of how QoS routers are chosen and their connection mode significantly influence the performance of QOSRN. According to the result of the simulation, we proposed some reasonable arrangement schemes, under which QOSRN achieves high performance while the load of the network does not increase excessively.
2 QoS Routing Network
2.1 Architecture Definition 1. Virtual link
According to some rules (discussed in later section), each pair of QoS routers is con- figured connected or disconnected. The minimal-hop path between the connected QoS routers is called virtual link. It consists of the routers and the physical links on the path.
QoS Routing Network (QOSRN) is composed of interconnected QoS routers and the virtual links between them. Fig. 1 shows an example of QOSRN, which is com
Fig. 1. QoS Routing Network
posed of 7 QoS routers A-G from 4 autonomous systems (ASes). The QoS routers are connected via virtual links. Each of the virtual links is usually composed of sev- eral physical links.
Several QoS-aware routing protocols are used in QOSRN. SQOSPF[4], whose ad- vantages include easy implementation, multi-constrained QoS support, high-speed convergence and multiple QoS routing algorithms support, can be used in small- scaled QOSRN. In large-scaled QOSRN, hierarchical architecture must be adopted to enhance scalability, such as the combination of SQOSPF and the QoS extension of BGP[5].
2.2 QoS Routing
There are three phases in the IP packet transmission by QOSRN:
1. Sending IP packet from source to a chosen QoS router (source QoS router) in the same AS. The rule for choosing source QoS router will be discussed in the later sec- tion.
2. Transmitting IP packet within QOSRN using QoS routing and sending it to a chosen QoS router (destination QoS router) in the AS which contains the destination of IP packet. The rule of how destination QoS router is chosen will be discussed in the later section, too.
3. Sending IP packet from the destination QoS router to the destination.
Arrows in Fig. 1 show a complete packet transmission process using QOSRN.
Host H1 in AS1 sends IP packets to Host H2 in AS2. Firstly, H1 sends the packet to QoS router F in AS1. F determines that the destination of the IP packet is in AS2 and chooses QoS router C as the destination QoS router from AS2. Then the routers in QOSRN forward the packet along a path that satisfies the QoS requirements of packet (in Fig 1, the chosen path is F-E-D-C). The black arrows show the forwarding path in QOSRN, and the grey arrows show the actual path in the underlying network.
2.2.1 Sending IP Packet from Source to Source QoS Router
We encapsulate the actual sent IP packet in a new IP packet called QoS IP packet.
The destination of the new IP packet is the address of the chosen source QoS router.
The protocol type field of the new packet is set to 126, indicating that the data after the new header is the actual sent IP packet and the IP packet is transmitted within the same AS.
2.2.2 Transmitting IP Packet in QOSRN
When QoS router receives an IP packet whose destination address is router 's local address and protocol type field is 126, it will determine the AS which contains the destination of the actual IP packet and choose a QoS router as destination QoS router from that AS. The actual sent IP packet is also encapsulated in a new IP packet whose destination field is the address of the chosen destination QoS router. The new packet 's protocol type field is set to 127, indicating that the packet is transmitted in QOSRN. Then, QoS router seeks a feasible path in the QoS routing table subject to the QoS requirements of the packet, and forwards it.
2.2.3 Sending IP Packet from the Destination QoS Router to the Destination When QoS router receives an IP packet whose destination address is router 's local address and the protocol type field is 127, it is indicated that the destination of the actual IP packet is in the same AS. Then the router decapsulates the actual sent IP packet from the packet and forwards it to the destination.
2.2.4 Choosing Source and Destination QoS Routers
There may be several QoS routers in one AS. When end system wants to use QOSRN to transmit data packets, it must choose one as the source QoS router.
Because routing from source to the source QoS router is best effort, we prescribe that the QoS router with minimal-hop path to source should be chosen as the source QoS router. The destination QoS router can be chosen in the same way. As men- tioned above, QoS router distributes routes information acquired by exchanging OSPF protocol with traditional routers among QOSRN. According to these routes information, the source QoS router can choose destination QoS router with mini- mal-hop path to the destination.
3 Simulation Setup and Performance Metrics
Definition 2. QOSRN Routing
The routing mode in QOSRN, which combines Best Effort Routing and Complete QoS Routing, is called QOSRN Routing. The Best Effort Routing is widely used in current Internet, which selects the path with minimal hop count. The Complete QoS Routing is used in the network constructed entirely by QoS routers.
3.1 Simulation Setup
The goal of an effective QOSRN includes suitable proportion of QoS routers, high QoS guarantees to IP packets transmission and lower extra load. In order to construct such an effective QOSRN, we conduct simulation to evaluate the performance of QOSRN under different arrangement schemes. In the simulation, the rule of how QoS routers are chosen and their connection mode are taken into account.
The simulation is based on a 200-node hierarchical network topology generated by GT-ITM[6]. The 200 nodes are divided into 10 ASes, and each AS has 20 nodes. In an AS, the nodes connected with other ASes are named border nodes. Then, three types of QoS metrics which all obey uniform distribution between 1 and 100 are con- figured to each physical link. For convenience, we assume that these three types of QoS metrics are independent.
In the simulation, two nodes in different ASes are chosen as source and destination randomly, and 1000 QoS requirements with three metrics are used to test the per- formance of three routing mode (Best Effort Routing, Complete QoS Routing and QOSRN Routing). Each metric of QoS requirement obeys uniform distribution be- tween 1 and 100D, where D is the diameter of the network topology. For each differ- ent arrangement scheme, we run the simulation 1,000 times and get the average result.
3.2 Performance Metrics
In order to evaluate the performance of QOSRN, we focus on two performance met- rics: Improvement Ratio (IR) and Failure Ratio (FR).
Definition 3. Improvement Ratio (IR)
For a certain amount of QoS requirements, the Improvement Ratio (IR) is defined as follows:
) (
) (
CompQoSR BE
Num
QOSRN BE
IR Num
∧
= ∧ , where Num(BE∧QOSRN)
andNum(BE∧CompQoS)are the numbers of the QoS requirements which Best Ef- fort Routing cannot satisfy but can be satisfied by QOSRN Routing and Complete QoS Routing respectively.
Definition 4. Failure Ratio (FR)
For a certain amount of QoS requirements, the Failure Ratio (FR) is defined as fol- lows:
.) (
) (
QoSReq Num
BE QOSRN
FR= Num ∧ , whereNum(QOSRN∧BE)is the number of the QoS requirements which QOSRN Routing cannot satisfy but can be satisfied by Best Effort Routing.
QOSRN consists of a few QoS routers. Compared with the network constructed entirely by QoS routers, it lacks sufficient global network state information. So QOSRN can only provide a certain degree of QoS guarantees. That is to say, QOSRN Routing can only satisfy a part of QoS requirements that Complete QoS Routing satis- fies. Improvement Ratio is used to evaluate this relative degree, and reflects QOSRN 's ability of providing QoS guarantees. On the other hand, QOSRN Routing some- times cannot satisfy some QoS requirements that Best Effort Routing satisfies for the lack of sufficient information. It's Failure Ratio that reflects the negative impact of QOSRN upon the IP packets transmission.
4 Simulation Result
During the simulation, we vary the rule of how QoS routers are chosen and their con- nection mode to investigate the factors that influence the performance of QOSRN.
The simulation results are shown as follows.
4.1 Rule of Qos Router Choosing
In this simulation, full connection is also adopted to connect all the chosen nodes.
Two rules of how QoS routers are chosen will be studied. One is to choose randomly;
the other is to choose border node first.
The variations of IR and FR with different selection rules are shown in Fig. 2 and Fig. 3 respectively. The x-axis is the proportion of QoS routers. We observe that QOSRN performs better when the border nodes are chosen first. The reason is that the interdomain data transmission must pass border routers. Choosing border routers as QoS routers can provide better QoS guarantees according to dynamic network state.
Fig. 2. Improvement Ratio vs.
Proportion of QoSRouters (Ran dom Border & Router First)
Fig. 3. Failure Ratio vs. Pro- portion of QoSRouters (Ran dom & Border Router First)
Fig. 4. Improvement Ratio vs.
Proportion of QoS Routers(Full Connection & Incomplete Connec- tion)
Fig. 5. Failure Ratio vs. Proportion of QoS Routers(Full Connection &
Incomplete Connection)
Fig. 6. Virtual Link Number vs. Proportion of QoS Routers (Full Connection & Incomplete Connection)
- -
4.2 Connection Mode
In this simulation, the second selection rule is adopted, and we study the impact of two types of connection mode upon the performance of QOSRN. One is full connec- tion mode; the other is incomplete connection mode. By the latter mode, a virtual link will be deleted from the full connected graph if there is another QoS router on the minimal-hop path of a pair of QoS routers.
The variations of IR and FR with different connection modes are shown in Fig. 4 and Fig. 5 respectively. The number of virtual link of the two modes is shown in Fig.
6. The x-axis is the proportion of QoS routers. We observe that the performance of the full connection mode is higher than that of the incomplete connection mode when proportion is below 20%, and the two modes have almost the same performance when proportion is above 20%. However, the number of virtual links of the second mode is far less than that of the full connection mode. Because the load of most QoS-aware routing protocols are proportional to the number of virtual links, the load of the in- complete mode is far less than that of the full connection mode, especially when the proportion of QoS routers is high. Therefore, during the construction of QOSRN, if the proportion of QoS router is low, full connection is better because QOSRN has a good performance and its load is not very high. And if the proportion is high, the second connection mode should be chosen because it has the same performance as full connection mode and far lower load.
5 Conclusion and Future Work
In this paper, we proposed a solution QOSRN to provide QoS guarantees in the Inter- net and evaluate its performance under different arrangement schemes. QOSRN is composed of a few interconnected QoS routers and the virtual links between them.
Two metrics (Improvement Ratio and Failure Ratio) are introduced to evaluate the performance of QOSRN. In the simulation, the rule of how QoS routers are chosen and their connection mode are take into consideration to further analyze the impact of the arrangement of QoS routers upon the performance of QOSRN. Extensive simula- tions show that by adopting the reasonable arrangement scheme, e.g. deploying the border routers first, QOSRN achieves high performance while the load of the network does not increase excessively.
To deploy QOSRN more practically, further research is required on the QoS-aware routing protocol and the impact of underlying network topology upon QOSRN.
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