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					Computer Networks

                        Computer Networks

                              Table of Contents
      What is computer networking?

      Windows Connect Now Overview

      Why visualize connectivity?

      Network map
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Computer Networks

      Link Layer Topology Discovery (LLTD)

           o   How LLTD works overall

           o   How the LLTD Responder works

      OSI and Protocol Stack

           o Data Framing
           o Error Detection/Correction
           o Services to the network layer
           o Flow control

      TCP/IP Hierarchy

      Call to action

What is (Computer) Networking?
Networking is the practice of linking computing devices together with hardware and software
that supports data communications across these devices.

Windows Networking and Device Connectivity
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Computer Networks

             “It Just Works” experience for users

             Simple protocols, APIs and DLLs for partners
             and developers

      Secure and Reliable

             Built-in security to enable higher user confidence

             Make reliability a fundamental part of the solution

      Foundation for the Future

             Continue enabling compelling new user experiences

  Windows Connect Now Programs
          Technical                                Consolidated
          Guidance                              Licensing Program

                               Access to
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Computer Networks

  Windows Connect Now Technologies


                                                      Function Discovery
                                                                               Devices Class APIs
                                                                                                              WMC, Media
                                  WCN Configuration                           (Digital Still Cameras,
             Network Topology

                                                                             Portable Media Players,
                                                                                  Printers, etc.)

                                                                                       MTP/IP, RDP,
                                                                           PnP-X                         WS-D, UPnP

                                                                                       IP Network
                                                                                       (IPv4, IPv6)


                                                                           Windows Connect Now Technologies

Why Visualize Connectivity?

         Users having difficulties setting up their network

                                Users don’t know or want to know how their networks are wired

                                We still have a way to go until networking is truly “plug and play”

         Users have difficulties troubleshooting issues on their network

                                Multiple points of failure

                                                      Hubs, Switches, Gateways, APs, Bridges, Cables

                                Requires technical skill set to fix

                                Tedious to check power, connectivity, link integrity to discover issues

                                Remote support effectiveness limited by lack of network connectivity

         Difficult support experience

                                Takes up time and generates user frustration

                                                      Cannot properly describe topology to support technicians
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Computer Networks

             Erodes customer satisfaction and trust

             Expensive for vendors to support

             Blame the issue on the wrong device; may result in product return!

The solution is the Network Map and Link Layer Topology Discovery!

Network Map

      Shows the devices physically connected to the network

             Provides basic information about the device

                    Device name, manufacturer info, IP address, etc.

             Keeps history of last known topology per profile
             to see if things have changed

      Shows how the devices are connected together

             What’s plugged into what

             What’s the path to the Internet

             What’s the path to other devices on my network

      Adds diagnostic information on top of topology map to help users resolve issues

             Shows where the issue is on the network

             Provides entry point for diagnostic tasks

      Integrated with the Network Explorer

             Unified location for seeing PCs and network devices

      How the Network Map gathers information

             Function Discovery


                    Universal Plug and Play

             Link Layer Topology Discovery
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Computer Networks

Link Layer Topology Discovery

       Layer 2 protocol for:

              Discovery and mapping of network devices

              Performing time-probe QoS tests

       Does not need IP connectivity to work

       Consists of a Mapper and a Responder

       Not all devices need to implement Responder for discovery and mapping to work

              The more Responders on the network, the better we can map the topology
              of the network

Value of LLTD
       Lower support costs

              Users can troubleshoot issues themselves

              Users can describe their network topology accurately

       Enhanced presence in Windows Networking UI

             LLTD Architecture on Windows Longhorn

                                      Network Map                        Application

                                                    Mapper               Responder
                      Function Discovery
                                                    Service              Module

                                               Mapper    Responder       LLTD
                               IP                                        Mapper
                                               Driver      Driver        Modules

                                           NDIS                          OS
                                                                                    Page 6
Computer Networks

  LLTD Architecture on Network Devices

                                   WS-                         Legend:
                                Discovery                        LLTD
                                            Responder            Module
                           Network Interface                     OS

LLTD Mapper and Responder

             Service that queries for devices on the network

             Sends out requests to Responders to run tests

             Interprets results from Responders to create the topology map

             Sends topology map information to Network Map for rendering


             Implemented on network-attached devices

             Performs tests on the network to

                    Determine what other devices are on the same segment

                    Determine what infrastructure device it is attached to

                    Determine quality of service between devices

             Four states

                    Quiescent, Hello, Command Loop, Emit
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Computer Networks

Quiescent State

       Responder waits for a Mapper to start the mapping process

              Listens to broadcast frames waiting for a MapBegin

       After Responder sees a MapBegin frame, it moves to the Hello state to begin
       association process with a Mapper

              A Responder can be associated with only one Mapper at a time.

Hello State

       Responder associates with a Mapper

              Mapper gets a list of Responders on the network

              A generation number (unique identifier for the mapping session) is created

              Responders pay attention to avoid network overload on large networks

       Subsequent Mappers are told that a mapping session is already occuring on the

       After association with Mapper is complete, a Responder moves to the Command
       Loop state

Command Loop State

       The Command Loop state is where Responders spend most of their active time

       Interface is in promiscuous mode

       Responders execute Emit and Query commands received from a Mapper

              Emit includes a list of probe tests, each of which requests that the
              Responder transmit frames with the given source and destination Ethernet

              Query asks the Responder to return its list of probe information

       Responders go to the Emit state when they have a valid Emit frame from Mapper
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Computer Networks

Emit State
      Each entry from the existing list of Emit requests is serviced in turn

       A Responder continues to handle incoming protocol frames

               Drops incoming Emit and Query requests

       After all the requests are serviced, the Responder returns to the Command Loop

   Responder State Diagram




Required Type Length Values (TLVs)


       Physical Medium

       IPv4 Address

       Link Local IPv6 Address (if applicable)

       Wireless Mode (if applicable)

       BSSID (if applicable)
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Computer Networks

Optional TLVs

      Machine / Device Name

      Contact Info

      Friendly Name

      Manufacturer Name

      Link Speed


      Management URL

      Icon URL

The OSI Reference Model
                              Page 10
Computer Networks

The Data Link Layer Functions
Concerned with reliable, error-free and efficient communication
between adjacent machines in the network through the following functions:

   1   Data Framing:

       The term “frame” refers to a small block of data used in a specific network.
    The data link layer groups raw data bits to/from the physical layer into discrete
frames with error detection/correction code bits added. Framing methods:
           – Character count.

           –   Starting and ending characters, with character stuffing.

           –   Starting and ending flags with bit stuffing.

           –   Physical layer coding violations.

   2   Error Detection/Correction:

           –   Error Detection:

                   •   Include enough redundant information in each frame to allow the
                       receiver to deduce that an error has occurred, but not which error
                       and to request             a retransmission.

                   •   Uses error-detecting codes.

           –   Error Correction:

                   •   Include redundant information in the transmitted frame to enable
                       the receiver not only to deduce that an error has occurred but also
                       correct the error.

                   •   Uses error-correcting codes.

   3   Services to the network layer:

           –   Unacknowledged connectionless service:

                   •   Independent frames sent without having the destination
                       acknowledge them.

                   •   Suitable for real-time data such as speech and video where
                       transmission speed is more important than absolute reliability.

                   •   Utilized in most LANS.
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Computer Networks

           –   Acknowledged connectionless service:

                   •   Each frame sent is acknowledged by the receiver.

                   •   Acknowledgment at the layer level is not essential but provides
                       more efficiency than acknowledgment at higher layers (transport)
                       which is done only for the whole message.

                   •   A lost acknowledgment may cause a frame to be sent and received
                       several times.

           –   Acknowledged connection-oriented service:

                   •   The sender and receiver establish a connection before any data

                   •   The message is broken into numbered frames.

                   •   The data link guarantees that each frame sent is received exactly
                       once and in the right order.

   4   Flow control:

    Protocols to control the rate the sender transmits frames at a rate acceptable to the
receiver, and the ability to retransmit lost or damaged frames. This insures that slow
receivers are not swamped by fast senders and further aids error detection/correction.
            – Several flow control protocols exist, but all essentially require a form of
                feedback to make the sender aware of whether the receiver can keep up.

                   •   Stop-and-wait Protocols:

                          –   A positive acknowledgment frame is send by the receiver
                              to indicate that the frame has been received and to indicate
                              being ready for the next frame.

                          –   Positive Acknowledgment with Retransmission (PAR);
                              uses timeouts

                   •   Sliding Window Protocols:

                          –   Data frames and acknowledgement frames are mixed in
                              both directions.

                          –   Frames sent contain sequence numbers

                          –   Timeouts used to initiate retransmission of lost frames.
                                                                                   Page 12
Computer Networks

TCP/IP Hierarchy
Transmission Control Protocol
    Connection-Oriented, Reliable, Byte Stream Service

   1. Set up connection

   2. Transfer data

   3. Close connection

TCP : State Diagram
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Computer Networks

Call To Action

      Implement the LLTD Responder in your device

             Available under the Windows Connect Now licensing program launching

             Royalty free

             What you get

                    Responder protocol spec

                    Reference Responder code

                    Test validation tool
                                                                          Page 14

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