csp07-08 - implementing a network 1 implementing a network lecturer: smilen dimitrov cross-sensorial...

1

CSP07-08 - Implementing a network

Implementing a network

Lecturer:Smilen Dimitrov

Cross-sensorial processing – MED7

2


Introduction

• The immobot base exercise• Work on the network • Goal – implement a simple network• Now not concerned with

rest of system• Setup:

– 2 PCs– Switch or router

3


Setup

• Setup for a PC:

1. Microsoft Visual Studio2. Max/MSP/Jitter (for testing)

• This time we only discuss basics of network implementation, so we will mostly work outside of the scope of the base exercise system

• Needed because we need to send the results from audio and video processing algorithms (in Max/MSP) to an application in Virtools on a third PC

• Network code will be ported in the context of the base exercise next time

4


Goal of the network implementation

•

5


Socket approach - Server/client architecture

• A network server or client functionality is implemented using sockets

– in both cases, the sockets can read and write data – the difference is mostly in the roles in the interaction, during

phase of initiation of communication

• Definitions from: http://en.wikipedia.org/wiki/Internet_socket

• An Internet socket (or commonly, a socket or network socket), is a communication end-point unique to a machine communicating on an Internet Protocol-based network, such as the Internet.

• By Cisco definition, "The combination of an IP address and a port number is referred to as a socket."

6



• Operating systems combine sockets with a running process or processes (which use the socket to send and receive data over the network), and a transport protocol (i.e. TCP or UDP) with which the process(es) communicate to the remote host.

• Usually sockets are implemented over TCP but this is not required.

• The concept of a socket is an entity that implements an API, regardless of the implementation. Two widely used Internet socket types are:

– Datagram sockets, which use UDP– Stream Sockets, which use TCP

• In contrast with the use of TCP connections directly, using sockets makes a distinction between client and server, and it is able to implement a queue of clients over a given server socket. Sockets usually are implemented by a library (such as Berkeley sockets or Winsock)

7



• The question is what kind of a network to implement between the three computers, TCP or UDP?

• We would want to stream data in real time – that means specific data, which in time comes one after another, should also arrive one after another in the network

• TCP (Transmission Control Protocol) is a reliable protocol that guarantees that packets sent in one order, arrive in the same order -

• UDP (User Datagram Protocol) is an unreliable protocol – it does not guarantee the order of the packets (although, for a wide bandwidth local network, without traffic to the Internet, in most cases, packets will arrive in order); but it can do multicast.

• Thus, we will implement a TCP server / client network here.

8



• General server / client model

• TCP – Connection oriented protocol – establishing communication analogue to a phone call

• The role of the – client socket is to send a request – upon which a

communication link is established and data is exchanged (the client is the one that makes a telephone call - “dials a number”)

– server socket is to wait for requests (the server “waits by the telephone” and picks up the handle when the client rings).

9



• Our 3 PC system would be connected on a local network, using a switch or router

• On this network, the PCs are assigned local IP network addresses (192.168.*.*)

• the sockets themselves (running in the PCs) are bound to a port number.

• How to set up the client/server architecture?

10



• Our 3 PC system is easy to conceptualize in terms of network needs: – PC 1 and 2 perform processing on data incoming from sensors,

so they need to send data to the third PC– PC 3 needs to receive data from the first two PCs and perform

additional processing

• This however does not determine the client-server roles

• Good starting point is to see into the already available network objects in Max/MSP – then it is easier to decide on the architecture

• First we look into the OSI network model

11


Layers in OSI model

• OSI model never got fully implemented• still a useful academic metaphor for abstracting different stages in

the computer networking process.

12


Layers in OSI model

• Layer 1 - physical layer, which defines all electrical and physical specifications for devices

• Layer 2 - data link layer, which also operates on a physical level – within the networking card – so it uses hardware networking addresses (MAC or Media Access Control addresses). Ethernet is a layer two protocol.– This is the layer at which bridges and switches operate.

Connectivity is provided only among locally attached network nodes.

• Layer 3 - network layer. Performs network routing, flow control, segmentation/desegmentation, and error control functions. The protocol that operates on this level is called Internet Protocol, or IP. – This is the layer at which router operates – makes Internet

possible

13


Layers in OSI model

• Layer 4 - transport layer- provides transparent transfer of data between end users.– This is the layer at which sockets are defined – Sockets can be connection-oriented (stream sockets - TCP) or

connectionless (datagram sockets - UDP), and each has their own protocol

– Winsock, as a library that we can use to program the socket functionality with Windows, is an interface standard between applications (layers 5 and above) and the transport (layer 4)

• Layer 5 – session layer - provides the mechanism for managing the dialogue between end-user application processes – establishes checkpointing, adjournment, termination, and

restart procedures – is responsible for setting up and tearing down TCP/IP sessions.– (part of specific application code)

14


Layers in OSI model

• Layer 6 – presentation layer - deals with data representation and encryption.– this layer encompasses the job of deciding how the data stream

will be formatted - and thus we specify how the data is coded and decoded.

• Layer 7 - application layer. This layer interfaces directly to and performs common application services for the application processes. – This is the layer at which HTTP (Hyper Text Transfer Protocol) is

defined – it represents a layer seven protocol

• Comparison between TCP stackand OSI model layers:

15


Layers in OSI model

• OSI Layer comparison (from a project with custom network development):

16


Networking capabilities of Max/MSP

• There are no native objects that provide socket connectivity in Max/MSP

• There are some objects made by Olaf Matthes, which can be downloaded on the web

– The first is a pair of objects known as netsend and netreceive

– There is another object called flashserver

17



• The pair of objects known as netsend and netreceive– Two boxes are meant for communication between two

Max/MSP programs on different PCs on a network– they support both the TCP and UDP mode.– netreceive represents a listening socket (server), whereas – netsend initiates connections - so it is a client.

18



• The object known as flashserver– meant for communication between Max/MSP program and

Adobe (Macromedia) Flash– TCP/IP socket connection – listening network socket; a socket

server– Maximum number of possible clients is 256– More suitable?

• We will try to test these Max/MSP networking objects

19


Testing connections between PCs (Windows)

• Using ipconfig to retrieve the PC addresses• Testing with ping• Handling the firewall

20


Testing the netsend, netreceive and flashserver objects

• In the previous discussion we determined that– netsend is a client which can only send– netreceive is a server (listening socket) which can only receive– flashserver is a server (listening socket) which can both send

and receive

• Testing– Netsend with netreceive– Netsend with flashserver– telnet (as client) with flashserver– Netsend with flashserver, captured with Ethereal

21


Implementing a receiver

• We could interface with any of the Max/MSP networking objects.

• Since we need to send from Max, we can use either netsend or flashserver.

– If we use netsend, as it is a client, we would correspondingly need to program a server.

– If we use flashserver, as it is a server, we would correspondingly need to program a client.

• Here we will try both approaches as standalone Windows executables – programmed in C/C++, using the Winsock library. – Server receiver – test with netsend– Client receiver – test with flashserver

• Netsend handles quick data better – so will use that, and server receiver– Two-thread server receiver – test with two netsend clients

csp07-08 - implementing a network 1 implementing a network lecturer: smilen dimitrov cross-sensorial...

Documents