Book: TCP/IP, Signature Edition by Sidnie Feit (1999, McGraw Hill)
Class notes and slides: http://www. cju .com/classes/ITI510-02
Hands on exercises
By asking lots of questions….
Call or email anytime
Agenda: Meeting 1
Introduction to networks
Network devices – high level overview
LAN vs. WAN
IP – The Internet Protocol
A few small Exercises
What is a computer network?
Formal Definition: Computer Network
A series of points or nodes interconnected by communication paths. Networks can interconnect with other networks and contain subnetworks.
Simple Definition: Computer Network
Connecting computers and/or devices in such a way that they can interact with each other.
Sometimes characterized by Topology
i.e. bus, star or ring network
…by Spatial Distance
Wide Area Network, Local Area Network
…by Type of Data Transmission or what it carries
IP Network, Voice Network, Data Network
…by Type of Physical Link
Fiber Optic Network, Ethernet Network,
In the context of communication networks, a topology pictorially describes the configuration or arrangement of a network, including its nodes and connecting lines.
Three general network topologies:
A bus network is a network topology in which all devices are directly attached to a line and all signals pass through each of the devices. Each device has a unique identity and can recognize those signals intended for it.
“Single String” of network wire
Antiquated technologies such as 10Base2 are considered a bus network.
Examples of Bus Networks
A single wire or a group of small wires is used to create one data path that all traffic flows through.
2 simple examples:
Bus Networks: Advantages and Disadvantages
If one single point in the network is severed, hosts may experience connectivity loss
Possible bandwidth constraints
Each device is attached along the same signal path to two other devices, forming a path in the shape of a ring.
Each device in the ring has a unique address.
Information usually flows in one direction and there is usually a controlling device that intercepts and manages the flow to and from the ring.
Popular ring network technologies are Token Ring and FDDI
Examples of Ring Networks
Simple Example of a Ring Network:
Ring Networks: Advantages and Disadvantages
If a single point of the physical cable is detached, traffic can begin to flow in an the opposite direction – no loss of connectivity.
Possible bandwidth constraints – one single pipe for all traffic
In most cases, every computer sees every bit of traffic across the ring
Each device has a unique path to a central point that distributes data
Each device “hangs” off of a piece of hardware, such as a hub or a switch
Very popular today: Traditional 10BaseT, 100BaseT Ethernet networks use this topology.
Example of Star Networks
Advantages of Star Networks
A single cable break will usually only disrupt service for a single host within a local network segment.
Newer technologies allow you to dedicated and guarantee high bandwidth rates for each individual host or network hanging off of a central switch.
The ability to eliminate packet broadcasts – every computers does not have to see every packet on the network.
Where Networks are Going…
10 Years ago: The 80/20 Rule
80% of all traffic stays on the LOCAL network and only 20% of traffic is sent off to other networks or to the network “backbone”
Typically describes the “workgroup” model of computing: access devices on your local network like file servers, printers, other workstations.
Today: The 20/80 Rule
20% or all traffic stays on the LOCAL network and 80% of traffic is sent to other networks or the network backbone.
Cause by the Increased use of WAN technologies and distributed computing models.
LAN vs. WAN
Local Area Networks (LANs): a group of computers and associated devices that share a common communications line and typically share the resources of a single processor or server within a small geographic area like an office building. Usually privately-owned.
Wide Area Networks (WANs): a geographically dispersed network. It may be privately owned or rented, but the term usually connotes the inclusion of public (shared user) networks like the Internet or the PSTN (Public Switched Telephone Network)
We may use different network technologies, protocols, hardware, etc. to connect devices within a WAN than we use when connecting devices in a LAN.
The OSI Model
OSI (Open Systems Interconnection) is a standard description or "reference model" for how messages should be transmitted between any two points in a telecommunication network.
Its purpose is to guide product implementers so that their products will consistently work with other products.
Developed by representatives of major computer and telecommunication companies in 1983 – now a standard way of examining computer network technologies.
The OSI 7 Layer Model
The general OSI model contains 7 layers (layers 1-7 respectively):
Each layer has a specific function
Depiction of the 7 Layer Model
Layer 7 (Application) is a “high layer”
Layer 1 (Physical is a low layer)
APPLICATION PRESENTATION SESSION TRANSPORT NETWORK DATALINK PHYSICAL Netscape, Outlook, FTP Programs, Internet Explorer HTTP, POP, SMTP Application ports 25 (SMTP), 23 (Telnet) etc. TCP, UDP IP Cables, ASDL, POTS, CAT5, FDDI, etc. SLIP, PPP, Ethernet
TCP/IP 5 Layer Model
TCP/IP, a very popular protocol used in LANs, WANs and the Internet, usually groups the 7-layer model’s Application, Presentation and Session layers into one “Application” layer, resulting in a 5 layer model.
APPLICATION TRANSPORT NETWORK DATALINK PHYSICAL Web Services, Email Services, News Services, etc. TCP, UDP IP Cables, ASDL, POTS, CAT5, FDDI, etc. SLIP, PPP, Ethernet
Description of the 5 Main OSI Layers (5 Layer Model)
Layer 5: The application layer ...This is the layer at which communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. (e.g. Funcationality provided by web browsers, mail reader programs and their associated protocols like HTTP and SMTP)
Layer 4: The transport layer ...This layer manages the end-to-end control and error-checking of network traffic. It checks to see if all packets have arrived and ensures complete data transfer between parties. (e.g. TCP and UDP protcols)
OSI Layers, con’t.
Layer 3: The network layer ...This layer handles the routing of outgoing data (making sure that a packet is sent to the right place) and also handles incoming data. (e.g. IP)
Layer 2: The data-link layer ... This layer defines the rules for sending and receiving data across the physical connection between two systems. (e.g. Ethernet, PPP, SLIP)
Layer 1: The physical layer ... This layer governs hardware connections and byte preparation for transmissions. It is the only layer that involves a physical transfer of information between network nodes. It’s usually responsible for translating electrical impulses into 1s and 0s.
Sending and Receiving Data
Layers only interact with other layers directly above and below them.
When data is sent, it originates at the application layer and moves “down” the OSI layers until it is transmitted to another host.
When data arrives, it originates at the physical layer and moves up the OSI model until it’s received by the application layer.
Typical Flow From Layer to Layer: Sending Data APPLICATION TRANSPORT NETWORK DATALINK PHYSICAL You use MS Outlook to send an email to your friend, [email_address] . The Email “packets” are sent to the Transport Layer The transport layer takes the email and packages it in a format that ensures it will be completely delivered. The Network layer makes sure the email knows how to get to the hotmail.com server The physical layer creates the necessary electrical impulses and trasmits the data over the physical medium. The DLL converts the information from the layers above into 1s and 0s that can be understood by a “peer” on the other end of the phone line or network connection (e.g. your ISP’s modem?) Email Sent Move from Top to Bottom
Typical Flow from Layer to Layer: Receiving Data APPLICATION TRANSPORT NETWORK DATALINK PHYSICAL Your email server receives the full email from the Transport layer and you use a client program (Outlook, Eudora) to read it. The transport ensures that all the pieces of the email have arrived. When it has, it’s passed to the application layer. The Network layer verifies where the email originated from (e.g. What IP address?) The physical layer decodes the electrical impulses it receives into 1s and 0s The DLL converts 1s and 0s received from the physical layer and passes them onto the network layer Email Arrives Move from Bottom to Top
OSI Example Diagram
The OSI model allows hardware and software manufacturers to keep a limited scope when developing and manufacturing
A vendor only has to create a product that can function within its specific layer and interact with only the layers directly above and below
For example, a manufacturer of network cards need only know how to operate within the Physical layer and how to pass data to the Data Link layer – the network card does not need to know anything about the network, transport or application layers.
Example 2: If you are writing a web browser (Application layer), you only need to know how to interact with the Transport layer (usually referred to as the TCP Stack within an operating system)
Introduction to the Internet
The Internet is a global network that is comprised of smaller networks owned by commercial entities, educational institutions, government agencies, etc.
No one “owns” the Internet.
Traffic is carried through the Internet using a hardware (physical layer) and communication links (data link layer).
Host-to-host communication is accomplished using TCP/IP or UDP/IP – the combination of the TCP or UDP transmission layer protocols and the IP (Internet Protocol) network-layer protocol.
IP – The Internet Protocol
In an IP network, individual hosts are distinguished by a unique address, known as an “IP address”
An IP address is comprised of four Octals (8-bit numbers), separated by a decimal point, e.g.:
Each decimal number (126, 14, 34, 18, etc.) has a BINARY equivalent that is used many network equations.
Internet service providers (ISPs) are assigned blocks of IP addresses, which they are free to use on their Internal networks.
ISPs form “peering agreements” with other service providers so they have a pathway other other provider's networks.
ISP networks are connected through hardware devices knows as routers , which are responsible for directing traffic to and from other networks.
IP Networks - Example Rutgers Network 128.6.*.* IP Block UUNET Network 63.*.*.* IP Block SPRINT Network 24.*.*.* IP Block Rutgers obtains connectivity to the Internet from UUNET, their Internet Service Provider UUNET peers with Sprint, which gives UUNET access to Sprint-connected networks and Sprint access to UUNET networks. = Router
IP Addresses: The Numbers Behind the Name
The “common” internet hostnames we use everyday (www.yahoo.com, iti.rutgers.edu, etc.) all have corresponding IP addresses behind them.
Routers move packets and messages from network to network based on IP address – not based on hostname.