Compare physical interface and cabling types

Cisco certification is NOT just all about routers and switches; remember, those routers and switches are connected together through a media and the media is connected into some interfaces. So, as a network engineer, you must know these interfaces, the cables and the physical connection options that exists between them, understand the pros and the cons, limitations in speed and bandwidth. Another concept to look at here will be Power over Ethernet (PoE) which is another important topic, as many critical devices available today now supports and depend on network-delivered power. 

Physical Interfaces

From Cisco’s documentation, there are two main categories of switches: modular and fixed configuration. There are variations among these categories of network switches, but the primary definition of each remains the same. 

Modular switches

Modular switches let you add expansion modules as needed, giving you flexibility as network requirements change. Expansion modules are application-specific and include those for firewalls, wireless connectivity, or network analysis. They may also allow for additional interfaces, power supplies, or cooling fans. This type of switch provides you with the most flexibility, but at a higher cost. 

Below is a Cisco Catalyst 9200 switch with 48x 10/100/1000 copper POE-enabled ports and an extension module, C9200-NM-4X which provides 4x SFP/SFP+ slots as shown.

Here, we have SFP modules on the left and direct-attach Twinax copper cable on the right. This cable combines 2 connected SFPs and is a cost-effective way to connect devices in the same or adjacent racks.

Fixed-configuration switches

Fixed-configuration switches provide a fixed number of ports and are typically not expandable, which makes them less expensive overall. Fixed-configuration switches include unmanaged switches, smart switches, and managed switches. 

Modern Catalyst switches, such as Catalyst 9000 series, have 2 types of copper interfaces:

• 10/100/1000Mbps
• Multigigabit with speed up to 10Gbps

Both types of interfaces support several standards and can negotiate different speeds with the connected device. For example, 10/100/1000 copper ports of Catalyst 9200 switch shown in Figure 1 support 10Base-T, 100-BaseTX and 1000Base-T. Multi-gigabit ports can negotiate 100Mbps, 1Gbps, 2.5Gbps, 5Gbps, and 10Gbps.

802.3 Standards (Ethernet)

IEEE 802.3 family of standards defines physical interface specifications for the wired Ethernet. It Provides asynchronous networking using “carrier sense, multiple access with collision detect” (CSMA/CD) over coax, twisted-pair copper and optical fiber media. 

The table below shows some 802.3 Standards, Speed and Physical Media

802.3z standard is called Ethernet over Fiber-Optic at 1Gbit/s and references multiple other standards. Example are 1000Base-SX (multi-mode fiber) and 1000Base-LX (multi-mode/single-mode fiber). The most commonly used standard options are 10GBase-SR, 10GBase-LR. 

Small Form-factor Pluggable Transceivers (SFPs)

SFPs are network interface modules. Their specifications are developed and maintained by industry vendors and not by IEEE. While the modules manufactured by different companies should be compatible, many vendors, including Cisco, support only their own branded SFPs. QSFP has a larger size and the picture below shows the difference between SFPs and QSFPs modules, as well as switch-side sockets. In this example, it is a Catalyst 9300 48-SFP+ port switch with a C9300-NM-2Q network module (accepting 2x QSFP+ modules).

The table below lists different types of SFPs along with the supported speed. 

Unshielded Twisted Pair

Copper connectivity is based on Unshielded Twisted Pair (UTP) cabling of different categories. A higher category number refers to the newer standard and better parameters. REFER to the 802 Standards above  where you see for example UTP Cat 3, Cat5, Cat6 and so on. An Ethernet cable consists of 8 wires, which are twisted together in pairs. The maximum distance for copper cabling is 100m. The connector is  referred to as RJ45.  There are 2 standards defining how individual wires are terminated within the connector – T568A and T568B. T568A wiring pattern is recognized as the preferred wiring pattern for this standard because it provides backward compatibility to both one pair and two pair USOC wiring schemes. The T568B standard matches the older AT&T 258A color code and is/was (?) the most widely used wiring scheme.

To connect  (host to host back-to-back), or (switch to switch) crossover cable is required. A crossover cable has a connector with T568A pin-out on one side and T568B pin-out on another side. Many modern switches can automatically switch their ports between MDI-X and MDI. They can use straight-through cables to connect to each other and don’t require a crossover cable.

Optical Fiber

Optical fiber cabling is usually more expensive to install, however, it has many benefits when compared to copper. In most cases, fiber cables can provide higher bandwidth over greater distances.

Fiber cabling is divided into 2 types:

• Multi-mode with categories of cables OM1, OM2, OM3, OM4 and OM5
• Single-mode of two types – OS1 and OS2

Connectors

Cisco fiber SFPs and some QSFPs have a duplex LC connector. Some QSFPs can also have MPO connectors. 

More on Fiber optics section (1.3.a) 

• 1.3.a Single-mode Fiber, multimode Fiber, Copper