Networking is a concept to connect group of computers. These computers talk to each other. They share data in their local group (LAN) or over wider branch offices (WAN). In turn these would connect to other LANs, WANs or centrally located Data-centers. Here, the physical layer plays the backbone for the LAN, WAN and Internet.
Physical layer sends the raw bits signals over a communication channel. These channels are of two types – Guided Media and Unguided Media. In this article we discuss, the physical layer in detail. The main component being the CAT cables for the guided medium.
In Cable TV network – Each signal is allotted different frequency and suitable gap maintained. So, when frequency channel is tuned, TV shows that channel. This is also called multiplexing. In fact it is FDM – Frequency Division Multiplexing.
While, in CAT cables, data is transmitted asymmetrically over time in the cable. It is as per the data size and availability of the source and destination. This is called Time Division Multiplexing.
What is AWG mentioned in the CAT cables?
AWG is American Wire Gauge is standard made in 1857 for solid non-ferrous conducting wires. Rule of thumb is lower the gauge value, higher is the diameter of the wire. And higher is the current flow capacity. And also higher the resistance per length of the wire and vice versa. CAT 5E, CAT 6, CAT 6A differ in AWG.
Diameter d (AWG) = 0.127 (mm) x 9236-n/39
So, d23 = 0.127 x 9239-23/39 = 0.572 mm. d24 = 0.127 x 9239-24/39 = 0.511 mm.
Hence, 23 AWG conductor has 0.572 mm diameter and 24 AWG has 0.511 mm diameter. These are dimension of each small 8 wires in the CAT cables of OSI Layer
OSI Layer (Open Systems Interconnection)
It is important to understand the layers of networking. OSI was developed in 1984 by International Organization of Standardization. It defined 7 layers of architecture in networking. Each layer catering to specific roles and functions.
OSI layers defines the path of data from end user to the physical medium to another end user in the network.
We will discuss Physical and Data Link Layer in this article.
Physical and Data Link Layer
Physical layer over Twisted Pair = PLS signalling + MAU (Medium Attachment Unit). MAU consists of following:-
Data Link layer has LLC (Logic Link Layer) and MAC (Media Access Control). LLC have protocols that reports to higher layers in the OSI model. MAC does Data Encapsulation and Collision Handling. LLC does multiplexing and de-multiplexing, error control, sequencing of the frames, acknowledgement tracking.
Why do we need Frames?
Frames avoid blocking of path. Too many system trying to send and receive data using same medium. It is better to send smaller packets of data to avoid collision. Frames wraps data with MAC address and error checking. This is data encapsulation.
What is 802.3 Ethernet?
In 1980, February, the Institute of Electrical and Electronics Engineers (IEEE) was formed. They created several committees or working groups to standardize the networking technologies. 802 refers to the year of establishment – 1980 – “80” and “2” refers to the month of February. 802.Xy, X refers to each unique working group. “y” is the updates to the technology. X can be 3 – Ethernet, 11 – Wifi, 15 – PAN, 16 -WiMAX, etc.
DIX – DEC, Intel, Xerox were the working group for 802.3 Ethernet. They also developed CSMA/CD network.
Following diagram shows which 802.X standards are active and which are inactive. This also shows relation of Data Link Layer (or Logical Link Layer) with Physical Layer with various 802.X standards.
Listed below is the active Ethernet over Twisted Pair cables (“y”) :-
What are TIA 568 A, B, C, D?
Telecommunications Industry Association (TIA) are set of standard for structured wiring over twisted pairs. They establish the 8 pin pair connections over 100 ohm cables.
These standard define cable types, connectors, termination standard, performance characteristics and testing.
What is are various CATegory Cables?
Under 802.3 standard, Ethernet cables connects various group of computer. Since 1990, various types of physical cables are available in the market. They differ in the AWG, LAN Standard support, Bandwidth, Encoding, Topology, Pitch (Twists per meter), POE etc.
Listed below defines the different CATegory cables available in the market :-
As can be seen from the table, AWG ranges from 26 in CAT 5 to 23 in CAT 6. Hence, it is becoming thicker. Real Bandwidth is post the encoding and other deductions in frequency. It is increasing upto 400 MHz in CAT 6A. Accordingly the speed of the cable is increasing from 10 Mbps in CAT 3 to 10,000 Mbps in CAT 6A. Also, the pitch or the twists per meter is increasing from around 20 in CAT 3 to CAT 6 around 200 to CAT 6A with more than 250 twists per meter. Topology supported is same as STAR.
Interesting part is that in 1999, CAT 5E supported 802.3ab (1000 BASE T). But in 2016, it is revised to 802.3bz (2.5G BASE T). So, the same network can now support 2.5 Gbps. No need to install new wire. It can be implemented with installation of updated devices of the upper layers (Switches and Routers).
What are the various Ethernet Cable Types?
We know magnetic fields are produced when electricity passes over a wire. This induces electricity over another cable. There are various ethernet cable types that helps to decrease crosstalk and attenuation. This can solve interference problem with other cables and among each of 8 wires. Application varies with complexity of wires in the building. UTP cables are best preferred over open cable with minimal interference.
If the building has bunch of other LAN cables, wiring of another nature, it is best to go for some shielding. This can discussed with your networking engineer on site.
Listed below are the available ethernet cable types :-