ENTERPRISE EQUIPMENT SWITCHES: Jump-start Your Network

TECHNOLOGY OPTIONS



Switches are devices that filter and forward packets between LAN segments.

Switches operate at the data link layer (layer 2) and sometimes the network

layer (layer 3) of the OSI Model and therefore support any packet protocol. LANs

that use switches to join segments are called switched LANs or, in the case of

Ethernet networks, switched Ethernet LANs.

Switches have multiple ports, each of which can support an entire Ethernet,

FDDI or Token Ring segment. With a different segment connected to each of the

ports, it can switch packets between them as needed. In effect, a switch acts

like a very fast multi-port bridge because packets are filtered based on the

destination address. Switches are starting to replace hubs and routers in many

installations.

Switching technology is increasing the efficiency and speed of networks. This

technology is making current systems more powerful, while at the same time

facilitating the migration to faster networks. Switching directs network traffic

in a very efficient manner. It sends information directly from the port of

origin to only its destination port. Switching increases network performance,

enhances flexibility and eases moves, adds and changes. Switching establishes a

direct line of communication between two ports and maintains multiple

simultaneous links between various ports. It proficiently manages network

traffic by reducing media sharing, traffic is contained to the segment for which

it is destined, be it a server, power user or workgroup.

Switches come in different categories:



l Unmanaged switch: These

switches come in the 4 to 24 port varieties. These switches allow simultaneous

transmission of multiple packets via an internal high-speed data channel. The

learning function in the switch stores the address and corresponding port number

of each incoming and outgoing packet in a routing table. This information is

subsequently used to filter packets whose destination address is on the same

segment as the source address. Unmanaged switches are inexpensive, but lack

features for management. These are comparable to an unmanaged hub, except they

have the speed of a switch.

Some features of an unmanaged switch are

Automatic detection of MDI-X and MDI crossover function

Conformation to IEEE 802.3 10BASE-T and IEEE 802.3u 100BASE-TX

specifications.

Store-and-forward scheme to forward packets

Frame filtering and forwarding function for each port.

Automatic MAC address learning and aging function

Automatic local traffic filtering

Auto-negotiation on duplex mode

l Workgroup switch: Similar

to unmanaged switch, except provide management of the unit. Sometimes they also

provide Gigabit ports to uplink to larger backbone switches.

l Stackable switch: They

usually have proprietary cables to interconnect them together. It allows a stack

of switches to only use one IP-address for management. Some use Gigabit links to

interconnect them and to uplink them to backbone switches.

Features of a stackable switch include

Fault tolerance so that if one switch fails, the other switches in the stack

can continue to operate

Port redundancy so that if one port fails, a backup port can be automatically

substituted

Hardware and software to let the user manage the switches

using the Simple Network Management Protocol (SNMP)

l Chassis

Switch, Backbone Switch or Core Switch: Usually support Layer 3 switching,

along with Layer 2 switching and many high level protocols. The Chassis have

blades similar to high-end routers. So one can mix and match different

interfaces for connecting different types of networks together.

Switches are also classified according to the functionalities

of the OSI model.

l Layer 2

Switches (Data-link Layer) operate using physical network addresses.

Physical addresses, also known as link-layer, hardware, or MAC-layer addresses,

identify individual devices. Most hardware devices are permanently assigned this

number during the manufacturing process. Switches operating at Layer 2 are very

fast because they are just sorting physical addresses, but they usually are not

very smart–i.e., they do not look at the data packet very closely to learn

anything more about where it is headed.

l Layer 3

Switching (Network Layer) attempts to reduce the performance bottlenecks

associated with traditional routers. Layer 3 switches use network or IP

addresses that identify locations on the network. They read network addresses

more closely than Layer 2 switches–they identify network locations as well as

the physical device. A location can be a LAN workstation, a location in a

computer’s memory, or even a different packet of data traveling through a

network. Switches operating at Layer 3 are smarter than Layer 2 devices and

incorporate routing functions to actively calculate the best way to send a

packet to its destination. But although they are smarter, they may not be as

fast if their algorithms, fabric, and processor do not support high speeds.

l Layer 4

(Transport Layer) of the OSI Model coordinates communications between

systems. Layer 4 switches are capable of identifying which application protocols

(HTTP, SMTP, FTP, and so forth) are included with each packet, and they use this

information to hand off the packet to the appropriate higher-layer software.

Layer 4 switches make packet-forwarding decisions based not only on the MAC

address and IP address, but also on the application to which a



packet belongs. Because Layer 4 devices enable one to establish priorities for
network traffic based on application, one can assign a high priority to packets

belonging to vital in-house applications such as Smartstream, with different

forwarding rules for low-priority packets such as generic HTTP-based Internet

traffic. Layer 4 switches also  provide an effective wire-speed



security shield for your network because any company- or industry-specific
protocols can be confined to only authorized switched ports or users. This

security feature is often reinforced with traffic filtering and forwarding

features.

l Layer 5

Switches: This aims to use session level information in addition to layers

2,3, and 4 information to route traffic in the network. The system consists of a

switch core to which a number of custom- built intelligent port controllers are

attached. In addition, it is equipped with a processor complex. The job of the

port controllers is to identify the packets that require layer 5 processing and

forward them to the processor. The port controllers process the rest of the

packets. As the CPU processes only a very small fraction of the packets, it

achieves very high speeds while delivering useful layer 5 functionality. In fact

application level proxies, which are functionally equivalent to the L5 switch,

have been around for years. L5 combines the functionalities of an application

layer proxy and the data handling capabilities of a switch into a single system.

Though it can be used anywhere in the network the L5 switch is most useful as a

front-end to a server cluster. It makes it possible to partition the URL space

among the server nodes thus improving the performance of the server cluster.

BUYING TIPS

l Enhancing Performance:

A switch will improve performance for any file servers or workstations connected

directly to it. Small networks can use a switch instead of a hub to give

workstations maximum speed. If a network is large, it should have at least one

switch in every high-traffic workgroup. As a general rule, try to get every file

server, critical workstations, and print server connected directly to a switch.

l Running

High-speed Applications: When a network will be using high-speed

applications like multimedia or video generally speaking, every workstation and

file server that will be using multimedia or video should be connected to a

switch to avoid transmission delays. Anywhere a 10/100 Fast Ethernet hub is

required small workgroups and large network alike will benefit more from using a

10/100 switch to maximize performance over a mere 10/100 hub alone.

l Proper

Assessment: It is imperative to have a proper assessment of the LAN

requirements of an organization. One important aspect to be kept in mind is the

sort of applications that are normally used, as the LAN capacity/speed would be

dependent on that.

l Security

Concerns: Many switches are now coming with in-built security modules and

solutions like firewall or IDS.

MARKET INFORMATION

Switches are one of the fastest growing segments in the LAN equipment

market. Dropping prices and a rapidly growing user base has made this the killer

technology of the networking industry.

The market for switches has been witnessing a growth rate of

more than 70 percent. It is going through a consolidation phase at the moment.

This increased level of activity is due to more and more enterprises setting up

a LAN infrastructure and becoming more and more conscious of resource

utilization. Switches enable the user to control bandwidth. In the process it

makes usage of bandwidth more effective.

Switching access technology might undergo a major technology

leap in the next year. Currently, most corporates use 100 Mbps for access and

1000 Mbps (1Gbps) for backbone infrastructure. This will be enhanced to 1000

Mbps (1Gbps) for access and 10,000 Mbps backbone (10 Gbps) for backbone

infrastructure.

Users prefer switches because of the flexibility it provides.

For instance, only a switch can allow multiple services on the same network to

support voice, data and video. LAN switches and WAN routing technologies are

being converged onto a single platform called switch routers. This is expected

to provide another major boost to the switching segment. The convergence might

see the SOHO and SME segment going in for switches in a big way.

The market is likely to witness a fight between layer-2 and

layer-3 technology. Vendors like D-Link believe that Layer-2 switches will

become the default in managed switches. But ultimately in the days to come,

industry analysts believe that both technologies will co-exist with each other,

catering to different segments of the market. For example, Layer-3 switches are

defined more towards large networks with more than 100-150 users. Though it can

be used by smaller networks, it is more useful as a backbone for the network.

Hubs vs Switches

Traditional Ethernet LANs run at 10Mbps over a common bus-type design.

Stations physically attach to this bus through a hub, repeater or concentrator,

creating a broadcast domain. Every station is capable of receiving all

transmissions from all stations, but only in a half-duplex mode. This means

stations cannot send and receive data simultaneously. Nodes on an Ethernet

network transmit information following a simple rule: they listen before

speaking. In an Ethernet environment, only one node on the segment is allowed to

transmit at any time due to the CSMA/CD protocol (Carrier Sense Multiple

Access/Collision Detection). Though this manages packet collisions, it increases

transmission time in two ways. First, if two nodes begin speaking at the same

time, the information collides; they both must stop transmission and try again

later. Second, once a packet is sent from a node, and Ethernet LAN will not

transfer any other information until that packet reaches its endpoint. This is

what slows up networks. Countless hours have been lost waiting for a LAN to free

up.

When a single LAN station is connected to a switched port it may operate in

full-duplex mode. Full-duplex does not require collision detection, there is a

suspension of MAC protocols. A single device resides on that port, and therefore

no collisions will be encountered. Full-duplex switching enables traffic to be

sent and received simultaneously. (Hubs between a workgroup and a switch will

not run full-duplex, because the hub is governed by collision detection

requirements. The workgroup connected to the hub is unswitched Ethernet).

The bottom line is a 24 port 100 Mbps hub is only capable of sharing the full

100 Mbps with all 24-ports, which averages out to 4.16 Mbps for each port. While

at the same time a 24-port 100 Mbps Switch has 24 individual 100 Mbps ports. The

switch is capable of 2400 Mbps or 2.4 Gigabits per second. Also a switch can

operate in full-duplex mode, so it has a theoretical throughput of 4800 Mbps or

4.8 Gbps.