Asma - Fawziah

Layer 2 Technologies

Layer 2 is responsible for logical link control, media access control, hardware addressing, error detection and handling, and defining physical layer standards. It is often divided into the logical link control (LLC) and media access control (MAC) sub layers.

·         Bridged (Ethernet) Internetworking Ethernet frames that are extracted from the attachment circuit are sent over the pseudo wire. In the case of 802.1q, the VLAN tag is removed. The pseudo wire functions in Ethernet (VC type 0x0005) like-to-like mode, and the IW function at the NSP performs the required adaptation based on the attachment circuit technology. Non-Ethernet frames are dropped.

·         Routed (IP) Internetworking IP packets that are extracted from the attachment circuit are sent over the pseudo wire. The pseudo wire functions in IP Layer 2 Transport (VC type 0x000B) like-to-like mode, and the IW function (NSP) performs the required adaptation based on the attachment circuit technology. Non-IPv4 packets are dropped.

In general, you use Layer 2 IW to connect different Layer 2 technologies at both attachment circuits by means of a pseudo wire. The actual type of IW typically depends on the end-to-end application type, such as bridged or routed. If you want to interconnect different attachment circuit technologies and carry protocols other than IP, the only current option is bridged IW.

Homework3

*Explain what is meant by the following and show their role when it comes to network reliability:

Bit errors: class of failure.  a 1 is turned into a 0 or vice versa.

Packet loss: a complete packet is lost by the network.

 

*Explain the role of encapsulation in network design?

a method of designing modular communication protocols in which logically separate functions in the network are abstrscted from their unerlying structures by inclusion or information hiding within higher level objects.

 

*T/F: the process of encapsulation is repeated at each level (explain how):

*T/F: in networking systems, peer-to-peer communication is almost always indirect (explain how)?

 True, The hardware level where peers directly communicate  with each other over a link, peer-to-peer communication is indirect. each protocol communicates with its peer by passing messages to some lower-level protocol.

*Write about: Process-to-process communication vs host -to-host communication?

 

*Define the following terms (as referred to in the text book):

Protocol: A protocol provides a communication service that higher-level objects, use to exchange messages.

Frame: The message delivered to the end lost.

Packet: Blocks of data as corresponding to some piece of application data such as a file , apiece of emai.

Header: A small data structure, that is used among peers to communicate with each other 

Trailer: Control information is sent at the end of the messages.

OSI architecture: One of the first organizetion to formally define a common way to connect computers.

TCP/IP architecture: Is the basic communication language or protocol of the Internet. It can also be used as a communications protocol in a private network (either an intranet or an extranet. (
Architecture: A blueprints that guide the design and implementation of network.

TCP: Provide a reliable byte-stream channel.

IP: Protocol that supports the interconnection of multiple networking technologies into a single logical internetwork.

Propagation delay: is the amount of time it takes for the head of the signal to travel from the sender to the receiver.

Transmission delay: the delay caused by the data-rate of the link.

Queuing delay: is the time a job waits in a queue until it can be executed. 

Bandwidth: a measure of the width of a range of frequencies.

Latency: is an expression of how much time it takes for a packet of data to get from one designated point to another.

RTT: Is the length of time it takes for a signal to be sent plus the length of time it takes for an acknowledgment of that signal to be received.

 

Homework2

v  Layering (in network design) provides two nice features, explain how ?

 * Decomposes the problem of building a network into more manageable components .

*It provides a more modular design.

v  Define the following terms :

http: The underlying protocol used by the World Wide Web.

URL: the address of a specific Web site or file on the Internet.

link: Some physical medium, such as a coaxial cable or an optical fiber.

node: (connection point) refer to the computers it connects.

packet: Blocks of data as corresponding to some piece of application data such as a file , apiece of email.

Store-and-forward: Packet-switched networks typically use a strategy.

Switched: Store and forward packets.

hosts: Network nodes which use the network.

Router: A node that is connected to two or more networks.

Routing: The process of determining systematically how to forward messages toward the destination node based on its address.

Node address: An identifies a specific computer or terminal in a group of interconnected computers on a network.

Multiplexing: A system resource is shared among multiple users.

Congestion: A switch receive packets faster than it can send them for an extended period of time, then the switch will eventually run out of buffer space, and some packets will have to be dropped, when a switch is operating in this state.

Bit error: A 1 is turned into a 0 or vice versa.

OSL: a standard description or "reference model" for how messages should be transmitted between any two points in a telecommunication network.

TCP/IP:is the basic communication language or protocol of the Internet. It can also be used as a communications protocol in a private network (either an intranet or an extranet. (
Architecture: A blueprints that guide the design and implementation of network.

Homework 1

 - Explain why connectivity is a major network requirement and explain how is it possible for different  hosts to be sharing the same link ?

Because a network must provide connectivity a set of computer.

More than 2 nodes may share a single physical link a (multiple access).

 

- Explain why is meant by a switched network, and write about: packet -switched vs circuit -switched ?

Switched network : data received on one link is for worded on the other one .

*Packet-switched :

•  The important feature of packet-switched networks is that the nodes in such a network send discrete blocks of data to each other.
• These blocks of data as corresponding to some piece of application data such as a file, a piece of email, or an image.
• We call each block of data either a packet or a message.
• Packet-switched networks typically use a strategy called (store-and-forward).                                

 *Circuit-switched :

• Establishes a dedicated circuit across a sequence of links and then allows the source node to send a stream of bits across this circuit to a destination node.
• The major reason for using packet switching rather than circuit switcging in a computer network is etficiency.

- What are the two key challenges of statistical multiplexing ?

• Like STDM in that the physical link is shared over time.

• Unlike STDM, data is transmitted from each flow on demand rather that during a predetermined time slot.