Communication Networks NETW 501 Tutorial 3 Prepared by: Eng. Minar El-Aasser

NETWORK INTERFACE LAYER TCP & UDP/IP TCP/IP Model Protocol consists of 4 layers. The hourglass shape of the TCP/IP protocol is what makes this protocol very powerful. APPLICATION LAYER (Application, Presentation, Session) TRANSPORT LAYER INTERNET LAYER (Network Layer) NETWORK INTERFACE LAYER (Data link, Physical) HTTP RTP DNS SMTP UDP TCP IP Network Interface 1 Network Interface 3 Network Interface2 TCP/IP Protocol Graph

Application Layer (TCP/IP Model) Provide services that can be used by other applications. It incorporates functions of the top three OSI model. Examples protocol: HTTP (Hyper Text Transfer Protocol) Publishing and receiving HTML pages SMTP (Simple Mail Transfer Protocol) Sending E-mails towards a server. DNS (Domain Name Service) Helps to map ASCII strings to IP addresses. RTP (Real-Time Transfer Protocol) Delivering Audio and Video over the Internet.

Transport Layer (TCP/IP Model) Offers 2 basic services: TCP (Transmission Control Protocol) UDP (User Datagram Protocol) TCP UDP Connection Oriented Transfer (must establish a connection before data is transferred) Apply error recovery and flow control. Concerned with applications that need reliable connections i.e. minimize message bit error, yet delayed is increased. Examples of application protocols running on top of TCP: HTTP, SMTP Connectionless Oriented Transfer. No flow control or message sequencing. Concerned with applications that require quick delivery but have tolerance to some information loss. i.e. minimize delay, yet message bit error is increased Examples of application protocols running on top of UDP: DNS, RTP

Internet Layer (TCP/IP Model) Bus Networks Assume 2 BUS topology networks connected by router. The router is the gateway for each network to the other one. Station (1.1) will send data to station 2.3. Next Hop station is the first station will receive the data from the Tx. Interface is the station in the network domain that will send to the next hop or the Rx station. Router knows that address (1.x) is in network 1 and (2.x) is in network 2

Network Interface Layer (TCP/IP Model) Automatic Resolution Protocol: A protocol that determines/ requests the physical MAC layer of a node when only its IP address is known. Within the same network data are forwarded to destination using MAC address (Physical address). If any station changes it IP address, it can be still recognized.

HTTP EXAMPLE SUMMARY Send the datagram to 2.3 HTTP HTTP TCP TCP IP IP Cleo.guc.edu.eg CNN.com HTTP Send HTTP Request to CNN.com HTTP Establish a connection to 2.3 at port 80 TCP Open TCP connection to 2.3 port 80 TCP IP datagram is a TCP segment for port 80 Send a datagram (which contains a connection request) to 2.3 Send IP data-gram to 2.3 Send IP datagram to 2.3 IP IP IP Frame is an IP datagram Frame is an IP datagram Send the datagram to 1.4 Send the datagram to 2.3 Ethernet Ethernet Ethernet Ethernet Send Ethernet frame to 3f Send Ethernet frame to 1g Router C Router C 2.3 1.4

Encapsulation in TCP/IP model & De-capsulation Data Segment Packet Frame Bits Transport header Network header Frame header 10101110100010101011011001 Protocol Data Unit (PDU) is the generic description to what’s known as segments in transport layer, packets in network layer and frames in data link layer. Packet is the logical grouping of information that includes a header containing control information and data. And it is often interchanged with PDU, segment, datagram, frame..

Peer – Peer Communication Protocol Data Units (PDUs) Piece of data exchanged between peer entities. A GENERIC DESCRITPTON TO WHAT IS KNOWN AS SEGMENT, PACKET or FRAME. Service Data Units (SDUs) Piece of data handed to a layer by an upper layer PDU = SDU + optional header or trailer Service Access Point (SAP) Interface between an upper layer and a lower layer. An SAP has an address that uniquely identifies where the service can be accessed.

Peer – Peer Communication cont’d Data sent from Layer n+1 <-> Layer n Contact Point In layer n Data sent from layer n <-> layer n

Packet Tracer PT has 2 modes: Real time mode; in which networking protocol operate with realistic timings. Simulation mode; you can watch your network run at a slower pace, observing the path that packets take and inspecting them in detail. You can graphically create PDU [Add Simple PDU (ping) or Add Complex PDU] You can allow a scenario to be simulated either dynamically using [Auto Capture/Play] and pause it by repressing [Auto Capture/Play] or manually running the step forward one step in time by pressing [Capture/Forward] You can record or capture what happens as your PDU propagate through the network [Event List]

Packet Tracer Ping : A computer Network tool used to test whether a particular host is reachable across an IP network. In Packet tracer, the Add Simple PDU button is essentially a quick, graphical way to send one-shot pings.

Packet Tracer Packet Sniffer/ Protocol Analyzer: A computer software that can intercept and log data traffic passing over a data network. As data streams travel back and forth over the network, the sniffer "captures" each protocol data unit (PDU) and can decode and analyze its content One of Packet Tracer features is it works as Software Protocol Analyzer or Packet Sniffer - Simulation mode in Packet Tracer captures all network traffic flowing through the entire network but only supports a limited number of protocols. Other packet sniffers software: Wireshark, nytimes

Packet Tracer Activities Activity 3 - Objectives: Explore how PT uses the OSI Model and TCP/IP Protocols.  Creating a Simple PDU (test packet)  Switching from Real-time to Simulation Mode  Examine Packet Processing and Contents  Accessing the PDU Information Window, OSI Model View  Investigating Device algorithms in the OSI Model View Inbound and Outbound PDUs  Animations of packet Flow

Packet Tracer Activities Activity 4 - Objectives: Capture a ping from a PC command prompt.  Run the simulation and capture the traffic.  Examine the captured traffic. Capture a web request using a URL from a PC. 

Event List shows the frame/packet sequence Using Packet Tracer as Protocol Analyzer [HTTP Client/Server Communication Example] Event List shows the frame/packet sequence Clicking on the colored square box shows the encapsulation for its frame

Successive screenshots of packet tracer event-list; showing the sequence of HTTP client/server communication.  

DNS Query – [HTTP Client/Server Communication Example Cont’d] DNS Query & Reply

TCP 3 Handshake Connection Setup [HTTP Client/Server Communication Example Cont’d] TCP Connection Setup

HTTP Request & Response [HTTP Client/Server Communication Example Cont’d]

Encapsulation Check the highlighted fields Protocol Type of data encapsulated from upper Layer (IP) Protocol Type of data encapsulated from upper Layer (TCP) Incoming traffic details (of the selected event) Outgoing traffic details (of the selected event) Check the highlighted fields

Encapsulation Check the highlighted fields

Questions?