Core stateless distributed admission control at border routers
for guaranteed IP datagram routing
Takahiro Oishi Masaaki Omotani Kohei Shiomoto
NTT Network Service Systems Laboratories, NTT corporation 3-9-11 Midori, Musashino, Tokyo 180-8585, Japan
Phone: +81 422 59 4645/ Fax: +81 422 59 4549
E-mail:{ooishi.takahiro,Omotani.Masaaki,Shiomoto.Kohei}@lab.ntt.co.jp}
Abstract
This paper proposes a distributed bandwidth management control for high-speed IP datagram networks. Each border router maintains topology database including shortest path tree to other border routers and reserved bandwidth on each link. User requests traffic demand to the border router, in which it is accommodated. The border router checks whether sufficient bandwidth can be reserved along with the shortest path tree originating from the border router to all possible border routers to provide the traffic demand. If sufficient bandwidth can be reserved, the traffic demand is admitted. Otherwise it is rejected. The requested traffic demand is notified between border routers via BGP-4 so that other border routers can perform the same admission decision. Thereby the admission decision is performed at each border router in a distributed manner. The proposed method can be applied to large-scale Internet backbone network. We demonstrate the proposed bandwidth management control is simple yet efficient through numerical examples.
Introduction
Differentiated service (diffserv) model is discussed for scalable Internet QoS service architecture in the core network[1]. In the diffserve model, treatment of IP packet at the core router is associated with the special IP header field, i.e., diffserv code point (DSCP). The association between treatment and DSCP is referred to as per-hop behavior (PHB). There are three PHB classes already defined: expedited forwarding (EF), assured forwarding (AF), and best effort(BE). The EF class is designed to implement the virtual leased-line(VLL) service in connection-less IP datagram forwarding networks. The sufficient bandwidth is reserved so that the rate of incoming flows should not exceed the rate of the outgoing flows at each hop in the core network minimizing the queueing delay in the core network. Service level specification (SLS) is contracted between user and network. Traffic demand can be included in the SLS. The traffic injected into the network is enforced at the ingress border router of the network (See Fig1). Such network resource as bandwidth and buffer is reserved to maintain the SLS in the network.
BR: border router CR: core router Figure1: Diffserv Internet QoS model
In diffserv , the resource provisioning for CRs is performed by the bandwidth broker (BB)[6]. (See Fig. 2)
Figure2: Bandwidth Broker (BB)
A BB is set up at each domain, and a BB manages the QoS resources within a given domain based on the SLS in each domain. So the BB gathers and monitors the state of QoS resources within its domain and on the edges of the adjacent domains. When users want to allocate request bandwidth, Resource Allocation Request(RAR) is issued, and the BB of the user’s domain responsively allocates the resource based on the SLS.
To provide sufficient bandwidth to maintain the traffic demand, MPLS-diffserv interwork was proposed [2][3]. Label switched path (LSP) is established, along with
Network2 Network3 Network1 Network4 shaper BR CR CR BR BR BR Network5 BB1 BB2 BB3 SLSs RARs service users Inter-domain Communication Intra-domain Communication SLSs
which the sufficient bandwidth is provided. This method requires the core router to handle MPLS protocol. Signaling and forwarding need to be implemented in the core network. The core router needs to maintain the state information on the LSP including the incoming and outgoing labels and the required bandwidth. The core router should be as simple as possible to be able to be used in large-scale Internet backbone.
The MPLS-diffserv interwork method has another drawback. The destination address may not be necessarily specified in the SLS. Suppose that there is a customer who needs the specific bandwidth to the commercial web server to minimize the response time. The customer may not be able to specify all destination addresses of potential users. In this situation it is very difficult to specify the reserved bandwidth in a point-to-point fashion (also known as "pipe model") rather than in a point-to-any fashion (also known as "hose model")[4].
In this paper we propose a distributed bandwidth control method to make admission decision for the new flow requesting EF class. Only border routers are aware of the bandwidth management in the propose method. Only the IP datagaram packet delivery with PHB is required in the core routers. The border router maintains the shortest-path tree to all possible other border routers and traffic demand associated with it. The border router calculates the residual bandwidth on receipt of user traffic demand. The user traffic demand is distributed among the border routers by using the internal border-gateway protocol (IBGP) sessions. Thereby the proposed method can be applied for the large-scale Internet backbone.
The rest of the paper is organized as follows. In Chapter 2 we propose a distributed bandwidth control method. In Chapter 3 we demonstrate the effect of the proposed method through quantitative analysis. In Chapter 4 we draws the conclusions and address the future research items.
Distributed bandwidth management control 2.1. SA-SPT
There are three types of routers in the network: access, border, and core routers. Access router is directly connected to user facilities i.e., hosts and routers. It is directly connected to more than one border routers and is not directly connected to any core routers. Border router is located at the border of the network. Border routers are located between access router and core router. Border router can be connected to access, border, and core routers. Border router is used to connect other network: border router is connected with border router in the other network. (See Fig.3 ).
In this paper we assume that interior gateway protocol (IGP) is used for routing in the core network. The border and core routers speak IGP. The shortest path is selected by the IGP. Exterior gateway protocol (EGP) such as BGP-4 is used to exchange the reachable network address prefix between access and border routers in the same network and between border routers of the adjacent networks. We also assume that the reachable network address prefix is propagated using internal BGP (IBGP) session [5].
User's SLS includes traffic demand. Sufficient bandwidth is reserved in the network to guarantee the traffic demand. If the specific destination address is included in the user's SLS, the shortest path from the source border router to the destination border router is calculated and the sufficient bandwidth is reserved along with the path. If the specific destination address is not included in the user's SLS, the shortest path tree originating from the source border router to all possible destination border routers is calculated and the sufficient bandwidth is reserved along with the tree, which we refer to as the SA-SPT (source-border-router to all-border-router shortest path-tree). In this way we consider the worst-case scenario unless the specific destination is included in the user's SLS.
Figure 3 explains the SA-SPT. Suppose that a user connected to the border router BR1 is requesting the traffic demand x [Mb/s]. We calculate the SA-SPT1, the shortest-path tree originating from the BR1 to other border routers BR2, 3, and 4. We assume that the traffic demand is offered to all the links in the SA-SPT1. In Figure 3 , the SA-SPT1 is depicted in solid line while the physical links not used in the SA-SPT1 are depicted in dashed line. Each border router has the complete topology database of the network because link-state type IGP is used in the network. Each border router tells how much bandwidth need to be reserved for the users it is directly connected to via BGP-4 as mentioned later. In this way it calculates the reserved bandwidth for all request from all border routers on each link in the network in a distributed manner. By subtracting the reserved bandwidth from the link capacity, it tells how much bandwidth can be allocated for a new request.
Figure3 : Shortest path tree originating from the border router to all other border routers
2.2. Admission decision algorithm description
Notations are introduced to describe the admission decision algorithm formally :
Given parameters:
•
V={v
i}; the set of nodes
•
E={e
k}; the set of links
•
G=(V,E) ; all topology
•
H
i=(V
i,E
i)
•
; SA-SPT topology from BR
i•
V
BR; the set of BRs
•
V
CR; the set of CRs
•
N
BR; the number of BR(=||V
BR||)
•
N
CR; the number of CR(=||V
CR||)
•
B
k; reserved bandwidth of link k
•
C
k; link capacity of link k
•
F
i; input traffic from BR
iVariable parameters:
•
v
y; BR which acts admission decision
•
R
i; acceptable bandwidth from BR
iDefinition of set operation
•
V
BR|{v
y}= V
BR−{v
y}
Admission decision algorithm is formally described in what follows.
l
reserved bandwidth calculation
for all k{
B
k=0 （e
k∈
E）
}
for all i s.t. v
i∈
V
BR|{v
y}{
for all k s.t. e
k∈
E
i{
B
k= B
k+F
i}continue k
}continue i
l
admission decision(about v
y)
i = v
yfor all k s.t. e
k∈
E
i{
Ri= min(C
k−B
k)
}
If Ri≧0 Ri is acceptable bandwidth from BRi
2.3. Bandwidth information exchange between border routers
Each border router needs to know traffic demand from, which all border routers are requested to provide to their users. The user requests the traffic demand only to the border router it is accommodated by. Mechanism to notify the traffic demand to other border routers is required. 2.3.1. Traffic demand exchange via BGP-4
BGP-4 is a EGP, which is used to notify the network address prefix between autonomous systems. Network address prefix is learned from the adjacent autonomous system via BGP-4. The learned prefix is then advertised to the other border routers in the autonomous system via IBGP sessions. BGP-4 carries attributes associated with each network prefix to perform policy routing. A set of attributes defined in the standard document includes LOCAL PREFERENCE, MED, AS_PATH, and COMMUNITY. We defined a new attribute by extending BGP-4. It is a BANDWIDTH_AGGREGATE (Bw_agr) attribute.
2.3.2. Bw_agr attribute
The attribute Bw_agr is used to notify the total traffic demand injected to the border router. Figure 4 shows how the attribute Bw_agr is used. The total bandwidth injected
SA−SPT from BR1 to all BRs
X[Mb/s] BR3 X X X X X physical links BR4 BR1 BR2 CR CR2 CR AR1
from the BR 1 is denoted by X1 and is notified as the Bw_agr attribute. In this way the total traffic demand injected from BR1 is notified to all the other border routers, BR 2, 3, and 4. The same mechanism is used for traffic demand injected from BR 2, 3, and 4. By using this mechanism, the complete information on the traffic demand from all border routers is shared by all border routers. Thereby the border router can calculate the residual bandwidth in a distributed manner.
Figure4: bw_agr attribute 3. Performance evaluation
Bandwidth efficiency achieved by the proposed method is examined. We applied the proposed method to the mesh network shown in Fig. 5. We calculated the admissible traffic demand from BR5 under the assumption that the traffic demand from border routers except BR5 is identical x [Mb/s]. The shortest path, which is calculated from the cost of each link shown in Fig. 6, is used for packet routing. We assume that the capacity of each link is 50 [Mb/s].
The relationship between the admissible traffic load from BR5 y and ones from all the other border routers x is shown in Fig. 6. We observe that the admissible traffic from BR5 is decreasing at the small rate as the traffic demand from the other border routers increase.
Figure 5 : Network model
Figure 6: Bandwidth efficiency achieved by the proposed method
3.2. Link failure
In Fig. 7, we show the admissible traffic load from BR5 by a dotted line when one link failure occurs in the topology which shows with in Fig. 5.
The admissible traffic load decreased in comparison with the case of no link failure. As a result of link failure from BR1 to BR7, this admissible traffic load decrease was lead. This analysis is future work.
AS1 AS2 CR BR1 CR AS4 AS3 BR4 BR3 192.60.1.1 B11 X3 [Mb/s] X4 [Mb/s] X2[Mb/s] X1[Mb/s] EBGP IBGP IBGP IBGP BR2 AS5 AS_path Bw_agr X1 attribute 192.60.1.1 1 AS_path Bw_agr X1 attribute 192.60.1.1 1 AS_path Bw_agr X1 attribute 192.60.1.1 1 2 3 2 2 3 3 3 1 1 1 1 1 1 1 1 1 y [Mb/s] = X＋α X 1 X X X X X CR9 CR10 BR3 BR7 CR8 BR6 BR5 BR2 BR1 BR4 0 5 10 15 20 0 50 40 30 20 10 traffic demand ( X [Mb/s]) α y = x
acceptable bandwidth from BR5
Figure7: Bandwidth efficiency achieved by the proposed method when a link failure occurs
4. Conclusion
We proposed the distributed bandwidth management method for datagram network. The total traffic demands injected from all border routers are notified among border routers each other via BGP-4. They are maintained and used to make admission decision for the traffic demand by each border router in a distributed way. The proposed method does not require any new mechanism in core routers. Thereby the backbone network element can be simplified and intelligent mechanism is required only at border routers. We argue that the proposed method is suitable for future high-speed IP datagram backbone network architecture.
References
[1] S. Blake, D. Black, M.Carlson, E. Davies, Z. Wang, and W. Weiss,”An architecture for differentiated services,” RFC2475, Dec.1998.
[2] P. Ford, F. Baker, Y. Bernet, R. Yavatkar and L.Zhang,”A framework for end-to-end QoS combining RSVP/IntServ and differentiated services,” draft-bernet-intdiff-00.txt, Mar.1998.
[3] G. Huston, Internet performance survival guide, John Wiley & Sons, Inc., 1 edition, Feb. 2000.
[4]
B.S. Davie and Y. Rekhter, MPLS technology and applications, Morgan Kaufmann Publishers, 1 edition, May 2000.[5]
H. Ballabi and D. McPherson, Internet routing architectures, Cisco Press, 2 edition, Jan. 2000.[6]
L. Dunn, R. Neilson, V. Narayan, F. Reichmeyer, B. Teitelbaum, S. Hares, ”Internet2 QBone:building a testbed for differentiated services,” IEEE Network, Sep./Oct. 1999.0 5 10 15 20 0 50 40 30 20 10 traffic demand ( X[Mb/s] ) α y = x
acceptable bandwidth from BR5
