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					 The Laboratory of Computer
Communication and Networking

Broadband Access Networks
                              Project Team

Submitted by:   Alex Kogan          sakogan@t2 Technion
                Alex Reitbort       sreit@t2      Technion
                Alex Umansly        salexu@t2     Technion

Instructor: Chen Genossar Optical Access

Supervisor:     Itai Dabran         idabran@cs    Technion
            Project Goal

   Develop a simulator of a
    broadband access network, in
    order to simulate real broadband
    access networks behavior and find
    bottlenecks of the network.

   For the past several years, the computer communication
    industry has witnessed an explosive growth in the
    demand for non-voice types of services, like movies,
    video-conferencing, etc.

   For these fixed and mobile services, currently existing
    access networks can’t offer the enough bandwidth to
    meet the demands.

   One of the biggest challenges currently network
    operators are facing, is to find cost effective solution for
    supporting broadband access, both fixed and wireless.
             Background (Cont.)

   The key factor here is the need to find solution that is
    able to satisfy both residential and business customers.

   These two sectors have considerably different
    requirements in terms of both service basket and
    bandwidth usage.

   It may be that the separate networks are required to
    support those requirements, but there could be a
    significant advantage in terms of economies of the
    scales and network manageability if a single solution can
    be found.
Background (Cont.)
               Background (Cont.)

   In the previous figure, the final connection is
    depending on the services provided.

    For Video-on-Demand (VoD) service, the final
    connection could use twisted pair by VDSL/ADSL
    technologies. Or instead we can use coaxial
Background (Cont.)
              Background (Cont.)

   The previous figure shows the possible
    FTTH/FTTC/FTTB/FTTN architectures for comparison.
    For example, in FTTC architecture, the signals from
    the Center Office (CO) are routed through to an ONU
    by fiber.
   It needs to deploy the fiber connection to every
   Compared with deploying fiber, free space optical
    mesh architecture is more easily to deploying and
    more cost-effective.
           Project Description

   The simulated network is defined as a graph
    consists of arcs and nodes.
   The arcs represent the physical connections.
   The nodes represent servers or users.
   Simulator provides special “Internet” nodes,
    which will represent gateways to the Internet.
   Project provides a GUI interface in order to
    define the network topology, links, servers,
    users and their features.
BANS GUI Interface
        Project Description (Cont.)

Server features:
       Server type (may be more than one):
          •   Audio
          •   Video
          •   Local content
          •   TV
          •   Router
        Number of maximum simultaneous requests
        Number of failures per day
        Maximal bandwidth (processing rate) – will be defined for
        each type of service provided by server.
Server Properties Window
   Project Description (Cont.)

User features:
     User upload/download stream per hour (Mb/s)
     Target of upload/download stream – Video

      server, Internet surfing, etc. – is defined for
      each two hours.
  It is possible to define (and save/remove)
  network-using patterns and to ascribe each of
  them to users. Such patterns define the previous
  two features.
     Designated server for each type of service
User Properties Window
    Project Description (Cont.)

Link features:
     Maximal Bandwidth

     Number of failures per day (when the link is

     Blocking service - the acceptable percentage

      of the data that is actually transmitted through
      the link from the total data that was intended
      to be sent through the link (due to the
      limitation of link’s bandwidth, some of the data
      might get lost)
     Cost (between 1 and 16)
Link Properties Window
         Project Description (Cont.)

   Project provides option of saving/loading current
    network topology into/from file. In addition, it will be
    possible to import network from previously saved file
    into the current topology or export part of the network
    into file.

   Thus, some typical network topologies (tree, mesh,
    bus) could be prepared ahead for more convenient
    work in the future.
           Project Description (Cont.)

   Project provides different types of simulations on current
           Simulation over selected time period
           Simulation until first failure.
            The failure will be defined as one of
            the following:
                  • Link bandwidth exceeded

                  • Server bandwidth exceeded (for some type of

                  • Network (part of users) inaccessible (because of

                    link/server failure as a result of predefined failure
   The result of the simulation will be displayed graphically and
Run Simulation Window
Simulation Results Window

The simulator implements number of algorithms in order to
simulate the real traffic in network.

Shortest Single Source Path (SSSP):
The simulator needs this algorithm to find the shortest path
between some user and server. Actually, it comes to
simulate the work of OSPF since all links and their costs are
known in the network.
    We have chosen to implement Dijkstra algorithm.
            Algorithms (Cont.)

Find Designated Server:
This algorithm decides which router in the network will be
chosen to supply requested service to the user and which
path to it will be taken. It uses previously defined SSSP
algorithm in order to make path choice optimal.
This algorithms provides full support for all options of the
simulation. In case that designated
server was chosen for some user, this algorithm should be
called with list of servers that
contains only the designated server. Otherwise, all servers
in the network should be delivered.
                 Algorithms (Cont.)

       There is an option to find the server with
    closest path only (if user has chosen appropriate
    option in Simulation Setting dialog or run the
    simulation with this option as default).
        Actually,this approach represents the method that is
        employed in most current routing algorithms.

 In this case, a server that provides needed service
  with shortest path from the user, is chosen and
  returned from the algorithm.
             Algorithms (Cont.)

     This algorithm tries to locate the nearest accessible
    server that can provide needed service with required
    bandwidth to user.

     In case that some accessible server is found, but
    path to it is overloaded (can not allow additional
    traffic with required bandwidth), some link on its
    path is removed and new paths are recalculated.
     This is done in order to allow traffic on another cheap path.
           Algorithms (Cont.)

 The same is true regarding routers in the chosen path-
if some router is overloaded and can not accept more
traffic, then another, more free path is chosen after the
overloaded router is taken out of the network.

 After some path was found (or failure was reported if
any path was not chosen), all components taken from
network are placed back in order to try use them for
other users and services.
                 Algorithms (Cont.)

 If any path will not be found (or the shortest path in case of “Do Not
  Look For Alternative Paths/Servers” option) available, failure will be
  reported in simulation results under one of three reasons:
     Server is unreachable (in case any server was found)
     Link failure (in case path was found, but some link was
     Router failure (in case some path was found, but some router on
      it was not capable of delivering requested traffic)
 Two last failures might be reported for the same user, because both
  of them represent some bottleneck in the network.
               Algorithms (Cont.)

Find Designated Web Gateway:
 This algorithm decides which gateway in the network will be chosen
to supply Internet requests (i.e. requests generated by user while
surfing in the Internet) from user.

 Its principles are very similar to the previously discussed algorithm –
the main difference is that we do nor need to check if gateway can
accept new user and provide required bandwidth, since we assume
that comparing to local servers, backbone gateways are very powerful
machines with unlimited resources (however, all local links and routers
are limited by the predefined resources, thus it is still possible that
network will fail to provide Internet service to some user ).
   Simulation Examples – Example 1

 In this network, both users
request 1 MB/s bandwidth to
the internet at 20:00.
 All servers in the network
are routers with routing
capacity 2 MB/s.

 Both links from users to servers have (bandwidth, cost) = (1,1). Links
between servers have (bandwidth, cost) = (1,10) for left one and (1,1) for right
 Links from server to a gateway are both (2,1) (they are drawn wider that
links with smaller capacity).
                     Example 1 (Cont.)

We expect that the traffic will go on the cheaper path first, and only if there is no
choice - on the more expensive. The results of the simulation are as following:

                                                         There is a path between
                                                         each user and gateway,
                                                         which can carry
                                                         requested bandwidth, and
                                                         thus there are no failures
                                                         in the network.
                      Example 1 (Cont.)

   When we set
    bandwidth of the
    righter link from user
    to server to 0.5MB/s,
    we discover failure of
    this link, since it can't
    provide needed
    bandwidth and user
    have no any other
    available paths.
            Example 1 (Cont.)

 As we can see, results are no different from what we
 Since there is no path that can provide required bandwidth
  from users to internet gateway, then one of the links in
  available path will fail.
 This has to be a link between servers since they are the one
  who can't provide needed bandwidth.
 Failed right link, because it has lower cost, thus routers tried
  to send data through
 In order to fix the network, we can, for example, change
  bandwidth of righter link between servers from 0.5 to 1, as
  suggested, or decrease its blocking service.
Simulation Examples – Example 2

In this example each user want to get 1 MB/s of audio each hour except
14:00, then they want 2 MB/s of audio.
Left server is router and right server is audio, each with maximum users 5
and maximum bandwidth 10.
Links from users to router are (3,1) and from router to audio (9,1).
                 Example 2 (Cont.)

As we could guess before, link between servers failed at 14:00. It misses 1
MB/s of bandwidth.
  Simulation Examples – Example 3

In this example each user wants to get 1 MB/s of internet each hour.
All serves are routers with maximum users 1 and maximum bandwidth 1.
All links are (1,1).
            Example 3 (Cont.)

As we could expect, there are no failures in this network.
      Simulator Presentation

   And now – to the real thing (simulator) …

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