What is forwarding?
Moving packets from router’s input link to output link. It is an action local to routers
What is routing?
Determines the route taken by packets from source to destination. It is a global action
What is a forwarding table?
Inside the router, a forwarding table stores mappings from datagram header values to output links. The next route is determined by finding an entry in the table who’s header value matches the packet header value
Name 2 services for individual datagrams
- Guaranteed delivery
2. Guaranteed delivery with less than 40ms delay
Name 3 services for a flow of datagrams
- In-order datagram delivery
- Guaranteed minimal bandwidth
- Guaranteed maximal inter-packet timespacing
What does ATM stand for?
Asynchronous Transfer Mode
What does the Internet Network Architecture provide a guarantee on?
Nothing - not bandwidth, loss, order or timing
What is the difference between a datagram network and a virtual circuit network? Give an example of what architecture uses each
A datagram network (e.g. Internet) provides connectionless services, virtual-circuit network (e.g. ATM - telephony) is connection-oriented.
How is performance guaranteed in virtual circuit networks?
- There are setups and teardowns of each call before data can flow
- Every routers on source - destination path maintains a state for each passing connection
- Link and router resources (e.g. bandwidth, buffers) may be allocated/dedicated
- Each packet carries virtual-circuit (VC) identifier
What 3 components make up a VC?
- Path from source to destination
- Series of VC numbers, one for each link along the path
- Entries in forwarding tables in routers along path
What happens to a forwarding table in each router when a VC network is torn down?
The routers erase the entries in their forwarding tables
What is longest prefix matching?
When looking for forwarding table entry for given destination address, use the longest address prefix that matches destination address
Given two destination address ranges and link interfaces:
1) 0001 1000 - interface 1 &
2) 0001 1*** - interface 0
Which interface do the following addresses belong in:
a) 0001 1110
b) 0001 1000
a) 2
b) 1
