Chapter 4: Network Access

The data link and physical layer

Data is transmitted through a physical cable

Data is transmitted using radio waves. To offer wireless capability, devices on a wireless network must be connected to a wireless access point (AP).

Integrated Sevice Routers (ISRs)

Ethernet NICs (Network Interface Cards)

WLAN (Wireless Local Area Network) NICs

The means to transport the bits that make up a data link layer frame across the network media. This layer accepts a complete frame from the data link layer and encodes it as a series of signals that are transmitted onto the local media. The encoded bits that comprise a frame are

The Signals are patterns of electrical pulses.

patterns of light

patterns of microwave transmissions

Encoding or line encoding is a method of converting a stream of data bits into a predefined "code". Codes are groupings of bits used to provide a predictable pattern that can be recognized by both the sender and the receiver. In the case of networking, encoding is a pattern of voltage or current used to represent bits; the 0's and 1s.

data transfer speed. *The capacity of a medium to carry data* Bandwidth is the capacity of a medium to carry data. The amount of data that can flow from one place to another in a given amount of time

Kilobits per second > kb/s Megabits per second > Mb/s Gigabits > Gb/s

The measure of the transfer of bits across the media over a given period of time. Throughout = A measure of the transfer of bits across the media. *The measure of the bits transferred across media over a given period of time* The maximum throughput between any two nodes on a network is determined by the slowest link between those nodes.

UTP > Unshielded Twisted-Pair STP > Shielded Twisted Pair Coaxial

[1] Single-mode fiber (SMF): Consists of a very small core and uses expensive laser tech to send a single ray of light. Popular in long-distance situations spanning hundreds of kilometers, such as those required in long haul telephony and cable TV applications. [2] Multi-mode Fiber (MMF): Consists of a larger core and uses LED emitters to send light pulses. Light from an LED enters the multimode fiber at different angles. popular in LANs because they can be powered by low cost LEDs. It provides bandwidth up to GB/s over link lengths of up to 550 meters.

Bluetooth!

Concentrates the wireless signals from users and connects to the existing copper-based network infrastructure, such as ethernet.

Logical Link Control (LLC): this upper sublayer communicates with the network layer. Media Access Control (MAC): this lower sublayer defines the media access processes performed by the hardware. It provides data link layer addressing and across to various network technologies

Without the data link layer, network protocols such as IP, would have to make provisions for connecting to every type of media that could exist along a delivery path. Moreover, IP would hav to adapt every time a new network technoplogy or medium developed. This process would hamper protocol and network media innovtioon and development. This is a key reason for using a layered apprtoachj to networking

*Physical Topology*: refers to the physical connections and identifies how end devices and infrastrcuture devices such as routers, switches, and wioreless access points are interconnected. Physical topologies are usually point to point or star. *Logical Topology*: refers to the way a network transfers frames from one node to the next. This arrangement consists of virtual connections between the nodes of a network. These logical signal paths are defined by data link layer protocols. It is the logical topology that influences the type of network framing and media access control used.

Point to point, Hub & Spoke, Mesh *Point-to-Point* - This is the simplest topology that consists of a permanent link between two endpoints. For this reason, this is a very popular WAN topology. *Hub and Spoke* - A WAN version of the star topology in which a central site interconnects branch sites using point-to-point links. *Mesh* - This topology provides high availability, but requires that every end system be interconnected to every other system. Therefore, the administrative and physical costs can be significant. Each link is essentially a point-to-point link to the other node.*

The TCP/IP network access layer is the equivalent of the OSI data link layer (Layer 2) and the physical layer (Layer 1).

Rollover. UTP cable wire pairs can be terminated in different configurations for use in different applications. To use a UTP cable for consoling into a Cisco router from a PC serial port, it must be terminated as a rollover or console cable.

transmitting bits across the local media The physical layer is responsible for transmitting the actual signals across the physical media as bits. Exchanging frames, controlling media access, and performing error detection are all functions of the data link layer.

to identify which network layer protocol is being used. Defining the media access processes that are performed by the hardware and providing data link layer addressing are functions of the MAC sublayer. The data link layer accepts Layer 3 packets and packages them into data units that are called frames.

1. Greater distances per cable run 2. Limited susceptibility to EMI/RFI 3. Greater bandwidth potential

A straight-through cable can have either a T568A or T568B standard termination at one end and the same at the other end. A crossover cable has a T568A standard termination at one end and a T568B standard at the other end. A rollover cable can have either a T568A or T568B standard termination at one end, and at the other end have the same standard, but with the wires connected in reverse order. A fiber-optic cable is not terminated using RJ-45 connectors.

CSMA/CA *Refer to curriculum topic: 4.2.4* Carrier sense multiple access with collision avoidance (CSMA/CA) is used with wireless networking technology to mediate media contention. Carrier sense multiple access with collision detection (CSMA/CD) is used with wired Ethernet technology to mediate media contention. Priority ordering and token passing are not used (or not a method) for media access control.

The transmitting node inserts start and stop bits into the frame.

Error Detection

To Verify the integrity of the received frame

LLC - Logical Link Control

Twisting the wires together into pairs

Full Duplex

[1] It Provides media access control and performs error detection [2] It accepts layer 3 packets and encapsulates them into frames

They allow for full-duplex connectivity

RJ-45 (check answer)

Data Link Layer

The distortion of the transmitted messages from signals carried in adjacent wires

[1] To distinguish data bits from control bits [2] To identify where the frame starts and ends

[1] Security [2] Coverage Area [3] Interference The three areas of concern for wireless networks focus on the size of the coverage area, any nearby interference, and providing network security. Extensive cabling is not a concern for wireless networks, as a wireless network will require minimal cabling for providing wireless access to hosts. Mobility options are not a component of the areas of concern for wireless networks.