Bridge and gateway, are the backbone devices of the networking. A “bridge” operates on two layers, a physical layer, and a data link layer. A “gateway” operates on all the seven layers of the OSI model. The primary difference between a bridge and a gateway is that a “bridge is used only to transfer the frame to the expected destination, in a most efficient path”. A gateway “converts the format of the packet in one protocol to the format of the packet in another protocol”.
Let study, the difference between these two in a comparison chart below.
Content: Bridge Vs Gateway
|Basis for Comparison||Bridge||Gateway|
|Basic||Bridge transmits the frames between two separated segments of LAN.||Gateway is a protocol converter.|
|Layer of Operation||Operates on two layers, physical and data link layer.||Operates on all the seven layer of OSI model.|
|Work||Checks the destination address on received frame and forward the frame to the address it belongs.||It allows two different network using different protocols to communicate with each other.|
Definition of Bridge
A bridge operates on two layers of OSI model that are, physical layer and a data link layer. A bridge can divide a large network into smaller segments and is also used to connect two originally separated LANs. The purpose of a bridge is to transmit the frame between two separate LANs.
When a bridge receives a frame, it regenerates the signal and checks the destination address of the frame and forwards the new copy of the frame only to the segment to which it belongs. A bridge does not broadcast the frame to all the stations in the receiver segment; it only forwards the frame to destination/receiver station.
Let us understand the working of a bridge in the following steps:-
- A bridge receives a frame which contains its destination address on it.
- A bridge maintains a look-up table which contains the physical address of all the stations that are connected to it.
- It compares the destination address in the frame, with the addresses in the look-up table.
- If a match is found, then the bridge recognises to which segment the packet belongs and forward the packet to its destination station.
Types of Bridge
- Simple Bridge: It is the least expensive bridge. Connects only two LANs. Addresses in the lookup table are fed manually. Maintenance is time-consuming than cost-saving.
- Multiport Bridge: Connects more than two LANs.
- Transparent Bridge: Dynamically builds its look-up table and keeps the table updating during its bridging operations.
Definition of Gateway
A Gateway operates on all seven layers of OSI model. A gateway work as a “protocol converter”. A router can accept and transfer packets only across a network using similar protocols. But, a gateway can accept and transfer the packet across networks using a different protocol. A gateway is software installed within a router.
The steps performed by a gateway when it accepts a packet formatted in a protocol are as follow:-
- A gateway accepts a packet which is formatted for a protocol (e.g. Apple Talk), used by the sender’s network.
- It then converts that packet to be formatted for another protocol (e.g. TCP/IP), used by the receiver’s network.
- After converting the format of the packet, a gateway forward that packet to its destination/receivers network.
Sometimes the modification is needed only to header and trailer of the packet and sometimes a gateway has to adjust the data rate, size, and format of the packet.
Key Differences Between Bridge and Gateway
- A bridge is always used to regenerate the signal and find the most efficient path to transmit the frame. A gateway is used to increase the compatibility to establish communication between two networks using two different protocol.
- A bridge always operates on frames, and the gateway operates on packets.
- Bridge operates on the physical layer and data link layer whereas, a gateway can operate on all the layers of OSI model.
A bridge operates only on a data link layer and a physical layer where the data is in the form of frames. A gateway operates on all the seven layers of OSI model where the upper layer contains data in the form of packets.