Block 1 unit 4
Layer _ Presentation layer
(6) responsible for formatting and code conversion of the information sent to the application layer for further processing or display. ensures that the information sent is reformatted back into the same format as the original and renders the underlying code into words, pictures, video or audio supported by the application in the application layer.
Layer _ Application
(7) the programs that the user will interact with, it open what was sent or creates what is to be sent. It includes but is not limited to resource sharing, remote file access, remote printer access and network management processes. Information at this layer is referred to as data.
the following should be done at this layer: (distribution layer)
- Implement tools such as access lists, packet filtering, queuing, security and network policies; including address translation and firewalls. - Redistribute between routing protocols, including static routing. - Route between VLANs and other workgroup support functions. - Define broadcast and multicast domains.
MMF features
- Larger core (50 to 62.5 microns) - Light Dispersion (Can use LED light as source - Long distance application under 2 km
SMF features
- Small Core (8 to 10 microns) - Less Dispersion (Uses laser light as source) - Suited for long distance application up to 100 km (62 miles)
802.11b
11 Mbps, 2.4 GHz
802.11ac
2.4 GHz or 5 GHz; 1.3 Gbps
802.11n
2.4GHz or 5GHz up to 600mbps
802.11a
5 GHz, 54 Mbps
802.11g
54 Mbps, 2.4 GHz
Guided/Bounded Media
A LAN using coaxial cable, twisted-pair cable, or fiber optic cable is using ______
Bridge
A bridge is a network device that connects two or more network segments and effectively joining them into one physical network at layer 2.The two segments being joined together do not have to be the same topology (the way the network is physically laid out). they also join two different types of media together.
4
A category type STP cable contains ____ pairs of wire where each pair is wrapped in an insulating metallic foil. The ____ insulated pairs are then wrapped together in an outer metallic braid or foil called the jacket
Mesh Topology
A mesh topology is a highly advanced network topology that offers superior redundancy and reliability. Each device is connected to every other device by separate cabling. This configuration provides redundant paths throughout the entire network so that if any connection fail, another will take over the traffic. Therefore in a __ topology communication will never cease, all device will always communicate even when there is a link failure because a path can be found through another host.
Switches
A network ____ is a networking device that connects host devices together on a LAN. ____ will receive, process and forward frames to the destination device based on the MAC address.
Domain controller
A server that is responsible for allowing host access to Windows domain resources. The __ are the centerpiece of the directory service known as Active Directory. It stores user account information, authenticates users and enforces security policy for a Windows domain.
SNMP - Port 161
A set of protocols created to permit remote monitoring and management of devices such as Switches and Routers over the network
Application
All networks are built to do something. This is where the __ comes into play, it might be that your network is for playing games, streaming content (audio/video) or processing data. Whatever it does, it must have the application program that support it.
application layer; transport layer; Internet layer; network interface layer
An analogy of how the TCP/IP network communication process works can be compared to our postal system when sending a letter. First - you write the letter (____); second - you determine how you are going to send it, regular mail or special delivery (____). On the network this is automatically done based on the protocol used at the application layer. Third - you package and address the letter, on the network this too is automatically done based on how it is being sent (____). Fourth - you mail the letter by putting it in a mailbox (____).
DARPA ; TCP/IP model
Another model grew out what the __ was doing and it became known as the __ of simply the DOD model.
Layer 7
Application layer.
WWW (World Wide Web)
As WANs are connected to other WANs they form an even larger WAN that encompasses the world. A global network commonly referred to as the internet.
Networks (cont. detention)
As a minimum all __ will have at least 2 connected devices. The devices are connected together through either copper wire, fiber optic cable or wireless via radio frequency and infrared light beams.
Layer 4 - Transport Layer
At the sending computer, this layer packages data by dividing it into manageable parts called segments and adds source and destination port numbers in the header of each segment. At the receiving computer, the __ opens the segments and reassembles them into the original data format and structure. Typically, this layer also sends an acknowledgment that the data was received. If a segment arrive with error, this layer will request a retransmission of the erroneous segment.
Scalability for the Core
Avoid expanding the core when the internetwork grows (that is, adding routers). If performance becomes an issue in the core, give preference to upgrades over expansion.
CAN (Campus Area Network) or BAN (base area network)
College campuses, universities, hospitals, schools or military installations
Networks
Connecting computers together to share files, folders, or other resources.
Port 53
DNS (Domain name service)
Layer 2
Data Link Layer
Reliability and Redundancy for the Core
Design the core for high _ and _. Consider technologies or Medias that facilitate both speed and redundancy.
Workgroups for the Core
Don't support ____ access by connecting devices that belong to the access layer. This defeats the concept of the hierarchical model and the core layer.
Layer 6 - Presentation Layer
Encryption and data compression is also typically done at this layer.
Port 21
FTP Control (Establish connection)
Port 20
FTP Data (Data transfer)
MAN (Metropolitan Area Network)
Geographic area the size of a town or a city; it is mainly determined by the sociopolitical boundary of where the district authority control extends.
WAN
Geographically dispersed network that can span across the city, state, country or worldwide. It may be privately owned or rented, but usually denotes inclusion of public (open) networks
Port 80
HTTP (Hypertext Transfer Protocol)
Port 143
IMAP4 (Internet message access protocol version 4)
P2P
In this environment each computer will assume both the role of being a server and a client depending on where the information is located and what it is trying to do. If the information is on "Host A" and "Host B" wants to access that information, then "Host A" will be the server and "Host B" will be the client. The roles will reverse as necessary during the retrieval of information for all the computers in this type of environment.
CLIENT / SERVER
In this type of environment the computers are dedicated to a specific role throughout its life on the network. Its role will not change from being a __ to a __ or vice versa
TCP/IP Model - Layer 3 - The Transport Layer
It is responsible for flow control of data between hosts and will use one of two vastly different transport protocols: Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). It also acknowledges when a packet has reached its destination
Star Topology
It uses a central node called a switch to connect peripheral nodes. The switch offers a common connection for all devices (host, nodes) on the network. All transmissions go through the central switch, which simultaneously re transmits the data to the respected attached nodes on the network. Other attached nodes can be a printer, IP-phone, server, secondary switches or gateway router that the central switch is connected to.
router port
It's important that you understand that each ______ (interface) is also consider a broadcast domain, and is used as the default gateway for all hosts connected to it. Without routers there would not be any way to distinguish one network or subnet from another; in fact the internet would not exist as we know it. Therefore, routers will have multiple interfaces where each interface will be connected to a different network or subnet as well as having different Network/subnet addresses.
Advantages of Unguided Media
Mobility - Since there is no physical cabling to tie the node/host to a specific location; a mobile device can truly be mobile so long as it is within range of an AP.
Port 137
NBNS (Microsoft NetBIOS Name Service)
Media Access Control (MAC) address.
NICs are encoded with an address commonly referred to as the ________. This ______ address is sufficient for the device to communicate on the local area network (LAN) but is not capable of communicating over the internet. To achieve internet communication another protocol such as Internet Protocol (IPv4 or IPv6) is employ.
Layer 3
Network Layer
Proxy servers
Normally reside between a client program (typically a Web browser) and an external server (typically another server on the Web) to filter requests, improve performance, and share connections.
Hybrid
Often, a mesh topology is used in conjunction with other topologies to form a __ topology, this allows for redundancy in critical areas while keeping cost under control.
Port 110
POP3 (Post Office Protocol version 3)
Layer 1
Physical Layer
Layer 6
Presentation layer
Intranet
Private network that is established for internal users of a company or organization. Think of the 338th TRS.
1-20 (GHz)
Radio waves used for networking purposes are typically microwave frequencies in the ____ range.
Port 25
SMTP (Simple Mail Transfer Protocol)
Port 161
SNMP (simple network management protocol)
Web server
Serves static content to a Web browser by loading a file from a disk and serving it across the network to a user's Web browser. This entire exchange is mediated by the browser and server talking to each other using HTTP
Layer 5
Session layer
The following functions would be included at this layer: (Access Layer)
Shared bandwidth devices Switched bandwidth devices Layer 2 functions such as VLAN membership Traffic filtering based on MAC Breaks up collision domains.
GAN (Global Area Network)
Single network with access (connection) points spread around the world. Think of it as a private intranet with world wide access points.
LAN
Small network usually confined to a single building, or group of buildings, or group of buildings that normally doesn't exceed two kilometers in diameter and contains a modest number of computers.
Port 23
TELNET (TELetype NETwork)
Port 69
TFTP (Trivial file transfer protocol)
must be capable of handling large amounts of traffic
The Distribution layer is also an aggregation point for multiple access switches and ________. Both layer 2 Ethernet Switches and layer 3 Routers are employed at this layer.
OSI Model
The __ established a 7 layers system where each layer is responsible for managing a particular aspect of the network operation. After each layer completes its function it will send the data to either the layer above or below itself depending on if it is sending or receiving data. Thus each layer is always in communication with two other layers.
major benefit of STP
The ____ is that it reduces electrical noise both within the cable (pair-to-pair crosstalk) and outside the cable (Electromagnetic Interference (EMI) and Radio Frequency (RF) Interference).
NIC
The _______ can be wired to accept the RJ45 connector for category type wiring, fiber optics connectors or wireless using the 802.11 Wi-Fi standard.
Access Layer
The access layer ensures that frames are delivered to the end user computers. It is an aggregation point where switches connect nodes (hosts) such as workstations to the network. Referred to as the desktop layer as well.
Media
The cable that will connect the devices together. Devices can also be connected wirelessly eliminating the need for the physical cable.
NIC (Network Adapter aka Network Interface Card)
The device that will allow the (host) computer to actually connect to the network. NICs can be wired or wireless.
Distribution Layer
The distribution layer is the communication point between the access layer and the core layer. The primary function of the __ is to provide routing, filtering, WAN access and to determine how packets can access the core when necessary. The distribution layer must determine the fastest way that user requests are serviced (for example, how a file request is forwarded to a server). Remote services too.
Bus Topology
The simplest topology form is the bus which consists of a main cable also called Trunk or Backbone with only two end points. When installed it runs from area to area usually in ceilings with short drop cables attached by T- connectors or an attachment user interface (AUI) cable.
Uninterruptible Power Supply (UPS)
These act as "battery backup" to plug the network devices into. They will convert the battery direct current (DC) to alternating Current (AC) to power the device in the event of power fluctuation, brown out, or a loss of power for any reason.
Nodes (Host or Client Server)
These are the devices that are connected to the network. They can be the computers that the users will use to access the resources or they can also be an online resource device (i.e. printers or servers). In either case it will have a unique IP address to identify it on the network
Facility (Backup) generators
These are used in conjunction with UPS' to maintain power to the network (or facility) during loss of commercial power. These generators normally require a fuel source such as natural gas, diesel, or gasoline, and will automatically startup at the loss of commercial power.
Resources
This can be any of the devices that is shared over the network. It can be Servers, Printers, Scanners, and Folders; anything that the users will access over the network.
Router
This device is essential if you want your network to have access to the internet or other LANs and WANs. The __ will be the gateway device for all the hosts on your local network.
Other Unguided media
This includes Laser, Microwave, Bluetooth and Infrared. Laser is a line of sight (LOS) media and can be defeated by various atmospheric conditions such as rain, fog, dust and bright sun light. Precise alignment between the transmitter and receiver is essential to ensure communication.
CSMA
This is a contention method that network devices use for accessing a common shared network media. The protocol will check the media to determine if there is any data being transmitted by listening for a carrier signal before attempting to use the media (Carrier Sense)
FTP - Port 20 & 21
This is a method of transferring data files from one device to another over a network by dividing files into several segments and assigns a reference number to each one. These segments are transmitted in a sequence which the receiving device reassembles as an exact copy of the original.
CD
This is a set of rules that determines how network devices respond when two devices should simultaneously access the media to transmit data, this is the collision. Standard Ethernet networks use ______ to monitor the traffic on the cable
TCP/IP Model - Layer 2 - The Internet Layer
This is identical to layer 3 of the OSI model and has the same function and responsibilities. It is responsible for IP addressing, routed and routing protocols, along with Internet Control Message Protocol (ICMP), and Internet Group Management Protocol (IGMP).
TCP/IP Model
This model is often referred to by different names such as the internet model, DOD model or DARPA model; it has four layers that correspond to one or more of the OSI model.
Physical Topology
This refers to the physical interconnection of network devices. Simply put it is the physical (geographic) layout of the network devices and their interconnections.
Mail servers
This server is setup to manage mail receipt and delivery over the networks whether on a LAN or across the Internet.
File Transfer Protocol (FTP) server
This server makes it possible to move files securely while providing organization as well as transfer control.
Application servers
This server usually houses database and other common access apps programs that is used across the network by the users at the clients workstations.
File server
This server usually serves as a repository on the network for users to store and retrieve files. You can also see the server being referred to as network attached servers (NAS).
Redundant power supplies
This will enable a device to stay powered on when there is a loss of the primary hardware power unit. These are normally internal to the device itself.
Layer 4
Transport Layer
3 to 6 feet
Typically a patch cable can be ____ in length but can be longer or shorter depending on where it is used or what it is used for.
8
UTP for computer network contains _____ insulated wires where two wires are twisted together to form each pair, a precise number of twist per meter helps to reduce any crosstalk that may occur
Multimedia servers
Used to bring audio and video capabilities to the network by enabling them to broadcast streaming multimedia content.
protocols
__ only communicate with another protocol of its own kind (i.e. Transmission Control Protocol (TCP) will only communicate with TCP). This added complexity to building networks as organizations would use their own proprietary protocols and hardware for their network.
Speed for the Core
____ layers must be designed with speed in mind. Don't do anything to slow down traffic such as applying access control lists, routing, and packet filtering when possible.
SSH - Port 22
____ replaced Telnet for remote management (administering) of a device. It encrypts both login and data sent during the session. This protocol is used primarily for remote management of switches and routers as it allows the administrator the ability to login and execute commands on a remote device.
CA
a network contention protocol but it listens to the network first in order to avoid collisions. After listening to the network and not detecting a carries signal ____ will transmit an intent signal to reserve the frequency band stopping other devices from using it. After this the device reserving the frequency band is free to (use it) transmit data without any collision occurring.
HTTP - Port 80
a protocol that allows you to browse websites using a web browser
Gateways
can be a router or a special purpose device, it will acts as a translator or connector between networks that are using different operating systems, protocols, data format structures, or network hardware.
TCP/IP Model - Layer 1 - The Network Interface Layer
combination of the Physical (layer 1) and Data Link (layer 2) of the OSI model. It does everything from defining how the NIC will connect to the network to MAC address and frame structuring the data
TCP/IP Model - Layer 4 - The Application Layer
combines the features of the top three layers of the OSI Model into one layer. Every __ must know how to initiate, control, and disconnect from a remote system; there is no single method for doing this so each application may uses its own method.
STP
combines the techniques of shielding to a twisted pair of wires to further protect against signal degradation.
Roll Over
commonly referred to as a console cable, and is used to connect a computer to the console port of a switch or router to be configured. The pins are exactly opposite on the ends of the cables. Pay close attention to all the wire colors on both connectors.
Cross-Over
connect like devices, such as switch to switch or router to router. The transmit (TX) and receive (RX) pins on the end of an Ethernet cable are swapped. This allows for the TX of one device to connect to the RX of the connected device on the opposite end of the cable. Pay close attention to pins 1, 2, 3 and 6 on both connectors.
Straight Through
connect two unlike devices. This type of cable primarily serves as an extension from one device output to another device input.
UDP
connection-less protocol that provides a much simpler service to the application layer. It just sends packets of data called datagrams from one host to the other, but there is no guarantee that the datagrams reach the other end.
Fiber Optic Cabling
converts electrical signals (ones and zeros [binary]) into optical signals (on and off lighting). Optical signals are transmitted through a thin glass fiber. At the receiving end the light signals are converted back into electrical signals to recreate the binary ones and zeros. Since ______ are light-based transmission they are immune to interference generated by RF and EMI devices.
Layer 1 - Physical layer
defines how the Network Interface Card (NIC) will connect to the network. For example, will it connect through wired technology such as fiber optic cable, copper twisted pair (i.e. Cat 5), wireless using radio frequency (RF) or other technology.
DHCP Server
eases the administrative burden of assigning specific static IP addresses to each device on the network by automating the assignment process. Other information the ___ will provide also includes subnet masks, default gateway and DNS.
Protocols for the Core
elect routing __ with lower convergence times or extremely fast and efficient switching devices like Asynchronous Transfer Mode (ATM).
Layer 2 Data Link Layer
ensures communication between the network layer and the physical layer. It provides structure to the raw bit stream by grouping the bits into a logical frame.
Open System Interconnect (OSI) reference model
established a committee that developed a conceptual network model that took into account hardware interfaces, software interfaces, and the protocols that defined how network entities relate to each other.
Layer 5 Session layer
establishes communication sessions between processes on different devices. establishes controls and ends the sessions between local and remote applications.
Cisco Hierarchical Model
industry wide internetworking model used for designing a reliable, scalable, and cost-efficient network. involves dividing the network into discrete layers. Each layer provides specific functions that define its role within the overall network. This helps the network designer to optimize and select the right network hardware, software, and features to perform specific function at that layer
Network Gateway
inter-networking system capable of joining together two networks that use different base protocols. A _____ can be implemented completely in software, completely in hardware or a combination of the two. Depending on the types of protocols they support, _____ can operate at any layer of the OSI reference model and will also act as translators.
DHCP - Port 67
is a protocol for automatically assigning dynamic IP addresses to devices on a network.
Redundant Options
is essential to maintain a quality of service or service in general. Simply put, it is the duplication of connections, devices, or power units that can be used in the event the primary connection, device, or power unit failure.
Logical Topology
is how the information is passed through the network. It is bound to network protocols and usually referred to as signal flow. By definition it is the way the network operates or how the data travels or moves through the network.
Default Gateway
is the device that passes traffic from the local subnet to other subnets. Routers are the _____, the place where two or more networks connect; thus they are also defined as the entry/exit point to/from a network or subnet
Telnet Port 23
is used to connect a host to a remote device. This protocol is useful for remote management of switches and routers, however, it is not secure and has been replaced (in most environments) by Secure Shell (SSH).
Application Layer Protocols
it deals with how humans will enter information and receive information.
Redundancy disadvantage
it would be cost. This is also what makes redundancy impractical for many networks. Providing redundancy for every vital link, piece of equipment, or constant power will eat deep into the networking budget. Redundancy must be balance against mission criticality or the cost of recovering the data that would otherwise be lost during power outage or equipment or link(s) going down.
Radio Frequency
may be land-based or space-based transmissions or they can also originate from a land based system and bounced off satellites. The larger the broadcast range of space-based transmissions, the more susceptible they become to being monitored
Twisted pair
most common wired media for network connectivity. The __ configuration limits signal degradation (cross talk) from electromagnetic interference (EMI) and radio frequency interference (RFI). ___- has precise specifications governing the number of twists or braids permitted per meter. Twisted pair is a copper wire-based cable that can be either unshielded (UTP) or shielded (STP).
UTP
most economical (by default most popular) choice among communication cables. In most cases, ____ is implemented using inexpensive, modular telephone-type connectors such as the RJ-11 (two pair, common telephone line) and the RJ-45 (four pair, data) connectors.
Routers
networking devices that operate at layer 3 (Network Layer) of the OSI model. They are needed to establish the various networks and subnets that hosts are connected to. They will intelligently forward frames/packets from one broadcast domain to another.
TCP
onnection-oriented protocol that provides a reliable flow of data and ordered data reconstruction between hosts (End to end transmission). Because this reliable flow of data is provided by the transport layer, the application layer can ignore all these details.
Layer 5 - Session Layer
performs name-recognition and other functions, such as security and synchronization that are needed to allow applications to communicate over the network.
Protocols
present at all layers of every networking model in use. They define how addressing is done (IP), how the devices will communicate (TCP or UDP), how files are transferred (FTP, HTTP), and others.
A Switch
provide connectivity for all the devices that will be on the network. Also with multiple hosts connected, the __ will provide a dedicated connection for each device
DNS - Port 53
provides a friendly hostname to IP address for devices on the network. It lets you use a hostname rather than the IP address to refer to device.
The topology
refers to the way the network is physically connected or how its signal will flow to communicate.
Layer 3 Network Layer
responsible for addressing packets with a logical addresses such as IP and routing of packets. It specifies how addresses are assigned and how packets of data are forwarded from one network to another. It determines which path packets should take to get to their destination by using Routing protocols. Access control lists are also applied at this layer to control packets flow and user access. Data units at this layer are called packets.
Layer 4 Transport Layer
responsible for flow control, end-to-end error recovery, and data delivery to the appropriate application process on the host computers. ensures data is delivered error free, in sequence, and without losses or duplication.
The American National Standards Institute (ANSI)
specifies categories of UTP in terms of data rates they can sustain. Categories describe the media as well as the types of connectors to be used.
PROTOCOLS
system of rules that governs how computer networking devices will communicate
Core Layer
the top of the hierarchy literally is also called the backbone. This layers' only purpose is to transport large amounts of traffic reliably and quickly. The traffic transported across the __ is common to a majority of users.
Layer 2 - Data Link Layer
this layer is the protocol layer that transfers data between adjacent network nodes in a wide area network (WAN) or between nodes on the same local area network (LAN) segment based on the MAC address.
E-mail Gateway
translate messages from one vendor's messaging application to another vendor's application. It also incorporates advanced security features that allow for defense against phishing attacks, malware and other email-borne threats such as spam, viruses, bulk emails, directory harvesting, and denial of service attacks.
Unguided/Unbound Media
transmissions are wireless. They have no physical constraints confining the signal to a set path. Atmospheric conditions, natural structures and man-made structures can impair wireless transmission, degrading the signal strength and quality. The lack of physical cabling to tie down a node to a specific location on a network enables the hosts to be flexible or mobile. Wireless media includes laser-light transmissions, infra-red (IR) and radio frequency (RF).
Layer 1 Physical Layer
transmits the unstructured, raw bit stream over a physical medium (such as the network cable) hardware- oriented and deals with all aspects of establishing and maintaining a physical link between communicating computers. The physical layer carries the signals that transmit data generated by each of the higher layers.
MMF
typically has a core diameter of 50 to 100 microns. This relatively large core allows many modes, or paths, of light to propagate down the optic cable. _____ is good for when using inexpensive couplers or connectors that does not require precise tolerances when plugged in, and LED light sources.
Patch Cables
used to make a variety of connections between devices on the network, to interface with a device to configure it or aid in troubleshooting an issue. The Telecommunications Industry Association (TIA) has establish the pin layouts for some patch cables based on the T-586A standard for network cables.
SMTP - Port 25
used to transfer e-mail messages and attachments. This protocol is built into the e-mail client and e-mail server software. SMTP operates in the Application, Presentation, and Session layer of the OSI Reference model.
core
user data is processed at the distribution layer, and the distribution layer forwards the requests to the __ when necessary. Keep in mind that a failure in the __ will affect every user especially to the outside world. Therefore, fault tolerance at this layer is essential through redundancy.
SMF
uses a glass fiber that is approximately 10 microns in diameter and permits a single mode (path) of light to be propagated using lasers as the light source. ____ can support much longer segments than any other guided media.
Advantages of Star Topology:
• Easy to expand (i.e. add more devices, switches, nodes, host, etc.) • More suited for larger networks. • Easy to monitor and troubleshoot individual devices. • Can accommodate different types of cabling. • Allows nodes to communicate with any/all other nodes. • A break in an individual host cable will only affect that host, not the entire network. • Central switches are easy to maintain and manage.
Advantages of Mesh Topology:
• Greater fault tolerance. • Maintains stability, privacy, and safety. • Point-to-point links make fault identification and fault isolation easy.
Disadvantages of a Bus Topology:
• Limited cable length and number of stations. • Performance degrades as additional computers are added. • Difficult to troubleshoot if the entire network shuts down. • Terminators are required at both ends of the bus (backbone cable). • A break in the Central Backbone cable (bus) shuts down the entire network.
Disadvantages of Star Topology:
• Requires large amounts of cable. • Can be expensive depending on size of the network. • Single point failure (i.e. failure of the switch will isolate all attached nodes.) • Bottlenecks can occur because all data must pass through the switch.
Advantages of a Bus Topology:
• Requires less cabling than other topologies. • Typically the cheapest topology to implement. • Easy to connect a computer or peripheral to a linear bus. • Well suited for temporary networks that must be set up in a hurry. • Relatively easy to install, extend, and maintain for small networks.
Disadvantages of Unguided Media
• Security is poor because the signals are more susceptible to interception and monitoring. • Distortion and Interference due to atmospheric conditions, physical structures and other RF emanation. • Speed is usually slower over the unguided media than on guided media; this is primarily because the ____ is shared by all devices on that frequency.
Disadvantages of Mesh Topology:
• Very hard to administer (large scale) and manage because of many connections. • Very expensive (the larger the network, the more expensive the cables and interfaces needed to connect).
