2) During normal IP packet forwarding at a router, which packet fields are updated? (5%) p327
3) Please briefly describe the sameness and differences between switches and routers.(5%) p475
Sameness：They are both store-and-forward devices.
Differences：But routers are network layer devices (examine network layer headers) and switches are link layer devices. Routers forward packets using IP address. Switches forward packets using to MAC address.
Routers maintain routing tables, implement routing algorithms
Switches maintain switch tables, implement filtering, learning algorithms
traffic isolation plug & play optimal routing cut through hubs no yes no yes routers switches yes no yes no yes yes no yes
4) Please compare CSMA/CD of IEEE 802.3 with CSMA/CA of IEEE 802.11.? (5%) p517
5) Briefly describe circuit switching and packet switching. (5%) P15
(1) A circuit-switched network can guarantee a certain amount of end-to-end bandwidth for the duration of a call. Most packet-switched networks today (including the Internet) cannot make any end-to-end guarantees for bandwidth.
(2) In a packet switched network, the packets from different sources flowing on a link do not follow any fixed, pre-defined pattern. In TDM circuit switching, each host gets the same slot in a revolving TDM frame.
6) What are the four causes of packet delay? (5%) p37
7) Describe how TCP sets its retransmission time-out (RTO) value。(5%)p239
8) Show the packet flows for TCP termination. (5%) p251,252
9) Give the forwarding and learning algorithm for Ethernet switches. (5%) p471 10) What are the two types of transport services that the Internet provides to applications? What are some characteristics of each of these services? P61
11) Which layers in the TCP/IP protocol stack does a router process? Which layers does a link layer switch process? Which layers does a host process? P63
12) Which multiple access protocols can be used for a sharing broadcast channel? (5%)
p432
Answer: Channel partitioning, random access, taking turns protocols. 13) Why IEEE 802.11 uses CSMA/CA instead of CSMA/CD? (5%) p518
Answer: It is costly to build hardware that can detect a collision for IEEE 802.11. It can’t detect all the collisions due to hidden terminal problem and fading. Since it can’t use collision detection, it uses collision avoidance.
14) Show the packet flows for TCP connection establishment. (5%) p251 Answer: Three-way handshake
15) What is the reliable data transfer service offered by TCP? Describe how TCP
provides reliable data transfer。(5%) p201,239
Answer: All the transferred data bits are not corrupted, lost. All are delivered in the order in which they were sent.
16) Give the forwarding and learning algorithm for Ethernet switches. (5%) Answer: P471. Learning is accomplished with source MAC address. Forwarding uses destination MAC address to search the forwarding table got by self-learning.
17) What are some characteristics of the two types of transport services provided by TCP and UDP? (5%) p13 61 q4
Answer: TCP: Connection-oriented service, reliable data transfer, flow control and congestion control.
UDP: Connectionless service, high efficient data delivery.
18) What are the five layers in the Internet Protocol stack? What are the principal responsibilities of each of these layers? (5%)p62 q23
Answer: Application Layer, Transport Layer, Network Layer, Data link Layer, Physical Layer. 19) Which layers in the TCP/IP protocol stack does a router process? Which layers does a link layer switch process? Which layers does a host process? (5%) p62 q22 Answer: router: Network Layer, Data link Layer, Physical Layer link layer switch: Data link Layer, Physical Layer
host: Application Layer, Transport Layer, Network Layer, Data link Layer, Physical Layer.
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