UBM as a Multilayer Switch

Multilayer Switch

Definition of a multilayer switch

A switch is defined as computing network device that switches on OSI layer 2 like an ordinary network switch and provides extra functions on higher OSI layers. A network switch is a small hardware device that joins multiple computers together within one local area network (LAN). Technically, network switches operate at layer two (Data Link Layer) of the OSI model. One of the main advantages of a multilayer switch is its ability to forward traffic at very high speeds and with extremely low latency.

The reference to multilayer in multilayer switch is the OSI layer (which has 7 layers) The core of this standard is the OSI Reference Model, a set of seven layers that define the different stages that data must go through to travel from one device to another over a network. In this article, you'll find out all about the OSI standard.

These layers include:

Think of the seven layers as the assembly line in the computer. At each layer, certain things happen to the data that prepare it for the next layer. The seven layers, which separate into two sets, are:

Application Set

• Layer 7: Application - This is the layer that actually interacts with the operating system or application whenever the user chooses to transfer files, read messages or perform other network-related activities.
• Layer 6: Presentation - Layer 6 takes the data provided by the Application layer and converts it into a standard format that the other layers can understand.
• Layer 5: Session - Layer 5 establishes, maintains and ends communication with the receiving device.

Transport Set

• Layer 4: Transport - This layer maintains flow control of data and provides for error checking and recovery of data between the devices. Flow control means that the Transport layer looks to see if data is coming from more than one application and integrates each application's data into a single stream for the physical network.
• Layer 3: Network - The way that the data will be sent to the recipient device is determined in this layer. Logical protocols, routing and addressing are handled here.
• Layer 2: Data - In this layer, the appropriate physical protocol is assigned to the data. Also, the type of network and the packet sequencing is defined.
• Layer 1: Physical - This is the level of the actual hardware. It defines the physical characteristics of the network such as connections, voltage levels and timing.

The following are description so how the multilayer switch works at the different OSI layers:

Layer 2

A network typically consists of computers, a connecting medium (wired or wireless) and specialized network equipment like routers or hubs. Using the Internet as an example all of the above components work together to allow your computer to send information to another anywhere in the world. Switches are a fundamental part of many networks because they speed the whole communication process up. Switches allow different computers of a network to communicate directly with another in a smooth and efficient manner.

Whereas a hub restricts or slows the process of communication between computers by stopping packets and waiting for their turn to move across the network, a switch eliminates the restrictions and speeds up the process by not waiting and going direct to the receivers end.

In a large network, with many pc users the likelihood of more network delays is greater with a hub. Therefore a switch is more beneficial. It is also possible to use a combination of both hubs and switches throughout the Local area network.

Another main difference between a hub and switch is that all the pc’s connected to a hub share the bandwidth amongst themselves. Whereas any device connected to a switch is able to use the full bandwidth. For example 10 pc’s using a hub on a 10Mbps network would receive 1Mbps each. Whereas with a switch within the same environment could receive up to 10Mbps.

A multilayer switch can be modelled as a switching system consisting of a number of simpler components. At the data-link layer, it consists of a number of logical layer 2 switches.

Routers and Layer 3 switching

Most switches operate at the data layer (layer 2) of the OSI reference model, whereas some also incorporate features of a router and operate at the network layer (layer 3) as well.

A layer 2 (data networking) switch relies on the MAC addresses to determine the source and destination of a packet. When a router (or layer 3 switch) receives a packet, it looks at the layer 3 source and destination addresses to determine the path the packet should take.

The fundamental difference between a router and a layer 3 switch is that layer 3 switches have optimised hardware to pass data as fast as layer 2 switches, yet they make decisions on how to transmit traffic at layer 3 just like a router. Within the LAN environment, a Layer 3 switch is usually faster than a router because it is built on switching hardware.

The major difference between the packet switching operation of a router and that of a Layer 3 switch is the physical implementation. In general-purpose routers, packet switching takes place using a microprocessor, whereas a Layer 3 switch performs this using application-specific integrated circuit (ASIC) hardware.

A Multilayer Switch (MLS) can prioritize packets by the 8 bits in IP DSCP (differentiated services CodePoint).

Many MLSs implement QoS differentiated services and/or integrated services in hardware

Each switch handles traffic from a specific VLAN (Virtual LAN). It also implements its own instance of the spanning tree protocol. At the network layer, it consists of a logical router that provides connectivity between the different VLANs.

Layer 4-7

Some switches can use up to OSI layer 7 packet information; they are called layer 4-7 switches.

Layer 4-7 switches are typically used for load balancing among groups of servers. Load balancing can be for HTTP, HTTPS and/or VPN, or for any application TCP/IP traffic using a specific port.

Some of the layer 4-7 switches can perform NAT at wirespeed.
Layer 4-7 switches can often also be used to perform standard operations such as SSL encryption/decryption to reduce the load on the servers receiving the traffic, and to centralise the management of digital certificates.

Layer 4 Load balancer

A typical network router simply sends incoming packets onto the appropriate IP address on its network. A layer 4 router, more correctly a NAT with port and transaction awareness, uses a little trickery and sends incoming packets to one or more machines which are hidden behind a single IP address.

The Layer 4 refers to the 7 layer OSI model. The router is on the Transport Layer and makes decisions on where to send the packets. Modern load balancing routers can use different rules to make decisions on where to route traffic. This can be based on least load, or fastest response times, or simply balancing requests out. This is also a redundancy method, so if one machine is not up, the router will not send traffic to it.

At the upper layers, the device may also implement advanced switching functions such as Layer 4 management, Quality-of-Service (QoS), and support for IP multicasting.