Communication Networks NETW 501 Tutorial 3

1. Communication Networks NETW 501Tutorial 3 Eng. Minar El-Aasser minar.elaasser@guc.edu.eg C3.314

2. 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.

3. 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

4. Connection-Oriented & Connectionless Services • Connection-Oriented • Established in three-phases: • Connection setup between two SAPs to initialize state information • SDU transfer • Connection release • E.g. TCP, ATM • Connectionless • Immediate SDU transfer • No connection setup • E.g. UDP, IP • Layered services need not be of same type! • e.g.: TCP operates over IP, IP operates over ATM

5. 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. HTTP SMTP DNS RTP TCP UDP IP Network Interface 1 Network Interface2 Network Interface 3 TCP/IP Protocol Graph

6. 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.

7. Transport Layer (TCP/IP Model) • Offers 2 basic services: • TCP (Transmission Control Protocol) • UDP (User Datagram Protocol)

8. Internet Layer (TCP/IP Model) • 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 Bus Networks

9. 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.

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

11. Encapsulation in TCP/IP model & De-capsulation • 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.. Data Data Data Data Data Segment Transport header Data Packet Network header Transport header Data Frame Frame header Network header Transport header Data Frame header 10101110100010101011011001 Bits

12. Segmentation & Reassembly • A layer may impose a limit on the size of a data block that it can transfer for implementation or other reasons • Thus a layer-n SDU may be too large to be handled as a single unit by layer-(n-1) • Sender side: SDU is segmented into multiple PDUs • Receiver side: multiple PDUs are re-assembled into one SDU Segmentation n-SDU n-PDU n-PDU n-PDU Re-assembly n-SDU n-PDU n-PDU n-PDU

13. 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

14. 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.  • Run the simulation and capture the traffic.  • Examine the captured traffic.

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

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

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

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

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

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

21. Encapsulation Check the highlighted fields

22. Questions?