Which osi layer has the function of providing reliable transit of data between end hosts?

Cisco Semester 1 (Lessons 6-9 notes)
Instructor: Michael P. Harris

Review

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• Which OSI layer is responsible for reliable data transport?
• Which OSI layer is responsible for providing end
• Which layer of the OSI model is responsible for end
• Which layer provides the end

 OSI Model

----- Host Layers: provide accurate data delivery between computers

7. Application Layer (Network services to apps) - Layer 7 of the OSI reference model. This layer provides services to application processes (such as electronic mail, file transfer, and terminal emulation) that are outside of the OSI model. The application layer identifies and establishes the availability of intended communication partners (and the resources required to connect with them), synchronizes cooperating applications, and establishes agreement on procedures for error recovery and control of data integrity.

6. Presentation Layer (Data representation) - Layer 6 of the OSI reference model. This layer ensures that information sent by the application layer of one system will be readable by the application layer of another. The presentation layer is also concerned with the data structures used by programs and therefore negotiates data transfer syntax for the application layer.

5. Session Layer (Interhost communication) - Layer 5 of the OSI reference model. This layer establishes, manages, and terminates sessions between applications and manages data exchange between presentation layer entities.

4. Transport Layer (End-to-end connection reliability) - Layer 4 of the OSI reference model. This layer is responsible for reliable network communication between end nodes. The transport layer provides mechanisms for the establishment, maintenance, and termination of virtual circuits, transport fault detection and recover, and information flow control.

----- Media Layers: controls physical delivery of the message over the network

3. Network Layer (Addresses and best path) - Layer 3 of the OSI reference model. This layer provides connectivity and path selection between two end systems. The network layer is the layer at which routing occurs.

2. Data Link Layer (Assess to networking media) - Layer 2 of the OSI reference model. This layer provides reliable transit of data across a physical link. The data link layer is concerned with physical addressing, network topology, line discipline, error notification, ordered delivery of frames, and flow control. The IEEE has divided this layer into two sublayers: the MAC sublayer and the LLC sublayer. Sometimes simply called link layer. Bridges and Switchs operates at the data link layer.

1. Physical Layer (Binary transmission; wires, connections, voltages, and data rates) - Layer 1 of the OSI reference model. The physical layer defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems. The function of the physical layer is the transmission of data. Typically such transmission is accomplished through the use of such things as wires, connectors, and voltages. Repeaters operate at the Physical layer.

----- The upper 5 layers are software only
----- Layer 2 is hardware and software
----- Layer 1 is hardware only

Lesson 6

Filter - Generally, a process or device that screens network traffic for certain characteristics, such as source address, destination address, or protocol, and determines whether to forward or discard that traffic based on the established criteria. - Disadvantage of a Reteater (cannot filter traffic)

Hub - 1.) Generally, a term used to describe a device that serves as the center of a star-topology network. 2.) Hardware or software device that contains multiple independent but connected modules of network and internetwork equipment. Hubs can be active (where they repeat signals sent through them) or passive (where they do not repeat, but merely split, signals sent through them). 3.) In Ethernet and IEEE 802.3, an Ethernet multiport repeater, sometimes referred to as a concentrator.

Bit - Binary digit used in the binary numbering system. Can be 0 or 1.

Port - 1.) Interface on an internetworking device (such as a router). 2.) In IP terminology, an upper-layer process that is receiving information from lower layers; 3.) To rewrite software or microcode so that it will run on a different hardware platform or in a different software environment than that for which it was originally designed; 4.) A female plug on a patch panel which accepts the same size plug as an RJ45 jack. Patch cords are used in these ports to cross connect computers wired to the patch panel. It is this cross connection which allows the LAN to function.

Interface - 1.) Connection between two systems or devices; 2.) In routing terminology, a network connection; 3.) In telephony, a shared boundary defined by common physical interconnection characteristics, signal characteristics, and meanings of interchanged signals; 4.) The boundary between adjacent layers of the OSI model.

Segment - 1.) Section of a network that is bounded by bridges, routers, or switches; 2.) In a LAN using a bus topology, a segment is a continuous electrical circuit that is often connected to other such segments with repeaters.

Collision - In Ethernet, the result of two nodes transmitting simultaneously. The frames from each device impact and are damaged when they meet on the physical media.

Collision domain - In Ethernet, the network area within which frames that have collided are propagated. Repeaters and hubs propagate collisions; LAN switches, bridges and routers do not.

Backoff - The retransmission delay enforced when a collision occurs.

Algorithm - Well-defined rule or process for arriving at a solution to a problem. In networking, algorithms are commonly used to determine the best route for traffic from a particular source to a particular destination.

Multi-port repeaters - often called hubs. (In Ethernet 'concentrators' - not intelligent) Generally speaking, the term hub is used instead of repeater when referring to the device that serves as the center of a star topology network. (Operate at OSI layer 1)

* Amplifies signals
* Propagates signals through the network
* no filtering
* no path determination or switching
* used as network consentration point

Bridge - Device that connects and passes packets between two network segments that use the same communications protocol. Bridges operate at the data link layer (layer 2) of the OSI reference model. In general, a bridge will filter, forward, or flood an incoming frame based on the MAC address of that frame. Bridges are only concerned with passing packets, or not passing packets, based on their destination MAC address. Bridges can solve the problem of too much traffic on a network by breaking down the network into segments - but if inter-segment traffic is high a bridge can actually be a bottleneck and slow down the network.

* Internetworking device
* Divides network into segments
* Operates at data link (layer 2) layer of OSI model
* Are not concerned with OSI network layer protocols
* Are required for protocols that do not have an associated network layer
* Filters traffic based on the MAC address
* Used to reduce traffic and minimize likelihood of collisions

Bridge types: transparent and source route

* more intelligent than a hub - can analyse incomming packets and forward (or drop) based on addressing information
* collect and pass packets between two network segments
* control broadcasts to the network
* maintain address tables
* different types of bridge
- transparent
- sourse route (used primarily in Token-Ring LANs)

Mapping - In order to filter or selectively deliver network traffic, bridges build tables of all MAC addresses located on a network and other networks and maps them.

Lesson 7

Broadcast - Data packet that will be sent to all nodes on a network. Broadcasts are identified by a broadcast address.

Broadcast Storm - Undesirable network event in which many broadcasts are sent simultaneously across all network segments. A broadcast storm uses substantial network bandwidth and, typically, causes network time-outs.

IP address - 32-bit address assigned to hosts using TCP/IP. IP addresses are implemented in software and occur at the Network layer of the OSI model. IP addresses use a hierarchical addressing scheme. An IP address belongs to one of five classes (A, B, C, D, or E) and is written as 4 octets separated with periods (dotted decimal format). Each address consists of a network number, an optional subnetwork number, and a host number. The network and subnetwork numbers together are used for routing, while the host number is used to address an individual host within the network or subnetwork. A subnet mask is used to extract network and subnetwork information from the IP address. Also called an Internet address. IP addresses provide an addressing scheme that not only contains the address of the device itself but the network the device is located on as well.

IP - Internet Protocol. Network layer protocol in the TCP/IP stack offering a connectionless internetwork service. IP provides features for addressing, type-of-service specification, fragmentation and reassembly, and security. Documented in RFC 791. See IP address.

Lesson 8

In networking there are two addressing schemes. One uses the MAC address, a data link or layer 2 address, and the other uses the IP (or IPX) address located at the network layer or layer 3 of the OSI model.

Router - Network layer device that uses one or more metrics to determine the optimal path along which network traffic should be forwarded. Routers forward packets from one network to another based on network layer information.

The problem of excessive broadcast traffic can be solved by using a router. Routers are able to do this, because they do not forward broadcast frames unless specifically told to do so.

Routers differ from bridges in several respects. First, bridging occurs at the data link layer or layer 2, while routing occurs at the network layer or layer 3 of the OSI model. Second, bridges use physical or MAC addresses to make data forwarding decisions. Routers use a different addressing scheme that occurs at layer three to make forwarding decisions. They use IP or logical addresses rather than MAC addresses. Finally, bridges are primarily used to connect segments of a network. Routers are used to connect separate networks and to access the world wide Internet. They do this by providing "end to end routing".

Because IP addresses are implemented in software and refer to the network a device is located on, sometimes these layer three addresses are referred to as protocol addresses or network addresses.

Logical address = Network address

Protocol address = Network address

Network address - Network layer address referring to a logical, rather than a physical, network device. Also called a protocol address. Compare with MAC address

Physical or MAC addresses are usually assigned by the NIC card manufacturer and are hard-coded into the NIC card. IP addresses on the other hand are usually assigned by the network administrator.

Internet - Term used to refer to the largest global internetwork, connecting tens of thousands of networks worldwide and having a "culture" that focuses on research and standardization based on real-life use. Many leading-edge network technologies come from the Internet community. The Internet evolved in part from ARPANET. At one time, called the DARPA Internet. Not to be confused with the general term internet.

Network number - each network must have a unique network number. This unique network number is incorporated into the IP address assigned to each device attached to the network.

Network address - Path part of an IP address used by the router

Node address - Specific port or device on the network

The interface where a router connects to a network has the same network number as the network.

Frame - logical grouping of information sent as a data link layer unit over a transmission medium.

Header - control information placed before data when encapsulating that data for network transmission.

Routing table - Table stored in a router or some other internetworking device that keeps track of routes to particular network destinations and, in some cases, metrics associated with those routes.

Lesson 9

Dotted notation - See Dot address

Dot address - Refers to the common notation for IP addresses in the form where each number a represents, in decimal, 1 byte of the 4-byte IP address. Also called dotted notation or four-part dotted notation.

Byte - Term used to refer to a series of consecutive binary digits that are operated upon as a unit (for example, an 8-bit byte).

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Which OSI layer is responsible for reliable data transport?

Which OSI layer is responsible for providing end

Which layer of the OSI model is responsible for end

Which layer provides the end