Term Paper• Phase-I is Due on Tuesday, February

19 in class timing —Submit a Hard Copy of your paper (MS word

Document)—Follow the instructions in “Term Paper

Specification” document for Deliverables

• Make group (3 students) by Friday, February 01—Send email to me ‘srizvi@bridgeport.edu’

and CC to GA ’farain@bridgeport.edu’ with the Research Topic, group member’s names, UB-IDs, and emails

OPNET Lab

•Lab 1 (OPNET) is due on next Tuesday, February 04 (2:30 Pm) —Group (2 students)—Make a Report in (word document)—The Report Should have Cover Page—Save the word doc starting from your

“Last Name” plus the “Lab #” (e.g., Rizvi-Lab1)

—Email Report to me ‘srizvi@bridgeport.edu’ & CC to ‘farain@bridgeport.edu’

• GA for CPEG-471 Office hours (Faraz Arain)—Tuesday (12:00 to 2:30 Pm)—Thursday (12:00 to 2:30 Pm)— Other time (send email to farain@bridgeport.edu)

William StallingsData and Computer Communications

Chapter 2Protocols and Architecture

Need For Protocol Architecture• E.g. File transfer

—Source must activate comms. Path or inform network of destination

—Source must check destination is prepared to receive

—File transfer application on source must check destination file management system will accept and store file for his user

—May need file format translation

• Each problem needs to address separately • Task broken into subtasks• Implemented separately in layers in stack

Key Elements of a Protocol• Syntax

—Data formats—Signal levels

• Semantics—Control information—Error handling

• Timing—Speed matching (e.g., indicates flow control)—Sequencing (e.g., avoid packet duplication)

Protocol Architecture • Implementation of File Transfer

—File transfer example can have 4 problems—Implementation of “File Transfer” could use

three modules• File transfer application (Top most layer)• Communication service module (Middle Layer)• Network access module (Lower Layer)

Implementation of File Transfer Architecture

Module-1 Determine weather file transfer app at sys Y is ready to receive file?

Layer1 Determine weather file translation is required or not?

Module-2 Determine weather Computer Y is ready to receive the Data?

Module-3 Determine weather a direct link or an indirect link exists between X & Y

A Three Layer Model1. Network Access Layer2. Transport Layer3. Application Layer

A Three Layer Model• Network Access Layer

—Exchange of data between the computer and the network

—Sending computer provides address of destination—May invoke levels of service (i.e., QoS

parameters)—Dependent on type of network used (packet or

CKT switched Network etc.)

• Transport Layer—Ensures reliable data exchange between 2 hosts

• Application Layer—Support for different user applications—e.g. e-mail, file transfer

Protocol Architectures and Networks

Port

IP Address

A Three Layer Architecture

SAP-1 SAP-2

Y+ SAP-2

Y Y

Y+ SAP-2

Destination SAP

Protocol Data Units

Message-1 Message-2

Protocol data unit (PDU)

Operation of a Protocol Architecture

Open Systems Open Systems Interconnection Interconnection

(OSI)(OSI)

OSI Definition • Open Systems Interconnection

• Developed by the International Organization for Standardization (ISO)

• It has seven layers

• TCP/IP is the refinement of OSI

• Questions —Why TCP/IP doesn’t have presentation & session

layers?—How many layers a reference model should have ?

OSI – Advantage of 7 Layers Model• Each layer performs a subset of the required

communication functions— Sub tasks are assigned to one of the layers depending on the

nature

• Each layer relies on the next lower layer to perform more primitive functions— such as application layer relies on transport layer to send the

data and commands..

• Each layer provides services to the next higher layer— Such as Network layer offer services to Transport layer that can

be used at N/W-Layer SAP

• Changes in one layer should not require changes in other layers— Layers are entirely independent and transparent to other layers

The OSI 7-Layers functioning

OSI as Framework for Standardization

Services are well defined: (Service Definition)

Protocols are well defined:

(Protocol Specification)

Service Primitives and Parameters• Services need to be well defined by means of

service definition

• Services between adjacent layers expressed in terms of primitives and parameters

• Primitives specify function to be performed—Just like Op-code in Assembly

• Parameters pass data and control info—Just like Op-rand in Assembly

TCP/IP Protocol Architecture• TCP/IP was originally developed by the

US Defense Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET)

• 5 Layers of TCP/IP.1. Application Layer2. Transport Layer or Host to host3. Internet Layer or Network Layer4. Network Access Layer or Data Link Layer5. Physical Layer

1- Physical Layer• Responsible to deal with interface

between source & destination• Physical interface between data

transmission device (e.g. computers) and transmission medium or network

• Characteristics of transmission medium• Signal levels• Data rates• etc.

2- Network Access Layer or Data Link Layer

• Exchange of data between end system and the network• Responsible to deliver frames reliably from hop to hop (hop

could be DLL device such as bridges or switches)• If within the LAN, upper layers can leave reliability issues

(error/flow control) on the DLL• Guarantee Error Free Delivery of Data from one hop to

the other (not N/W to N/W OR not end-to-end)• DLL is divided into 2 sub layersDLL is divided into 2 sub layers

Network

Host A

Router

Host B

Host C

Router

Host D

LAN-1 LAN-2

DLL DLL DLL

3- Internet Layer (IP) orNetwork Layer

• Systems may be attached to different networks (such as Host-A at LAN-1 & Host-D at LAN-2)

• Lowest layer that deals with end-to-end transmission• Implemented in end systems and router• Guarantee Error Free Delivery of Packets from one

N/W to the other N/W (not end-to-end)

Host A

Router-1

Host B

Host C

Router-2

Host D

LAN-1 LAN-2

DLL DLL DLL

Network

N/W LayerN/W Layer

R

R

R

R

Layer 4 and Layer 5• Layer 4 Transport Layer

—Guarantee Error Free Delivery of Message from source-host to the destination-host (End-to-End reliability)

—Offers connection oriented and connection less services—Reliability includes: Error detection and correction, flow

control, packet duplication etc…—Runs only on host not on the network

• Layer 5 Application Layer—Provide interface between end-user &

applications—Support several users applications

• For example: FTP, Telnet, SSH, SMTP

OSI v TCP/IP

TCP and UDP• TCP (connection oriented Protocol)

—Establish a reliable logical connection between the source & the destination hosts

—Need to know the source & destination port addresses —Logical connection is monitored by TCP —TCP segments (TCP PDU) can be transmitted through the

secure connection —TCP is reliable but allow relatively slower communication

• UDP (Connection Less Protocol)—Is a connection less protocol—Does not guarantee the reliable transmission of UDP

segments—UDP header has limited control information—Faster but not reliable at all

• Which protocol should I use then (TCP or UDP ???)

TCP/IP Concepts

PDUs in TCP/IP

Some Protocols in TCP/IP Suite

Required Reading• Stallings chapter 2• Comer,D. Internetworking with TCP/IP

volume I• Comer,D. and Stevens,D. Internetworking

with TCP/IP volume II and volume III, Prentice Hall

• Halsall, F. Data Communications, Computer Networks and Open Systems, Addison Wesley

• RFCs