Network-Coding Multicast Networks
With 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 highspeed 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 = {tij} 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 congestionfree 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.