Communication Networks NETW 501 Tutorial 2 Eng. Hadil Hesham hadil.hesham@guc.edu.eg C3.307 Eng. Minar El-Aasser minar.elaasser@guc.edu.eg C3.307

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 TCP: DNS, FTP

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.

Network Interface Layer – Star Network (TCP/IP Model) 10.1 PC1 10.2 PC2 Send data to 10.3 Data 10.3 PC3 Internet Router Switch My MAC is 3B MAC Port 1F 1 2A 2 3B 3 7D 4 2C 5 Who has IP 10.3, reply With MAC Address PC4 10.4 PC5 10.5

Application Request Sequence - EXAMPLE Connection Establishment Data Transfer Interface between TCP & IP

HTTP EXAMPLE : HTTP requesting application Get … HTTP Client HTTP Server 200 OK … (Status) HTML Content Web browser runs an HTTP client program Web server runs an HTTP server program HTTP Protocol HTTP client sends its request message to download the webpage: (Get …message) which includes: Server’s IP address : 2.3 Filename : index.html Host’s IP address : 1.1 HTTP server sends a status response HTTP server send HTML data content

HTTP EXAMPLE (cont’d): TCP connection Establishment HTTP Client It is a logical interface to help the transport layer identify which application process should be contacted [Port : transport-Service Access Point] Q: What is Port? Establish a TCP Connection from port z of 1.1. to port 80 of 2.3 Connection Established Port z Port 80 TCP Connection Request from 1.1 port z to 2.3 port 80 TCP Client TCP Server ACK, TCP Connection Request from 2.3 port 80 to 1.1 port z ACK Before the HTTP client can send anything, a TCP connection must be established TCP connection uses a three-way handshake N.B: At this phase, we have yet to get the HTTP server involved in any communications

HTTP EXAMPLE (cont’d): TCP connection Establishment HTTP uses the TCP connection to transfer data in both directions HTTP Client HTTP Server Get … OK, 200 HTML Content Get … OK, 200 HTML Content Port z Port 80 TCP Send (80, z, Get) TCP Client TCP Server ACK TCP Send (z, 80, Response) ACK

HTTP EXAMPLE (cont’d): Interfacing TCP and IP protocols HTTP Client HTTP Server TCP Client TCP Server Send IP datagram to 2.3 Datagram Received Send IP datagram to 1.1 Datagram Received IP Client IP Network IP Server The role of the IP layer is to attempt its best (best-effort service) to forward data-grams towards their target destination.

HTTP EXAMPLE (cont’d): SUMMARY 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

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