Commit e237c538 authored by wx002's avatar wx002

ch4 done

parent e1e65162
This chapter is going into details of the 5 layer network model, focusing on the network layer.
Forwarding and Routing:
- Network Layer: move packet from sending host to receiving host
- Forwarding: packet arrive, route move such packet to the appropriate output link
- Routing: The path for the packet to take as it flow from sender to receiver. There are specific routing algorithms to calculate the path needed to take
Every router have a forwarding table. The table is built using incoming packet header and index the arriving packets. The table indicates the outgoing link of packets based on that index. Depending the way of network layer implementation, the header could be destination address or indicating which connection the packet really belong to.
There are different types of packet switches.
- ink-layer switches: forwarding decision on values in the fields of the link-layer frame
- routers: forwarding decision on the value in the network-layer field
Another important network layer function is connection setup, similar to how authentication handshakes worked.
Possible services Network Layer Provides:
- Guaranteed delivery
- Guaranteed delivery with bounded delay
- In-order packet delivery
- Guaranteed minimal bandwidth - ensure packet delivery when under bandwidth constraints
- Guaranteed maximum jitter: guarantees that the amount of time between the transmission of two successive packets at the sender is equal to the amount of time between their receipt at the destination
- Security services
Virtual Circuit and Datagram Network:
Similar to the transport layer, network layer could also offer connection/connectionless services. The major differences between network layer and transport layer are listed below.
- services that are host-to-host provided by network layer are for the transport layer
- network layer provides either a host-to-host connectionless service or a host-to-host connection service, but not both
- virtual Circuit network: provide only a connection service at the network layer
- implementation of these services are different for network and transport layer
Router:
This section focus on the internal details regarding routers.
Router consist of the following:
- input ports
- Switching fabric
- Output ports
- Routing processor
The input ports performs physical layer function of terminating an incoming physical link at a router. It also performs link-layer functions needed to interoperate with the link layer at the other side of the incoming link.
Switching fabric connects the input ports to the output ports. It's a network inside a network of routers.
Output stores packets coming from switching fabric and sent them out to out going links for necessary link and physical layer functions.
Routing processor executes the routing protocols and maintaining routing tables within the router. This serve similar like the CPU for a computer.
Collectively, forwarding functions are referred as router forwarding plane.
Internet Protocol(IP):
The IP protocol consist of the following functions:
- addressing conventions for forwarding and routing
- standardize the datagram formatting
- enforce packet handling conventions
Routing Algorithms:
Packet normally have to travel to multiple routers before reaching its destination. Often sometimes, it would require substantial effort for packet to be delivered due to the amount of routers there are within the internet. Hence, there are various algorithms to determine which route packet should take to make this process optimal.
Packet start off with the default router that's attached to the sending host, refer as the default router(first-hop router). When packet is sent, this is referred as the source router and its destination is called the destination router.
The idea of routing algorithm is that for packet start at the source router, what is the most effective way a packet to travel to its destination router. Each path consist of a cost, and the algorithm are based on weighted graph traversal algorithms where each hop would be the weight. Some algorithms pick the shorts amount of hops or the least weight.
Broadcast and Multicast Routing:
- broadcast routing: network layer provides a service of delivering a packet sent from a source node to all other nodes in the network
- multicast routing: a single source node to send a copy of a packet to a subset of the other network nodes
Reflection:
This chapter went in much depth regarding the network layer talking about routing and the structure of networks. It is definitely interesting to see how all of these are being applied physical within our daily lives. This chapter goes well with our class activity of the auto learn algorithm of building the forwarding table based on incoming packets. This is also related to our ICMP and Traceroute labs, where we saw how packets are being exchanged in detail using Wireshark.
Question
1. 60%
2. Three fragments are created with offsets 0, 480 and 960.
3. all of the above
4. the input ports
5. there is no queuing delay in the router
6. The sending IPv6 router creates an IPv6 datagram and puts it in the data filed of an IPv4 datagram.
T/F
1. T
2. T
3. T
4. T
5. T
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