elc 537 communication networks

ELC 537 – Communication Networks

Prepared by:

Dr. Nelly Muhammad Hussein

Modern Academy for Engineering and Technology

Electronics Engineering and Communication Technology Dpt.

Sections & Objectives

Principles of Networking

Explain components and types of computer networks.

Networking Standards

Explain the purpose and characteristics of networking standards.

Physical Components of a Network

Explain the purpose of physical components of a network.

Basic Networking Concepts and Technologies

Configure network connectivity between PCs.


Computer Networks• Computer Network Devices and Components

• Host Devices – any device that sends and receives information on the network (computer, printer, etc.)

• Intermediary Devices – exist in between host devices

• Media – component over which the message travels from source to destination

• Can you name each device or component shown here?


Types of Networks• Major types of networks include:

• Local Area Networks (LANs)

• Wireless Local Area Networks (WLANs)

• Personal Area Networks (PANs)

• Metropolitan Area Networks (MANs)

• Wide Area Networks (WANs)

• Peer-to-Peer Networks• No dedicated servers

• Each computer decides which resources to share

• No central administration or security

• Client-Server Networks• Server with software installed for client access

• Resources controlled by centralized administrator


Reference Models• Organizations, such as lEEE, IETF, and

ISO, develop open standards for networks so that any client running any operating system can access network resources.

• The OSI model and the TCP/IP model are both reference models used to describe the data communication process.

• As application data is passed down through the layers, protocol information is added at each level. This is known as the encapsulation process.


Wired and Wireless Standards• When Ethernet operates in half-duplex, the IEEE 802.3 standard specifies that a

network implement the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access control method.

• The 802.3 standard also specifies cable types for Ethernet including:• 10Base-T

• 100Base-TX

• 1000Base-T

• 10GBase-T

• The IEEE 802.11 standard specifies that wireless LANs use Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA).

WLAN standards include 802.11a, 802.11b, 802.11g, 802.11n, and 802.11ac

When configuring an 802.11 WLAN, use the strongest encryption available.

Since 2006, the strongest encryption has been WPA2.


Network Devices• Modems convert a computer’s digital data into a format that can be

transmitted on the ISP’s network.

• Switches microsegment LANs by sending data only to the computer that needs it.

• Wireless access points (APs) connect wireless devices. Routers use IP addresses to forward traffic to other networks.

• In a home or small office, a route often includes a switch, a firewall, and an AP.


Cables and Connectors• Coaxial and twisted-pair cables use electrical signals over

copper to transmit data. Fiber-optic cables use light signals to transmit data. These cables differ in bandwidth, size, and cost.

• There are several types of coaxial cable: 10Base5 (thicknet), 10Base2 (thinnet), RG-59 (cable TV), RG-6 (better than RG-59)

• Twisted-pair cables are terminated with an RJ-45 connector. Twisted-pair comes in two types:

• Unshielded Twisted-Pair (UTP)• Shielded Twisted-Pair (STP)

• Fiber-optic cables are broadly classified into two types:• Single-mode fiber (SMF) - Uses lasers to send a single ray of light that

can travel hundreds of kilometers.• Multimode fiber (MMF) - Uses LEDs to send multiple light signals that

can travel up to 550 meters.


Cables and Connectors• Twisted-pair is the most popular type of cabling used in

LANs today.

• There are two different twisted-pair wiring schemes: called T568A and T568B.

• Each wiring scheme defines the pinout, or order of wire connections, on the end of the cable.

• Two types of cables can be created: a straight-through cable and a crossover cable.

• A straight-through cable is the most common cable type. The wiring scheme is the same on both sides.

• A crossover cable uses both wiring schemes. T568A on one end of the cable and T568B on the other end of the same cable.


Networked Equipment Addressing• The MAC address is hard coded onto the network interface card (NIC) by the

manufacturer.• The MAC address is 48 bits represented in hexadecimal

• The Internet Protocol (IP) address is assigned by network administrators based on the location within the network.

• Two versions of Internet Protocol (IP) Addressing:• IPv4: 32-bit represented in dotted-decimal• IPv6: 128-bit represented in hexadecimal


Networked Equipment Addressing• Host devices need both addresses to communicate on the network.

• MAC addresses do not change when devices move from one network to another.• IP addresses change because they are based on where the device is in the network.


Networked Equipment Addressing• An IPv4 address is composed of two parts. The first part identifies the

network. The second part identifies a host on that network.

• Computers and routers use the subnet mask to calculate the network portion of the destination IPv4 address.

• A one bit in the subnet mask means that bit is part of the network portion. So the first 24 bits of the 192.168.200.8 address are network bits. The last 8 bits are host bits.


Networked Equipment Addressing• Two rules help reduce the number of digits needed to represent an IPv6

address.• Rule 1 - Omit Leading 0s• Rule 2 – Omit All 0 Segments


Transport Layer Protocols• The two protocols that operate at the transport layer are Transport Control

Protocol (TCP) and User Datagram Protocol (UDP)• TCP is considered reliable, because it ensures that all of the data arrives at the destination. • UDP does not provide for any reliability.


Transport Layer Protocols• TCP and UDP use a

source and destination port number to keep track of application conversations.

• The destination port number is associated with the destination application on the remote device.

• The source port number is dynamically generated by the sending device.

What is a Protocol?

• Allows entities (i.e. application programs) from different systems to communicate

• Shared conventions for communicating information are called protocols

• Includes syntax, semantics, and timing

Why Use Protocol Architecture?

• Data communications requires complex procedures• Sender identifies data path/receiver

• Systems negotiate preparedness

• Applications negotiate preparedness

• Translation of file formats

• For all tasks to occur, high level of cooperation is required

Modular Approach

• Breaks complex tasks into subtasks

• Each module handles specific subset of tasks

• Communication occurs• between different modules on the same system

• between similar modules on different systems

Advantages of Modularity

• Easier application development

• Network can change without all programs being modified

Three-Layer Model

• Distributed data communications involves three primary components:• Networks

• Computers

• Applications

• Three corresponding layers• Network access layer

• Transport layer

• Application layer

Network Access Layer

• Concerned with exchange of data between computer and network

• Includes addressing, routing, prioritizing, etc

• Different networks require different software at this layer

• Example: X.25 standard for network access procedures on packet-switching networks

Transport Layer

• Concerned with reliable transfer of information between applications

• Independent of the nature of the application

• Includes aspects like flow control and error checking

Application Layer

• Logic needed to support various applications

• Each type of application (file transfer, remote access) requires different software on this layer

Addressing

• Each computer on a network requires a unique address on that network

• Each application requires a unique address within the computer to allow support for multiple applications (service access points, or SAP)

Data Transmission

• Application layer creates data block

• Transport layer appends header to create PDU (protocol data unit)• Destination SAP, Sequence #, Error-Detection Code

• Network layer appends another header• Destination computer, facilities (e.g. “priority”)

Simplified Architecture

Protocol Architecture Operation

Standardized Protocol Architectures

• Vendors like standards because they make their products more marketable

• Customers like standards because they enable products from different vendors to interoperate

• Two protocol standards are well-known:• TCP/IP: widely implemented

• OSI: less used, but widely known and still useful for modeling/conceptualizing

TCP/IP

• Transmission Control Protocol/Internet Protocol

• Developed by DARPA

• No official protocol standard

• Identifies 5 Layers• Application

• Host-to-Host (transport)

• Internet

• Network Access

• Physical

TCP/IP Physical Layer

• Physical interface between a DTE (e.g. computer or terminal) and a transmission medium

• Specifies:• Characteristics of medium

• Nature of signals

• Data rate

TCP/IP Network Access

• Exchange of data between systems on a shared network

• Utilizes address of host and destination

• Can also prioritize transmission

• Software at this layer depends on network (e.g. X.25 vs. Ethernet)

• Segregation means that no other software needs to be concerned about net specifics

TCP/IP Internet Layer

• An Internet is an interconnection of two or more networks

• Internet layer handles tasks similar to network access layer, but between networks rather than between nodes on a network

• Uses IP for addressing and routing across networks

• Implemented in workstations and routers

TCP/IP Transport Layer

• Also called host-to-host layer

• Reliable exchange of data between applications

• Uses TCP protocols for transmission

TCP/IP Application Layer

• Logic needed to support variety of applications

• Separate module supports each type of application (e.g. file transfer)

TCP & UDP

• Most TCP/IP applications use TCP for transport layer

• TCP provides a connection (logical association) between two entities to regulate flow check errors

• UDP (User Datagram Protocol) does not maintain a connection, and therefore does not guarantee delivery, preserve sequences, or protect against duplication

IP and IPv6

• IP provides for 32-bit source and destination addresses

• IPv6 (1996 standard) provides for 128-bit addresses

• Migraqtion to IPv6 will be a very slow process

TCP/IP Applications

• SMTP (Simple Mail Transfer Protocol)• Basic e-mail facility, transferring messages among hosts

• FTP (File Transfer Protocol)• Sends files from one system to another on user command

• Telnet• Remote login capability, allowing a user to emulate a terminal on the remote

system

Internetworking

• Interconnected networks, usually implies TCP/IP

• Can appear to users as a single large network

• The global Internet is the largest example, but intranets and extranets are also examples

Routers

• Equipment used to interconnect independent networks

• Several essential functions• Provide a link between networks

• Provide routing and delivery of data between processes on systems from different networks

• Provide the above functions without requiring modification of the attached networks

Router Issues

• Addressing schemes

• Maximum packet size

• Interfaces

• Reliability

TCP Segment (TCP PDU)

• Source port (16 bits)

• Destination port (16 bits)

• Sequence number (32 bits)

• Acknowledgment number (32 bits)

• Data Offset (4 bits)

• Reserved (6 bits)

• Flags (6 bits) : URG, ACK, PSH, RST, SYN, FIN

• Window (16 bits)

• Checksum (16 bits)

• Urgent Pointer (16 bits)

• Options (variable)

IPv4 Header

• Version (4 bits)

• Internet header length (4 bits)

• Type of Service (8 bits)

• Total Length (16 bits)

• Identification (16 bits)

• Flags (3 bits

• Fragment Offset (13 bits)

• Time to Live (8 bits)

• Protocol (8 bits

• Header Checksum (16 bits)

• Source Address ( 32 bits)

• Destination Address (32 bits)

• Options (variable)

• Padding (variable)

Why Study OSI?

• Still an excellent model for conceptualizing and understanding protocol architectures

• Key points:• Modular

• Hierarchical

• Boundaries between layers=interfaces

OSI

• Open Systems Interconnection

• Developed by ISO

• Contains seven layers(see page 358)

• Application

• Presentation

• Session

• Transport

• Network

• Data Link

• Physical

OSI Lower Layers

• Physical

• Data Link

• Network

OSI Physical Layer

• Responsible for transmission of bits

• Always implemented through hardware

• Encompasses mechanical, electrical, and functional interfaces

• e.g. RS-232

OSI Data Link Layer

• Responsible for error-free, reliable transmission of data

• Flow control, error correction

• e.g. HDLC

OSI Network Layer

• Responsible for routing of messages through network

• Concerned with type of switching used (circuit v. packet)

• Handles routing between networks, as well as through packet-switching networks

OSI Upper Layers

• Transport

• Session

• Presentation

• Application

OSI Transport Layer

• Isolates messages from lower and upper layers

• Breaks down message size

• Monitors quality of communications channel

• Selects most efficient communication service necessary for a given transmission

OSI Session Layer

• Establishes logical connections between systems

• Manages log-ons, password exchange, log-offs

• Terminates connection at end of session

OSI Presentation Layer

• Provides format and code conversion services

• Examples • File conversion from ASCII to EBDIC

• Invoking character sequences to generate bold, italics, etc on a printer

OSI Application Layer

• Provides access to network for end-user

• User’s capabilities are determined by what items are available on this layer

TCP/IP - OSI Comparison

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Switched Communications Networks

• Long distance transmission between stations (called “end devices”) is typically done over a network of switching nodes.

• Switching nodes do not concern with content of data. Their purpose is to provide a switching facility that will move the data from node to node until they reach their destination (the end device).

• A collection of nodes and connections forms a communications network.

• In a switched communications network, data entering the network from a station are routed to the destination by being switched from node to node.

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Simple Switching Network

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Switching Nodes

• Nodes may connect to other nodes, or to some stations.

• Network is usually partially connected• However, some redundant connections are desirable for reliability

• Two different switching technologies

• Circuit switching

• Packet switching

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Circuit Switching

• Circuit switching:• There is a dedicated communication path between two stations (end-to-end)• The path is a connected sequence of links between network nodes. On each physical link, a

logical channel is dedicated to the connection.

• Communication via circuit switching has three phases:• Circuit establishment (link by link)

• Routing & resource allocation (FDM or TDM)

• Data transfer• Circuit disconnect

• Deallocate the dedicated resources

• The switches must know how to find the route to the destination and how to allocate bandwidth (channel) to establish a connection.

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Circuit Switching Properties

• Inefficiency• Channel capacity is dedicated for the whole duration of a connection• If no data, capacity is wasted

• Delay• Long initial delay: circuit establishment takes time• Low data delay: after the circuit establishment, information is transmitted at a fixed data rate

with no delay other than the propagation delay. The delay at each node is negligible.

• Developed for voice traffic (public telephone network) but can also applied to data traffic.• For voice connections, the resulting circuit will enjoy a high percentage of utilization because

most of the time one party or the other is talking.• But how about data connections?

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Public Circuit Switched Network

Subscribers: the devices that attach to the network.

Subscriber loop: the link between the subscriber and the network.

Exchanges: the switching centers in the network.

End office: the switching center that directly supports subscribers.

Trunks: the branches between exchanges. They carry multiple voice-frequency

circuits using either FDM or synchronous TDM.

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Packet Switching Principles

• Problem of circuit switching• designed for voice service

• Resources dedicated to a particular call

• For data transmission, much of the time the connection is idle (say, web browsing)

• Data rate is fixed• Both ends must operate at the same rate during the entire period of connection

• Packet switching is designed to address these problems.

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Basic Operation

• Data are transmitted in short packets• Typically at the order of 1000 bytes

• Longer messages are split into series of packets

• Each packet contains a portion of user data plus some control info

• Control info contains at least• Routing (addressing) info, so as to be routed to the intended destination

• Recall the content of an IP header!

• store and forward• On each switching node, packets are received, stored briefly (buffered) and passed on to the

next node.

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Use of Packets

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Advantages of Packet Switching

• Line efficiency• Single node-to-node link can be dynamically shared by many packets over time

• Packets are queued up and transmitted as fast as possible

• Data rate conversion• Each station connects to the local node at its own speed

• In circuit-switching, a connection could be blocked if there lacks free resources. On a packet-switching network, even with heavy traffic, packets are still accepted, by delivery delay increases.

• Priorities can be used• On each node, packets with higher priority can be forwarded first. They will experience less

delay than lower-priority packets.

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Packet Switching Technique

• A station breaks long message into packets

• Packets are sent out to the network sequentially, one at a time

• How will the network handle this stream of packets as it attempts to route them through the network and deliver them to the intended destination?• Two approaches

• Datagram approach

• Virtual circuit approach

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Datagram

• Each packet is treated independently, with no reference to packets that have gone before.• Each node chooses the next node on a packet’s path.

• Packets can take any possible route.

• Packets may arrive at the receiver out of order.

• Packets may go missing.

• It is up to the receiver to re-order packets and recover from missing packets.

• Example: Internet

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Datagram

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Virtual Circuit

• In virtual circuit, a preplanned route is established before any packets are sent, then all packets follow the same route.

• Each packet contains a virtual circuit identifier instead of destination address, and each node on the preestablished route knows where to forward such packets.• The node need not make a routing decision for each packet.

• Example: X.25, Frame Relay, ATM

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VirtualCircuit

A route between stations is

set up prior to data transfer.

All the data packets then

follow the same route.

But there is no dedicated

resources reserved for the

virtual circuit! Packets need

to be stored-and-forwarded.

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Virtual Circuits v Datagram

• Virtual circuits• Network can provide sequencing (packets arrive at the same order) and error control

(retransmission between two nodes).• Packets are forwarded more quickly

• Based on the virtual circuit identifier• No routing decisions to make

• Less reliable• If a node fails, all virtual circuits that pass through that node fail.

• Datagram• No call setup phase

• Good for bursty data, such as Web applications

• More flexible• If a node fails, packets may find an alternate route• Routing can be used to avoid congested parts of the network

elc 537 communication networks

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