- What are some of the possible services that a link-layer protocol can offer to the network layer? Which of these link-layer services have corresponding services in IP? In TCP?
One of the services is framing. This service is also available in IP and TCP. Another service offered is link access. The third service is reliable delivery which is also available in TCP protocol. There is also a service of flow control that is also available in TCP. Another service that is available is error detection that is available with both IP and TCP. Another service is error correction in the network. The last service is full duplex, a service that is also available in TCP (Jacques et al., 2011).
- Compare the frame structures for 10BASE-T, 100BASE-T, and Gigabit Ethernet. How do they differ?
The three frame structures differ in their speeds. The speeds of the three are 10, 100, and 1000 Mbits/second respectively. The three use standard Ethernet frame format. The other features that differentiate them is that 10BASE-T which is 10Mbits/s (equivalent to 1.25MB/s0 is transmitted over twisted pair. The IEEE standard equivalent is 802.3i, and was developed in 1990. The 100BASE-TX, 100BASE-T4, or 100BASE-FX fast Ethernet whose speed is 100Mbits/s (equivalent to 12.5MB/s) has auto-negotiation capability. The IEEE standard equivalent is 802.3u; it was released in 1995. The third one is 1000BASE-T GBits/Ethernet travels over twisted pair at 1GBits/s (equivalent to 125GB/s). The IEEE standard equivalent is 802.3ab, and was released in 1999 (Dalleggio, & Rystsov, 2005).
- According to Figure 5.14 in the textbook,i. Which node, B or D, first realizes a collision has happened?
D realizes that a collision has happened. ii. If Bs packet is addressed to A, does A realize that a collision has happened? Please explain. What is the jamming signal and who is going to generate it?
A will realize that a collision happened only if a jamming signal is sent to A. A jamming signal is a signal that is sent by a node to the sending node that a collision occurred. In this situation, if D backed off immediately it realized that there is a collision, then B might not realize that there is a collision. Node D will send a jamming signal to B that there was a collision in the network. iii. Draw a graph scenario where a collision does happen, yet only A manages to receive the whole packet.
iv. Draw a graph scenario where a collision does not happen altogether.
v. What would happen if the backoff is not exponential? Give an example.
There would be an infinite collision because the nodes that sent frames that collided will wait for the same period. An example is node B and node D realized that a collision occurred, they will wait for a certain period before retransmitting. If there is no exponential backoff, the time that B retransmits will coincide with the time that D will retransmit. This will go on forever (Jain, & Das, 2008).
References
Dalleggio, A., & Rystsov, D. (2005). U.S. Patent No. 6,954,466. Washington, DC: U.S. Patent and Trademark Office.
Jacques, A., Kowalski, J., Lomp, G. R., & Ozluturk, F. M. (2011). U.S. Patent No. 7,903,613. Washington, DC: U.S. Patent and Trademark Office.
Jain, S., & Das, S. R. (2008). Exploiting path diversity in the link layer in wireless ad hoc networks. Ad Hoc Networks, 6(5), 805-825.
