Skip to main content

Symmetric and asymmetric switching / Memory buffering

Symmetric and asymmetric switching 
4.2.8 This page will explain the difference between symmetric and asymmetric switching.
LAN switching may be classified as symmetric or asymmetric based on the way in which bandwidth is allocated to the switch ports. A symmetric switch provides switched connections between ports with the same bandwidth. An asymmetric LAN switch provides switched connections between ports of unlike bandwidth, such as a combination of 10-Mbps and 100-Mbps ports.
Asymmetric switching enables more bandwidth to be dedicated to the server switch port in order to prevent a bottleneck. This allows smoother traffic flows where multiple clients are communicating with a server at the same time. Memory buffering is required on an asymmetric switch. The use of buffers keeps the frames contiguous between different data rate ports.
The next page will discuss memory buffers.
Memory buffering 
4.2.9 This page will explain what a memory buffer is and how it is used.
An Ethernet switch may use a buffering technique to store and forward frames. Buffering may also be used when the destination port is busy. The area of memory where the switch stores the data is called the memory buffer. This memory buffer can use two methods for forwarding frames, port-based memory buffering and shared memory buffering. 
In port-based memory buffering frames are stored in queues that are linked to specific incoming ports. A frame is transmitted to the outgoing port only when all the frames ahead of it in the queue have been successfully transmitted. It is possible for a single frame to delay the transmission of all the frames in memory because of a busy destination port. This delay occurs even if the other frames could be transmitted to open destination ports.
Shared memory buffering deposits all frames into a common memory buffer which all the ports on the switch share. The amount of buffer memory required by a port is dynamically allocated. The frames in the buffer are linked dynamically to the destination port. This allows the packet to be received on one port and then transmitted on another port, without moving it to a different queue.
The switch keeps a map of frame to port links showing where a packet needs to be transmitted. The map link is cleared after the frame has been successfully transmitted. The memory buffer is shared. The number of frames stored in the buffer is restricted by the size of the entire memory buffer, and not limited to a single port buffer. This permits larger frames to be transmitted with fewer dropped frames. This is important to asymmetric switching, where frames are being exchanged between different rate ports.
The next page will describe two switching methods.

Comments

Post a Comment

Popular posts from this blog

Windowing

Windowing 11.1.5 This page will explain how windows are used to transmit data. Data packets must be delivered to the recipient in the same order in which they were transmitted to have a reliable, connection-oriented data transfer. The protocol fails if any data packets are lost, damaged, duplicated, or received in a different order. An easy solution is to have a recipient acknowledge the receipt of each packet before the next packet is sent. If a sender had to wait for an ACK after each packet was sent, throughput would be low. Therefore, most connection-oriented, reliable protocols allow multiple packets to be sent before an ACK is received. The time interval after the sender transmits a data packet and before the sender processes any ACKs is used to transmit more data. The number of data packets the sender can transmit before it receives an ACK is known as the window size, or window. TCP uses expectational ACKs. This means that the ACK number refers to the next packet that is...
Post a Comment
Read more

OSI layers / Peer-to-peer communications / TCP/IP model

OSI layers 2.3.4 This page discusses the seven layers of the OSI model. The OSI reference model is a framework that is used to understand how information travels throughout a network. The OSI reference model explains how packets travel through the various layers to another device on a network, even if the sender and destination have different types of network media. In the OSI reference model, there are seven numbered layers, each of which illustrates a particular network function. - Dividing the network into seven layers provides the following advantages: • It breaks network communication into smaller, more manageable parts. • It standardizes network components to allow multiple vendor development and support. • It allows different types of network hardware and software to communicate with each other. • It prevents changes in one layer from affecting other layers. • It divides network communication into smaller parts to make learning it easier to understand. In the foll...
Post a Comment
Read more

1.2.2 RIP V2 Features

 1.2.2 RIP V2 Features This page will discuss RIP v2, which is an improved version of RIP v1. Both versions of RIP share the following features: It is a distance vector protocol that uses a hop count metric. It uses hold down timers to prevent routing loops – default is 180 seconds. It uses split horizon to prevent routing loops. It uses 16 hops as a metric for infinite distance. RIP v2 provides prefix routing, which allows it to send out subnet mask information with the route update. Therefore, RIP v2 supports the use of classless routing in which different subnets within the same network can use different subnet masks, as in VLSM. RIP v2 provides for authentication in its updates. A set of keys can be used on an interface as an authentication check. RIP v2 allows for a choice of the type of authentication to be used in RIP v2 packets. The choice can be either clear text or Message-Digest 5 (MD5) encryption. Clear text is the default. MD5 can be used t...
Post a Comment
Read more