1. Communication Networks NETW 501 Tutorial 2
Eng. Hadil Hesham C3.307
Eng. Minar El-Aasser C3.307

2. 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

3. 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 s 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.

4. 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

5. 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

6. 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.

7. 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

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

9. 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

10. 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

11. 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

12. 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.

13. 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

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

15. 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.

16. 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

17. Questions?