14 Determination of the path. Routing. Operations router. Routable protocols and routing protocols.

Path determination occurs at network Layer. The path determination function enables a router to evaluate the available paths to a destination and to establish the preferred handling of a packet.  Data can take different paths to get from a source to a destination. At network layer, routers really help determine which path. The network administrator configures the router enabling it to make an intelligent decision as to where the router should send information through the cloud. After the router determines which path to use, it can proceed with switching the packet: taking the packet it accepted on one interface and forwarding it to another interface or port that reflects the best path to the packet’s destination.

A router is a programmable device that works with other routers, via a routing protocol, to establish the best path on which to forward a packet with a given address. A router can consider the network as a whole in determining the route for a given call

Operation of a Router

Routers can be divided into three key components: a routing engine, a forwarding engine and a management agent. The function of the routing engine is to process routing information (exchanged between routers using a routing protocols such as the Border Gateway Protocol, BGP) so as to compute routes (using a shortest path algorithms) that are stored in routing information bases (RIB) and that are composed by a destination, a next-hop interface, and a metric. The function of the forwarding engine is to transfer incoming traffic to an outgoing interface directed towards a router closer to the traffic destination by performing a longest match prefix lookup using the incoming traffic destination address. This forwarding process is connectionless implying that at each hop the forwarding decision is taken independently for each datagram.

Routing Protocols

• There are different routing protocols. OSPF (open shortest path first), RIP (Routing Information Protocol), and EIGRP (Enhanced Interior Gateway Routing Protocol) are three examples. These protocols pickup network information from remote locations and store them on a router.

Routable Protocols

• Routable protocols will have a source and destination address in the packet that they send out, just like an envelope. The other parts of the packet will have data. Two examples of routable protocols are IP (Internet Protocol) and SNA (Systems Network Architecture ). All network and Internet operations use IP. Internal network operations use SNA to connect to a mainframe computer.

15. Gigabit Ethernet. Network technology

Gigabit Ethernet is an escalation of the Fast Ethernet standard using the same IEEE 802.3 Ethernet frame format. Gigabit Ethernet builds on the Ethernet protocol but increases speed tenfold over Fast Ethernet, to 1000 Mbps, or 1 Gbps.. Like Fast Ethernet, Gigabit Ethernet is compatible with earlier Ethernet standards. However, the physical layer has been modified to increase data transmission speeds: The IEEE 802.3 Ethernet standard and the American National Standards Institute (ANSI) X3T11 FibreChannel. IEEE 802.3 provided the foundation of frame format, CSMA/CD, full duplex, and other characteristics of Ethernet. FibreChannel provided a base of high-speed ASICs, optical components, and encoding/decoding and serialization mechanisms. The resulting protocol is termed IEEE

802.3z Gigabit Ethernet.

Gigabit Ethernet supports several cabling types, referred to as 1000BaseX. IEEE 802.3z specifies operations over fiber optics, and IEEE 802.3ab specifies operations over twisted-pair copper cable. It has become a dominant player in high-speed LAN backbones and server connectivity. Gigabit Ethernet uses Ethernet as its basis, and network managers have been able to take advantage of their existing knowledge to manage and maintain gigabit networks.

Gigabit Ethernet is often used for connecting buildings on the campus to a central multi-layer gigabit switch located at the campus data center. Servers located at the campus data center would also be connected to the same gigabit multilayer switch that provides connectivity to the entire campus.

topology	star
transfer rate	1000 Мбит/с
access method	CSMA/CD
Transmission medium	Twisted pair and fiber optic
collision	Yes