network-coding multicast networks with qos guarantees yuanzhe xuan and chin-tau lea, senior member,...
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Network-Coding Multicast NetworksWith QoS Guarantees
Yuanzhe Xuan and Chin-Tau Lea, Senior Member, IEEE
IEEE/ACM TRANSACTIONS ON NETWORKING, VOL. 19, NO. 1, FEBRUARY 2011
Speaker: Lin-You Wu
Outline
I. INTRODUCTION
II. OPTIMAL ROUTING FORMULATION
III. SOLVING THE OPTIMAL ROUTING
PROBLEM
IV. NUMERICAL RESULTS
V. CONCLUSION
I. Introduction
• It is well known that without admission control, network congestion is bound to occur.
• However, to implement admission control is difficult in IP-based networks, which are constructed out of the end-to-end principle.
• Even if routers can perform admission control internally, the path computation and the state updating activities required for setting up and tearing down each flow will overwhelm the network.
• A new QoS architecture, called a nonblocking network, has been proposed recently, and it requires no internal admission control and can still offer hard QoS guarantees.
• In this architecture, as long as each edge node admits not more than a specified amount of traffic, the network will never experience link congestion.
• For multicast networks, the main problem with this approach is low throughput.
• Multicast architectures with hard QoS intentions can be divided into two types.
• One performs multicast at the network layer [Fig. 1(a)], and multicast is done by the routers (IP or MPLS type).
• The other, like a content distribution network (CDN), performs multicast at the application layer [Fig. 1(b)], and multicast is done by the servers.
• Data transmission in both architectures consists of two parts:
• Transmission in the backbone network– covers a long distance– bandwidth is more expensive
• Transmission between a client and its local server– handle by LANs– bandwidth is relatively ample
• Local data transmissions can also be tackled with the P2P technology as in a hybrid P2P network.
• The focus of this paper will be on the QoS guarantees in the backbone network.
• It is well known that without admission control, congestion inside a network is bound to occur, but to implement admission control in a high-speed IP-based network is difficult.
• One reason is that IP-based networks are constructed out of the end-to-end principle and major signaling protocols.– meaning that a signaling message’s semantics can
only be interpreted by the signaling servers located at the edge of the network [see Fig. 1(a)].
• Another reason is that even if every node understands the semantics of a signaling message, as it is the case in Fig. 1(b)
• where each node is a server, the activities of checking bandwidth availability and setting up the paths for each flow can overwhelm the network.
• A new QoS architecture has been proposed recently that requires no admission control inside the network and can still guarantee the congestion-free property.
• It applies to both shortest-path-routing (IP-like) and explicit-routing (MPLS-like) networks.
• The most salient property of the network is the following:
• As long as the traffic of the ingress and egress directions admitted by edge node I is less than ai
and bi respectively, the network will be congestion-free and none of its links will experience overflow.
• Suppose that the network in Fig. 1(a) is a nonblocking network with ai= bi =900 Mb/s for all edge routers.
• Suppose also that each edge router connects to three video servers, and each server is allocated 300 Mb/s (even allocations are not a requirement).
• Routing in a conventional network is based on the assumption that the traffic matrix T = {t ij} is given, where tij represents the traffic rate from edge node I to edge node J .
• However, ai and bi are given in a nonblocking network (this pattern is called a hose-model pattern.)
• For a unicast network, this means that only the row and column sums of T are known (ai =Σj tij
and bi= Σj tji) ,but not its tij.
• For a multicast network, the relationship between the traffic matrix T and(ai, bi) is more complicated (see Section II-A).
• Finding an efficient routing algorithm for a nonblocking network is not a simple task because there are infinite traffic matrices that can satisfy the constraint (ai, bi) , and a feasible routing scheme must guarantee the congestion-free property for all of them.
• The task becomes even harder if the network needs to support multicast traffic.
• As far as a nonblocking network is concerned, the most significant benefit of network coding is that it allows us to treat a multicast connection with q destinations as q unicast connections in formulating the flow optimization problem.
• we are able to prove two important results in this paper. Both results apply to explicit-routing and shortest-path routing networks.
1.The optimal paths between a source–destination pair in a nonblocking unicast network are also the optimal paths for the pair in a nonblocking multicast network with network coding.
2.An immediate consequence of the result of 1) is that a nonblocking multicast network can admit the same amount of traffic as in a nonblocking unicast network.
II. OPTIMAL ROUTING FORMULATION
• The formulation of the optimal routing problem of a nonblocking multicast network with network coding is given in this section.
• The discussion applies to both explicit routing (MPLS-like) and shortest-path routing (IP-like) networks.
A. Traffic Unevenness
• A network can be described as a directed G(V,E) where V is the set of vertices and E is the set of links.
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