Switches and Routers

The main difference between a switch and a router is that a router forwards data packets along the network path and is connected to a minimum of two networks.  Typically a router sits between the internet and your network or between your ethernet network and your wide area network.  A switch filters and forwards data packets between difference segments on the local area network.  A switch will typically operate at the data link layer which is layer 2 and on occasion the network layer (layer 3) if it is performing functions that may also be considered more routing.

The OSI model consists of 7 layers.  OSI stands for Open Systems Interconnection.

Layer 1 is the Physical Layer

Inside the physical layer is hardware connection layer.  This is where you’d see issues as far as physical connections including pins connection from a network card to the switch, establishing of the protocols to establish flow control, and this includes the physical cabling (fiber optic / ethernet)

Standards within this layer include: EIA/TIA, IEEE 802.11, IEEE 802.15, IEEE 802.16, SONET/SNH, BlueTooth, RS-232, USB, RS-49, PON, OTN…


Layer 2 is the Data Link Layer

The data link layer controls the link between two nodes and maintains reliability by detecting and correcting any errors caused by Layer 1

Standards within this layer include: ATM, SDLC, IEEE 802.3, X.25, PPP, Frame Relay, SLIP, CSLIP, HDLC, Q.921 LAPD…


Layer 3 is the Network Layer

Layer 3 provides the means for transferring the data from one node to another on the same network.

Standards within this layer include: IP v4, IP v6, Apple Talk, IPX, IPsec, ARP, X.25 PLP, IGMP, ICMP


Layer 4 is the Transport Layer

Layer 4 sends data packets between addressed nodes on the network with data transfer services to the upper layers

Standards within this layer include: TCP, SPX, DCCP, SCTP, UTP


Layer 5 is the Session Layer

Layer 5 controls the dialog between computers.  This opens and closes sessions and checks for recovery of connection. This layer is responsible for applications using remote calls.

Standards within this layer include: PPTP, RTP, NetBIOS, SPDY, SOCKS


Layer 6 is the Presentation Layer

Layer 6 is often called the syntax layer as it formats and encrypts data to be sent across a network.

Standards within this layer include: MIME, XDR


Layer 7 is the Application Layer

This layer communicates with software and also decides whether there is an established network or communication to perform requested tasks.  File Transfer Protocol, HTTP (web browsing), and Email occur in the application layer.

Standards within this layer include: SNMP, NTP, NFS, DHCP, HTTP, Gopher, FTP, DNS, SIP, SSI, NNTP