Voice Over Internet Protocol (VoIP) Copyright © 2006 Heathkit Company, Inc. All Rights Reserved Presentation 5 – VoIP and the OSI Model

2 Objectives At the end of this presentation, you will be able to:

3 Name the layers of the OSI model. Place the layers in their proper order. Describe the basic functions of each layer. Describe how VoIP signaling, encoding, transport, and gateway control fit in the OSI model.

4 The OSI Model Open Systems Interconnection model Developed by the International Standardization Organization, or ISO Theoretical model of an ideal network that provides a way of classifying network components and tasks. Made up of seven layers that specify the functions and capabilities that must be available to the network

5 7 layers of the OSI Model Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer

6 Memory Aid to OSI Layers A way P izza S ausage T hrow N ot DoDo P lease Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer

7 OSI layers exist at both ends of the network connection. Application Presentation Session Transport Network Data Link Physical End Device 1 Application Presentation Session Transport Network Data Link Physical End Device 2 Physical Connection

8 Each layer acts as if it is communicating with its peer layer. Application Presentation Session Transport Network Data Link Physical End Device 1 Application Presentation Session Transport Network Data Link Physical End Device 2

9 Application Presentation Session Transport Network Data Link Physical End Device 1 Application Presentation Session Transport Network Data Link Physical End Device 2 But in reality, all communications must go through the physical connection. Connection Physical Connection

10 Application Presentation Session Transport Network Data Link Physical End Device 1 Application Presentation Session Transport Network Data Link Physical End Device 2 In fact, each layer communicates only with its adjacent layer.

11 Application Presentation Session Transport Network Data Link Physical End Device 1 Application Presentation Session Transport Network Data Link Physical End Device 2 Messages Travel Down the Layers in the Sending Device… Connection

12 Application Presentation Session Transport Network Data Link Physical End Device 1 Application Presentation Session Transport Network Data Link Physical End Device 2 … and Up the Layers in the Receiving Device Connection

13 Whatever a layer does on one side, it “undoes” on the other. Connection Application Presentation Session Transport Network Physical End Device 1 Data Link Application Presentation Session Transport Network Physical End Device 2 Data Link Encodes and attaches CRC Encodes and attaches CRC Removes and decodes CRC Removes and decodes CRC

14 Whatever a layer does on one side, it “undoes” on the other. Connection Application Presentation Session Network Data Link Physical End Device 1 Transport Application Presentation Session Network Data Link Physical Transport Breaks long messages into smaller ones. Breaks long messages into smaller ones. Reassembles smaller messages into a large one. Reassembles smaller messages into a large one. End Device 2

15 H2H3H4DataH7H6H5T Application Presentation Session Transport Network Data Link Physical End Device 1 On the transmit side, each layer adds a header. DataH7DataH7H6DataH7H6H5H4DataH7H6H5H3H4DataH7H6H5H2H3H4DataH7H6H5T Frame or Packet Frame or Packet

16 At the receive side, each layer strips off a header. H2H3H4DataH7H6H5T Application Presentation Session Transport Network Data Link Physical End Device 2 DataH7DataH7H6DataH7H6H5H4DataH7H6H5H3H4DataH7H6H5H2H3H4DataH7H6H5T

17 The OSI Model Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer

18 Physical Layer Is the physical connection between network devices (nodes). Cables, connectors, hubs, and network interface cards (NICs) operate at this layer. Makes no decisions. Does not modify the contents of the Frame.

19 Data Link Layer Responsible for creating, transmitting, and receiving the message packet. Provides services for the various protocols in the Network layer. Specifies and controls the network at the Physical level, including the operation of bridges and switches.

20 Addressing at the Data Link Layer Every network node has a unique physical address called the MAC address. Blocks of numbers assigned by IEEE. 12-digit Hexadecimal Number.

21 Network Layer Describes how nodes on different network segments find each other. Makes decisions based on the network addresses. Routers and gateways operate at the Network layer level.

22 VoIP gets its name from its Network Layer Protocol. Internet Protocol (IP) The most popular networking protocol suite on the planet is TCP/IP. Internet Protocol is the IP part of TCP/IP. TCP/IP is the protocol suite used by the Internet. IP determines the Internet’s basic packet structure and its addressing scheme.

23 IP Address A logical rather than a physical address. How it is entered into your computer: Manually, by you or the network administrator. Automatically, via the Dynamic Host Configuration Protocol (DHCP). Works at the Networking Layer of the OSI model.

24 Each node on a network that uses the TCP/IP protocol must have its own unique IP address.

25 IP Address 32-bits

26 IP Address 4-Octets

27 IP Address Convert each octet to decimal

28 IP Address Dotted-Decimal Notation

29 Where does the IP address come from? If you are not connected to the Internet, your network administrator can “make up” a range of IP addresses and assign you one. If you are connected to the Internet, the IP address must be registered with the Internet Network Information Center (InterNIC).

30 Usually, you get your IP addresses from your local Internet Service Provider.

31 The IP Address is divided into two parts: Network ID (Assigned by InterNIC) Host ID (Assigned locally)

Network ID Or Network Address Host ID Or Node Address

33 Router 1 Router 3 Router 2 Router 4 Network A Network D

34 Router 1 Router 3 Router 2 Router 4 Network A Network D

35 Paths are determined with the aid of: Routing tables which contain routing information Routing algorithms which maintain the routing tables and determines the optimal path. Shared routing information from other routers.

36 Router 1 Router 3 Router 2 Router 4 Network A Network D Network C Network B I know the route to Network B. I know the route to Network D. I know the route to Network C. I know the route to Network A.

37 Internet Protocol (IP) Delivery service. Delivers packets to an IP address. Not connection-oriented, not guaranteed reliable. Data viewed as a packet. No acknowledgement that packet was received. Provides routing information from the sender to the receiver.

38 Subnet Layers Network Data Link Physical

39 Role of the Transport Layer Application Presentation Session Transport Network Data Link Physical Application/Service- Oriented Layers Delivery and Verification Services Layer Communication/Network- Oriented Layers

40 Transport Layer Manipulates data and prepares it for delivery (transport) through the network. At the sending end, it breaks large messages into several smaller ones. At the receiving end, it reassembles the smaller packets back into the original message. It has mechanisms for numbering and sequencing packets and for ensuring that messages are complete. Delivers packets to and accepts packets from appropriate “ports”.

41 Transmission Control Protocol (TCP) Connection-oriented, reliable delivery service. Demands that a connection be established before communications can begin. Views data as a stream that is broken into segments and assigned sequence numbers. Delivers packets to a “port”.

42 Connection-Oriented Protocol Setup Request Setup Response Sending Host Receiving Host Network

43 Connection-Oriented Protocol Data Sequence Acknowledgement Sending Host Receiving Host Network

44 Connection-Oriented Protocol Connection Clear Clear Response Host Network

45 Setup Request Setup Response Data Sequence Acknowledgement Connection Clear Clear Response Session

46 User Datagram Protocol (UDP) Another delivery service. Delivers to a particular port. Has some of the features of both TCP and IP. Like TCP, it breaks data into a sequence of packets. Operates at the Transport layer of the OSI Model. Connectionless service, no guarantee of delivery.

47 The Concept of the “Port” TCP/IP Host Port 80 HTTP Port 20 FTP Port 25 SMTP Port 5004 RTP Port 5060 SIP

48 A TCP/IP host may perform many different functions: Transfer web pages Transfer files Transfer media packets between VoIP nodes Transfer SIP commands between SIP nodes

49 Each of these functions uses a different protocol: Transfer web pages – Hypertext Transfer Protocol (HTTP) Transfer files – File Transfer Protocol (FTP) Transfer media files between VoIP nodes – Real- time Protocol (RTP) Transfer SIP commands between SIP nodes – Session Initiation Protocol (SIP)

50 Each of these functions is given a different Port Number: Transfer web pages via HTTP – Port 80 Transfer files via FTP – Port 20 Transfer files via TFTP – Port 69 Transfer media files between VoIP nodes via RTP – Port Transfer VoIP commands between nodes via SIP – Port 5060

51 Socket Connection based on an IP address and a port number. The IP address indicates the host at the other end of the connection. The Port Number indicates the function being performed or the protocol being used.

52 Socket IP Address Port Number Format: : 5004 IP AddressPort Number

53 TCP vs. UDP Connection-oriented Reliable Delivery High overhead Often used by VoIP to setup and control the session. Connectionless “Best-effort” Delivery Low overhead Often used by VoIP to transfer the voice packets.

54 How are TCP and UDP similar? Both are Transport Layer Protocols. Both deliver to ports. Neither was originally intended for voice. Neither is optimized for voice. Either can serve as a delivery mechanism for protocols more suitable to voice such as Real-time Protocol (RTP). Either or both can be used for VoIP.

55 Session Layer Establishes, maintains, and terminates the network connection between nodes. Manages transmission records. Responsible for synchronizing and sequencing the dialog.

56 Presentation Layer Insures that data is in a suitable format. Data conversion Compressing and decompressing data Encoding and decoding character sets In VoIP, it insures that sending and receiving nodes use the proper algorithms to encode and decode the voice.

57 Application Layer Does not contain any of the applications, such as a word processor, that are running on the system. Determines when access to network resources are required, and directs the request to the proper computer. Allows applications to communicate as if they were in the same computer.

58 The OSI Model Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer

Voice Over Internet Protocol (VoIP) Copyright © 2006 Heathkit Company, Inc. All Rights Reserved End