1. Switching and High-Speed Networks
Dr. Marina Lipshteyn

2. What is a High Speed? Delay Bandwidth Bandwidth-×-delay product
D end-to-end
d per hop
Bandwidth
B aggregate
b per flow
Bandwidth-×-delay product
number of bits in flight on a high-speed path
b [bits/sec] × d [sec] = [bits]

3. Components of High-Speed Network
– network components
– protocols
– network: a complex system of systems
– end-to-end delivery of data to applications
– applications that use and drive high-speed networks

4. Lecture 1: Data Switching
Definition of switching
Distributed / Central switching
Switching vs. Routing
Ingress/Egress terms
3 types of switching: circuit, TDM and packet.
Circuit/Packet switching – advantages and disadvantages
Virtual Circuit Packet switching

5. Data Switching
Definition of a switch: functional unit that allows multiple inputs to be varyingly connected to multiple outputs.
Switching is the act of making those varying connections.

6. Trivial Solution – fully connected network
N(N-1) links
N(N-1) transmitters, N(N-1) receivers
Channel distance cost:
Each node accepts N-1 bandwidth of a single link – Type A node
If N is increased, upgrade of nodes is needed
A lot of time links may be empty
Each node can use only one channel at a time - Type B node
If N is increased, upgrade of nodes is not needed
Channels have to wait before they get bandwidth
Actually node of Type B is a distributed switch!

7. Distributed Switching
There is no central switch unit, but switch embedded into each application node.
It is possible to get from any node to any node by making one or more hops across the node-to-node links.
Each node recognizes destination of a packet. If the node is not the destination, the node forwards the packet to a link. Otherwise, the packet is used by the application.
Distributed switching is not used in practice since:
Communication capacity of each node vary. Therefore each node either should have scalable resources or maximum resources.
However distributed switching has a lot of similarity with routing.

8. Routing
Switching of high level protocols (eg. Internet) is called routing.
Router is responsible to find a route in the network for each packet.
Router is different from switch.
However, each router has an embedded switch. The switch is providing the varying connectivity, once the route is determined.

9. Ingress / Egress

10. 3 types of switching Switching of physical circuits
Switching of Time-Division-Multiplexed signals
Switching of Cells and/or Packets

11. Switching of physical circuits
Transmit the analog signal received on one of the ingress port to a predefined group of egress ports.

12. Switching of TDM signals
In the physical layer, the bandwidth is divided into separate time slots in some repeating cycle of allocating timeslots.
If there are N nodes with G time slots each.
Each ingress sample position is fixed into some egress fixed position.

13. Switching of Cells and/or Packets
Protocol divides the bandwidth into fixed length cells or varying length packets.
Packets/cell are not fixed into a fixed position.
Instead each cell/packet is carrying address (or other routing instruction) that directs it to a specific output port.
Thus switching mechanism is derived from the packet itself and not from static control system.

14. Packet switching
With packet switching there is no assurance that packets from all ingress ports will be routes to one output port creating a “hotspot”.

15. Special Services
Unicast: switching from an ingress port to an egress port.
Broadcast: switching from an ingress port to all egress ports.
Multicast: switching from an ingress port to a specified set of egress ports.